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This cob extension provides a healthy environment as part of a

150 year old farmhouse.Key dates

Conception and architectural design of the project : end of 20103-month active building phase from April to July : 2011Rrendering and finishing touches : 2012

The owners wished to enlarge their earth-built house to better suit the needs of the family, including several children of varying ages. One major preoccupation was to preserve the existing structure and materials whilst complementing the house with other eco-materials (recycled newspapers, wool, fibres and wood) that are available locally and used with the knowledge of local craftsmen.

Introduction

Saint Brieuc

Quimper

Vannes

Rennes

Maroué

Montès

South facade - Photo © Robert Junalik

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The Objective for the owners was to expand the living area of the house (from 105 sq m to 220 sq m in total) in order to create interdependent living spaces for each member of the family (there is a mixture of adolescents and young children). The aim was to build three bedrooms, one living room and one bathroom. The idea was to «compartmentalise» the building and create separate and

Contextautonomous living spaces. The owners, aware of the eco nature of the build, wanted the work carried out using sustainable materials and to enable the use of traditional building techniques. The extensions were planned to be built on the east and west sides of the property; the northern side is not an option as it is attached to a hangar.

Plans © Cabinet l’Epineguen

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French-British collective Libnam3

Building overviewThe existing frame of the building had been made with stone and earth mortar. The equipment room of the house that has not been renovated has a wood pellet boiler installed. This room has been insulated from the outside : installation of a wooden framework in OSB (Oriented Strand Board), Fibragglos (rigid insulating wood cement panels) and an insulation of cellulose padding. The final coat is a lime and sand render.The extension to the east was built using the remains of a barn. The existing walls (made of Cob) were raised by 50 cm so the roof would be at the same level as the roof of

the main building as well as allowing for more living space in the upper storey of the extension.The walls of the extension were brought back to their original state using a coating of earth, sand and straw on the outside of the walls, with no topcoat or insulation added in order to preserve the natural inert thermal capacity of the earth wall and its hygroscopic properties.A raw earth plaster was used on the interior walls.The floor was excavated and a granular infill of stone was laid (dimension 20/40) this was covered with a 60 mm layer of cork panels (with a thermal resistance of 1.71) and a thin lime and sand screed that incorporated the under-floor

Earth/sand/fibre plaster - Photo © Robert Junalik

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heating. The floor is finished using terracotta tiles and a lime grout.In addition the partitioning of one of the rooms of the east side extension has been done in wattle and daub.Openings have also been created to link the extension to the original building both on the ground floor and upstairs. The installation of wooden frames for the windows and door allows more light into the building.Finally the roof of the extension was covered in larch shingles. The building has been insulated with wood-wool in wooden fibre panels

and covered in either lambris (wooden tongue and groove panelling) or gypsum (Fermacell) on the inside. As for the western extension that houses the indoor garden , the chosen solution was a timber frame made of Douglas fir insulated with sheep wool. The roof was covered in Zinc that has been cut to measure. An under-floor heating system using wood pellets and thermal solar panels has been installed.

Laying shingles - Photo © Robert Junalik

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Technical focus : Wattle and daubThe «wattle-and-daub» partitioning in one of the rooms on the ground floor was designed for comfort and better heat insulation. The partitioning is also intended to improve the humidity levels in the building by improving the flow of water vapour in the walls and the uptake of excess humidity in the room. In addition to this, the mixture of earth and straw provides better sound insulation.To achieve these partitions, after laying a resilient strip in cork on the

ground and a smooth bottom plate in Douglas fir, they fixed vertical rafters 8 cm thick every 40 cm.After installing all the electrical boxes and sheaths, latticework was nailed either side of the rafters. On one side of the frame it was nailed horizontally every 5 cm top to bottom and on the other side it was only fixed every 30 cm to allow the manual filling of the earth and straw insulating mixture. The latticework was then completed after this process. The moisture in the mixture should be that of soft dough. It is very difficult to form balls with the mix, which should be very sticky and

