Spray Foam Insulation
WHY USE SPRAY FOAM INSULATION?
Spray polyurethane foam (SPF) is better than any other type of insulation at reducing air leakage.
With foamed-in-place insulation, it is relatively easy (though not inexpensive) to fill wall and ceiling cavities completely. Closed-cell spray foam provides a higher R-value per inch (6.5) than less expensive insulation types like cellulose and fiberglass (3.5 to 3.7).
Most spray polyurethane foam is called “two-component” foam. Two ingredients—conventionally called “A” and “B” components—are mixed on site using special equipment mounted in a trailer or truck. Heated hoses convey the components to a mixing gun that sprays the chemicals on the surfaces to be insulated.
A chemical reaction begins as soon as the chemicals are mixed. The liquid mixture foams, expands, and eventually hardens.
WHAT TYPES OF SPRAY FOAM INSULATION ARE USED?
Two-pound foam, also known as closed-cell foam, has a density of about 2 lb. per cubic foot and an R-value of 6 to 6.5 per inch. Two-pound foam is significantly more expensive than half-pound foam.
Closed-cell foam is a vapor retarder. Two and a half inches of closed-cell foam have a permeance of 0.8 perm.
The blowing agents in most types of closed-cell spray polyurethane foam are hydrofluorocarbons (HFCs) with a high global warming potential. Because the global warming potential of these damaging blowing agents is 1,430 times more potent than carbon dioxide, many green builders avoid the use of closed-cell spray foam.
Closed-cell is more expensive and does not perform well in this zone.
Half-pound foam, also known as open-cell foam, has a density of about 0.5 lb. per cubic foot and an R-value of 3.5 or 3.6 per inch.
Open-cell foam is relatively vapor-permeable. Three inches of open-cell foam have a permeance of 16 perms.
Some of the low-density foams are made in part from bio-based raw materials — for example, soybean oils — in place of a portion of the petrochemicals. Open-cell foams use water or carbon dioxide as the blowing agent.
Compared with closed-cell polyurethane, open-cell products use significantly less material, making them attractive from a resource-use standpoint. However, open-cell foams have a lower R-value per inch than closed-cell foams.
Open-cell seals as well as closed and is more economical than Closed-cell and performs well in this zone. For this reason, Pyramid Homes uses open-cell spray foam insulation when building homes.