SPF Roof Systems
By Robert L. Swisher
- The spray polyurethane foam (SPF) roof system offers a number of key advantages
- To many people, a roof is simply the outside top covering of a building, but this simple definition does not come close to capturing the complexity of roof systems today or the value of choosing the right roof system. Although no single type of system is the answer to all roofing needs, our experience with SPF and coating systems indicates several distinct advantages.
- Advantages of SPF
- One of the benefits of an SPF roof system is its Ieak-free performance. The primary function of any roof system is to keep water from entering the building. The polyurethane foam used in SPF roof systems is a closed-cell material that does not allow water to travel laterally. On the other hand, water travels freely throughout boardstock insulation, such as perlite or fiberglass. saturating large areas of insulation from a small penetration through the membrane above.
- Energy conservation is another benefit to using the SPF system.
- Polyurethane foam has the highest thermal resistance value (R value) used in the roofing Industry, with an aged R value of 6.25 per inch. To obtain an equivalent thermal resistance in a roof assembly would require 1.7 inches of fiberglass insulation (at 1.5 pounds per square foot) or 2.2 inches of perlite insulation (at 2 pounds per square foot).
- The SPF roof system is also seamless and self-flashing. Because it is spray-applied, there are no scams or joints in the insulation or the membrane to cause problems and leaks.
- Flashing roof penetrations, perimeter edges and parapet walls use the same SPF and coating system as the field of the roof, eliminating material compatibility concerns that may occur when using different flashing materials with conventional systems. Also, polyurethane foam can be applied in varying thickness to create slope during the spray application, ensuring proper drainage.
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The system is also lightweight. When covering an existing roof, the added weight of the new roof system should be one of the first considerations.
- In a re-cover application using an SPF system over an aggregate surfaced BUR, the net weight of the new roof is less than the existing BUR roof This is because the loose aggregate is removed before the new SPF system is applied.
- The lightweight benefit of the SPF roof system is ideally suited for re-cover applications, as it saves tear-off and disposal costs, and minimizes the environmental concerns of taking debris to a landfill.
- Maintenance is generally quite simple with an SPF roof system. Unlike conventional roof systems that often require adhesives, membrane. felt, mastic or asphalt, maintenance of an SPF system is usually accomplished with a knife and a cartridge of sealant that is compatible with the coating material.
- Polyurethane foam requires a coating to protect it from ultraviolet (UV) degradation and water. Organic coatings, which arc available as single- or multiple-component materials, include urethane, acrylic, butyl, Hypalon and asphalt. The primary advantage of an organic coating is its initial toughness. However, organic coatings tend to weather and lose their initial properties with time when exposed to UV rays.
- The inorganic coatings used with SPF roofing are silicones, and they arc available as single- or double component materials. Silicones arc breathable coatings, allowing water vapor to pass through without damaging the foam or coating. Most silicones have perm ratings of three or greater.
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In addition to breathability, silicone coatings demonstrate exceptional weather-ability, good chemical resistance and outstanding performance in temperature
extremes, remaining flexible over a temperature range from - 35 F (- 37 C) to 302 F (150 C).
- In Conclusion
- While no single roof system is fit for every application, the benefits of the SPF and coating roof system match several key needs of today's building owner. The system is leak-free, energy efficient, self-flashing, seamless, lightweight and easy to maintain.
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Robert L Swisher is a roofing specialist for Dow Corning Corp.
Source: Professional Roofing