Topic: Fire Barrier Requirements for 2 Part Foam Plastic Insulation and Rigid Foam Board Insulation
The increased use of foam plastic insulation in CSG’s Home Performance programs makes it necessary to clarify what types of fire barriers are needed to cover this material, as required by code. Code requirements for fire barriers fall into three categories: Not required, thermal barrier and ignition barrier. The definition of not required is clear. The definitions of thermal barrier and ignition barrier when applied to foam plastic insulation follow:
Thermal Barrier: A ½ inch thickness of gypsum wallboard or an equivalent thermal barrier material that will limit the average temperature rise of the unexposed surface to no more than 250⁰F after 15 minutes of fire exposure complying with the ASTME 119 or UL263 standard time temperature curve. There is a list of alternative thermal barriers at the end of this document.
Ignition Barrier: A fire resistant barrier that can be used in place of a thermal barrier if these two conditions exist.
- Attic or crawl space access is required by code.
- The space is entered only for the purpose of repairs or maintenance.
- If the two above conditions exist, the following are approved ignition barriers that can replace the thermal barrier. (Note: there are other acceptable materials, but this list is expressly identified in the IRC.)
1 ½ inch mineral fiber insulation
¼ inch wood structural panels
3/8 inch particle board
¼ inch hardboard
3/8 inch gypsum board
.016 inch thick corrosion resistant steel
In practice this means that any attic or crawl space that can be accessed will need some type of fire barrier installed over the foam plastic insulation unless the insulation itself is rated as a thermal barrier. It should be noted that spray foam insulation applied to the joist header and sill plate in crawl spaces is not required by the 2009 IRC to have a thermal barrier.
Some uncertainty is introduced when deciding whether a space is being entered only for “repairs and maintenance” vs. storage. The Spray Polyurethane Foam Alliance (SPFA) provides clear guidance on this issue in their publication entitled “Thermal Barriers and Ignition Barriers for the Spray Polyurethane Foam Industry” which is attached to this document. The following excerpt from this document clarifies how to…
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