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I recently walked my roof. There are some low spots, like little depressions. What causes this and should I be concerned? It seems that the plywood underneath is good but it seems like the underlayment has degraded. Is this normal?

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How far apart are your trusses? Do you have any dormers sitting on the roof? – aphoria Aug 9 '10 at 15:04
@aphoria: Not sure what a dormer is – Brian Aug 9 '10 at 19:42
Have you checked in your attic or crawl space? Anything suspicious up there? Any recent construction/demolition in the attic or crawl space? – Jeff Widmer Aug 17 '10 at 3:38
Is it a flat or pitched roof? – ChrisF Aug 21 '10 at 12:13
How big are the "little depressions"? – Tester101 Sep 3 '10 at 16:36
up vote 2 down vote accepted

Plywood generally doesn't sag permanently unless it's been wet for an extended period of time. Can you get into the attic to check for water stains around those areas?

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