Despite low life-cycle costs and a track record that extends back to the 1960s, a lack of knowledge about spray polyurethane foam (SPF) roofing among facilities executives means that, too often, it isn’t considered when roofing alternatives are evaluated. But this is changing as facilities executives come to understand the performance characteristics of the system.
Put simply, SPF roofing is a watertight, closed-cell foam system applied with a spray gun. It is then coated to prevent ultraviolet light degradation. Typically, SPF roofs are covered with an elastomeric coating, but about 10 percent of facilities executives choose to cover the foam with an aggregate, according to Joe Stockdale, business manager at BaySystems.
The coatings can also be used to achieve other desirable results. They can inhibit moisture-vapor transmission, enhance the aesthetics of the roofing system if it can be viewed publicly, increase the impact and abrasion resistance of the system or achieve flammability code requirements.
SPF roofing is shipped to the location as two separate liquid components — an isocyanate, commonly called the “A” component, and a polyol resin, which is the “B” component. Both components are fed from drums into a device called a proportioner, which heats the liquids, mixes them at a one-to-one ratio, and then routes them through a spray nozzle for application.
This equipment is expensive when compared to the equipment used by most roofing contractors, and several manufacturers suggest that the initial equipment cost is part of the reason relatively few SPF roofing contractors exist.
Nevertheless, equipment cost is coming down at the same time that more accurate applications are possible.
“In the last several years the equipment has become more sophisticated and easier to operate,” says Jim Andersen, manager for applications and training at BASF Polyurethane Foam Enterprises. “The use of electronics to record pressures, heats and flow rates provide the applicators a readout of how the materials have been processed. The settings are dialed in and semi-automatically controlled to provide for proper processing.”
The foam is applied in layers one-half to one and one-half inches thick per pass, and cures to a watertight surface within 30 seconds, according to Rick Tucker, Honeywell’s marketing manager for North America.
Because the materials need to cure, SPF must be applied between 50 and 100 degrees Fahrenheit, and applicators need to pay attention to dew points and ambient humidity to ensure the application process isn’t adversely affected by the weather.
Although wind screens are available to applicators, SPF roofing should not be applied in strong winds.
In addition to being a roofing material, SPF is also used in rigid pre-cut panels as insulation, so many facilities executives might recognize SPF from those applications.
Although SPF commands only four percent of the roofing market, the touted benefits read like a wish list for roofing systems:
- Self-adhering. SPF roofs do not require fasteners and, in retrofit applications, can be sprayed onto 95 percent of existing roof systems, according to BASF. The lack of fasteners reduces thermal bridging, thereby increasing energy efficiency. Lack of fasteners also vastly improves wind-uplift resistance.
- Watertight. Because of its closed-cell structure, sprayed foam is watertight and will remain so for more than 50 years when protected from UV light. The spray-on nature of SPF roofing means that it is self-flashing, and can be sprayed to varying thicknesses to accommodate slope-to-drain requirements.
- Insulating value. Aside from lack of thermal bridging, SPF roofs traditionally receive an R-value rating of approximately 7 per inch of material. Because of the product’s light weight, applicators can make multiple passes on the same roof, building up a relatively thick layer of roofing material and insulation. In some test cases, energy savings have resulted in a payback of less than five years.
- Longevity. The physical properties of foam change very little over time. Tests indicate little to no thermal drift of SPF during a 50-year life cycle. The initial application of a roof is expected to last 20 years before a recoating is needed. After that, recoatings are necessary roughly every 10 to 12 years. According to Stockdale, recoatings are approximately 20 percent the cost of a new roof.
- Lack of business disruption associated with tear-offs. According to Stockdale, one significant benefit of choosing SPF roofing is saving the mess, hassle and disposal costs of tearing off an old roof.
“Tremendous amounts of construction materials end up in landfills every year,” he says. “Because SPF roofing can be applied to nearly any substrate, those disposal costs usually don’t exist for SPF.”
- Lower maintenance cost. Additionally, the system may offer lower maintenance costs. “You can clean-up, repair small damage and recoat numerous times with this type of system,” says Mike Briese, warranty inspection and training leader for the Conklin Company. The cost of recoating is lower than the cost of a new roof.
Care and Maintenance
Every facilities executive knows that roofs typically do not receive the maintenance they deserve.
“Ease of maintenance is one advantage of SPF roofing,” says Stockdale. A twice-annual inspection, usually in the spring and again in the fall, is all that’s required for SPF roofing. Additional inspections are also advisable following any event that might have caused missile damage or punctures to the elastomeric coating.
The coatings are typically easy to care for. And when a recoating is needed, there’s no tear off of existing materials — just a soap and water clean-up of the surface, says Briese.
When facilities executives discover damage, repairs can be made quickly with a compatible caulk. In fact, Texas A&M University was able to reduce its maintenance team, due largely to its use of SPF roofing. The university’s 35-man roof maintenance crew is now down to three people since switching to spray polyurethane foam roofing systems more than 10 years ago.
To test real world performance of SPF roofs, a field study examined the hail resistance performance of urethane-coated SPF roofs in Torrington, Wyo., and the Dallas/Fort Worth area. Although many of the metal mechanical penetrations on the roofs showed damage from severe (golf-ball-sized) hailstones, none of the roofs showed any rupture. Furthermore, the damage did not result in any premature failure of the SPF system.
In the wake of Hurricanes Katrina and Rita, the National Institute of Standards and Technology (NIST) commissioned a report on physical structures within the paths of those hurricanes. The reports indicated that the SPF roofing systems observed by the NIST team — some more than 20 years old — survived the storms with little or no damage.
Independent inspections of Florida roofs following the 2004 hurricane season — one of the worst hurricane seasons Florida has ever seen, with four major hurricanes hitting in little more than one month — show that SPF roofing fared exceptionally well. According to BASF, there were no instances where SPF failed or separated from the substrate. Many SPF roofs survived undamaged or with minor surface damage. Application of SPF as a repair and patch method between storms was very successful, proving to be more wind-resistant than the original roof systems.
Likewise, BASF cites studies conducted by Thomas L. Smith of TLSmith Consulting Inc. after Hurricane Andrew devastated Dade County, Fla., in 1992. Two SPF roofs sustained minor damage from flying debris, while other buildings with traditional roofing systems in a 200-foot radius suffered significant damage.
The Spray Polyurethane Foam Alliance (SPFA) was founded in 1987 as the Polyurethane Foam Contractors Division. The trade organization develops and publishes educational materials and technical resources for all aspects of the spray foam industry — not just roofing. However, the SPFA has begun to tout the benefits of SPF roofing more aggressively.
Although SPFA is an independent trade organization, it has a continuing relationship with the American Plastics Council (APC). SPFA helps to identify regulatory and legislative activities with the assistance of APC’s Government Affairs Department and coordinates responses and action.
Testing for Hail Resistance
In the lab, three major coating types with varying thicknesses, SPF foam densities, weathering and granulation were subjected to a simulated hail test. It involved dropping a 356-gram (0.8-lb) steel ball with a 45-mm (1.75-inch) diameter from a height of 5.4 meters (17.8 feet) to replicate severe hail impact. Systems that passed the initial test were then re-tested at freezing and sub-zero temperatures.