Hi, I’d like to ask about Table 705.5 (Fire-Resistance Rating Requirements for Exterior Walls Based on Fire Separation Distance) in the IBC.
For example, let’s say there are two buildings on the same lot—a school building and an office building—both of Type IB construction and located 25 feet apart.
To determine the minimum fire-resistance rating for their (non load bearing) exterior walls, how should the fire separation distance be applied in this case? I believe an imaginary lot line needs to be established between the two buildings, as referenced in Section 705.3, in order to determine the applicable fire separation distance and then use Table 705.5 to find the required fire rating.
Is this the correct approach? And what would be correct fire rating for each building?
Hi @giyoungoh,
Thanks for writing in! You are correct in your approach for this scenario. Note that Exception 1 in Section 705.3 states that the buildings can be regulated as either separated buildings or considered portions of one building, depending on the aggregate area (in relation to area limits per Chapter 5).
Considering the 25 feet between buildings, an imaginary lot line would be placed the middle (12.5’ to each building); Type IB construction; B & E (assuming the school building is through 12t grade) occupancy groups = 1 hour fire-resistance rating on exterior walls are required.
You would then reference Table 70.5 to determine the maximum area of exterior wall openings, based on fire separation distance and degree of opening protection.
Hope this helps!
Kiara Galicinao, AIA, NCARB
Black Spectacles
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