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Have You Sealed Your Crawlspace?

1624 Views 11 Replies 8 Participants Last post by  LLigetfa
Our summer place has a crawlspace. Years ago the pipes and beams had a lot of condensation. We laid plastic sheets on the dirt and added ventilation which stopped the condensation but the first floor of the house is still damp most of the time. The thin plastic is beginning to decompose and some of it has been moved around over the years. I believe that most of the dampness is coming up from the crawlspace. From what I've read, the new theory is not to ventilate but to seal it off completely. They do this by laying a 20 mil vinyl fabric on the dirt, sealing the pieces together. They also run it up the block walls and seal it at the top and around the footings. Then they close off all the vents and place removable covers on the access points. Sealing drains and dehumidifiers are also available if necessary. The job is fairly costly. I could get the materials and do it myself but I hate going down there anymore because some areas have only 1 foot of clearance. :eek: Has anyone sealed their crawlspace with "Clean Space"? :)
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The crawlspace has to have some air movement.

The newfangled way of doing it is called a "conditioned" crawl space. That's what we did on our place. Put down some sand, then the plastic membrane which got glued to the foundation walls with nasty poly caulking. Then we had a spray foam contractor come and spray the inside of the foundation walls with about 4" of foam.

We do not have any insulation in the floor.

Works great, but you do have to move some air.

Normally with a HVAC system you leave a large gap at the bottom of your interior doors to act as you return. In our house we have a vent to the crawl space in each room to act as the return. Then we have a HRV (heat recovery ventilator) that comes on intermittently and sucks stale are from the crawlspace, spits it outside, draws fresh air from outside and introduces it into the HVAC return air. This is a great thing to install if your house is pretty tight and you keep your windows closed during the seasonal extremes. It has a heat exchanger in it, so it splits the difference between the incoming and outgoing air... these things have been used for years on commercial buildings.

It is a neat system, so far has worked well for us. Electricity is pretty expensive out here, we've been pleased with our utility bills in the new house. Our July bill was about $90.00, for a 2500 square foot house, in a dry climate with seasonal extremes. (gets into the 100's in the summer).

You will probably have to get some sort of alternative building material variance permit, or something like that. Our house was the first conditioned crawlspace our local building inspector had seen. Or just get busy under the house... (probably what I would do).

If you decide to go with spray foam... shop around! I had quotes vary from $2400-$4000. (this was for about 770 square feet of area)
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Tyvek tape is great for plastic seams... figured that might be useful info.
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