Severe weather is the toughest test for any roof system. Each year, insurance claims for hail damage average $1.94 billion and wind damage claims are more than $160 million1. In 1996, serious hail storms near Dallas and Big Springs, Texas, resulted in an estimated $25 million in property and roof damage2. Ten years ago, Hurricane Andrew wrought unprecedented economic devastation, resulting in more than $26 billion in damage in the United States3. Before the September 11 terrorist attacks, Hurricane Andrew was the most expensive disaster in U.S. history. It is still the costliest natural disaster the country has ever experienced.

The insurance industry identifies roofing as the primary contributor to disaster-related insured losses. As a result, building owners face escalating insurance premiums and contractors are being asked to provide roofing systems with proven hail- and wind-resistance abilities.

Manufacturers, consultants, industry associations and contractors spend countless hours and dollars every year conducting in-field performance testing of various roofing systems in the hopes of identifying those that can withstand severe weather, provide superior performance throughout the lifecycle, offer increased sustainability, reduced energy consumption and still remain affordable for the average building owner.

Recent studies and several published papers by industry leaders have discussed the in-field performance, installation and self-flashing capabilities, durability, sustainability and energy efficiency of spray polyurethane foam roofing systems. But how do these systems perform when Mother Nature does her worst?


In his paper "Hail Damage to Roofing: Assessment and Classification," which was presented at the Fourth International Symposium on Roofing Technology, William C. Cullen of the National Roofing Contractors Association examines hail damage susceptibility factors for eight generic roof systems.

Mr. Cullen's study shows that among all the systems tested, only SPF protects the substrate from damage during a hailstorm. By protecting the substrate, SPF also protects the building interior and contents.

But these results are for "generic" systems, and SPF is an engineered material. Manufacturers can-and do-modify the components of the system on the molecular level to provide best performance for a specific application, geographic location or challenge facing the system in the field. One such modification has resulted in the ALPHA Roofing System.

The Performance Based Studies Research Group ( was developed by Dr. Dean Kashiwagi at Arizona State University's Del E. Webb School of Construction in 1994. The PBSRG, a non-profit research group, developed the ALPHA Research Project to analyze performance information and identify high-performance roofing systems, specialty contractors and facility systems in the construction industry.

For the purposes of the ALPHA project, an ALPHA Roof System is defined as any low-slope roofing system with a documented performance that meets or exceeds that of a conventional, 20-year-life-expectancy, low-slope, built-up roofing assembly.

The program is open to all roofing systems. Any manufacturer, product or group of contractors that can demonstrate-when randomly sampled by PBSRG every other year-that 98 percent of their customers are satisfied with their roofs, 98 percent of their roofs don't leak, and they are willing to have all newly installed roofs over 5,000 square feet surveyed yearly, qualifies for inclusion in the program.

Since its inception in 1996, only one system has qualified for ALPHA: spray-applied polyurethane foam and coating. In addition, according to the publicly available PBSRG Web site reports, there are 10 ALPHA contractors across the United States. To date:

Four hundred eighty-four roofs have been inspected.

Three hundred forty-one customer responses have been received.

The oldest installation is 30 years old.

The average installation is 10 years old.

Ninety-nine percent of the jobs are completed on time.

Ninety-nine percent of the roofs do not leak.

Ninety-nine percent of the customers are completely satisfied.

The average contractor performance rating is 9.7 out of 10.

Ongoing research at the PBSRG evaluates the performance and hail resistance of different types of elastomeric coatings for SPF roofing, both in the laboratory and in the field. In the published report, "Hail Resistance Test of Sprayed Polyurethane Foam (SPF) Roof Systems," the following findings were discussed.

In the lab, three major coating types with varying thicknesses, SPF foam densities, weathering and granulation were subjected to the FM-SH test of dropping a 356-gram (0.8-pound) steel ball with a 45-mm (1.75-inch) diameter from a height of 5.4 meters (17.8 feet) to simulate severe hail impact. The successful systems were then re-tested in freezing and sub-freezing temperatures.

The results showed that urethane-coated SPF had the highest resistance to the simulated hail damage with the minimum-specified system of 30 mil of coating and 40-psi compressive strength SPF. Granulation, accelerated weathering procedures and temperature did not influence the performance of the urethane-coated samples in the lab testing.

In the field, urethane-coated SPF roofs with documented hail resistance performance in Torrington, Wyo., and Dallas/Fort Worth, Texas, were selected for the study. It was noted that many of the metal mechanical penetrations on the roofs showed damage from severe (golf-ball sized) hailstones, but none of the roofs showed any rupture, and the damage did not result in any premature failure of the SPF system.


SPF has gained recognition with industry experts for its ability to withstand high wind uplift and blow off. It offers superior adhesion with no need for fasteners and because it is monolithic and spray-applied there are no joints or edges for the wind to grab onto. Lightweight yet rigid, it provides extra strength to help the roof stand up to the forces of nature.

After Hurricane Andrew, Thomas L. Smith of TLSmith Consulting, and then research director for the National Roofing Contractors Association, went to Florida to see first-hand how SPF had weathered the storm.

In his published report of his findings post-Andrew, Smith provides a detailed assessment of the wind performance of 11 SPF roofs. Three of the buildings were in areas of very high winds, one in an area of high winds and seven in areas of moderately high winds.

Two of the three in the very high wind zones were SPF over old BUR, the third SPF over thin-shell concrete. Two of the three roofs sustained minor damage from missiles. One of the SPF-over-a-BUR roofs experienced peeling that did not progress beyond an area of missile impact.

Other buildings with traditional roofing systems in a 200-foot radius surrounding the SPF-over-a-BUR roof that peeled suffered significant damage including gable-end wall failure and collapsed trusses, as well as blown-off sheathing panels and asphalt shingles. One building had reportedly had its BUR blown off.

Underwriters Laboratories and FM Global test various roofing systems for wind uplift performance and then publish the results in their directories. Designers can look for systems that meet the UL designations class 30, class 60 and class 90, or FM1-60, FM1-90, or higher where needed.

The Spray Polyurethane Foam Alliance reports that during laboratory testing of SPF systems, SPF's wind-uplift resistance exceeded the capacity of UL's equipment. UL also observed that SPF roofs applied over BUR and metal increased the wind uplift resistance of those roof coverings. FM Global testing showed similar results over concrete, metal and wood.

In addition to high wind uplift resistance, SPF roof systems are resistant to progressive peeling failure due to missile impact, deck failure, or a lifting and peeling failure at the roof edge, along with the ability to resist water infiltration after being impacted by missiles.

Refernces, Performance Based Studies Research Group at Arizona State University's Del E. Webb School of Construction

1 "Hail Damage to Roofing: Assessment and Classification," William C. Cullen, from the Proceedings of the Fourth International Symposium on Roofing Technology

2 "Hail Resistance Test of Sprayed Polyurethane Foam (SPF) Roof Systems," Dean T. Kashiwagi, Manoj K. Pandey and Thomas Tisthammer, from the Proceedings of the Fourth International Symposium on Roofing Technology

3"How Did PUF Roofs Perform During Hurricane Andrew?" Thomas Smith, Professional Roofing, January, 1993

"The Answer to Blowing in the Wind," Roofing Contractor, August, 2002