Straw bale building is an increasingly popular natural and sustainable building method. Safe, energy-efficient and remarkably resistant to fire, straw bale buildings even stand up well to earthquakes.
While loose straw burns easily, when it’s compressed tightly and tied into a bale it is almost impossible to set it alight – just as loose paper will burn, but not a telephone directory. When straw bales are covered in render, their performance is even better. They have been fire tested beyond doubt and have even satisfied the Australian Bushfire Tests, while fire tests in Canada and USA suggest that bale walls provide a two-hour fire rating, better than timber-framed buildings.
Moisture is a real enemy of straw bales, as if bales get wet and/or have a moisture content above 20%, they will rot. However, by applying a few simple rules during the build this is easily prevented.
● Paint: Make sure that paints used on the render are permeable so moisture isn’t trapped in the wall. Straw bales typically contain fewer insects than wood, and once it’s plastered they can’t get in.
● Render: Limewash is a popular alternative to concrete and plaster-based renders, but it’s very expensive. Another choice is ‘earth plaster’, also known as adobe, an inexpensive rendering ideal for covering straw bale walls both inside and out. Non-toxic, it takes a while to dry to a hard surface giving you more time to work it. For more info, see ehow.
● Foundations: these should be a minimum of 15-20cm above ground level with a good damproofing course, and the roof should have an overhang of 50cm. Along with regularly limewashing the exterior render, moisture will be kept out.
Rats and mice need cavities between walls in order to hide and move around, and in straw bale walls there are no cavities.
Straw bale buildings are as safe if not safer than any conventional building. They have been thoroughly tested for load bearing and are capable of supporting structures far in excess of accepted building requirements. Even when loaded to failure point that they fail in an unspectacular fashion when compared to conventional building materials. Straw bale construction has also been tested in earthquake simulations and found to be remarkably stable, as the straw walls are thicker than conventionally-built walls and also absorb more of the energy of the quake.
While the bales themselves are cheaper than most other wall materials, everything else costs the same as on a conventional build. The big difference is in year-on-year energy costs, as buildings constructed with bale are super-insulated. It’s often possible to save on actual construction labour costs, and bales are easier to work with than, for example, bricks.
While in the UK we have only been building with bales since the 1990s there are buildings in the USA that are over 100 years old, and one in France dating from 1921.
Loads of information on carbon-neutral homes, alternative energy sources and a wide range of construction techniques of which straw bale is only one.
The Strawbale Building Co
Offering courses and workshops as well as straw bale construction, they welcome enquiries – with no obligation – for all straw bale projects from basic advice to actual building work.