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Straw bale construction
Straw bale makes for an excellent building material. While it may not be for everyone its tough to deny the benefits of straw bale construction and the high level of insulation it provides. This insulation is achieved through the thickness of the walls (around 45cm) and the subsequent air trapped inside which makes a poor heat conductor.
Straw bale houses are utilise 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. Straw bale houses can be 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 water to enter the straw.
On the sustainability front, straw is an annually renewable building material and in many places can be sourced locally. This reduces the amount of transport energy required in the construction of the house. Houses built of straw are 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. Having a good overhang on the roof and making sure the walls are well coated with plaster or cement will help to remedy any possible chance of leakage.
Although you might expect a higher fire risk with a straw bale house, in reality this is not the case. Because straw is compressed, even if a match was applied to the straw, it would smolder rather than burst into flames.