How is a leaking skylight repaired on a roof?
Short answer. A roofer repairs a leaking skylight by removing the shingles around it, taking off the old flashing, wrapping the curb or frame with a self-adhered membrane, installing new apron, step and head flashing, and weaving the shingles back in. If the glass seal has failed or the unit is old, the skylight itself is replaced during the same visit.
Curb-mounted or deck-mounted?
Older skylights often sit on a wooden box, called a curb, built up above the roof, with the skylight fastened on top. Newer ones mount directly to the decking with a factory flashing kit made for that model. Curb units can be reflashed and the dome or glazing replaced separately; deck-mounted units are usually reflashed with the manufacturer's kit.
The repair sequence
- Remove shingles a course or two out on all sides.
- Pull the old flashing and check the curb and decking for rot; replace soft wood.
- Wrap the curb or frame with self-adhered membrane lapped onto the deck, uphill pieces over downhill ones.
- Install the apron at the bottom, step flashing up each side one piece per course, and the head flashing at the top, with the uphill shingles lapping over it.
- On a curb unit, add counterflashing or a cap so water cannot run behind the step flashing.
- Reshingle, seal exposed fasteners, and clean up.
Inside repairs
A stained light shaft needs drying, a stain-blocking primer and paint, or new drywall if it has gone soft.
When to replace the unit instead
Fog between the panes, a cracked or yellowed acrylic dome, a rotted frame, or a unit around 20 years old. The most economical time is during a reroof, when the shingles are off anyway. See skylight replacement with a new roof and roof flashing explained.