The Beauty of Straw Bale Construction

Straw bale construction is taking a bold leap forward and straw bale homes are being built with an increasing frequency.


| April/May 2001



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Time should be spent planning the on the subtleties of the build site.


Courtesy of Bill Steen

It wasn't long after the appearance of baling machines in the 1850's that straw and hay bales began to be considered a building material. Historical patents for bale walls date back to the 1880's in Indiana. The first significant use of bales as a building material occurred in the Sandhills of Nebraska, a vast tract of desolate, grass covered hills. An abundance of wild grasses, combined with the lack of timber and good building soils, provided incentives to devise new building techniques using unconventional materials. The oldest bale building on record is a school built in Scott's Bluff County in 1886 or '87. Ultimately, the school was devoured by cattle.

Although many houses built from natural materials are beautiful, the use of such materials does not guarantee beauty. We have seen many straw bale houses that appear no different than any other building. When incorporated into conventional construction, natural materials are subjugated to the same stresses and patterns. Straw bale walls can rapidly become a very insignificant part of the whole house. We once asked a friend how she liked her new house; she responded, "I really wanted a straw bale home, but what I got was a house with straw bales in the walls."

The Right Straw

Bales used for building should be dense and compact, capable of supporting a substantial amount of weight without changing shape or deforming. The strings should be tight, holding the bale securely together. Most importantly, straw used for building should be bright golden-yellow with no signs of discoloration, which indicates moisture damage. Simply put, you should only use bales that have been kept out of the weather.

The R-Value of Straw Bales

R -value means "resistance value," using a rating system for measuring the relative capacity of insulating materials to resist heat transfer.

The first R -value tests of straw bales were conducted on individual bales by Joe McCabe; he achieved results that ranged on average, depending on the size and orientation of the bale, from R-40 to R-50. Later tests conducted on whole wall assemblies of straw bales got lower results: Oak Ridge National Laboratories had R-31.2, while the California Energy Commission adopted a value of R-30 based on testing conducted by Nehemiah Stone. These results were disappointing to those who thought that the tests for wall assemblies, including allowances for losses, would be similar to results for individual bales. However, the same disparity holds true for other materials. For example, 2x6 framed walls that are nominally rated at R-19 only achieved whole-wall ratings of R-12.8 at Oak Ridge, even with properly installed insulation (it often is not). By these terms, straw bale walls compare very impressively.

It's also very important to remember that laboratory tests are conducted under steady state conditions. In the real world, consistent conditions rarely exist for more than a minute or two. The true test of any material is the amount of energy required, over time, to maintain a reasonable level of comfort. Rather than measuring just R-values, it is essential to consider the overall contributions of a wall's thickness and the thermal mass provided by interior and exterior coatings. Together, these provide comfort and thermal performance much greater than R-value alone would indicate.





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