Stacked Duplex. Fire Ratings

[Tim Kunz]

I purchased an SFR in Sacramento, it's currently a studio over a 3 car garage. We're planning on turning the garage space into another unit with the goal to get it zoned as a duplex. Has any in California converted a property in a similar situation. I'm running into hangups with code section R302.3.1 which seemingly requires not only the floor separating the units to be fire rated but all the walls below supporting that floor to be fire rated (ie all exterior walls and load bearing interior walls on the first floor), which may mean extremely expensive fire rated windows at the lower unit. Anyone run into this issue?