Saturday, March 12, 2011


In preparation for insulating the house, which will occur within the next month, I found a local insulation company that provides expanding spray foam. After two missed appointments, the owner of the company finally came by on Friday to give me an estimate. He seemed a bit surprised at my request for expanding foam insulation, and was almost ready to talk me out of it. I'd done my research and pointed out the benefits that I wanted which mostly centered around more R value per inch as well as the all-important air-tightness that foam cavity fill provides.

He seemed fairly intent on talking me out of the foam product, and we finally settled on a quote that involved a hybrid system. His quote was to provide a one-inch cavity spray on all exterior walls, which I would then fill with fiberglass batts. I also asked him to provide a quote for spraying the top of the roof to an R30. Since the current tar and gravel roof is serviceable, this could wait until later, however, I'll be installing at least three new skylights and changing around several roof vents for plumbing and fireplaces, etc. It would be nice to do everything at once. I've explored several modalities for roof coverings, ranging from a living roof (my dream) to an EPDM roof, to new rolled double-layer fiberglass systems.

The life-cycle costs all seem to be about the same, therefore the main variables that come into consideration are the ease of installation and environmental impact.

I was a little bit surprised when I received the quote in my email this morning, and the price quoted was $13,500.
This involved the following:
Spray one inch of polyurethane foam into the exterior wall cavities (giving us approx R5)
Spray the floor joists with one inch of polyurethane foam (R5)
Spray the roof with 4.5" polyurethane foam (R30)

After spending $13k, I would still be left with the task of insulating the remaining 2.5 inches of the wall cavities, plus 9" of the floor joists.

The options I am entertaining at this point are:

  • 4.5" foam board application on roof with a membranous covering
  • Cavity fill polyurethane foam system. In this case I would apply a 6mil poly after passing the rough plumbing and electrical inspections. I would purchase the required product, which I found on Ebay and pour the insulation into the cavities. To ensure a good, seamless pour, I was contemplating pouring four feet of height at a time. This system would allow me to obtain R7 per inch, plus an excellent air-tight seal, effectively giving me almost R25 in my exterior walls.
  • 9" fiberglass batting on the floor joists, coupled with a 6mil poly underlay. This gives me R28 on the floors, not including the insulating effects of the radiant barrier that I am installing prior to the radiant floor pour.
  • Foam Board XPS (Owens Corning  Formular 15) Roof R5 per inch, 4 inches at $1.55 per square foot. Total material cost of $2558 for R20  Pros: easily available from Home Depot, easily transported to work site, perfectly flat surface as a base for whatever covering we choose. Cons: potential gaps between joints means a possibility for air leakage.
  • Pour in place two part polyurethane foam from these people which will give me R7 per inch, 4 inches at $1.53 per square foot. Total material cost of $2524.50 for R28. Pros: ease of application, minimal waste, can be poured in place relatively quickly providing a seamless roof covering. Higher Rvalue per inch. Cons: not a perfectly flat surface, leading to the possibility of dips in the roof and a potential for standing water.
  • Estimate of 600 cubic feet of wall space. Pour in place two part polyurethane is $2760 giving an Rvalue of 34.5. Pros: Air sealing of building envelope, higher Rvalue per inch. Cons: Difficulty of installation, involves multi-step process of 6mil poly, several pours per wall cavity, plus the risk of cavitation.
  • Fiberglass batting. Estimated material costs: $1700. Pros: Low cost, ease of installation. Cons: No air sealing, substantially lower Rvalue per inch.
  • Fiberglass batts with 6 mil poly in a staple-up configuration. 9.5 inches of fiberglass batting will provide R28 on the floors. Total cost $975.


  1. Did you see the aircrete link I sent..I can't help but think you could do expanding foam for less than that. Why was he talking you out of it? Price?

  2. Hey Heather, Thanks for the link. I called them and found out that their closest dealer is in Washington State. They offered me a franchise, but at $60k, it is cheaper to just find another solution. Thanks so much for doing some research on my behalf. Librarians everywhere would be so proud :-)