A-1 Skylight Installation

Q: I want to install a skylight in my house, but I’m nervous about causing moisture problems. I’ve heard stories about wintertime condensation ruining the drywall that lines the inside of the tunnel leading from the ceiling to the skylight unit in the roof. If condensation is a possibility here, what installation steps can I take to prevent it from forming?

A: That's a great question and you're wise to have asked it. Yes, condensation can occur in skylight tunnels, but only if they're not built properly. The thing to remember is that a structure like this must be built to the same standards as an exterior wall because the attic space will be very cold in winter. This means fiberglass or rigid foam insulation between the 2x6 framing members, a well-sealed vapour barrier on the warm side of tunnel walls, and a complete layer of painted drywall on the visible surface of the tunnel. If you do all these things you can be absolutely sure that no condensation will form on the walls. Occasionally, the panes of glass on economy-grade skylights will form enough condensation to run downwards, but not usually with well-made units. If condensation does occur on the glass during very cold weather, a small fan mounted on the edge of the opening and blowing towards the skylight will eliminate the problem.