How do I know the leak is from flashing and not the shingles?
Flashing leaks tend to appear beneath joints: valleys, walls, vents and dormers, and show up after wind-driven rain. Shingle leaks come from broken or missing shingles in an open slope. Only a roofer on the roof can be sure, and a single ceiling stain may have more than one cause.
A useful habit is noting when the water shows up. Drips that begin during a heavy, driven rain and stop soon after often point to a joint. A drip that appears after days of snow melting points to something at the edge.
Photograph the stain, note the weather, and mark the spot on the ceiling in pencil. That gives the roofer a map to follow. See also the page on roof leak repair.
Is roof cement a good fix for bad flashing?
It is a short-term patch at best. Sealant dries, shrinks and cracks as roofs heat and cool, and thick layers can trap water behind them. Cement may hold a small gap for a season, but metal that is bent or rusted needs replacing, not coating, and joints must shed water by lapping.
Seeing a heavy black coating around a chimney or vent is common on older homes. It tells you somebody tried to stop a leak, and it tells the roofer where to start. Often the coating hides the real failure underneath.
A repair that lasts depends on how the layers overlap. If you are quoted a fix that is only sealant, ask what the metal underneath looks like.
Why does flashing fail faster on older houses?
Old flashing has been through many seasons of expansion and contraction, and its fasteners and sealant have aged. Older houses also have been re-roofed over the years, which can leave metal reused, buried or cut short. Roofs that have been patched several times often hide several generations of repairs.
In a freeze and thaw climate, every temperature swing moves the metal slightly against the masonry or siding beside it. Over decades that motion loosens nails and splits sealant. Corrosion where two different metals touch, or where water sits, adds to it.
When a roof is replaced, new flashing is part of a good job. It is worth asking whether the quote includes new metal at valleys, walls and vents or only new shingles.
Can wind damage flashing as well as shingles?
Yes. Strong wind can lift or bend metal at edges and walls, and a bent piece lets rain run behind it. After a gusty storm, check from the ground for metal standing off the roof or siding, and ask a roofer to look at joints even if shingles look fine.
A bend can be small and still matter, since water follows the gap. Some wind damage shows only as a leak weeks later.
The page on wind damage roof repair covers what a roofer checks after a blow.
