Rays197' date=' I assume that this building has a rated roof/ceiling assembly, based on the code sections you site. Is this correct? Are you referring to the dryer exhaust duct system for the 4th floor units only, or are you including the systems from the lower floors as well? Is the exhaust duct penetrating the top plate of a wall cavity within the unit or is it penetrating the ceiling membrane of the roof/ceiling assembly? You bring up a very tough question. These sections in the IMC and the IBC are not written well at all, and I have had to struggle with them as well. Just remember, this is not a partition penetration, so there is no exception permitted for fully ducted systems penetrating 1 hour partitions in fully sprinklered buildings
[/quote']The fourth floor ceiling is 1 hour rated. Each apartment is sprinkled but not the common attic. Yes, in reference to the dryer exhaust ducts are for the fourth floor only. The contractor is installing dryer vent boxes in the interior walls, up thru the top plate with nail plates and fire caulked. The dryer ducts are terminating up and out thru roof. Draft stopping every 3000 sq ft. in the common attic.