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RE: Deflections

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That is always a debated topic.  I consider gyp. Bd. the same as plaster because once it cracks it will always be visible no matter how you repair the crack or bad tape job.  I know others that use the l/240.   It is always a problem in 2x wood trusses roof systems.  No one considers the differential deflections of adjacent trusses, especially ignorant (clueless) contractors and truss suppliers.



Joe Venuti,  P.E.

Joven Engineering

La QuintaCA


From: J. D. Coombs [mailto:jcoombs(--nospam--at)]
Sent: Thursday, February 18, 2010 8:06 AM
To: seaint(--nospam--at)
Subject: Deflections


In the 2003 IBC “Deflection Limits” Fig 1604.3, it gives the limit for Plaster Ceilings.  Does that include drywall, or does drywall fall under Non-Plaster?

Drywall is considerably more flexible than plaster.

I generally use the tighter limits, but this is a situation that truly doesn’t need tight limits.




Jerry D. Coombs, P.E.
Coombs Engineering Services