15 Minute Thermal Barrier in Attic For Spray Applied Foam Insulation

[BayPointArchitect]

While looking at Chapter 13 today of the IRC, I noticed that the section related to the treatment of foam insulation is the same in Chapter 26 of the IBC. The scenario in this particular case is the foam insulation (open cell... but that doesn't matter) is spray applied within the attic directly to the underside of the roof sheathing within the attic space. A layer of 5/8" Type "X" Gyp.Bd. is applied to the bottom chord of the roof truss. Sounds good to me. But it is difficult for me to know whether-or-not strict interpretation of the IRC would require a layer of 3/8" gypsum board to be applied more directly over the spray-applied foam insulation.

within an attic space that is already enclosed from the living area below with the use of 5/8" Type "X" Gyp.Bd. is the additional layer of some type of thermal barrier required more directly over the spray foam insulation?

Thanks

ICC Certified Plan Reviewer

Registered Architect

 

[Francis Vineyard]

Must have meant Chapter 3 of the IRC and the language used to describe how the foam plastic is installed has change from 2006. Noted the prescribed ignition barrier protects the foam from sources of ignition and it is not necessary to place the barrier directly over the foam plastic. However the alternative approved coating as stated in the manufacturer installation guide is to be applied to all of the foam plastic exposed including where the foam is installed in another area and is interconnected.

It will be up to the AHJ as to what is a source of ignition from maintenance and repairs.

Allow me to take this opportunity though the code does not reference the manufacturers installation guide be approved to AC377 effective Nov 1st, 2010 with appendix X; under R316.6 with the AHJ approval some manufacturers have finally formulated the foam plastic to be applied without any ignition barriers. Caution what is advertised as a 15-minute thermal barrier meets ASTM E-84; not E-119.

 

[Yankee]

the thermal barrier need not be directly in contact with the foam, only between the foam and the living space. The 5/8 Type x is fine for this scenario as far as I can see from here.

 

[BayPointArchitect]

Very good. So long as there is no air exchange between the attic space (location of the foam) and the living space below the drywall ceiling, I will consider the ceiling the 15 minute thermal barrier. If cyanide gas is created during an attic fire - my thinking is that when the toxic gas makes it's way into the living area, it will be accompanied by a blazing inferno. Hopefully the family has either responded to smoke detectors or they are safely at school and work during that time.

 

[peach]

doesn't apply if there is equipment up there, though. I agree, the ceiling is the thermal barrier.