Wattle and daub partition - Photo © Robert Junalik

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muddy and have water content of between 20% and 35%. The wattle and daub mix requires 2 m3 of clay and 1 extra m3 is needed for the topcoat render ( hemp chippings are then added to the mixture).The quantity of earth and soil in the mixture will change its sound and heat insulating qualities, if you add earth it will be more sound proof, if you add hemp it will provide more thermal insulation.Before the wattle and daub filling is applied, you must mark the edge of the render with a wooden plate boundary on which the door mounts are fixed.While filling the partition any excess mixture coming through the latticework is plastered on to it to fully form a topcoat render. This will then be smoothed off using a trowel.The wattle and daub is then left to dry out naturally ; the length of time this takes will depend on the airflow within the room, or may be speeded up with the use of a dehumidifier.Once the mixture is dry you can then apply the topcoat. For the interior walls of the room they used a mix of earth,clay, sand and vegetable fibres (hemp chippings). On the corridor side of the walls the topcoat is sand and lime mix. The wattle and daub partitioning provides an exceptional level of comfort to the room. The earth used in the wattle and daub partitioning is sourced from a quarry only 5km away from the house.

Barriers and solutionsEach section of the build was carried out successfully within the time limits specified.The owners also acted as project supervisors, allowing the working relationship between each section of the build to proceed without major problems.Each craftsman understood and practised the traditional techniques used during this build (roofing: larch shingles, wattle and daub partitions, earth render and cob walls). These craftsmen also pride themselves on providing work of the highest quality.

Window frame - Photo © Robert Junalik

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The work was carried out by a small work force that worked well together. One example is how the stonemason was able to modify the system that was suggested by the carpenter for the upstairs flooring in one of the extensions. He wanted to make a lintel supported by posts at each corner of the room, having only moderate confidence in the cob walls, in order to support the joists. Ultimately, he succeeded in securing the joists straight into the cob walls.Among the obstacles encountered during the project : the owners wished to replace the conventional septic tank with a phytodepuration system (Waste water treatment

system through plants ) that encountered a problem in getting planning approval. The CSTB (Centre Scientifique et Technique du Bâtiment) had only validated the system for households containing 4 inhabitants and not 5 as would be the case in this house. In the face of this setback this particular project has been abandoned for now. In addition, an eco-interest loan was denied on first request. It required the installation of a single form of insulation contrary to the two that were planned. Finally, the loan will be issued after some clarification but the work has been delayed by three months.

Bedroom- Photo © Robert Junalik

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StakeholdersOwner : Mr. and Mrs. Montès Architect : Cabinet l’Epineguen (Guingamp) Extension and framework : Habitat et Environment (Kerfot) Masonry and terracotta floors : Entreprise Junalik (St Vran) Under-floor Heating : ABE (Trégueux) Pellet boiler : Armor Energies Nouvelles (Pléneuf Val André) Exterior insulation : Avalenn Productions (Plouër-sur-Rance) Timber frames and Wood : Tamm Koad (Plouër-sur-Rance)

Costs The total cost of construction amounted to £70,605 VAT, including £23,535 for the single West extension. Eco-interest loan obtained amounts to £23,535 and covers 3 main areas: the replacement of woodwork, insulation from outside of the equipment room and the installation of solar panels (5sq m). Roof shingles cost £5,491 for 30sq m of roof area. The cost is high but the result is remarkable.

The boiler (power 14kW) uses 6 tonnes of wood pellets per year for a 220 sq m living area, with an annual cost of £1,355. Hot water is provided by the boiler and the solar panels (for 60% of yearly needs) and electricity complements the system when not heated by the sun. The electric bill is about £390 / year. The owners also have a rainwater collection project thanks to 700 sq m roof (shed included).

PerformanceTerracotta tiles - Photo © Robert Junalik

Contactétudes ET chantierswww.ecbpdl.org