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Licensed copy from CIS: DUBLIN, DUBLIN INSTITUTE OF TECHNOLOGY, 07/02/2014, Uncontrolled Copy. Part 7 Roofs

7.1 Flat roofs and balconies

7.2 Pitched roofs Licensed copy from CIS: DUBLIN, DUBLIN INSTITUTE OF TECHNOLOGY, 07/02/2014, Uncontrolled Copy. Part 7 Roofs Chapter 7.1 Flat roofs and balconies Licensed copy from CIS: DUBLIN, DUBLIN INSTITUTE OF TECHNOLOGY, 07/02/2014, Uncontrolled Copy. 7.1 Flat roofs and balconies

CONTENTS SCOPE

DESIGN Clause Page This Chapter gives guidance on meeting the Technical Design standards D1 1 Requirements and recommendations for flat roofs and balconies with a fully supported continuous weatherproofing Statutory requirements D2 1 membrane. Loadbearing structure D3-D4 1 Principles of design D5 2 Structural deck D6 2 Thermal insulation and vapour control layers D7 2 Waterproofing and surface finishes D8 2 Rainwater drainage D9 2 Guarding to balconies D10 3 Access for maintenance D11 3 Provision of information D12-D13 3

MATERIALS Materials standards M1 3 Waterproofing M2 4 Structural timber M3 4 Profiled metal M4 4 Green and proprietary roofs M5 4

SITEWORK Sitework standards S1 4 In-situ reinforced concrete S2 4 Precast concrete S3 4 Profiled metal S4 4 Timber S5 5 Structural decks S6 5 Drainage S7 6 Thermal insulation and vapour control layers S8 6 Waterproofing S9 6 Guarding to balconies S10 7 Protection of materials from weather S11 7 7.1 APPENDIX 7.1-A Commonly used flat roofs 8 APPENDIX 7.1-B Surface treatments 13 APPENDIX 7.1-C Construction details of flat roofs and 14 balconies APPENDIX 7.1-D Balcony access, weatherproofing and 16 drainage

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at 2.0m centres (maximum) (see Sitework (b) in-situ reinforced concrete DESIGN STANDARDS clause 7.1 - S5(d)). In-situ reinforced concrete construction should be designed in accordance 7.1 - D1 Design shall meet the Technical (c) durability with BS EN 1992-1-1 and, where Requirements Technical Requirement R3 states that the appropriate, Chapter 2.1 ‘Concrete and Design that follows the guidance below will structure shall, unless specifically agreed its reinforcement’. A concrete mix with be acceptable for flat roofs and balconies. otherwise in writing with NHBC, have a life low shrinkage characteristics should be of at least 60 years. specified. For the purposes of this Chapter: The use of timber in balconies should be • generally, a flat roof has a maximum (c) precast concrete limited to secondary elements which in slope of 10° from the horizontal; Precast concrete construction should be turn are supported by materials other than however, many flat roof systems can be designed in accordance with BS EN 1992- timber. Timber can be used in the following used at greater pitches, in some cases 1-1. situations provided it has the appropriate up to vertical. Specifications for sloping The design of concrete elements should durability - see Chapter 2.3 ‘Timber roofs are generally the same as for flat allow for the following: preservation (natural solid timber)’: roofs, but will require mechanical fixings • continuity or anti-crack reinforcement • cantilevered solid timber joist balconies to hold the materials in place • allowance for movement at about 15m with a waterproof membrane above the • ”deck” is the structural substrate of a intervals and at abutments. flat roof joists • ”decking” is the upper trafficked • open balcony constructions with timber (d) profiled metal surface of a balcony (commonly a decking. The decking may be supported The manufacturer’s load/span tables for hardwood assembly laid onto the roof on solid timber joists which in turn are each profile should be consulted and or substantial paving tiles bedded to the supported by materials or components should include the relevant applied safety surface). other than timber factor. Profiled metals used for roof decks • balustrading. should have a profile with crowns of at Note: Profile sheeted roofing acting as the Timber should not be used for: least 50% of the profile width (not the waterproofing is outside the scope of this • gallows brackets supporting a balcony sheet width) for bonded systems and Chapter because it is discontinuous and • posts or columns supporting a balcony 45% for mechanically fixed systems, in not continuously supported. • guard rails or their support. order to provide adequate support for the remainder of the roof build-up. STATUTORY 7.1 - D4 Structural design shall be undertaken to a recognised standard REQUIREMENTS to ensure that loads are transmitted to 7.1 - D2 Design shall comply with all the supporting structure without undue relevant statutory requirements movement Designs should be in accordance with Items to be taken into account include: relevant Building Regulations and other (a) timber (where appropriate) statutory requirements. Structural design should be in accordance profile width with one of the following: • BS EN 1995-1-1 LOADBEARING crown width • appropriate load/span tables published STRUCTURE by TRADA in support of Building 7.1 - D3 Flat roofs and balconies, Regulations and associated documents including associated elements such as • I-joists and metal web joists should support and guarding, shall be designed be specified in accordance with the crown width to be not less than 50% to resist the applied loading and have manufacturer’s recommendations, of the profile width for bonded systems 7.1 adequate durability but not used in situations where any and 45% for mechanically fixed systems. part of the joist is exposed to external Structural design shall be undertaken in conditions. Construction loadings, including point accordance with a recognised standard. loads imposed by foot traffic, storage of Joist hangers should be the correct size materials and loads imposed by following Items to be taken into account include: for the timber joists being supported and trades should be taken into account. (a) dead and imposed loads meet with BS EN 845. Protection sheets, such as plywood, Dead and imposed loads should be should be used to prevent damage if such Pre-drilled vertical holding down straps calculated in accordance with BS EN loadings are expected. 1991-1-1, BS EN 1991-1-3 and BS EN 1991- should be at least one metre long, and 1-4. Where a flat roof is to act as a roof 30mm x 2.5mm in cross section. Fixing to the structure should be in accordance with the manufacturer’s terrace, roof garden or car parking area, All mild steel straps and fixings should be instructions and BS EN 1991-1-4. Unless appropriate provision should be made for protected against corrosion in accordance the manufacturer agrees otherwise, the the additional loadings. Intensive green with Tables A.1 and A.2 of BS EN 845-1. roofs should only be used in conjunction deck should be side stitched to ensure it with concrete decks. See clause 7.1 - D3 for guidance on the use performs as a continuous plane layer. of timber in balcony construction. (b) wind loads The frequency of fixings should meet the Wind loads appropriate to the site should Reference should be made to Materials manufacturer’s recommendations, and be be calculated in accordance with BS EN clause 7.1 - M1 and Chapter 2.3 ‘Timber calculated to resist the wind uplift figures 1991-1-4. The design should resist uplift preservation (natural solid timber)’ derived from BS EN 1991-1-4. from wind forces either by anchorage to (Design) for timbers requiring preservative (e) structural steelwork the main structure or by being of sufficient treatment. Structural steelwork should be designed weight to prevent lifting. Holding down in accordance with BS EN 1993-1-1 and straps, where required, should be provided

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Technical Requirement R5. Supporting STRUCTURAL DECK The manufacturer of the membrane steelwork and purlins should be square, system for a green roof should confirm true and free from twists or sagging. 7.1 - D6 Flat roof decks shall be of that the overall roof design is compatible adequate strength and moisture with the system. The complete green (f) differential movement resistance roof should be installed by a contractor Allowance should be made for movement Deck materials suitable for the different trained and approved by the membrane in larger roofs (e.g. roofs to blocks of flats), types of roof design are given in Appendix manufacturer. particularly where the span of the roof 7.1-A. deck changes, e.g. in L-shaped buildings. Once completed the waterproof membrane Joints should be continuous through the should be visually inspected and vertical upstands, walls and edges of the THERMAL INSULATION electronically tested for waterproofing building. Details are shown in Appendix AND VAPOUR CONTROL integrity, faults rectified, and the roof 7.1-C. re-tested before further layers, such as LAYERS reservoir or filter layers and the subsoil and (g) lateral restraint 7.1 - D7 Flat roofs (and balconies topsoil are placed. The tested membrane Where walls require lateral restraint, this functioning as roofs) shall have adequate should be protected from damage until may be provided by joists and concrete thermal insulation subsequent layers are applied. roof elements. The bearings for concrete elements and timber joists where they are The BRE Report “Thermal insulation: The results of the test should be made built in should be at least 90mm. avoiding risks” discusses aspects of available to NHBC. insulation relevant to flat roofs and Where joists or concrete beams are parallel The waterproofing for an intensive roof balconies. In England and Wales account should be of reinforced bitumen membrane to walls, restraint straps at 2m centres should be taken of “Accredited Details”. (maximum) should be provided. (RBM) or mastic asphalt and the design Thermal insulation materials suitable for should include protection of the membrane (h) sound transmission the different types of roof design are given from possible damage during maintenance Where the roof is a terrace above another in Appendix 7.1-A together with materials of the garden e.g. from weeding/planting. dwelling, care should be taken to ensure for vapour control layers and their position A filter layer should be placed above the that the design is in accordance with in the construction. The insulation material reservoir layer in accordance with the relevant Building Regulations. for inverted roofs should be suitable manufacturer’s recommendations. for external use and to withstand any PRINCIPLES OF DESIGN anticipated traffic. OTHER FLAT ROOF COVERINGS These are given in Materials clause M1 and 7.1 - D5 Flat roofs shall be to a Where insulation is mechanically fixed the should be used in accordance with the recognised design fixings should be of sufficient length to following: ensure they have adequate penetration Appendix 7.1-A shows the three flat • zinc sheet CP143-5 ‘Code of Practice for into the supporting structure. roof constructions acceptable to NHBC sheet roof and wall coverings’ with variations for timber and concrete • copper sheet CP143-12 ‘Code of Practice structural support. WATERPROOFING AND for sheet roof and wall coverings’ • lead sheet BS 6915 ‘Design and They are: SURFACE FINISHES construction of fully supported lead 7.1 - D8 Flat roofs (and balconies sheet roof and wall coverings’. warm roof - concrete deck functioning as roofs) shall adequately - timber deck resist the passage of moisture to the RAINWATER DRAINAGE - profiled metal deck inside of the building 7.1 - D9 Flat roofs and balconies shall inverted - inverted concrete deck have adequate rainwater disposal to a warm roof The roof coverings and surface finishes 7.1 suitable for different types of roof design suitable outfall green roof - intensive* are given in Appendices 7.1-A, 7.1-B, 7.1-C, Rainwater drainage design is covered in - extensive* 7.1-D. Chapter 7.2 ‘Pitched roofs’. * A green roof should be a complete system Appendix 7.1-A includes typical details In addition, the cumulative effects of water from the membrane manufacturer and not suitable for the following: discharging from multiple balconies in individual components or materials. • built-up Reinforced Bitumen Membrane vertical alignment should be taken into The details for green roofs in Appendix 7.1-A (RBM) roofing (formerly called “felt”) account to ensure satisfactory in-service are intended to be a guide and may vary depending on the individual manufacturer’s • mastic asphalt roofing performance and avoid issues such as the system. • single-ply roofing systems premature staining of the facade. • green roofs (intensive and extensive). Further guidance for balcony drainage can Appendix 7.1-B includes details of surface be found in Appendix 7.1-D. Cold roofs are not recommended, due to treatments. the difficulty of providing: Items to be taken into account include: • an effective vapour control layer at Appendix 7.1-C includes typical details for (a) falls ceiling level flat roofs and balconies. GENERAL • the required level of ventilation Appendix 7.1-Dincludes guidance for Other than the exceptions given below, all • an unobstructed ventilation space above balcony waterproofing and drainage. flat roofs and balconies should be designed the insulation of 50mm with a fall of not less than 1:40. A fall of • ventilation at both ends of each joist GREEN ROOFS 1:40 should be used for the design of flat void. Intensive and extensive green roofs are roofs and balconies, unless a detailed shown in Appendix 7.1-A. The details in analysis of the roof is carried out including Appendix 7.1-A are intended to be a guide overall and local deflection, to ensure the and may vary depending on the individual finished fall is not less than 1:80. Open manufacturer’s system.

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slatted balcony decking should drain away below ground’, where necessary. The Provision should be made for safe future from the dwelling. roof design should incorporate rainwater access to flat roofs for the purposes of outlets from flat roofs that are accessible maintenance. Allowance for deflection should be made for maintenance. For green roofs an in the structural design where falls are accessible and visible inspection hatch achieved using screeds, particularly on PROVISION OF should be provided at every outlet. large roofs. INFORMATION (c) prevention of flooding 7.1 - D12 Designs and specifications shall Where a flat roof or balcony has an be produced in a clearly understandable upstand on all sides, an overflow outlet format and include all relevant should be provided through parapet information walls or perimeter upstands to prevent a build-up of water in the event of other Clear and fully detailed drawings should fall outlet outlets becoming blocked. The position be available on site to enable work to be and height of the overflow should be such carried out in accordance with the design. that any build-up of water will not enter The drawings should include: the building. The capacity of the overflow • the specification for intensive or fall away from door should not be less than the size of the extensive green roofs dimension : outlet (or the aggregated capacity of the • extent and direction of falls and position at least 150mm outlets, if there are several outlets). of outlets at least fall 50mm • sections through the construction GUARDING TO BALCONIES indicating how the falls are formed, and means of ventilation, if required 7.1 - D10 Balconies and flat roofs to • size, specification and position of all fall not less than overflow which persons have regular access other 1:40 (for design the roof components, including the purposes) than for maintenance shall be guarded vapour control layer, insulation and adequately waterproofing layer Where decking or paving to a balcony is to Items to be taken into account include: • all treatment and protection of materials to achieve the necessary durability be installed above the waterproofing but (a) provision of guarding • details of construction at critical less than 150mm below the sill, it should be Guarding should be designed as follows: junctions of a type and design that prevents a build- • the balustrading should not be easily • details of balustrading and method of up of standing water (see Appendix 7.1-D). climbed fixing • any glazing in the balustrading should • details of fixing methods and fixings for TAPERED INSULATION TO ACHIEVE be toughened or laminated glass or insulation and surfacing. FALLS glass blocks Drainage falls to warm-decked roofs using • balustrading should not be fixed through tapered insulation should be designed 7.1 - D13 All relevant information shall be the waterproofing unless special distributed to appropriate personnel by the insulation manufacturer, with falls precautions are taken (see Appendix of not less than 1:60. They should be laid 7.1-C). Ensure that design and specification directly onto the vapour control layer, information is issued to site supervisors with the primary waterproofing above. (b) stability of guarding and relevant specialist subcontractors and/ Cross-falls should be achieved using mitred Parapet walls and balustrading should or suppliers. joints. be designed to resist horizontal loading as required by the relevant Building METAL SHEET ROOFS Regulations or BS EN 1991-1-1. Particular MATERIALS STANDARDS

Flat roofs with metal sheet roof coverings care is needed when the design 7.1 should be designed with a fall of not less incorporates balustrading fixed to parapet 7.1 - M1 All materials shall: than 1:30 to ensure a finished fall of not walls to ensure stability and prevent (a) meet the Technical Requirements less than 1:60. overturning. End fixings or returns may be (b) take account of the design needed to ensure stability. Materials that comply with the design and GREEN ROOFS the guidance below will be acceptable for In balcony walls (especially long balconies) Green roofs should be designed to retain flat roofs and balconies. some water, to support and nurture the the structural stability should be checked vegetation, and to manage the run-off, but as the dpc at the base of the wall can Further guidance for the selection of the waterproofing should have falls of not create a slip plane that can seriously limit materials can be found in Technical less than 1:60 or in accordance with the the ability of the wall to resist horizontal Requirement R3 (see Chapter 1.1 system manufacturer’s recommendations. forces. In such cases, it may be necessary ‘Introduction and Technical to incorporate a ring beam or other Requirements’). (b) outlets support to ensure stability. The size and number of outlets should Appendix 7.1-A lists the materials suitable be designed to meet the expected In the design of parapet walls, movement for: should be allowed for. Reference should be rainfall intensity in accordance with BS • waterproofing, including flashings EN 12056-3. For flat roofs bounded by made to Chapter 6.1. ‘External masonry walls’ clause D3(g). • structure, deck and decking parapets at least two outlets (or one outlet • thermal insulation plus an overflow) should be provided. • vapour control layer Outlets should have a recessed mouth to ACCESS FOR • preservative treatment. allow the free flow of water. MAINTENANCE Rainwater drainage design is covered in 7.1 - D11 Adequate access shall be Chapter 7.2 ‘Pitched roofs’. Reference provided to flat roofs for the purpose of should be made to Chapter 5.3 ‘Drainage maintenance

