2.2 ROOF EXTENSIONS Extending the roof to make it a habitable space is one of the most common and affordable types of development. 3 There are times when only a small alteration, such as 2 the installation of a dormer window could make your loft space habitable by providing more space and headroom. 4 1 STREET As part of your preparation to alter or extend This assessment could be done by walking the roof of your property, a preliminary site along your street and surrounding area assessment is recommended, to consider to observe the roof forms. You could also BACK OF STREET the following: use Google or Bing Maps images for an 5 aerial or birdseye view of your property and • The existing roof form and of any surroundings. previous extensions to it; • The roof visibility and prominence You can find out if a certain extension has a from gardens, streetscene and wider planning record by searching for planning area, considering land topography; applications on the Council’s website. • The pattern of development of A successful roof extension would neighbouring buildings to include consider the overall roof form of the historic extensions and new types of existing building, adjoining buildings and development; INDICATIVE EXAMPLES OF DIFFERENT impact in key views (when relevant) and TYPES OF ROOF EXTENSIONS • Other roof extensions present at be proportionate to the roof slope being 1. Dormer the neighbouring buildings which extended. 2. Rooflight obtained permission though planning 3. Mansard application or permitted development. 4. Inset balcony 5. Balcony If your property is in a Conservation Area, check the Conservation Area Appraisal and the information about roof extensions. Photo 21 Photo 22 44 CPG HOME IMPROVEMENTS HOME IMPROVEMENTS - ROOF EXTENSIONS 45 2.2.1 DORMERS Dormers are defined as a window that projects out of a sloping roof. The aim Dormer windows fall within permitted development rights of of the dormer structure is to house a single family dwelling houses vertical window to bring in more light (not flats) outside Conservation and air into the loft space and make it Areas subject to limitations habitable, without adding to the overall and conditions set out under roof height. Town and Country Planning (General Permitted Development) The design of a dormer should therefore (England) Order 2016 (as emphasise the glazing element and the amended) Schedule 2, Part 2, solid structure should complement this in a Class B. form and scale appropriate to the roof being Check the order and Householder extended. Technical Guidance by Gov. Roof dormers should sit within the roof slope and appear as an extension to the existing roof whilst the existing roof form is maintained. Photo 23 Photo 24 STREET BACK OF STREET Indicative examples of different types of dormers for properties in Conservation Areas. Photo 25 Photo 26 46 CPG HOME IMPROVEMENTS HOME IMPROVEMENTS - ROOF EXTENSIONS 47 There are certain considerations that should • If not done already, consider insulating your be taken into account when designing a whole roof; dormer window to ensure it is sensitively • Include insulation materials into the dormer and appropriately designed for its context. A design; dormer window should: • The internal height of the existing loft space • Consider whether the roof of your property is sufficient to allow adequate habitable is part of an unbroken roof line which is of space more than 2m - headroom from heritage value (this may depend on the age staircase; and form of the property); • Dormers should be subordinate in size to • Consider whether there are other existing the roof slope being extended; extensions in proximity, even if they are • The position of the dormer should maintain older or constructed under permitted Existing character with even distances to the roof margins (ridge, development; front dormers along eaves, side parapet walls); • Consider whether the dormer would have the street. Likely that a similar extension would • Design of dormers should consider the been permitted development if the property had not been converted into flats; be acceptalbe under a hierarchy of window openings in terms of planning application. size and proportion, which generally result • On front roofslopes dormers could be a in smaller dormer windows than the ones at harmful addition due to its great visual lower levels; impact to the streetscene, especially in an • The type, design and alignment of windows unbroken roofscape. If your neighbouring should relate to the ones below; properties do not have front dormers, then it is likely that this type of development • The proportion of glazing should be greater would not be supported at application than the solid areas and dormer cheeks stage. Consider rear dormers and front should be of a high quality design and rooflights instead; materials; • For side dormers you should balance • Innovative approaches are encouraged and carefully the dormer’s quality and detailed supported by pre-application advice; design with its impact on streetscene • Dormer materials should complement the and wider area. Side dormers in between main building and wider townscape. Given buildings should carefully consider the the existing building stock, the use of existing architectural features on side traditional materials (timber, lead, hanging elevation, such as chimney breasts and tiles) is encouraged; innovative approaches pots, and impact on the neighbouring are encouraged and supported by pre- amenity in terms of overlooking; On an unbroken application advice; • Generally roofs of properties in roofslope, front dormers Conservation Areas are part of the area’s are unlikely to be character, and as a general rule, dormer supported by officers. windows should retain a greater area You should consider rear of roof slope than properties outside dormer and front rooflight conservation areas in order to preserve this instead. character. 48 CPG HOME IMPROVEMENTS HOME IMPROVEMENTS - ROOF EXTENSIONS 49 2.2.2 NEW ROOF LEVEL Extending properties with a new storey There are two types of mansard roof at roof level is a well established extensions: a true mansard (A) and a flat method to increase the useable space topped mansard (B). In order to be designed successfully, you should follow the details of properties. This type of extension below: would retain more space at ground level available for greenery, garden • The lower slope (usually 60-70°) should rise from behind the parapet wall, storage and outdoor activities. separated from the wall by a substantial set back and gutter; The most common type of extensions to the • Retention of roof features such as original roof are mansards, traditionally associated cornice, parapet, and chimney stacks; with Georgian or Victorian buildings, as the • Windows should respond to the existing roof structure with front parapets or fenestration character of the host building valley roofs allow for a simple insertion of a and generally project at right angle similar new level in this traditional form. to a dormer window with timber sash openings; and In general, a traditional approach for mansard extensions would be preferred • Materials to complement the existing for traditional buildings. You are also roof and building and respond to the encouraged to think about different neighbouring context. approaches to additional roof levels. It is recommended that pre-application advice Photo 27 is sought where it is unclear what design If you live in a terraced building Left - Bad example of mansard extension which Right - Good example of roof extension preserving approach would suit the host building. and your neighbours have already did not take into account the existing V shape roof the V shape roof parapet. Better design could have extended their roofs with a parapet. been achieved with framless glass (or railings) and traditional mansard, then it is likely reduced glazing. that a similar extension would be an acceptable development. 49-70° (max) depending on circumnstance Butterfly profile retained Hopper-head level Hopper head Rainwater pipe Mansard roof extensions: A. True mansard (left); B. Flat topped mansard Example of mansard on butterfly roof 50 CPG HOME IMPROVEMENTS HOME IMPROVEMENTS - ROOF EXTENSIONS 51 There are certain considerations that should • Be aware of the prominence of your home’s be taken into account when designing a an roof to appreciate what impact an additional additional roof level, to ensure it is sensitively roof level would have on the streetscene and appropriately designed for its context. and wider area; A new roof level should: • There are cases when an additional roof level could help re-unite a group of buildings and wider townscape. You should consider the scale of the adjacent development if proportionate to the host • Be subordinate to the host building; building and streetscene and reflect this into your proposal; • Include features informed by the surrounding context; • In Conservation Area, erecting a roof extension on a building within a complete • Take the form of a traditional mansard, a terrace or group that currently has no modern interpretation or a more innovative extensions can be difficult to achieve approach, supported by pre-application successfully. It is strongly recommended Photo 28 advice; that you seek pre-application advice before submitting an application of this type. You should discuss your proposal with your neighbours to explore the possibility of a joint application; • Consider the installation of green roofs and/ • Where a group