Building Area vs Fire Area

[rosegamble]

Hello, All. I have a somewhat basic question about the 2021 SC BC.

I am looking for some clarification on the definitions portion of the code.

Area, Building (from the official commentary)...
"Allowable building areas (as established by the provisions
of Chapter 5 and Table 506.2) are a function of
the potential fire hazard and the level of fire endurance
of the building’s structural elements, as established
for the types of construction in Chapter 6. A
building area is the “footprint” of the building; that is,
the area measured within the perimeter formed by the
inside surface of the exterior walls."

"Building Area" therefore does NOT include the thickness of the exterior walls. It is measured to the inside face.

However, then there is "Fire Area," which is defined as "the aggregate floor area enclosed and bounded by... exterior walls." So does fire area include exterior wall thickness while building area does not? Are you all including the exterior wall thickness in your "Fire Area" measurements?

Thanks!

 

[RLGA]

It appears South Carolina has revised the IBC definition of Building Area to be more comprehensible by the casual code user.

Although the IBC has a slightly different way of defining Building Area than it does for Fire Area, (i.e., "area included within" vs. "area enclosed and bounded by"), they are intended to have the same meaning. Why did they decide to use a different phrasing? I don't know.

A fire area is to be determined just as you would for a building area. For a building with only one fire area, the building area should equal the fire area, except if the fire area includes another story (i.e., no separation between stories) or a mezzanine.

 

[rosegamble]

Thank you for your thoughts. That clip I included was actually from the commentary, not the code itself.

So fire areas should add up to building area essentially. How are you guys counting a covered porch? I know this is included in both building area and fire area. If exterior walls are not included, the green area below is the typical interior building area. For a covered porch, are you defining it as edge of exterior wall above (A) or edge of inside face of exterior wall above? A small detail but one that has me scratching my head sometimes, just as a concept.

 

[Yankee Chronicler]

I measure fire areas the same as I measure building areas -- to/from the inside surface of the exterior walls.

The concerns impacting fire area limitations are the amount of fuel load potentially present. A bigger space allows more flammable "stuff" to be housed in the space. In the case of a single-tenant building, IMHO it would make no sense to say the building area is 5,000 square feet but the fire area is 5,304 square feet.

Areas under roofs but without enclosing walls are counted as building area when they are potentially subject to occupancy and/or when they may shelter a fuel load. For example, a rectangular building with a 5-foot by 8-foot recess at the main entrance door -- I don't include the recess in the building area, and I don't think anyone I know would do so. On the other hand, a building such as your example -- if the porch is 20' x 20' or 30' x 30' and will be used by people, with "stuff" on the porch (especially stuff that can burn), then the porch gets included.

As to how to determine the extent of the porch -- the plain language of the definition of "building area" suggests that your example 'A' is the applicable interpretation. That's supported by the IBC Commentary graphic:

 

[steveray]

I measure fire areas the same as I measure building areas -- to/from the inside surface of the exterior walls.

The concerns impacting fire area limitations are the amount of fuel load potentially present. A bigger space allows more flammable "stuff" to be housed in the space. In the case of a single-tenant building, IMHO it would make no sense to say the building area is 5,000 square feet but the fire area is 5,304 square feet.

Areas under roofs but without enclosing walls are counted as building area when they are potentially subject to occupancy and/or when they may shelter a fuel load. For example, a rectangular building with a 5-foot by 8-foot recess at the main entrance door -- I don't include the recess in the building area, and I don't think anyone I know would do so. On the other hand, a building such as your example -- if the porch is 20' x 20' or 30' x 30' and will be used by people, with "stuff" on the porch (especially stuff that can burn), then the porch gets included.

As to how to determine the extent of the porch -- the plain language of the definition of "building area" suggests that your example 'A' is the applicable interpretation. That's supported by the IBC Commentary graphic:

View attachment 15743

Well said…I had an argument on a big y grocery store and whether their front overhang (that they were sprinklering) was building area or not…

 

[Yankee Chronicler]

Well said…I had an argument on a big y grocery store and whether their front overhang (that they were sprinklering) was building area or not…

Well, let's see ...

At my local supermarket, there are two entrances separated by a projected section of the building that houses the in-store bank, the customer service counter, a stairway to admin offices on the upper level, and a couple of other functions. The roof overhang extends both ways from that projection to the ends (side walls) of the building.

Viewed from the parking lot, the overhang portion to the left shelters cart storage, two 25-pound propane tank cages, and occasional seasonal displays. The overhang portion to the right of the central area shelters the stack of bagged firewood for sale, potted plants for sale during the spring planting season, and various seasonal displays at other times of the year. So both overhang areas are used for display of merchandise -- I'd say they count in the building (and fire) area.

 

[rosegamble]

Interesting. So it boils down to use. The tricky thing is how the code requires you to measure building area (and, we have concluded, fire area) to the inside face of exterior walls, but then has you include covered outdoor usable space in the calculation. In that case... while I also have the commentary and see that figure Yankee Chronicler sent over, it seems inconsistent. Exterior wall thickness IS included, but just at the outdoor space.

 

[Yankee Chronicler]

Interesting. So it boils down to use. The tricky thing is how the code requires you to measure building area (and, we have concluded, fire area) to the inside face of exterior walls, but then has you include covered outdoor usable space in the calculation. In that case... while I also have the commentary and see that figure Yankee Chronicler sent over, it seems inconsistent. Exterior wall thickness IS included, but just at the outdoor space.

And that's because (I believe) with a physical wall surrounding the space, you can't fill the portion occupied by the exterior walls with highly combustible excelsior packing materials, but with a supermarket exterior area under a roof overhand you can install a cage full of propane bombs. Right at the edge.

 

[steveray]

Dan did not agree…

Well, let's see ...

At my local supermarket, there are two entrances separated by a projected section of the building that houses the in-store bank, the customer service counter, a stairway to admin offices on the upper level, and a couple of other functions. The roof overhang extends both ways from that projection to the ends (side walls) of the building.

Viewed from the parking lot, the overhang portion to the left shelters cart storage, two 25-pound propane tank cages, and occasional seasonal displays. The overhang portion to the right of the central area shelters the stack of bagged firewood for sale, potted plants for sale during the spring planting season, and various seasonal displays at other times of the year. So both overhang areas are used for display of merchandise -- I'd say they count in the building (and fire) area.

 

[Yankee Chronicler]

Dan did not agree…

Yeah --

Formal interp, or off-the-cuff guff?

 

[steveray]

Yeah --

Formal interp, or off-the-cuff guff?

Off the cuff…I was helping out someone that was helping out a town that was between BOs…pretty sure the acting or incoming bo and FM let it go…