Airsealing Around Windows and Doors

Q: Is it normal to have a 1/2-inch space between inner window frames and the surrounding rough house frame? My home is a few years old, and when I lifted a piece of trim I saw gaps extending the full depth of the outside wall, with no insulation or sealing that I can see. The builder says this is normal and doesn’t require any repairs. Is he correct? It seems hard to believe.

A: While it is normal to have a gap between the rough frame that surrounds windows and doors during construction, these gaps should be filled before trim is applied. Otherwise you've got an area with almost no insulating value that’s also subject to internal condensation. Some builders stuff fiberglass insulation into these gaps, but a far better approach employs low-expansion polyurethane foam. This is injected into the gap where it expands slightly as it hardens. The cured foam not only offers excellent insulation properties but also effectively seals the building envelope, preventing warm, moist heated air from entering the gap, condensing and forming liquid water droplets Although it’s hard to see this problem while it’s happening underneath the trim, it can cause serious trouble in time. Several years of internal condensation can lead to mold growth within walls.