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RE: Retrofit Diaphragm Blocking

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I've seen this deficiency repaired with framing clips attached one leg to
added blocking and the other with short screws to the underside of the
plywood.
It would be better to remove the roofing, block and nail it as specified.
The cost of removing and replacing shingles and paper may be about the same
cost as the retrofit.
If it has eaves, did they also miss blocking there?...shear transfer? 

Sharon Robertson Bonds, PE
Salerno/Livingston Architects
363 Fifth Avenue, Third Floor
San Diego, California  92101
(619) 234-7471



-----Original Message-----
From: Caswell, Philip J [mailto:pcaswell(--nospam--at)bonestroo.com]
Sent: Wednesday, December 12, 2001 11:56 AM
To: 'SEAINT(--nospam--at)SEAINT.ORG'
Subject: Retrofit Diaphragm Blocking


Ok, say you have a plywood diaphragm that was shown and specified to be
blocked (Vmax > 420 plf), but the building is now built, with the roof
shingles installed and gyp board covering the wood truss roof bottom chords
- but no blocking.  The unblocked allowable shear is only 285 plf.

Has anyone had experience retrofitting blocking to a plywood roof from the
underside?  Can an adhesive be used for this?  Intuitively, if the adhesive
can achieve failure of the wood fiber, it should work.  Is there anything
published that can be referred to?

TIA,
Philip J. Caswell, P.E.
St. Paul, MN

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