THE STRAW BALE HOUSE

by Dorienne Robinson

Editor's note: some of this information is now outdated or inaccurate, and The Straw Bale House is currently in the process of being re-written and updated.

Building homes with straw bales is not a new idea; it's not my idea, but it is an idea that has inspired me to dedicate a great deal of time and energy into making these types of houses a reality in this country. My inspiration came from a book called "The Straw Bale House" written by Athena Swentzell-Steen, Bill Steen and David Bainbridge with David Eisenberg.

Most peoples' first reaction to the idea of a straw bale house is an image of bugs and the smell of moulding hay with possibly the whole lot going up in smoke at the first barbecue. Bale houses can in fact be anything you want them to be; from a one room dwelling to a mansion. Using straw and grasses to build with has been around for a long time. We still thatch houses. In Cornwall, where I live, the old cob walls made of mud, horse hair and straw are still to be found standing and quite serviceable. On the whole these methods all gradually gave way to modern breeze block and brick, sand and cement.

In the late 1800's in the United States the first horse and steam powered baler was invented and the first tightly packed bales were made. It was in the timber-poor lands of Nebraska that the first bale houses were built, simply because there was nothing else to build from. They were easy and simple to use, like huge building blocks. At first only meant as temporary structures it was soon discovered how durable and comfortable they were in the extremes of the Nebraskan summers and winters. They were soon plastered and adopted as permanent housing. The oldest documented building is a one room school house built in 1886. In 1903 a homestead was built near Alliance, Nebraska and was occupied until 1956.

To date there are bale houses in Canada, France, Mexico and Russia, many of them having been built in the late 1980's and 1990's. The bale house has proved its' versatility in all climates from snow to baking heat. Environmentally the bale house is a winner as it uses readily available, sustainable material which in many countries is a waste product. Burning of waste straw creates tremendous air pollution. In California where tests were done on this pollution it was discovered that annual straw burning produced more carbon monoxide and particulates than all of the electric power generating plants in the state combined. The smoke has been found to be carcinogenic, containing tiny particles that irritate the lungs. Rice straw may be even worse because of its' high silica content.

The bale house is a very easy structure to build and is ideally suited to self build projects. It would take a lot more space than this article to give detailed instructions but the basics are easy to grasp. A standard foundation is necessary with a damp proof course. Into this metal bars are sunk while the concrete is still wet; they will act as spikes onto which the first row of bales are speared to hold them firmly in place. Another row of bales is placed on the first being sure to break the joint in the same way as block walls are built. A metal bar identical to the bars in the footings called a rebar is hammered through the second bales into the first to hold them together. Every fourth or fifth row a longer rebar is driven down through several bales to make the structure absolutely rigid. Windows are placed where needed and are simple wooden frames the same depth as the bales with a lintel over. Doors are done in the same way. A roof plate is then placed on top of the bales with a rebar securing it to the walls. The roof can then be put on. Next the walls are covered inside and out with wire mesh and rendered. The wiring and plumbing are done at the same stage as with a conventional house.

The finishing steps of plastering and colouring the walls can be the most satisfying. In addition to the look of the finish the breathability of the walls has to be taken into account. Walls can be completely sealed or finished so that they can breathe. A breathing wall allows outside air to be heated or cooled as it passes through the mass of the wall before mixing with the interior air. A wide range of plasters exist that are suitable for use with bare walls. They vary in finish from very hard minimum maintenance to softer plasters like earth and gypsum which are pleasing to the touch, easy to repair and have good acoustics. You can have very straight flat walls, softly curving walls, float finished grainy walls or you can texture them by hand to produce beautiful patterns. The beauty of self building is the ability to personalise, possibly incorporating wind and solar power and maybe a composting toilet to make it a truly eco-friendly house.

Because of the insulating qualities of straw the bale house is highly energy efficient. Insulation is rated by R-value, the resistance to heat flow. The R-value of wood is 1 per inch, brick is 0.2 and fibreglass batts are 3.0. The higher the value the better the insulation. The University of Arizona found the R-value for both wheat and rice bales was about R-2.4 per inch with the grain and R-3.0 per inch across the grain which would give a three string bale laid flat (23 in. wide) an R-value of R-54.7 and laid on edge (16 in. wide) R-49.5. That is two to three times better than the wall systems of most well insulated homes and five to ten times better than some older houses.

Most peoples' worries about building and living in a bale house are its' strength, its' fire resistance and bugs. In America where bale houses have been tested since the early seventies they have passed all tests with flying colours and are even showing positive results when tested for seismic resistance. Initial structural strength tests carried out at the University of Arizona showed that pinned unplastered three string bale walls were strong and withstood lateral and vertical loads well. The first part of the study measured compressive strength. The hydraulic press used for the testing sensed a change in the resistance of the bales at about 72,600 pounds per bale or 10,000 pounds per square foot. In the wall panel test for lateral loading a wind simulation of one hundred miles per hour showed a maximum deflection of just under one inch.

In the mid 1980's the National Research Council of Canada carried out fire and safety tests on plastered bales and found them to be more fire resistant than most conventional building materials. The mortar encased bales passed the small scale fire test with a maximum temperature of only 110 degrees F over four hours. The plaster surface withstood temperatures of up to 1850 degrees F for two hours before a small crack developed. In 1993 fire tests completed in New Mexico showed equally positive results. Two tests were conducted, one on an unplastered straw bale wall panel and the second on a straw bale wall that had been plastered on the heated side and stuccoed on the outside. The first test conducted on the unplastered wall section met the standard requirements of exposing the interior face of the panel to 1,000 degrees F within five minutes and increasing to 1,550 degrees F after thirty minutes. The temperature rise on the unheated side of the panel was 1.97 degrees F. It took thirty four minutes for the fire to burn through the centre of the wall, not through the middle of the bale, but at the joint where bales met. In the second test furnace temperatures reached 1,942 degrees F during a two hour test period. Flames and hot gases did not penetrate the test wall, and the temperature rise on the unheated side was about 10 degrees F.

Bugs and beetles are if anything slightly less of a problem as there are fewer spaces and havens for them in comparison to timber framed houses. If a good coat of plaster is applied and maintained access for even smaller bugs is significantly reduced. Walls left unplastered are another matter. Clean bright straw has very little mould or allergy potential. Asthmatics have had problems with mouldy straw which should be avoided. Once sealed in a wall though, even less clean straw seems to be acceptable.

So far as I know no-one has built a bale house in this country. I imagine most of the problems will come from planning permission and building reg's which will not have come across this type of structure before. The fact that bale houses are being built in other countries does show success coming from perseverance. I would be delighted to hear from anyone interested in bale houses and if I can help or encourage in any way I would be only too happy.

Dorienne Robinson, Moorview, Tregony Hill, Tregony, Truro TR2 5RU.

"The Straw Bale House" is available from Green Books, Foxhole, Dartington, Totnes, Devon, TQ9 6EB.

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