Exterior Wall Fire Rating

Per IBC section 705.5 when two buildings have a separation distance greater than 10’-0" the rating of exterior walls shall comply with both requirements in tables 601 and 602 whichever is stricter, because the danger is assumed to come from the inside. When the buildings are less than 10’-0" the danger is assumed to be from the exterior due to the possibility of self-ignition. The wall must then be rated for both interior and exterior.

My question is how do we determine rating of an exterior wall with an existing adjacent building less than 10’-0" with a different construction type? Do I use table 706.4 regardless of construction types?

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Hi @gfilcidor !
@coachbryanhadley Do you mind answering this question?

Hi @gfilcidor,
Appreciate the thought you put into this question.

As ever, building codes are interpretive, but I’ll do my best to give you a clear answer.

I imagine two scenarios. #1 - a new building to be placed within 10 ft of an existing building, and #2 - two new buildings to be placed within 10 ft of each other. The IBC is written more toward scenario #1 but can be made to work for the latter #2 scenario as well.

So, take scenario #1. The occupancy / construction type of the adjacent existing building doesn’t matter. You only need to satisfy requirements for the new building. Let’s say you are getting ready to submit plans for a class B occupancy, type IIB construction outpatient clinic with exterior load bearing walls to be separated on one side by 7 ft from an adjacent hospital. You’d first go to table 601 and you would find that the exterior load bearing walls will need to provide 0 hr fire resistance.

You would then look to see if there are any additional requirements pertaining to separation distance in table 602. You would find that the exterior bearing walls, at 7 ft from the adjacent existing hospital building, would need to provide 1 hr of fire resistance.

You would not need to consult table 706.4, which pertains to fire separation walls within your building.

Now scenario #2. Same thing - simply satisfy the requirements for each building independently and you’ll be all set!

Hope it helps,


Thank you for the clear explanation. This really helps

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