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Re: Plywood shear walls with 3x sills...

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The change to 3x sills and plate washers was in response to the large number of
split sills observed at Northridge and some follow-up testing in So. Cal.  The
splitting could be caused by the cross-grain bending that occurs when the
sheathing panels rotates.  (This is a significant problem with loose, highly
loaded, tie downs.) Or, more likely, by the unequal loading at the foundation
bolts caused by poorly drilled holes in the sill. (Typically these holes are
oversized  1/8" to 1/4" and not inspected.)  Or by a combination of the two.
    In either case, a pair of 2x sills are not likely to perform as well as a
single 3x.  If you could be sure that the sills were carefully match drilled as
a pair, it might not be too bad if the loads aren't too big. If  they are
drilled separately, it could be much worse.  Unless someone stands there and
watches I don't know how you'd know.
    I'm still waiting to see my first pair of properly inter-nailed 2x.  That
many nails just don't look right to the carpenters.
Chuck Utzman