Building area calculations - IBC

[ATSE]

When calculating building areas for mixed use and occupancy, are demising walls split between the two areas?
That is, if you have a CMU rectangular building with a CMU wall dividing an office area (B occupancy) from an automotive repair shop (F-1 occupancy), does the area of the shop include all of the shop exterior wall and 1/2 of the interior dividing wall (4" of CMU wall width x the length of the wall)?

 

[JKW05]

That's how I have generally handled it...

 

[stookeyfpe]

Which edition of the code? The method between the 2006 and 2009 IBC bounces around like a bee bee in a box car.

And a demising wall (at least how I define them) can't be used as means of separating an occupancy.

 

[ATSE]

2009 IBC is the basis for design.
Demising wall was the incorrect term. Thanks for the correction.