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Question DetailsAsked on 8/8/2012

I had new roof put on in Jan. They put new plywood on over the old. Now the shingles are popping up & moderate lumps. What's wrong?

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5 Answers


When you say that they put new plywood over the old, what was the old? Was it old plywood? The next questions is why did they put wood over wood? Did they build it up to create an air gap or did they lay it right over the top?

Normally the only time we install wood over wood is in 100 year old houses with spaced decking and we need a nailable surface. This isn't a problem is you fix the bad wood first and nail into the existing rafters. That's the key nailing into the rafters.

It could also be that they didn't use the proper nails. I have seen roofers use roofing nails to nail wood, which require a different kind of nail.

It sounds to me like possibly the problem may be that they didn't nail into the rafter, that possibly they nailed the new plywood into the old wood. You won't get enough holding power doing this. If this is what they did, the roof needs to be replaced.

it could also be possible that perhaps they did not leave a 1/8" gap on all sides of the plywood for expansion and contraction. We like to place a nail between the boards to get this proper gap. If wood is cold and contracted when it is January and now it's the hot steamy summer and wood is expanded, it needs a place to go, thus the gap. If no gap you get a wavy roof surface with wood buckling at the plywood joints. If this is what they did, your roof needs to be replaced.

I'm really curious why they put wood over wood and didn't tear off the old wood. But it could have nothing to dow ith the wood. Cold weather roofing is very picular requiring numerous additional attentions to details you need to worry about, that you don't need to worry about the rest of the year. This is why I am not an advocate of winter time roofing. It could be the same expansion and contractors issues mentioned above, but expansion of the shingles instead of expansion of the wood.

Is there any way you can post a picture?


Answered 5 years ago by ReliableAmericanRoof


I put the roof on in Jan because the flashing around chimney was leaking and leaking inside. They buildt cricket and couldn't match shingles. Stated plywood rotted. Have no idea why they didn't removed old plywood instead of putting new plywood on top of the old. I was taking care of my sick mother.I will take a picture and post for you thanks.

Answered 5 years ago by Guest_9170275


I think if the plywood was rotten, then placing new plywood over the old was a bad idea. Why didn't they tear off the old plywood? I don't know the exact answer. Lazy? Cheap? These are the answers that come to mind.

What did their proposal say they would do in the event of rotten wood discovery? Our proposals reads,

"Remove any old roofingnails, refasten any loose wood and replace any rotten or damaged wood asnecessary to properly install new roofing. Replaced wood will cost additional.($XX for one sheet of 1/2” CDX plywood or $X.XX per linear foot of 1”X8” board) "

Key word being "Replace".


Answered 5 years ago by ReliableAmericanRoof


Any updates on this?

+1 to Reliable's commentary that rotted plywood needs to be removed.

Going over inadequate thickness plywood for a more solid deck or skip sheathing is fine as long as they pay special note to the ventilation and home the roof is designed to vent.

That must always be accounted for in the roofing design process.

Answered 4 years ago by WoWHomeSolutions


The previous rotted ply wood could of been in a difficult spot to get out for instance if it's near the over hand of the fascia or soffit it could be possible that they couldn't get it out so they decided to go over iT or under where a lower roof ties into a upper section and only way to get that out is taking out the fascia soffit possibfear after tails even compromising the structure in that paticular area hope this helps

Answered 4 years ago by yamaha575

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