2012 frontage increases (what, when and ching errors?) [506.2 and 506.2.1]



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    Jonathan Chertok

    building construction illustrated 2010 page 76.

    why are they using 50 in the numerator? should it be 55?

    also, is it not using the "weighted average" just to simplify the example or something?

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    Jonathan Chertok

    basically same question. why are they using 40/30 and not 55/30. net result is the same but it is confusing. what is the 40 public way showing? guess i need to look it up in the definitions or does anyone know where it ends?

    second example seems like a clear case of needing to use the weighted average. not using it to keep things "simple"?

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    Jonathan Chertok

    this is a clear weighted average example since they are using the equation. it seems to me that they have a typo in leaving out L1 of 80' in the Building Perimeter (F). so the first zero in the denominator should be 80 which would mean it is 9350 sf / 410 sf = 22.8'. right now they are using 330 feet instead of 410.

    sort of a procedural thing but if they used Wn x Ln instead of Ln x Wn it would be a whole lot easier to keep track of the "truncated" W's where they plugged in 30. so ignore the red dot at the 20'. it is the value of L2.

    bona fide typo or am i missing something?


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    China Clarke

    Reagrding the post directly above: my question is: what happens when W4 is less than 20 ft but increases to greater than 20 ft on the other end of L4? (and how to upload pics)

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    Lilia Grigoryan

    The F is 330 because open space less than 20’. The building perimeter must open on a public way or open space with at least 20’ wide. Enything less than 20 not calculated. 

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    Jonathan Chertok

    hi china,
    i’ll drop in here. 1. there are errors in most everything on this issue. possibly the right answers but incorrect steps imho. 2. IBC code commentary is very good for this. but i believe i found 1 error there as well that i may submit at some point. 3. i have /never/ heard of anyone excepting a couple early post asking about this topic for the exams. like in over a year and a half. i seriously doubt you need to know it. that said, perhaps someone can follow up if they think it is worth spending anytime on outside of actual professional practice.
    in short, i’d feel pretty confident ignoring it for the exams...
    if it is important i have a couple summaries on the topic but i’d have to dig them out. but again i’m not sure it is worth anyone’s time outside of actual professional practice.

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    Albert Wang

    I've noticed the same frustrating W issues reading through the BCI and also various practice problems.  While extremely frustrating, for exam purposes, I've noticed that the result is always the same, you end up with >30 which amounts to W=30/30.  My plan for the exams if this type of question comes up is to use the weighted average equation as described here:




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    Tony Young



    The reason that L1 is not used is because it is not setback more that 20' look at W1 its distance is only 10' therefore L1 would not be included in (F)

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