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WATERPROOFING BS EN 12588 ‘Lead and lead alloys. Rolled IN-SITU REINFORCED lead sheet for building purposes’. 7.1 – M2 Waterproofing materials shall CONCRETE be of adequate durability and resist the STRUCTURAL TIMBER 7.1 - S2 In-situ reinforced concrete flat passage of moisture to the inside of the roofs shall be constructed to ensure 7.1 – M3 Structural timbers shall be building they achieve the required design, of the appropriate grade and size to strength and durability REINFORCED BITUMEN MEMBRANES, support the imposed loads FORMERLY REFERRED TO AS “FELTS”. Items to be taken into account include: Items to be taken into account include: Only high performance reinforced bitumen (a) accuracy of formwork membranes should be used, i.e. those • appropriate load/span tables published by TRADA in support of Building The formwork should be constructed including polyester reinforcement (e.g. accurately. Type 5U, 5B/180, 5E/250 to BS 747). Type Regulations and associated documents 5 reinforced bitumen membranes are • structural softwood for internal use Items to take into consideration are: colour coded blue for identification. should be dry graded to BS 4978 and • accurate location of holes marked ‘DRY’ or ‘KD’. • adequate support SINGLE PLY MEMBRANES I-joists and metal web joists should • proper allowance for placing of (THERMOPLASTIC) be specified in accordance with the steelwork Examples of single layer materials manufacturer’s recommendations. They • cast-in features, such as drips and include PVC (polyvinyl chloride) and should not used in situations where any weatherchecks TPO (thermoplastic polyolefine). part of the joist is exposed to external • surface finishes. These materials soften with increasing conditions. Where a metal deck is used as permanent temperatures. Laps are welded, using shuttering, drying of the concrete will either hot air or a specific solvent to melt take place from the top surface only. A and fuse them. These materials should PROFILED METAL temporary roof should be provided to be assessed in accordance with Technical 7.1 – M4 Profiled metal roof decks shall allow drying to take place. The permanent Requirement R3. be of the quality, type and dimensions waterproofing should only be installed required by the design LIQUID SYSTEMS when the deck has fully dried. Profiled metal roof decks should be: These materials are applied as a liquid, (b) concrete grade often laid in two or more coats. Most • galvanised steel to BS EN 10147 and used in compliance with BS EN 1993-1-3, Reference should be made to Chapter include a reinforcement scrim to distribute 2.1 ‘Concrete and its reinforcement’ for the tensile stresses. or • aluminium to BS EN 485-2. guidance on concreting. The design should • cold-applied flexible polyurethane have specified a concrete mix with low systems GREEN AND PROPRIETARY shrinkage characteristics. • hot melt rubberised bitumen systems. ROOFS These are applied hot in two 3mm coats, PRECAST CONCRETE 7.1 – M5 Green roofs and proprietary with reinforcement between, and with a 7.1 - S3 Precast concrete flat roofs shall substantial reinforced bitumen membrane roofing systems shall be suitable for be constructed to ensure they achieve protection sheet. They should only be used their intended use the required design, strength and in buried applications, such as inverted Green roofs, both intensive or extensive, durability roofs, green roofs, podium areas, etc. should be a complete system from These materials should be assessed in the membrane manufacturer and not The supporting structure should: accordance with Technical Requirement R3. individual components or materials. • be even and true • have a minimum 90mm bearing for the

7.1 MASTIC ASPHALT The waterproofing for an intensive roof pre-cast units unless the design shows a To BS 6925 type 988 T25, 20mm thick on should be of reinforced bitumen membrane lesser dimension. the flat, laid on black sheathing felt. (RBM) or mastic asphalt. Precast units should be: For green roofs, three coats horizontally The complete green roof should be • installed to provide an even surface (30mm total thickness) and two coats installed by a contractor trained and • grouted, where required by the design. vertically (20mm total thickness) are approved by the membrane manufacturer. required. Proprietary roofing systems, which do not PROFILED METAL Polymer modified asphalt waterproofing meet with the principles given in Appendix 7.1 - S4 Profiled metal flat roofs shall be should be assessed in accordance with 7.1-A, should be assessed in accordance constructed to ensure they achieve the Technical Requirement R3. with Technical Requirement R3. required design, strength and durability Appendix 7.1-B gives suitable surface Items to be taken into account include: treatments for the waterproofing. SITEWORK STANDARDS (a) material type and protection against corrosion SHEET METAL 7.1 - S1 All sitework shall: Sheets should be checked for conformity Materials should be in accordance with the (a) meet theTechnical Requirements with the design and specification when following: (b) take account of the design they are delivered to site. BS EN 501 ‘Specification for fully (c) follow established good practice and supported roofing products of zinc sheet workmanship (b) adequate storage ’BS EN 504 ‘Specification for fully Construction that complies with the design Profiled sheets should be stored to prevent: supported roofing products of copper and the guidance below will be acceptable • rusting of cut edges sheet’ for flat roofs and balconies. • severe scratching of the galvanising BS EN 506 ‘Specification for self • sheets being bent or deformed. supporting products of copper or zinc sheet’

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(c) fixings Strutting should be located as follows: joists cut accurately The number, type and location of fixings so that gap is not Joist Rows of strutting hanger bearing more than 6mm should in accordance with the design and directly on span masonry specification. [m] (d) installation Up to 2.5 none needed The supporting steelwork and purlins 2.5 to 4.5 1 (at centre of span) should be square, true and free from Over 4.5 maximum 2.5m centres, Spaced no gap between twists or sagging. Unless the manufacturer equally along the span hanger and wall agrees otherwise, deck materials should be side stitched to ensure the deck performs notch to keep In cold deck roofs, the strutting should not ceiling line level as a continuous plane layer. prevent free cross ventilation. Assembly of the roof, end laps, etc. should (d) holding down metal strapping be in accordance with the design; any If the design specifies holding down straps variation from this should be approved by to prevent the roof being lifted off the STRUCTURAL DECKS the designer. supporting structure, they should be at 7.1 - S6 The structural deck shall Protection sheets, e.g. plywood, should be 2.0m centres (maximum). be installed to form a satisfactory used in areas of the roof deck subjected Where straps are fixed to masonry, substrate for the waterproofing system to construction loadings, including point hardened nails 4mm in diameter x 75mm loads imposed by foot traffic and storage Items to be taken into account include: long or No 12 wood screws x 50mm long of materials. Loads imposed by following (a) fixing of plywood and oriented strand into plugs should be used. trades should be taken into account. board The number of fixings should be in Tongued and grooved boards laid either Any deformed sheets should be stripped accordance with design requirements and with the long edge at right angles to the and replaced, before the waterproofing the lowest fixing should be within 150mm joists or parallel to the joists should have and insulation system is installed. of the bottom of the vertical strap. the short edge supported on a joist or nogging. TIMBER strap with cross section of 30mm x 2.5mm Oriented strand board should be laid over 7.1 - S5 Timber flat roofs and (where supports in the direction indicated on the appropriate) balconies shall be boards. The stronger axis should be laid at constructed to meet the required right angles to the supporting joists. at least 4 design,strength and durability screw fixings per strap Roof perimeter edges of boards which Items to be taken into account include: do not coincide with joists should be lowest fixing not (a) grades and sizes of joists more than supported on noggings. Materials delivered to site should be 150mm from bottom of strap Unless the design specifies closer centres checked for conformity with the design oriented strand board and plywood fixing and specification. centres should not exceed 100mm. (b) the spacing and bearing required to strap at least 1m long Movement gaps at abutment with rigid achieve reasonably level support for upstands should be not less than 10mm firrings and deck and gaps between square edge boards Timber joists should be: (e) timber quality should not exceed 3mm. • level - where necessary, hard packing Timber should be rejected if it: 10mm for OSB and

should be used, e.g. tiles or slates 7.1 • is excessively bowed, twisted or plywood when it abuts a rigid upstand for square edge bedded in mortar. Loose or soft packing, cambered boards, 3mm for OSB including timber, should not be used • is excessively wet and plywood • spaced at the centres specified on • has large edge knots or shakes the drawing (not more than 600mm • has a waney edge more than half the centres). thickness The use of regularised timber joists will • has fissures help to achieve a level deck. • has any sign of rot. Where preservative treated timber has (c) strutting been cut after treatment the cut edges Strutting should be one of the following: Oriented strand board should be fixed should be re-treated with a coloured • herringbone type (timber 38mm x with flat headed ring shank nails, 3mm in preservative. 38mm) diameter at least 2½ x board thickness long and not less than 9mm from the edge • solid blocking (38mm thick timber x¾ (f) joist hangers of the board. depth of joist) The joist hanger should be the correct size • proprietary steel strutting. for the timber joist or trimmer and nailed Plywood should be fixed with ring shank in accordance with the design. nails, at least 50mm long x 3mm in The masonry course to carry the joist diameter. hangers should be level and at the correct height. The walling should not becut into. (b) fixing of softwood boarding Softwood tongued and grooved boarding should be closely clamped together. Each board should be nailed with two ring shank nails to each joist or firring. Nail heads

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should be punched below the timber ceiling. Where laid across the joists, firrings Insulation should be bonded or surface. End joints should be staggered. should be not less than the following sizes: mechanically fixed inaccordance with the manufacturer’s recommendations. (c) protection of structural deck Joist Minimum firring dimensions [mm] The deck should be installed in dry Centres [mm] conditions and be protected from wetting until the roof is complete. The joints in width depth sheet materials which are pre-felted or 400 or 38 38 coated should be sealed immediately after 450 ensure adequete fixing. bearing area for two continuous 600 38 50 composite deck beads or sealant beneath each The area of deck installed in any working board day should be no greater than can be quickly protected from wetting. noggings are required to support all cross Damaged materials and materials that joints have been adversely affected by moisture

should be discarded. Composite decks require noggings under minimum firring dimensions as in table above transverse edges. The joist width should DRAINAGE be in accordance with the design to ensure (c) tapered insulation systems 7.1 - S7 Flat roofs shall have effective the insulation has adequate bearing. The manufacturer’s specific design and drainage layout drawings should be followed. The The foil underface of a composite deck Falls and gutters should be constructed sequence of installation should ensure should be sealed with two beads of sealant in accordance with the design. Flat roofs that boards are waterproofed and the along all board joints to maintain the and balconies should have a finished fall roof sealed at the end of each day, or integrity of the vapour control layer. of not less than 1:80 except flat roofs with before the arrival of inclement weather. INVERTED ROOFS metal sheet roof coverings and green roofs Successive roof layers should be laid with a The insulation material for inverted roofs which should have a finished fall of not less minimum of delay, to avoid trapping water should be in accordance with the design, than 1:60. during construction. be suitable for external use and withstand Appendix 7.1D provides guidance on (d) access to rainwater outlets any anticipated traffic. weatherproofing and drainage of balconies Rainwater outlets from flat roofs should be GREEN ROOFS Items to be taken into account include: accessible. For green roofs an accessible and visible inspection hatch should be Where the vapour control layer has been (a) falls on concrete roofs provided at every outlet. used as a temporary waterproofing layer CEMENT/SAND SCREEDS any damage should be repaired using a full Cement sand screeds should be 1 : 4, width section of membrane. cement : sand. Minimum screed THERMAL INSULATION thicknesses should be as follows: AND VAPOUR CONTROL COLD ROOFS Ventilation should be provided at both Location of Thickness [mm] LAYERS ends of each joist void, and should not be screed 7.1 - S8 Insulation and vapour control blocked by the thickness of the insulation. Bonded nominally 40mm (25mm layers shall be installed in accordance monolithically to minimum) A minimum of 50mm clear air space above with the design insitu or pre-cast the insulation should be maintained. concrete Appendix 7.1-A gives details of suitable 7.1 materials for insulation and vapour control WATERPROOFING Unbonded (on nominally 70mm (50mm layers for the different types of roof separating minimum) designs. 7.1 - S9 Waterproofing shall prevent layer) water entering the building WARM ROOFS Items to be taken into account include: The design should indicate that the vapour Reference should be made to Chapter 8.3 (a) preparation of surfaces control layer is below the insulation and ‘Floor finishes’ for further guidance on The structure and the surface to receive that it is sealed to the waterproofing at laying screeds. the waterproofing should be checked and the perimeter and at all penetrations approved by the waterproofing contractor. through the roof, e.g. at outlets and pipes. LIGHTWEIGHT SCREEDS All nails should be well punched below the In single ply roofing systems the vapour Lightweight screeds should be laid only surface, which should be even and dry. by specialist contractors. Lightweight control layer is generally not sealed to the concrete screeds should have a topping of waterproofing. The manufacturer’s recommendations on priming upstands, roof outlets, etc. should 1 : 6, cement : sand, 13mm thick. Insulation boards should be kept dry at all be followed to achieve a satisfactory bond stages to prevent: SCREED FINISH with the waterproofing. • lack of bonding Screeds should be free from ridges and • trapping of moisture. indentations. They should be finished with (b) construction sequence a wooden float to provide a smooth, even The area of insulation laid at any time Waterproofing systems should be surface for the vapour control layer and should be that which can quickly be laid in accordance with the design waterproof finish. covered by the waterproofing or protected and specification following the from wetting. recommendations of the manufacturer. (b) falls on timber roofs Some proprietary systems should be laid Firring pieces should be used to form falls, only by specialist roofing contractors unless the design shows sloping joists and

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approved by the manufacturer. See clause GUARDING TO BALCONIES S9(d) for green roofs. 7.1 - S10 Guarding to balconies shall It is preferable for one contractor to lay be of adequate strength and height to the vapour control layer, the insulation, the minimise the risk of people falling, of waterproofing and the surface finish. The adequate durability and fixed securely contractor should ensure that the deck and the insulation boards are waterproofed Items to be taken into account include: and the roof sealed at the end of each day, (a) strength and movement of masonry or before the arrival of inclement weather. balcony walls Masonry balcony walls should be built Successive roof layers should be laid so as in accordance with Chapter 6.1 ‘External not to trap water during construction. masonry walls’. In particular: Membrane laps near outlets should not • walls should incorporate strengthening impede drainage. as required by the design • movement joints should be provided in (c) weather conditions accordance with the design The manufacturers’ recommendations • copings should be firmly bedded. for conditioning, (unrolling in advance of laying, etc) should be followed. (b) fixing of balustrading and guard rails Balustrading and guard rails should Generally, sheet membranes should not be be fixed in accordance with the design laid or handled when the air temperature details. Reference should also be made to is 5°C or below unless the manufacturer Appendix 7.1-C. agrees otherwise. Some self-adhesive reinforced bitumen membranes should not PROTECTION OF be laid below 10°C. For such systems, the manufacturer’s specific instructions should MATERIALS FROM be followed. WEATHER Membranes should not be laid on damp or 7.1 - S11 Moisture sensitive material shall frosted surfaces or when any rain, sleet or be protected from wetting snow is falling. Timber-based roof decking and insulation (d) green roofs materials should be stored under cover to Green roofs should be laid in accordance prevent wetting. with the design and the membrane Timber-based roof decks that have been manufacturer’s recommendations, taking fixed in position should be temporarily into account: covered to prevent wetting, unless the • root barriers waterproofing is to be laid immediately. • height of upstand in relation to soil height and flashings Zinc coils and sheets should be stored in • integrity of waterproofing prior to dry conditions before being installed. burying • protection, reservoir and filter layers • moisture control of the soil.

Green roof systems should be installed by 7.1 operatives who: • are competent • are familiar with the system being installed • hold a certificate confirming they have been trained by the system membrane manufacturer or distributor.

(e) correct detailing Appendix 7.1-C gives, for the different roof types, typical details of: • abutments • parapets • edge details • fixing of guarding • projections through the waterproofing • roof lights.

