Straw bale building is a better way to build. It is the most resource-efficient way to build a superinsulated energy-efficient building. Insulation is the key to energy efficient buildings because it makes the most of the energy used to heat or cool the building. Insulation is measured in R-value, which rates a material’s resistance to heat flow (the higher the number, the higher the resistance). A well-built 2”x6” wood-framed wall is R19, a straw bale wall is between R30 and R40.
Less energy goes into building a straw bale building and less energy is require to run it. Straw bale buildings are two to three times more resistant to heat flow than conventional buildings. Other forms of superinsulation exist but require large amounts of high-embodied energy materials such (as foam or fiberglass) to achieve the same result. The embodied energy of straw is 1/4th that of the amount of fiberglass insulation needed to reach the same insulation value.
Straw is an annually renewed agricultural waste product: it is the by-product of the production of grain. Except for the energy used to bale the straw, all the energy used to create a straw bale was necessary for the production of food. Though there are some other uses for straw (animal bedding and erosion control) much more straw is produced than is needed. Until recently, farmers would burn the straw in the fields which produced significant air pollution.
Because plastered bales have little oxygen available for fire, straw bale buildings have a better fire-resistance rating than most conventional buildings (1 hr for clay-plastered, 2 hrs for lime-cement plastered). Plastered straw bales replace the insulation, drywall, paint, and some of the wood used in a conventional system. The plasters can be created with very low-embodied energy materials such as local clay soil mixed with leftover straw.
Clay plastered straw bale walls deal with indoor moisture well, storing excess moisture when it is damp and then releasing it when the air becomes drier. Plastered straw bale walls provide good sound insulation and have been able to withstand winds in excess of 130 miles per hour. Anecdotal evidence from Israel tells us that straw bale walls can stop bullets from an AK47.
Frequently Asked Questions:
Won’t straw burn? - Like a page of the phone book, the surface of an unplastered straw bale is flammable, but the center is so dense that it does not burn easily. Once plastered, the surface is no longer flammable. Unlike stud construction which effectively creates a series of chimneys in the wall, the center of a bale wall is so dense that there is little oxygen available to feed a fire. Straw bale buildings have a higher fire resistance rating than conventional buildings.
Won’t straw rot? - Most building materials, including wood, will rot if exposed to too much moisture. If kept dry, straw will not rot. Building any structure properly involves specific attention to keeping water out and making sure vapor doesn’t get trapped. Straw bale buildings are no different.
Won’t bugs eat it? - Straw is the stem of the plant with the seed head removed. There is very little food value in a straw bale. Straw is less attractive to most kinds of termites than wood, but normal termite precautions should be taken. Also, termites require a damp environment to thrive, which should be avoided in any building.
Won’t rodents live in it? - Although rodents will nest in a loose stack of bales in a barn, bales are stacked in the wall so tightly that there is no access for rodents and they do not try to nest there. Unlike hay, straw does not contain seeds to attract rodents. In fact, there is more room in a conventionally built wall for rodents to nest than in a straw bale wall.
Won’t the Big Bad Wolf blow it down? - With more than 730 straw bale buildings in the US, there have been no reported wolf-induced failures. There are even a few examples of straw bale buildings that have withstood the test of time (and wolves) for almost 100 years.
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Watch our video about the basics of stacking bales, demonstrated in miniature.