On Thu, 14 Feb 2013 14:10:57 -0800 (PST), jamesgang
wrote:

On Thursday, February 14, 2013 2:58:20 PM UTC-5, wrote:
I'm going to have to replace some sections of roof sheathing as part of a re-roof project. What is there now is 1/2" plywood. I guess it's been OK because it's lasted almost 30 years. Is 1/2" still OK as far as code goes, etc? The part that is a problem was due to not being vented correctly, which I'm going to fix. It's actually one entire section of roof where that whole section needs to be replaced. I'm going to get quotes and want to make sure everything is spec'd. What is typically used now for roof sheathing? Is OSB ok? is at as good or better than plywood? Oddly looking at Lowes and HD, it doesn't look like they have sheathing in 1/2". Closest is 15/32. I guess maybe lumber yards have true 1/2"?

Nobody has true 1/2" any more. OSB is fine. Stronger and cheaper. OSB is used for almost all new construction. Get the little clips to keep it spaced properly. Why'd the original fail? Should have lasted longer than 30 years. Get wet?

The major disadvantage of OSB is that if it gets exposed to
significant amounts of water or moisture, the edges expand by up to
15%. . . especially if they are cut edges. This swell will then
telegraph onto the shingles or some flooring. When plywood gets wet,
it expands evenly throughout the panel, dries more quickly and shrinks
down to its original size more rapidly than OSB.

The "little clips" are definitely not used to keep the sheathing
"spaced properly." They are to provide additional support between the
rafters when using minimum code sheathing.