Sagging Roof-Is It Moisture Related?

Old 11-17-05, 09:21 AM
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Sagging Roof-Is It Moisture Related?

The portion of the roof above our kitchen (300 sq ft) has a noticeable sag in it. When we had some roofers out for estimates on leaks around the chimney and valley in this section of the roof, none of them seemed concerned about the structural integrity of the roof related to the sag.

A previous owner tried to make a semi-finished loft by putting roll insulation with a vapor barrier (down) under the roof and sheet rocking over that. There are multiple problems as mentioned (chimney and valley flashing failed) but all of the sheet rock bleow the roof in this loft has slumped.

Getting to my questions:
It would appear that the insulation was laid flush against the roof. Could this have created a condensation problem from lack of ventilation that caused the sheet rock to slump and, more importantly, the roof to sag?

If it is a prime suspect, should I fix it?

If I correct the problem, I am not likely to put sheet rock back up. We just use the loft for storage but the kitchen below is a cold room and I would like to insulate the roof...if you think it would help. There is a finished pine wood floor in the loft (can't really insulate easily there). When I look above the tiles of the ceiling in the kitchen the insulation looks like a mangled mess...probably not doing any good.

Any advice or theories are welcome. Thanks.

Old 11-17-05, 10:24 AM
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I am not an expert in this field but I would remove at least a portion of the sheetrock and check the joists for bending or cracks. If you re-insulate the roof, I would use the ventilation panels that attach to the roof. They allow the roof to breathe. They are plastic and have "airways" that allow air to travel the length of them at the inside of the roof. Good luck and watch this post for the expert opinions.
Old 11-17-05, 10:33 AM
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... also not an expert in this area, but my guess would be that the weight of the drywall, the roofing, and the high humidity in the rafter bays due to improper venting has caused the rafters (likely "undersized", since they were not meant to be ceiling joists) to sag.

To straighten them out, you would likely have to shore up the rafters by either adding additional framing next to the existing, or adding a beam underneath them while transferring the weight to a load bearing location.
Old 11-17-05, 04:08 PM
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I have often seen older homes with 2x4 rafters sagging horribly.
A localized leak can damage the wood in that area but it sounds more like undersized timbers. You can strength rafters with kneewalls but you can't
straighten them out. Proper ventelation is very important if you have interior moisture problems from crawl spaces holding a lot of water, Humidifiers running too high. In cold weather this moisture rises and condenses on your roofboards and can completely rot them out in 10-15 years.I've seen rainforests in peoples attics in eztreme cases.

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