Can Styrofoam Insulation Be Installed on a Rooftop?

Roofmate

• Dow sells Styrofoam construction insulation under many product names, including Cladmate, Deckmate, Wallmate and Roofmate, each of which is designed for a specific use. Styrofoam board is used to insulate exterior walls, basements and roofs. Roofmate is preferred for roofing over other polystyrene insulation because it has a higher compressive strength so it will not bend or dent when stepped on by roof workers.

High R Value

• Styrofoam roofing panels have a high R value, or heat resistance measurement, of R 5 per inch and typically are 1 1/2-inches thick for a top roof insulation of R 7.5. Thicker panels are used in colder climates which require more roof and attic insulation. Loose fill or other insulation placed in attics under the roof decking provides additional insulation.

Styrofoam on Decking

• Roof panels are added after the decking, usually oriented strand board is nailed on, Styrofoam panels typically are laid opposite the OSB, so the seams do not line up; that is, if OSB panel are installed lengthwise, Styrofoam would be laid vertically, up the slope of the roof. Styrofoam roof panels are nailed in place with galvanized roofing nails. Seams are butted together or secured with tongue and groove connections.

Vapor Barrier

• Styrofoam roofing must be installed with a vapor or moisture barrier on the underneath side; panels usually come with this facing, which goes on the decking. The panels also must be sealed at the joints with a special Styrofoam tape. The tape is rolled on the edges of the two adjoining panels and pressed into place. This is done before shingles or other roofing is installed.