[Greenbuilding] Crawlspace
nick pine
nick at early.com
Sat Jun 2 20:22:00 CDT 2012
Stuart Fix <sfix at renubuildings.com> wrote:
> Humidity within the crawlspace should be controlled via poly on the ground
That would seem to invite condensation from warm moist house air in a cold
climate, without a vapor barrier below the floor and insulation below that.
> and proper ventilation (either passive screens or active fan/humidistat).
Passive screens would seem to invite condensation from warm moist outdoor
summertime air. So would automatic foundation vents that are open at 70 F...
http://www.amazon.com/AIR-VENT-RABL-AUTO-FOUNDATION/dp/B000IJWOV6 How about
a smart vent, ie a fan with a differential absolute humidity control...
http://www.smartvent.biz/ ?
If a simple humidistat turns on a fan to move outdoor air through a
crawlspace when the crawlspace RH is too high, say higher than 60%, what
prevents the fan from moving warm moist outdoor summertime air through the
crawlspace, with condensation?
> Eli's comment:
> The issue I am trying to understand is how to maintain in a ventilated
> crawlspace to be warmer than dew point. The vapor barrier on the ground
> only stops ground sources of humidity. A high standard thermal barrier in
> the floor keeps the ac cooling from cooling the bottom surface. However,
> the shading will keep the crawlspace cooler than outside. Could this
> cause condensation?
> Response...
> The only way to STOP condensation from occurring, in the situation you've
> described, would be to heat the crawlspace, or to ventilate the space at a
> high enough rate that it maintains the same conditions as outdoors. Both
> are likely a waste of energy.
The second way seems especially wasteful, since maintaining exactly the same
conditions as outdoors requires infinite fanpower :-)
Gary BIs <gary at builditsolar.com> wrote:
> I converted my crawl space to a conditioned space as discussed in this:
> http://www.builditsolar.com/Projects/Conservation/Insulation/CrawlSpace29238.pdf
Do they suggest a vapor barrier under the floor? They say "Air sealing
between the house and crawlspace is less critical" with crawlspace wall
insulation.
> I put two layers of poly on the dirt and sealed it around the edges and at
> seams. I blocked all the vents and I foam can sealed all around the rim
> joist. Then insulated the crawl space walls with polyiso foam board with
> tape on the seams... its been about 6 years, and its worked fine for me.
> The crawl space feels dry. I do live in a dry climate (SW MT)...
Amen?
Nick
More information about the Greenbuilding
mailing list