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This timber framed building took an innovative approach to straw

bale insulation.

The Governors of the Bishop Cornish School had a vision of the inspiring space they wanted for their children. Completely undeterred by a lack of funding, they pursued their vision for six years to make the building a reality. The Education Centre has transformed the services they are able to offer – and was built with a huge amount of support and goodwill from the community. The building itself is a highly insulated timber-framed structure featuring straw bales, solar panels and a green roof. An important innovation is that the bales are stacked vertically inside the timber frames.

Introduction

Truro

Exeter

Saltash

Bishop Cornish School

Key dates 2004 : the Governors of Bishop Cornish Church of England Primary School set up and incorporated a Charity - the Bishop Cornish Education Centre2004-09 : fundraising by the school and community2009 : constructionMarch 2010 : official opening by the Countess of Wessex

Outside - Photo © Bishop Cornish School

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ContextIn 2004, the Governors of the Bishop Cornish School set up a charity with the aim of building an Education Centre to extend the range of services they could offer to the community. The charity’s trustees wanted a building to accommodate before and after-school care, pre-school, music and environmental education. They were due to start looking at estimates for a standard prefabricated building, when they heard about a pre-school building at Lanlivery in mid-Cornwall, which had won a prestigious RICS International Sustainability Award. After talking to the architect, Martin Penk from Arco2 Ltd, they visited Lanlivery and realised this was exactly the type of building they

really wanted. The decision to commission a fully bespoke sustainable building set the trustees on a path that would take years of planning and fundraising, but which led to an inspiring story of community support and resulted in a unique building. The building ethos as defined by the trustees was:“To design, construct and use an Education Centre that will serve as an educational tool through being an exemplar of innovative and sustainable development. In particular : maximise the use of natural sunlight, apply the principles of passive solar design

Plan © Arco2 Architecture

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French-British collective Libnam3

and effortlessly accommodate the sloping site.All materials assessed to ensure that only those with a low embodied CO2 content (through sourcing, processing and transportation) are used.The life cycle of materials considered to minimise wastes arising at all stages. Recycled materials used where available.”

The architect worked closely with the school to achieve these aims and the resulting building comprises 280 m² of interior space including; a main carpeted play area, spaces for soft and for messy play, a quiet area and semi-circular music room.

Building overviewThe focus for material selection was to use natural materials with low embodied CO2, sourced from Cornwall where possible. Where high embodied energy materials

were required, the design ensured they were kept to a minimum. With this in mind, the foundations are restricted to cement concrete pads each measuring 750 mm x 750 mm. This method enabled the architect to easily accommodate the sloping site. The pad foundations support posts holding a frame of natural timber and glulam beams (engineered timber made from low grade wood laminated together to form extremely strong structural elements). The external walls are formed from untreated Douglas fir cladding, bitumen board panels and straw bale insulation. Bargeboards, fascias and soffits are all in untreated Douglas fir and cedar. The timber window and door frames are pre-treated with water-based preservative coatings. The floors are insulated with natural sheep’s wool beneath 18 mm chipboard and are finished in a variety of materials including engineered oak and natural linoleum.Part of the building is roofed in

Elevation © Arco2 Architecture

Elevation plane © Arco2 Architecture

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Technical focus : Straw balesStraw bales insulate all the external walls and are sandwiched between two timber frames.The key design innovation in the Bishop Cornish building is that the bales are stacked vertically inside the timber frames. Most straw bale buildings use the bales horizontally

recycled rubber tiles and part has a green roof composed of sedum planted in 50 mm substrate over a waterproof membrane, marine grade ply wood and sheep’s wool insulation. The building has underfloor heating which was originally served by a high efficiency condensing gas boiler, and has since been replaced by a biomass boiler. The school has also installed a 9.6 kW solar photovoltaic array.

– stacking them in a pattern similar to brickwork. Vertical stacking means that the 380 mm-390 mm wide bales can be fitted in between vertical studs spaced at 400 mm along the length of the walls. This in turn means that standard width (e.g.1200 or 2400 mm) sheet materials can be used throughout – making the build faster, more efficient and less wasteful. This method has proved very effective and has since been adopted in a pre-fabricated straw bale system, «Ecofab», developed by Arco2 Architects – Bishop Cornish has thus been an important innovator for straw bale construction in Cornwall. The exterior timber frame is sheathed in 22 m Steico sarking board and the interior frame with two layers of plasterboard. A

Timber frame - Photo © Bishop Cornish School

French-British collective Libnam5

25 mm service void sits between the two layers of plasterboard; the double layering also acting as a fire retardant feature. The depth of the bales gives 500 mm of insulation between the two timber frames. The internal and external frames are tied together by 200x500 mm plates of OSB board fixed between the corresponding studs on each frame at a height of 800 mm and 1600 mm. During construction, the outer skin of sarking board and the OSB plates were installed first, and the straw bales packed against these. The 400mm spacing between the studs meant that the bales had to be squeezed in tightly and it was sometimes difficult to make them fit. Around windows and in other irregular spaces, sheep’s wool was

packed in as an alternative to the straw. The bales are placed so that the string which binds them is protected between the bales and the cut ends of the straw are pressed against the interior and exterior sheet materials. This means that the grain of the straw runs across, rather than with the direction of, the wall and contributes to its rigidity. An advantage of this construction method is that it uses standard timber frames which do not demand specialist skills. The contractor for Bishop Cornish had not used straw before, but he and the architect had worked together and through good on-site communication the build did not present too many technical challenges. The size and dramatic form of the building, with its curved music room, pushed the limits of this type

Entrance - Photo © Bishop Cornish School

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Barriers and solutionsThe principle obstacle faced by the project was one of funding, and the

school turned this into a virtue by making it the focus of a campaign to bring the community together and created a real sense of local investment in the project.

Working tirelessly, the charity and community raised over £350,000. Parents and friends of the school supported the project through a plethora of fundraising activities including repairing bicycles, valeting cars and by donating materials, labour and skills to the construction. Generosity from local companies included the donation of water pipes and roofing tiles. HMS Raleigh provided manpower to help

of construction in Cornwall. It has thus served as an exemplar of the scale, form and function that can be realised using timber and straw, a fact which was recognised by its inclusion in the 2014 edition of the Pevsner Guide to Cornwall. The straw bales used in the building were locally sourced from ex-parents of the school who are farmers.The school always recognised the importance of the building as a learning tool and the children learnt about sustainable construction by helping to install the straw bales.

Green roof - Photo © Bishop Cornish School

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Awards2010 • RICS South West Community Benefit Award • National Green Apple Award for Best Educational Establishment • Finalist, RICS International Sustainability Award2011 • National Winners • Outstanding School Governing Body of the Year 2011 (National Governors Association) for the vision, leadership and

StakeholdersClient : Bishop Cornish Church of England Voluntary Aided Primary SchoolArchitect : Martin Penk, Arco2 Architects, BodminPrime contractor : Shaun Bunney, BodminGlazing : Stonehouse Glass, PlymouthWindows : NordanMarmoleum flooring : Forbo NairnKitchen : Howdens, Saltash

commitment that resulted in the provision of the Bishop Cornish Education Centre2014 • Inclusion in the new 2014 edition of the Pevsner Architectural Guide : The Buildings of England - Cornwall

in the installation of the sedum roof. The project brought together the entire School and wider community.

Music class - Photo © Bishop Cornish School

ContactCornwall Sustainable Building Trusthttp://csbt.org.uk/