Remove and replace delaminating roof decking, or just put a new layer on top?
Our roof decking (new construction) is warping and delaminating (defective plywood) and we are dealing with the APA on a claim.
They suggested that we add a second layer of new plywood over the bad, leaving the bad in place, rather than tearing off the bad decking and reinstalling new over the bare trusses. They said it will save on labor and pose less risk of damage to the trusses. (their motivation is certainly the labor savings as they will be paying for labor).
What are the pros/cons of a tear-off and re-deck vs just overlaying another new layer of plywood on the bad? The decking is 5/8″, so it would be two layers of 5/8″ with the bottom layer of sheets defective.
Thoughts?
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IMO they're correct and it's probably safer for the crew but I would want to double check that the roof can carry the extra weight of the additional layer of plywood.
In most of snow country, the extra weight of new plywood is noise compared to snow load.
I can't think of why you 5/8 is better than a thicker deck, removing the old plywood doesn't get you anything.
The only thing to watch is they use the correct length fasteners, they have to be now longer to get the right amount of embed into the trusses.
Also check that there are not too many shiners after the install, it will be harder to see where the trusses are and easier to miss them.
Hi Lightnb,
If it were me, I'd want to get a professional third-party opinion on this, perhaps an engineer. Maybe you can roll those costs into the claim, I don't know. But even if you have to pay for it, this is a new build, why would you go forward with a potential problem lurking?
Thanks guys. The truss mfg says the extra layer is fine in terms of weight.
Engineers are rare in our area. Maybe only one does residential in our area and has a months-long waiting list.
The concern with leaving the old decking I think, was, if it's going to rot or disintegrate under there, then the new decking would be "floating" 5/8" off the trusses. Also, I don't know if the delaminating ply could force the clean layer on top up and create visible bumps in the roof.
Structurally, good plywood direct to trusses is stronger without some weak material (or air) between them. Similar to Zip-R sheathing (which would be weaker without additional nails).
Is there are a possibility of mold/mildew/rot/etc getting trapped between the layers, or will all moisture work its way out through the attic side?
We're in a summer south-eastern weather pattern where it storms almost every day.
That depends on the rest of the roof assembly. Do you have any information on what will be installed above and below the roof deck?
Tear it off please. Did you use OSB? Are the trusses 16 or 24" center? Is there excessive moisture? Was it left exposed for a period of time? We want to correct the cause first then look at remedy solutions.