Why do skylights always leak?
Short answer. Skylights do not always leak, but they get that reputation because they put a large opening in the roof and depend on flashing that is often installed or reused poorly. Most skylight leaks trace back to caulked or improperly woven flashing, debris dams on the uphill side, aging seals, or condensation that looks like a leak, while a quality unit with the manufacturer's flashing kit can stay dry for its whole life.
Why the reputation exists
- Bad installs: many older skylights sit on site-built curbs sealed with roof cement instead of being stepped and counterflashed.
- Reused flashing: during reroofs, skylight flashing is sometimes left in place and caulked to the new shingles.
- Location: a skylight just below a valley or a taller roof takes concentrated water.
- Debris: pine straw and leaves pile up on the uphill side and push water under the head flashing, a common problem on wooded Georgia lots.
- Plastic domes: they crack and craze in the sun, and hail finishes them off.
- Condensation: humid bathrooms and kitchens drip from cold glass in winter.
What makes a skylight stay dry
- A deck-mounted unit with the manufacturer's flashing kit made for your roofing material.
- Self-adhered membrane around the frame before any metal goes on.
- Step flashing woven course by course, with the head flashing tucked under the shingles above.
- Placement away from valleys and roof to wall corners.
- New flashing, or a new unit, at every roof replacement.
- Keeping the uphill side clear of debris.
See skylights and roof replacement, roof flashing explained and pine needles and leaves on the roof.