(f) balconies Appendix 7.1D provides guidance on weatherproofing and drainage of balconies

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Appendix 7.1-A

Commonly used flat roofs Three types of flat roof are shown here to illustrate the principles of their design:

WARM ROOF (insulation on top of deck) concrete deck timber deck profiled metal deck surface surface surface treatment* treatment* treatment* waterproofing waterproofing insulation insulation waterproofing vapour control vapour control insulation layer layer vapour control screed deck layer metal deck deck

* mineral surfaced or solar reflective treatment where required

INVERTED WARM ROOF (insulation on top of waterproofing) concrete deck

ballast filter layer insulation

waterproofing screed

deck

GREEN ROOF intensive (requires regular maintenance. Plants contained within soil) extensive (requires periodic maintenance. Plants generally contained in the sedum blanket

sedum blanket filter layer 7.1 root barrier waterproofing soil and vegetation insulation (up to 1m deep) vapour control layer filter layer screed drainage/reservoir layer protection layer concrete deck root barrier (profiled metal decks waterproofing may be an alternative depending on loadings) insulation vapour control layer screed

concrete deck

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WARM ROOF (concrete deck)

surface treatment

waterproofing

insulation *

vapour control layer

screed to falls *

concrete deck

plaster or plasterboard

* falls can be created by either screed to falls or tapered insulation

Surface treatment See Appendix 7.1-B

Waterproofing and insulation Waterproofing should be one of the following: • reinforced bitumen membrane (RBM) to BS 8747 from the following table:

Type of Reinforced Bitumen Membrane (RBM) Insulation material Method of fixing first layer First/preparatory Second layer/underlay Final layer/cap sheet layer Type 3G perforated layer S2P3 S5P5 with either integral Rigid Urethane Foam (RUF) Loose laid and lapped, to produce mineral finish or separate solar boards (polyurethane (PU) partial bonding. protection and polyisocyanurate (PIR) Type 3G perforated layer Elastomeric underlay Elastomeric capsheet achieving achieving S2P3 S5P5 S2P3 fully bonded S2P3 S5P5 with either integral Compressed cork, rock Full bitumen bonding, per BS 8217 mineral finish or separate solar fibre or glass fibre boards, protection cellular glass slabs, perlite boards, or composite S2P3 fully bonded Elastomeric underlay Elastomeric capsheet achieving products achieving S2P3 S5P5 7.1 Note: torching onto insulation boards, except rock/glass fibre or perlite is not acceptable. Note: Elastomeric (i.e. SBS polymer-modified) bitumen membranes, with greater extensibility and flexibility, especially at low temperatures, are likely to provide longer service life.

• mastic asphalt, 20mm thick on the flat, laid in two layers, all to BS 8218 onto black sheathing felt • a thermoplastic single ply membrane, assessed in accordance with Technical Requirement R3, either bonded to the insulation, mechanically fixed to the deck through the insulation, or loose-laid, sealed and ballasted. Refer to the manufacturer’s instructions for details. Vapour control layer The vapour control layer should consist of at least one layer of bitumen roofing membrane (S2P3) fully bonded to the structural deck and all laps sealed with bitumen.

Concrete deck and screed Concrete roof deck, suitably primed, with sand/cement screed topping to achieve the falls. The screed should be in accordance with Clause 7.1-S7(a).

Detailing Typical details are shown in Appendix 7.1-C.

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WARM ROOF (timber deck) WARM ROOF (profiled metal deck)

surface treatment surface waterproofing treatment waterproofing insulation *

vapour control layer insulation * vapour control layer deck

profiled metal deck* joist and firring* plaster or plasterboard

plaster or plasterboard * falls can be created by either tapered insulation or installing the deck at 1 : 40

* falls can be created by either firrings or tapered insulation

Surface treatment Vapour control layer See Appendix 7.1-B In bonded systems the vapour control layer should consist of at least one layer of bitumen roofing membrane (S2P3) fully bonded Waterproofing and insulation or nailed to the structural deck and all laps sealed with bitumen. In Waterproofing should be one of the following: mechanically fixed systems the vapour control layer should consist of • reinforced bitumen membranes (roofing felt) to BS 8747 from the suitable polyethylene sheet sealed at all laps. following table: Preservative treatment Type of Reinforced Bitumen Membrane Insulation Method All roof timbers, joists, wall plates, blocking, strutting, battens, (RBM) material of fixing firrings, noggings to be preservative treated, unless naturally first layer durable. Chapter 2.3 ‘Timber preservation (natural solid timber)’ First/ Second Final layer/ gives details of preservative treatments. preparatory layer/ cap sheet layer underlay Deck Type 3G S2P3 S5P5 with Rigid Urethane Loose laid Timber or timber-based decks should be one of the following: perforated either Foam (RUF) and lapped, layer integral boards to produce Material Thickness of deck (mm) mineral (polyurethane partial finish or (PU) and bonding Joist centres (mm) separate polyisocyanurate 450mm 600mm solar (PIR) protection Pre-treated plywood, WBP grade 15 18 Type 3G Elastomeric Elastomeric Marine plywood, WBP grade 15 18 perforated underlay capsheet layer achieving achieving Oriented Strand board Type OSB3 15 18 S2P3 S2P3 Pre-treated timber planking - tongue and 19 19 S2P3 fully S2P3 S5P5 with Compressed Full bitumen grooved (‘close boarded timber’) Max. board bonded either cork, rock fibre bonding, width 100mm. integral or glass fibre per BS 8217 mineral boards, cellular Reference should be made to Sitework clause 7.1 - S6 for fixing of the 7.1 finish or glass slabs, deck to joists. separate perlite boards, solar or composite Joists protection products For sizes and spacing, reference should be made to appropriate load/ S2P3 fully Elastomeric Elastomeric span tabales published by TRADA in support of Building Regulations bonded underlay capsheet and associated documents. achieving achieving S2P3 S2P3 Detailing Note: torching onto insulation boards, except rock/glass fibre or perlite is not Typical details are shown in Appendix 7.1-C acceptable. Note: Elastomeric (i.e. SBS polymer-modified) bitumen membranes, with greater extensibility and flexibility, especially at low temperatures, are likely to provide longer service life.

• mastic asphalt, 20mm thick on the flat, laid in two layers, all to BS 8218 onto black sheathing felt • a thermoplastic single ply membrane, assessed in accordance with Technical Requirement R3, either bonded to the insulation, mechanically fixed to the deck through the insulation, or loose-laid, sealed and ballasted. Refer to the manufacturer’s instructions for details.

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INVERTED WARM ROOF (concrete deck) (NOT suitable for slopes greater than 10°)

ballast

filter layer

insulation

waterproofing screed to falls

concrete deck

plaster or plasterboard

Ballast Ballast should consist of paving slabs, or of rounded pebbles of minimum diameter 19mm to the depth specified in the design.

Filter layer Geo-textile layer, laid over insulation boards to prevent fines from reaching the membrane surface.

Insulation Insulation should be of a type unaffected by exposure to the weather and capable of supporting the weight of the ballast. Only the following materials are suitable: • extruded polystyrene (XPS) • extruded polystyrene, with cementitious surface.

Waterproofing Waterproofing should be one of the following: • reinforced bitumen membranes (roofing felt) to BS 8747 from the following table:

Type of Reinforced Bitumen Membrane (RBM) Deck material Method of fixing first layer First/preparatory Second layer/ Final layer/cap sheet 7.1 layer underlay Type 3G perforated S2P3 S5P5 with either integral mineral finish or Concrete, or concrete with sand/ Loose laid and lapped, to layer separate solar protection cement screed produce partial bonding Type 3G perforated Elastomeric underlay Elastomeric capsheet achieving S2P3 layer achieving S2P3 Mineral surfaced on exposed upstands, etc. Note:Concrete or screeded substrates should be adequately dry to receive waterproofing system Note: Elastomeric (i.e. SBS polymer-modified) bitumen membranes, with greater extensibility and flexibility, especially at low temperatures, are likely to provide longer service life

• mastic asphalt, 20mm thick on the flat, laid in two layers, all to BS 8218 onto black sheathing felt. • a thermoplastic single ply membrane, assessed in accordance with Technical Requirement R3, either bonded or mechanically fixed to the deck, or loose-laid, sealed and ballasted. Refer to manufacturer’s instructions for details.

Concrete deck and screed Concrete roof deck, suitably primed, with sand/cement screed topping to achieve the falls. The screed should be in accordance with Clause 7.1-S7(a).

Detailing Typical details are shown in Appendix 7.1-C. Note: Inverted roofs should only be used with timber (solid or I-joist) or metal profiled decks if they have been designed to support the loads, particularly from the depth of ballast needed to retain the insulation material.

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GREEN ROOF A green roof, either intensive or extensive, should be a complete system from the membrane manufacturer and not individual components or materials. The details given below are intended to be a guide and may vary depending on the individual manufacturers system. The following identifies the two types of green roof:

INTENSIVE EXTENSIVE

soil and vegetation

sedum blanket and growing medium

filter layer

drainage/reservoir layer protection layer root barrier waterproofing insulation

vapour control layer

screed to falls

concrete deck

concrete deck (profiled metal deck may be an alternative depending on loadings)

plaster or plasterboard

Summary Intensive Extensive Feature requires regular “intensive ”maintenance e.g. similar to a normal requires minimal maintenance e.g. annual attention garden a sedum blanket contains the plants provides a normal garden environment uses natural topsoil at least 150mm deep and normal plants Structure roof design to allow for full weight of wet soil roof loadings less than Intensive roof 20° maximum roof pitch Falls and drainage falls 1:60min 45° maximum roof pitch moisture irrigation system may be required to support plants in dry spells drainage falls 1:60min control irrigation system may be required to support plants in drought conditions Vapour control Fully bonded polyester-reinforced RBM (S2P3) Fully bonded polyester-reinforced RBM (S2P3) layer Insulation Insulation material to have adequate compressive strength to Insulation material to have adequate compressive strength to withstand 7.1 withstand likely applied loads likely applied loads Where the insulation is above the weatherproofing, only Where the insulation is above the weatherproofing, only extruded extruded polystyrene (XPS) should be used polystyrene (XPS) should be used Waterproofing See separate table. A root resistant element such as a See separate table. A root resistant element such as a copper foil or copper foil or “Preventol ”treatment is required above the “Preventol ”treatment is required above the waterproofing membrane waterproofing membrane Protection and A filter layer and protection layer (or board), above the Follow the manufacturer’s recommendations filter layers waterproofing membrane, is required to prevent damage. These to be in accordance with the manufacturer’s recommendations

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Type of Reinforced Bitumen Membrane (RBM) Insulation Material Method of fixing firstlayer First/preparatory Second layer/ Final layer/cap sheet layer underlay Type 3G perforated layer S2P3 S5P5 with either integral mineral finish or Rigid Urethane Loose laid and lapped, to produce separate solar protection Foam (RUF) boards partial bonding. (polyurethane (PU) and Type 3G perforated layer Elastomeric underlay Elastomeric capsheet achieving S2P3 polyisocyanurate (PIR)) achieving S2P3 Mineral surfaced on exposed upstands, etc. S2P3 fully bonded S2P3 S5P5 with either integral mineral finish or Compressed cork, rock Full bitumen bonding, per BS 8217 separate solar protection fibre or glass fibre boards, cellular glass S2P3 fully bonded Elastomeric underlay Elastomeric capsheet achieving S2P3 slabs, perlite boards, or achieving S2P3 Mineral surfaced on exposed upstands, etc. composite products Note: torching onto insulation boards, except rockwool or perlite is not acceptable. Note: Elastomeric (i.e. SBS polymer-modified) bitumen membranes, with greater extensibility and flexibility, especially at low temperatures, are likely to provide longer service life. Mastic Asphalt Mastic asphalt to BS 8218. Three coat horizontally (30mm total thickness), two coat vertically (20mm total thickness).

Appendix 7.1-B

Surface treatments Maintenance only for roofs up to 10° Access roof, walkway or terrace deck Further information may be obtained from Reinforced Bitumen • mineral surfaced capsheets (e.g. • pre-cast semi porous concrete tiles Flat Roofing Alliance Membranes (RBM) Type S5P5) or reflective stone bedded in bitumen or other approved www.fra.org.uk/ chippings, bedded in a dressing adhesive, or compound, or • pre-cast concrete proprietary paving • a suitable thickness of washed, slabs on supports or sand/cement rounded 20 - 40mm shingle blinding2, or ballast laid loose • proprietary timber decking systems 3 Mastic Asphalt • reflective stone chippings 1, • pre-cast semi porous concrete tiles Mastic Asphalt Council bedded in a bitumen based bedded in bitumen or other approved www.masticasphaltcouncil.co.uk/ compound, or adhesive, or • a solar reflective paint, as • pre-cast concrete proprietary paving approved by the Mastic Aphalt slabs on supports or sand/cement Council blinding2 Thermoplastic • products do not require • proprietary flexible, non-slip walkway Single Ply Roofing Association Single Ply supplementary solar reflective sheets or tiles, compatible with the www.spra.co.uk/ Membranes coatings or other finishes membrane product 7.1 • where laid loose, membranes • pre-cast concrete proprietary can be ballasted with suitable paving slabs on adjustable supports thickness of washed, rounded or suitable non-woven polymeric 20-40mm shingle ballast laid on a protection layer non-woven polymeric protection • proprietary timber decking systems layer with bearers set on additional membrane or suitable non-woven polymeric protection layer

Notes 1 Loose surface finishes should be prevented from being removed by weather and discharged into gutters and drain pipes. Chippings should be not less than 12.5mm limestone or white spar, not pea gravel. 2 Cement/sand blinding should be laid on two layers of waterproof building paper or two layers of 1000 gauge polyethylene separating membrane. The slabs should be kept back 75mm at perimeters and a 25mm movement gap incorporated for every 9m2 of paving laid. 3 Timber decking systems should only use compatible preservative treatments. The undersides of the bearers should have large, smooth contact areas, with no sharp edges or corners.

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Appendix 7.1-C

Construction details for flat roofs and balconies This Appendix contains common details for flat roofs and balconies. The following sketches show examples of typical common construction details and illustrate general principles. Further information on specific waterproofing systems may be obtained from BS 8217 ‘Reinforced bitumen membranes for roofing - Code of Practice’, the Flat Roofing Association, Mastic Asphalt Council or Single Ply Roofing Association.

CONCRETE DECK

Pre-formed capping OSB or plywood capping upstand metal flashing surface treatment 150mm min (if required) waterproof membrane insulation vapour barrier screed vapour control layer

surface treatment (if required) concrete deck waterproof membrane insulation vapour barrier screed

concrete deck Upstand Handrail fixing • upstand may be fixed to wall • upstand should be formed in concrete roofs • upstand to be at least 150mm high • similar details apply to inverted roofs with concrete decks OSB or plywood capping fixed to one kerb only preformed kerb mineral surfaced top layer to upstand and 75mm min over expansion joint 150mm min surface treatment (if required) 150mm min waterproof membrane waterproof membrane insulation insulation vapour control layer vapour control layer screed screed

concrete deck concrete deck

Skirting to rooflight or ventilator kerb Twin-kerb expansion joint • similar details apply to inverted roofs. Allow for thickness of • expansion joint is similar for both warm and inverted concrete ballast to achieve upstand dimension. roofs. 7.1

TIMBER DECK

surface treatment (if required) battens, tiles/slates waterproof membrane tilting fillet insulation surface treatment (if required) vapour control layer 150mm min OSB or plywood layboard metal flashing waterproof membrane battens, tiles/slates insulation vapour control layer insulation insulation

Mansard edge Pitched roof abutment • All elements should be firmly fixed to prevent peelback in high winds

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TIMBER DECK (Continued)

waterproof membrane cavity tray metal cover flashing surface treatment (if required) upstand of edge trim insulation board built-up timber kerb 150mm min surface treatment (if required) insulation 300mm min waterproof membrane insulation vapour control layer vapour control layer timber deck

Verge detail Independent skirting detail • similar details apply to inverted deck • upstands should be kept separate from wall - allow for movement • upstand should be at least 150mm high • similar details apply to cold deck timber roofs

surface treatment (if required) apron flashing waterproof membrane bonded to pipe vapour control layer sleeve around pipe insulation

150mm min vapour control layer surface treatment (if required) waterproof membrane insulation vapour control layer

insulation around pipe

Welted drip to external gutter Pipe passing through roof • similar details apply to cold deck timber roofs • vapour control layer should be bonded to waterproofing • inverted timber decks need special consideration to avoid • detailing of upstand and flashing is similar for all roofs insulation being lifted by wind suction. An alternative detail should be used. surface treatment (if required) waterproof membrane

50mm 7.1 vapour control layer turned back mineral surfaced over insulation top layer to face of timber kerb surface treatment (if required) 150mm min waterproof membrane

vapour control layer

insulation

50mm x 50mm triangular fillet insulation around pipe and outlet

Upstand to ventilator or rooflight kerb Rainwater outlet • similar details apply to cold and inverted roofs. The thickness of • the opening should be properly trimmed ballast in inverted roofs, to achieve upstand dimensions, should be • the outlet should be at the lowest point in roof allowed for. • similar details apply to concrete roof • ensure outlet is fixed securely to decking to prevent displacement by thermal expansion of rainwater pipe.

