Massive timber construction without glue - Brettstapel Acharacle Primary School, Argyll
Project Information Background Building description
Client: Highland Council Acharacle is a small and remote community The original school was housed in a on the south-west tip of Loch Shiel, some 40 Victorian building on the same site. To allow Completion date: May 2009 miles west of Fort William. For many years the it to continue to function as a school during Architect: Gaia Architects village had campaigned for a new primary construction, the new single storey school is Frame Sohm Holzbautechnik school and community space to replace the built on the original playground. With input manufacturer / GmbH, Austria old Victorian buildings, which were becoming from the community carefully taken into erector: difficult and expensive to maintain. In 2004, account, the design has two wings leading Highland Council invited tenders to compile off a central entrance. The classroom wing Infrastructure MacGregor Construction, a brief for the development of a new primary is orientated to face south and make best and fit out / finish: Inverness school. use of daylight and solar gain, while the administration and community areas run north, The Highland Structure Plan 2001 and a with glazing facing east and west. document “Designing for Sustainability Performance Issues in the Highlands”, in draft at the time, set Massive timber using hardwood dowels requirements including - supporting viable communities; contributing to a prosperous The Brettstapel method Sustainable construction and vibrant local economy; safeguarding and Timber frame construction met many of Multi-use building enhancing the natural and built environment. the requirements of the scheme. However, Within this context, Gaia Architects were Low in-use energy because of our relatively mild and wet climate, appointed to compile a brief for the school. much home grown timber is too fast growing They then continued as project architects. so inadequate for structural grades. Although Gaia were keen to develop a scheme which there are currently no manufacturing facilities had minimal environmental impact, while in the UK, the Brettstapel method has raised satisfying the needs of the users. They guided heads here, as a possible future solution for the client and the community in many of the using more locally sourced timber in structural design choices to be made. applications.
The Brettstapel method uses timber which may otherwise be unsuitable for structural use. It comprises untreated softwood studs pinned together with hardwood dowels, and can be used to form solid, load-bearing timber
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Timber Solution | Massive timber construction without glue - Brettstapel 1 Massive timber construction without glue - Brettstapel Acharacle Primary School, Argyll
Building Description Cont. walls, floors and roofs. Brettstapel translates into English as “stacked planks”. Various manufacturers each have their own ways of orientating and fixing studs together to create their own unique product. Typically, diagonal holes are drilled though several studs and then dowels of much lower moisture content than the softwood studs are installed into them. The dowels pick up moisture from the surrounding softwood, expand and thus become locked into place.
As there is no need for glue or metal fixings, the makers claim that Brettstapel products are more sustainable and do not emit harmful toxins. Panels can be cut to size both in the factory and, if required, on site without the risk of hitting any metalwork within them. It is argued that as no adhesive, pressing or drying is required, Brettstapel construction is cost-effective compared to many of its competitors. Large Brettstapel panels can be manufactured to any size, limited only by transport restrictions. The large size of the panels also assists in the speed of construction, as fewer sections are required to complete a structure. Although the majority of buildings constructed to date are two-storey houses, four-storey buildings have been erected in Germany and Austria. With spans Prefabricated external wall panel being craned into position. up to 15 metres also possible, a variety of bridges and industrial units have been built in Switzerland, Austria and Germany.
The finish is likely to be determined by its end use -whether the timber is exposed and if so, how clean the finish should be. Panels can be manufactured unplaned, with knots and stains visible, for hidden work, or made from carefully selected timbers with few defects and a planed finish where they can be left exposed as a feature of the building. By chamfering stud edges, or staggering studs as they are assembled into a panel, different visual effects can be achieved. Acoustic profiles are also possible, by machining gaps of a particular shape into studs before assembly into a panel. These gaps are designed to absorb airborne sound.
Large Brettstapel wall and roof panels being craned into position.
