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Open Roads Forum  >  Travel Trailers

 > Which Roof plywood to use

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americandb

Oregon

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Posted: 06/28/12 10:39pm Link  |  Print  |  Notify Moderator

Hello, I'm going to replace the roof on my 92 Aljo 26' Travel Trailer, any tips on which plywood to install before gluing down the rubber roofing from the following choices: 1. OSB 7/16" strand board. 2. 1/2" CDX/shop plywood. 3. Exterior grade 1/2" plywood?. I have seen several people use 7/16" strand board, probably because it's the cheapest, but not sure if it's the most durable for RV roof sheathing?
Thank You! your input and or experience will be most appreciated!

SteveAE

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Posted: 06/28/12 11:10pm Link  |  Print  |  Notify Moderator

americandb,

I have never glued rubber roofing on. I have however built a camper with fiberglass roofing.

Assuming your trusses are 24" on center, I would be inclined to use a good quality exterior grade 1/2" plywood. Watch out for the Home Depot plywood’s as many only have three ply’s and/or voids. (there really is a reason it costs less at Home Depot and Lowes) If using CDX, sort through material to make sure that the better (C) side is smooth as if there are any depressions the roofing won't stick at that spot and will leave a bubble.

Steve

BobsYourUncle

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Posted: 06/29/12 01:58am Link  |  Print  |  Notify Moderator

I have never been a fan of OSB. (Oriented Strand Board)Actually I have never been a fan of any of the cheaper substitutes for plywood. Not sure where the Oriented comes from. Maybe they have a bunch of cheap laborers in there orienting the strands in a certain direction !!

Apply a little moisture to any of the composition boards and they swell, weaken and fall apart.

Yeah, sure, plywood will rot if it gets wet, but so will the composition panels.

Use plywood, make sure there are no leaks or ay chance of moisture entry and you should be good for a long time. And spend the extra 4.50 a sheet to get the good stuff instead of the degrade factory reject.

Always amazes me how people will sacrifice quality for a few bucks in savings.


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Posted: 06/29/12 06:25am Link  |  Print  |  Notify Moderator

#3


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enblethen

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Posted: 06/29/12 07:44am Link  |  Print  |  Notify Moderator

Good quality 3/8 plywood with exterior rating.
Shop that did ours, used floor leveling compound over all joints to smooth out any ridges.
We did not put EDPM rubber roof back on. We went with Brite tec. Much easier to maintain. It is similar to TPO but has a backing.


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LastOfTheBohicans

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Posted: 06/29/12 08:18am Link  |  Print  |  Notify Moderator

BobsYourUncle wrote:

I have never been a fan of OSB. (Oriented Strand Board)Actually I have never been a fan of any of the cheaper substitutes for plywood. Not sure where the Oriented comes from. Maybe they have a bunch of cheap laborers in there orienting the strands in a certain direction !!

Apply a little moisture to any of the composition boards and they swell, weaken and fall apart.

Yeah, sure, plywood will rot if it gets wet, but so will the composition panels.


The strands are laid down mechanically in a roughly horizontal pattern (Orientated), soaked on a glue/wax compound and then compressed.

It gives the board strong vertical strength so its great for sheathing. But it has lousy horizontal strength. It has to be much thicker than plywood to get the same amount of load bearing strength.

There use is purely economics. They can use crappy wood for the strands instead of needing older growth trees.


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westend

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Posted: 06/29/12 08:19am Link  |  Print  |  Notify Moderator

I would first match the dimension of the original roof sheathing, if it's 1/2", then that would be the NOMINAL dimension (it's less than 1/2", actually). OSB rated board for roof sheathing has more structural strength than plywood of the same dimension. The strands of wood fibers are oriented in different directions to develop the total strength rating.
Marine grade plywood, where the individual plys are set with fiberglass and the faces are also treated, has the best durability in high moisture conditions It is also the most expensive by an order of up to 10x. Void free plywood is available from lumber distributors and is the next down the chain in structural integrity and price. Following this in the price scale will be gading of finished faces from A down to D. OSB is the cheapest, in most cases.
If it was me, I'd aim for a sheet rated for 24" roof spacing and one finish side of at least B grade. Depending on what type of adhesive is used for the rubber membrane, it may be possible to paint or seal the sheets when all is assembled. That would add to the moisture resistance of the roof sheathing.
Good luck with your roof!


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ScottG

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Posted: 06/29/12 09:38am Link  |  Print  |  Notify Moderator

The last layer on a membrane roof is 1/4 luan paneling. They use this because of how smooth it is which makes the glue stick better. Personally I would use a layer of 1/2 plywood (OSB is too fragile) and then add the luan. If your going to have a the sheathing off then I would add good quality insulation too.


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Dr Quick

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Posted: 06/29/12 11:46am Link  |  Print  |  Notify Moderator

I replaced the roof on a previous trailer because it had water damage. Original roof was 1/4" thick with 16" joist spacing. I used 3/8" exterior grade plywood and installed a new rubber roof over it. Had trailer another 3 years and never had a problem with roof.

When I replaced the roof I cut the rubber at the joints of the wood deck, and removed one panel at a time trying to minimize damage, so that I could use old panel as a template for new deck for cut outs and size. By doing one section at a time, I always had a solid surface to work from as I worked to rear of trailer.


Dr Quick


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