Gross Floor Area Calculations

[gbsvazquez]

Under IBC 2018, if my new building design has an umbrella-shaped structure casting shade from upper floors onto the ground level, and the shaded ground floor includes interior circulation cores, exterior parking, and driveways, is all that space from the ground floor considered part of the gross floor area calculations? The circulation core is the only enclosed space in the ground level.

 

[steveray]

umbrella-shaped structure casting shade from upper floors onto the ground level, and the shaded ground floor includes interior circulation cores, exterior parking, and driveways,

I gotta see what this looks like....If it is truly just a shade structure, maybe not...If it is weather protection, probably so.....

 

[Yankee Chronicler]

From the 2021 IBC Definitions:

AREA, BUILDING. The area included within surrounding exterior walls, or exterior walls and fire walls, exclusive of vent shafts and courts. Areas of the building not provided with surrounding walls shall be included in the building area if such areas are included within the horizontal projection of the roof or floor above.

From the 2021 IBC Commentary on the above definition:

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. This excludes spaces that are inside this perimeter and open to the outside atmosphere at the top, such as open shafts and courts (see
Section 1205). Where a portion of the building has no exterior walls, the area regulated by Chapter 5 is
defined by the projection of the roof or floor above [see Commentary Figure 202(5)]. The roof overhang on
portions of a building where there are exterior enclosure walls does not add to the building area because
the area is defined by exterior walls.

This illustration has been in the Commentary for a very long time.

 

[gbsvazquez]

I gotta see what this looks like....If it is truly just a shade structure, maybe not...If it is weather protection, probably so.....

Let me clarify this:

It is not just a shade structure, the upper levels include program. The ground floor program only encloses the interior circulation core. The parking area and driveways located at the ground floor is shaded by the upper levels of the building. My question is if I should count the parking area and driveways as part of the gross floor area just because they are located under the horizontal projection of the floor above.

 

[steveray]

And here is the wrinkle as ridiculous as it sounds...We don't have a definition of "roof" for this purpose

[BS] ROOF ASSEMBLY (For application to Chapter 15 only). A system designed to provide weather protection and resistance to design loads. The system consists of a roof covering and roof deck or a single component serving as both the roof covering and the roof deck. A roof assembly can include an underlayment, a thermal barrier, insulation or a vapor retarder.

[A] BUILDING. Any structure utilized or intended for supporting or sheltering any occupancy.

But my take is if it sheltering an occupancy from the weather, it counts as a roof and building area and/ or fire area....

 

[classicT]

is all that space from the ground floor considered part of the gross floor area calculations?

The OP has asked about gross floor area calculations... and so far, the response has focused on building area calculations.

I tend to understand why others have answered regarding building area, as it seems likely that the OP is looking at the Ch. 5 & 9 requirements.

That said, further clarification from the OP is needed. @gbsvazquez, are you looking at building area (Ch. 5/9), or are you working on occupant loads and using the correct terminology of gross floor area (Ch. 10)?

2021 IBC (non-amended)
[BE] FLOOR AREA, GROSS. The floor area within the inside perimeter of the exterior walls of the building under consideration, exclusive of vent shafts and courts, without deduction for corridors, stairways, ramps, closets, the thickness of interior walls, columns or other features. The floor area of a building, or portion thereof, not provided with surrounding exterior walls shall be the usable area under the horizontal projection of the roof or floor above. The gross floor area shall not include shafts with no openings or interior courts.

 

[e hilton]

It would be helpful to see a floor plan, rendering, photo ...

 

[Yankee Chronicler]

But my take is if it sheltering an occupancy from the weather, it counts as a roof and building area and/ or fire area....

I don't think it has to be sheltering an occupancy. The code says, and the Commentary confirms, that if it's under an overhanging roof or story of the building, it counts toward the floor area of the story below the overhanging portion. Neither the code nor the commentary makes any mention of what the overhung area with no exterior walls is used for.

 

[steveray]

I don't think it has to be sheltering an occupancy. The code says, and the Commentary confirms, that if it's under an overhanging roof or story of the building, it counts toward the floor area of the story below the overhanging portion. Neither the code nor the commentary makes any mention of what the overhung area with no exterior walls is used for.

Yeah but.....We all know if it is an eave overhang we are not calling it building area....Once we start using it for SOMETHING...storage, occupancy, retail, dining, congregating...that is where I draw the line....Just like a canopy over stairs, just weather protection for "egress" not BA or FA....Canopy "roof" over a dining area, well that is another matter...