Plywood vs. OSB? Which one is better,how thick should it be?

thanks again for the info on my previous posts…

now one other question:

i get estimates with 5/8 ply, 1/2 OSB. 1/2 ply.

my gable roof has 2 foot on center 2x6 rafters .
it was built in 1926.

any suggestions on what i should ask for?

thanks again.

If you are patching a plank deck you will want to use 3/4", OSB or plywood doesn’t matter, they are equivalent.

If you are patching a plank board deck, you should remove and replace with like kind of nominal width new plank boards.

If, for some reason, you are removing all of the old existing plank boards currently in place, with a 24" OC, I would prefer the 5/8" CDX over either of the other 2 products, although they all wil meet minimum code probably in your area.

Congratulations, you met minimum code on your test, your grade is a D-

With the wider span, the thicker CDX will provide substantially more dimensional stability and less potential bowing between the rafters.


If you have beams 2’ OC use 3/4" IMO. Plywood is laminated wood, OSB is compressed wood chips. I wouldn’t use OSB on my house.

thanks guys.
the roof is coming off, and what’s left under the three layers is the 24" on center 2x6 s. at least they are TRUE 2x6 boards. really 2" wide.

anyhow, i figured the thicker the base, the better.

it isn’t weird to ask a roofer to use a thicker OSB/ply than he suggested, is it?

one guy i liked (based on refs and meeting him) suggested 1/2 OSB. It shouldn’t cost much more to upgrade to 5/8 or 3/4, right?

You need to use material of the same thickness, it is best to replace plank with plank, osb with osb and plywood with plywood, it is not that big a deal though.

It is important that the new material is the same thickness though, if you use 1/2" when your roof deck is 3/4" you will have a noticeable depression in the roof.

I agree that plywood is best, it holds fasteners very well, but there are different grades and the lower grades can warp and delaminate.

If given the choice between plywood and OSB, I would pick plywood every time. This is especially true when you tell me the rafters are 24 inches o.c. Personally, I wouldn’t go with anything less than 5/8" CDX plywood and be sure to use H-clips in the joints.

Plywood if replacing all the decking (i like 3/4")…if you are patching…use must use like kind of existing decking…unless you want spots of the roof higher than other parts…