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Thermal/Fire Barrier FAQ

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Q: What is a thermal/fire barrier?

 A: A thermal or fire barrier is a material or coating, applied over polyurethane foam, designed to slow the temperature increase of the foam during a fire, and to delay the foam's involvement in a fire.  The building code definition of an approved thermal barrier is one which is equal in fire resistance to 12.7 mm (1/2 inch) gypsum board.  Such thermal barriers limit the temperature rise of the underlying polyurethane foam to not more than 250 F after 15 minutes of fire exposure complying with the standard time temperature curve of ASTM E 119.  Thermal barriers meeting this criterion are called "15-minute thermal barriers" or classified as having as "index of 15."

 Q: Where is a thermal barrier needed?

 A: All building codes require an approved thermal barrier on the habitable side of a structure between the interior of the structure and the polyurethane foam.  Spray-applied polyurethane foam should not be applied to the interior of a building without an approved thermal barrier as defined by the applicable building code. 


  1. For spray-applied polyurethane foam applied on the exterior of the structure (i.e. roof insulation), a thermal barrier is not normally required. 
  2. For foam installed in attics and crawl spaces where entry is made only for the service of utilities, a different standard must be met, requiring "protection from ignition" in the form of approved materials or coatings.  In some cases, where these spaces are protected by a sprinkler system, this requirement is waived.
  3. Finally, another alternative to the thermal barrier requirement targets specialized rigid polyurethane foam board or panels.  Under this section, "foam plastic is not required to comply with the requirements of Sections 2603.4 through 2603.7 when specifically approved based on tests such as FM 4880, UL 1040 or UL 1715 listed in Chapter 35.  Such testing shall be performed on the finished manufactured foam plastic assemblies and on the maximum thickness intended for use". 

 Q: Why do codes require thermal barriers?

 A: Spray-applied polyurethane foam, like most other organic materials, is combustible.  When exposed to fire sources such as welding arcs, cutting torches or red-hot metal, unprotected spray polyurethane may ignite, resulting in a flash fire. In a limited number of situations when other flammable materials are not involved, sprayed polyurethane foam fires tend to be flash fires of relatively short duration.  Codes require thermal barriers for interiors to reduce the risk of a flash fire and to extend the time at which the foam would reach its auto-ignition temperature should a fire originate from other sources. The thermal barrier should have a valid building code certification that lists a report number and date.  In some cases, a local building code official will allow the use of a thermal barrier which has been tested to the satisfaction of the official, but is not certified by a code agency. To learn more about thermal/fire barriers, click here.