Posted by: greenpinkies | May 29, 2011

The Crawlspace or The land down under revisited

Ideally, we would have liked to have included the crawlspace under the house as our ‘conditioned space’. (See blog, “we all Live in a Yellow Submarine” dated Nov. 7th, 2010).

There are definitely two different camps of opinion when it comes to how to deal with a crawl space.

The first camp suggests putting down visqueen as a vapor barrier entirely over the dirt of the floor, then foaming up the cinderblock walls but leaving the floor between the house and crawlspace uninsulated.  The logic behind this is that the crawlspace is no longer vented to the outside and becomes a trapped air zone where the air temperature remains a pretty constant 59 degrees.  This blanket of underneath air will moderate what’s going on up above in the main house.

The second camp suggests using the visqueen on the dirt as a vapor barrier but not foaming the cinderblock walls and leaving all vents open to the outside. Then open cell foam is sprayed as a blanket between the floor of the house and the crawlspace.  Open cell foam lets moisture through, closed cell foam does not.

We will digress here a bit: The rule of thumb regarding foam insulation seems to be:  When foaming walls or floors, there must always be the ability for moisture in the air to flow in or out of the floor or wall in at least one direction.  This prevents mold.  For instance, if you foam the exterior walls with the closed cell foam or coat them with plastic and then also stick vinyl wallpaper on the inside of those walls, you have put a moisture barrier on both sides of the wall and the wall cannot ‘breath’ or ‘let off steam’ or whatever it needs to do, and the potential for too much moisture build up, resulting in mold, exists.

Back to the crawlspace.

Interestingly, for the purpose of the HERS rating of a house.  The computer model shows that scenario #1, visqueen plus foaming the cinderblocks but not the floor, will yield a lower HERS rating and is considered more energy efficient.


Alas, we had to opt for scenario #2 because we had the added complication that, even though the crawlspace is 2/3 dry, the other third is subject to water during rain storms. True, the water soaks in and goes away fast, but, it is there.  Therefore, Natural State Insulation did not feel comfortable totally sealing off the crawlspace from all outside air. We wanted to keep the vents open and have airflow, just in case. The open cell foam was necessary under the floor because a few of our flooring choices have moisture barriers incorporated into them.

Now here is the progression of pictures from the beginning to now on the crawlspace:

Wed. Aug. 18 Lauren, crawling in the crawl space. Actually…more accurately, rolling in the crawl space. After crawling on the rocks for a ways, it was found the most efficient way to get from point A to B was to roll. Heck, the suit went all the way around, so why not roll!

Clean out, stripped of all insulation, underside of the house.


crawl space after foaming and visqueen




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