Calculated Fire Resistance — Wood Assemblies
IBC §722.6 Component Additive Method (CAM): membrane + framing + insulation, capped at 1 hour.
Table 722.6.2(5): glass fiber / mineral wool batts ≥ 2 pcf, rockwool or slag mineral wool ≥ 3.3 pcf, or cellulose ≥ 2.6 pcf nominal density. Walls only — no insulation bonus for floors/roofs.
Calculated rating
| Membrane (fire-exposed side) | 40 min |
| Wood studs, 16" o.c. (walls) | 20 min |
| Total | 60 min |
Qualifies as a 1-hour assembly under IBC 722.6 (calculated ratings are capped at 1 hour).
How the method works (IBC 722.6)
- Rating = membrane on the fire-exposed side + framing contribution + insulation bonus. The membrane on the unexposed side is not counted (interior walls still need membranes on both faces).
- Walls with different membranes on each face are rated on the weaker side; exterior walls are rated for fire from the interior side only, with the exterior face per Table 722.6.2(3).
- Floor/roof assemblies are rated for fire from below; the upper membrane must be a flooring/roofing system per Table 722.6.2(4).
- Framing spaced 16" o.c. or less; studs min nominal 2x4; joists min nominal 2" thick. Gypsum on ceilings runs perpendicular to framing with joints finished.
- Maximum calculated rating under §722.6 is 1 hour. For 2-hour+ assemblies use a tested listing (see the Assemblies library).
Values from 2021 IBC Tables 722.6.2(1), 722.6.2(2) and 722.6.2(5); cross-checked against AWC DCA 4. Browse tested assemblies →
Disclaimer: This calculator is for reference only. Confirm the tables in your adopted code edition and any local amendments, and verify the design with your building department. Consult a qualified design professional for project-specific requirements.