If there is no vapor barrier, double it to one square foot of NFA for every 150 square feet of attic floor space (half for intake, half for exhaust). These are broad guidelines, so be sure to check with your local building code. (Source: NRCA, Stanley Complete Roofs and Siding, Air...
SPF also provides superb capabilities as both an air and water barrier. Not only does it protect against water and moisture intrusion, but it also reduces air movement through the roof system, improving indoor air quality and lowering the energy use of the building. Because the roof of any s...