This article does a great job explaining the important steps in Foam Roof installation. The many exceptional benefits are plainly spelled out. It fails to mention that sprayed foam is the ONLY insulation material that does not soak up water. The closed cell insulating spray foam is unique in this feature.

Insulating the ‘Building Envelope’ on Low Slope Roofs

by Randy Feriante, President since 1981 of Dura-Foam Roofing and Solar Center

Dura-Foam inc. roofs, using closed-cell sprayed foam have unique benefits that are not available using any other material or installation method. Placing the insulation on the absolute outer surface of the ‘building envelope’ creates benefits that cannot be duplicated or even approached using any other insulating or waterproofing materials or methods.

Moisture Condenses on Cold Surfaces

Moisture build-up is an unavoidable problem under nearly all roofing materials, like tar and gravel, single ply, cap sheet and IB roofing. Water vapors, mostly in the form of indoor humidity during winter, gradually migrate to the cold underside of the membrane. Water condenses on this cold surface and moisture and vapors build up in the foam boards, fiberglass, wood and fiberboard under the membrane roof. Metal fasteners that secure foam boards under a roof, get very cold, and attract water condensation. This moisture destroys the potential insulating properties of dry materials, feeds dry rot and mold and shortens the life of the structure.

Spray foam grey basecoat
Images courtesy of the Spray Polyurethane Foam Alliance.

R-Value can be easily understood when you know that R-1 equals the insulating value of 1″ thick wood.

Sprayed foam is rated close to R-7 in R-Value per inch. This is not affected by humidity, since the cellular structure is closed. With the very common 4×8 foam boards and fiberglass insulation, the R-Value is figured at R3.1 – to R3.6. This number represents ideal circumstances, with no humidity in the materials. With open cell insulation, it is safe to say that actual R-Values in place will always be less than the numbers R3.1 to R3.6.

IN-Gassing vs. OUT-Gassing

There is much discussion today about ‘out-gassing’ of plastic materials. Sprayed foam is inert and non-toxic. All concerns are eliminated when you realize that sprayed foam IN-Gasses. When closed cell sprayed foam roofing is first installed, at a temperature between 125 and 140 degrees Fahrenheit, the initial R-Value is about R-10. The inert, non-conducting, harmless gas inside the foam is an excellent insulator. Since the material is hot, it will cool to ambient temperature within several hours. This cooling creates a slight negative pressure inside the sprayed foam – eliminating any out-gassing concerns. Over the first several months, local air can gradually be absorbed into the foam, lowering the R-Value to about R-7. Foam sprayed in dry climates will have a final R-Value higher than foam sprayed in humid climates.

Spray foam white topcoat recoat

Summary

Placing the world’s best insulator, that does not soak up water, on the outside of the building envelope creates a dry, durable, energy efficient barrier that cannot be approached using any other material or method. This high performing foam roofing is the only roofing material that is ‘sustainable’. This means the surface coating that covers and protects the sprayed foam from damaging UV rays can be renewed when needed. During the first 30 years, our roofs are in very good condition if they get a thin coat of protective coating at 5 years.

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One thought on “Insulating the Building Envelope on Low Slope Roofs”

  1. My foam roof (almost flat) was installed seventeen years ago, in 2000. We are having some leaking. If you sweep aside the gravel that covers the foam, and press the foam with your finger, the foam gives a little. It has a slightly spongy feel to it. Is this a sign that the roof needs to be replaced? Note that the leaking is limited to the perimeter of the roof, the portion that slopes up the parapet.

    Reply

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