05/31/2026
Standing water in a roof valley is one of those things that looks harmless until it isn't.
Valleys are where two roof planes meet, and they move more water than almost any other part of the roof. When debris builds up, leaves, twigs, moss, the water slows down instead of sheeting off. Slow water sits. Sitting water works its way under shingles over time, especially at the edges of the valley flashing where there's a seam.
We see this a lot in the Pacific Northwest because we've got the rain volume AND the organic debris to feed it. A valley that drains fine in summer can back up by November when the fir needles start dropping.
The fix early on is usually just a cleaning. If it's been sitting long enough to lift the shingle tabs or compromise the flashing, that's a different conversation, but catching it at the standing-water stage is the cheapest version of this problem.
If your valleys haven't been looked at in a few years, that's a good place to start.
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