Allowable Area Calculations based on 2007 CBC

This is the first time doing the calculations and understanding the area calculations. I have attached a sketch and the calculations to understand if the method I have followed is that correct.

There was an Allowable Area Calculation spread sheet on one of the posts, but that did not fit my requirements so had to do a more mathematical method approach.

All feedback is appreciated.


Original Post
I'm assuming this is an R-1 or R-2 occupancy of Type VA construction.

Your use of 3 for the sprinkler increase is incorrect. Since the building is multiple stories, I(s) is limited to 2.

How did you determine that basements are allowed unlimited area if the rest of the building has a limited area?

Also, when comparing actual building area to allowable building area, you should also compare the actual area of each floor to the allowable area per floor to show that no single floor exceeds it.

Also, you're missing the "1" in "144,000" at the end of Part-2 calculations.
Another question I have as I need to redo the calculations due to my error of the Is factor, when we are using P - perimeter, do we use perimeter of the entire building or just the part of the building as we are considering it separate due to the fire wall.

As this can also change the entire calcs considerably.
Good question...

Just the part of the building considered. Since the fire wall creates two separate buildings, each are treated as such. Obviously, the length of the fire wall cannot be considered frontage (F) that opens on a public way; and, neither can the walls of the courtyard side of the buildings.
rlga_AZ, Thank you for your input. I have redone the calcs and would like to have your opinion in the calculation for the perimeter. I have assumed as these are 3 separate building for the area calculations, the P value to be the perimeter of each part not the entire building, am I correct in assuming this.

I have not taken the building facing teh couryard as my frontage, only the length that fronts the road.

The basement is S-2 separated by the residential by 3 hour separation therefore being assumed to be unlimited area.

Your input is appreciated.


I've reviewed it, and it appears to be correct. Although you don't need the frontage increase for Part-3, why did you consider that there is no frontage? The ends on Devonshire and Evandale are obviously open. What is the fire separation distance from the building to the property line to the north (at least I assume that is north)?

You say the building is sprinklered, you should indicate that the sprinkler is in accordance with Section 903.3.1.1 (NFPA 13). R occupancies are required to be sprinklered by any of the systems in Section 903.3, but only the NFPA 13 can be used for the sprinkler increase.

Also, you don't state that the S-2 is a parking garage. Only an S-2 parking garage can be used used according to 509.2.

Hopefully somewhere else on the sheet you indicate occupancies and construction type.

Finally, I'm looking at some alternatives to avoid fire walls; Can the buildings A, B/C, and D be treated as separate buildings? Do they have adequate fire separation distance? What are the opening areas per floor at these ends, or do they even have openings?
I have the entire sheet which talks about the occupancies and their type of construction and separation.

On Part 3 I could use the open side, but also the code says min. 25% facing the street, so I did not take into account that part.

all sides are 15' away from the property line.

We were not able to divide the building into A, B, C and D as we have openings in the units facing the small open area, which are 14' between A and B.

Also the roof is conituous, so forming one building.

Also I could not find anywhere what is the min. distance required between 2 buildings on the same property?
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