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Re: Ventilation

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A few thoughts:
I just looked a comm'l bld. yesterday where the entire floor (2000 s.f.) had rotted out due to lack of crawl space/ventilation
In my contracts I specifically exclude ventilation & waterproofing design. I usually offer the arch some free advice but this stuff stays off my drawings as much as possible.
IIRC the vent area can be reduced by adding a vapor barrier (6 mil visqeen)--always a good idea in moist locations
Usually 4" or 6" x 14.5" screed vents are distributed around the perimeter as required on the AD elevations
Chuck Utzman,P.E.

Lloyd Pack wrote:
On 26 Jan 2006 at 9:39, S. Gordin wrote:

Good morning,

Recently, I have to deal closer with the crawlspace ventilation

According to CBC/UBC 2306.3 (IBC 1203.3.1), 1square foot of net-
open area should be provided - close to the corners - for each 150
square feet of the crawlspace. This means that for a 1600-sq. ft (say
(40x40 ft) single-story house,about 11 sq. feet of vents (net) need to
be installed, not counting the vents in the interior stem walls. 

This, in turn, means that at each house corner there should be 
anopening of 20" square (or (2) 14"x14"). If distributed along the
walls (although it is contrary to what the code requires), there
should be, say, (4) 6"x16"openings. 

To put it mildly, in this position am not quite understood by the
contractor or even by the architect. Any opinions?

Steve Gordin SE
Irvine CA
In the new IBC there is an exception to allow 1/1500 ratio of opening
to crawlspace sq. ft. if the ground under the floor is covered with
a vapor barrier.  Do you have that option under the CBC? If so,
does that change your position?

I'm a little lost as to what you are asking?  Can you ask a more
specific question, please?

Take Care,
Lloyd Pack

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