Plywood layers

My mother needs to install a new roof. The original plywood is buckled inward. One contractor recommends installing a new layer of plywood over the old layer. Is this a sound practice? Another contractor recommends ripping off the old layer, thinks an extra layer would add too much weight. Both have been on the roof, and one looked in the attic and both say the plywood is not rotted, just buckled from being installed vertically instead of horizontally over the rafters. The house is 50-60 years old and this is the original plywood. Anyone have an opinion on this? Thanks much.


Tear it off and install a nice 1/2 inch or maybe 3/4 instead of leaving garbage buried …

that is my suggestion …


Both will work. Nothing will happen either way.

You decide which way you want it done and then that is it.

We have a lot of 1" x 12" or skiped sheathing and we put a layer of plywood over to give a flat surface.

I vote tear off old and replace with new. Do it right the first time. Who knows if your roof can hold all the extra stress from 2 layers of wood. That is alot of weight and i have seen first hand many homes like that with busted and cracked drywall from settling.

Either way would be fine. My only concern is that the new plywood if fastened improperly, may take the same shape as the old plywood. Only fasten the new plywood to the rafters.

I just dont agree with going over bad wood. Problem is when you go over the wood you must offset the wood from the other if you do go over then you will have all sorts of problems finding the studs. It to me is just not a good idea.


Problems finding rafters?

I just wont do it. I will remove all wood and replace but never go over any bad wood. I think it just is not right that way. We all do things differently i was just taught old school on alot of stuff. I will never go over anything no mater what it is.

I’ve done it both ways and when i lay over i rip my first row to 2’ and stager the seems and have no problem finding rafters and plywood is ligher than shingles 8)

tear off old plywood.
install new.


Thank you all for your responses. They’ve been very helpful.


Tear off old and put new plywood on. One of the city codes here in indiana it is written that bad wood needs to removed before new wood is replaced.


He was not talking about rotton wood.

Regaurdless the plywood will delaminate if you go over it. THen you will have some real fun later. Its just bad business if it is plywood and go over it IMO. Do whatever it is you want but please undertsand im old school and well i make sure it done right the first time. BTW im the esimator so i get to call the shots.


Why will it delaminate?

Every roof i have torn off with 2 layers of wood on it has 3/8’s that has been delaminated to the point of no return. The second problem doing this is acctually hitting the studs because you must stagger the ply differently than the original wood, going over with the same pattern could cause problems down the road. Third problem is the weight of the added prlywood, many contracotrs i have noticed use a heavier wood on the second layer like 1/2 and i have seen 3/4 over 3/8. 4th problem to me atleast is it is just being lazy when you could tear off the original layer 1 sheet at a time and replace with new wood and not have any problems. To me it is cutting corners when you go over any plywood with another layer. Yes i know there is no code against it but when snow and ice combined with 24 inch centers and 2 layers of wood thats when problems can occur. Shake is a different story all together.

IMO it is not the way to go. You can do whatever it is you want but i feel better just doing things old school and not rushing. I will never cut a corner. And im a firm believer of 1 layer of wood on a home. Do whatever it is you want. Missing a stud will only make the new plywood in the cold stick up and curl slightly and then you have a water problem. I just dont believe in doing things that way.

Well I was talking about any wood whether it was delaminated or rotted.

That was not directed to you SKi lefty asked me. I dont care if it is bad or not i will not go over any wood unless its a shake roof that has gaps between the wood.