IBC Table 506.3.3 (2021 and later Editions)

[RLGA]

Consider me old-fashioned (I do like a good "old fashioned," but that's irrelevant here), but I prefer using Equation 5-5 (and Equation 5-4 when necessary) from the previous editions over the new table (tables, if you consider Table 506.3.3.1). So, I have a couple of questions I would like to ask:

1. (For building officials) Would you allow or (for others) have you ever asked to allow the use of Equations 5-5 and 5-4 instead of Tables 506.3.3 and 506.3.3.1 if your jurisdiction has adopted the 2021 or 2024 IBC? Why (for building officials) or what was the outcome (for others)?
2. Just how are you supposed to interpolate these tables per Footnote 'a'? (The Commentary does not offer an example.)

 

[Joe.B]

I've never seen 5-5 (or 5-4), went back and checked old code cycles, have not existed in CA code as far as I can tell. Before the merger, CA was UBC based.

 

[RLGA]

I've never seen 5-5 (or 5-4), went back and checked old code cycles, have not existed in CA code as far as I can tell. Before the merger, CA was UBC based.

The equations have been in the CBC 2019, 2016, 2013 (as Equations 5-2 and 5-3, respectively), and 2010 (Equation 5-2 only) editions.

 

[Joe.B]

The equations have been in the CBC 2019, 2016, 2013 (as Equations 5-2 and 5-3, respectively), and 2010 (Equation 5-2 only) editions.

Correct, I have seen those, but never 5-4 or 5-5. Unless you're saying they're the same thing?

 

[RLGA]

Correct, I have seen those, but never 5-4 or 5-5. Unless you're saying they're the same thing?

Here is what I am talking about...

These are the equations in the IBC for frontage increase for the 2018 editions and earlier (except they were under different equation numbers for the 2012 and earlier editions):



Here are the tables I am referring to from the 2021 and 2024 editions (there are no equations in the 2021 and 2024 editions):

 

[Yankee Chronicler]

Consider me old-fashioned (I do like a good "old fashioned," but that's irrelevant here), but I prefer using Equation 5-5 (and Equation 5-4 when necessary) from the previous editions over the new table (tables, if you consider Table 506.3.3.1). So, I have a couple of questions I would like to ask:

1. (For building officials) Would you allow or (for others) have you ever asked to allow the use of Equations 5-5 and 5-4 instead of Tables 506.3.3 and 506.3.3.1 if your jurisdiction has adopted the 2021 or 2024 IBC? Why (for building officials) or what was the outcome (for others)?

When we adopted IBC 2021, we adopted it with the tables. Going back to a previous edition of the code would require blessing from the State Building Official. I'm not aware of anyone having asked to do that and, if someone were to ask, I'm sure she would start by asking why they'd want to do that.

1. Just how are you supposed to interpolate these tables per Footnote 'a'? (The Commentary does not offer an example.)

The tables (506.3.3, and 506.3.3.1) all have clearly defined cut-offs There's is nothing there that lends itself to interpolation. IMHO, the footnotes (a.) are in error.

 

[Paul Sweet]

I'm with you, RLGA. I find it easier to do a little arithmetic than to try to comb through multiple tables. The revised height & area tables also made things more complicated.

 

[Sifu]

I was accustomed to the old equation (not to be confused with "good" at the old equation), I had a heart palpitation on the first plan I reviewed when they removed it in favor of the tables. On that first one I did it both ways to check my understanding and as I recall the result was the same. It seems there were some differences in some cases as I played around with it but I can't recall for sure. It irks me when I finally figure something out then they completely change it, but that is the way the world turns.

 

[LR419]

The tables (506.3.3, and 506.3.3.1) all have clearly defined cut-offs There's is nothing there that lends itself to interpolation. IMHO, the footnotes (a.) are in error.

The only logical interpolation possible is in the first row of both tables, and the first column of 506.3.3.

 

[Joe.B]

This spurred me to review all of this section again I'm curious how you interpret item two in 506.3.2?

506.3.2 Minimum frontage distance. To qualify for an area factor increase based on frontage, the public way or open space adjacent to the building perimeter shall have a minimum distance of 20 feet (6096 mm) measured at right angles from the building face to any of the following:

2. The entire width of a street, alley or public way.

Would you measure it like this:


Or: