Building material of the month: Strawbale

Strawbales have been a popular and favoured exterior wall choice for many natural builders since the 1990s. They can be used to build strong walls with a very high insulation value, with proper construction methods they become highly fire resistant and with a good group of people helping, can go up very quickly. Straw bale construction rates highly for buildability because it can be very straightforward and is well suited to workshop and volunteer-based building programs. Many volunteer and workshop-based bale raisings happen around Australia. There are several dedicated straw bale builders across the southern regions of Australia, many of whom also offer training opportunities and volunteer experiences.

Strawbales were first used for building over a century ago by settlers in Nebraska, USA, shortly after the invention of baling machines. Straw is derived from grasses and is regarded as a renewable building material since its primary energy input is solar and it can be grown and harvested. Straw is also a waste product and can be sourced reasonably locally across Australia (and on some other continents too).

Straw is the springy tubular stalk of grasses like wheat and rice that are high in tensile strength. It is not hay, which is used for feeding livestock and includes the grain head. The Australian straw bales suitable for domestic construction have two strings (American how-to books often show three-string bales) and are typically 900mm long x 450mm wide x 350–400mm high and weigh 16–20kg.

There’s two main ways that strawbales can be used for exterior walls – as a load-bearing arrangement (with no other uprights and the roof resting on the bales) or as infill, with a wooden or steel frame creating the main frame of the structure.

In-fill strawbale walls – the most common approach to building with this technique in Australia, means you build the posts and roof first. This is advantageous as you have a big roof to work under (a much loved aspect of any building site), and it means internal building works can proceed while the exterior walls are filled and compressed. Infill strawbale buildings are also typically easier to get approval for from councils, as the technique is seen as less ‘weird’ than load-bearing strawbale.

Load-bearing strawbale walls means the walls of a structure must up all at once, and is less complex as you’re not working around wall frames, so it can be quicker that infill. The other potential problem is that if it rains before you’ve completed the walls the bales might get wet if you haven’t put your roof up, which would be a problem for the longevity and durability of your walls! (not good).

Strawbale homes can still be labour intensive, though the basic materials are relatively cheap. The walls may only be 14-20% of the cost of a building but includes the bales themselves, materials to apply compression to the bale walls, and the cost of rendering a minimum of 3 coats. A contract built house can cost from $1750 square meter upwards depending on the level of finish and the home design.

Strawbale building has been a legitimate, popular and growing natural building modality in Australia since the 1990s and there are dozens of companies working with strawbale, teaching its techniques and contracting for jobs across the south east, WA and Tassie where straw is most plentiful.  Check out our directory for some strawbale professionals, more will be added in coming months.

For more information check out the YourHome page on Strawbales

For information on volunteering check out this article in sustainable house magazine Renew

Check out our directory for some strawbale professionals, as more will be added in coming months.

Image Viva Homes

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