strawbale.sustainablesources.comStraw Bale Construction – Sustainable Sources LLC

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Straw bale are traditionally a waste product which farmers do not till under the soil, but do sell as animal bedding or landscape supply due to their durable nature. In many areas of the country, it is also burned, causing severe air quality problems. It is important to recognize that straw is the dry plant material or stalk left in the field after a plant has matured, been harvested for seed, and is no longer alive. Hay bales are made from short species of livestock feed grass that is green/alive and are not suitable for this application. Hay is also typically twice the price of straw. CONSIDERATIONS: This technique for constructing walls has been recently revived as a low cost alternative for building highly insulating walls. The technique was practiced in the plains states in the latter 1800’s and early 1900’s. Many of the early structures are still standing and being used. The technique has been applied to homes, farm buildings, schools, commercial buildings, churches, community centers, government buildings, airplane hangars, well houses, and more. Straw is also being used as a building material currently in sheet materials such as sheathing and wall panels. However, the approach of using bales directly, despite its history, is a new technique from a regulatory standpoint. In the 1990s a number of cities passed a straw bale construction building code, followed by the state of California. We expect to see straw bale codes adopted in coming years. Building walls with straw bales can be accomplished with unskilled labor, and the low costs of the bales make this technique economically attractive. However, it is important to realize that the cost of straw bales will differ depending on what time of year they are harvested and how far they need to be transported. They are cheaper at the time of harvest rather than after they have been stored from the previous season and, of course, cheaper if they are transported shorter distances. Bales must also be protected from getting wet. Costs also begin to rise when one considers the type of stucco and its application. An earthen plaster taken from site soil, applied by the owner/builder, and maintained by the owner is quite inexpensive, but may take a long time to apply. A cement stucco applied by a contractor is accomplished quickly and lasts a very long time without any maintenance, but also costs money. As with any style of construction, the more labor input by the owner and the less by the contractor, the less costly it will be. Two basic styles of straw bale construction have been used: post and beam construction with straw bale infill, and structural straw bale construction or “Nebraska” style (the weight of the roof is supported by the bales). There are a number of straw bale buildings now located in the Austin area and local expert consultation and construction is readily available. (See Resources ) Commercial Status Implementation Issues T E C H N O L O G Y S U P P L I E R S C O S T F I N A N C I N G A C C E P T A N C E R E G U L A T O R Y Strawbale Satisfactory Satisfactory in most conditions Satisfactory in Limited Conditions Unsatisfactory or Difficult COMMERCIAL STATUS TECHNOLOGY: Experimentation with straw bale construction continues. A good deal of standardization and refinement in regard to techniques, tools, and associated materials is now appearing. SUPPLIERS: Straw is plentiful in many locations. However, distribution systems are not developed for straw to be used construction. COST: This can be one of the most economical wall systems. Houses have been constructed for as low cost per square foot (floor area) for very basic accomodations to high end homes at well over $100.00 per square foot. IMPLEMENTATION ISSUES FINANCING: Building code acceptance will be key to obtaining conventional financing. PUBLIC ACCEPTANCE: The appearance of a completed straw bale structure is similar to a southwestern adobe style building. This look is generally positively viewed . There will be hesitation among mainstream buyers to this technique at first since it is new and unusual. Significant interest in this type of construction exists in our region, although the adobe style is not typical for this area. REGULATORY: Any unusual building technology must be evaluated by the code enforcement authorities before approval can be granted. This is typically done by review of another code agency’s approval or position on the technology or by review of test data supplied by a reputable independent laboratory. In the case of straw bale construction, there are precedents of approval in other jurisdictions. Anyone wishing to receive approval in Austin should follow the local straw bale construction code. The inspections department in other areas can refer to the Green Building Program for locations of precedents from our as well as other building inspection departments. There are numerous examples of this construction in the Austin regulatory jurisdiction and in the greater Austin area at this time. If test data is needed, the building inspection officials will indicate what is needed. Testing is currently being done in Arizona, California and New Mexico. At this time, there are also a number of insurance companies and lending institutions in the Austin area that have given their approval to straw bale construction. GUIDELINES 1.0 Summary Recommendations and Brief Overview Straw bale construction exhibits R values from R-30 and up to R-45. The bales are typically covered with concrete mortar/stucco or earthen/lime plaster, achieving a high degree of fire resistance. Two hundred million tons of straw are burned annually in the US. The stability and lack of weathering in straw is not desirable in agriculture but quite desirable in construction. Straw in straw bale structures has not shown evidence of termite infestations. Dry bales should be used. Moisture levels in use and in storage should be below 14%. The bales should be kept dry after construction. Bales may ...