Spray foam insulation is a great product that air seals and insulates a home better than any material currently on the market. However, closed cell spray foam is really the only great choice because it does not allow for moisture to be absorbed because the cells are closed. This avoids issues with mold and mildew and makes the closed cell spray foam its own vapor barrier after 3 inches of nominal material is applied. Combining closed cell spray foam with open cell spray foam may be the most energy efficient system for interior cavity insulation that can be performed.
Combination Spray Foam Insulation System
In order to reach a point in with the dew point that occurs within the insulation material does not form condensation inside framing cavities, there needs to be a minimum of 2 inches of closed cell spray foam insulation at an R-7 per inch applied. Ideally, 3 inches nullifies the dew point and meets residential building code as a vapor retarder. In order to save money, however, many insulation contractors apply 2 inches of closed cell spray foam and then fill the rest of the framing cavity with fiberglass or cellulose. But filling the remainder of the cavity with open cell spray foam, allows for the best possible coverage and greatest amount of air sealing of any current insulation system.
Combination Spray Foam Insulation System Application
The closed cell spray foam is sprayed in at a nominal depth of 2 inches in typical applications. Because there is a significant amount of heat generated when spraying closed cell foam, the application has to be allowed to cool for an hour before applying the open cell spray foam. This usually is not an issue as the insulation technician can start on one end of a home and work toward the other end giving the insulated cavities plenty of time to cool.
The open cell spray foam is then applied in every other framing cavity in order to give the insulator room to cut the insulation flush with the framing cavities. The remaining cavities are then insulated after the initial cavities have been trimmed.
Using this type of insulation system is more expensive than conventional insulation systems, but will see significant savings compared to any other form of insulation system. The only other insulation system that will perform better is using closed cell spray foam for the entire application. However, the costs to apply the same amount of insulation would be dramatically more and the payback much longer.