Insulating a slightly-damp crawlspace

Question

I've got a crawlspace under my living room that's connected with the basement for the rest of the house. In the winter the floor of the living room gets cold, even though there's R19 fiberglass between the joists. I was thinking of insulating the exterior walls (CMU) of the crawlspace, since two out of 3 of the walls are completely above grade.

The crawlspace is mostly dry, but when it rains there's a bit of moisture that seeps through 1 wall (below the ground level). I can't easily seal the outside, since it's right under a deck.

Is it a good idea to add insulation there? What's the best material to use? Options I've seen:

1. Foam insulation. I could use XPS or EPS foam, but then I'd need to add framing and attach drywall, and I'd worry about the moisture damaging the drywall. I've looked into Dow Thermax, but I've seen concerns about how that handles moisture.
2. Fiberglass blankets with facing, but those also could have moisture problems.

Answer 1

You don't say if the crawlspace is heated or has access to heat. I'll assume that it is not heated.

Your floor is cold despite the insulation because the crawlspace is sucking the heat out of your livingroom through the wood joists. Wood has an R-value of about 2 per inch, which will bypass the R-19 insulation you have between the joists.

Insulation on the crawlspace walls is a good idea if you plan to add heat to the space. Ideally, you should stop the water or apply some kind of drain to move the water out of the area because of humidity buildup in the sealed space. Alternatively, identify the area of seepage, frame around it and insulate the remainder. Be prepared to use a dehumidifier in the space when you cannot ventilate.

If not, and you have the clearance, apply an air barrier with a rigid fiberboard insulation or taped Extruded Polystyrene insulation to the underside of the joists to reduce heat loss through the wood joists. The amount to apply depends on clearance, budget and will.