Polyurethane Foam

NOTE:See also Accepted Roof Deck Insulation products by clicking on this link.

Polyurethane foam is the result of a chemical reaction between two liquids, isocyanate and polyols, in combination with additives and catalytic agents. The mixture begins to foam instantly and quickly expands to approximately 30 times its original volume. The foam hardens into an airtight mass, becoming tack-free in minutes.

The insulating properties of the foam are derived from fluorocarbon vapour trapped in the foam's cells. Polyurethane roof insulation boards are generally available in either:

• flat sheets of varying size and thickness that have been cut from large buns (or billets)
• surfaced boards where the polyurethane is foamed between two skins (felt, aluminum foil, etc.) which become an integral part of the product.

Polyurethane foam roof insulation is combustible and, when used on steel decks or over a roof that is subject to fire exposure from below, a fire-rated underlayment or thermal barrier (such as gypsum board) should be installed between the roof deck and the insulation.

Polyurethane foam roof insulation is presently manufactured to two standards:

CGSB 51-GP-21M applies to unfaced polyurethane rigid insulation boards intended for applications where the continuous use surface temperature does not exceed +80°C (+176°F). This standard establishes three types (Type 1, 2 and 3) and three classes (Class 1, 2 or 3) of polyurethane insulation. The type is determined by the physical properties of the material and the class is determined by its surface burning characteristics. CAN / CGSB-51.26-M86 applies to faced polyurethane rigid insulation boards intended for applications where the continuous use temperature is within -60°C to +80°C (-76°F to +176°F). This standard establishes four types (Type 1, 2, 3, or 4), four facing categories (Facing 1, 2, 3, or 4), and two surface burning characteristic classifications (surface burning characteristic “a” or “b”). The type is determined by the physical properties of the foam, the “facing” is determined by the product the polyurethane is foamed between, and the surface burning characteristic is derived from the final product's flame spread classification.

Polyurethane insulation provides the following properties and advantages:

• Compatible with asphalt
• Compatible with roof system components
• Resistant to the effects of moisture
• Resistant to cell deterioration
• Resistant to impact
• Resistant to thermal conductivity
• Unaffected by asphalt application temperatures.

The possible disadvantages or precautions involved in the use of polyurethane foam insulation include:

• Flammable (combustible)
• Requires an insulation overlay (fibreboard, vented base sheet, etc.) to prevent potential asphalt blistering
• Aged thermal resistance should be used for design calculations
• Felt skin may change dimensionally if exposed to weathering (provide protection prior to installation)
• Heavy equipment may compress insulation, causing deflections in the deck and debonding of the insulation
• Will not retain nails (requires screws and plates)