Contents at a Glance...
BUILDING WITH STRAWBALES
STRAW BALE BUILDING IN AUSTRALIA
A wide variety of systems have been used to build walls out of baled materials, yet many new ones remain to be explored and refined. Each building seems to add another improvement to the field of bale building. The adaptability of bales as a building material makes it possible for them to be used with a wide variety of styles, methods, materials and variations of individual ingenuity.
Some of the methods used have been born out of necessity: the historical Nebraska houses, for example, used hay bales for loadbearing walls due to the scarcity of other building materials. Recently, some structures have used bales as in-fill, with other structural combinations to meet (building) code requirements and in cases where there has been a question of whether bales possessed sufficient structural integrity.
The system that is adopted for a particular building will usually be determined by a variety of factors, including codes, size, building design, costs, availability of materials, climatic and engineering considerations such as snow, wind, and seismic loads, and personal preferences. The potential for loadbearing bales to be used even more efficiently and appropriately may lie within the realm of a completely new style of building and method of construction, dictated by the bales themselves and not by the standards and aesthetics of modern construction.
Known wall methods that have been developed for use with bales to date, include:
· Loadbearing walls - in which bales are stacked in a running bond like bricks and pinned together.
· Mortared, loadbearing walls - in which the bales are stacked either in a running bond or in vertical stacks with no overlaps, and mortar is used in the joints between the bales.
· Bale infill or bale wrap walls - in which another structural system supports and attaches the roof and the bales are either inserted as in-fill material between the columns of a structural framework, or the bale walls wrap a structural framework.
· Hybrid structures - that use a combination of the above methods;
· Retrofits - of existing buildings and mobile homes;
· Multiple storeys;
· Light clay straw walls - in which a clay binder is used with large volumes of straw to form a wall in-fill material.
Load-bearing Bale Walls and Roof Plates
In loadbearing walls, each bale sits over the vertical joint between the two bales beneath it. The bales are pinned together with any material that suitably reinforces the wall. A horizontal structural member or assembly (a roofplate) that is laid on top of the bale walls is used to stabilise the walls; to bear and distribute the weight of the roof; and to provide the means of connecting the roof to the foundations. The walls of the structure will settle, or compress from the weight of the roof within a short period of time. They can also be intentionally pre-compressed. Once the compression process is completed, the walls are plastered.
Loadbearing bale walls were pioneered in the Nebraska Sand Hills with the availability of baling equipment that was developed to facilitate handling, storage, and shipping of hay. Early balers, often powered by horses, produced bales that tended to be looser than the compact, modern bales. Despite the fact that the Nebraska houses used those older style bales, a number of them remain in good condition, demonstrating that loadbearing straw walls can endure the test of time.
Simplest and Most Economical
For some structures, this may the simplest and most economical method of bale construction; however, there are several basic principles that require attention when building loadbearing bale walls. The most important point to understand is that bales are a compressible building material, in contrast to conventional structural wall materials, which do not compress. Roof loads will cause the bales to compress - the greater the load, the greater the compression. With very dense, compact bales and ordinary loads, the compression may be minimal, but even under those conditions, the roof design and door and window openings can concentrate loads in certain areas and cause problems.
If the bale walls had no openings and the roof distributed its loads relatively equally to all the walls of the building, compression would theoretically be equal in all the wall panels. In practice, different roof configurations and door and window designs create unequal loading of wall panels, often resulting in uneven compression of the bale walls.
For example, when the spacing of door or window openings leaves only narrow columns of bales between them, those columns can be subject to greater loading than the rest of the wall panels. This is especially true where lintels are used, because lintels take the load from over the opening and distribute it to the columns of bales on either side of the opening. Since the bales next to the openings are already carrying their normal roof load, this can more than double the loads on those bales, resulting in additional compression. If custom-sized bales next to the openings have not been retied to the same density of the other bales, more compression can result.
Small, isolated loadbearing columns of bales and very short walls without corners or returns (short, intersecting wall sections) should be avoided or used with great care for reasons similar to those stated above. it is also important not to mix loadbearing bales and non-compressible structural supports in the same wall section.
Smaller and simpler structures, and those with fewer or smaller window openings, naturally have fewer problems. Potential differences in load distribution grow as wall lengths increase and the roof structure becomes larger. Live loads, such as snow, further increase the potential differences.
A roof plate that is stiff enough in the vertical plane to resist bending or sagging while carrying the load will help significantly in evenly distributing roof loads. The more effectively the roof-plate spreads the roof load without deforming, the less likely it is that differential settling will occur.
Loadbearing walls have traditionally been best suited to small structures of relatively uncomplicated design, with few windows and small window openings. Some builders think that loadbearing walls are most appropriate for use with structures under 400 square feet (4 squares). Much larger loadbearing structures with large window openings have successfully been built, however, and many of the historical bale structures are about 900 to 1,000 square feet. It is possible to build even larger loadbearing structures.
