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A town council builds a nursery out of straw bales.

Key dates Choice of architect : May 2012. Planning permission granted : September 2012. Works : April 2013 to August 2014.

In 2014, the Muël village welcomed a nursery for local children. Thanks to the drive of councillors, the building has been built out straw, wood and clay. These materials give excellent inside air quality and the community was able to be involved in the building process.

Introduction

Saint Brieuc

Quimper

Vannes

RennesMuël

Muël

Garden - Photo © Servane Guihaire - Constructys Bretagne

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ContextThe Saint-Méen-Le-Grand district council was lacking facilities for infants, which is why they decided to build a nursery.More precisely, The Education Commission, proposed a building using 90% natural materials, local if possible, to reduce its carbon footprint and the release of harmful products in the air.In order to accommodate 12 children in the best conditions, several meetings took into account expectations from all sides. The site on which the 400 sq m crèche was built is on a 2386 sq m plot

in the middle of a village of 880 inhabitants. The site was not shaded so the building was able to be south-facing to make the most of the sun.In order to raise awareness of sustainable development, the council invited the population to be involved in the construction of the straw bale walls (7days) and the earth rendering (5 days).

Plan © Atelier Jean Pierre Ingrand

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French-British collective Libnam3

Unable to use expensive cork, the concrete slab was insulated with blown polyurethane.A double timber frame using local untreated Douglas fir was used with a raised threshold and supporting beams. The structure is not braced with boards but with cross braces made of solid Douglas fir to enable rendering on both sides of the wall. The bottom plate and high rail are made of glued, laminated wood (Lamibois). In the living areas, the frame is insulated with straw bales topped up with wood wool (Steico) in less accessible areas. In maintenance areas and for the roof,

Building overviewthe insulation is made of cellulose fibre from recycled newspaper (Isocell) : 22cm in walls and 30 cm in the roof. The straw walls are rendered with earth from the site for the inside and a lime and sand mix for the outside. The other walls are clad with treated oiled spruce (flax oil).The internal walls are insulated with wood fibre panel (Homatherm) between gypsum boards (Fermacell).The roof water-proofing was achieved by the use of recycled rubber membrane (EPDM-Carlisle).The suspended ceiling is also made of wood fibre («Organic» - Knauf). Tiles, rubber or marmoleum (natural linoleum) are used for floors depending on the room usage.

St Andrew’s cross- Photo © Servane Guihaire - Constructys Bretagne

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Technical focus: Building with straw balesParts of the building insulation are straw bales. The straw used was grown without herbicide or pesticide in a neighbouring village, before being tied up and stored for drying for a year.450 bales (30x40x90 cm) were used on site. Their density, size, weight

There are sun shields on several sides of the building. The windows are double-glazed units filled with argon.A pellet burning stove supplies the low temperature underfloor heating system (12 kW). Solar panels are used for hot water and ventilation comes from a heat exchanger.A 5 cubic meter rain water tank will supply water for the garden, bin storage area and toilets when it is authorised.To further improve air quality, all the furniture is made of solid wood.

Earth render - Photo © Servane Guihaire - Constructys Bretagne

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and humidity level (20% max) were ascertained to maintain consistency.. The layout of the frame took into account the dimension of the bales, so the space between the frame posts is smaller than the width of the bale in order to compress them horizontally. Furthermore a system of jacks and wedges gives vertical compression. The insulation is therefore stable within the frame. Straw bale building regulations have been complied with. For instance,

the first row of bales have been laid 30cm above ground, the fitting of windows and doors is guaranteed water-proof.The building was made weather tight quickly to avoid the invasion of rodents. This risk remains under control with sufficient compression and anti-rodent mesh, as well as the removal of the seeds from the straw.The risk of fire is almost non-existent, as compressed straw does not hold much oxygen. However, during the build, cleanliness was important to avoid the scattering of brushwood.

