Fixing a crawl space

The home we are trying to buy has no foundation vents and no moisture barrier over the dirt floor of the crawl space. There doesn’t seem to be wood rot or visible mold, but there is condensation on pipes below the house and a musty smell so this needs to be remedied and the sooner the better. The floor is also uninsulated.

From what I can tell, there seems to be a few ways to deal with this.

  1. put in foundation vents and put in a plastic moisture barrier and insulate the floor

  2. encapsulate the crawlspace in some kind of system of flexible material to keep moisture out

  3. install a drain and line the crawlspace with a plastic moisture barrier and then line it with concrete

Anyone have any experience with these? Are there other options? How much do each cost for a crawlspace of 24’ X 29’ X 3’?

#1 is the way they do it around here. I do have some mold under my house when it’s really hot and humid in the summer though.

My WAG as far as cost would be $800 or so, probably installing the vents would be the hardest part.

My first thought was to put insulation in the floor, then put the moisture barrier outside of that, attached to the bottom of the joists, but I don’t know if that’s the right approach.

So I’d say #1 is the right choice. As to cost, I couldn’t even guess. Would you do it yourself or have it done?

Does this house have a basement?

The two ways crawl spaces are generaly done are:

  1. The crawl space is under an addition or such and is open to the basement. In this case you put down plastic over the ground and insulate the walls of the crawl space.

  2. The crawl space is not part of a larger basement. In this case you would still put the plastic down. You’d insulate the floor and vent the area to the outside.

This is a topic of constant debate in contracting circles and amongst code officials. My two cents of wisdom is that if the crawl space foundation isn’t vented-good! Once you’ve eliminated outside air as a source of humidity, then it can only come from one of two spaces-inside the dwelling, or from the ground. Sealing off the earth of the crawl space to the foundation walls with a heavy (6 mil or better) poly sheet will establish an effective vapor barrier. Once that is done, the only moisture which can condense on pipes is coming from within the basement adjacent to the crawl space, or is moving through the floor assembly, the latter being unlikely.

We learned that this has to be taken care of before the sale due to laws around here. The crawl space has to be dried, any mold present has to be eliminated, and a vapor barrier has to be put in place. The crawlspace is under 3 feet in height, so the contractors we talked to recommend sealing it with an encapsulation system, which includes installing a drain, a sump pump, lining the area with a vapor barrier, and then lining the whole basement and possibly insulating the floor. The other alternative is the vent and plastic sheeting. I don’t know under what conditions the crawl space can remain unvented according to code. The owner says that it is moist from a sewer back up two or three weeks ago and is usually drier. The inspector is saying that the mold is not everywhere and does not appear that extensive, so this may be the truth, but there is no way for the space to get dry now.

I want to make sure this does not queer the sale. The house has readily remediable issues, the only real question here is who pays and can we get them corrected to suit the VA and the state before close.