Building with straw - Architekt Dirk Scharmer

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Building with straw

Bales of straw, wood and clay – renewable raw materials from close by – can be used to easily build highly thermally insulated, salubrious and eco-friendly homes. This is not a recent building technique: At the end of the 19 th century settlers constructed homes made of straw bales in the sparsely wooded areas of Nebraska – with load-bearing walls but without any timber frames. Some of those houses are inhabited and in perfect condition to this day. Between 1940 and 1980 the building technique fell into oblivion and had not been rediscovered until the mid-1980s. For 15 years now it has globally gained in importance.

In contrast to the historic examples set by the settlers, today timber frames are filled with bales of straw. In Germany this load-bearing building technique with the straw bales supporting the roof as well as the floor loads like oversized bricks is still under way. By this means, one could cut down on expenses, time and effort while at the same time improve the insulation value.

Healthy homes from nearby fields
The essential components of straw bale buildings – wood, clay and crop straw – are renewable and therefore almost indefinitely available. Using clay as natural plastering provides a comfortable and healthy indoor climate as well as an optimal compensation of moisture. The building owners can save money by helping to embed and plaster the bales of straw.

Features of structural engineering
Moisture in straw bales outdoors will not raise a problem if a construction pervious to vapor plus an adequate exterior cladding are being used. They also need to be effectively protected against driving rain. The indoors plastering has to be free of cracks and as airtight as possible. That way, neither rodents and vermin nor mildew, wind and weather can harm professionally installed bales of straw.

Straw bales provide an excellent thermal insulation – a wall 35 cm in width equates to passive house standard. U-factors from 0,17 to 0,12 W/m²K are possible.

Approval of German building laws
According to German building supervision, bales of straw are permitted as insulant since 2006. Furthermore, for deviant construction projects an individual approval under building law can be requested and will generally be approved without any difficulty. A general certification report by the building supervision guarantees the applicability as a fire-retardant outside wall (F-30).

Eine sonnenbeschienene unverkleidete Strohwand unter einem weiten Dachüberstand
 
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