R-value is the term given to thermal resistance to heat flow. The higher the R-value of an insulation product, the more effective the insulation properties. Spray polyurethane foam comes in a range of densities and cel structure. Low density foams are referred to as Open Cel SPF while higher density foams are referred to as Closed Cel foam. 1.8-2 pound polyurethane foam has the highest R-value of readily available spray foam insulation used in homes and buildings.[4] 

Roof Spray Foam Insulation

Closed-cell (aka two-pound foam) is denser than open-cell at about 2 pounds per cubic foot. Its R-Value is between 6-6.5 per inch. As a result, this kind of foam is much more expensive than its counterpart. The reason closed-cell doesn't need a vapor retarder is because it already has one. It's permeance is 0.8 perm, which means it can handle cold climates without the use of an additional board or drywall. Closed-cell uses hydroflurocarbons (HFCs) as part of its makeup. However, this material has been known to have a high global warming effect. If you want a green insulation solution, this is not the material to use. A way to avoid this and still use closed-cell is by installing it alongside fiberglass batts. http://www.youtube.com/embed/ggLAUsiuI_o
The roof must be thoroughly cleaned, and allowed to dry thoroughly. This is a critical step to ensure a successful coating application. Be careful not to damage the lap seams. Care should be taken when pressure washing not to disturb the integrity of the underlying roof membrane particularly where there are adhered seams. Refer to the specific coating manufacturer you are using for their specific requirements for roof preparation.
I've seen this only once, and it was with closed cell foam, but I've heard of it happening with open cell foam, too. I don't know the details, but I've heard it could result from a bad batch of chemicals, improper mixing, or too high a temperature. Whatever the cause, it's not a good thing. The photo below shows how the spray foam pulled away from the studs. A little bit of uninsulated area like that adds up to a lot of heat loss/gain when the whole house has that problem, as it did here.

How Much To Spray Foam A Shipping Container

I'm in the process of redoing my basement and read through the posts. I took out one inch styrofoam covered by 1/4 " beadboard and installed 2X4s and plan on putting in fiberglass batts between them(r-13) with 1/2 in drywall over top of that. Do you think I will see a significat increase in heat control? Should I have done more?... it's a little after the fact, but still curious to know if I will see a big difference based on your experience.

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