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Sagging roof


jingram105's Avatar
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11-12-03, 01:29 PM   #1 (permalink)  
Sagging roof

My roof has several places where it is visually sagging. We just had new asphalt singles put on, and the roofer assured us that he could take of the sagging. Now with the new shingles, the sagging isn't as visible, but I can still see it--and the sagging is one of the primary reasons for which we had the roof reshingled.

Now the roofer says that he doesn't see any structural damage in the attic, so it must just be the decking. If the decking itself is the problem, shouldn't it have been replaced, if necessary, prior to putting on the shingles. Afterall, the sagging was one of our major concerns. Now with the shingles already up, I'm afraid that it might be too late to take care of the problem. I'm worried about both appearance and resell.

Is there another solution other than ripping off the new tiles and the decking, and starting again. I'm meeting with the contractor tonight and would like to be knowledgeable when I talk with him. I really like this guy, and don't want a confrontation, but I do want my roof right. I've already put a lot of money into this house, and I do want to feel like it's been money well spent.

Sorry for the long speech, but I would appreciate any advice that you can give me.

Thanks.

 
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Ed Imeduc's Avatar
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11-12-03, 03:05 PM   #2 (permalink)  
Roof

When they had the old shingles off.They should have checked the roof all over and fix anything then before the new shingles went on. He should have found what was what when he was up in the attic. You dont say if its the decking or is it in the rafters. ED

 
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11-12-03, 06:34 PM   #3 (permalink)  
MattG_
re Sagging Roof

Re-shingling is probably not the answer to a sagging roof.

Damaged decking can cause sags. Decking most commonly consists of 4'x8' plywood sections, but may be planks or slats if an older home. If you have access to an attic or crawl space, check the decking for rotten, infested, or warped boards. Your roofer should have already eliminated this as a problem prior to laying shingles.

Inadequate joists and rafters can also cause roof sag. Prior to 1950 2x6 boards were commonly used, after 1950 2x4's supported by trusses (2" dimensional lumber brace between the rafter and ceiling joist). You will not have to remove shingles if this is the problem. Reinforcing is the solution.

I would get additional opinions once decking has been eliminated as the source of your problem, preferably from a structural engineer.

 
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11-14-03, 04:45 PM   #4 (permalink)  
Grumpy
A sagging roof could be decking, but if it was decking you would see waves. The deck would sag but the rafters would be solid so you sould see many high and low points.

If the rafters are sagging, which it sounds like they are, then you may have one very low point. This is common with old houses. It's nothing to worry about but since you are worried:

To fix this problem you need to re-inforce the rafters. You may consider cross-ties or a knee wall. We've done this kind of work, and it's more of an art, then an exact science.

Old houses were commply built with 2" x 4" 24" oc, which is inadequate for less than an 8/12 roof, in my opinion.

 
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11-17-03, 01:20 PM   #5 (permalink)  
hexnemisis
Make sure you have vented soffits and styrovents in your attic, also make sure you have the proper amount of vents for the size of your roof (by this I mean the square vents near the ridge).

 
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11-17-03, 03:57 PM   #6 (permalink)  
Grumpy
Are styrovents a type of "rafter baffle"?

 
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11-17-03, 09:43 PM   #7 (permalink)  
hexnemisis
thats exactly what they are, thanks for clearing that up, down here when I say baffle to anyone they seem puzzled.

 
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11-18-03, 07:05 AM   #8 (permalink)  
If you're going to put in rafter-mates, (baffles, styrovents) why would put those ugly square static vents on the roof? Put in a good quality ridge vent system and do tyhe job right. Just my opinion, but I really hate to see those ugly things on a new roof.

 
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11-18-03, 10:26 PM   #9 (permalink)  
Grumpy
Yes always use a ridge vent where possible. It allows more air to espace than the normal mushroom/breahter vents.

ventilation is a science and every type of house has different ventilation requirements, but ventilation is key.

Hex, here is Chicago we only use rafter baffles when insulation is installed inbetween the rafters. It is used to keep a positive air flow... If the attic space is open and the attic floor is insulated, not the rafters, they aren't required. YES! If you insulate your rafters, as in the case of a vaulted ceiling, you NEED rafter baffles.

 
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11-19-03, 09:18 AM   #10 (permalink)  
vents

I find its best to use the so called baffels or extruded foam rafter vents all the time. This will let the vents in the over hang get to the attic. We also have the ceiling line now go out into the over hang with a knee brace in the truss at the plate. This gives us the room for a R30 or R40 insulation to cover the whole inside ceiling on out over the ouside wall plate. We also use power roof vents on a tstat all the time. Also find that the ridge vents with the filters in them just jam up with dust and pollen so after a short time they dont work.

My .02 cents ED

 
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