# Plywooding over old roof deck



## Pheasant89 (Apr 1, 2011)

I am going to be doing my mothers roof soon. I did her roof 24 yEARS AGO AND SHE HAS 3/8 IN PLYWOOD , i want to go over it with 1/2 in to save work and time . Is there any problem with this I am not worried about weight but I am worried about moisture in between. I f it is not good to do it I would tear off the 3,8 if need be just trying to save work on a free job!


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## griz (Nov 26, 2009)

You talking about sheathing over the existing roof material? or peeling it down to the 3/8" sheathing?

I can't recall seeing 3/8" on a roof. What would bother me is how mickey mouse the roof is framed if someone sheeted it with 3/8.

In the above scenario weight could be an issue.

IMO, strip it & do it right.:thumbsup:


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## dougger222 (Jan 29, 2004)

If you say weight is not an issue, go over it even stronger.

We deck over plank boards with 7/16 osb all the time.


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## Tom Struble (Mar 2, 2007)

lotsa roofs sheeted with 3/8 around here in the 70s


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## thomasjmarino (May 1, 2011)

Why would there be moisture in between?
If the 3/8 is dry before you go over it and nail it correctly, there shouldn't be a problem.
Roof structure will definitely be stronger.

What size rafters are there now?
Should probably be sized correctly.
24 years ago we were framing with 2x8's and 10's depending on run.

You will be ok as long as their not 2x6's.


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## woodworkbykirk (Sep 17, 2008)

its really common here too , to see 3/8 plywood used on roofs from the 70's. we resheet with 1/2 osb right over top of the old all the time be it 3/8 ply or old t&g boards

in the case of the old t&g boards, it makes for a flatter surface plus greatly lessons the chance of nailing into the gap between boards.

have at er bai!!


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## jmiller (May 14, 2010)

thomasjmarino said:


> Why would there be moisture in between?


The same reason you see frost on roofing nails from in the attic in winter, condensation.


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## thomasjmarino (May 1, 2011)

jmiller said:


> The same reason you see frost on roofing nails from in the attic in winter, condensation.


Well I ain't no roofer so I can't argue with you on that point, but don't make no sense to me if you're nailing dry on dry. 
If you nail the piss out of it then it pretty much becomes one.
I mean, with that mentality wouldn't all of your exterior headers with plywood in between be capable of moisture buildup? :confused1:


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## mbobbish734 (Apr 28, 2011)

woodworkbykirk said:


> its really common here too , to see 3/8 plywood used on roofs from the 70's. we resheet with 1/2 osb right over top of the old all the time be it 3/8 ply or old t&g boards
> 
> in the case of the old t&g boards, it makes for a flatter surface plus greatly lessons the chance of nailing into the gap between boards.
> 
> have at er bai!!


Same here also.


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## Splinter hands (Aug 31, 2011)

I'm with Griz on this. Where I am I find all kinds of stuff that was done chincy the first time on older homes, probably because that's all they had at the time. Many times when I get into it I find other stuff too. And hey it's your moms house do it right for her even if it is for free.


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## mbobbish734 (Apr 28, 2011)

One thing to consider when stripping off the old plywood is to remove and replace as you go. If you remove it all then reinstall you can have cracking and popping of the drywall ceiling.


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## Pheasant89 (Apr 1, 2011)

The house was built in 1953 it is a rancher In 1987 when I did her roof for her after my parents just moved in there was 3 coats of shingles on it , "we thought 2" . The rafters are 2x8s with a 12' span 16in oc. The 3 coats of those old shingles is way heavier then the plywood would ever be.And I know it is 3/8 because I replaced alot of the 1st row at that time which was rotted. But it can use a roof now and I will ice shield up 6 " and in the valleys with a dimensional shingle.


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## jmiller (May 14, 2010)

thomasjmarino said:


> Well I ain't no roofer so I can't argue with you on that point, but don't make no sense to me if you're nailing dry on dry.
> If you nail the piss out of it then it pretty much becomes one.
> I mean, with that mentality wouldn't all of your exterior headers with plywood in between be capable of moisture buildup? :confused1:


You can nail the piss out of cedar shakes, but that doesn't mean they become one with the felt/decking. That's why cedar breather was invented.


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## Randy Bush (Mar 7, 2011)

Although I have never ran into it , I have heard of older houses here being done with exterior sheetrock on the roofs and guys would step though them when doing a tear off. So they had to be resheeted then.


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## jmiller (May 14, 2010)

What is exterior sheetrock?


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## Tom Struble (Mar 2, 2007)

sheetrock with like a black asphalt? facing,ive seen it on sidewall but never on a roof:blink:scarry


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## Randy Bush (Mar 7, 2011)

jmiller said:


> What is exterior sheetrock?


It is a exterior grade of sheetrock ,comes in like 2x8 sheets has like black paper wrapped on all edges, Lot of house 70s here have it on side wall sheeting , and like said some was used on roof sheeting. 
I have ran across in on side walls when residing and it is a pain to deal with. Thankfully they stop using it along with the IKO board ( tar coated fiber board) along with foam board and no sheeting under it.


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## WildWill (Jun 6, 2008)

Randy Bush said:


> It is a exterior grade of sheetrock ,comes in like 2x8 sheets has like black paper wrapped on all edges, Lot of house 70s here have it on side wall sheeting , and like said some was used on roof sheeting.
> I have ran across in on side walls when residing and it is a pain to deal with. Thankfully they stop using it along with the IKO board ( tar coated fiber board) along with foam board and no sheeting under it.


And don't forget about Homasote for exterior sheathing. I don't know if they ever tried that for roofing, I sure hope not..


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## Pheasant89 (Apr 1, 2011)

That black exterior gypson was used here in the SE. Pa. area from the 50s to the 70s


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## thomasjmarino (May 1, 2011)

jmiller said:


> You can nail the piss out of cedar shakes, but that doesn't mean they become one with the felt/decking. That's why cedar breather was invented.


I think there may be a slight difference between cedar shakes and plywood.... :no:


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