via the Spray Foam Industry website
Thermal Barriers
Building codes require that foam plastic insulation, such as spray polyurethane foam (SPF), be covered with a thermal barrier to slow their involvement in fire situations. Thermal barriers are discussed in the International Building Code (IBC) in Section 2603 and in the International Residential Code (IRC) in Section R314.
½-inch thick gypsum board is one commonly used thermal barrier. It and other thermal barriers are designed to "limit the average temperature rise of the unexposed [foam plastic insulation] surface to no more than 250 oF (121 oC) after 15 minutes of fire exposure to the ASTM E 119 standard time temperature curve." [IRC 2003, Section R314.1.2]
But, there are MANY exceptions to the thermal barrier requirement. For example:
1. Building code authorities may approve coverings based on fire tests specific to the SPF application. For example, covering systems that successfully pass large scale tests (such as the small room corner test) may be approved by code authorities in lieu of a thermal barrier.
2. SPF protected by a 25 mm (1-inch) thickness of masonry does not need a thermal barrier.
3. Certain SPF roof covering systems do not require a thermal barrier between the SPF and the interior.
Ignition Barriers
Another exception to the thermal barrier requirement is in attics and crawl spaces where entry is made only for the service of utilities. In these cases, SPF must be protected from ignition by covering with 38 mm (1 1/2 inch) mineral fiber insulation, 6.4 mm (1/4 inch) wood structural panels, 9.5 mm (3/8 inch) gypsum board or other code prescribed material. These materials which offer protection from ignition are called "ignition barriers" (the building codes do not use the term "ignition barrier"; this term is a common vernacular used by the building trades to describe these and equivalent materials).
As with thermal barriers, code authorities may accept alternatives to the above prescribed based on fire tests specific to the SPF application.
In General
Materials which are not specifically prescribed by the building codes may be approved by building code authorities for use as a substitute or an exception to the requirement of a thermal barrier or ignition barrier when based on fire tests specific to the SPF application.
Just because a material is advertised as a "thermal barrier" or "ignition barrier" does not mean that it has been tested in conjunction with SPF and approved by a code agency or a local code official. Ask for test data and code body approvals, listings, or other written indications of acceptability under the code to be sure that the product selected offers the fire protection that the code demands.
For more information, refer to SPFA Document AY 126 Thermal Barriers for the Spray Polyurethane Foam Industry and API Document AX 230 Fire Safety Guidelines for Use of Rigid Polyurethane and Polyisocyanurate Foam Insulation in Building Construction.
