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Re: 3/4" (48/24) Plywood Diaphragm

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I've been called in twice in my career to investigate 'spongy' plywood floors.  In both cases the project hadn't yet been completed (like yours) and the cause of the 'sponginess' was that the plywood was Interior Grade - and had not been protected from the elements during construction.
IMO, 7 months in the open, in severe storms, is a long time - even for Exposure I plywood.  Find the APA Grade stamp on the plywood, then check with the APA to confirm the grade and exposure rating.  My guess is this is a case of too much rain and inclement weather, over too long a period.  If that's the case, then the burden to repair it falls on the Contractor for not protecting the plywood, or for poor project management for allowing it to be exposed for too long.  Depending on how much rain there was, and if it wasn't predictable, the Contractor might have insurance to cover construction risks like this.
Good Luck,
Lew Midlam, PE
-----Original Message-----
From: PERRY TABOR <tabor(--nospam--at)>
To: seaoc(--nospam--at) <seaoc(--nospam--at)>
Date: Friday, April 10, 1998 10:20 PM
Subject: 3/4" (48/24) Plywood Diaphragm

Q: Plywood Floor Diaphragm: How do I get an authority/checklist of items to review within the field to attest to plywood intrigrity (veneer separation, grading, etc.).
Situation: Our office has an unusual condition which our structural plans specify 3/4" (48/24) T&G floor plywood without blocked edges