Fire-Resistant I-Joists

Weyerhaeuser – Flak Jacket I-Joists

Upcoming changes to the International Residential Code (IRC) pertaining to the fire protection of floor assemblies could limit your ability to use I-joists for some flooring systems, unless you want to cover the bottom of the joists with drywall or install a sprinkler system. (Given that only three states have adopted the residential-sprinkler requirement in the IRC, that’s unlikely to be the case.) Another alternative is to use a new Weyerhaeuser product called Flak Jacket, which complies with the new one-hour flame rating.

Flak Jacket I-joists are coated with a proprietary covering that puffs up when flames lick at it. “It’s an intumescent,” says Glen Robak, senior engineer for new products at Weyerhaeuser. “It’s similar to the stuff you might have seen sprayed on steel beams in commercial buildings.” An intumescent is a substance that swells when exposed to heat and keeps flames away from the material it covers.

As the material on Flak Jacket expands, it prevents flames from reaching the 3⁄8-in.-thick I-joist web, which would burn through a lot faster than the 2x chords. When you look at the Flak Jacket joists, you’ll see that the intumescent doesn’t cover all sides of each piece. “It doesn’t need to,” says Robak. “When the material expands, it swells out from the web and encapsulates the chords.”

Weyerhaeuser is market-testing the product and expects it to be widely available by the beginning of 2013. The price for Flak Jacket isn’t set in stone yet, but a company spokesperson says it will be a lot less than the cost of the time and materials to hang gypsum board on the underside of a floor system to comply with the new code

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