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• a balcony upstand of minimum 75mm building. This can be achieved by using Appendix 7.1-D below the underside of the threshold. one outlet and an overflow (not less than The balcony upstand is measured from the the capacity of the outlet) or two outlets Balcony access, balcony drainage layer to the underside of connected to independent downpipes. the projecting sill. Note: the drainage layer Alternatively, the balcony kerb can be set a weatherproofing and drainage may not be the waterproofing layer. For minimum 25mm below the level of the door This Appendix contains guidance on the example, with an inverted roof the drainage threshold to allow safe spillage in the event principles to adopt for the weatherproofing layer would be the top of the insulation and of water build up. An outlet chute through and drainage of balconies which may then not the waterproofing layer below. This is perimeter construction into external hoppers have an accessible threshold. Depending because drainage between the insulation can also act as the overflow if it is of an on the design, specific fire, thermal and and waterproofing layer could become silted appropriate size to serve both the discharge acoustic issues may also need to be taken resulting in the majority of rainwater flowing and overflow capacities. into account. over the top of the insulation. • drainage gaps between any decking or The design and construction of accessible • a waterproofing layer designed to paving and at balcony perimeters balcony thresholds should incorporate all of prevent ponding and associated stagnant Drainage gaps between individual lengths the following: water. of decking or between each paving slab Finished falls should be a minimum 1:80 should be a minimum of 10mm. A similar • a door threshold with an upstand of not away from the building to the rainwater continuous drainage gap should be provided more than 15mm outlet(s). Where balconies are designed with between decking or paving and the threshold The 15mm threshold upstand is measured falls toward or parallel to the building care sill, perimeter walls and kerbs. Spacers at the door position. Additional sloping must be taken to ensure any blockage of and supports to raised decking or paving transition elements, such as a small internal the outlet(s) cannot cause flooding into the should not obstruct the flow of rainwater to ramp and external sill, may be provided building. Waterproofing layers at zero falls outlet(s). The position of drainage outlets either side of the upstand. The maximum will only be accepted if the waterproofing beneath decking or paving should be clearly slope on ramps and sills should be 15 membrane has a third party assessment identifiable and accessible for maintenance. degrees. specifically for that use. The membrane • a minimum 150mm high splash zone • a door threshold with a minimum 45mm should also be fully protected from direct above the decking or paving projecting sill and drip. trafficking, for example by provision of The design of the wall for minimum 150mm The sill should have a minimum 45mm paving slabs or decking, and be UV resistant above decking or paving should ensure that overhang and drip to shed rainwater unless fully protected from daylight. any splashing off the decking or paving does away from the interface between the The membrane should be capable of not reach any part of the wall that could waterproofing layer and the sill and to avoid withstanding any point loads from supports be adversley affected by the presence of reliance on exposed joint sealants and their to decking or paving. moisture. This may be achieved by the use limited design life. • an effective drainage system and of an impervious wall finish/cladding or an suitable overflow extension of the balcony waterproofing layer The drainage arrangement should ensure to form an upstand with cover flashings and that if an outlet or downpipe becomes cavity trays if required. blocked it will not lead to flooding into the INVERTED BALCONY

7.1

1 2 3 4 5 6 7 8

fall

11 10 9

Key

1 finished floor level 2 projecting sill and drip - minimum 45mm overhang 3 minimum 10mm gap 4 minimum 150mm splash zone (where applicable) 5 raised and drained decking or paving on drained supports 6 drainage layer is top of insulation 7 overflow/warning pipe outlet to be a minimum 25mm below the underside of the door sill 8 rainwater outlet and hopper - discharge should avoid passing through accommodation below 9 supporting slab 10 waterproofing layer with falls to outlet 11 minimum 75mm upstand

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WARM DECK BALCONY

1 2 3 4 5 6 7 8

fall

11 10 9

Key

1 finished floor level 2 projecting sill and drip - minimum 45mm overhang 3 minimum 10mm gap 4 minimum 150mm splash zone (where applicable) 5 raised and drained decking or paving on drained supports 6 drainage layer is waterproofing layer 7 overflow/warning pipe outlet to be a minimum 25mm below the underside of the door sill 8 rainwater outlet and hopper - discharge should avoid passing through accommodation below 9 supporting slab 10 waterproofing layer with falls to outlet 11 minimum 75mm upstand

CANTILEVERED BALCONY 7.1

1 2 3 4 5 6 7 8 9 10

fall

13 12 11

Key

1 finished floor level 2 projecting sill and drip - minimum 45mm overhang 3 minimum 10mm gap 4 minimum 150mm splash zone (where applicable) 5 raised and drained decking or paving on drained supports 6 drainage layer is waterproofing layer 7 rainwater outlet 8 balustrading 9 low kerb - minimum 25mm below the underside of the door sill to act as overflow 10 alternative hopper discharge 11 supporting slab 12 waterproofing layer with falls to outlet 13 minimum 75mm upstand

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INDEX

A I S Access 3, 7 Insulation 2, 3, 6, 7, Screeds 6, 9, 12 Accuracy 4 9, 11, 12, Sheet metal decks 4 B 13, 14 Single ply membranes 4, 9, 11, Balconies 1, 2, 3, 4, 5, Inverted roofs 2, 6, 8, 11 12, 13 7, 17 J Sound transmission 2 Balustrading 1, 3, 7 Joist hangers 1, 5 Straps 1, 2, 5 Boarding 5 Joists 1, 3, 5, Structural steelwork 1 C 6, 10 Strutting 5, 11 Car parking 1 L Surface treatments 2, 4, 13 Cold decks 2, 6 Lateral restraint 2 T Concrete deck 1, 4, 8, 9, Lead sheet 2, 4 Thermal insulation 2, 6 11, 12, 14 Liquid systems 4 Timber 1, 2, 4, 5, Concrete grade 4 Loads 1, 4 6, 7, 8, 10, D M 14, 15 Deck 1, 2, 3, 4, 5, Mastic asphalt 2, 4, 9, 12, Timber deck 8, 14, 15 6, 10, 14, 13, 14 V Decking 1, 2, 3, Movement 1, 2, 7 Vapour control layers 2, 3, 6, 4, 14 O 9, 10, 12, Design 1, 2 Outlets 3, 6 14, 15 Drainage 2, 3, 6 P Ventilation 2, 3, 5, 6 Durability 1, 3, 4, 5, 7 Precast concrete construction 1, 4 W F Preservative treatment 1, 3, 11, 13 Warm roofs 2, 8, 9, 10 Falls 2, 3, 6, 12 Profiled metal 1, 2, 4, 8, Waterproofing 2, 4, 5, 6, Flood prevention 3 10, 12 9, 10, 11, 17 Formwork 4 Proprietary roofs 4 G Protection 4, 5, 6, Green roofs 2, 3, 4, 6, 7, 12 7, 8 R Guarding 1, 3, 7 Rainwater drainage 2, 3 Reinforced bitumen membranes 4, 7, 9, 10, 11, 13, 14 Reinforced concrete construction 1 Roof gardens 1 7.1

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CONTENTS SCOPE

DESIGN Clause Page This Chapter gives guidance on meeting the Technical Requirements and recommendations for pitched roofs, Design standards D1 1 including trussed rafter and traditional cut roofs, vertical tiling, Statutory requirements D2 1 weatherproofing and insulation. Loadbearing structure D3-D4 1 Trussed rafter roofs D5 1 Traditional cut roofs D6 2 Timber treatment D7 3 Weathertightness D8-D9 3 - 4 Insulation and control of condensation D10-D11 4 Fire spread D12-D13 5 Access D14 5 Roof drainage D15 6 Provision of information D16-D17 6

MATERIALS Materials standards M1 6 Structural timber M2-M3 6 Restraint straps and holding down straps M4 6 Roofing materials M5 6 Reclaimed materials M6 7

SITEWORK Sitework standards S1 7 Wall plates S2 7 Strapping S3 8 Trussed rafters S4-S6 8 Traditional cut roofs S7-S8 9 Water tank supports S9 10 Fascias, bargeboards and soffits S10 10 Roofing materials S11 10 Flashings and weatherings S12 12

7.2 Fire-stopping S13 14 Thermal insulation S14 14 Roof drainage S15 14

APPENDIX 7.2-A Roof tile fixings 15 APPENDIX 7.2-B Bracing requirements for trussed rafter roofs 16 APPENDIX 7.2-C Tank support details 18 APPENDIX 7.2-D Sizes and spacing of tile battens 19 APPENDIX 7.2-E Strutting for attic trusses and cut roofs 19 that have a floor APPENDIX 7.2-F Durability classification of natural slates 19 INDEX 20 Licensed copy from CIS: DUBLIN, DUBLIN INSTITUTE OF TECHNOLOGY, 07/02/2014, Uncontrolled Copy. Pitched roofs 7.2

(d) sizing and spacing of members (c) lateral restraint straps DESIGN STANDARDS Sizing and spacing of rafters and ceiling For dwellings of masonry construction, joists should be as: restraint should be provided at rafter level 7.2 - D1 Design shall meet the Technical • clause D5 for trussed rafter roofs for gable walls. Larger gable or separating Requirements • clause D6 for traditional cut roofs. walls may also require restraint at ceiling Design that follows the guidance below will level. See sitework clause S3. Generally, the spacing of rafters and ceiling be acceptable for pitched roofs. joists should be not more than 600mm. Guidance in assessing when ceiling The spacing of ceiling joists should suit restraint is needed can be found in STATUTORY the thickness and size of the plasterboard Building Regulations. sheets or other ceiling finish. Plasterboard REQUIREMENTS Lateral restraint straps should have a sheets may be fixed at the following joist minimum cross section of 30mm x 5mm 7.2 - D2 Design shall comply with all centres: relevant statutory requirements and a minimum anchorage downturn • 9.5mm sheets - up to 450mm of 100mm. The level of galvanizing for Designs should be in accordance with spacing straps and their fixings should be in relevant Building Regulations and other accordance with Tables A.1 and A.2 of statutory requirements. • 12.5mm and - up to 600mm 15mm sheets spacing BS EN 845-1(reference should be made to Appendix 6.1-F). Sheradizing is not LOADBEARING Proprietary roof systems should be acceptable in Northern Ireland and the STRUCTURE designed by an Engineer in accordance Isle of Man. Straps should be of sufficient with Technical Requirement R5. length to be fixed to three trusses and 7.2 - D3 All pitched roof structures shall should be fixed with solid blocking. be designed to support applied loads and (e) size and spacing of tile battens self weight without undue movement The size and spacing of tile battens should In framed roofs, as an alternative, purlins and pole plates can also provide restraint Items to be taken into account include: be in accordance with the roof covering manufacturer’s recommendations, but not if the timber abuts a gable construction. (a) dead and imposed loads less than shown in the table in Where purlins are used to provide restraint Dead and imposed loads should be Appendix 7.2-D. they should not be spaced at more than calculated in accordance with BS EN 2m centres, unless the design shows they Nails for fixing battens should be 3.35mm 1991-1-1,BS EN 1991-1-3 and BS EN 1991-1-4. are adequate at greater spacing. (10 gauge) x 65mm long. Galvanized Dead loads include the self weight of smooth round nails are acceptable, except In trussed rafter roofs, an alternative is to the roof structure and the roof covering. where the maximum basic wind speed is provide restraint through gable Imposed loads include snow loadings and over 26m/s (from National Annex Figure ladder detailing. the weight of water tanks, insulation, etc. NA.1 of BS EN 1991-1-4), where ring shank (d) timber frame construction nails should be specified. Structural timber should be specified For dwellings of timber frame according to the strength classes in BS EN 7.2 - D4 All pitched roof structures shall construction, the designer should ensure 338. Timber specifications when using BS stability in accordance with BS EN 1995-1-1. 4978 grading rules (eg GS) should be in be designed so as to transmit loads accordance with BS EN 1912 or strength and give restraint to the supporting class specified and also include the structure without undue movement TRUSSED RAFTER ROOFS timber species. Items to be taken into account include: 7.2 - D5 Trussed rafters shall be designed to support applied loads and (b) wind loads (a) wall plates self weight without undue movement Wind loads appropriate to the site location Normally, trussed rafter roofs and 7.2 should be calculated in accordance with BS traditional cut roofs should be supported Items to be taken into account include: EN 1991-1-4. The roof should be designed on timber wall plates. (a) recognised design standards to resist wind uplift. This resistance is Trussed rafters should be designed often provided by the weight of the roof Wall plates should be as detailed in Clause in accordance with PD 6693-1. Truss itself but holding down straps should be D6(b) with regard to the table concerning manufacturers may have their own provided where the self weight of the roof minimum sizes. Fixings to connect the computer programs for calculating truss is insufficient. roof structure to the wall plate should be specified having regard to the roof designs in accordance with the British (c) holding down straps construction and the exposure conditions Standard. Holding down straps may be required in of the site. (b) design information certain geographical locations and with For trussed rafter roofs not subject to To ensure that trussed rafters are correctly certain types of roof construction. Some uplift, the minimum fixing should be two designed and fabricated, and are suitable roof covering manufacturers provide 4.5mm x 100mm long galvanized round for their intended purpose, an accurate detailed guidance. wire nails, skew nailed, one from each side specification is necessary. Where holding down straps are necessary, of the trussed rafter. Alternatively, truss PD 6693-1 gives a list of information to they should have a minimum cross clips can be used, fixed in accordance with be supplied to the truss manufacturer, section of 30mm x 2.5mm and be fixed at manufacturers’ instructions. including the: maximum 2m centres. Steel straps with a In Scotland, nails should be appropriate to • height and location of building with galvanized finish are normally acceptable. wall plate dimensions. reference to unusual wind conditions The design should detail how straps are • profile of the trussed rafter, including to be fixed and what materials are to be (b) holding down straps camber, if required used. The durability of fixings should be In situations where the roof is required • span of the trussed rafter compatible with the straps. to resist uplift, skew nailing is unlikely to • pitch or pitches of the roof provide sufficient strength. Appropriate metal straps should be used.

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• method of support and position (i) combined trussed rafter and cut roofs of supports Particular care is needed where trussed • type and weights of roof tiles or rafters and a cut roof are combined in a covering, including sarking, insulation roof design. The designer should provide trimming and ceiling materials trussed details of the complete roof. Trussed • size and approximate position of any rafters rafters supporting traditional cut roof water tanks or other equipment to be members should be designed by an supported on the trussed rafters Engineer in accordance with Technical • overhang of rafters at eaves and other Requirement R5. eaves details • positions and dimensions of hatches, a (j) strutting to attic trusses chimneys and other openings c The part of an attic truss which forms a b • use of the building with reference to any floor should have strutting in accordance • unusual environmental conditions b with Appendix 7.2-E. • type of preservative treatment, (e) mono-pitch trusses and girder where required trusses TRADITIONAL CUT ROOFS • spacing of trussed rafters and special Hipped roofs constructed with trussed 7.2 - D6 Cut roofs shall be designed to timber sizes, where these are required rafters will generally require a series support applied loads and self weight to match existing construction. of diminishing mono-pitched trusses without undue movement supported by a girder truss. The building designer should ensure Items to be taken into account include: that the design of the roof as a whole The bearing of mono-pitched trusses into is satisfactory in achieving the overall shoes should be as follows: (a) recognised design standards stability of the complete structure. Sizes of certain roof members for basic This includes its connection to, and Span Minimum Minimum pitched roofs are given in TRADA Eurocode compatibility with, the supporting bearing thickness 5 span tables (3rd edition) and BS 8103. structure and adjacent elements of length of truss the building. member Where spans, sizes, spacing or strength classes of timber are outside the scope of Less than 4m 50mm 35mm (c) bracing authoritative tables or where the form of The building designer should specify 4m or more 75mm 35mm roof is other than a basic pitched roof, the all bracing. Trussed rafter roofs should roof should be designed by an Engineer in be braced in accordance with Table 1 in Alternative bearings should be designed by accordance with Technical Requirement Appendix 7.2-B, unless the roof is designed an Engineer in accordance with Technical R5. Calculations should be based on and braced in accordance with PD 6693-1. Requirement R5. BS EN 1995-1-1 and PD 6693-1.

