Skylight Leaks
Most "skylight leaks" are not the skylight. They are the flashing kit around it, the curb it sits on, or condensation forming on cold glass in a humid room.
Leak or condensation?
Condensation appears as water on the inside of the glass and down the frame, worst on cold mornings, and it happens in bathrooms and kitchens regardless of whether it is raining. It is a ventilation problem, not a roofing one.
A genuine leak correlates with rain and usually shows staining on the ceiling drywall around the shaft rather than clean water on the glass. The distinction saves people a great deal of money.
Where real skylight leaks come from
- The flashing kit, particularly at the uphill head flashing
- Step flashing along the sides, where it should be woven into the shingles
- A site-built curb that was never properly flashed, common on older installations
- Perished gasket or seal on a unit at end of life, typically twenty-plus years
- Failed sealant used instead of flashing by a previous repair
Repair or replace the unit
If the glass seal has failed or the unit is decades old, replacing it is usually better value than reflashing around an obsolete frame — and the flashing has to be redone either way.
If the unit is sound, a proper reflash with a manufacturer's flashing kit for that model is the correct repair.
While the roof is open
If your roof is due for replacement, this is the moment to decide about skylights: replace the units, reflash them into the new roof, or remove them and deck over. Doing it later means opening a new roof.
Common questions
Why does my skylight leak only in cold weather?
That pattern usually means condensation rather than a leak — warm humid indoor air meeting cold glass. Improve ventilation in that room and see whether it correlates with rain or with cold mornings.
Can an old skylight be resealed?
A failed glass seal cannot be restored. The flashing around it can be renewed, but on a unit past twenty years replacing it while the area is open is usually better value.