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There are three techniques for building in straw: loadbearing walls, infill panels and mortared bales.

The loadbearing-wall system is the purest form. As the name suggests, the bales are structural components and bear the weight of the roof. They are laid “dry”, one on top of the other and are pinned both to each other, and to the foundations. A wooden roof plate is then fixed across the top. Windows and doors are typically fitted between whole bales of straw.

In the infill system, straw makes up the walls within a conventional post-and-beam or timber-frame house. The timber is loadbearing and the bales are ecofriendly insulation. This technique is more expensive because of the joinery work required.

The third system, in which mortar is used to join the bales, is Canadian in origin. The obvious advantage of this type of construction is that the mortar adds rigidity and mass. However, designers view it as less eco friendly.

The mild, damp British climate has encouraged the use of bricks and mortar above all other building systems, and at first glance, the weather would seem to rule out building in straw. The problems posed by rain and humidity need to be addressed at the design stage (for example, by the use of high plinth walls, self-draining foundations and large overhangs). It is also recommended that straw-bale walls be raised off the ground by 22.5cm to 45cm to protect the bottom bale from damp problems.

Not enough straw houses have been built to give a guide to costs of this type of structure. The materials are inexpensive, but finding builders who are experienced and/or comfortable with this type of project may be a problem.

Martyn Hocking is editor of Build It magazine

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