Straw bale walls require well-made bales that have a minimum calculated dry density of 7 pounds per cubic foot. Tight strings! That is, for the average Aussie bale we need a dry weight of 36 pounds or 16 kilograms. Calculate the dry weight of a bale by reducing the actual bale weight by the weight of the moisture content. The moisture content of a straw bale should not exceed 10% although 15% is acceptable. Most bales that we have tested have been well below 10%.
We prefer wheat straw above all others however rice straw and barley straw also bale well and can be used in the build.
We have an excellent supplier who is based in the centre of New South Wales and we normally source our bales from them.
• The common bale size is 900 mm long by 450 mm wide by 350 mm high. The height can vary and some bales are 400 mm and we have used some at 300 mm. You need to know the sizes of the bales before you build or even plan.
- Other sizes are: 2.4 metres x 900mm x 900mm JUMBO Bales or
- 2.4 metres x 1.2 metres x 900mm or
- 2.4 metres x 900mm x 600mm
We have built with all of the above sizes now.
• Load-bearing bales should be laid on their flat however we have built load bearing walls with the bales laid on their edge.
• Maximum height 5.6 to 1, e.g. a bale 450 mm wide will support a wall 2.520 high for pure load bearing walls.
You will need to have ready the following sub-assemblies at the time you raise the walls:
• termite protection barrier
• moisture anti-wick barrier
• top plates (see Top Plates section)
• window and door frames (see Window and Door frames section)
• roof assembly, e.g. trusses (see Roofs section).