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Construction Type II-A vs. I-B

nealderidder

Sawhorse
Joined
Dec 7, 2010
Messages
402
Location
Sacramento, CA
Currently have a project classified as a type II-A, considering upping that to a I-B. It's a four-story office building around 50k SF per floor in CA. Proposing a new fifth floor roof deck that's <750 SF (B Occ). If I want to enlarge that roof deck I'll have an A Occ and need the I-B to get that on the fifth floor.

Other than going from 1HR to 2HR in table 601, am I opening up a can of worms for myself? I can make either type work as far as the required rated assemblies but I keep thinking there are other consequences I'm not thinking of...

Anything pop into your head?
 
Read Section 503.1.4 and see if that answers your question.

I'm clear on the effect of putting enclosed space on the roof and the jump from B to A if I get over 750 SF etc. My question is only about construction type (regardless of the project or design) and what it means to go from II-A to I-B.

Is it only the change in fire ratings in table 601 or is there more to it? Does it complicate the fire alarm, require me to have more notification, require rated corridors, or something else I'm not thinking of? I feel like there is a surprise waiting for me somewhere. The fire flow requirements change for the better (less hydrants) when you go to II-A. Is there anything else like that you can think of when going from II-A to I-B?

I know this is a ridiculous request. I'm asking you to tell me what I don't know. But I thought something obvious might pop into someones head that they could share with me.

Thanks,
 
The reason I suggested looking at Section 503.1.4, is that you have a 4-story building but plan on putting a Group A on an occupied roof--you may not need to go to Type IB construction.

Per Table 504.4, a Type IB building allows a Group A to be on the 11th story for nonsprinklered ("NS") buildings and on the 12th story for sprinklered ("S") buildings. However, Type IIA construction allows a Group A to be on the 3rd story for "NS" buildings and on the 4th story for "S" buildings.

Assuming your building is sprinklered throughout and you're not using the sprinkler for an area increase (it's a California thing), then you can use Type IIA construction because Section 503.1.4 states if the occupancy group is permitted on the story below the occupied roof, then you can have that occupancy group on the occupied roof. Thus, you don't need Type IB construction to allow a Group A on the "fifth floor."

If you're using the sprinkler for an area increase, then Type IB construction is what you'll need. for a 4-story building that won't affect enclosed stairways and elevator hoistways. However, all penetrations in horizontal assemblies (except the roof) will need to be 2-hour assemblies. One of the benefits of going to Type IB construction is that the walls for shafts (stairways, elevator hoistways, chases, etc.) can be supported by the floors since they have a fire-resistance rating equal to the shaft enclosures.
 
The reason I suggested looking at Section 503.1.4, is that you have a 4-story building but plan on putting a Group A on an occupied roof--you may not need to go to Type IB construction. Exactly the pickle I'm in. Met with the B.O. to discuss options and what he was comfortable with. We're looking at either <750 SF of enclosed roof deck (Type II-A, 5 stories, all B use) vs. >750 SF (Type I-B, 5 stories, with A3/B use). To get down to II-B, 4 stories, I can only pop up the elevator and have no enclosed or covered space on the roof level.

Per Table 504.4, a Type IB building allows a Group A to be on the 11th story for nonsprinklered ("NS") buildings and on the 12th story for sprinklered ("S") buildings. However, Type IIA construction allows a Group A to be on the 3rd story for "NS" buildings and on the 4th story for "S" buildings.

Assuming your building is sprinklered throughout yep and you're not using the sprinkler for an area increase (it's a California thing), nope then you can use Type IIA construction because Section 503.1.4 states if the occupancy group is permitted on the story below the occupied roof, then you can have that occupancy group on the occupied roof. Thus, you don't need Type IB construction to allow a Group A on the "fifth floor." B.O. disagrees. He says anything over 750 SF on the roof = 5 stories and an A3 use = I-B.

If you're using the sprinkler for an area increase, then Type IB construction is what you'll need. for a 4-story building that won't affect enclosed stairways and elevator hoistways. However, all penetrations in horizontal assemblies (except the roof) will need to be 2-hour assemblies. One of the benefits of going to Type IB construction is that the walls for shafts (stairways, elevator hoistways, chases, etc.) can be supported by the floors since they have a fire-resistance rating equal to the shaft enclosures.
The added complication is that this is a renovation of an existing structure that is 3/4 cast-in-place concrete (which is great) and 1/4 structural steel (the pain in my behind if going to 2 hour ratings). I came up with a table of the options I'm looking at (attached).
 

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Nealderidder: You can have a rooftop canopy or enclosed space provided that it does not cover more than 1/3 the area of the roof deck (Section 1510.1.1).
 
Also forgot to mention - I did bring up 503.1.4 but was trumped by 503.1.4.1. B.O. said - yes you can have an occupied roof and not have an A use as long as you're not enclosing anything over 4' tall. That's not going to work for my storage room, bathrooms, and covered seating...
 
Also forgot to mention - I did bring up 503.1.4 but was trumped by 503.1.4.1. B.O. said - yes you can have an occupied roof and not have an A use as long as you're not enclosing anything over 4' tall. That's not going to work for my storage room, bathrooms, and covered seating...
That is a section I have some heartburn over. Section 1510.1 addresses "rooftop structures" in general and Section 1510.1.1 on area limitations mentions "penthouses and other enclosed rooftop structures." Although Section 1510 provides requirements for some specific types of rooftop structures, there is no definition of what constitutes a rooftop structure. I have previously used Section 1510.1.1 successfully for similar conditions, and then they came out with Section 503.1.4.1. I think this will probably be modified (relaxed) in editions to come. For one, liability. A 4-foot limitation means that plexiglass panels and other "enclosure" components that could prevent accidental or intentional fallers would be prohibited. A limitation on canopy-type structures would be reasonable, even if less than the 1/3 area permitted for rooftop structures; but a pure prohibition is a bit much.
 
That is a section I have some heartburn over. Section 1510.1 addresses "rooftop structures" in general and Section 1510.1.1 on area limitations mentions "penthouses and other enclosed rooftop structures." Although Section 1510 provides requirements for some specific types of rooftop structures, there is no definition of what constitutes a rooftop structure. I have previously used Section 1510.1.1 successfully for similar conditions, and then they came out with Section 503.1.4.1. I think this will probably be modified (relaxed) in editions to come. For one, liability. A 4-foot limitation means that plexiglass panels and other "enclosure" components that could prevent accidental or intentional fallers would be prohibited. A limitation on canopy-type structures would be reasonable, even if less than the 1/3 area permitted for rooftop structures; but a pure prohibition is a bit much.

Agreed! I made a plea for 1/3 area or even 10% (accessory size) but lost the argument based on his interpretation of 1510 and the 4' tall limitation.

So I'm back to I-B.
 
Actually, there is a definition for rooftop structure--it's just not italicized like other terms in the IBC.

Chapter 2: Rooftop Structure: "A structure erected on top of the roof deck or on top of any part of a building."

Anyhow, this doesn't help your situation--it looks like you're a new victim of Section 503.1.4.1. Good luck!
 
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