Allowable Area

[swampcypress]

I am doing the old allowable area calculation for a new building. The tabular area has me confused (since changes to the code) I know the basics but the most basic thing is bothering me. Is the tabular or basic allowable number (in this case Type III B) for a single floor or used for the entire building ? I wish I could find in the code that it is specifically referring to a floor level - it probably is and I am not finding it. My first floor is 22,000 SF and my 2nd is approx. the same. No basement, and I know its going to check out - I just want to know if the table # is for a floor or the whole building

 

[cda]

Welcome back

not my area experts will advise you

Not sure if this helps per code you are using

https://www.specsandcodes.com/articles/code_corner/The%20Code%20Corner%20No.%2016%20-%20Allowable%20Building%20Area%20Part%201.pdf

https://www.specsandcodes.com/articles/code_corner/The%20Code%20Corner%20No.%2017%20-%20Allowable%20Building%20Area%20Part%202.pdf

Articles - specsandcodes.com

 

[ChrisCampbell]

What edition of the code are you using?

You can check out an allowable area calculator based on the 2015 IBC here: https://www.buildingcode.blog/allow...ulator---non-separated-mixed-occupancy.html#/

 

[Paul Sweet]

I just love the way the IBC changed one simple table into 3 complicated tables.

The top number (NS) in 2015 IBC Table 506.2 is what used to be the tabular area (area per floor). This number is used for non-sprinklered buildings and to calculate frontage (perimeter) increase (506.3).

S1, S13R, & SM are areas per floor for sprinklered buildings. They already include the sprinkler increase (300% for single story, 200% for multi-story), which used to be calculated separately. You have to add the frontage increase (based on NS) to get the allowable area Aa (506.2.1 - 4).

Buildings over 3 stories get a little more complicated. You have to multiply the allowable area by 3 for most buildings or 4 if it has a NFPA 13R sprinkler system to get the allowable area of the entire building. No individual story can exceed the allowable area.

I'm puzzled why a 13R sprinkler, which is less comprehensive than an NFPA 13 system, gets a greater increase.

I think the 2018 & 2021 codes are basically the same, except for table or paragraph numbers.

 

[SH225]

I just love the way the IBC changed one simple table into 3 complicated tables.

The top number (NS) in 2015 IBC Table 506.2 is what used to be the tabular area (area per floor). This number is used for non-sprinklered buildings and to calculate frontage (perimeter) increase (506.3).

S1, S13R, & SM are areas per floor for sprinklered buildings. They already include the sprinkler increase (300% for single story, 200% for multi-story), which used to be calculated separately. You have to add the frontage increase (based on NS) to get the allowable area Aa (506.2.1 - 4).

Buildings over 3 stories get a little more complicated. You have to multiply the allowable area by 3 for most buildings or 4 if it has a NFPA 13R sprinkler system to get the allowable area of the entire building. No individual story can exceed the allowable area.

I'm puzzled why a 13R sprinkler, which is less comprehensive than an NFPA 13 system, gets a greater increase.

I think the 2018 & 2021 codes are basically the same, except for table or paragraph numbers.

A building with the NFPA 13R does get to multiply the floor allowable area by up to four floors, but the floor allowable area table value with 13R is only one-third as much as with NFPA 13.