Timber Solution | Massive timber construction without glue - Brettstapel 2 Massive timber construction without glue - Brettstapel
Acharacle Primary School, Argyll
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Timber Solution4 | Massive timber construction without glue - Brettstapel 3
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5 6 Massive timber construction without glue - Brettstapel Acharacle Primary School, Argyll
Key
1. Wind turbine located on hill to rear of school to provide power to building (via interters and grid connection)
2. Redundant schoolhouse to be converted to accommodation
3. Private garden
4. Sprinkler pumphouse
5. Sprinkler system supply tank so internal linings don’t have to be treated for fire.
6. Highly air-tight timber superstructure (measured value 0.27 m3/hr/m2 @ 50pa)
7. Careful attention to all materials to ensure no/very low toxicity
8. Brettstapel (untreated, glue-free, massive timber) construction for whole building
9. Profiled Brettstapel roof surfaces in all high noise areas, eg classrooms, entrance hall and multi-purpose hall
10. Natural ventilation to all rooms except internal WCs and stores
11. Hygroscopic finishes through (clay plaster, untreated timber)
12. Mix of soft and hard play areas
13. Nursery garden
14. School playground
15. Welcoming entrance and communal entrance hall to encourage integration of building users
16. Cycle racks
17. Drop off area
18. Bus stop
19. Pond
20 Timber entrance piazza
21 Existing stream reshaped to form poind to increase biodiversity and reduce stormwater runoff rate
22. Untreated timber cladding to all facades
23. All furniture developed to minimise off-gassing
24. Individual gardens for each classroom
25. Solar control blinds to classroom and nursery windows
26. South-facing classrooms to maximise solar gain
27. Classroom shape designed to improve acoustics
28. Break-out space for each classroom for independent learning
29. Support spaces (WC’s stores, pupil support room) to north
30. Specialist colour used internally throughout school to enhance wellbeing
31. Daylight maximised in principle rooms and circulation through careful use of windows and roof lights
32. Low-flow water outlets and rainwater harvesting tank to minimise mains water consumption
33. Highly insulated timber superstructure (typical U-value 0.125W/m2k for walls and roofs and 0.8W/m2k for external windows and doors)
34. Hidden gardens to rear of building
35. Car park
Timber Solution | Massive timber construction without glue - Brettstapel 4 Massive timber construction without glue - Brettstapel Acharacle Primary School, Argyll © Gaia Architects 2008 © Gaia Architects WC / changing Storage Multi-purpose / dining Teaching spaces Teaching Circulator Administration Floor plan
Timber Solution | Massive timber construction without glue - Brettstapel 5 Massive timber construction without glue - Brettstapel Acharacle Primary School, Argyll
Options considered
Option Commentary Post and beam vs Brettstapel Brettstapel was chosen for cost saving and innovation. It also had the advantage of delivering a product free of chemicals – a theme which was carried through the development, right down to the choice of furniture. Fire resistance None of the timber used was treated, for fire resistance. This avoided the use of chemicals. The mass of timber used within the building ensures built in fire resistance to the structure. A sprinkler system is also installed to provide additional reassurance. Timber preservation None of the timber used was preservative treated against fungal/insect attack. Again, this avoided the use of chemicals. Material choice suitable for location, good detailing and workmanship meant that preservative treatment was not considered necessary. Service integration Care was taken to keep service penetrations though the building envelope to a minimum. This helped to deliver an enviable air tightness rate. Some services were concealed within the structure using routes and ducting installed during fabrication. Many services have been surface mounted to allow easy access for maintenance and alterations during the life of the building. Multi-use building To meet the needs of the council and Acharacle residents, the building is not just a school. Space within it is set aside for community use and a nursery. The building is designed to allow integration of these uses on site as required. Sustainability Through careful material choices, orientation, layout and technology, the school achieves low impact on its environment, while fulfilling its function as a school and community building.
Site overview showing original school building, the sloping site and partially complete copper roof to the new classroom wing.
