Fire-rated SIPs

Q: I've read about construction systems that use foam and wood panels instead of traditional wooden frames, and I'm wondering about their fire resistance. How do foam systems hold up in a blaze?

A: The building approach you're thinking of is called structural insulated panels (SIPs), and it's gaining popularity both in residential and commercial applications. According to figures I've found in the leading text on SIPs construction (Building With Structural Insulated Panels by Michael Morley), SIPs structures have the same fire resistance as wood frame buildings when lined with 1/2-inch drywall. When two layers of 5/8-inch firecode drywall are installed inside (as you might find in commercial buildings), a SIPs wall develops a 1-hour fire rating. In Winfield, Illinois, fire officials ran a test on a 12-foot by 14-foot furnished room built with SIPs panels. They set the room on fire with the doors and windows open, and let internal temperatures rise to 2000F before closing the windows and doors. This extinguished the fire by starving it of oxygen. Further inspection of the cooled shell revealed no delamination of the wood sheathing and drywall from the SIPs inner core. According to the National Research Council of Canada, toxicity factors associated with burning polystyrene foam (the kind used most often in SIPs), is lower than that produced by burning white pine lumber.