All timber bracing to trussed rafters should (f) water tank support (b) member sizes be at least 100mm x 25mm in section and Where water tanks are supported by roof Unless the roof is designed by an Engineer twice nailed to each trussed rafter and to trusses, their load should be transferred to in accordance with Technical Requirement the wallplate. Nailing should be 3.35mm the node points of the trussed rafter and R5, traditionally, nominal sizes of members (10 gauge) x 65mm long galvanized round spread over at least three trussed rafters would be as follows: wire nails. in accordance with PD 6693-1. Member Minimum size (d) spacing A correct method of water tank support is (mm) Trussed rafters should not be spaced at shown in Appendix 7.2-C. Struts and braces 100 x 50

7.2 centres greater than 600mm. Where this Proprietary tank support systems should cannot be achieved, eg to accommodate be assessed in accordance with Technical Wall plates (Scotland) 100 x 25 hatch openings or chimneys, the spacing of Requirement R3. trussed rafters may be increased as shown Wall plates (Northern 100 x 38 below provided that the spacing between Ireland & the Isle (g) multiple trussed rafters of Man) centres of trimming trussed rafters does All multiple and reinforcing timbers to not exceed 2 times the design spacing of simple or multiple trussed rafters should Wall plates (other) 75 x 50 trussed rafters and that b is smaller than be designed to be permanently fastened Hips rafter cut + 25 or equal to 2a - c, where: together. The timber members should be Valleys 32 thick a = design spacing of trussed rafters either fixed together during manufacture or, alternatively, fully detailed drawings Ridges rafter cut + 25 b = distance between centres of trimming and specifications showing the fixing trussed rafter and adjacent method should be supplied to the site (c) triangulation trussed rafter to enable the components to be In the design of a cut roof, timber members assembled correctly. c = nominal width of required opening. should be triangulated or otherwise arranged to form a coherent structure. All (h) roofs incorporating valleys or other forces inherent in the design should be special features resolved. The method of fixing or jointing Roofs with hips, valleys or other special members should be specified. features should be designed by an Engineer in accordance with Technical Particular care should be taken to ensure Requirement R5. Standard designs adequate triangulation when designs supplied by manufacturers which incorporate hips and valleys, and when cut incorporate these features will usually roofs are used in conjunction with be acceptable. trussed rafters.

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Details of all structural members should of Appendix 7.2-A, unless the manufacturer (f) rigid sarking be provided. specifies otherwise. In areas of severe exposure, a rigid sarking with underlay is recommended and is Fixings for single and double lap tiles (d) strutting to cut roofs normal practice in Scotland. Any part of a cut roof which forms a floor should be designed in accordance with should have strutting in accordance with BS 5534 and BS EN 1991-1-4. Where tile The choice of rigid sarking should take Appendix 7.2-E. manufacturers have computer programs account of the type and fixing of the roof based on these British Standards, their covering.The following materials TIMBER TREATMENT recommendations should be followed. are acceptable: • tongued and grooved or square edged Tables 2 and 3 of Appendix 7.2-A contain 7.2 - D7 Measures shall be taken to boarding to BS 1297 minimum fixings for tiles. The tile ensure durability of timber • bitumen impregnated insulating board manufacturer will be able to advise on to BS 1142 : Part 3 (sarking and Items to be taken into account include: any additional nails or clips required for sheathing grade) a particular location. A fixing schedule (a) treatment against House • exterior grade plywood to BS EN 636, produced by the tile manufacturer, based Longhorn Beetle service class 3 on The Zonal Method, is acceptable. In some areas of the UK, treatment against • type P5 chipboard to BS EN 312 House Longhorn Beetle is required. To avoid the use of small sections of cut • oriented strand board type OSB3 to Reference should be made to relevant tiles, which are difficult to fix, double tiles, BS EN 300 Building Regulations. Reference should tile-and-a-half or half tiles should be used • proprietary products which have been also be made to Chapter 2.3 ‘Timber where available from the manufacturer. assessed in accordance with Technical preservation (natural solid timber)’ (Design). Requirement R3. (c) slates (b) timber requiring treatment Natural slates should be fixed in To avoid damage from condensation, The following timber members should be accordance with BS 5534 and BS EN proprietary insulation boards should either naturally durable or suitably treated: 1991-1-4. Each slate should be nailed twice be used strictly in accordance with • fascias when centre nailed. the recommendations given in the • bargeboards independent assessment. • soffits (d) roof coverings other than tiles or (g) flashings and other weathering • tiling battens slates details where a pitched roof abuts a • other trim. Lead sheet roofing should be in accordance with BS 6915. vertical surface These timber members should, where Where a roof abuts a vertical surface, appropriate, also be painted or stained in Other types of sheet roofing should be in cover flashings, stepped cover flashings, accordance with the recommendations accordance with the relevant parts of soakers, secret gutters and back or in Chapter 8.5 ‘Painting and decorating’ CP 143. parapet gutters should be provided as necessary. Where the roof is over an (each section). Roofs with the following traditional enclosed area the wall construction should coverings should be designed in In pitched roofs with a fully supported include cavity trays linked to the flashings. accordance with satisfactory custom weatherproofing membrane, the following Reference should be made to Sitework and practice: timber members should be either naturally clause 7.2 - S12(f) for details. durable or suitably treated: • natural stone • rafters • shingles Cover flashings should be tucked 25mm • purlins • thatch. into a brick joint or chase not less than 75mm above the intersection with the roof. • ceiling joists Thatching should be as recommended

• bracing 7.2 by the Thatch Advisory Service or other Flashings and soakers should be of non- • sarking appropriate authority in accordance with ferrous metal and of the same material to • wall plates Technical Requirement R3. avoid electrolytic action. • battens for fixing vertical cladding • porch posts. Proprietary roof coverings including roof Where lead is used, soakers should be lights should be assessed in accordance at least Code 3 and flashings, gutters, The level of durability of all the above with Technical Requirement R3. saddles, etc should be Code 4 or better. members can be achieved by natural durability or treatment with preservative. (e) roof underlays In the case of gutters behind parapet walls, Reference should be made to Chapter 2.3 An underlay should be provided for all provision should be made for an overflow ‘Timber preservation (natural solid timber)’ tiled roofs. in case the outlet becomes blocked. (each section) for guidance. The underlay may be felt to BS EN 13707 or (h) weathering details where a pitched WEATHERTIGHTNESS a proprietary sarking membrane complying roof intersects with a continuous with Technical Requirement R3. Where waterproof membrane 7.2 - D8 Roofs shall be designed to the underlay is exposed at eaves level it For information on intersections with flat satisfactorily resist the passage of rain should be UV resistant or type 5U felt. roofs, gutters or valleys, reference should and snow to the inside of the building Alternatively, proprietary eaves guards be made to Sitework clause 7.2 - S12(e). may be used. A type 1F felt may be used Items to be taken into account include: for the remainder of the roof. (i) pipes (a) weathertightness of roof coverings Where soil pipes, vent pipes or other pipes To prevent the underlay sagging at the penetrate roof tiling, a lead slate flashing, Roofs with a tile or slate covering should eaves and forming a water trap behind the be designed in accordance with BS 5534. or a purpose-made accessory supplied by fascia, the underlay should be supported the roof covering manufacturer to form a by a continuous fillet or proprietary eaves (b) tiles weathertight joint, should be used. support tray. For tiled roofs, the pitch, gauge and lap should be within the limits given in Table 1

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If lead slates are used, they should be (m) verges (c) fixing supported (e.g. using exterior grade Where slates or plain tiles are used, the Every tile or slate should be nailed twice plywood) to prevent the lead sagging. verge should project 38mm to 50mm and comply with the general requirements beyond the gable wall or bargeboard. of BS 5534. (j) chimneys Interlocking tiles can project 30mm Flashings should connect with the chimney to 60mm. (d) weathering details dpcs. The normal flashing components Bottom edges should be finished with an are shown in Sitework clause 7.2 - S12(g). Unless a proprietary dry verge system under-course tile. At dormer cheeks, the Components will vary depending on or cloaked verge is used, tiles should be tiles or slates should be specified to be whether the chimney intersects the roof at bedded into a minimum 100mm wide bed cut close to the slope of the roof, over a eaves or ridge level and the type of of mortar on an undercloak of cement flashing fixed to the side of the dormer. roof covering. Reference should be based board, plain tile or slate which in At internal or external angles, purpose made to roof covering manufacturers’ turn should be bedded onto the gable wall made corner tiles or soakers should be information sheets. with mortar or suitable bedding sealant. Plain tiles should not be used as an used to form a weathertight joint. For more detailed information on the undercloak below 30°pitch or on Where pitched roofs abut masonry walls, construction and weatherproofing of a bargeboard. a stepped flashing should be specified, chimneys, reference should be made to turned behind the tiles. Details are shown Chapter 6.8 ‘Fireplaces, chimneys Where verge clips are specified, these in Sitework clause 7.2 - S12. and flues’. should be twice nailed to battens and sized to ensure that they are in direct contact For information regarding vertical tiling (k) ridges and hips with the top surface of the verge tile. or slating on walls, reference should be All ridge and hip tiles should be made to Chapter 6.1 ‘External masonry mechanically fixed with self sealing At verges: walls’ (Design and Sitework) or Chapter 6.2 non-ferrous fixings into timber battens. • cut plain tiles are not acceptable and ‘External timber framed walls’. Where proprietary systems are used purpose made plain tile and a half they should be fixed in accordance with should be used manufacturer’s recommendations. • small sections (less than a half tile INSULATION AND width) of cut single-lapped interlocking CONTROL OF Where ridge and hip tiles are bedded tiles should not be used on mortar to rolled tiles, concealed or • natural slate verges should be formed CONDENSATION decorative dentil tiles should be fully with full slates and either slate-and-a- 7.2 - D10 Roofs directly above habitable bedded into all joints in excess of half or half slates that are a minimum rooms shall be adequately insulated 25mm thick. 150mm wide • all tiles and slates should be The BRE Report ‘Thermal insulation: mechanically fixed at the verge in avoiding risks’ discusses aspects of accordance with Appendix 7.2-A. insulation relevant to pitched roofs. In England and Wales account should be (n) Proprietary roof coverings taken of Accredited Construction Details. Proprietary roof coverings should comply with Technical Requirement R3. Insulation should be of sufficient thickness to meet the requirements of 7.2 - D9 Vertical tiling and slating shall Building Regulations. adequately resist the passage of rain To reduce the risk of freezing, and and snow to the inside of the building condensation on pipework, the guidance in Items to be taken into account include: 7.2 Sitework clause 7.2 - S14 should be followed. (a) moisture barrier Proprietary dry fixed systems should be A moisture barrier should be provided 7.2 - D11 Measures shall be taken to assessed in accordance with Technical behind all vertical tiling and slating. control condensation Requirement R3. Moisture barriers should be: Items to be taken into account include: (l) valleys • underfelt or equivalent where the wall Valleys should be formed with structure is brickwork or blockwork. (a) ventilation of main roof spaces purposemade valley tiles or as an open See Design clause 6.1- D14(c) Pitched roofs with insulation at ceiling valley lined with glass reinforced plastic • a breather membrane where the level should always be ventilated to the (GRP), lead or other material acceptable supporting structure is of outside air to minimise the risk under Technical Requirement R3. timber construction. of condensation. Where slates or plain tiles are used, a For detailed information on the use of For roofs that incorporate a high water laced valley, swept valley or mitred tiles moisture barriers in association with vapour resistance (type HR) underlay (e.g. with soakers may also be used. Valley tiles timber frame construction, reference types 1F/5U felts): should be fixed in accordance with the should be made to Chapter 6.2 ‘External • eaves ventilation should be provided manufacturer’s recommendations and timber framed walls’. on opposite sides of the roof to permit small cut tiles should be avoided. cross ventilation. Reference should be (b) batten size made to Sitework clause 7.2 –S11(a) for GRP or other materials should be lapped Batten sizes should comply with illustrations showing where ventilation in accordance with manufacturer’s Clause D3(e). should be provided recommendations. Minimum Code 4 • where the roof pitch is 15°or more, lead or other suitable saddle flashing is cross ventilation should be provided to required at the head of all valleys. the roof void equivalent to a 10mm slot running the full length of the eaves

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• where the ceiling follows the slope of a Acceptable protection of openings can be ‘cold roof’ regardless of pitch or where provided by using materials complying firestop between battens a cold roof has a pitch less than 15°, with Materials clause 7.2 - M5(j). above underlay cross ventilation should be provided A spacer in the eaves should be used so to the roof void equivalent to a 25mm firestop below that ceiling insulation can be installed underlay slot running the full length of the eaves. over and beyond the wall plate. This A nominal 50mm clearance should be minimises the cold bridge without blocking maintained between the insulation and the ventilation. The spacer should be the roof underlay of sufficient length to maintain the • where the roof pitch exceeds 35°or ventilation above the insulation. when the span exceeds 10m, high level cavity closed ventilation, equivalent to a continuous cold roof at eaves 5mm opening, should be used in cavity spacer maintains cavity barrier of barrier in 25mm clear air way mineral wool or separating wall addition to eaves ventilation above insulation fire-resisting board • the means of providing cross ventilation in boxed eaves

to mono-pitched roofs should be in accordance with BS 5250 which Where a wall separates an integral indicates eaves ventilation together with garage from the rest of a dwelling, other the equivalent of a continuous 5mm slot insultation above cavity closer and arrangements are possible provided the at high level wall plate avoids a cold bridge principle of half-hour fire separation is maintained. For unventilated cold roofs that incorporate a low water vapour resistance ventilation (type LR) underlay (e.g. a vapour ACCESS permeable underlay): (e) other methods of reducing 7.2 - D14 Roof voids shall be provided • ridge or high level ventilation equivalent with suitable access to a continuous opening of 5mm should condensation be provided in accordance with BS 5250. Methods of reducing condensation, such as Access should be provided to: draughtstripping loft hatches and sealing Where vapour permeable underlays are holes for services, are given in Sitework • the main roof space, and used on sloping roofs, with areas over clause 7.2 - S14. • roof voids that contain cisterns, tanks covered by non-permeable materials and the like. (eg flat roofed areas of mansard roofs), FIRE SPREAD Access is not required to other roof voids ventilation equivalent to a continuous containing only water pipes. opening of 5mm should be provided at the 7.2 - D12 Roofs shall adequately resist fire spread highest point of each roof slope. SIZE OF OPENINGS Items to be taken into account include: Access openings should be not less than (b) position of vapour checks 520mm in any direction. Vapour control layers should be used in (a) roof coverings roof constructions where the ceiling board Slates and concrete or clay tiles are Where equipment (e.g. heating and is fixed to the rafters. designated AA when tested to BS 476 : ventilation equipment) is located in a roof space the size of the opening should Where the ceiling below a cold pitched Part 3 and therefore can be used without permit its removal. roof incorporates a vapour control layer, limitation on any pitched roof. The use of some other materials is restricted the design should take account of the Access openings should not be located by statutory requirements, particularly ventilation to the dwelling to prevent directly over stairs or in other in relation to their distance from site 7.2 condensation problems in the home. hazardous locations. Further guidance can be found in BS 5250. boundaries (reference should be made to Building Regulations). These include: PROVISION OF WALKWAYS Vapour control layers, where required, • bitumen felt slates Boarded walkways should be provided: U1 should be placed on the warm side of • wood shingles • between the access opening and any insulation. • thatch. cistern or other permanent equipment (c) ventilation of dormers (b) chimneys and flue pipes located in the roof space, and Pitched dormers should be ventilated from Combustible material, such as roof timbers • at each cistern or other permanent eaves to eaves or, where necessary, from and sarking felt, should be kept away from equipment suitably located for 2 eaves to ridge. heat sources as described in Chapter 6.8 maintenance purposes and at least 1m ‘Fireplaces, chimneys and flues’ (Design). in area. Flat roofed dormers of cold deck Boarding should be securely fixed without construction should be ventilated. The 7.2 - D13 Junctions between roofs and compressing the loft insulation. ventilation path should not be blocked compartment or separating walls shall by the timber structure, strutting, etc adequately resist fire spread (reference should be made to Chapter 7.1 The junction between a separating or ‘Flat roofs and balconies’ (Design compartment wall and a roof should and Sitework)). be firestopped. If there are gaps, fire, (d) methods of ensuring unobstructed smoke and flame can spread from one ventilation compartment to the next across the wall. Ventilation openings where the least Mineral wool fire-stopping should be used dimension exceeds 10mm should be to allow for movement in the roof timber, protected to prevent the entry of birds, etc. and avoid ‘hogging’ of the roof which is often associated with mortar fire-stopping.

