We have a crawlspace under a portion of our house and the floor is very cold above it. I set out to add some insulation to try to reduce heat loss and improve comfort.
Notes:
- The crawlspace is below the portion of the house furthest from the furnace. The pressure in the air ducts in this area is pretty low, which no doubt contributes to the cold floors.
- The crawlspace is conditioned space, but because its so far away from the furnace, the air temperature and pressure being delivered is quite weak.
- The previous owners had already installed spray foam insulation in on the crawlspace walls and where the foundation meets the framing. I goofed and planed this project without realizing there was insulation on the wall (I thought it was only where the foundation meets the framing), but decided to proceed anyway because the spray foam is only ~1.5” thick on average, which is probably ~R6-9. Its recommended to insulate crawlspaces with R15-20 so there was room for improvement.
- I installed 4” of foam board insulation, in 2x2” thick layers. In total I used 16 4’x8’ sheets, (512 sqft) at $47 each, for a total of ~$750.
- Because the foam board was installed over an uneven spray foam surface, I had to fill the gap from between the wavy spray foam and the rigid foam board. I used 20oz cans of “Great Stuff” spray foam for this. Not ideal, but it ended up working out. In total I spent ~$120 on additional supplies (tape, construction adhesive, spray foam).
- It was a rather physically demanding job. The space was cramped, dark, and I had to manipulate and cut a bunch of rather large foam board pieces into place. Took probably 8-10 hours total, and was really hard on my knees in particular (I didn’t have knee pads and I regretted it).
- Not sure how much it will actually end up helping. I have a digital thermometer in the space and I’ve been monitoring pre- and post-, and am watching to see if I notice an improvement in the temp. Before I did the job I saw temps of 52, 55, and 57 degrees. It could be that with the spray foam on the walls (even only 1.5”), most of the heat loss of is through the concrete floor. If I don’t see an improvement, I might consider adding a layer of foam board insulation on the floor.
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