Podium Construction and IBC 510.5

[aldidog]

Has anyone worked on a project that has used section 510.5 of the IBC? Not sure if it matters, but I am looking at the 2018 version of IBC. It allows you to increase the height of type IIIA construction. However, we have a podium construction where the first floor is type IA construction. 510.5 specifically stipulates you can increase the height IF "the first floor assembly above the basement as a fire-resistance rating of not less than 3 hours and the floor area is subdivided by 2-hour fire-resistance walls into areas of not more than 3,000 square feet."

A questions I am running into:
1. The project has no basement, just the first floor podium of type IA construction. So which level would be considered the "first floor assembly above the basement"? The elevated slab of the second level? The slab on grade? or does this mean 510.5 is not even applicable?
2. Has anyone seen where they actually divide the upper floors into 3,000 areas separated by fire walls. It appears this is more geared towards townhouses. It would be really hard to get a double loaded corridor of an apartment building divided that small. You would be looking at 2-3 apartments per area before needing a firewall.

 

[Jay Smith]

510.5 might be a non-issue for you. A podium of type IA construction is covered in 510.2.

 

[aldidog]

Agreed. I think section 510.5 does not apply to the project since a podium is provided under 510.2. However, when looking into 510.5 it got me thinking, and was curious on everyone's opinion.

 

[steveray]

Bad section....Doesn't tell you which floor gets separated either....Above or below....

 

[steveray]

Or I guess all the way through....

 

[aldidog]

Oh wow, I didn't even think of that applying to the level below the 3-hour horizontal assembly. Took a quick peak at the 2021 IBC. Its written exactly the same... Guess no one has questioned it over the last few code cycles.

 

[gtyler75]

Reviving this thread; specifically wondering if anyone has proposed this exemption in combination with 510.2 (using the top of podium as "ground plane"). The firewalls may be tricky to overcome, practically-speaking, but still has potential application on a project I'm working on.

TIA

 

[JPohling]

Gtyler. Others may have more experience on this matter. Here is a definition from the 22 California Building Code. I do not see how the grade plane would be altered to allow what you are discussing. It is all relative to the actual grade and finished ground level.

 

[Shams Gannon]

Reviving this thread again... My understanding is that in 2018 we were allowed to build the full number of stories (say... five for type IIIA) over a one or multi-story podium, as the 3 hr separator created two different buildings, which btw, helped you get to the allowable height (85' for type IIIA).

In 2021 they adjusted the language to read 'above grade', which was specifically to indicate that the below grade stories (basements) didn't count against your allowable stories. This had the unintended effect of nullifying podiums, so they added an additional piece to 510.5 that allowed your building to get a single story and height bonus for a slightly more robust podium.



IMO this is a poorly written piece of code. Previously there was a clear benefit of building two stories of Type 1A podium and five stories of Type IIIA for a 7 story building. It was the dominate form of development here in Austin, and we're having a hell of a time clawing this one back. There is nothing about limiting the allowable heights in the code change proposal...

 

[steveray]

Reviving this thread again... My understanding is that in 2018 we were allowed to build the full number of stories (say... five for type IIIA) over a one or multi-story podium, as the 3 hr separator created two different buildings, which btw, helped you get to the allowable height (85' for type IIIA).

In 2021 they adjusted the language to read 'above grade', which was specifically to indicate that the below grade stories (basements) didn't count against your allowable stories. This had the unintended effect of nullifying podiums, so they added an additional piece to 510.5 that allowed your building to get a single story and height bonus for a slightly more robust podium.

View attachment 14698

IMO this is a poorly written piece of code. Previously there was a clear benefit of building two stories of Type 1A podium and five stories of Type IIIA for a 7 story building. It was the dominate form of development here in Austin, and we're having a hell of a time clawing this one back. There is nothing about limiting the allowable heights in the code change proposal...

Can you use 510.2?

 

[redeyedfly]

Reviving this thread again... My understanding is that in 2018 we were allowed to build the full number of stories (say... five for type IIIA) over a one or multi-story podium, as the 3 hr separator created two different buildings, which btw, helped you get to the allowable height (85' for type IIIA).

In 2021 they adjusted the language to read 'above grade', which was specifically to indicate that the below grade stories (basements) didn't count against your allowable stories. This had the unintended effect of nullifying podiums, so they added an additional piece to 510.5 that allowed your building to get a single story and height bonus for a slightly more robust podium.

View attachment 14698

IMO this is a poorly written piece of code. Previously there was a clear benefit of building two stories of Type 1A podium and five stories of Type IIIA for a 7 story building. It was the dominate form of development here in Austin, and we're having a hell of a time clawing this one back. There is nothing about limiting the allowable heights in the code change proposal...

That doesn't nullify 510.2 at all. The Type III building starts at the top of the podium. By the definition of story above grade plane you can still build 5 stories of Type III. 510.5 is still as useless as it has always been; I've never seen that used one time.

 

[jar546]

Based on the discussion so far, it seems clear that Section 510.5 is rarely applicable in practical podium construction scenarios, especially for larger multi-family or mixed-use developments. The requirement to subdivide floor areas into 3,000-square-foot sections with 2-hour fire walls feels more appropriate for smaller residential applications, such as townhomes, and is impractical for apartment layouts with double-loaded corridors. In podium construction where the first floor is Type IA, Section 510.2 remains the dominant approach, as it clearly allows the upper stories to start at the top of the podium and avoids the restrictive conditions imposed by 510.5. While the ambiguity in 510.5 about the "first floor assembly above the basement" complicates its interpretation, it’s evident that 510.5 has limited utility compared to 510.2, which better supports modern construction practices. The challenges in applying 510.5, combined with its unclear intent, highlight the need for further clarification or rethinking of this section in future code cycles.

 

[Shams Gannon]

Aaaaaahhhhh, the lightbulb just clicked... 504.4 doesn't say measured from grade, it's just referring to stories that are not below grade. Got it.

Thank you all.

510.5 is still as useless as it has always been; I've never seen that used one time.

Conceivably, this should allow a 5 story type VA over a type IA podium though, no? If the podium were to be divided up into smaller sections and provide fire walls... strange I've never see this used either.

 

[Yankee Chronicler]

A former employer was involved in generating the concept of what we now know as "podium" buildings. The intent was, and is supposed to be, that the "lid" of the podium creates a second ground plane, and the number of stories in the superstructure is counted from the lid of the podium.