by Bob Armbrister, on Apr 24, 2020 12:00:00 AM
Q: Are IT closet plywood backboards required to be fire rated with the rating showing in closets that are sprinklered?
A: No. Section 220.127.116.11 of the 2012 LSC requires all interior finish to be either Class A or Class B. Class A is all materials that have a flame spread rating of 0-25, and Class B is all materials that have a flame spread rating of 26 -75. The average plywood, including flame-retardant type, has a flame spread rating around 150. So, on the surface, it would appear that plywood cannot be used as an interior finish. But wait, there’s more! Section 10.2.8.1 allows Class C materials where Class B is required if the area is protected with sprinklers. Class C is all materials that have a flame spread rating between 76 – 200.
So, plywood, even the non-flame-retardant type, is permitted as an interior finish in a room that is protected with sprinklers since it has a flame spread rating of about 150, which is less than the maximum allowed of 200. But, to qualify as interior finish, the plywood has to be secured to the wall with a layer of gypsum board between the plywood and the steel studs. In other words, the plywood cannot be attached directly to the steel studs. If it did, it would no longer be considered interior finish but part of the structural wall and combustible materials are not permitted in walls of Type I and Type II construction buildings.