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[SEAOC] Re: [SEAOC] Plywood Shear Wall over Gyp Board

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CarlS95(--nospam--at)aol.com wrote:
> 
> At the risk of sounding dumb, I would like opinions on using plywood over gyp
> board for a seismic retrofit.  The building is an existing tilt-up concrete
> building with a large existing wood mezzanine.  One wall of the mezzanine has
> gyp board on both sides which is inadequate for resisting shear.  The
> question:  To save money, can (or should) plywood be attached directly over
> the gyp board without first removing the gyp board?
> 
> Thanks.  Carl S.
> 
The 1994 UBC has allowable shear values for shearwalls with plywood over
gyp board.  It is in Section 16 in Volume II.  I don't have the UBC in
front of me, but it is in the tables for shearwalls.  You have to use
the longer 10d nails instaed of the regular 8d nails when nailing
plywood directly onto the studs.  Also, you have to make the correction
for using wood that is not Doug-Fir.  By using the 10d nails, you get
the same allowable shear as 8d nails without the gyp board.

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