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Achille76 02-11-2013 11:36 AM

Converting Vented Crawl Space to Unvented/Conditioned
My home was built in the 1970s with a full basement; however, in the early 1980s two extensions were added using crawl spaces, rather than digging out a full basement. Each crawl space is vented, one has a dirt floor, the other is over the old concrete patio (which has multiple cracks). They are both separated from each other by a cinder block wall. Each space is accessible from the basement through the old basement windows. I have never had an issue with water entering the space, although in the summer it does get very humid in the basement.

In recent weeks I've noticed large deer mice entering the kitchen up through the hole where the drain pipe runs through. In the summer, black ants have also come in. After inspection I noticed the following:
- Insulation has mostly fallen down from the crawl space ceiling, likely from the humidity that is present in the summer. (Northeast)
- The space above the old basement foundation wall, where the joists run into the crawl space, is completely open. This was not sealed up. So if mice were able to enter the crawl space they can easily climb through this space into the basement.
- There is no vapor barrier on the ground within the crawl space
- One of the exterior crawl space walls has a crack in it. (1/4" or so).

My question is:
- Would converting these crawl spaces to a conditioned space be my best option for sealing up this space, preventing rodents from entering, and increasing the efficiency of the house in general?
- If so, would it be adequate to seal up the vents, repair the wall crack, lay a 6 mil barrier on the floor and 1 foot up the wall, and have the crawl space walls spray foamed with closed cell insulation? Then remove the old ceiling insulation and leave the old basement windows open to this space, giving it some circulation? Total size of crawl space 1 is about 10'x10'; crawl space 2 is about 20' x 10'.

Obviously, the goal is to clean this area up to prevent rodents/insects from entering the house/basement, as well as increase the insulating efficiency of the home (as the areas above the crawl space have always been too cold).

Any thoughts or suggestions would be appreciated. From what I have read, conditioned/unvented crawl spaces appear to be the most preferred method these days.


Dave Sal 02-11-2013 09:07 PM

It's a great idea to seal up the crawl spaces and turn them into conditioned spaces.

Achille76 02-12-2013 08:20 AM

Another question I have is would it be better to have a concrete slab poured in that space, or is the vapor barrier sufficient? Again, the objective is to keep rodents out.

HomeSealed 02-12-2013 08:49 AM

Sounds like you are on the right track. Concrete would have been ideal in there, but probably not the most cost-effective option at this point. The plastic will be sufficient. You will also want to run the plastic up the walls a little bit, foam the sill boxes, etc. Somebody will post a link for you with the details I'm sure. ;)

Greg761 02-19-2013 09:10 PM

Conditioned crawlspace
I bought a cabin in Northeast PA where the crawlspace was an absolute nightmare. There was a foot of water in it, everything was starting to rot, carpenter ants everywhere, sewage spilling in it, mice, you name it.
I tore down all the old insulation, put a sump in and 20 tons of 2B stone. I put down a thick plastic vapor barrier and ran it up the walls up to the sill plate. Then I perimeter insulated with 3" foam board against the block walls down to the footer. I sprayed all the wood- sill plate, band joists, all floor joists, under side of sheathing with a mixture of hot ethylene glycol and DOT (Octoborate- Borathor). I treated everything twice. It stopped all dry rot and got rid of all the carpenter ants. I was reluctant to foam the cavities along the band joist so I can inpsect them, so I used regular insulation in them, but the mice are making swiss cheese of that.
So, put down thick plastic, run it up to the sill plate and cover the walls with foam board. I bought long tapcon screws and screwed a furring strip over top of the foam board ever so often to hold up the foam board.
No more ants, rot and frozen plumbing. Oh, I run a dehumidifier a few hours a day in the summer down there. Borathor is the balls. It's non-toxic to mammals. I'll use that everywhere now before I drywall anything up. It keeps on killing.
That blue lumber you see is treated with DOT.

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