Crawl space is currently vented, we plan to seal the two crawl vents to outside, install foam board insulation on exterior walls, install a new felt underlayment and a 20-mil vapor barrier on crawl floor and up concrete block walls, and dehumidifier with pump that drains to outside.

1. The existing vapor barriers—there are ~2 different 6-mil sheets stacked on top of each other (previous owners) over gravel-- is wet/damp underneath with mold growing once you pull the sheets back a couple of feet.

a. Should we leave the existing vapor barrier(s) in place and overlay our felt and 20-mil on top? Or remove them both and start from scratch?

b. Should we put any chemicals down to treat the mold? Or anything that might keep the mold from coming back?

2. We have a ~6” pipe that’s part of a RADON remediation system that runs through the crawlspace, it has several holes drilled into it that (effectively) pulls air from the crawlspace and vents it outside the house.

a. Should we put the vapor barrier below this (RADON remediation) pipe? Or above it? I initially thought the vapor barrier should go below the pipe but then considered that having those vent holes below the vapor barrier could help to remove any gases that come up through the dirt/gravel. I read some people find their vapor barriers get a large air bubble from the gas.

3. We have an HVAC duct (sheet metal w/ three flex pipes coming off it) in this space that is hanging from the floor joists and is very close to one wall and worry that I won’t have the access to properly seal the vapor barrier against the concrete block wall.

a. Any ideas of how to seal this?

4. Our crawl space entry access is a ~3’ x 3’ notch in a concrete block wall. The bottom of this access sits only an inch above the gravel floor. When I go to attach the vapor barrier to the concrete block wall, I won’t have enough real estate to properly secure the vapor barrier to the concrete block wall. I’m thinking of taking the vapor barrier up the 1” concrete block wall—sealing it there-- and then onto the bottom of the crawl access sealing it there as well.

a. Sound reasonable? Other thoughts?

5. Which order should the foam board insulation and vapor barrier get installed onto the concrete block (exterior) walls (I’ve seen online guidance/videos showing both of the following):

a. Foam board insulation first, vapor barrier over top of foam board insulation?

b. Vapor barrier up the concrete block wall first, and then foam board insulation on top?

6. I also noticed that a corner of our crawlspace has a little (2” x 2”) hole that goes down at least a couple of feet—I couldn’t see further--, I think it is also the low point in this space. I’m wondering if the builder put that there for water drainage. There is no sump pump in the space.