When considering ecologically sound construction methods and materials, few if any have as many layers of redeeming value as straw-bale construction. For starters, the raw material is 100% waste of another industry, the growing of grain for food, and in many cases is otherwise burned, causing serious pollution. The material is also packaged in a convenient and user-friendly form.
Straw-bale construction is a proven method of long-lasting durable building. Homesteaders in the Great Plains started building with bales in the late 1800’s, and many of these structures still stand today. Properly built and maintained, straw buildings can have a useful life span of at least 90 years.
Straw walls place all the wall elements in the right location. Protective layer on the outside, ample insulation at the the center, and thermal mass to the interior. These area the ingredients of high-performance wall systems, in this case utilizing natural, healthy materials. When laid flat and stacked like bricks in a ‘running bond’ pattern, a plastered or stuccoed straw-bale wall is ±27" thick and yields an insulating value of R-57. Stacked ‘on edge’, with straw parallel to the plane of the wall,similar insulation levels are achieved in 25% less width (±18"). The State of California has established R-30 as the accepted value, still several times the value of typical insulated wood walls. The cost of construction with straw-bales is comparable to wood frame construction. As the cost of wood rises, and bale systems are refined, straw bale will be less. When energy savings over time are factored in, straw-bale is the economical choice. One family in California's hot Central Valley was able to obtain a higher mortgage for their straw-bale home by showing that their cooling costs would be substantially less.
Straw-bale can have great aesthetic value, and lends itself to a variety of styles and finishes. The thick walls present opportunities for niches, deep window sills and seating areas, and “truth windows”. The substitution of bales for lumber can relieve the pressure to log old-growth forests, preserving ecosystems for wildlife habitat, air-quality and soil-stabilization. And, as Matts Myhrman once said, "You can do anything with straw-bales, except have skinny walls!"
In the right circumstances monolithic earth walls are an effective construction system, providing durable walls that mediate the daily and seasonal temperature swings. Earth construction may well be the oldest method of building in the world, as ancient cities of Mesopotamia were built of rammed earth and stone. It is the quintessential local building material, with a large variety of types and styles suited to an equally large variety of climates and soil types.
We are familiar with several of these systems – including adobe, light straw-clay, cob, and hybrid adobe – but in our practice we have most frequently worked with rammed earth or the sprayed soil-cement variation known as PISE. Soil-cement is typically reinforced, and stabilized with cement or lime, important when working in locations with seismic concerns.
Without an insulating layer, monolithic earth construction should only be used in relatively mild climates and with careful attention to solar orientation, shading and passive design. The mass helps mediate diurnal temperature swings, but spaces may become too warm or cool during unseasonable periods of weather. We generally prefer to use earth as a finish on straw-bale or other insulating systems, or as a thermal mass wall within an insulating envelope. This way the full benefits of the earthen walls are enjoyed in a wider variety of climatic conditions.
Aesthetically a variety of textures and finishes can be achieved depending on technique – from the striations of a rammed earth wall, to a textured or troweled sprayed wall – giving structures a natural, timeless quality.