How do we define building levels?
So here I use the terms floor, floor level, level and story interchangeably. I'm not entirely sure whether that's appropriate or not, but the International Building Code would define what I’m talking about as a building story.
Ultimately, what we're really concerned about here is the number of stories that are above grade plane. This drives limitations for things like NFPA 13R or the allowable number of stories that our building can have. Counting the number of stories in a building seems easy enough, and in many cases it could be very obvious if we have a flat site and a few floor levels that are all above a grade level slab, but in other cases it might not be so obvious.
So, take for example a sloped project site where the lowest level is half sunk in into a hillside. How many floor levels, or more appropriately as the IBC would define them? How many stories are above grade?
Just like when we were looking at building height, to figure this out we go to the applicable building code and we want to check the definitions. In the International Building Code, this would be chapter 2 in going in and looking at the definitions for both a story and a story above grade plane.
Today, as an example, we're going to use the 2021 edition of the International Building Code. But if your applicable building code has been modified or is a different edition, you need to go to that and look up for yourself because this is all subject to change over time.
If you're looking for more detail about how we're looking at measuring grade plane, go to our last video where we talked about building heights and we look at that in a lot more detail.
So, in order for a story to be considered above grade, it has to meet one of three key criteria when we're under the International Building Code.
The first is that the story has a floor surface that is entirely above grade plane. Here in our first scenario, we can see the floor level is entirely above this grade plane level, which is measured at the lowest level within six feet of the building or the lowest level between the exterior wall and the lot line if the lot line is closer than 6 feet.
This is pretty straightforward.
We have a slab. It's above the lowest point. It's above grade. Our story is above grade.
Our second scenario. Well, really our second and third scenario, take measurements from the floor level above the level that we're considering. If the finished surface of the floor level above the one we're talking about is more than six feet above our grade plane. Then the story that we're looking at would also be considered above grade plane. Basically, what they're doing is not allowing us to cheat and sink our slabs six inches below the ground, just to have that story be considered below grade level.
This scenario number 2 kinda knocks that out and defines the height for that six measurement is from the floor level above.
Our third scenario is somewhat similar. It involves measuring the finished surface of the floor level above. If that finished surface of the floor level above is more than 12 feet above the finished grade level at any point, then the story that we're looking at is considered to also be above grade. The finished ground level is where the grade comes into contact with our building's exterior wall.
So when can we call a floor level a basement? Well, a basement is a story that is not considered above grade. If a floor level that we're looking at does not meet any of those three scenarios above, then it can be considered a basement and would not count as a floor level above grade.
That's all great but what about mezzanines? What about equipment platforms?
Those are both good topics to break out and discuss in a lot more detail, which we will do in the future. But in short, a mezzanine is considered part of the story below and itself is not considered its own story. Mezzanines carry limits for how large they can be, how open they need to be, and they have their own means of egress requirements, and it's covered in chapter 5 of the IBC.
So, now that we've looked in some of the nuances of how we're defining a building story above grade below grade. Why does it matter?
Chapter 5 of the IBC gives us the maximum number of building stories that are allowed above grade based on the occupancy, whether it's sprinklered and what its type of construction is. We can't build a building that exceeds the number of allowable stories under the building code and maintain code compliance.
Now, there's provisions for increasing the number of allowable building stories and all of that, which we'll go into detail later. But in general, we just can't add an unlimited amount of stories to our building. We're limited by the building code, depending again, on the occupancy, whether it's sprinklered and the type of construction.
Also, this matters when we go back and consider limitations for certain standards like NFPA 13R, which limits the number of building stories whenever we use that standard. So, the actual number of building stories above grade can affect which standard we're even allowed to use.
So, in summary, how do we define building levels? Well, we go to our applicable building code, we check the definitions in a few key areas. This includes the definitions for grade plane, story above grade plane, and basements. These definitions lay out the specific rules for how we go about determining how many floors we have in our building that are above grade.
I'm Joe Meyer, this is MeyerFire University.
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