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 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:
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.
Example of an SPF-based roof system
NRCA does not make any recommendations about which SPF products or manufacturer to use; however, NRCA does recommend that SPF products meet standards established by ASTM International.
ASTM D6083, "Specification for Liquid Applied Acrylic Coating Used in Roofing"
ASTM D6694, "Standard Specification for Liquid Applied Silicone Coating Used in Spray Polyurethane Foam Roofing Systems"
ASTM D6947, "Standard Specification for Liquid Applied Moisture Cured Polyurethane Coating Used in Spray Polyurethane Foam Roofing System"
ASTM D7425, "Standard Specification for Spray Polyurethane Foam Used for Roofing Applications"
When purchasing a new roof system, there will be two warranties to consider. First, there will be the manufacturer's warranty. In general, these warranties cover defects in the manufacture of the roof membrane. Please read NRCA's consumer advisory bulletin addressing roofing warranties for more information. Once the project is complete, be sure the contractor provides you with a certificate for your records.
Second, the roofing contractor will provide you with a warranty covering his workmanship. Typically, this will cover installation and related issues. The warranty should contain what items are covered and what will void them. Many contractors offer one year or two years of coverage; however, there is no industry standard.