Bohdan Dorniak & Co. Pty. Ltd. » Strawbale Construction

Sustainable material

Straw is a by-product of the grain industry (be it wheat, rice, sugarcane, or barley stalks) that can be baled into a relatively tight bale. Compared to mainstream building materials, straw has relatively low environmental footprint and, grown as an annual crop, is very sustainable.

Insulative properties

Rendered strawbale walls have a high insulation value known as the R value (which rates the ability to resist heat flow). The higher the R value, the better the insulation. A strawbale construction may typically provide values around R8.0 to R9.0., compared to R2.6 to R3.0 for a standard brick veneer build, although the R value achieved will be dependent upon the compactness of the straw, as very compact bales have a lower R value.

Pest resistant

There have been very few problems reported regarding insect or rodent infestation in strawbale buildings. Fully rendered strawbales seal the walls, and the bales themselves provide very little food for pests.

Termites seem to be adverse to straw. It has been observed that termites have entered a strawbale home, left the straw alone and damaged timberwork. However, all homes and buildings of strawbale construction should be protected against termite infestation in accordance with best practice as outlined in the building regulations.

Fire rating

Rendered strawbales had been tested by the CSIRO and results indicated that rendered strawbale walls were suitable for construction in bushfire zones (bushfire attack level 29 – high). However, following recent Bushfires in Victoria and NSW and the introduction of a new test regime with higher specifications, further testing will need to be carried out to determine the suitability of strawbale construction in high risk areas. If you’re considering building a strawbale house in a bushfire zone, please contact for an individual risk assessment.

Moisture Resistance

Moisture is perhaps the biggest problem strawbale homes face. In conventional construction the exterior cladding of a building is generally waterproofed. This is not the case for rendered strawbale walls and the reliance is on “water resistance”. Renders that are “permeable” or breathable will allow water vapour to dry out.

The use of a “toe up” on the floor (a raised base), will help prevent any liquid that may be spilled from “wicking up” into the wall. All walls should be built on a damp proof membrane (similar to a brick wall) to minimise exposure to moisture.

Rendering

Rendering is the most labour intensive aspect of strawbale wall construction, but also the most crucial. Render gives the walls stability, wind resistance, thermal mass, fire resistance, rodent resistance and, most important of all, makes your strawbale building weatherproof. There are a number of finishes that can be used for rendering strawbale walls in Australia.

Cement

A cement render creates a hard, brittle skin for your walls. Although cement renders are more waterproof than others, they are not very “breathable” and are more harmful to the environment (high energy footprint).

Cement Lime

A cement lime render creates a hard surface for your walls, but has a higher “breathability than cement render. Cement lime renders share similar disadvantages to cement renders.

Lime

Lime-based renders create a smooth, strong and slow curing skin that, when correctly applied, will revert to its original form – limestone. A lime render is more breathable than cement and is water and weather resistant. The application of lime is hazardous, as lime is highly corrosive when wet and care is required in its application.

Earth

Earth or clay renders create a soft, slightly flexible skin that has good passive qualities. Earth renders are the most breathable of all renders and, as a reusable resource, have the least embodied energy compared to cement and cement/lime renders. The disadvantages of earth renders is they are more labour intensive and quality control of the mixes can be difficult, however commercial earth mixes are available to help create a more consistent result.

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