Hello,
my girlfriend and I are possibly purchasing a house that has an addition on the rear, and the work seems very well executed. However, this d addition is supported by 8" sonotube concrete posts, and there is crawl space under the addition. This crawl space is very restricted, between 18" and 24". I took a look underside, and the wood is clean, no traces of moisture or rot. This addition is not insulated from below. Considering the high prices of electricity, we would like to insulate the underside.

Am I correct in assuming that urethane expansive foam (the purple one) would be the best insulation/vapor barrier? What would you reccomend if not this product?

The home is located in Quebec, where the winters can be quite harsh.

Thank you.

 

I can't imagine the addition got completed and inspected without a provision for insulation.

Not only would I be doing the sprayed foam, I would be trying to create a wind barrier at the perimeter of the structure to prevent wind washing of the underside of the structure.