Ease of Construction
Building walls from straw is much less labour intensive than using other materials such as concrete block, brick, adobe or stone, and requires considerably less skill. Bale building is forgiving, encourages individual creativity, and leads to final structures that are climatically-adapted and energy-efficient.
Many people would have a great deal of fear and anxiety about building a home with more conventional materials. The complexity, skill required, time involved and cost can seem prohibitive and daunting. Building with straw bales relaxes the whole construction process and allows inexperienced and unskilled people the opportunity to become directly involved in creating their own homes.
It has been demonstrated that the basic methods of straw bale construction can be learned in a two-day workshop. One of the great beauties of this system is that everyone can participate in building a home, including women, children, and others who have been 'disenfranchised' from the building process. This coming together of people to help each other build often generates a great deal of excitement. Group wall-raisings facilitate community-based projects that might not otherwise happen.
After the original Tree of Life Nursery in Southern California burned down, the owners received a broad outpouring of community support offering to help them put up a new building. In response to that enthusiasm, owners Mike Evans and Jeff Bohn decided to construct their new building out of straw bales because it would afford community members the greatest opportunity to participate. The event was conducted much in the spirit of an old-time barn raising, and the food, music and work were so delightful that Mike and Jeff have decided to host an annual wall raising whether they need a building or not!
* For details of the authors' book 'The Strawbale House', see Books, Non Timber Building, Strawbale in the Alternative Directory.)
"This straw appears small and light, and most people do not know how really weighty it is. If people knew the true value of this straw, a human revolution could occur, which would become powerful enough to move the country and the world."
- Masanobu Fukuoka, One Straw Revolution
The Merrigalah Project was established to 'officially' bring strawbale building to Australia. The author has since published a step by step manual* for newcomers to the technique. Leo lived in the US for ten years, working in construction, which is how he came across strawbale building. Realising its value, he is now working hard to promote the concept here.
Why Build with Straw?
Straw is a sustainable, low-cost material, suitable for building almost any structure, even freeway sound and safety walls. Straw is a waste product, consisting only of cereal plant stalks left after the food portion has been stripped from the plant; it is nothing but waste material, and is usually burned. Straw is virtually identical to wood in chemical composition. It is possible to use the straw of wheat rice, oats, rye, flax, barley, grass and perhaps sugarcane waste, or even baled waste plastic, cardboard or paper.
Strawbale building on a large scale could reduce the logging of native Australian forests by as much as 25-30 percent: there was enough rice straw burned in New South Wales in one year to have built the walls of 15,000 twenty-square homes.
Straw is like a thin, hollow and very small tree! The large-scale adoption by Australians of strawbale as a building material may result in some very substantial enironmental benefits.
To put the Australian situation into perspective, our research has already indicated that in Australia last year 9.9 million tonnes of native forest timber was logged.
This volume of logged native forest timber is equivalent to a stack 25 metres wide, ten metres high and four kilometres long. About one-third of this native forest timber went to construct domestic dwellings. Few Australians pause to think that it takes an average of 40 years of regrowth to replace the lost timber alone, and almost 200 years before the native forest itself can fully regenerate.
We hear that the timber industry "deeply regrets" the cutting of trees from native forests, while sanctimoniously talking about the "unavoidable need to cut the timber for family homes". Well, it is avoidable! If the present rate of logging were to continue, during that 40-year (average) regrowth period, the Australian loggers would be cutting native forest timber equivalent to a stack 24 metres wide, ten metres high and 160 kilometres long! During just one year, in just one State (NSW), rice farmers burn over 600,000 metric tonnes of rice straw, releasing 30,000 tonnes of carbon dioxide and 2,000 tonnes of solids directly into the atmosphere! This figure does not include the wheat, barley, oats or rye straw also burned, nor does it include the figures for the rest of Australia.
Logically, during the 40-year period of native forest regeneration, 24 million tonnes of rice straw will be burnt; so, in addition to the ongoing environmental degradation of these destroyed forests, if nothing is changed, the rice growers will release 1.2 million tonnes of carbon dioxide and close to 50,000 tonnes of solid particle matter into the atmosphere from NSW alone. On the other hand, 24 million tonnes of baled rice straw could: provide enough material for the walls of over 580,000 homes (of 180 square metres in size); reduce native forest timber demand by about 20 to 25 percent. How tragic, and how environmentally absurd it is to needlessly cut such huge volumes of native forest when there is an alternative! How foolish it is to burn such vast quantities of a perfectly viable building resource.
* For details of Leo's book 'Construction with Strawbale', see Books, Strawbale, in the Alternative Directory.