Timber Solution | Massive timber construction without glue - Brettstapel 6 Massive timber construction without glue - Brettstapel Acharacle Primary School, Argyll
Design Challenges Fabrication Low energy
The project was originally conceived as a When using prefabricated panels, even small Although the Brettstapel panels used were post and beam timber frame structure, with design changes at a late stage can cause constructed in Austria and delivered by road infill panels. But after higher than anticipated delays and additional expense. The more to Acharacle, a journey of nearly 2000 km, the costings were received for this, the client specialist and prefinished a panel is, the less amount of CO2 locked away in timber exceeds realised that an alternative method needed practical adapting panels on site becomes. that used in construction and transportation. to be found. The challenge was to find a Great care was therefore needed in the Most structural timber used in the UK is solution which reduced costs, but retained planning of the Brettstapel wall, floor and roof imported here anyway and much of it comes many of the original sustainability ideas and panels to ensure that site construction went from Northern Europe. By demonstrating the design concepts. In a previous year on study smoothly. Site conditions, panel connections, qualities of Brettstapel in the UK, those who tour, both Gaia Architects and the client had service integration and required finishes were champion it here hope that soon it will gain witnessed at first hand a variety of novel all carefully considered during the planning. sufficient popularity to be made using British school buildings in Scandinavia and Europe. Much of the planning already carried out for grown timber and manufactured here too. Its This led them to the Brettstapel method and the original concept meant that converting own environmental credentials will then be a fabricator, Sohm Holzbautechnik GmbH of the school design to Brettstapel proved to be hard to beat. Austria as a possible supplier for their school relatively straightforward. The architects took building. Costs for the Brettstapel method the precaution of working closely with the The school has an enviable list of were submitted and came in lower than fabricator to solve design and manufacturing environmental credentials, including: the timber frame post and beam originally issues. They based themselves at the factory • Glue free mass untreated timber proposed. With forward thinking, the Highland in Germany for a week to ensure that key construction: chemicals which would Council decided that they were prepared to aspects of the design and construction were normally be present for preservation and accept this novel method of construction. The thoroughly considered. An example of this is structural performance are absent in first large Brettstapel building for the UK was that the school wing rises slightly on a slope, Brettstapel. It is claimed that this creates set to get underway. so the best way of detailing a stepped roof a healthier environment for the occupants. using this form of construction needed to be worked out. Another involved the location and • Glue free mass untreated timber routing of services around the building. construction: chemicals which would normally be present for preservation and structural performance are absent in Brettstapel. It is claimed that this creates a healthier environment for the occupants.
• A very low tested air permeability of 0.27m3/m2/hr@50Pa. Great care was taken during design and construction to reduce air leakage. This is an important part of the strategy to reduce energy used for heating to a minimum. Services were kept away from external envelope wherever possible to reduce penetrations.
• A U-value of 0.128 W/m2K for walls and roof: this was achieved using 280mm of wood fibre insulation.
• A U-value of 0.098W/m2K for floors: this was achieved using blown in cellulose insulation and wood fibre insulation between the timber floor joists/battens.
• A wind turbine for water heating and power: an exposed hillside above the school was chosen to site a 6kW wind turbine. This heats hot water within the school.
• Rainwater harvesting: used to flush the toilets.
School corridor showing natural day lighting and accessible service runs.
Timber Solution | Massive timber construction without glue - Brettstapel 7 Massive timber construction without glue - Brettstapel Acharacle Primary School, Argyll
Detailed construction sections - roof and wall
Key
1. Copper roofing Roof 2. 24mm timber boarding as substrate for roofing
3. 100mm ventilated cavity
4. 16mm sheathing board (DWD); if roof pitch <15˚ then additional fully adhered 1 sub-membrane 2 5. 280mm timber construction with wood 3 fibre insulation between 4
6. Vapour control layer Vap 2000 5 6 7. 16mm 3-ply amber board fir, quality C/C 7 8. 140-220mm double diagonal Brettstapel 8 panels with profiled lamellae, fir, 4mm 9 shadow gap or acoustic profile
9. Copper rainwater goods
10. 22mm untreated heartwood of European larch closed profile cladding 10 11. 40-80mm ventilated cavity 11 Wall 12 12. 16mm formaldehyde-free sheathing board (DWD) 5 13 13. 16mm 3-ply timber board (fir) 14 14. 100mm double diagonal Brettstapel panels with profiled lamellae, fir, flush surface
Detailed construction section - floor
Key
1. 50mm washed river gravel solum Floor 2. Ventilated cavity below floor panels
3. 19mm 3-ply timber board fir
4. 240mm timber construction with blow-in cellulose insulation
5. 19mm 3-ply timber board, fir with bituminous membrane over 1 6. 100mm timber battens with 2 3 woodfibre insulation between 4 5 7. 60mm timber battens with woodfibre 6 7 insulation between 8 8. 16mm formaldehyde-free chipboard
© Gaia Architects 2008
Timber Solution | Massive timber construction without glue - Brettstapel 8 Massive timber construction without glue - Brettstapel Acharacle Primary School, Argyll
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Timber Solution | Massive timber construction without glue - Brettstapel 9