Skylight Insulation // Vancouver Island BC, CZ 4C

A homeowner on Vancouver Island is redoing a cathedral roof, swapping concrete tile for standing-seam metal, and adding two 36x36-inch skylights near the ridge of a steep, 15-foot-high ceiling. The new roof includes rigid metal panels, a peel-and-stick waterproofing layer, plywood sheathing, a ventilation gap, R22 Rockwool mineral-wool batt insulation between the rafters, a tightened poly vapor barrier, and a tongue-and-groove cedar interior ceiling. The open question is how much insulation the skylight "lightwell" — the boxed shaft that runs from the roof opening down to the ceiling opening — and its 6-inch curb need to avoid condensation and mold, since that area is hard to reach and repair once finished.

This is a discussion thread, not a finished answer: the homeowner got conflicting advice, ranging from "no extra insulation needed" to "wrap both the outside of the curb and the inside of the shaft in rigid foam board or risk rot." No expert reply had been posted yet.

For anyone with skylights, especially in a cold, damp climate, the underlying issue applies at home too: skylight shafts are a common weak spot for condensation and mold because they combine thermal bridging with hard-to-access corners. If you're planning a re-roof or skylight installation, it's worth asking your contractor specifically how the lightwell and curb will be insulated and air-sealed, not just the main roof deck.