Spray Polyurethane Foam-Based (SPF) Roof Systems

SPF-based roof systems are constructed by mixing and spraying a two-component liquid that forms the base of an adhered roof system. SPF can be installed in various thicknesses to provide a slope to drain or meet a specified thermal resistance (R-value). A protective surfacing is then applied to the foam to provide protection from the elements.

The first component of an SPF-based roof system is rigid, closed-cell, spray polyurethane foam insulation. The foam is composed of two components: isocyanate and polyol. Transfer pumps are used to get the components to a proportioning unit that properly meters the two at a one-to-one ratio and heats and pumps them through dual hoses. The components are mixed at the spray gun, which is used to apply them to a substrate.

The second component, the protective surfacing, typically is a spray applied elastomeric coating, though hand and power rollers can be used. The protective surfacing also can be a membrane, such as a fleece-backed thermoset single-ply membrane. The purpose of the surfacing is to provide weatherproofing, protect the foam from UV exposure, provide protection from mechanical damage and assist with the fire-resistant characteristic of the roof system.

The generic types of coatings used on SPF-based roof systems include:

• Acrylic
• Butyl Rubber
• Hypalon™
• Silicone
• Aromatic Polyurethane Elastomer
• Aliphatic Polyurethane Elastomer
• Modified Polyurethane Elastomer

Mineral granules or sand may be broadcast into a coating to provide increased surface durability and aesthetic value.

The chemicals used to produce polyurethane foam compounds are manufactured or blended to perform in various temperature ranges. Manufacturers of spray polyurethane foam-based roof systems offer materials in different reaction profiles. Profile change is created by altering the chemical ingredients, usually with a catalyst, to compensate for ambient temperature changes. Conditions such as wind speed, sunlight, surface moisture, humidity and temperature of the substrate can affect the reaction of the polyurethane foam.

Information provided by National Roofing Contractors Association.