# Building Area Calcs



## ELLEN09US (Mar 18, 2015)

In a new single family house, our plan checker is telling me that the story above the stairs count as building area on the second floor... how can I proof he's wrong? is there any code section?

thank you!


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## JPohling (Mar 18, 2015)

In the commercial world there is BOMA.  They establish the method to measure buildings to determine rentable and usable area.  They also have a method for multi family housing.  In all methods "major vertical penetrations"  like stairs and shafts are never counted.


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## cda (Mar 18, 2015)

ELLEN09US said:
			
		

> In a new single family house, our plan checker is telling me that the story above the stairs count as building area on the second floor... how can I proof he's wrong? is there any code section?thank you!


and the reason for the question?


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## Rick18071 (Mar 18, 2015)

Hope this helps, 2009 IBC:

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.

Allowable building areas (as established by the provisions of Chapter 5 and Table 503) are a function of the potential fire hazard and the level of fire endurance of the building's structural elements, as defined by 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 1206). When 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 Figure 502.1(1)]. 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.


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## ELLEN09US (Mar 18, 2015)

Rick18071 said:
			
		

> Hope this helps, 2009 IBC: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.
> 
> Allowable building areas (as established by the provisions of Chapter 5 and Table 503) are a function of the potential fire hazard and the level of fire endurance of the building's structural elements, as defined by 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 1206). When 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 Figure 502.1(1)]. 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.


seems like it counts!


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## steveray (Mar 18, 2015)

I think what CDA was trying to say is....Why does it matter? But you are Cali, so it might matter there...


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## cda (Mar 18, 2015)

ELLEN09US said:
			
		

> seems like it counts!


That is ibc

Not calif IRC


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## jdfruit (Mar 18, 2015)

ELLEN09US:

Please explain what is driving your question. Usually there is not an issue with floor areas unless you are dealing with a planning/zoning limit on home area vs. lot size.

Is the "plan checker" building or planning?

The CA residential code does not define floor area, here is the res code reference for terms defined in other CA codes:

R201.3 Terms defined in other codes. Where terms are not

defined in this code such terms shall have meanings ascribed

to them as in the California Building Standards Code, Title

24, California Code of Regulations.

Here is the CBC for floor area, gross and net:

FLOOR AREA, GROSS. The t100r 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, closets, the thickness of interior

wans, 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.

FLOOR AREA, NET. The actual occupied area not including

unoccupied accessory areas such as corridors, stairways,

toilet rooms, mechanical rooms and closets.


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## ELLEN09US (Mar 18, 2015)

The Planning department says that the footprint counts.

It matters because if I dont count the void space I can add to my useable space - instead of just void staircase.

I have limit for building area.


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## jdfruit (Mar 18, 2015)

ELLEN09US;

It appears you are dealing with planning (rash assumption hopefully doesn't result in adjective)

Floor area for planning uses is usually defined by zoning ordinance and most planning departments/divisions have those definitions available. Get the info & if not clear for definition, get back to the Forum.

Please let us know what you find out.


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## mjesse (Mar 18, 2015)

It's a zoning issue here.

We have a maximum Floor Area Ratio (FAR) as the house size relates to the lot size. This is used to control bulk regulations.

Our zoning code states any building area over 16' high shall be counted at twice the floor area.


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## ELLEN09US (Mar 31, 2015)

Thanks everyone!

The planning dep said the footprint counts!


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