Plywood on Roof

What type of plywood can you get away with on the roof?
1. 1/2" or 5/8" or 3/4" 2. 3-ply or 4-ply
??
Thanks
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Where is the house? If it's going to hold snow, you need to consider the weight of the snow and the plywood vs. the strength. You'll get a hundred opinions on this, but I live in New England, and I have 3/4 4-ply.
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Philadelphia, PA. What do you think?
Michael O wrote:

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Beyond checking what your local building inspector wants, you want your roof to be supportive and flexible, I'd go with 3/4.
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I would suggest starting by checking the local code. I would guess it also may depend on the span. I believe I have also seen different specs for T&G and flat.
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Depends on the span bettween rafters, roof pitch, and more. Often 5/8" is enough. Greg
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Depends on local codes, spacing of trusses, and in our area, the type of covering as well. Our minimum is 5/8, but 3/4 is most common.
Jeff
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I just reroofed after 19 years and found that my roof plywood is not quite 1/2 in. I believe it was 15/32. Not quite thick enough as it would really sag when I was standing between the rafters and I only weigh 165. Of course after the roof and underlayment was on, I didn't notice any sagging.
I would guess that my builder, General Homes, used the cheapest plywood they could find, so I certaintly wouldn't recommend doing what they did.
PJ
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I recently completed the roof of our new house which has rafters and trusses spaced at 24" OC. I looked at two different options, 1/2" OSB and 1/2" CDX plywood. The span ratings are stamped right on the plywood sheets. Either would span 24" fine, but the CDX had slightly higher span ratings and more important to me the sheets were lighter. Much nicer when you have to get those big sheets up on the roof in the first place.
Anyway, my final choice was 5-ply CDX plywood. I also used metal "H-clips" midspan between each rafter. I weigh over 200 pounds and the roof feels plenty strong to me with virtually no deflection between rafters.
Of course, if you regularly get heavy snow, have a low slope roof, or just want to upgrade the roof ply, then by all means go with 5/8" or 3/4". It'll just cost you more money, and you'll have a slightly harder time lifting the sheets up to the roof.
Anthony
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