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badflyr 03-31-2008 09:46 AM

sagging roof between the trusses
i have a 4/12 pitch that has two layers of shingels .the plywood/osb is sagging the question i have is after the tear off can i re deck over the top of the old sheeting with 5/8 and stager the sheets? or will the just start sagging over time? or is it to much weight for the trusses? just for the record im not roofing it a family friend is and i have seen alot of his work he does a good job but he was honist with me and said he has never riped all the wood off a house and redecked it
thanks rob

johnk 03-31-2008 10:34 AM

I would tear off the roof and then tear off the sagging section of osb and see what the shape of trusses are and replace or repair accordingly.:yes:

RippySkippy 03-31-2008 11:10 AM

I'm with johnk...and to add, I don't think you want to have a double layer of sheathing, besides being wasteful if you don't need to do the whole roof, just making it look good doesn't necessarily fix the issues. How far apart are the trusses?

Ed the Roofer 03-31-2008 11:30 AM

Going over the sagging deck sheathing would be akin to sweeping dirt under the carpet. It may look better, but the dirt is still there.

Also, it may be a violation of your local building codes.

If your friend is good at just installing the shingles, (don't take this the wrong way, please.), he is not truly capable of tackling this work, unless you agree to be his experimental lab rat.

I see so manu unqualified contractors who use sub-contracted labor who do not know the proper way to lay out and nail the sheathing, that it is ridiculous. 6" O.C on the perimeter edges. 12" on the interior rafter nail paths, is the most common method, but to be certain, check your local code and the APA, American Plywood Association, becuase it varies due to rafter spacing and deck sheathing rated thickness.

Additionally, you may be covering up some structural issues causing the sag and by installing additional weight on the structure, you may be looking at further structural damages.

Usualy, but not always, that is not the case. Typically I find that several things have occurred to bow the decking.

It may have been installed with the grain in the wrong direction.

It may have encountered prolonged, yet even minor leakage, diminishing its structural stability.

It may not have been nailed properly from the initial instalation.

Your attic may be super heated from a lack of balanced Fresh Air Intake Ventilation and Roof Top Exhaust Ventilation. The resultant internally contained heat and humidity levels have continually permeated the sheathing, causing a weakening of the product.

You should have a professional, who knows how to install decking along with the roofing provide you a proper analysis and solution.


darylbrands 04-03-2008 08:23 PM

What needs to be determined is
Why is the Roof Sagging?

Where and How is the Roof Sagging?

Joints with out H or Roof Clips?
This can be fixed if accessible from inside the attic with a 2 x Nailed between the Trusses.

If the Problem is Sagging Framing Members this may need additional supports to correct.

Proper Fastening is essential to prevent buckling and as it is such a minor thing to add extra fasteners to seams it is such a shame when you can see each 4 x 8 sheet of O. S. B on the new homes due to lack correct fasteners. Good Point Ed.

Tearing Off an Entire Side of Plywood or O.S.B. is not the normal procedure and does not happen very often as it usually is not in the home owner's best interest.
What would be the point of repairing the sheathing?
Is it Water Damaged everywhere?

the roofing god 04-04-2008 10:20 PM

ed and darryl are right .replace what`s bad,and resupport if proper clips weren`t used,I wouldn`t want the additional weight of extra plywood on roof trusses either

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