Crawl Space Conversion

I’m looking at retrofitting the crawl space in my house to add stego crawl vapor barrier to the floor and insulation to the walls, I’m in zone 5 as well.
Currently there are two separate conditions in the crawl space. The main part of the house is unvented, has no vapor barrier on the floor, has no insulation on the CMU stem walls, and no insulation at the rim joists. This space is currently conditioned by a single supply air register.
The second condition is a crawl space that originally appeared to be vented but batt insulation has subsequently been placed in the vents to “plug” them. The floor joists in this space are insulated along with a deteriorating 1″ layer of EPS on the cast in place concrete walls.
In both instances the stem walls are approximately 24″ tall and the grade is anywhere from 7-14″ below finished floor elevation so the majority of the crawl space is below exterior grade. The exterior wall assembly in both instances working from outside to inside consists of Brick, 1″ Air Gap, 1″ Rigid Insulation, 6″ CMU or CIP Wall.
I’ve been trying to sort through all of the papers and research out there and trying to come up with the best solution to where to terminate the vapor barrier and how to best insulate the walls.
Currently I am contemplating insulating the walls and rim joists with 1.5″ xps or eps with fully taped joints and then covered with mineral wool to act as the thermal barrier (i believe there are some products that allow this like rockwool comfortbatt 80 based upon the bulletin i have read). I’ve sketched up what i am thinking in the attached and am hoping to get some feed back as to if i am on the right path. I may be going overkill with the insulation but would rather do that, than underkill.
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Replies
jalb32,
Your plan looks sound to me. I would run the vapour-barrier up the walls to the sill-plate. That sill-plate is my only concern. If it doesn't have a capillary break between it and the masonry below, I would be worried about eliminating its ability to dry as it will also be colder once enclosed by the foam.
I assume there is no real good solution to no capillary break there? Right now the sill plate is set only on what appear to be just batt insulation for a sill sealer in lieu of the newer plastic sill seals.
With the majority of the sill plate being above grade and the other parts that are not above grade being in non-irrigated mulch beds I assume the need for heavy drying to the inside or concern of moisture at the sill plate would be minimal?
jalb32,
The risk comes from moisture traveling up the masonry walls from the footings through capillary action. There is a very good chance insulating the sill-plates will be fine. The problem is it is so case specific you can't really predict whether that will be true. I'd be inclined to leave the top of the plates exposed. You suffer a slight energy penalty, but maintain their ability to dry.
You can slightly jack up the sills and insert a thin plastic sheet, but that's a big job.
One more question, I've been thinking about where to place the vapor barrier I will be installing here and stumbled upon a calculator that helps to find the dew point in the wall/insulation setup I described above. I've attached a photo of this with the conditions from this morning for an example. In a majority of the winter the dew point will be within the mineral wool insulation layer, with that said would it be best to place the vapor barrier so that it encapsulates the mineral wool layer to keep the warmer/moist air out of that layer? Or is it best to place the vapor barrier directly against the wall/rigid insulation, similar to what I've shown previously.
A link to this calculator is below in case anyone else finds this handy. https://ageng.w3.uvm.edu/walls/index.html
jalb32,
I missed that you had that much mineral wool. Like any wall, above or below grade, you want the ratio of permeable to impermeable to be such that the dew point is in the foam. Otherwise you will get condensation on the interior surface. See Assembly #2 in this link: https://www.greenbuildingadvisor.com/article/three-ways-to-insulate-a-basement-wall
The vapour retarder needs to go against the concrete. The interior (batt) portion of the wall needs to be vapour-open so it can dry to the inside.