Characteristics of a good building bale
Typical Residential Building Bale
The early Nebraska bale buildings where mostly made from baled meadow grasses, thus hay. Hay is usually baled green; it is leafy and contains seeds. These make it prone to decay and attractive to rodents, hence it is not recommended as building material. It is also more expensive than straw as it is baled for fodder and is not regarded as a waste product. In contrast, straw is baled from the dry stalks remaining after the harvest of grain; it is tough and fibrous, a renewable resource grown annually and, as a by-product of grain production, usually regarded as a waste product. Most commonly the strawbales used for building are from wheat, barley and rice crops.
Good building bales should be uniformly well compressed. To assess tightness of a bale, pick it up by its strings. The strings should not separate from the bale by more than 2 centimetres (your knuckles should touch the bale) and they should not twist or sag when lifted. A well-compressed and tight 2-string bale should weigh 18 kilograms or more (or between 90 and 120 kilograms per cubic metre) in an acceptable dry condition.
Bales are usually tied with polypropylene string, sisal twine or wire. It is best to choose poly-string, as sisal is not as strong and prone to rot and wire may rust if it is not galvanised.
For residential building two string bales are the most commonly used. Their general size is about 350 millimetres high, 900 millimetres long and 450 millimetres wide.
However, these dimensions are not as important as the close uniformity of size, especially the proximal consistency in height and width is.
Dryness of the bales is one of the most important characteristics you need to observe for. Like any organic material, straw will decompose if the right conditions of moisture and temperature exist. The moisture content of a bale suitable for building should be less than 15 percent.
A specialised moisture meter can measure the percentage of moisture content of a bale, the farmer or farmers supply shop may be able to lend you the tool.
However, there are many other simple signs and methods to check for moisture in a strawbale. Open the strings of several bales and have a good look inside the straw. Feel if it is moist to touch and check if it has a damp smell. The bales should have a golden yellow colour; any sign of black mould is a sign of composting. Observe the storage facilities carefully; check that there are no leaks in the roof, that the floor and walls are dry. Always sample a number of bales from different places in the stack to allow for highest accuracy in the assessment of your bales.
Each bale has a cut and a folded side; the folded side is the shaggier one. Look at both sides and make sure they are relatively even as they will require less trimming later on.
Observe that the straw is clean. If too much grain is left mixed in with the straw it may attract pests and activate microbial activity.
The average costing of a strawbale lies between $4.00 and $8.00. The price mainly depends on if you can load and pick them up yourself or if they need to be delivered and how far they come from. You need about 3 bales per square metre when laid flat.
We are happy to help if you have problems sourcing the right bales, please e-mail us at firstname.lastname@example.org for supplier contacts.
If you need to store the bales before use they are best stored in a dry barn or shed. If you build infill walls you may stack the bales under the finished roof construction. If you cannot store them properly have them arrive on the day of your wall raising.
Concluding a few recommendations on safe handling of the bales. Wear gloves when lifting bales by strings to avoid pinching or cutting skin. Long shirt sleeves help to avoid scratching and itching to arms. If the bales are very dusty or you suffer from allergies/asthma use a face mask when handling bales. Remember proper lifting techniques such as bending knees, no twisting of body, and getting help if it is too heavy.
Do not forget to install fastening points where you plan to hang heavy items to walls later on. One method is to hammer wooden pegs into walls where needed, or at regular intervals if no plan for hanging things is as yet in place. For very heavy wall hangings you can secure the pegs with a large plywood square on the outside wall. Mark location of pegs etc. on a diagram to be able to find them after bales are rendered.