One of our clients has been erecting a post frame home in Colorado Springs, which is over a crawl space. Here is our discussion in regards to insulating the crawl space.
“While I have your ear, I had asked you a question earlier about getting the code required R30 in the 2×6 floor joists of my raised floor. I looked into your suggestion of spray foam and I got some quotes from local companies and I was shocked! One company quoted me $16,000 to do 3″ in the floor and walls with some performance charts showing that the 3″ would satisfy the code (I’m a bit skeptical). I got another general quote of $1.10/board foot and that it would take 5″ (i.e. $5.50 / sq ft) or $12,650 just for the floor. The second company did suggest though that El Paso county allowed the R30 around the crawl space perimeter and no insulation in the floor… which leads me to my question…
What would be your thoughts of a non-vented crawl space using something like 15 mil plastic on the ground and up the sides the 18″ to the floor and the R30 spray foam from the ground to the floor level? I could get that done for around $2500. I’m still haven’t completely decided if I will used dense pack cellulose or BIBs for the walls but I’m pretty sure I don’t have the budget for spray foam in the walls.”
Mike the Pole Barn Guru Responds:
When I moved to Oregon from Eastern Washington in 1979, I was amazed at how different the construction techniques were from what I had grown up with. Eastern Washington was the land of full basements, whereas Western Oregon was predominately crawl spaces. The typical crawl space would have 6 mil black visqueen draped down the sides of the foundation and covering the ground, with R-19 unfaced batts used to insulate directly beneath the floors.
A variant of this was to use the crawl space as an air plenum, eliminating the need for heat ducts, and placing the unfaced insulation against the foundation.
This variant is basically a very slight spin away from what you propose to do.
Performance charts always frighten me as they general require some hocus pocus involving dead air space. Closed cell spray foam is R-7 per inch, so a claim of three inches in a system making R-30 sounds bogus unless the balance of the cavity is going to be filled with something like unfaced fiberglass batts. There is no question about closed cell spray foam being expensive, even the work I had done when we added the elevator shaft on the back of our home ran $2.80 per square foot for four inches thick.
Personally, I have no issues with what you propose to do and would probably take it a step further and utilize the principles of Frost Protected Shallow Foundation insulation below the base of my wall steel. https://www.hansenpolebuildings.com/2016/11/frost-protected-shallow-foundations/.