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 them at a 1:1 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 is a protective surfacing which is typically a spray-applied elastomeric coating. 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 and mechanical damage, and assist with the fire-resistant characteristic of the roof system.

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