Most code-approved building materials in North America are manufactured using industrialized processes that create components of uniform size and form, with predictable performance characteristics such as fire resistance, permeability ratings, insulation values, and structural properties. Since the process of testing such materials for code approval is extremely expensive, only large manufacturers who intend to produce, package, and sell a product for wide distribution can afford to test. This product-oriented approval process is not geared toward the analysis and acceptance of nonproprietary unprocessed natural building materials and it has all but closed the door on 9,000 years of preindustrial building technology.
There is at least one exception to this trend that perhaps serves as a model in this country for future code approval of other natural building materials. Wood is a naturally occurring, minimally processed building material that has universal code acceptance even though it is flammable and subject to shrinkage, comes with inconsistent structural properties, and will rapidly deteriorate through rot and insect infestation if left unprotected. In spite of its embarrassingly preindustrial nature, it remains the dominant building material in residential construction, and building codes have succeeded in creating safe guidelines for its classification and use.
Why consider alternative natural materials such as earth and straw as an option for healthy housing? These historically derived methods of construction differ from standard cavity wall construction in that manufactured petrochemical-based barriers are not installed to retard the flow of vapor through the walls. Instead, vapor is allowed to flow naturally. The massive walls employ hygroscopic natural materials to increase the capacity of the wall to handle the transfer of moisture from the interior and the exterior surroundings and
to release vapor back into the surroundings as climatic conditions change. Because temperature change occurs very slowly in the flowthrough process, and because dried clay — based materials have the ability to absorb and desorb large amounts of moisture without deteriorating,1 accumulation from condensation is insignificant. When a home is properly constructed using these mass wall techniques it will be an extremely comfortable environment with superior temperature and humidity stability. Furthermore, because the solid walls provide insulation and can be finished with a covering of plaster or furred-out wood applied directly to them, the need for synthetic exterior sheathing, batt insulation, gypsum board, joint fillers, and paint is eliminated. Many volatile organic compound contamination sources are thereby eliminated as well.
In the philosophy of Building Biology, a
