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?

  • How far apart are your trusses? Do you have any dormers sitting on the roof?
    – aphoria
    Aug 9, 2010 at 15:04
  • @aphoria: Not sure what a dormer is Aug 9, 2010 at 19:42
  • 1
    Have you checked in your attic or crawl space? Anything suspicious up there? Any recent construction/demolition in the attic or crawl space? Aug 17, 2010 at 3:38
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    Is it a flat or pitched roof?
    – ChrisF
    Aug 21, 2010 at 12:13
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    How big are the "little depressions"?
    – Tester101
    Sep 3, 2010 at 16:36

1 Answer 1


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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