# Confused - Building Area calculation



## tuzi (Jun 14, 2016)

I am from Canada and new to USA and IBC. For the building area calculation, my college told me to take the area from outside face of studs. Is that true for all types of buildings? Also, in the definition of "Area, Building", it says " 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 o floor above". Does it mean the space under a porte cochere should be included in the building area? It doesn't seem like they do that in my office.


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## cda (Jun 14, 2016)

Welcome 

Trying to read English codes, that's the problem


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## cda (Jun 14, 2016)

Get a commentary or just look at this one

They are your friend


http://publicecodes.cyberregs.com/icod/ibc/2009f2cc/icod_ibc_2009f2cc_5_par003.htm?bu2=undefined


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## mtlogcabin (Jun 14, 2016)

tuzi said:


> Does it mean the space under a porte cochere should be included in the building area? It doesn't seem like they do that in my office.


 Yes they should be included.


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## cda (Jun 14, 2016)

Here is a good book, I have seen the 2009 but not later editions


http://shop.iccsafe.org/building-co...n-the-2012-international-building-code-1.html


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## cda (Jun 14, 2016)

One more great resource have not heard from RGLA in awhile?

http://www.specsandcodes.com/articles/default.html


One example:;

http://www.specsandcodes.com/articl...r No. 16 - Allowable Building Area Part 1.pdf


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## cda (Jun 14, 2016)

If the Porte cochere is not attached to the building, would not count it


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## tuzi (Jun 14, 2016)

My project is using 2015 IBC, though. Any difference on this definition? 2009 seems like you measure the building area from inside face of exterior walls.



cda said:


> Get a commentary or just look at this one
> 
> They are your friend
> 
> ...


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## tuzi (Jun 14, 2016)

Thanks, that's a good website to learn!




cda said:


> One more great resource have not heard from RGLA in awhile?
> 
> http://www.specsandcodes.com/articles/default.html
> 
> ...


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## tuzi (Jun 14, 2016)

That makes more sense to me. Thanks!



cda said:


> If the Porte cochere is not attached to the building, would not count it


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## cda (Jun 14, 2016)

tuzi said:


> My project is using 2015 IBC, though. Any difference on this definition? 2009 seems like you measure the building area from inside face of exterior walls.




Will have to look. 

A guess is no


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## cda (Jun 14, 2016)

tuzi said:


> Thanks, that's a good website to learn!





Two more


http://publicecodes.cyberregs.com/icod/index.htm

http://codes.iccsafe.org/app/book/toc/2015/I-Codes/2015 IBC HTML/index.html




http://codes.iccsafe.org/I-Codes.html#all


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## cda (Jun 14, 2016)

Plus more, you to can help support this site 


Always a commercial


Sawhorse status is the best:::


http://www.thebuildingcodeforum.com/forum/account/upgrades


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## Examiner (Jul 14, 2016)

Building area to determine construction type is taken from the inside face of the exterior perimeter walls.  For occupancy area calculations it depends on the occupancy group where mixed occupancies occur in a building you may have to use the inside face of some interior walls.  Exposure to fire for the allowable perimeter increase is to the outside face of the exterior walls skin finish.  Yes, any roof overhangs that can be used for expansion of the building’s exterior walls, such as attached covered entry’s, are part of the building area.  At one time a building code defined the roof extension had to be used in the building area if the roof extension was 15-ft or greater.  Roof extensions that could be used to cover an addition to the building easily under the roof was the basis.   You do not consider any type of wall attached canopies such as being used over a door.  If you have a porte cochere separated from and not attached to the building, then the porte chchere structure is a separate building thus you would have two buildings maybe too close to each other.  If the porte cochere is attached then it is part of the building’s area.


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## JBI (Jul 14, 2016)

Other than the fact that building area has nothing to do with determining construction type (Actually construction type is one of 2 criteria needed to determine allowable area), I agree with Examiner. Inside face to inside face.


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## Examiner (Jul 14, 2016)

Sorry I did not make myself clear.  Construction type is a balance between the occupancy use group used to size the building based on the construction type you choose that will work for the occupancy use group.  Did that make sense?


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## RANDOM (Jul 18, 2016)

tuzi said:


> I am from Canada and new to USA and IBC. For the building area calculation, my college told me to take the area from outside face of studs. Is that true for all types of buildings? Also, in the definition of "Area, Building", it says " 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 o floor above". Does it mean the space under a porte cochere should be included in the building area? It doesn't seem like they do that in my office.



There is no official system to measure building areas. Here at the office, we use two types of systems to measure the gross area of a building.

*1. BOMA (Builders, Owners & Managers Assoc.)*

1.1 Exterior Gross Area (EGA):

The total floor area contained within the measure line (follow the exterior face of the building wall). Unenclosed areas are typically excluded, except circulations.

Typically the exterior face must coincide with the "drip line" of the building. And so you might find yourself including void spaces, recessed openings and areas that would not be included using systems such as CBC.

1.2 Construction Gross Area (CGA):

This is the EGA area plus other areas that have a structural floor and are covered by a rood or canopy. These areas can also be unenclosed but have to be within the building perimeter.

