Over the years, we have had many insulation contractors, builders and architects ask us how they can achieve a one hour fire rated wall using cellulose insulation. The simple answer: Check the International Building Code!
The International Building Code includes guidelines to calculate fire resistance ratings for both load-bearing and non-load bearing wood frame assemblies. Cellulose insulation was incorporated into this code by the International Code Council in 2000.
The calculation method is intended only for one-hour rated assemblies, and the process is quite simple. Just add the fire resistance rating of each wall component together. For example, a frame consisting of wood studs 16 inches on center is given a 20-minute rating, 5/8 inch gypsum wallboard used for the interior finish adds another 30 minutes. By filling this all with cellulose insulation, an additional 15 minutes of protection brings the calculated fire resistance of this wall above a one-hour rating. This rating can also be achieved using other types of wallboard, such as ½-inch Type X gypsum.