Duct And Light Penetrations Of Fire Rated Assemblies


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?


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.

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