I came across a question in "arequestions"...
"What is the minimum fire resistance requirement of a partition wall that separates an adjacent high school and office buildings if both buildings are Type IIA and the party wall extends vertically 32
above the highest roof point in both buildings?
Answer: 2 HR
Here's the logic.
According to IBC, Chapter 7, Section 706 FIRE WALLS: if two different occupancies are adjacent to each other as is described in this question, the party wall that separates them should be a Fire Wall. To check the fire resistance requirements of fire walls, we refer to Table 706.4. According to this table, the required fire rating is 2 hours. Because according to the footnote (a) in the same table, for Type II occupancies there is an exception for fire rating of the fore walls for occupancy types B and E. Instead of 3 hours, this exception makes two hours enough for this scenario.
OK. My first question is how do we know that we have to use a Firewall to separate these two Occupancies?
The office could be an incidental use, but we are not given that information. In fact, we are not given any heights or areas of each Occupancy.
But if, instead of making a beeline to Firewalls on 706.4, we start at separation of occupancies in Chapter 5, Table 508.4, if we crosscheck Occupancy A with B, we see that the rating for sprinklered is 1 hour and for non-sprinklered, it's 2 hours. So, there is no reason that I see to assume initially that a firewall is required. In fact, a fire barrier may be sufficient. The statement in paragraph 508.4.4 seems pretty clear. Individual occupancies shall be separated from adjacent occupancies in accordance with Table 508.4.
My understanding is that Firewalls are typically used when an occupancy, or Mixed Occupancy, exceeds Allowable Area, and so must be broken into smaller "buildings" which each must then comply with Allowable Area limits.
I'd appreciate feedback from anyone who has some expertise in this.
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