Vapor barrier helpful with home insulation

Q. Will blow-in attic or wall insulation, or Styrofoam-brand insulation, without a vapor barrier rot house timbers? If either is injurious, what can be done? Can vapor barriers be added to the inside walls? W. C. Hutcheson Boydton, Va.

A. Fiber glass will not rot anything. However, moisture can be a problem. The Mineral Insulation Manufacturers Association, Summit, N.J., recommends the use of a vapor barrier. The trade group further suggests that homeowners get in touch with their local building department for recommedations on the use of a vapor barrier.

Temperature and humidity vary from one locale to another.

Climatic extremes call for different types of insulation and vapor barriers. A blanket answer is thus unwarranted.

Certain paints can be used on interior surfaces to provide a vapor barrier if one cannot be installed with the insulation. Interior paint systems that effectively control the moisture level of wood within wall cavities have been identified in research conducted at the Forest Products Laboratory, PO Box 5230, Madison, WI 53705.

With one minor exception, two coats of interior semigloss latex, exterior acrylic latex, or exterior soya-alkyd resin generally kept the moisture content of walls below 20 percent, even though 35 percent relative humidity was maintained indoors.

The research report by Gerald E. Sherwood is entitled: "Paint as a Vapor Barrier for Walls of Older Homes." Write for it.