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Fwd: Re: plywood shear transfer detail

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In a message dated 97-04-03 22:42:10 EST, you write:

<< Subj:	plywood shear transfer detail
 Date:	97-04-03 22:42:10 EST
 From:	HARRISENGR(--nospam--at)
 Reply-to:	seaoc(--nospam--at)
 To:	seaoc(--nospam--at)
       I am refering to residential wood frame construction, with plywood
 shear panels.
       Typically, on the plans, i see a top plate shear transfer detail that
 shows a plywood panel edge nailed to the upper plate ( wood 2 x 4 ) of the
 double top plate then a simpson a35 to a block above.
      While performing structural observation today i see a problem that must
 be common:    The plywood panel is 8'tall-1/8". The wood wall is 8'-1" (
 92-1/4" studs ). With a minimum  !/2" ( even 3/8 " ) the top edge nails are
 either in the crack between the two top plates or in the bottom top plate
 that may ( probably ) not have appropriate shear transfer to the upper top
 plate and the a-35 above.  
      If the nails are angled, they must be over/under penetrating the plies
 by the nailhead.
      Since this is such a common condition , i would appreciate any thoughts
 on this detail.
      This may be hard to understand in this text but next time you observe
 the top plate edge nailing of an 8' shear panel you may see what i mean.
      Tom Harris, SE
      Thousand Oaks, CA


This is a good reason for the need of structural observation of building
construction by the engineer of record.  Since the standard stud wall height
is 8'-1" or 97" tall (sill plate, stud, double top plate) and the plywood
sheet is only 95-7/8" tall this leaves a difference of  1-1/8".  The framer
needs to make sure they lift the plywood panel off of the floor about 1/2"
before they nail the sheathing to the wall. Using 1/2" edge distance for the
plywood nailing, you should still have about 3/8" to  1/2" to the bottom of
the top plate of the double top plate.  The same edge distances would also
apply at the sill plate.  Of course if you do not lift the plywood up, you
will be nailing in to the crack between the two plates if you use a 1/2" edge
distance.   After reading your post,  I will probably add a note about this
to our general notes regarding holding up the plywood sheathing.

I know that tradtionally for many years the clear height from floor to
finished ceiling is suppose to be 8'-0" (97"stud wall height minus 1" for
finish ceiling), but I am cursious to know why the 8'-0" clear height was
selected orignially as opposed to say a 10'-0" ceiling height which you often
might see in a custom home.  Was this originally because of costs or
manufactoring restrictions? 


Michael Cochran

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