The best thickness for spray foam is dictated by where the foam is going to be sprayed both in terms of geographic location and the exact location within the structure itself.
Your EcoInsulation technician will assist you in determining the right thickness of spray foam material to be applied. Spray foam can be contained or it can be left exposed. An example of a contained application is when you spray foam in wall cavities between studs and then after the foam has cured, cover the foam with drywall or another surface material. The thickness of the wall studs will determine the maximum thickness that you can achieve with spray foam. Foam can also be left exposed. If so, then there is little constraint on the thickness of spray foam. Places where foam is exposed include basements, attics, barns, inside of vans – places that need insulation but are not intended to be used as living spaces.
Your climate is a key determinant of how much spray foam you need to achieve the maximum comfort and energy savings from your investment in foam. Figure on an R-value of around 6.5 for closed cell foam and around 3.0 for open cell spray foam. The more R-value you desire, the thicker the foam application you will need. For an attic floor, your climate might dictate an R-value of 30. That means you will need 4-5 inches of closed cell foam to achieve that value. If you choose open cell foam, then you will need 10 inches. If your attic joists are not 10 inches thick, then using closed cell foam will be your best option. Also keep in mind that closed cell foam is also a vapor barrier and you may want to used closed cell foam to keep condensation out of your attic.
According to industry guidelines, wall insulation should have an R-value of from 13 to 20, and if these are basement or crawl space walls, 5 to 15 is recommended. Flooring is another place to utilize spray foam’s triple play (insulation, air sealer, moisture barrier). Depending on your region of the country, you could be looking at an R-value of 13 to 30.