The Seattle Department of Construction & Inspections recently published a code interpretation to ensure that membrane penetration for ductwork, fans, and lighting fixtures maintain the rated woodframe floor/ceiling assembly fire rating. This interpretation clarifies section 714.4 of the 2012 Seattle Building Code.

The interpretation provides diagrams and written descriptions depicting and describing the assembly requirements for openings less than 100 inches and greater than 100 inches per 100 square feet for different framing types.

The full interpretation and supportive instructions can be found here.