APA plywood or APA rated sheathing?

I always specify OSB. I think it is cheaper than plywood, and is still rated by APA.

DaveAtkins

APA Rated Sheathing Exposure I unless your design requires the additional Structural I designation.

OSB panels are included in this category.

I specify sheathing unless I or the client specifically want plywood.

I think it is always best to specify APA rated sheathing. I would avoid basing your design on Structural I unless you know it is available in the area the project is being built.

In most areas of the US, outside the west coast, Structural I Plywood is almost impossible to get. In the upper midwest Structural I OSB is usually available.

I generally spec CDX plywood and yes, I do get requests to use OSB in place of it. I really don't care, because from a structural standpoint there is nothing wrong with it. Some architects I work with refuse to use OSB, because it does still swell more than plywood when it gets wet. Using OSB around here is generally looked at as doing it the cheap way. Installed properly though (covered in a timely fashion), good results should be expected.

So, if the request comes to use OSB in place of plywood (this usually comes through value engineering), I say it if fine structurally, but relay my concerns about the swelling, and let the owner and architect make the decision.

not all OSB is the same. There is construction grade OSB that is not APA rated and is less expensive than plywood, especially APA rated plywood. On a recent wood framed project, the contractor purchased OSB for the shear walls because my general notes specified APA rated sheathing (plywood or oriented strand board). He did not purchase OSB bearing the APA rating stamp. He was angry that I refused to accept the OSB he purchased, but understood why I wanted APA rated sheathing. The APA rated OSB was slightly less expensive than APA rated plywood, but not alot.

I used to sympathize with plywood manufacturers tempted to cut costs by avoiding the APA rating.

Then I had non APA rated >>exterior<< grade plywood delaminate after a year or so of undercover outdoor service. At most Maybe it got rained on once, but maybe it didn't. It seems those folks who wished to skip the certification were convinced they also "knew" some manufacturing steps were un-necessary and skipped those as well.

I had no one to blame but myself.

Our standard is to specify APA sheathing with span ratings. Attached is a good explanation of this method.