*2. CBC (California Building code)*

This system is accomplished by drawing a line following the inside face of the building walls.


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## mark handler (Jul 18, 2016)

The reason *BOMA *uses the exterior of the walls is to make more rent.


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## JBI (Jul 19, 2016)

This IS the Building CODE Forum, isn't it? 
The Code does provide a method to determine building area, and it is to determine the actual usable area. 
People don't stand within walls... unless of course they work for BOMA apparently. LOL


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## steveray (Jul 19, 2016)

Deleted...I confused this with the EXIT sep thread...


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## JBI (Jul 19, 2016)

From the 2015 IBC Commentary...
1007.1.1.1 Measurement point. The separation distance required in Section 1007.1.1 shall be measured in accordance
with the following:
1. The separation distance to exit or exit access doorways shall be measured to any point along the width of the doorway.
2. The separation distance to exit access stairways shall be measured to the closest riser.
3. The separation distance to exit access ramps shall be measured to the start of the ramp run.

_Where exit access stairways are permitted to be unenclosed, the remoteness measurement for doorways
shall begin at the center of the top riser of the unenclosed stairways; this is consistent with the exit
access travel distance measurement in Section 1017.3. When enclosure is provided, distances are
measured to the door of the enclosure. Typically, travel distance is measured to the center of the door,
ramp or stairway; however, there is an allowance for that point to be at any location along the door, stairway
or ramp. The intent is to reduce subjectivity in the determination of exit/exit access configuration. The
result is that a designer could literally measure to the far extreme edge of the two doorways leading out of a
room to meet the separation requirements.
_
For the record, all of the figures/details show the measurement for the diagonal to the inside corners of the room or space.


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## RANDOM (Jul 19, 2016)

JBI said:


> This IS the Building CODE Forum, isn't it?
> The Code does provide a method to determine building area, and it is to determine the actual usable area.
> People don't stand within walls... unless of course they work for BOMA apparently. LOL



True, it seems BOMA is a bit "tricky". What do you usually use?


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## JBI (Jul 19, 2016)

RANDOM said:


> True, it seems BOMA is a bit "tricky". What do you usually use?



The Code...


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## Francis Vineyard (Jul 19, 2016)

http://media.iccsafe.org/news/eNews/2014v11n12/2012_ibc_handbook_23-24.pdf


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## ADAguy (Jul 20, 2016)

Nice of "some of you" to share with our "newbie" differences between useable and rentable square footage.
Many building departments base permit fees on net useable (minus columns and other non-occupiable spaces (vent and duct shafts) vs gross area.

It becomes a bit more complicated when the reflected ceiling is larger than the floor plate due to outward leaning walls (think upside down pyramid) (this can wracks havic with mechanical calcs.).


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## Yikes (Jul 20, 2016)

JBI said:


> People don't stand within walls... unless of course they work for BOMA apparently. LOL


As an aside, I recently heard a history podcast about Assyrian king Ashurnasirpal II.  He bragged about walling his enemies in alive, inside a masonry wall.  the term is known as immurement, (from Latin _im-_ "in" and _mūrus_ "wall"; literally "walling in").


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## Paul Sweet (Jul 22, 2016)

The only time I've seen areas measured to the inside face of exterior walls is for code area calculations.  Zoning wants to see the full physical size of the building, not just the occupiable part.  Cost estimates include wall area, which isn't free.  I expect that most people just go ahead and use the area to the outside face of the walls on their building permit application, unless the building is on the borderline for area limits.


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## Yikes (Jul 22, 2016)

Paul, the first sheet of our architectrue firm's building plans always have at least TWO calculations:
1.  Are per zoning code
2.  Area per building code/fire code

This is especially important if the project has a parking structure, because many zoning codes do not count parking structure area in their allowable Floor Area Ratio (FAR).  In that situation difference between zoning vs building area calculations can be very significant.
It is worth it to post both numbers. Our plans are intended not only to secure permit for the current project, but the also serve as a record for future reference.  When the client wants to add more floor area to their site in the future, the planning department knows which number to examine on our record drawings for FAR.

We may also have additional area numbers such as BOMA for investors and tenants, conditioned space for energy calculations, building footprint for planning and landscape calcs, pervious vs. impervious surface for stormwater calcs, etc.


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## RANDOM (Apr 4, 2017)

Yikes said:


> Paul, the first sheet of our architectrue firm's building plans always have at least TWO calculations:
> 1.  Are per zoning code
> 2.  Area per building code/fire code
> 
> ...



Do you include RFA in your title sheet. I typically do.


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## ADAguy (Apr 4, 2017)

Not confused enough?

However, the "bearing" weight of a building is inclusive of the out to out (exterior to exterior) size of a building which determines the compressive loading on the footings and soil beneath.
The out to out may also impact determination of FAR (Floor Area Ratio) vs allowable lot coverage.
Habitable area could be seen as occupiable area for tax accessors purposes.
A porte Cochere is a pass thru structure not intended for overnight parking or storage, unless as some do, it has a floor above it which should then be included in the calculations.


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