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Plywood vs OSB
3

Plywood vs OSB

Plywood vs OSB

(OP)
I am looking at a project from another engineer where the roof deck was designed as 5/8" plywood. The client wants to go to 3/4" OSB. My wood books are in a disarray, can anyone post a link to allowable capacities of 3/4" OSB.

Thanks,

Kaiser

RE: Plywood vs OSB

(OP)
Let me re-phrase my question. Simply put, what is the lateral capacity difference between 3/4" T&G plywood and 3/4" OSB? I know that plywood has much higher capacity, I just want to know how much. I haven't done wood design in about 4 years, so I can't even remember whe to look for these numbers.

Kaiser

RE: Plywood vs OSB

(OP)
Supporting framing are wood trusses @ 16" oc.   

Kaiser

RE: Plywood vs OSB

Umm, no.

OSB is actually stiffer as both shearwall and diaphragm. Capacity (or, more precisely, reference nominal unit shear capacity), for the same thickness is exactly the same for OSB and Plywood.

 

RE: Plywood vs OSB

(OP)
frv,

thanks for the quick responce. Where would I find shear values for both. I know they differ for the nail spacing and blocked/unblocked but say an idiot like me wants to see the plywood allowable values and OSB values, where would I look.

Plus, from your comment it appears that OSB=Plywood for same thickness in shear, is that right?

Kaiser

RE: Plywood vs OSB

Look at the NDS SDPWS, Tables 4.2A, 4.2B (OSB), A4.2A and A4.2B (Plywood).

The tables are exactly the same, save for the Ga values.

And yes, for the same thickness, the nominal capacity is the same. Keep in mind that the table lists nominal (not allowable) capacity, so you must apply your safety (or phi) factor.

RE: Plywood vs OSB

You will find the allowable shear values in the Chapter 23-Wood of the International Building Code (IBC), in the AF&PA Supplements or in the APA-The Engineered Wood Association material.

The Panel Grades for shearwalls & diaphragms are APA Structural 1. APA Rated Sheathing or APA Rated Sturd-I Floor. The panels can be manufactured from OSB or plywood. As long as the panels have the same Grade Stamp they are interchangable (but I wouldn't mix them on the same job). The engineer calls out the nail size, panel thickness and nominal width of framing and the codes give you the allowable shear in pounds per lineal foot.

I hope that this helps.

RE: Plywood vs OSB

kaisersoze:

Double posting for the same information is not allowed.  I am redflagging the post in the wood forum.  Please keep this in mind in the future.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Plywood vs OSB

(OP)
Mike,

Apologies for the double posting, I wasn't aware.

Kaiser

RE: Plywood vs OSB

No worries...

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Plywood vs OSB

2
They don't want you walking away from here with the possibility of twice as much information than what you deserve, so you shouldn't double post.  You can just imagine what they think of triple posting.  Mike once asked a question about a wood frame with three posts, and he was banned for a year.  So, if you want to double post, you should do it within the same thread, so as to conceal your evil intentions.

They don't want you walking away from here with the possibility of twice as much information than what you deserve, so you shouldn't double post.  You can just imagine .....

RE: Plywood vs OSB

(OP)
dhengr....deja vu brother, deja vu

Kaiser

RE: Plywood vs OSB

Yeah I clicked on the same thread twice one time - Caught a bad case of deja view.    

RE: Plywood vs OSB

(OP)
frv, OPM, boo: Gracias much for the responses. This forum has been very helpful.

So in conclusion, OSB, Plywood, Composite panels all have identical properties in shear and gravity loading provided they are the same grade.

Kaiser

RE: Plywood vs OSB

Capacity, yes. Stiffness, No. OSB is stiffer.

RE: Plywood vs OSB

As an aside, I would not use T&G plywood for anything but a floor.  APA recommends using a 1/8" gap between panel edges for a roof, which is usually achieved through the use of ply-clips.  This allows for expansion of the wood panel.   

Jason A. Partain, P.E.
www.myconstructionfinds.blogspot.com
 

RE: Plywood vs OSB

dhengr... another star... must be a slow day for Mikey... I sometimes double post because you may not find the expertise in the 'obvious' fora...

Dik

RE: Plywood vs OSB

Just make sure that either is APA rated.  There are some knock off imports out there....

RE: Plywood vs OSB

Dik:
My thoughts exactly, about occasional double posting...., where to ask the question.  If only everyone frequented every forum, all the time, one post might catch them all.
My thoughts exactly, about.....     Exactly.  Oh damn, I did it again, almost three times.
Otherwise, I was just pullin Mike's leg, or his post, a bit.
 

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