Duct And Light Penetrations Of Fire Rated Assemblies
Question:
In a small scale multi-family residential project, I'd like to use a wood truss floor-ceiling assembly to achieve a one hour separation between units. I'd like to directly attach the drywall to the underside of the trusses & use the truss space for ducts & lighting (the floor above will be lightweight concrete on plywood sub-floor). UL assemblies do not seem to address the duct/light penetrations in such an assembly. Can I achieve a one-hour rating in such an assembly and how are penetrations addressed? Can the ducts in the truss space serve both units above and below?
Answer:
There is at least one UL assembly that includes ducts: No. L546. This assembly, however, includes resilient or furring channel at 12” O.C. Regarding air ducts, protection systems and lighting (luminaires) in UL tested assemblies, see the following UL certifications: BXUV.GuideInfo and CDHW.GuideInfo. For details on additional rated truss assemblies, see SBCA Research Report 1509-01: Fire Resistance Rated Truss Assemblies.