Q. We typically build energy-efficient houses with 1-inch foil-faced polyisocyanurate foam on the interior of our walls. But more than one customer has questioned us about the potential health effects of the foam. Their concerns seem to stem from the outgasing of chemicals, more than the potential for the foam to burn. Are such concerns founded? What possible chemical hazards are present, and is there any evidence that these chemicals outgas at any substantial levels?

A.Alex Wilson responds: Toxic chemicals are used in producing polyisocyanurate foam. But after curing, the foam is considered very stable and safe. The primary health concern with this type of insulation is exposure of factory workers to the isocyanurate resin.

The outgasing that does occur from polyiso foam is HCFC-141b, which is used as the foaming agent. This gas, trapped in the foam cells, provides the high R-value, but as it gradually leaks out the R-value drops. In the atmosphere, HCFCs (hydrofluorocarbons) contribute to the destruction of the ozone layer and to global warming, but they are not considered toxic to humans.

Healthy-house consultant John Bower reports having tested pieces of polyiso foam on several chemically sensitive individuals, with no noticeable effects.

Alex Wilson is editor and publisher of Environmental Building News, a bimonthly newsletter published in Brattleboro, Vt. (for subscription information, contact EBN, RR 1, Box 161, Brattleboro, VT 05301; 802/257-7300).