Sprayed-in-place polyurethane foam (SPF) is arguably the most technologically unique roofing system available today. As recently discussed at a manufacturer's presentation, an SPF system is really not a built-up system, but it is. It's really a single-ply system, but it isn't. The main difference between SPF and other contemporary roofing systems is that these systems must be mechanically assembled at the job site.

SPF systems are actually "built-up" in place using a two-part component mixture - the "A" side, which is the isocyanate component, and the "B" side, which is the polyol component. These two components are mixed in place through special metering equipment specified by the manufacturer. Most manufacturers produce three "seasonal" grades of polyurethane foam - regular, winter and summer. All grades should have at a minimum certain properties that meet ASTM standards and include sprayed-in-place density, compressive strength, closed cell content, thermal conductivity and flammability.

Indeed, SPF systems can exhibit a wide range of physical characteristics that are influenced by factors such as manufacturers' formulations, ambient weather conditions, and applicator experience. It can be argued that the biggest factor affecting the final product is applicator expertise. The applicator must have a commanding knowledge of equipment and a commitment to good workmanship. They must also have detailed information on the physical properties and handling characteristics of the chosen SPF system in order to apply it correctly. Applicator experience can vary greatly depending on geography etc., but most manufacturers have extensive training programs in place that require the contractor to train employees/applicators in the most up-to-date methods and use of materials. In addition, most manufacturers require a third party to verify completed systems and for warranty purposes.

The industry has had several myths surrounding it for years.

Myth #1: SPF is an experimental roof system. In fact, SPF has been around since the 1940s, with numerous modifications to application parameters and equipment.

Myth #2: SPF is not a long lasting roof system. When properly applied, an SPF system can last 20+ years and be recoated periodically to increase service life.

Myth #3: SPF cannot be walked on. The Society of Plastics Industry's Polyurethane Foam Contracting Division requires that SPF used in roofing applications have a density of 2.8 to 3.0 pounds per cubic foot. This results in a compressive strength of 40 pounds per square inch, which is greater than most plastic foam boards utilized in other roofing applications.

Myth #4: Birds eat polyurethane foam. In fact, birds do not eat the foam, but for some unexplained reason, they peck through the coating. The problem can be solved with regular maintenance inspections and a caulk gun.

Myth #5: SPF cannot be utilized in all geographies. SPF has been utilized in all 50 states and worldwide. Application temperatures should be between 50 and 120 degrees F., wind should be less than 15 mph and humidity within 5 percent of the dew point. In addition, system coating should be applied within 24 hours of application.

Myth #6: SPF requires too much maintenance. All roofing systems should be inspected annually so that minor problems do not become major ones. Most damage to SPF is easily identified and repaired with manufacturer-approved caulks and sealants. Often, recoating of the waterproofing is required by a manufacturer's warranty and can be done to extend service life and warranty coverage. Timely recoating can save the building owner the cost of labor and materials otherwise required to install new foam and base coat.

Myth #7: Qualified contractors are hard to find. As stated earlier, there are many approved contractors nationwide. More than 250 are certified by SPI/PFCD and many are members of NRCA. While this in and of itself is not sufficient, most manufacturers recognize the need to certify and approve contractors for application of their systems. In addition, SPFA, the industry trade association, offers training throughout the year to keep contractors abreast of changes in the industry and train new employees and contractors. Most manufacturers have independent testing firms that ensure quality by inspecting the roof system periodically to ensure good roofing practices.

This applicator sprays SPF under  a domed tent to block the wind.

Myth #8: Contractors "foam everything". Most manufacturers recognize the need for a complete and detailed specification that requires the contractor to build expansion joints, control joints, curbs and flashing that are independent of foam application. A detailed specification is key!

Speaking of design, there are several factors that should be considered when selecting and designing an SPF system:

• weight requirements, including structural load
• configuration of structure
• location of drains, scuppers
• type and amount of foot traffic
• penetrations/rooftop equipment
• flashing details and building expansion joints 
• building occupancy and usage
• environmental factors such as extreme heat and cold, high winds, etc.
• accessibility of roof area
• type and condition of existing roof or substrate
• aesthetics - color, reflectivity
• compatibility with adjacent construction materials
• economic requirements
• ease of maintenance
• modification requirements
• recoatability

These are several of the factors that must be considered, others may be applicable depending on the project criteria.

Is an SPF system a viable option? Based on the appropriate conditions, I believe it is. Many misconceptions have surfaced over the years and most are unfounded. In part, this is due to problem jobs in the early days of polyurethane foam roofing, when application equipment was primitive, when foam densities were too low and when many applicators lacked adequate knowledge of SPF roofing principles. These problems have corrected themselves, in large part due to the manufacturers "policing" and cleaning up their industry. Watchdog organizations like SPFA, SPI/PFCD and the NRCA have also contributed to improved SPF system applications.

High performance sprayed-in-place systems are totally adhered, seamless, lightweight, self-flashing and enjoy extensive code approval. This, coupled with the improved applicator base and improved application methods, makes SPF a viable option in the right circumstances.