Introduction
In this second article in this series we shall look at straw as being the best natural green material for building.
Straw is the waste product from cereal crops such as wheat and barley. The farmers use it for spreading on the cowshed floor, plowing it back into the land or leave it to rot piled in the corner of the field.
This suits our plans to build a straw bale house as the bales will be cheap to purchase, although the transport cost could be high so it is better to purchase the bales as close to the building plot as possible.
Some years ago I was Project Engineer for a proposed straw burning heating system for a plant nursery here in the Highlands of Scotland. I had the opportunity to investigate the purchase and transport of the bales and designed the burner to accept the larger round bales, as these were the most popular available locally. I notice that there is still a prevalence of round bales in the fields, but we will go ahead on the premise of rectangular bales being available locally and that they are available use in building construction.
Remember these articles are not written as instructions on how to construct buildings from green materials. I have used general building techniques to illustrate how the two different materials are used in their construction.
We shall examine the suitability of straw bales as a green building material against the same criteria we used to access the suitability of wood logs in the preceding article as follows:
- Insulation Qualities – Compressed straw bales have one of the best insulation qualities, just a bit better than wood logs, and well above the National Building Regs.
- Aesthetic Qualities – Not as good looking as a wood log building, although if shaped nicely and rendered in a pastel shade, it beats the traditional brick building in looks.
- Ease of Handling and Construction – Straw bales can be handled by sliding them over a plastic sheet laid on the ground. Lifting them can be awkward and a job for two people. Shaping with a chain saw is an art and can be dangerous. There is also an art to re threading and tying the holding cord or strings.
- Durability in all Weathers – Provided a damp-roof membrane fitted between the bales and the foundations, the rising damp in the walls should not be a problem. The rendering will need water proofing and particular attention must be paid to roof and window sill overhangs that they do not allow constant dripping of water onto the walls.
This will be carried out in the summary at the end of the article, so now we go on to look at the construction techniques used to build dwellings from straw bales.
We covered the planning permission and choosing a suitable plot of land in the previous article on log buildings so we will start with the properties of straw bales.
