Perimeter roof joints for rated and unrated roofs

[chris macko]

I've got a large building with several different roof types, some with a 1 hour rating (IB) and some unrated (IIB). The rated roof deck is concrete over metal deck and the unrated is just a typical PVC membrane system. Both roofs terminate at an unrated exterior wall assembly with parapets. Section 715 has plenty of information on rated roofs and ceilings terminating at unrated curtain walls, but I can't find anything for the roof joints. We originally had a typical mineral wool draftstop assembly shown for both conditions, but we're getting questions from the contractor about alternate systems without mineral wool and some of them will not work if they need to stop hot gas and combustion products, but I don't know if that's actually required. Does anyone have any insight on the actual code requirements in these cases?

 

[RLGA]

Are openings permitted within the roof/ceiling assembly? If so, joints do not need to be protected (Exception to IBC Section 715.1, location #8).

Are the exterior walls curtain walls? if so, joints do not need to be protected (Exception to IBC Section 715.1, location #10).

 

[chris macko]

Thanks! That's the section I was looking for. it's 715.3 in 2021 IBC. Exterior walls are insulated metal panels, but are outboard of the floor and roof slabs, so it's a curtain wall configuration, but not a glass and aluminum assembly. I'm not seeing where they define what type of curtain wall they're talking about. The roof penetrations are generally unprotected, but there is a firewall that has roof opening restrictions within a certain distance that would make exception 8 conditional. If it all falls under exception 10, than it's easier.