FAQ: Material Issues
Durability?
As with all buildings, durability is obtained through the understanding of the building material, evidence based construction methods, and attention to detailing. The oldest existing straw bale building is in Nebraska, USA. It was built 1903.
What are these straw bale buildings like?
Straw buildings have a wonderful quality about them. They appear to have a connection to the earth, which is created by the thick undulating walls with deep recesses. Inside they are quiet, beautifully and comfortable. During construction everybody seems to have a sense or feeling that they are doing something "right". Straw is a by-product of an annually renewable by-product of grains. Locally grown straw has a low embodied energy. You can utilize low skilled labour, bringing people together to work co-operatively and is a great deal of fun. When combined with appropriate passive solar design, these buildings have great thermal capacity which creates stable, comfortable conditions in all climate zones of Australia.
Will the bales rot?
Straw has been found in excellent condition in Egyptian tombs, dated thousands of years old. It has been used as an insulating material for many centuries. This shows that kept in the right environment straw can last indefinitely, just like timber.
Without adequate protection straw bales can rot, like timber. Fungi and mites can live in wet straw, so it's essential to buy bales that have had no exposure to moisture. Bales must be kept dry prior and throughout construction.
To maintain an ideal environment after construction the appropriate render and paint should be selected. These should be “breathable” (i.e. permeable to water vapour) so that moisture doesn't get trapped inside the wall. The design of the building should be appropriate for the local climate, and prevent water concentrating anywhere on the straw bale walls.
Will pests destroy the straw walls?
Straw is made of cellulose which is not an attractive food source for pests. It is important to distinguish between hay and straw - hay is food; straw is a 'waste' product with little or no nutritional substance. Any animals or insects you get in your straw bale wall will be similar to those you get in your brick veneer home. Straw bales must be rendered on all sides to cocoon them in. Once rendered, any chance of access is eliminated as bales provide fewer spaces for pests than conventional wood framing.
There are few termites who like straw. However, as wood is still used in roofing/doors/windows in straw bale homes, the normal precautions against termite infestation should be followed.
What about the pesticides used in farming?
Some concerns have been raised about hay fever, toxins and pesticide residues. When the bales are rendered the irritants (if any) are unlikely to transfer into the building. For the extremely sensitive, there are organic farmers of cereals who bale organic straw.
Are straw bale buildings more prone to fire?
Rendered straw bales perform better against fire than many conventional building materials. Recent CSIRO bushfire tests (to AS3959) have shown that a rendered straw bale wall can withstand most bushfires. This is because the straw bales are compacted firmly and thus don't hold enough air to permit combustion. Stud construction, in contrast, forms a series of chimneys (stud cavities) which promote combustion.
Also, since plaster applied to the uneven bale surfaces tends to be thicker than normally found on buildings, the bales can be said to carry an extra layer of protection. Nevertheless it is important to apply a coat of render as soon as the walls are in place, as un-rendered bales and loose straw will burn.
Fire tests in Canada & USA suggest that bale walls provide a two hour fire rating, which is higher than timber-framed buildings.
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 Comments
 Luke on October 17 2009 19:42:29
Would the Durra panels (the pressed strawpanels) be an option? They both look nice and insulate at the same time.
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Tan on August 22 2009 11:04:47
I built a steel portal frame straw bale house with a loft and lined the ceiling with b-grade plywood and polyester insulation. What we did was to s...
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deannicholson on February 14 2009 07:18:26
It seems "to rely on a material that can be degraded by weather is unwise and fraught with danger"
At what level of moisture ( ammount and duratio...
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Jeff on January 20 2009 07:58:00
We are also looking to use portal frames, and had looked at using fridge panel covered with coverbond steel, or a product like Corrolink from APS V...
>>Read More
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