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ROOF DRAINAGE • supports for water cisterns in the (see Appendix 6.1-F). Fixings and straps roof space should be compatible. Sheradizing is not 7.2 - D15 Roof drainage shall adequately • restraint strapping acceptable in Northern Ireland and the Isle carry rainwater to an outfall • position, thickness and limits of of Man. insulation. Items to be taken into account include: Straps should be ordered to the correct (a) provision of gutters and downpipes 7.2 - D17 All relevant information shall length and with the correct number of 2 be distributed to appropriate personnel bends and/or twists required by the design. Roofs greater than 6m in area should be provided with rainwater gutters and Ensure that design and specification downpipes. Consideration should also information is issued to site supervisors ROOFING MATERIALS be given to the provision of rainwater and relevant specialist subcontractors and/ 7.2 - M5 Roofing materials shall be 2 drainage to roof areas less than 6m , for or suppliers. of the quality, type and dimensions example dormer and porch roofs. required by the design Rainwater pipes passing through dwellings MATERIALS STANDARDS Items to be taken into account include: should be insulated in accordance with Sitework clause 8.1 - S8(c). 7.2 - M1 All materials shall: (a) roof coverings The following roof coverings (b) sizes (a) meet the Technical Requirements are acceptable: Gutters and downpipes should be of (b) take account of the design • clay tiles and fittings to BS EN 1304 sufficient size to accommodate Materials that comply with the design and • concrete tiles and fittings to BS EN 490 normal rainfall. the guidance below will be acceptable for and BS EN 491 pitched roofs. Care is needed in sizing gutters where • fibre cement slates and fittings to BS dormer roofs interrupt the run-off from a Further guidance for the selection of EN 492 pitched roof. The gutter should be sized to materials can be found in Technical • natural slates to BS EN 12326 (see cope with the concentrated flows. Requirement R3 (see Chapter 1.1 Appendix 7.2 - F). ‘Introduction and Technical • shingles should be of Western Red (c) discharge from one roof to another Requirements’). Cedar, suitably treated and be Grade 1 to Where water from a large roof surface the Canadian Standards Association. discharges onto another surface, Natural stone should be used in precautions should be taken to prevent STRUCTURAL TIMBER accordance with established custom and erosion of the lower surface. 7.2 - M2 Structural timber shall be of practice. the appropriate grades and sizes to (d) discharge into drainage system support the imposed loads Thatch should be as recommended by Unless designed otherwise, shoes should the Thatch Advisory Service or other be provided to rainwater downpipes. Structural timber should be specified according to the strength classes in BS EN appropriate authority in accordance with Technical Requirement R3. PROVISION OF 338. Roof members are usually C16, C24 or TR26. Use of reclaimed materials is covered in INFORMATION Timber specifications when using the BS Clause M6. 7.2 - D16 Designs and specifications 4978 grading rules should be accordance Proprietary coverings should be assessed shall be produced in a clearly with BS EN 1912 or strength class specified in accordance with Technical Requirement understandable format and include all and also include the timber species. R3. relevant information 7.2 - M3 Structural timber shall be of

7.2 (b) fixings Full details of trussed rafter roofs should suitable durability Clout or slate nails for fixing slates and be available on site, including the following: tiles should be one of the following and at • layout drawing of trusses and Structural timber should be pre-treated least 38mm long: associated items with preservative where specified by • aluminium to BS 1202 : Part 3 • bracing requirements the designer. Chapter 2.3 ‘Timber • copper to BS 1202 : Part 2 • trimming around chimneys, access preservation (natural solid timber)’ • silicon bronze. hatches, etc (each section) recommends methods of • mono-pitch and lean-to roofs preservative treatment. Galvanized steel nails are not suitable for • girder trusses, multiple trusses and Use of reclaimed materials is covered in fixing slates and tiles because of the risk of diminishing trusses and how they are Clause M6. damaging the galvanizing but may be used fixed together and supported on truss to fix battens and underlay. Nails for fixing shoes, layboards or similar battens should be at least 30mm longer • roof intersections (ie hips and valleys). RESTRAINT STRAPS AND than the batten thickness. Ring shank nails should be used when specified by the Assembly drawings are also important HOLDING DOWN STRAPS designer. where there are complicated roof shapes 7.2 - M4 Strapping shall be of adequate or where trussed rafter and framed roofs strength and durability Tile clips should be of aluminium or are used in combination. Lateral restraint straps should have stainless steel. minimum cross section dimensions of The drawings should show: (c) flashings 30mm x 5mm. Vertical holding down • the number and type of fixings for The following are acceptable: straps should have minimum cross section roof coverings • rolled lead sheet to BS EN 12588. dimensions of 30mm x 2.5mm. • means of providing eaves ventilation Flashings, gutter linings, etc should be at • fire-stopping at separating wall and Mild steel straps and fixings should be least Code 4, soakers may be Code 3 boxed eaves protected against corrosion in accordance • aluminium and aluminium alloys to • flashing details at abutments, with Tables A.1 and A.2 of BS EN 845-1 BS 1470 (0.6mm to 0.9mm thick) and chimneys, etc

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1 protected from contact with mortar by a (g) insulation sharp sand should not be less than /3 of coating of bituminous paint Thermal insulation should be to the the total sand content. • zinc alloy to BS 6561 and 0.6mm thick design specification. Alternatively, proprietary mortar mixes • copper to BS 2870, 0.7mm thick is The following materials are acceptable: may be accepted by NHBC if they are suitable for gutters, 0.55mm thick fully shown to have similar strength, durability annealed is suitable for flashing, soakers and workability. and saddles. •mineral fibre mats to BS EN 13162 •blown mineral fibre to BS 5803 : To prevent electrolytic action where metal Part 2 RECLAIMED MATERIALS items may be in contact, eg flashings and soakers, these should not be of different •blown cellulose to BS 5803 : 7.2 - M6 Reclaimed materials shall be: metals. fibre Part 3 (a) of the type, size and quality required Proprietary flashings should be assessed •proprietary materials assessed in the design in accordance with Technical Requirement in accordance with Technical (b) suitable for re-use R3. Requirement R3. Materials recovered from older buildings, such as timber, slate or tile, may be (d) underlays Insulation of water pipes should be in re-used only with the prior agreement of Underlay may be felt to BS EN 13707. accordance with Chapter 8.1 ‘Internal the NHBC. Independent certification of Proprietary underlays should be assessed services’ (Materials). suitability may be required. in accordance with Technical Requirement R3. Manufacturers’ recommendations (h) fascias, bargeboards and soffits should be followed. Timber used for fascias, bargeboards, SITEWORK STANDARDS soffits, etc should be pre-treated with Where the underlay is exposed at eaves preservative. Reference should be made to 7.2 - S1 All sitework shall: level it should be UV resistant or type Chapter 2.3 ‘Timber preservation (natural 5U felt. Alternatively, proprietary eaves (a) meet the Technical Requirements solid timber)’ (Materials) for guidance on (b) take account of the design guards can be used. A type 1F felt may be preservative treatments. used for the remainder of the roof. (c) follow established good practice The following materials are and workmanship To minimise the risk of condensation in also acceptable: Sitework that complies with the design and the case of a fully supported underlay • exterior grade plywood to BS EN 636 the guidance below will be acceptable for above rigid sarking, underlays should have service class 3 pitched roofs. a low vapour resistance, preferably less • high density fibre reinforced calcium than 0.25MNs/g. Underlays with a higher silicate board that meets the WALL PLATES vapour resistance may need increased performance requirements of BS 3536 7.2 - S2 Wall plates shall be bedded to ventilation to the roof space and between • glass fibre reinforced cement (GRC) distribute roof loads and fixed to prevent the underlay and sarking. Manufacturers’ board that meets the performance wind uplift recommendations should be followed. requirements of BS 3536 (e) rigid sarking • proprietary products which have been Roof construction details should The following materials are acceptable: assessed in accordance with Technical be available on site, particularly for • tongued and grooved or square edged Requirement R3. combination and specialist roofs. boarding to BS 1297 (i) fire-stopping and cavity barriers Wall plates should be bedded to line and • bitumen impregnated insulating board Cavity barriers in boxed eaves should be level using nails or straps to hold them to BS 1142 : Part 3 (sarking and wire reinforced mineral wool blanket, at down in accordance with the

sheathing grade) least 50mm thick. Ordinary mineral wool design requirements. 7.2 • exterior grade plywood to BS EN 636 quilt is acceptable as fire-stopping above Wall plates should generally be in lengths service class 3 separating walls. • type P5 chipboard to BS EN 312 of not less than 3m but shorter lengths • oriented strand board type OSB3 to (j) protection to ventilation openings should extend over at least 3 joists/rafters BS EN 300 Ventilation openings where the least or trusses. Wall plates should be joined • proprietary products which have been dimension exceeds 10mm should be using half-lapped joints at corners and in assessed in accordance with Technical protected to prevent the entry of birds, etc. running lengths. In Scotland, where 100mm Requirement R3. x 25mm wall plates are used, they should Acceptable protection of openings can be be in long lengths and butt jointed. (f) battens and counter battens provided by: Battens and counter battens should be to • rigid fabrications with width of opening Where required, holding down straps the sizes specified in the design. Timber greater than 3mm and less than 10mm should be fixed to the wall plate at used for battens and counter battens (no restriction on length) maximum 2m centres. If the strap is not should be as listed in BS 5534 and be • rigid fabrications with round holes turned into a bed joint, it should be fixed to marked accordingly, (see Appendix 7.2-D). greater than 3mm and less than 10mm the wall with at least four screw fixings. in diameter Battens should be preservative treated • square or rectangular mesh where the unless the timber is naturally durable. clear opening size is greater than 3mm Reference should be made to Chapter 2.3 and less than 10mm. ‘Timber preservation (natural solid timber)’ (k) roof mortar (Materials) for guidance on the timber Roofing mortar should be 1:3 cement:sand types and classes requiring treatment. Cut with plasticiser. The mix should be based ends of battens that are in contact with on sharp sand with soft sand added to mortar should be treated with a liberal achieve workability. The proportion of brush coating of preservative.

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strap with cross section of STRAPPING 30mm x 2.5mm

7.2 - S3 Straps shall be used, where rafter necessary, to restrain gable and separating walls and hold down the roof at least 4 S against wind uplift screw fixings per strap RESTRAINT STRAPS lowest fixing not Restraint straps, or a restraining form more than 150mm from of gable ladder, are required to provide bottom of strap stability to walls. They should be installed as shown in the design and at not more ceiling tie than 2m centres for buildings up to three

storeys (two storeys in Scotland). Higher strap at least 1m long projection not more than: -50mm, or buildings straps should be spaced at not -one-third x S whichever is the greater more than 1.25m centres. TRUSSED RAFTERS Restraint straps should be fixed to solid noggings with a minimum of four fixings of 7.2 - S4 Trussed rafters shall be which one should be in the third rafter. The protected from damage before and Trussed rafters should be evenly spaced fixings should be four steel screws or four during construction and vertical. Temporary bracing should be 75mm x 4mm (8 SWG) round nails. provided to control the spacing and keep Items to be taken into account include: trusses vertical. Rafters should not be notched to make the straps flush with the rafter. Straps should (a) storage Trussed rafters should be fixed to the wall go under rafters and over ceiling joists. To avoid distortion and prevent damage, plates either: The turn-down should be on a substantial trussed rafters should be stored clear of • in accordance with the design, or piece of blockwork, preferably the centre the ground, either flat on level bearers • using double skew nailing or truss clips. of an uncut block. placed under joints (for short term storage) or vertically and propped (for long Avoid damaging the metal truss plates, packing between term storage). trussed rafters or wall plates. rafter and wall nogging fixed horizontally avoids twisting Trusses should be protected against The spacing or structure of trusses should restraint straps weather to prevent corrosion of truss not be altered without the plates and deterioration of the timber. designer’s approval. Ventilation should be provided. Where the width of gable ladders exceeds Any damaged trussed rafters or trussed that of the trussed rafter centres, noggings rafters with loose plates should be should be provided to reduce the span of rejected, not repaired. the roofing tile battens.

strap fixed to solid not more than 600mm centres strap held noggings with at least (b) handling tightly against four fixings of which block inner leaf at least one to be in To prevent distortion during construction, last trussed the third rafter rafter close trussed rafters should be carried upright to wall (if carried flat, bending can loosen HOLDING DOWN STRAPS the fasteners). If the design specifies holding down straps 7.2 7.2 - S5 Trussed rafters shall be to prevent the roof being lifted off the erected in accordance with fabricators’ noggings to supporting structure, they should be at 2m reduce span instructions of tile battens centres (maximum). Detailed guidance on the use and bargeboard Where straps are fixed to masonry, handling of trussed rafters is given in hardened nails 4mm in diameter x 75mm the International Truss Plate Association long or No 12 wood screws x 50mm long Technical Handbook available from trussed into plugs should be used. The gable ladder can be used to provide rafter suppliers. restraint to the external wall if: The number of fixings should be in Detailed drawings should be available • there is blocking between the last accordance with design requirements and on site to show the layout of the trussed trussed rafter and the inner leaf (at a the lowest fixing should be within 150mm rafters, especially at hips, valleys and maximum of 2m spacing), and of the bottom of the vertical strap. trimmings to chimneys, etc. • the soffit board is cut carefully and then fixed securely so as to restrain the Trussed rafters should be supported only outer leaf. at the junction between the ceiling tie and rafter, unless specifically designed 7.2 - S6 Trussed rafters shall be braced otherwise, e.g. as a cantilever. to prevent distortion The roof should be braced using at least 100mm x 25mm timber. All bracing should be twice nailed with 3.35mm (10 gauge) x 65mm long galvanized round wire nails to every trussed rafter it crosses and to the wallplate.

