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RE: wind lines and jurisdictions

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Yep, one must always be aware of "local modifications".  The City of
Detroit traditionally "tweaked" the wind speed and snow load to use when
the BOCA code was used.  I don't believe that they are permitted to do
that anymore because the State of Michigan now adopts codes (currently the
2003 IBC and IRC) for state-wide use.  But, then the State does "tweak"
some things...such as the ground snow load map (if I recall correctly,
they mainly fill in the the areas labeled as "CS" in the IBC - West side
of the State - with actual values to use).  Regardless, I usually call the
local code official and ask...and then use the worst case of what they
tell me and what the code says (i.e. IBC, ASCE 7, etc).

Regards,

Scott
Adrian, MI


On Mon, 15 Aug 2005, Bill Polhemus wrote:

> > Bill,
> >
> > And I do believe that wind speed maps specifically state that linear
> > interpolation between wind contours is permitted.  So, you can use a value
> > of 94.3 mph (assuming you believe that you can be that "accurate") for the
> > appropriate point between the 90 mph and 100 mph contour.
>
> Believe it or not, in Gulf Coast area this "interpolation" thing is not a
> small consideration. Of course, the contours are a bit closer
> together--and I think rounding up to, say, the nearest 5 mph is
> satisfactory.
>
> But "political considerations" definitely hold sway. For instance the City
> of Houston says "use 110 mph within the city limits, period." This is
> interesting because any wind speed over 110, and you have to use
> engineered design (although it can be according to WFCM for wood, e.g.)
> rather than the prescriptive code requirements according to R301.2.1.1 of
> the IRC.
>
> 110 mph is actually "conservative" for most of Houston, but there are
> areas in the south and southeast quarter of the city that according to the
> map are OVER 110--so if you buy or build there, beware!
>
>
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