Timber frame and straw bales - Photo © Echopaille

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Barriers and solutionsIn public building construction, the paperwork and regulations can be a barrier to eco-construction projects. The support from community networks such as

«Bruded» (www.bruded.org) can be useful. For instance, as the building specification was worth 40% of the environmental scoring, it was necessary to justify it, as the price difference reached 30% on certain materials. Equally, recycling water for toilets and the washing of reusable nappies required the approval of the health service.It was also necessary to explain the project to the insurance company as well as an independent auditor. Furthermore, health and safety inspectors had to be convinced that the local people involved in the build were working on a voluntary basis in safe conditions (e.g. no work undertaken at a height). Only a few companies were

Whatever happened, no tools using flames were used during the build.Straw is a heavy material to handle and requires a large work force. It also must be laid during the summer months.The supply chain would benefit from being more structured whilst taking into account the need of straw for the numerous farms in Brittany. For the build, the company Echopaille, got their supply from a farmer-baker who did not require the straw after the harvest.

Entrance- Photo © Servane Guihaire - Constructys Bretagne

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structured enough to bid for the contract to work with straw; except for self-employed or occasional builders, the number of skilled craftsmen remains limited. The employees of the company which won the the contract for the straw bale construction had to undergo one-year training in Quebec (GREB technique) to improve their knowledge. They also attended short training sessions by the French Straw Building Network.Compared to an ordinary building,

communication beforehand was necessary between the straw company and the carpenters to come up with detailed design features adapted to the size of the bales. Site meetings were held weekly, as it was important for the main contractor to be onsite to reassure the builders and even help them improve their skills.On the technical side, the particular point of attention was not the straw, but rather the risk of condensation in the roof. The frame company would have favoured wooden boards with no contact with a cold wall. However,

Inside- Photo © Servane Guihaire - Constructys Bretagne

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StakeholdersMain contractors : Communauté de communes de Saint-Méen MontaubanProject management : Atelier Jean-Pierre Ingrand (Ploërmel)Ground work : Colas (Loudéac)Structural work : SBK (Tremorel)Timber frame and roofing : Briero (Mauron)Locksmith : DSJ (Trémeur)Straw : Echopaille (Larré)Lime and earth rendering : Totem / Terre et couleurs (Saint Gonlay)Joinery : Carissan (Saint-Méen-Le-Grand)Internal walls : Brocéliande SARL (Saint Abraham)Flooring : Hervé Déco (Laillé)Decorating : Barbedor (Saint Gilles)Plumbing : GR énergie (Merdrignac)Electricity : IRCE (Médréac)

Costs Plot : £6,068 before taxSurveys and control studies : £11,660 before taxProject management : £30,085 before taxGroundwork : £45,796 before taxStructural work : £39,345 before taxTimber frame, insulation and roofing : £117,998 before taxLocksmith : £27,125 before taxStraw / lime and earth rendering : £28,049 before taxJoinery : £60,396 before taxInternal walls : £38,580 before taxFlooring : £32,855 before taxDecorating : £10,142 before taxPlumbing : £67,805 before taxElectricity : £23,362 before taxConstruction cost : £533,198 before tax or 1278 before tax /sq mSubsidies : £407,940 (Social Service, district council county council, European Union, government and Pays de Brocéliande association)

The Muël crèche underwent thermal tests, thermodynamic simulation and airtightness tests. The building should use less than 50 kW/h/sq m/ year. Furthermore, the air quality will be high, as proved by

Performance

building analysis straight after the completion of the build. In France the control of the presence of Formaldehyde, CO2 and Benzene is compulsory from the 1st January 2015 for nurseries, and will extend to all buildings by 2020. The materials used are 90% natural, which limits pollutants, irritants etc., during the life of the building for its users and the environment.

the building inspection noticed that the ventilation was good enough and the vapour barrier showed a high SD factor.The building cost was €1,630 per sq m, which is slightly more expensive than equivalent buildings. However most equivalent buildings have higher heating costs and lower air-quality.

ContactConstructys Bretagnewww.constructys-bretagne.fr