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The minimum bracing requirements • CEILING BINDERS and HANGERS: (d) dormer construction are shown in Appendix 7.2-B. Additional support long span ceiling joists On most dormers, the dormer cheek studs bracing may be needed in exposed areas. • POLE PLATES: similar to purlins but should be supported either by a double Check the design drawings for used where ceiling joists are above wall rafter or by a double floor joist.

special requirements. plate level. dormer rafter if carrying dormer All bracing should be completed before Positions of standard structural cheek studs starting to lay the roof covering. members are shown in the diagrammatic representation below: dormer Longitudinal binders should butt solidly cheek studs against the wall at each end. This is most easily achieved by fixing the binder in two

lap-jointed lengths. plate Braces and binders, where not continuous, ridge should have lapped joints and be nailed to pole plate double joist at least two trusses. spanning between carrying dormer loadbearing walls purlin cheek studs collar binders abuted tightly against gable and separating walls Where cheek framing does not extend binder strut hanger to floor level, a double rafter will give

binders fixed to ceiling ties of trussed rafters, wall plate necessary support to the cheek. The two if necessary using two lap-jointed lengths rafters must be fixed together.

loadbearing wall Trimming members around dormers The part of an attic truss which forms a should be large enough to take the extra floor should have strutting in accordance load from the cut main roof members and with Appendix 7.2-E. (b) prevention of distortion and dormer framing and cladding, as detailed overloading in the design. TRADITIONAL CUT ROOFS The design details for sizes of timber members should be followed. Dormers should be framed up so they are 7.2 - S7 Roof timbers shall be of the independent of the window frame, using a All framing should be completed before grades and sizes shown on the drawings suitable lintel over the opening. roof coverings are laid. Structural timber should be marked to show its strength class (normally C16 or If a roof is not a simple triangle, all trimmer takes load from cut rafters C24). Alternatively, evidence of species members should be fully supported and lay board and grade should be available to determine tied together. If necessary, temporary the equivalent strength class. support to long span members should be used until the framing is complete. The correct size of timber should be used for each member, as shown on the (c) valley and hip construction design drawings. Particular care is needed in the construction of valleys and hips: 7.2 - S8 Construction of traditional lintel supports • valley rafters carry load from both dormer roof cut roofs shall ensure adequate double rafter supports sections of the roof. Valley rafters will dormer cheek studs and load from the trimmer structural stability need to be larger than ordinary rafters

Items to be taken into account include: to take the extra load and to provide 7.2 full bearing for the splay cut of jack (a) location of members rafters. (Long valley rafters may need trimmer takes load All members should be accurately located. intermediate support.) from cut rafters Purlins and binders should be built in, • hip rafters provide spacing and fixing for where necessary. In a typical traditional jack rafters. They need to be a deeper roof, the basic timber members are: section than other rafters to take the (e) jointing of members • RAFTER: carries the weight of the roof top cut of the jack rafters. Purlins should All joints should be cut accurately to fit finish, eg tiles, tile battens and underfelt be mitred at hips, and lip cut to accept tightly. When they are nailed, care should • CEILING JOIST or TIE: triangulates the the bottom of the hip rafter. be taken not to split members. rafters, stopping the walls and roof valley rafter The following should be used at spreading outwards; supports the ceiling main connections: finish and any walkways, etc hip rafters • RAFTERS to ceiling joists: nailed lapped • RIDGE: provides fixing and spacing for joint. The rafter should be birdsmouthed the tops of rafters over and skew nailed to the wall plate • PURLIN: supports long span rafters to prevent deflection and increase stiffness jack rafters jack rafters • STRUTS: give support to purlins to prevent deflection and transmit roof loading to loadbearing structure below. rafters skew nailed to wall plate The following are extra members which may be used on large roofs: • COLLAR: ties the roof together at purlin level

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• RAFTERS to purlin: a birdsmouth joint Angle ties should be used on hipped FASCIAS, BARGEBOARDS should be used if the purlin is roof corners to prevent the wall plates fixed vertically spreading. For heavily loaded hip rafters, AND SOFFITS eg where they are carrying purlins, dragon 7.2 - S10 Fascias, bargeboards and ties or similar bracing should be used to soffits shall be selected, fixed and prevent hip rafter spread. treated against decay in accordance d with the design

birdsmouth joint Items to be taken into account include:

¹⁄³ x d (a) timber quality Timber for external feature work should timber angle tie prevents wall be free from waney edges, large knots and plates spreading resinous pockets, splits and other unsightly defects. dragon tie • PURLIN connections: support should prevents spread (b) fixing of hip rafter be provided directly under joint or use All joints should be cut and fixed neatly. a scarf joint. Any scarf joint should Mitred angles and splay joints should be made near a strut so that the joint be used to prevent exposure of end- supports the longer span. grain. Butt joints to fascias should be splayed. Fascia boards should have two halving joint in purlin when directly over strut plywood angle tie fixings into each rafter and be fixed at a prevents wall plates spreading height that maintains the correct pitch in accordance with the tile manufacturer’s recommendations. steel tie prevents spread of hip rafter (c) treatment against decay Where preservative treated timber is cut or planed, a liberal brush coating of preservative should be applied. All untreated timber that is to be painted should be knotted and primed all round before fixing. When timber requires a notch to fit over angle tie stained finish, one coat of stain should be applied before fixing.

angle tie ROOFING MATERIALS scarf joint near strut supporting longer span of purlin 7.2 - S11 Roofing materials shall be installed in accordance with the design Items to be taken into account include:

wedges and metal (f) strutting to cut roofs (a) ventilation plate to tighten joint Any part of a cut roof which forms a floor All roof voids should be ventilated to 7.2 should have strutting in accordance with prevent condensation problems. Appendix 7.2-E. Ventilation openings where the least dimension exceeds 10mm should be WATER TANK SUPPORTS protected with mesh to prevent entry of 7.2 - S9 Loads from water cisterns shall birds, etc. be transferred to: Where proprietary eaves ventilators are (a) the node points of trussed rafters used, they should be fixed in accordance

In trussed rafter roofs, tank stands should with the manufacturer’s instructions. be supported at the node points of the For roofs that incorporate a high water trussed rafters and the load spread over at vapour resistance (type HR) underlay least three trusses. ventilation should be provided on opposite Correct supports are illustrated in sides of the roof space, equivalent to a Appendix 7.2-C. continuous gap of the width shown in the following drawings: (b) suitable bearers in traditional 5mm 5mm where pitch cut roofs exceeds 35 o or span exceeds 10m In traditional cut roofs, tank stands should be supported as shown in the design.

10mm 10mm

ROOF PITCH OVER 15o

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For unventilated cold roofs that The underlay should be supported and 25mm 25mm incorporate a low water vapour resistance turned up at least 100mm at all abutments (type LR) underlay, (e.g. a vapour to prevent rain and snow being blown into permeable underlay) and insulation over the roof space. a horizontal ceiling, ridge or high level Particular care is needed where pipes ROOF PITCH BELOW 15o ventilation equivalent to a continuous project through the underlay. Torn opening of 5mm should be provided in underlay around pipes can lead to the accordance with the design. 5mm ceiling becoming wet and stained. To avoid water penetration the underlay should be 5mm continuous cut neatly to fit tightly around high level ventilation 10mm or 25mm with LR underlay to suit pitch service penetrations. (c) battens and counter battens Battens should be set out in straight lines, parallel to the ridge and to the gauge

MONO-PITCHED ROOF required by the tile or slate. The lap should not be decreased because this would

at least 50mm reduce weathertightness. The lowest clear airway 5mm 5mm batten should be fixed so that the tile at least 50mm (b) underlays clear airway projects not less than 50mm over 25mm Horizontal laps should be as follows: the gutter. Pitch Minimum horizontal lap 5mm Battens should be: (underlay not fully • at least 1.2m long 25mm 25mm supported) • supported by at least three rafters Less than 15° 225mm • butt jointed on a rafter, and • nailed to every rafter. ROOM-IN-ROOF (flat roof dormer) 15°to 34° 150mm Batten ends should be cut square and 35°and above 100mm nails skew driven on each side of the joint. Where battens are spaced at more than 5mm 5mm Vertical laps in the underlay should occur 200mm, not more than one batten in any 50mm only over rafters and be securely fixed. group of four should be joined over any Horizontal laps should be securely fixed by one truss or rafter. Not more than three regular roof battens. joints should be made together in twelve consecutive battens when the gauge is 25mm Underlay should be supported at eaves 200mm or less. level by a tilting fillet or proprietary eaves support tray. Where the underlay Battens on rigid sarking boards should is exposed at eaves level it should be UV be supported on counter battens to allow ROOM-IN-ROOF (partially sloping ceiling) resistant or type 5U felt. Alternatively, free drainage of any water that may reach proprietary eaves guards can be used. A the underlay. Counter battens should be type 1F felt may be used for the remainder fixed through to the rafters and not to the of the roof. sarking boards alone. Battens should be 5mm 5mm fixed through counter battens to rafters. 50mm Underlay or eaves guards should be 7.2 dressed into the gutter. Battens should be fixed with cut or wire nails. The nail shank can be smooth, annular ringed or helically threaded. Nails

25mm can be steel or aluminium. In coastal areas, steel nails should be hot dip galvanized.

(d) slates and tiles ROOM-IN-ROOF (completely sloping ceiling) Slates should be fully nailed over the lap to suit pitch of roof whole roof. The design should specify the number of underlay supported 10mm or 25mm 10mm or 25mm by tilting fillet and fixings for clay and concrete tiles. Tables 2 to suit pitch dressed into gutter and 3 of Appendix 7.2-A contain minimum fixings for tiles. Additional nails and clips Where traditional mortar pointing is used may be necessary in accordance with the to bed ridge tiles, the underlay should design. A fixing schedule produced by the extend over the ridge. Underlay should tile manufacturer, based on BS 5534 or continue over hips to form a 150mm The Zonal Method, is acceptable. minimum lap parallel with the hip rafter. Careful setting out will improve the At valleys, a strip of underlay should be finished appearance of the roof and PITCHED ROOF DORMER laid under the main roof underlay and held helps to avoid problems such as unequal down by the valley battens, where used. overhangs at verges and often makes it The main roof underlay should be cut to possible to avoid excessive tile cutting the valley batten line. at abutments, chimneys and similar obstructions. Small sections of cut tiles are

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7.2 Pitched roofs

difficult to fix and should be avoided. This Thatching should be as recommended Cut ends of tile battens that are in contact can be achieved by incorporating tile sizes by the Thatch Advisory Service or other with mortar should be treated with a such as double size tiles, tile and a half or appropriate authority in accordance with liberal brush coating of preservative. half tiles where these are available. Technical Requirement R3. At verges: Single lap interlocking tiles have a • cut plain tiles are not acceptable and tolerance of approximately 3mm in the FLASHINGS AND purpose made plain tile and a half joint. For double lapped plain tiles and WEATHERINGS should be used slates, joints should be slightly open. This • small sections (less than a half tile allows some flexibility in setting out and 7.2 - S12 Flashings and weatherings width) of cut single-lapped interlocking should avoid tile cutting. shall be constructed to prevent damp tiles should not be used entering the dwelling • natural slate verges should be formed Bottom edges of double lapped slate and Items to be taken into account include: with full slates and either slate-and-a- plain tile roofs should be finished with an half or half slates that are a minimum under-eaves course. (a) eaves 150mm wide Tiles should project not less than 50mm • all tiles and slates should be across the gutter. For slates or plain mechanically fixed at the verge in cut tiles tiles, an under-eaves course should be avoided accordance with Appendix 7.2-A. at eaves used. Fascia boards should be fixed at a height that maintains the correct pitch in 100mm accordance with the tile manufacturer’s verge tiles recommendations. bedded in mortar on tile-and-a-half undercloak tiles used for correct coursing coverings to project not less than 50mm 38mm to 50mm across the gutter or underlay taken Where verge clips are specified by the 30mm to 60mm over wall cavity manufacturer, these should be twice nailed to the tile batten and be in full contact with The undercloak should lap the roof the upper tile surface to prevent tile lift. underlay but not tilt inwards. Wet bedded Tiles to be bedded on mortar should be verge tiles or slates should be fully bedded on roofing mortar having a minimum width wetted first on their contact surface. underlay dressed into gutter below of 100mm. Verge slates or tiles should be Surface water should be allowed to drain under-eaves tiles before fixing. Substantial thicknesses bedded on the undercloak and completed in one operation. of mortar bedding may be needed, eg beneath rolled tiles. To prevent shrinkage Where required by the design interlocking To prevent the underlay sagging at the of large mortar joints, concealed or single lap tiles should be secured with clips eaves and forming a water trap behind the decorative dentil tiles should be fully and twice nailed in position at the tile lap, fascia, the underlay should be supported bedded into all joints in excess of as well as bedded in mortar. Verge clips by a continuous fillet or proprietary eaves 25mm thick. should be in full contact with the tile to support tray. Proprietary dry fixed systems should be resist uplift. assessed in accordance with Technical (b) verges (c) ridges and hips Requirement R3. All verge tiles and slates should be Where ridge and hip tiles are bedded

7.2 bedded on an undercloak. Alternatively, on mortar they should be mechanically (e) roof mortar proprietary dry verge systems should be fixed with self sealing non-ferrous fixings Roofing mortar should be 1:3 cement:sand fixed in accordance with manufacturers’ into timber battens. Where proprietary with plasticiser. The mix should be based recommendations. on sharp sand with soft sand added to systems are used they should be fixed achieve workability. The proportion of The undercloak should be installed to a in accordance with manufacturer’s 1 recommendations. sharp sand should not be less than /3 of true line and bedded on roofing mortar the total sand content. struck off flush with the external surface of the wall. Alternatively, a suitable Alternatively, proprietary mortar mixes underlay carried ridge tiles beddded exterior grade bedding sealant could be over ridge in mortar and may be accepted by NHBC if they are used in accordance with manufacturer’s mechanically fixed shown to have similar strength, durability recommendations. Where a bargeboard is and workability. used, the undercloak should be securely Mortar bedding and jointing should be nailed to a true line. completed in one operation. The undercloak should be installed at the correct level to ensure that the line of the (f) other roof coverings tiling is maintained where it passes over When using the following materials, the the wall. detailing and workmanship should follow the design and recognised good Where slates or plain tiles are used the Mortar bedding and pointing should be building practice: verge should project 38mm to 50mm completed in one operation and achieve beyond the gable wall or bargeboard. a nominal joint thickness of 10mm. To • sheet metal roofing including lead, Interlocking tiles can project 30mm prevent shrinkage of large mortar joints, copper and zinc to 60mm. concealed or decorative dentil tiles should • thatch be fully bedded into all joints in excess of • cedar shingles. Tile battens should finish 25mm to 50mm 25mm thick. See Design clause D8(k). from the face of the protecting undercloak.

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Where wet bedded tiles are used at hips, the manufacturer’s recommendations and exterior grade sealant in accordance with they should be supported at the base of small cut tiles should be avoided. the manufacturers recommendations. the hip by a galvanized hip iron and project For single lap interlocking tiles, purpose- Cavity trays should be linked to the to the centre line of the gutter. made valley trough tiles should be flashing to prevent water penetrating into (d) valleys and hidden gutters supported by gutter boards. Roof an enclosed area where a: Construction should be adequate in tiles should be cut to the correct rake. • flat or pitched roof over an enclosed relation to: Mechanical cutting gives a neater area abuts a wall • depth appearance than hand cutting. The tiles • balcony abuts a wall. • width should be bedded in mortar, leaving a • undercloaking minimum 100mm wide channel (125mm lead flashing • pointing minimum for pitches below 30°). wedged into joint • adequate support below wall dpc LEAD-LINED VALLEY • pitch. at least 75mm Lead-lined valleys should be Code 4 (colour underlay at least 150mm turned up Valleys should be formed using one of behind coded blue) or Code 5 (colour coded red) flashing clip free edge of flashing - method the following: and supported on gutter boards of 19mm depends on • pre-formed GRP thick exterior grade ply or as specified. exposure • valley coursing tiles (plain tiles) Lead in valleys should be laid in lengths • valley trough tiles (interlocking tiles) not exceeding 1.5m and be lapped 150mm • non-ferrous metal at each length for pitches above 30°. Tiles • a proprietary system. should be cut and bedded as for valley trough tiles except that the mortar should Where a pitched roof abuts the wall at an Where roof coverings are of plain tiles or be bedded on an undercloak (for example angle, a stepped cavity tray linked to a slates, laced and swept valleys may be slate) to prevent direct contact between stepped flashing should be used. Stepped used or, alternatively, a mitred valley with the lead and the mortar. Mortar should not flashings should be cut from a strip at soakers. The true pitch of the valley should bridge the welt detail. least 150mm wide. Soakers or a secret not be less than the minimum allowed gutter should be installed at abutments pitch and GRP or other materials should be (e) flat roof intersection where slates, flat interlocking tiles or plain lapped in accordance with manufacturer’s Where a flat roof adjoins a pitched roof, tiles are used. recommendations. Minimum Code 4 or where valleys or gutters occur, the soakers beneath lead or other suitable saddle flashing is waterproof membrane should be carried each tile overlapped flashing required at the head of all valleys. up under the tiling to a height of 150mm above the flat roof, valley or gutter and PROPRIETARY SYSTEMS lapped by the roofing underlay. stepped lead flashing held in mortar joints Proprietary gutter or valley systems should with lead wedges be securely fixed on to suitable supports The lowest course of tiles/slates should not and in accordance with the manufacturer’s touch the roof membrane. recommendations. Where ply is used for underlay overlaps support it should be exterior grade. weatherproofing

Non-ferrous metal saddle flashings or approx 150mm other approved proprietary flashings should be used at intersections and fall at least 150mm abutments. Lead flashings should be at least Code 4 (colour coded blue). 7.2

GRP valley gutter edge tiles cut to rake and bedded in mortar

underlay turned up Note at abutment Where the flat roof is over a dormer, it is recommended that the flat roof should be designed and constructed with a fall to the (g) projections through the roof front or sides. A purpose-made one-piece flashing and upstand should be used around pipes Flat roofs should comply with Chapter 7.1 projecting through the tiling. ‘Flat roofs and balconies’ (Sitework). valley undercloak strip plastic collar (f) abutments solvent welded All abutments should be weatherproofed to pipe using non-ferrous metal flashings. Lead flashings should be at least Code 4 (colour

coded blue), while soakers are normally welted edge VALLEY USING VALLEY TILES Code 3 (colour coded green). Normally, to flashing In roofs with plain tiles, purpose-made lead flashings should not exceed 1.5m in valley coursing tiles should be used. length, with laps of not less than 100mm. Adjacent roof tiles should be cut neatly to form a smooth junction, preferably cutting Flashing should be tucked into a mortar from tile-and-a-half tiles. joint or chase 25mm deep and at least 75mm above the tiling level and lead A laced valley, swept valley or mitred tiles wedged in place. The joint should then be with soakers may also be used. All valley pointed in cement mortar or using suitable tiles should be fixed in accordance with one piece flashing and sleeve around pipe

