Q: Is straw bale considered a green building material for houses? Does it meet the building code standards?
Straw is a renewable & natural material that has many useful applications in basketry, crafts and the production of biomass power. However, one of indigenous and prevalent uses of straw is to build and insulate houses. Straw is commonly mistaken for hay and it is important to make a difference between the two. Straw is the byproduct of cereal grains (barley, oats, rice, rye and wheat), after the removal of chaff and grain, while hay is a plant material that is cut, dried, and stored for use as food.
Is straw a suitable green building material for homes? Without any hesitation, the answer is yes. Here’s why: Straw satisfies several important criteria of sustainable living philosophy because it is a renewable resource, it can be harvested locally and it is completely natural and non-toxic. Yet another great feature of straw is that it has high R-values. According to Sandia Laboratories, the R-value for straw bale walls is 2.67 per inch of thickness; and its thermal values for range from 44 to 52. As a building material straw bales can be used as infill in construction, when a structural framework carries building loads. The straw bales can be also built into structural walls without extra framework.
As I already mentioned, straw is not food, but it may provide a pleasant dwelling for all kinds of microbes, insects, and small animals. For that reason straw bales need a protective finish. Once the bales have been stacked into walls and pinned together, they need to be covered with wire mesh and finished with stucco to make them weather tight and durable. It is also suggested to encapsulate the bales with Portland cement plaster.
Straw bale building is gaining popularity as a part of environmentally-minded building philosophy. Also, straw bale is a basic construction method that can be well executed without much of building experience, which makes it very attractive to DIY homeowners who try to juggle the issues of money and quality. One straw bale has an R-value of about 28, while the stucco finish protects it against fire and microbes. Meanwhile, the availability of straw is very dependent on your locality. Straw should be kept dry during construction and code officials in some parts of the country aren’t familiar with it so approval is not likely to be automatic.
It is ironic that most of the traditional building methods including straw bale and adobe are nowadays classified as “alternative” building methods. That is, indigenous and well known materials are required to confirm their capability to meet energy, structural, fire standards on a case by case basis. The testing is additionally aggravated by the fact that most testing standards were designed to accommodate specific materials and systems, which generally do not include straw or mud. The building code authorities require extensive testing of its abilities to perform even though straw has a history of being used to construct homes in the US.
This contest is additionally intensified as most native construction methods are not “proprietary”. Hence, no manufacturer wants to take a chance and pay for the test to validate conformity, even when appropriate test methods exist. Fortunately, green and sustainability-oriented groups are assisting in the creation of information and support network and straw bale construction has a solid system of designers, consultants and builders. The good news is that the straw bale with stucco finish walls passed the fire hose test with no suggestion of distress or malfunction.
Despite the difficulties the future of the straw bales as a construction material is positive. Many jurisdictions now allow straw bale buildings classified under the “alternative materials” and methods provisions of the existing codes. Moreover, there are some communities that have specific provisions for straw bale construction, including parts of Arizona, California, Colorado, New Mexico and Texas.
Johnston, D. & Gibson, S. (2008). Green from the ground up : sustainable, healthy, and energy-efficient home construction.
Spiegel, R. (2012). Green building materials : a guide to product selection and specification.
Stang, A. (2005). Green Houses: New Directions in Sustainable Architecture
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