Is it OK to use polystyrene on the interior of exterior walls underneath the sheetrock?
Mike writes from Frenchtown, New Jersey: “I am considering building a new home in central MA. Several years ago I lived in Rochester, NY where a builder was using polystyrene on the interior of exterior walls underneath the sheetrock. The builder claimed this method, using 2×4 construction, provided an R rating equivalent to 2×6 construction. I have been researching and trying to find information on this method but all I can find is applying the polystyrene to the outside of the exterior wall. Is applying polystyrene to the interior of an exterior wall an acceptable method, are there any concerns regarding moisture buildup and where can I find information on the method and materials?” Answer: The builder is correct. This has become a standard building practice in recent years to improve R-value in 2×4 exterior walls. If done properly using unfaced Fiberglass insulation, moisture should not be a concern. Owens Corning does not have literature showing this application but our technical s