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U 1 9 7.2 Pitched roofs

Chimney flashings should link with the A cavity barrier should be provided within The guidance above will assist in reducing chimney dpc trays. An example is boxed eaves. The cavity barrier should be the risk of condensation occurring but is shown below. wire reinforced mineral wool blanket, at least not acceptable as an alternative to cross 50mm thick, nailed to the rafter and carefully ventilation of the roof space. DETAIL OF BACK GUTTER cut to shape to fully seal the boxed eaves. To reduce the risk of freezing and cover flashing condensation on pipework, the following back gutter flashing supported firestop between battens precautions should be taken: by gutter boards above underlay • place roof insulation above and around water tanks but not below them firestop below underlay • locate water pipes below the main roof

at least 150mm insulation whenever possible cover flashing • insulate all water services above the main roof insulation, including cisterns and vent pipes.

lap tank pipes insulated cavity closed and loft when above at eaves insulation loft insulation

upper dpc tray cavity back cavity barrier of barrier in gutter mineral wool or separating wall flashing fire-resisting board in boxed eaves

THERMAL INSULATION

stepped side 7.2 - S14 Thermal insulation and flashing ventilation of roofs shall prevent the adverse effects of condensation rising main lower dpc tray insulated above To avoid condensation forming in the roof ceiling level space ensure that: • ventilation of the roof is provided in It is recommended that the cold rising front apron flashing accordance with the design main be insulated above ceiling level • insulation does not block any ventilation even if it is below the main roof insulation paths (condensation that forms on uninsulated (h) changes in roof slope • insulation is laid over the whole loft cold water pipes located below the main Flashings or soakers should be used where area, including the wall plate roof insulation can result in damage to there is a change in roof slope of 5° or • there are no gaps in the insulation. ceilings and decorations). more, eg at mansards and sprockets. cold roof A saddle flashing should be used where a spacer maintains ROOF DRAINAGE ridge meets the main roof. 25mm clear air way above insulation 7.2 - S15 Roof drainage shall adequately carry rainwater to an outfall Items to be taken into account include:

insultation above (a) fixing and jointing gutters 7.2 cavity closer and lead saddle wall plate avoids and downpipes flashing a cold bridge dressed Rainwater gutters and downpipes should over GRP valley gutter be fixed in the positions indicated by the ventilation design using the correct type of fittings for internal and external angles, outlets, The amount of moist air entering the etc to ensure efficient drainage of the loft space from the dwelling should be roof. Gutters and downpipes should be GRP valley gutter controlled by: supported and jointed in accordance with

• draughtstripping the loft hatch or using the manufacturer’s recommendations. U1 FIRESTOPPING a proprietary loft hatch Rainwater pipes passing through dwellings • ensuring that the hatch is heavy enough should be insulated in accordance with 7.2 - S13 Pitched roofs shall be (or suitably fixed) to compress the Sitework clause 8.1 - S8(c). constructed to offer adequate resistance draught seal to the spread of fire • the use of appropriate downlighters that (b) falls limit air leakage Gutters should be laid with sufficient fall Firestopping and cavity barriers should • sealing gaps where services pass towards the outlet, unless designed to be be provided: through the ceiling. flat, and be provided with stop ends. • at junctions between cavities • above separating walls (c) satisfactory outfall • within boxed eaves of separating walls. If a downpipe discharges above ground The separating wall should stop about 25mm level or above a drainage gully, a shoe below the top of adjacent roof trusses. should be fixed to the end of the pipe to prevent walls becoming saturated.

A soft fire-resistant packing, such as mineral loft hatch wool, should be used to allow for movement in draught gaps sealed stripped at services roof timbers and prevent ‘hogging’ of the tiles. cross ventilation

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Appendix 7.2-A

Roof tile fixings Table 1 - Recommended limits of pitch, gauge and lap for roof tiles

Type of tile Gauge Minimum head-lap (mm) Minimum permissible pitch(°)

1 Plain not more than /3 length-lap 65 normally for clay tiles 35 (clay) (double-lap) 75 in severe exposure conditions 35 (plain concrete) Concrete determined by design to comply with 75 or to manufacturer’s specific 30 (Note: For pitches below 30, (single-lap manufacturers’ recommendations recommendations evidence shall be provided interlocking) as to suitable performance)

1 2 Slates not more than /3 length-lap 54 minimum, increase with lower 20 subject to head lap (double-lap) pitch and severe exposure conditions

Notes 1 Clay tiles that do not meet the dimensional and geometric requirements given in BS EN 1304 should be laid at pitches not less than 40° 2 For pitches greater than 45° in sheltered and moderate exposure zones only. See BS 5534 table 5 for other pitches and exposures.

Table 2 - Minimum fixings for single lap interlocking clay and concrete tiles

Location Fixings Verges, abutments The end tile in each course should be fixed (nail and/or clip) and each side of valleys and hips Eaves and top edges Each tile in the first course at the eaves and last course at the ridge/top edge should be fixed (nail and/or clip) General roof area For rafter pitches below 45° - tiles should be fixed in accordance with manufacturer’s recommendations. For rafter pitches between 45° and 55° - all tiles should be nailed or nailed andclipped. For rafters pitches of 55° and above - all tiles should be nailed and the tail of each tile should be mechanically fixed.

Notes 1 Additional nails or clips may be required depending on pitch and degree of exposure. Follow the manufacturer’s recommendations. A fixing schedule produced by the tile manufacturer, based on The Zonal Method, is acceptable. Evidence of calculations in compliance with Technical Requirements R3 and R5 may be required. 2 Nails should be in accordance with BS 5534 and be not less than 3.35mm diameter and should penetrate at least 15mm into battens.

Table 3 - Minimum fixings for double lap clay and concrete plain tiles

Location Fixings 7.2 Verges, butments and The end tile in each course should be twice nailed each side of valleys and hips Eaves and top edges Each tile in the first two courses at the eaves and last two courses at the ridge should be twice nailed or otherwise mechanically fixed. General roof area Nibbed tiles For rafter pitches below 60° - each tile in every fifth course should be twice nailed. For rafter pitches 60° and above - all tiles should be twice nailed. Nibless tiles All tiles should be twice nailed.

Notes 1 Additional nails or clips may be required depending on pitch and degree of exposure. Follow the manufacturer’s recommendations. A fixing schedule produced by the tile manufacturer, based on The Zonal Method, is acceptable. Evidence of calculations in compliance with Technical Requirements R3 and R5 may be required. 2 Nails should be in accordance with BS 5534 and be not less than 2.65mm diameter and should penetrate at least 15mm into battens.

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Appendix 7.2-B

BRACING REQUIREMENT FOR TRUSSED RAFTER ROOFS

Type of bracing Position of bracing Where applicable A All trussed rafter roofs unless rigid sarking such as timber Diagonal rafter bracing or or boarding or plywood is used. (at approx. 45° on plan) Truss Span Truss

Alternative styles of bracing for roofs that are approximately square

or or Truss Span Truss

Alternative styles of bracing for larger roofs

X Intersection detail ‘X’ 22 x 97 x 600mm long timber splice plate nailed Truss Span Truss using minimum of 4 No. 3.35mm x 65mm long Bracing for narrow fronted roofs galvanised round wire nails (less than 6.6m wide) of detached each side of intersection or staggered/stepped buildings driven through bracing and clenched over Truss Span Truss

Alternative styles for monopitch trusses B All trussed rafter roofs unless rigid sarking such as OSB, Longitudinal bracing member timber boarding or plywood is used at ridge node point

C All ceiling node points, but may be omitted where spacing Longitudinal binders at ceiling between braced nodes does not exceed 3.7m node points

less than 3.7m

D less than 4.2m All rafter node points, but may be omitted where spacing Longitudinal bracing member at between braced nodes does not exceed 4.2m or unless rigid rafter node point sarking such as OSB, timber boarding or plywood is used

E Where the span exceeds 8m. For monopitch roofs of any Chevron bracing span and duopitch roofs over 11m span, bracing should between webs be designed by an Engineer in accordance with Technical Requirement R5. more than 8m 7.2 F Where not restrained by masonry wall, or cladding in Diagonal bracing to end vertical of plywood or similar rigid sheet material monopitch trusses

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CONDITIONS AND LIMITATIONS ON THE USE OF STANDARD TRUSSED RAFTER BRACING 1 The use of standard bracing does not apply to buildings erected on long stretches of open, level or near level country with no shelter. Examples include flat coastal fringes, fens, airfields and moorland. The height and location of the building, roof pitch and span are also important. Appendix A of BS : 5268 : Part 3 (AMD.5931) gives full details but as a general guide standard bracing is acceptable for the following situations:

Roof type Max pitch No of Maximum span (m) (°) storeys England Scotland N Ireland & & Wales the Isle of Man Duo-pitch 35 1 10.6 9.8 (8.6) 9.8 (8.6) 2 9.1 7.7 (7.2) 7.7 (7.2) 3 8.5 7.2 (6.0) 7.2 (6.0) 30 1 12.0 11.6 (10.6) 11.6 (10.6) 2 11.5 10.0 (8.7) 10.0 (8.7) 3 10.2 8.8 (7.5) 8.8 (7.5) Mono-pitch 35 1 5.6 4.9 (4.3) 4.9 (4.3) 2 4.5 4.2 (3.6) 4.2 (3.6) 3 4.3 3.6 (3.0) 3.6 (3.0) 30 1 6.6 5.8 (5.1) 5.8 (5.1) 2 5.8 5.0 (4.4) 5.0 (4.4) 3 5.1 4.4 (3.7) 4.4 (3.7) 25 1 8.1 7. 3 (6.5) 7. 3 (6.5) 2 7.2 6.4 (5.6) 6.4 (5.6) 3 6.4 5.6 (4.5) 5.6 (4.5)

Figures in brackets apply to areas of Scotland either north or west of Ullapool and to areas of Northern Ireland north east of Londonderry. 2 The maximum span of the trussed rafters is 12m, the maximum height of the building is 8.4m to the underside of ceiling tie and the maximum rafter spacing is 600mm. 3 The maximum length of unsupported masonry between buttressing walls, piers or chimneys is 9m. 4 The bracing is for either duo-pitched or mono-pitched roofs. 5 The minimum size for bracing members is nominal 25mm x 100mm (3mm tolerance). 6 All bracing members to be nailed with 2 No 3.35mm diameter x 65mm long galvanized round nails to every trussed rafter they cross. 7 The trusses are supported only at their ends. 8 The roof (including hip ends) is rectangular in shape. 9 Longitudinal bracing members may be lap-jointed provided the overlap is nailed to at least two trussed rafters. They should extend the full length of the roof and tightly abut gable and party walls. Longitudinal bracing members should permit diagonal bracing to pass. 10 At least four diagonal rafter braces are required in every roof. In narrow fronted roofs and mono-pitched roofs, where braces cross, use the intersection detail ‘x’ above. 11 Diagonal rafter bracing should be at approximately 45° to the rafters on plan. Chevron bracing should be at approximately 45°to the web members. Diagonal bracing and chevron bracing should be across all trussed rafters, but small gaps (2 trussed rafters between sets of 7.2 bracing and 1 trussed rafter adjacent to gable or separating walls) are permitted in the middle of an otherwise fully braced roof. 12 Rafter diagonal bracing and longitudinal bracing at rafter level may be omitted where rigid sarking boards are used. Rigid sarking boards (e.g. chipboard, plywood, osb) should be fixed with 3.0mm diameter x 50mm long galvanised round wire nails at 200mm centres to every trussed rafter. 13 All trusses should have a ceiling of plasterboard or other suitable material. (For trussed rafters at 600mm centres, 12.5mm plasterboard is required.) Where there is no plasterboard, such as in garages, longitudinal binder bracing (Type C above) is to be used at all ceiling node points and additional diagonal ceiling bracing is required. 14 Bracing to satisfy particular conditions shall be in addition to that detailed in the above table. 15 The ITPA Technical Handbook gives further details and advice on construction.

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Appendix 7.2-C

Tank support details

Offset bracing to clear tank Tank placed centrally bearers (for bracing details see section five)

Bearer ‘A’ placed as close to the node point as possible Node point

Bay size

Trussed rafter span LS

Node point Tank Tank S 3

S b b 2 S c S 2S a a 3 c 2 2S c 3 b a S

c S S b 2 S 3 Node point S 2 S = Trussed rafter spacing

Sizes for support members Total tank capacity to marked waterline Min. member sizes Max. trussed rafter span Max. bay size for other for Fink configuration configurations a and c b mm m m Detail A 47 x 72 2/35 x 97 or Not more than 300 L supported on four trussed rafters 1/47 x 120 6.50 2.20 47 x 72 2/35 x 120 or 1/47 x 145 9.00 2.80 47 x 72 2/35 x 145 12.00 3.80 Detail B 47 x 72 1/47 x 97 6.50 2.20

7.2 Not more than 230 L supported on three trussed rafters 47 x 72 2/35 x 97 or 1/47x 120 9.00 2.80 47 x 72 2/35 x 120 or 1/47 x 145 12.00 3.80 NOTE: Support members may be of any species with a permissible bending stress not less than that of European redwood/whitewood of GS stress grade (see 14.1).

Reproduced from PD 6693-1.

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Appendix 7.2-D

Sizes and spacing of tile battens The sizes and spacing of tile battens should be specified from the table below. Batten lengths should be sufficient to span over not less than three consecutive supports. The actual batten thickness (smaller dimension) should not be less than that given in the table nor more than 3mm oversize. Actual batten width should be within ±3mm of the basic size. BS 5534 requires delivery notes to accompany the battens and the batten to be marked with the following information - supplier, origin, “graded BS 5534”, and size.

450mm span 600mm span mm mm Slates (double lap) Natural: sized or random 25 x 50 25 x 50 Fibre cement or concrete 25 x 38 25 x 50 Clay and concrete tiles Double lap 25 x 38 25 x 38 Single lap 25 x 38 25 x 50

Appendix 7.2-E

Strutting for attic trusses and cut roofs that have a floor If the distance D exceeds 2.5m between - the node points which form the width of the floor of the attic truss or - the supports to a floor within a cut roof, then additional strutting should be provided as follows;

Distance D Rows of strutting Under 2.5 none needed 2.5 to 4.5 1 (at centre of span) Over 4.5 2 (at equal spacing)

Either herringbone strutting (38mm x 38mm timber) or solid strutting not less than three-quarters the depth of the floor and at least 38mm thick should be used. 7.2 Appendix 7.2-F

Durability classification of natural slates Natural slates should have the characteristics given in the table below:

Characteristics Code/grade from BS EN 12326 Water Absorption (not more than 0.6%) A1 Thermal Cycle T1 Carbonate Content (not more than 20%) S1

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INDEX

A H U Abutments 13 Hips 9, 12 Underlay 3, 7, 11 Access 5 Holding down straps 1, 6, 8 V B House Longhorn beetle 3 Valleys 4, 9, 13 Bargeboards 7, 10 I Vapour checks 5 Battens 1, 4, 7, 11, 19 Imposed loads 1 Ventilation 5, 7, 10 Bracing 2, 8, 16, 19 Insulation 7, 14 Verges 4, 12 C J W Cavity barriers 7 Jointing 9 Wall plates 1, 7 Chimneys 4, 14 L Condensation 4 Lateral restraint straps 1, 6, 8 Cut roofs 2, 9 M D Moisture barrier 4 Design 1 P Dormers 9 Proprietary roof coverings 4, 13 Drainage 6, 14 R Durability of natural slate 19 Ridges 4, 12 F Roof coverings 3, 5, 6 Fascias 7, 10 Roof mortar 7, 12 Fire-stopping 5, 7, 14 Roof spaces 4 Fixing(s) 4, 6, 10, 15 S Flashings 3, 6, 12, 13 Sarking, rigid 3, 7 Flue pipes 5 Slates 3, 11 G Soffits 7, 10 Girder trusses 2 T Tank supports 2, 10, 18 Tiles 3, 11, 15 7.2 Timber 2, 6, 10 Trussed rafters 1, 8, 16

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