Question
We have a customer asking for technical info regarding span ratings on 7/16″ OSB wall sheathing vs. 1/2″ CDX. Their architect is asking whether OSB will provide the same strength as CDX, and meet code requirements.
Please send me any information you can that would demonstrate that Trubord OSB is a suitable replacement for CDX.
Jim McFarland, Vandalia, OH
Answer
Thanks for the e-mail Jim and your question. Just some background – OSB and Plywood are measured on strength and not thickness and that is what determines the span rating. OSB is accepted by all North American building codes.
There are different factors that determine what should be used. Support Spacing is one and the first number in a span rating i.e. 24/16 is the maximum support spacing for roof/wall applications. The load the panels must carry is another component i.e. a clay tile roof will require a thicker panel to carry the weight and there may be other factors such as snow loads for example.
Take a look at APA Technical Note Q225 titled “Load-Span Tables for APA Structural-Use Panels” dated Feb 2011. On page 2 you will see the plywood sheathing info. There you will see that a 24/0 plywood panel has a uniform load at L/180 of 57 at 24″o.c. On page 6 is OSB Sheathing info and a 24/16 L/180 has a uniform load of 68 at 24″o.c.
Trubord 7/16 is rated 24/16 and 15/32 and 1/2 are rated 32/16.
Check to see what the span ratings your 1/2″ CDX has (it will be on the grade stamp) or maybe ask you customer to tell you the span rating is on what they use now (keep in mind the thickness being used may be specified for marketing reasons and not structural ones). It’s really up to the architect to specify what is used and if he needs a 32/16 rating then you can offer Trubord 15/32 or 1/2 and likely still save them money.