Wood has historically been used as a component of a breathing wall system, whether it be the half-timber, wattle-and-daub constructions of medieval Europe or the log cabins of our ancestors in North America. (See Division 4 for an explanation of the breathing wall concept.) Wood is an advantageous material in a healthy home because it has the property of hygroscopicity. This means it has the ability to absorb and release moisture, thus helping to balance humidity levels and the electroclimate. However, for many chemically sensitive individuals the natural terpenes found in wood, especially soft or aromatic woods such as pine or cedar, are intolerable. Certain woods may need to be eliminated from, or sealed when used in, a home for a chemically sensitive person.
In standard home construction, the air space between the wood studs may be filled with insulation laden with chemicals. The exterior sheathing often contains formaldehyde-based glue or asphalt backing. The gypsum board applied to the inside face of the studs may be finished with harmful joint compounds. If the home was built before 2004, the studs sit on a sill plate that is most likely pressure treated with a pesticide to prevent rot and insect infestation. When standard construction is the only option, we recommend that the most benign wall construction materials available be used and that a barrier be installed between the wall construction and the living space. Refer to Division 7 for air barrier product and installation information.
In some instances, creating a barrier for the purpose of blocking fumes can cause other problems when moisture from condensation becomes trapped inside the wall. Applying the gypsum board in an airtight manner will help block fumes but will not in itself block the normal movement of water vapor. See Division 9 for more specific details on creating a barrier using gypsum board.
Construction lumber is at risk of contamination by pesticides when farmed, when milled, during transportation, and in storage. For those who have severe sensitivities to pesticides, it is important to locate a source for uncontaminated wood. Wood that is sustainably harvested can be traced from source to sawmill to distributor and its pesticide history can be determined. Certified producers and processors are encouraged to use least-toxic pest management. Some regional certification organizations have mandated a ban of pesticides for sustainably harvested wood in their jurisdictions. Certain imported woods maybe
