Insulating a Crawl Space Ceiling
I’m looking for product suggests for insulating our crawl space ceiling.
The crawl space is “almost a basement” with 7 ft ceiling, ICF walls, and poured concrete floor. Due to flood mitigation requirements, it has no exterior doors and windows and can’t be used as a living space. It contains all of our HVAC and mechanicals. We are in Northern Alberta in a sub-arctic climate.
I have two goals for the insulation project:
1. Energy efficiency: We currently heat the main floor of our bungalow with a combination of passive solar, in-floor radiant and wood stove. A fair amount of heat leaks into the crawl space.
2. Cold Storage: The crawl space is a bit too warm to use as cold storage for garden produce. Most of the year it’s about 13 – 15 C (55-60 F). My goal would be to maintain about 7C (45 F). There are two wall panel electric heaters in the crawl space, set to kick in a 7C, but it never gets that cold.
Building code would require some kind of fire mitigation for any exposed styrofoam even through we don’t use any combustable fuels in the crawl space (100% electric). I’m trying to keep this project as cheap and simple as possible and DIY.
I’m wondering what’s the best insulation product to use and if there is any need for vapour barrier. Your suggestions would be much appreciated!
Caroline Wagenaar
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Replies
I don't think you're likely to get your basement/crawlspace to stay as cold as you want. I would insulate the walls instead. The easiest (but not cheapest) way to go would be to use a polyiso variant that is rated to be left exposed, such as Dow Thermax or Johns Manville's CI Max.
If you really want to try insulating the ceiling, I would use polyiso, but I'm not sure if the "rated to be left exposed" materials would be OK on a ceiling and still meet code. You'd want to check with the manufacturer if they have any data on that. That issue goes away if cover the insulation with drywall or plywood/OSB.
You could also use rigid mineral wool, which wouldn't need any fire barrier, but it's the most expensive option. A vapor barrier shouldn't be needed in this location unless you have a specific reason to want to use one.
Bill
Thanks, Bill. I didn't know about the rigid mineral wool and will check out the polyiso.and see if those products can be used exposed on the ceiling.
I'm curious about your suggestion to insulate the wall. They are ICF (R22) and only about 18" is above ground. The rim joists are insulated with rigid foam board sealed with spray foam and then a mineral wool batt (double wall construction). I was under the impression this would be adequate for a crawl space wall.
Sorry, I must have missed that you had ICF walls. There probably isn't a whole lot to be gained adding insulation to those. If those are already insulated, then I'm wondering a bit as to why you want to insulate the ceiling too? Usually only one or the other of the walls or ceiling will be insulated in a crawlspace or basement. If your concern is about energy loss, it might make more sense to add some insulation to the floor, or at least a skirt around the perimeter coming in maybe 4 feet or so from the bottom of the walls (assuming you don't already have subslab insulation).
Bill