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Timber-framed house in Alsace – France

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This house is located in Schnersheim, a village of 750 inhabitants, 20 km away of the head of the Alsace Region, Strasbourg. The house is a former farm and is constructed on a light slope. The basement and two walls giving to the national road are in rubbles of sandstone and limestone. The storeys are timber-framed, filled with cob or hand-made bricks produced on site. It has a heated area of 350 m² on two storeys. The basement and the attic are not heated. The house is not listed: it is a simple farmer house, as thousands of others all across the Alsace Region. But they are all being threatened with destruction, because they appear to most people as energy-consuming, not comfortable and difficult to retrofit. As the building is not located in a conservation area, the validation of the works by the Alsatian architectural review board was not required by regulation. But because the owner wanted to apply to a grant for exterior works related to heritage, a validation on these works was required anyway.

 

The retrofitting project lasted from 2010 to 2015. The owner wanted to restore his house to its original condition, but also to retrofit it and to obtain a low energy label. One particular objective was to prove, by a real example, that it is possible to live in that kind of heritage buildings with all modern conveniences. Retrofitting these buildings is also a answer to urban spread, very present in the region. Finally, the owner wanted to support the local craftspeople that are still working on heritage buildings (joiner, brick maker, traditional stove maker, carpenter, cabinetmaker) and the local materials (lime, naturel pigment, wood pellets).

 

External walls: a 2 to 18 cm of lime-hemp concrete was sprayed on walls. A dew point analysis was performed for walls, as well as for basement ceiling and attic floor, to validate the choice of this insulating material. The project team was aware that the post-intervention U-value was not as good as it should be but decided to compensate on other elements. Lime-hemp concrete was chosen because it is permeable to vapour and that it has so a similar behaviour to cob. Besides, lime-hemp concrete increases the sensation of comfort of the occupants, what was one of the objectives of the owner. To avoid air leakages and thermal bridges, the flooring from the second storey was removed in order to spray the lime-hemp concrete in a continuous way through the storeys. Some pieces of the wooden-frame were missing because they had been sawed for convenience, to install a window for example.

 

There was no painting on walls or other elements to preserve and the "Stub" has been repositioned after the works. So there is no real issue about the conservation compatibility, although the lime-hemp concrete is not a reversible intervention. The interior render was coloured with natural pigments from the local lime-burner. The plastic coating and the exterior organic render were removed, as the multiple layers of wallpaper and interior coating. No tiling and no wallpaper were put on the new interior lime render, to let vapour freely transit through the walls. The walls are indeed permeable to vapour from the exterior to the interior, thanks to the materials that were used.

 

  • U-value (pre-intervention) [W/m2K]: 1,75W/m²K
  • U-value (post-intervention) [W/m2K]: 0,39W/m²K

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