Can a leaking skylight be repaired or does it need replacing?

Greater Victoria has two skylight generations. The 1970s and 1980s acrylic bubble domes on Gordon Head, Broadmead and Colwood homes are now 40 years old, crazed and yellow, and their curb flashings were often site-built from roll aluminum; those almost always get replaced rather than repaired. The 1990s to 2010s glass units on Langford, Bear Mountain and renovated Fairfield homes usually leak at the manufacturer's flashing kit where debris has built up above the head, or at a perimeter seal that has dried out, and those are re-flashed for a few hundred dollars.

Moss and needles are the local aggravator. A skylight on a north slope under a Douglas fir in Saanich or the Highlands collects a dam of debris on its uphill side every autumn, and water sitting against the head flashing for a month finds any weakness. Clearing that dam is the first thing a roofer does, and sometimes it is the whole repair. On heritage homes in Rockland and Oak Bay, a leaking skylight is often a later addition cut into a steep slate-look or cedar roof, and re-detailing it properly is a flashing job rather than a skylight job.

From the roof, the roofer checks the flashing kit for lifted edges, the head for debris, the sealant for cracks and the curb for softness. From inside, they look at whether the staining is at the corners (flashing), all round (seal) or in the middle of the glass (unit failure). Condensation between panes cannot be repaired; the glazing unit has lost its seal. A curb that gives under thumb pressure means water has been in the wood for years and the whole assembly comes out. Everything else is a repair.

• Corner stain: flashing
• Ring stain all round: perimeter seal
• Cloudy glass: replace the unit
• Soft curb or stained decking: replace, plus decking

Re-flashing a skylight is disturbing the shingles around it, so on a roof that is due within a few years it is wasteful to pay $300 to $900 now and then pay again to re-flash the same unit during the re-roof. The better path is a temporary reseal to get through the winter and a new skylight installed with the new roof, where the unit is the only extra cost. Our cost pages price skylights as an adder to a replacement for exactly this reason.

Two repairs to the same skylight in five years is the signal. Acrylic domes and any unit past 25 years are also past the point where sealant is a good investment. And if the leak has reached the drywall in the light well, the water has been running for a while; a professional may reasonably want to see the decking around the curb, which means the unit comes out anyway.