Design for sealing open dirt floor crawl space
Hi I have a 28′ x 30′ crawl space that has a dirt floor and CMU walls. Ceiling of it is exposed with pipes and wires running around everywhere. I live in western Colorado so it’s dry most of the year. I get some ground dampness, but no flooding, during a few months of summer when my hillside gets saturated in places from a natural spring in the rock ridge above me. I have pipes outside of the crawlspace that provide drainage and I keep the soil sloped away from the home walls. My adjacent slab walkout basement has 4″ gravel, 2″ sand, and vapor barrier under the slab. It seems to drain well also.
I have radon gas coming up from the dirt so I’m having a contractor install the basic radon system, and then planning on sealing my crawl space floor, walls, vents and doors, but leaving its ceiling plain for now.
I want to block and pump out the radon gas as well as block out moisture that sometimes has made my wood joists get damp and grow small surface mold.
This is my plan, does it should good?
1. pay radon mitigation company $1,800 to install adjacent slab and crawlspace system to direct the radon upwards to roof. Confirm it’s working with retests.
2. Install a 26′ x 36′ plastic (non organic) underlayment on top of the radon vapor barrier, terminating it at the floor/wall corners. Unknown type or best kind at this time. Suggestions? The radon vapor sheet is 4 or 5mil string reinforced plastic sheet.
3. Install single sheet of 30′ x 40′ 45mil EDPM pond liner on top of the underlayment material. Seal it above the radon vapor barrier about 12″ – 18″ up the crawl space walls with a double bead of construction adhesive (2 to 3″ apart).
4. Install foil backed 1″ to 2″ foam insulation to the crawlspace walls from 3″ below the top to where the wall meets the ground, overlapping the pond liner by 12′ – 18″. Kind and type suggested? I was going to use Rmax Thermasheath-3, 1 in. x 4 ft. x 8 ft. R-6 Polyisocyanurate Rigid Foam Insulation Board. It’s $18.50 with tax per sheet. I have about 500 SF of wall to cover.
5. Cover this insulation with foil sandwiched bubble insulation to help reflect the heat that my crawl space emits from the floor above it (which has my wood stove on it), radiator oil heater (put on a timer), or future heat duct. This piece will be adhered evenly to the foam board insulation dimensions.
6. I was then going to cut about a 8″ wide piece of 6 or 10 mil clear plastic and glue it from the insulation top edge over the CMU wall top edge and terminate it just short of the sill plate. This maybe overkill. I don’t have termites here and don’t expect them, but it can be removed if necessary for such inspections without messing with the rest of the encapsulation materials.
I’m trying to lock out as much moisture, radon, dirty air, etc from the crawl space sources outside while locking in any heat that it collects from the sun (faces south and west sun) and household heat sources. I am going to use construction glue to adhere all materials together, or to the CMU walls, which I’ll dust a couple of times before applying. Should I use glue as planned on the insulation foam board or use masonry nails or some other mechanical hanging?
The pond liner and underlayment is priced at about $1,200 delivered. The insulation will be about $600 for both kinds together. And misc materials glue and hardware about $150. So about $2,000 for materials. Am I planning anything wrong?
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