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I am estimating a roof which shows signs of
sheathing delamination. This is due to a lack of
attic ventilation and insulation between rafters
laying up against the sheathing. The roof was
originally cedar, rafters 27″ OC, and was stripped
about 15 years ago, including 1×2″, and sheathed
with plywood directly over the rafters.
>My question concerns cost. I would rather remove
the existing 1 layer roof, resheath over the
existing plywood with 5/8″ ply, cutting away
damaged sections, rather than remove all existing
sheathing and resheath with 3/4″. The house is
tall, steeply pitched.
>Advice as to suitablity of sheathing over
existing sheathing would be app
Replies
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James, is the plywood delaming all over or only in certain places?
*if the roof is not too bad(delamination is limited to only a few areas) then it would be ok to sheet over, however i would screw the new deck down to eliminate any future problems.
*James,what size is the existing plywood and how big are the rafters? 27" on center sounds alittle much to me.But, I also don't see a problem with plywood over the existing as long as you replace the bad spots.Vince
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Thanks for the prompt responses.
Delamination appears to be limited to a few
areas. I planned to cut away the bad areas,
shimming up the rafters in those areas.
Thom Day, what concerns you that you prefer
screwing the deck down? I had planned on using an
Hitachi pneumatic framing nailer with 3" galv.
full head nails.
I am not certain what the thickness of the
existing plywood is. I would hope that it is at
least 5/8" or 3/4". The rafters are 2x6, with a
pitch of 10/12. I have found odd ball rafter
spacing before when wood shingles were the
original roofing system in houses built in the
early 1
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I have done what you propose several times with really good results,so I would not hesitate to do it again.(In fact I will be doing an insurance job this way in a few weeks)What I find is that the delaminated plywood is 3/8",the wood fibers still good but the glue non-existent.Screws would make good fasteners but we use nails.(used to use a gun exclusively but now we handnail a lot).
As long as the delamination isn't rotten or bubbled up so high as to prevent a smooth plane in the new layer of decking I wouldn't even be to worried about cutting out the delaminations.I would nail the snot out of it though.
Problems like this with plywood delaminating after one water exposure are why I switched to properly spaced osb about 6 years ago.
Good Luck,I am sure your job will go fine,Stephen
*James,I'm wondering if sheathing over the old sheathing is warrented if you are going to replace the bad areas anyway. With 2x6 rafters on odd centers, I might want to consider the extra weight factor of another layer of decking. If the original decking is 3/8" as suspected, I wouldn't want to see you put anything more that another layer of 3/8" on top of that unless you beef up the purlings.Just a thought,Ed. Williams
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I am estimating a roof which shows signs of
sheathing delamination. This is due to a lack of
attic ventilation and insulation between rafters
laying up against the sheathing. The roof was
originally cedar, rafters 27" OC, and was stripped
about 15 years ago, including 1x2", and sheathed
with plywood directly over the rafters.
>My question concerns cost. I would rather remove
the existing 1 layer roof, resheath over the
existing plywood with 5/8" ply, cutting away
damaged sections, rather than remove all existing
sheathing and resheath with 3/4". The house is
tall, steeply pitched.
>Advice as to suitablity of sheathing over
existing sheathing would be app