Allowable Area for Type II Building

[sbb-j]

I'm involved with a potential building of 100,000+ sf. We are considering structural systems and what kind of fire resistance will be required for the project. It will be an F-1 occupancy.

for cost reasons one option is a PEMB system for the building. Typically these are considered Type II-B which would only allow up to ~73K sf with the maximum frontage increase. If we want to make it a Type II-A building we would need add 1 hour of fire resistance to the structural frame, bearing walls, roof, etc. I believe that spray-on fire protection or intumescent paint would give us the rating on the building steel, but the roof assembly seems to be a challenge. The only UL assemblies I can find for a 1 hour roof/ceiling involve a full layer or gyp. bd. For a building of this size That would be tremendously expensive. It also seems like a lot of similar buildings I see of this type and size do not have ceiling like this. My question regarding this situation is:

1. Is there another way to provide a 1-hour roof assembly that doesn't involve a continuous layer of gyp. bd?
2. Is there an exception in the IBC (2021) that allows the roof to not be rated?

Another (more costly) option for our project would be to building it with a post/beam/bar-joist structure with pre-cast wall panels. I thing this would allow us to consider it a Type II-A, or even a Type I building. I know most big-box retail buildings are built this way as the structural steel is usually exposed. Do these types of building rely on intumescent paint to provide the fire resistance rating?

 

[steveray]

Welcome to the forum!....Can you use the unlimited area provisions?

507.4 Sprinklered, One-Story Buildings​

The area of a Group A-4 building not more than one story above grade plane of other than Type V construction, or the area of a Group B, F, M or S building no more than one story above grade plane of any construction type, shall not be limited where the building is provided with an automatic sprinkler system throughout in accordance with Section 903.3.1.1 and is surrounded and adjoined by public ways or yards not less than 60 feet (18 288 mm) in width.

We have a lot of unlimited area IIB buildings...

 

[classicT]

Have you seen the footnotes to Table 601? Footnote 'b' is not helpful given Group F-1; however, heavy timber could be a possibility under footnote 'c'. You would need to follow Section 603.1 #19 - Heavy timber as permitted by Note c to Table 601 and Sections 602.4.4.4 and 705.2.3.1.

 

[sbb-j]

I think Section 507.4 will help us. Reading that, with an F-1 occupancy as long as we keep a 60 foot public way or yard around the building, we can build as big as we need to and still keep it as a Type II-B construction.

Thank you for the reply.

 

[classicT]

Do keep in mind that your exit access travel distance is capped at 250-ft (Table 1017.2) unless complying with 1017.2.2.

2021 IBC 1017.2.2 Groups F-1 and S-1 Increase​

The maximum exit access travel distance shall be 400 feet (122 m) in Group F-1 or S-1 occupancies where all of the following conditions are met:

1. The portion of the building classified as Group F-1 or S-1 is limited to one story in height.
2. The minimum height from the finished floor to the bottom of the ceiling or roof slab or deck is 24 feet (7315 mm).
3. The building is equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1.