Floor assembly rating between R2's.

[Ryan Schultz]

We have existing 2 story Type VB with the following plan, that's currently unsprinklered.

We would like to convert one of the 1st floor (M) occupancies, to a (R2). We plan on sprinklering only the newly renovated dwelling unit with NFPA 13R.

We would like to realize 1012.1.1.2 Change of Occupancy Classification With Separation, therefore we assume per 508.4, that the wall between the new (R2) and existing (M) needs to be 2hr rated (marked blue below).

Question: does the floor between the new (R2) and the existing (R2) on the 2nd floor need to be rated for 2hr per 711.2.4.2 or can it be 1 hr rated per 420.3?

If 2hr rated, does the supporting exterior wall (marked green below) for the 2nd floor trusses, need to be rated 2hr as well, per 711.2.3?

If so, does this 2 hour rating need to apply to both the exterior part and interior part of the wall? Or can we just apply 2 layers of drywall to the inside to get the 2hr rating from the interior side?

If both sides.... man, does that seem overkill.

 

[Robert]

Ryan, good question about the 2 hour supporting construction (green). I had a plan checker require it on both sides as he said the code does not recognize an asymmetric fire assembly. But there is a provision in the code for asymetric exterior wall assemblies in 705.5 (California) based on fire separation distance. There is also something earlier in the same chapter about assymetric interior wall assemblies. I just don't know if it applies, so I'm watching this thread.