Moisture is the biggest risk to strawbale construction so attention to detail and building a house with well-designed water barriers is essential. Shower areas or baths shouldn’t be installed adjacent to strawbale walls without additional methods of moisture control. Laundries and kitchens sometimes flood internally so placing strawbale walls on a plinth or up stand to keep them above floor level by 50 -100mm is recommended. We recommend appropriately sized eaves and verandahs to aid in protecting strawbale walls from driving rains.
Rendered strawbale walls once are highly fire resistant. The tight dense bales with their 36mm coating of what is predominately sand (with cement, clay, lime or other additives) are in a state where there is minimal oxygen within them and very little air that is able to flow into the wall. Setting fire to a completed strawbale wall is like burning a telephone book, it is not until the wall is torn apart and air is available to feed the fire does it burn freely. Good construction detail is essential and there shouldn’t be any exposed straw left in the ceiling or on the tops of walls.
Building in Bush Fire Areas Strawbale building can adequately satisfy the Australian Standard (AS3959) for building in bushfire prone areas and can achieve compliance in all BAL 12.5 → BAL 40 and BAL FZ categories. To achieve a BAL rating the strawbale walls and render need to comply with requirements of the strawbale construction fire test results. Fire rated construction is usually more relevant for public, commercial and multi-unit dwellings. International test results, accredited in Australia, give rendered strawbale walls a 1 ½ hour fire rating (FRL 90-90-90). Fire rated walls do require specific structural construction methods in order to achieve this result.
Strawbale fire test results and details are available at https://ausbale.org/
Rodents and insects may decide to live in any type of wall. If you purchase good dense strawbales with no seed in them then there is no sustainable food source for rodents and they have to come out of the wall and forage elsewhere for food and water. Attention to detail when rendering the walls (not leaving any exposed straw, even in the ceiling space) will reduce the potential of infestation.
Under the National Construction Code (NCC) you are required to undertake some form of protection for termites regardless of what you build with. Strawbales are cellulose fibre (like trees) and to our knowledge there is NO species of termites that live solely on straw, though some species may eat straw. Strawbale walls are at no greater risk than the timber in doorframes, furniture or roofing members.
We have found no problem with council approvals for strawbale buildings where thorough documentation has been provided. We highly recommend the use of the Australian Strawbale Construction Guide since not all building designers, engineers, builders and trades people are familiar with strawbale construction. The guide is available at https://ausbale.org/
Some design companies offer generic building plans, with plans that suit several building materials. Our experience with these is that for owner builders or builders not experienced in strawbale building there is insufficient construction detail provided. Predominantly strawbale homes are individually designed.
In South Australia, the most experienced strawbale architect is www.bdcoarchitects.com.au
The most experienced engineer in SA is GW Wittman & Assoc. (firstname.lastname@example.org Mob: 0407 275 740)
The https://theownerbuilder.com.au/ often has other resources and information relevant to strawbale building.
Yes, you can. We can and often do subcontract for the installation of rendered strawbale walls to other builder's projects. We can consult with your builder about construction considerations e.g. timing of eaves lining and window installation. Lance is a licensed builder and can be your builder, but this does depend on the location of your project.
It is likely that it may take 9-12 months to complete a strawbale home build but this depends on the site, building design and its complexity, size and required finishes. Many owner builders can take longer than this.
The Australian rating gives a strawbale wall system an R-value of between 4.5 and 10. (American books say R40 or higher, note that it is the same value just calculated in different ways) Modern insulated timber framed walls achieve around R2.1, an insulated brick veneer wall system R2.1, an uninsulated brick veneer R0.5, a mud brick wall less than R1.0, a rammed earth wall less than R1.0, a timbercrete wall R1.0 and a 200m thick Hempcrete wall R 2.75.
The higher the R value the greater the resistance to heat loss/gain through the building material. As a general guide solid material transfers heat at a greater rate (have a lower R value) than materials that have air trapped inside them. Air trapped in each straw of the bale slows heat transfer thus giving a higher R-value.
Thermal mass relates to the ability of a material to store heat and coolness, important in well-designed buildings. Stone, brick, mud and concrete slab floors are high in thermal mass. Rendered strawbale external walls combine an internal 35mm render skin/cladding that is insulated from the outside by the straw, this provides thermal mass.
It is important to clad the exposed wall surface with a good sound water resistant render, usually in 3 coats. Earthen or lime renders are very satisfactory, however all renders need to be kept in good repair. Cement renders are sometimes used. The inclusion of mastic filled expansion joints is desirable to allow for the building to move and reduce uncontrolled cracking in the render. The addition of, or post construction application of water repellent agents (as used in mud brick or rammed earth) may be desirable under some conditions.
While stacking strawbales to form a wall is quick and relatively easy, it is only part of constructing a strawbale wall. Wall compression, netting around openings, rendering and installing control joints-whilst all the time paying attention to detail are necessary to get a good quality and long lasting strawbale building. We highly recommend that people attend a workshop before commencing to owner build. The hands-on experience that can be gained is invaluable.
It is likely that banks will require you to have a fixed price contract with a builder before they will lend money-of course this is dependant on your location and financial circumstances as well. We have found that owner builders and cost-plus contracts are less likely to be approved, making it more difficult for owners to be involved.
There are insurance companies that insure strawbale homes, and we suggest that you ensure the words strawbale walls/construction are written in your policy. Not all insurance companies/underwriters issue policies for all building types.
Strawbale walls are only 14-20% of the total cost of a building. Whilst strawbales are relatively cheap (around $12 each for construction grade) building with strawbales does not necessarily equate to a cheap house. The high level of insulation that strawbale construction provides (R8) is not easily or cheaply replicated in other building methods. Strawbale homes offer long term cost savings because of the high level of insulation they provide, reducing heating and cooling costs.
Contract-built houses can cost from $2500 square metre upwards depending on the house design and level of finish wanted.
Very energetic, resourceful hands on owner builders could build a house for around $1800 per square metre. Whilst this can be a good starting point to work out your finances most of us are not as energetic and resourceful as we would hope. Owner builders generally take on the challenge of creating a hand-built home, whether using second hand building materials or all new over a longer time period and can end up with beautiful homes that would have been out of their financial reach had they had it fully contracted.
(NB: Costings are as at 2020 and can be variable)