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Re: Valley Rafters

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In a message dated 9/10/05 11:03:45 AM, njineer(--nospam--at)att.net writes:
The conventional light-frame construction rules for framing can result in roof systems that cannot be rationalized.  Nevertheless, they seem to work O.K.

I agree that they often "seem to work O.K.," primarily because they've evolved to satisfy local conditions, including "real" snow loads, although I suspect their safety factor is often barely above 1.00, and they *never* get their full "design load."  Here in the San Francisco Bay Area I've seen many roofs that appear to be hanging from their fingernails, with 2x4 rafters @ 32" oc spanning 10' or so (with 3+ layers of shingles and significant sag), joists and beams that are notched at the supports, with major horizontal splits, and  rafters staggered such that the 1x4 ridge member looks like a slalom course.  I sometimes wonder how anyone could actually build such framing and then go home and sleep at night.  "Ignorance is bliss."  The work has survived only because we never get snow.  But once in a while someone piles new roofing materials on a roof and it all collapses. 

Ralph Hueston Kratz, S.E.
Richmond CA USA