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Re: 5/8" Thick WSP Panel Identification Index: 40/20 vs. 32/16

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I thought part of the reason that 5/8" WSP is not produced as 32/16, but instead is produced as 40/20 was economics.  40/20 is a more viable product commercially.  Why would someone pay for a 5/8" 32/16 span rating if they can get 1/2" plywood with the same 32/16 span rating which will cost less than 5/8" ply since there is less wood in the 1/2" plywood sheet. My understanding is that the plywood mills are very competitive and want to maximize the efficiency of the product that they produce...maximum span capability for thinnest piece of plywood...for least cost.  Producing a 5/8" 32/16 plywood sheet wouldn't be very competative in the marketplace
Mike Cochran
In a message dated 7/21/2004 7:18:05 AM Pacific Standard Time, tom.skaggs(--nospam--at) writes:

Paul is not technically correct, but he is practically correct.  On
paper, there is such a thing as a 5/8" WSP with a Span Rating of 32/16,
however, for all practical purposes this is NOT a common panel.  Please
see Table 5 of the Panel Design Specification, it provides nominal
thickness by Span Rating, and lists the most common panel thickness per
Span Rating.

If interested, I can explain why and how a company would Span Rate a
5/8" panel at 32/16, but the explanation is kind of long and tedious.

In short, a 5/8" 32/16 is not common and is typically not available.
Therefore, I would not anticipate your change in specification would
cause any heartburn.


Thomas D. Skaggs, Ph.D., P.E.
Senior Engineer
APA - The Engineered Wood Association
7011 S. 19th Street
Tacoma, WA 98466
ph: 253/565-6600
fx: 253/620-7235

-----Original Message-----
From: Bill Allen [mailto:T.W.Allen(--nospam--at)]
Sent: Tuesday, July 20, 2004 16:40
To: seaint(--nospam--at)
Subject: RE: 5/8" Thick WSP Panel Identification Index: 40/20 vs. 32/16

Paul -

Thanks for the info. The "design chart" I am referencing is Table
23-II-E-1 of the 1997 UBC/2001 CBC.

T. William (Bill) Allen, S.E. (CA #2607)   
Consulting Structural Engineers   
V (949) 248-8588    .    F (949) 209-2509   

-----Original Message-----
From: Paul Feather [mailto:pfeather(--nospam--at)]
Sent: Tuesday, July 20, 2004 4:16 PM
To: seaint(--nospam--at)
Subject: Re: 5/8" Thick WSP Panel Identification Index: 40/20 vs. 32/16

40/20 is 5/8 (19/32 actually).  32/16 is 1/2 or 15/32.  To spec a 5/8
32/16 would be technically incorrect, even if it is listed somewhere in
a design chart.  If a 5/8 panel is available it will be rated 40/20.

Paul Feather PE, SE
----- Original Message -----
From: "Bill Allen" <T.W.Allen(--nospam--at)>
To: <seaint(--nospam--at)>
Sent: Tuesday, July 20, 2004 3:22 PM
Subject: 5/8" Thick WSP Panel Identification Index: 40/20 vs. 32/16

> Is anyone aware of the physical differences between the two specs?
> plies? Cost? Availability?
> TIA,
> T. William (Bill) Allen, S.E. (CA #2607)
> Consulting Structural Engineers
> V (949) 248-8588 . F (949) 209-2509