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I have a heated crawlspace with a dirt floor. There are no vents, it is fully connected to the house, and currently has a pool liner and vapour barrier stretched over it, but it is not sealed. There are large gaps in the liner, in fact. The past owners simply lived with this.

I would like to seal it to prevent the moisture (and gases, etc) from entering the home. I live in a cold climate, and I am concerned if I put a vapor barrier liner (6mm) down with no insulation, that I may get condensation on top of it, due to warm air inside hitting the cold VBL/cold ground. It doesn't get too cold, but I did see frost last winter on the soil, so there is moisture there.

I was hoping to pay for a concrete slab, but have read that a 900sq ft 4" thick slab would hold ~400 gallons of water, and that water is now under your house, causing more issues (eg concrete isn't good for a retrofit).

I would like to avoid having to buy 4" closed cell foam, for below the vbl. Although ideal, I feel you couldn't walk on this at all without breaking their seals, and it is expensive.

What's the right way to do this? And then, can I get away with just the vbl, or am I going to have real problems? I do have a crawl space sump, it is inside a tub and the bottom is bone dry. The walls of the tub are fairly high however, higher than the grade of the soil.

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