A recent press release from the Icynene Corp. announced the release of a new open-cell spray foam, Icynene Classic Max, that has been tested and approved by the ICC-ES for residential use without an added ignition barrier. That’s not an entirely new development, since several open-cell foams on the market have already earned approval for the same use. But as that product category continues to grow, it’s worth considering what ignition barriers are designed to do, and how the new non-barrier foams fit into the picture.
Thermal barriers vs. ignition barriers. All polyurethane spray foams require a code-approved thermal barrier—ordinarily a layer of ½” drywall—between the foam and the living space. The thermal barrier is designed to make it more difficult for a fire inside the living space to gain access to the fresh source of fuel in the spray foam, leaving the home’s occupants with more time to escape.
Ignition barriers, on the other hand, are required in foam-insulated attics, crawlspaces, and other areas with limited access that can’t be used as living space. They offer a lower order of protection, and are intended simply to prevent a possible flame source from making direct contact with the foam. The IRC lists six prescriptive ignition-barrier materials: 1 ½” mineral fiber insulation; ¼ wood structural panels, such as plywood; 3/8” particleboard; ¼” hardboard; 3/8” gypsum board; and corrosion-resistant steel with a base-metal thickness of 0.016 inch or more. Apply any of these materials over the foam in areas where an ignition barrier is required, and you’ve met code.
Intumescent coatings and bare foam. These sorts of barrier materials take time and effort to apply—especially when you’re lying on your side in a low crawlspace or sealed attic. In many cases, it’s difficult or impossible to fit full-sized pieces of sheet material into such spaces to begin with.
Fortunately, prescriptive ignition barriers aren’t the only route to compliance. Spray foam can also be protected with an intumescent coating, which is applied like paint and bubbles up when exposed to heat, forming a flame-resistant barrier layer. Unlike prescriptive ignition barriers, though, such coatings must earn code approval on a case-by-case basis by passing a burn test—ACC 377, appendix X, also known ast the modified NFPA 286 test--administered by the ICC-ES. Virtually all spray-foam manufacturers now offer products that qualify for attic or crawlspace use when combined with an appropriate coating material.
In 2008, when the modified 286 test was under development, it was widely assumed that only foams with intumescent coatings would achieve a passing score. That turned out not to be the case. Subsequent tests revealed that most closed-cell foams pass the burn test with no protective coating at all. Because their lower densities, open-cell foams tend to be easier to ignite—as it’s easier to kindle a fire with pine than with hardwood—but a few reformulated open-cell products now pass the burn test as well.
As a result, builders now have three options for attic and crawlspace use: they can combine any spray foam with a prescriptive barrier; use an approved combination of foam and intumescent coating, or choose a foam that has been tested and approved by the ICC-ES test without any protective barrier.
Making the right choice. Given that both prescriptive barriers and intumescent coatings add a layer of cost, choosing a foam approved for use without an ignition barrier might seem an obvious way to boost profits, especially where an open-cell foam is called for. But spray-foam consultant Mason Knowles notes that non-barrier foams may cost substantially more than those that require added protection, cutting into any potential savings. Knowles also points out that spray foam protected by an ignition barrier will likely provide a greater margin of safety in an actual fire situation. “The foam with a prescriptive barrier and the non-barrier foam may both meet code,” he says, “but the added cost [of an ignition barrier or intumescent coating] does buy some improved performance.”
- Other things to keep when selecting a foam-and-intumescent-coating combination or non-barrier foam include:
Approval of a given intumescent coating with a given foam doesn’t mean it’s also approved for use with other, similar foams, although advertisements may imply that it does. Look for an ICC-ES report that references the specific coating and the specific foam you’ll be using.
- Foam that’s “close enough” might not be. Be aware that manufacturers often market a given foam product under several different brand names. Even if the version you’re using is from the same manufacturer and chemically identical to the one on the ICC-ES report, you could find yourself in hot water with the inspector unless the names match as well.
- Don’t exceed the thickness or density of the foam specified in the test report. If a non-barrier foam was tested and approved at a thickness of 6” and a density of .5 lb, that approval no longer applies if the thickness is increased to 8 inches. (You can, however, apply the foam at a lesser thickness than that specified in the report.)