Why Flash and Batt Makes Sense
Closed-cell spray foam and fiberglass batts can be used together to maximize performance and minimize cost.
Synopsis: Closed-cell spray polyurethane foam may be the best insulation available today, but it is expensive. Fiberglass batts, on the other hand, are inexpensive and insulate fairly well, provided they are installed correctly. Combining the two, in a system called flash and batt, couples the air-sealing strength of spray foam with the cost-effectiveness of fiberglass batts. Flash and batt begins with a thin flash coat of foam sprayed against the inside of the sheathing. The remainder of the framing cavity is then filled with fiberglass. This system can save up to $2 per sq. ft. over the cost of using foam exclusively. This article, by designer Michael Maines, includes a list of five critical details that must be attended to if flash and batt is to work properly: foam thickness, batt thickness, water vapor, humidity control, and climate.
Closed-cell spray-polyurethane foam may be the best-performing insulation available today. It seals against…