Building codes require foam plastics to be fire tested, usually with ASTM E84 as a minimum criterion. Some polyurethane foam manufacturers produce two formulations. One type is a class 2 foam with a flame spread of 30 and smoke development of 220 (class 2 foam is less than 75 flame spread and less than 450 smoke development) at Iм, and the other is a class 1 foam with a flame spread of 25 or less and smoke development of 210. All cellular plastics such as spray – foam products are required by building codes to be covered by a 15- minute thermal barrier when installed in a habitable area. A 15-minute thermal barrier can be 72" sheet rock, spray cementitious products, or other tested materials. Exposed foam is a potential fire risk and should be protected from open flames during the construction phase and prior to installation of the thermal barrier.
One manufacturer admitted that full-cavity applications of polyurethane foam are two to three times as expensive as conventional insulation systems. One should note, however, that a 2000- ft2 home with 2X4 walls, Iм of polyurethane foam, and an R-ll batt cost slightly more than the same wall with an R-15 batt.10