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Right House - A new approach to comfortable, healthy and energy efficient homes

Straw bale construction

Tuesday, December 19, 2006
Straw bale
Straw bale
Straw bale, in most situations, makes an excellent building material. The main benefit of straw bale construction is the high level of insulation it provides. This insulation is achieved because of the thickness of the walls (around 45cm) and the trapped air inside which makes a poor heat conductor.

Straw bale houses are generally constructed as post and beam construction on a concrete foundation, with the straw bales used as filler. The straw bales are stacked up and tied together to form the walls. A plaster of either cement mix or a lime based plaster is then applied. The plaster needs to ‘breathe’ to ensure moisture does not build up inside the straw. In general, straw bale houses are quick and easy to build, lowering the overall cost of construction.

A layer of insulation is used on the foundation to separate the straw from the concrete and act as a moisture barrier. This is important given the porous nature of concrete, which would allow the water to enter the straw.
On the sustainability front, straw is an annually renewable building material and in many places can be sourced locally reducing the amount of transport energy required in the construction of the house. Houses built of straw are very long lasting, if kept dry, and the extra insulation value lowers the long term energy consumption of the house.

It is important at all stages of straw bale construction, and during the life of the house, that the straw remains dry. Any dampness can cause the straw to rot. For this reason, the walls of a straw bale house should be well protected from leaks such as having a good overhang on the roof and making sure the walls are well coated with plaster or cement.

Although you might expect a higher fire risk with a straw bale house, in reality this is not the case. Because the straw is compressed, even if a match was applied to the straw, it would smolder rather than burst into flames – imagine putting a match to a closed phone book.