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Re: Ventilation

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Radon fans are, in fact, what usually gets used.  They're low flow, continuous rated beasts that will go 10 years unattended.  Since I'm in the Appalachian  mountain chain, a radon check is pretty common on resale, but you can't really do one until a house is closed up. The cheaper builders just put up the house and hope nobody calls them on it; the better ones spend the $300 to drop perforated pipes in the subslab aggregate (mostly basements around here) and put a vent stack up to the attic space for future use, if necessary.

Roger Davis wrote:
Another issue to be concerned about in some areas of the country is radon.  An unvented crawl space could be quite hazardous to your health.  Radon is usually vented by running a pipe up through the roof.  It seems to me that it would be very effective in venting any crawl space also - provided you had some inlets in the perimeter walls.  If that would be less painful to your client, you might see what the building official thinks about it.

"Jordan Truesdell, PE" <seaint1(--nospam--at)truesdellengineering.com> wrote:
Yes, you're really supposed to make swiss cheese out of the walls. Nobody does.  I also leave ventilation out of my contracts and off of my drawings. I have recommended powered ventilation fans for clients who cannot meet natural ventilation requirements. There's a continuous volumetric rate in the code, and it's very, very low.   There's still the possibility of condensation during hot, humid periods, but the moisture problem usually varies enough with the time of day to even out over most 24 hours periods, imho.

I'd tell them to seal it up and condition it, but there are so many things that can go wrong when sealing a crawlspace with common labor that half the time you end up with a moisture containment vessel under the house. *shrug*

Jordan

S. Gordin wrote:
Lloyd,
 
You are right, I should have been more specific.  And - yes, CBC has a similar provision/exclusion.
 
My problem is, that vapor retarders are rarely (if ever) placed in the crawlspaces, at least, here.  The "normal" (at least, based on the designs I've reviewed) practice, however, is not to provide as much vent area as is required by the code for such condition.  This is why the contractor and the architect are "not buying it."
 
Generally, it is not a structural engineering issue, so it's left to the architect.  This is, until structural moisture-related problems arise. I am investigating and providing repair specs for one of those (water is coming from outside). 
 
I was trying to get opinions of other engineers who may have been in the same situation and came up with solutions other than the knee-jerk idea of cutting large holes in the stem walls.
 
Steve Gordin SE
Irvine CA
 
 
 
 
 
 
 
 
 
 
 
 
 
  
----- Original Message -----
From: Lloyd Pack
Sent: Thursday, January 26, 2006 11:22 AM
Subject: Re: Ventilation

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

>
> Good morning,
>
> Recently, I have to deal closer with the crawlspace ventilation
> issues.
>
> 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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