Spray Polyurethane Foam Roofing

11/04/2008 by Rob Sommers

According to the US Department of Energy, heating and cooling costs account for 50%-70% of the energy used in an average home. Given the cost of energy, this is a concern for most of us. We know enough to turn off the lights to conserve energy but don’t think about insulating our homes/buildings in order to save energy, money and help the environment.

Spray polyurethane foam (SPF) is a type of insulation that is gaining market share over traditional types and methods of insulating. SPF is made up of two chemicals that, when mixed together in the proper proportions, will start a chemical reaction that causes the mixture to solidify and expand at a very rapid rate. Literally before your eyes, the surface onto which the SPF chemicals have been sprayed will fill up with dense, lightweight foam.

This foam has a very high insulating value. Closed cell SPF foams have an R-value of over 6 for every 1” of thickness. Due to the rapid expansion the foam efficiently fills in around gaps, blocking, piping, wiring and other obstructions in walls making it an even more efficient insulator. When used as roof insulation, SPF can act as its own flashing and can be applied to provide pitch to roof drains or form roof cants at the intersection of vertical obstructions.

Skilled applicators use an expensive delivery and mixing system that resembles a paint sprayer with a long supply hose. The big difference is that two chemicals are delivered to the tip of the sprayer. Pumping equipment delivers the liquids at a predetermined rate, and the applicator moves the spray head back and forth over the substrate. Immediately the chemical reaction begins and the liquids solidify and expand. By changing the speed at which the spray head is moved, or by applying multiple layers, the applicator can “sculpt” the foam into the desired shape, pitch or thickness.

Spray polyurethane foam is an extremely versatile building material. As floor ceiling and wall insulation it can provide high levels of R-value, while providing an air barrier and moisture control. For roofing, spray polyurethane foam eliminates thermal bridging through fasteners or gaps in decking while providing a roofing system that has a life that can be extended by re-coating or recovering. It can also help provide structural rigidity.

What Does It Cost?
According to the 2009 version of Means Building Construction Cost Data, closed cell spray polyurethane foam insulation costs about $1.08 per square foot per 1” thickness in wall cavities. When used as roofing, including the required spray on silicone coating, the cost is about $3.44 per square foot per 2” thickness.