Concrete free floor, conditioned crawlspace
deb1221
| Posted in General Questions on
Seeking opinions/info on a concrete free floor in conditioned crawlspace for a new build. Want to save on cost of concrete.
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I am about to start a build on a home with a 4 foot crawlspace, and plan to not put a slab in the crawlspace. I don't think you technically need anything other than the vaper barrier.
My current plan is to excavate the entire crawlspace to the bottom level of the 8" footers, and do something similar to what Steve Baczek and Michael Maines (https://www.greenbuildingadvisor.com/article/minimizing-concrete-in-a-slab-on-grade-home) have done in place of concrete slabs. I plan to do only a single layer of floor sheathing since it is really just for ease installing plumbing, electrical, etc, and to protect the vaper barrier. I am not going to get too fussy with getting the stone layer perfectly level. I plan to put the ERV in the crawlspace, with a damper limited inlet pulling air from the crawlspace (and a grill from the mudroom to the crawlspace). The erv will also pull air from bathrooms. I also plan to put a dehumidifier in the crawlspace, which is probably redundant to the erv pulling air from the crawlspace.
I plan to install a interior perimeter drain at bottom of footer level, tied to a sealed sump pit. I am still deciding whether to tie the radon vent to the sump, or keep it separate. From there, the following order:
6" layer of 3/4" gravel
10 mil poly vaper barrier
1.5" EPS rigid insulation laid between 2x4 sleepers (i don't think i am required to have insulation on the floor of the crawlspace, but i feel like a bit of insulation down there will keep my main level floor warmer)
floor sheathing (maybe avantech x factor)
My structural engineer was fine with this with the 4' walls. Much deeper, and he would be concerned about lateral forces pushing in the footers/stem walls.
I plan to install a floor drain tied to the sewer line in the crawlspace. I am thinking about using a poured shower pan drain for this so that it can clamp/seal to the vaper barrier, and then have the top of drain level with the sheathing. If there was ever a leak in the house, this would allow the water to escape the crawlspace. But i have to look at the final floor elevation to see if i need a backwater floor drain there (IRC section 714). I can drop the dehumidifier condensate drain into that fl0or drain as well.
Opinions of others is appreciated.
Tracy
Your plan sounds interesting! Wondering about the floor drain. Had not thought of that.
deb,
"Wondering about the floor drain"
Check your code. Ours here would require one.
Looks like you posted this twice with slightly different wording, so I'm only going to respond here.
You can just leave a "dirt floor" in a crawl space if you want, then use a 10 mil or thicker vapor barrier over that. You don't need to do anything else. I would recommend at least a 12 mil reinforced vapor barrier though, I used 20 mil in my own crawl space. The thicker material costs a little more, but it's much more durable and is less likely to be damaged in the future if you have to do any work in there.
Prior to putting down the vapor barrier, you want to get rid of anything on the floor that might damage the vapor barrier, so construction debris and rocks should all be removed. Ideally you want an even layer of sand or other "soft ground" as the floor so that the vapor barrier membrane will be protected.
Bill
Sorry for the duplicate post. Having tech issues. Should there be insulation under vapor barrier?
There can be, but it's not typically installed in these cases. If the floor of the crawl space isn't at least down at frost depth, you should consider extending your perimeter wall instulation inwards with "skirts" around the perimeter.
Note that you CAN install insulation on the floor if you want, but you'll want to put something over it to protect it. The usual way to do this is with a thing concrete "rat slab", but you could also use plywood to build a subfloor.
Bill