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RE: wood frame bldg deformation and windows

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Regis,

    This is an important issue you have raised, perhaps more so than you
know.  Did you ever think how much worse this problem would be in a building
with aluminum framed windows, or perhaps wood framed windows?  By stating
your question in terms of flexible vinyl, you are perhaps being too
generous.  In some cases, the window glass itself is mounted in the frame
with rubber seals.  These seals no doubt have some "give" to them and would
tolerate some differential movement without breaking the glass, but I doubt
this has ever been quantified.  I would be particularly concerned in a long
wall with little or no plywood shear paneling and a relatively larger window
opening.  I can well imagine that the window frame would actually be the
stiffest section of this wall, and would actually *attract* the shear load
to itself, assuming proper gapping was not provided.  Not a happy thought,
eh?  I doubt the window was designed to serve as a shear panel.  I'd sure
like to see the permit calculation for that one!
    What is particularly disturbing to me is the manner in which the window
issue is handled.  For a high rise, the sort of building that an upper class
person might live in, elaborate drift criteria are established for window
systems.  These window systems are carefully designed, and sometimes are
sent in for permit review.  On smaller buildings, the ones that you have
alluded to, where our nation's poor are most likely to live, there is rarely
any attempt made to address this issue.  I have never, I repeat *never*,
been asked by the window "designer" on such projects to contribute anything
for the drift criteria or permit review of these systems.  How unfair is
that, my fried?
    Perhaps someone with more experience with the IRC and other
prescriptive residential codes might be able to shed more light on this
problem.

Dick Sunshine, P.E.
Sunshine, Polk & Associates


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