By Mason Knolwes
Previous issues of Modern Materials have examined some of the myriad advantages to specifying spray polyurethane foam (SPF), especially its insulation value and air barrier qualities. This spray-applied, insulating foam plastic is installed as a liquid and then expands many times its original volume. These spray foam formulas can be tweaked to have many different physical properties depending on their desired use. For example, the same basic raw materials can make an insulation foam that is semi-rigid and soft to the touch, but can also create a high-density roofing foam resistant to foot traffic and water.1
As building insulation, SPF can provide high levels of R-value, while serving as an air barrier and offering assistance in moisture control.2 In roofing, it insulates and helps eliminate thermal bridging (e.g. through fasteners or gaps in decking), while helping to provide a long-lasting roofing assembly.
Whether by prolonging a roof’s service life or by improving the thermal performance of a building, spray polyurethane foam can enhance a building’s energy efficiency. However, one added bonus is the material’s ability to help improve structural integrity—a particularly salient advantage in areas facing the potential of high-wind events.
Riding out the storm
Marlene Hillen of Port Lucie, Florida, initially faced skepticism in getting her homeowners’ association to approve the installation of an SPF room over her existing shingle roof. However, her persistence in educating those about the possibilities of plastic products paid off. “In my neighborhood, more than 40 of my neighbors lost their roofs and most of their belongings last season from three hurricanes hitting us in ten months,” she says. “My roof that was sprayed with SPF didn’t leak a drop.”
A related example can be found in David Gautier’s Pascagoula Ice and Freezer Plant in Mississippi. The ice plant is a 4180-m2 (45,000-sf) complex consisting of the original turn-of-the-century building with additional sections added every 20 years or so. The original construction comprised brick walls with wood tongue-and-groove decking.
With its Category 4 winds—200 to 233 km/h (125 to 145 mph)—and an accompanying 7.6 to 9-m (25 to 30-ft) storm surge, Hurricane Katrina destroyed a vast area of the Mississippi Gulf Coast. However, the Pascagoula Ice and Freezer Co. sustained no damage in the SPF-insulated sections. (In places that lacked SPF, pressurization from the high winds blew out portions of the roof deck.)
“These building have not only survived Hurricane Katrina, but also three other major storms—Frederick, Elena, and George,” explains Gautier. “The spray foam definitely helped keep the buildings together.”
Building owners who request SPF be installed for thermal efficiency reasons could also benefit when more building officials recognize the material’s advantages in terms of structural integrity. By examining the characteristics of SPF, a better understanding can be gained of how this plastic product helps hold materials together, while also assisting in making the building more energy-efficient.
SPF is sprayed on as a liquid and then expands to form a rigid foam plastic with great adhesive characteristics. Since it bonds so tightly to a substrate, it is very hard to pull off in high winds. When installed over concrete panels, SPF resisted up to 47.4 kPa (990 psf) of pressure in Factory Mutual’s (FM’s) wind uplift pull test. It glues the whole structure together, increasing the structure’s rigidity with around 172.4 kPa (25 psi) of tensile strength. However, it still has some flexibility to allow building movement without cracking.
Monolithic water barrier
SPF is installed as a liquid and then rises and expands to fill in cracks and crevices. Closed-cell SPF has been approved by the U.S. Coast Guard and Army as a water-resistant flotation material and is accepted as a roofing system. The Federal Emergency Management Agency (FEMA) has added SPF as a recommended building product to reduce flood damage in buildings.
Adds structural strength
The National Association of Home Builders (NAHB) Research Center tested SPF and determined spray foam-insulated wall panels increased the racking strength of both wood and metal stud walls 70 to 200 percent, depending on the type of sheathing used. The NAHB report concluded, “in a racking event such as a hurricane, there would be less permanent deformation of the SPF-insulated walls.” (See “NAHB Racking Research.”) Versatile When installed to the outside of buildings, SPF reduces the profile and minimizes building movement so high winds are less likely to catch a corner or tear the substrate. When added to the inside of a structure, spray foam ‘glues’ the whole building together, enhancing overall wind and pressurization resistance.
SPF is a natural shock-absorber; even heavy wind-blown items such as tree limbs, metal panels, and concrete tiles usually only superficially damage spray foam substrates. When wind-driven debris damages the surface of the foam, it resists peel off and often continues to provide water resistance to the interior of the building.
Some deck and roof membrane failure occurs when high air pressure forced into, or developed inside, the building literally blows up the roof deck or roof membrane. SPF eliminates air infiltration that can let high air pressure inside the building. By ‘air sealing’ the building, SPF minimizes the potential for interior pressurization and its ensuing damage.
Typically, damaged SPF can be easily repaired with a compatible sealant or by cutting out the damaged portion and installing more foam.
1 As spray foam formulations vary by manufacturers, design professionals should consult their suppliers’ specification sheets to understand the chosen product’s exact properties.
2 As insulation formulation may vary from manufacturer to manufacturer, design professionals should consult the suppliers’ specification sheets to understand the exact properties over time, including the actual R-values. Factors affecting the R-value include thickness of application (i.e. the thicker the foam, the better the aged R-value), the substrate, and the covering systems used (i.e. the lower the perm-rated covering and substrate, the higher the aged R-value).
Mason Knowles is the executive director of the Spray Polyurethane Foam Alliance (SPFA). A frequent contributor to Modern Materials, he can be contacted via e-mail at email@example.com.