Fire Wall or Fire Rated wall?

[Mech]

2015 IBC

Existing building with F-1, S-1, S-2, B use groups. Proposed addition with F-1 and S-2 use groups.

I need to separate a 40 ft tall proposed addition from a 27 ft tall existing building with fire rated construction. The speed humps I encounter are that the structural engineer wants the addition to be about 3 feet from the existing building to minimize roof strengthening requirements due to snow drift loads on the existing lower roof and the owner wishes to retain a courtyard to maintain existing refrigeration equipment.

Since the proposed 3 hour FIRE RATED wall is not immediately adjacent to all existing building walls,
1. Can this still be considered a 3 hour rated FIRE WALL to create separate buildings?
2. Are the existing Type 3B non-rated building walls in violation of Table 602 for not having a minimum 30 ft fire separation distance?
3. Can the unrated overhead door be placed in the unrated wall?

Thanks

 

[RLGA]

First, what is driving the need for a fire wall? Does the combined area of the existing building and addition exceed the allowable area for the most restrictive construction type? Second, can the buildings be considered as separate buildings with an imaginary lot line between them?

 

[steveray]

Seems like it doesn't NEED to be a firewall, 2 buildings same lot FSD rated only.....

 

[Mech]

The existing building plus addition exceeds the maximum allowable area, even with sprinklers and frontage increase. The unlimited area building classification does not work due to the presence of an existing third floor.

The addition must be connected to the existing building with weathertight construction (walls and roof.) I see that my initial sketch missed a wall on the top side of the overhead door openings (and obscured by the nice photobucket ad); it's in there now.