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- To: seaoc(--nospam--at)seaoc.org
- Subject: 3/4" (48/24) Plywood Diaphragm
- From: PERRY TABOR <tabor(--nospam--at)ccnet.com>
- Date: Fri, 10 Apr 1998 18:36:25 -0700
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 over 2x12 floor joist at 24" o/c within residential framing (hardwood flooring veneer anticipated).
According to Table 23-II-E-1 (1997 UBC), the specified plywood span in accordance building code, except for the blocking noted above.
At this time, the plywood deflects (spongy)....I have never in my years seen plywood sub-flooring deflect this severely (four years residential construction experience and 15 years engineering experience w/ over 10 years operating a structural engineering company catering to residential construction)
Construction commensed in September and now is putting tar paper down at the roof (assembly has been open to the environment for over 7 months during sever rain storms in the Palo Alto area).
Current floor diaphragm exhibits bubbles, dips, swales and regions exhibiting standing water after four days of no rain.
Foundation plan consists of inter-locking grade beams with crawlspace accesses as determined by the architect. Referenced residence has 5 HVAC units, thus the crawlspace can be envisioned to be filled with duct runs every direction (superintentent expressed that the trunk line are 30" ducts) and not lending itself to cross-ventilation.
The architect has commented that the underfloor has not enough ventilation due to hardscape at the rear and side patio regions, not to mention the front entry.
The superintendent and architect mentioned that they have been pumping water out of the crawlspace since Fall.
Concern: General Contractor, owner and architect are making noice that we (structural engineers) have not performed our duties correctly and want us to participate cost associated in laying another 5/8" T&G over the existing flooring.
#1. The installation of another layer of plywood over the existing will not correctly solve the problem. We preceive the major problem resides with the underfloor ventilation and associated moisture damage (plywood delamination, deterination of wood fibres due to organic micororganisms within moist environment).
#2 Blocking of panel edges was recommended by our office during initial site observation - dismised due to the labor cost for installation, although floor diaphragm had not been installed.
#3 1 1/8" plywood floor diaphragm was recommend by our office during initial site observation as an alternative to the solid blocking noted above - dismised due the cost of restocking 3/4" plywood already delivered to project site, although none of the plywood had been utilized nor distributed about the site.
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