Please help with Occupant Load Factor!! (PA exam next week)

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    Breton Smith

    Question 1:
    Per IBC 2015 303.1.2, if the assembly room's occupant load is less than 50 people and /or is less than 750sf, you classify it as Groub B occupancy (excepting 303.1.3 about education and 303.1.4 religious assembly). If you have a book reference that suggests otherwise, post a screenshot so we can investigate.

    Question 2:
    The lobby area is likely concentrated without fixed seats. What if the theater is not in use but the lobby is used for a reception? Toilet rooms are specifically not occupiable space and only get counted in gross floor area calculations, however no such exception for lobbies exists (that I know of).

    Question 3:
    According to IBC 508.2.3, more than 10% accessory use on a given floor is simply not permitted, and you do not "reclassify" the accessory space so it becomes allowed. To solve the problem you enlarge the rest of the building/floor or remove some accessory space.

    Question 4:
    Please post the BCI content to discuss else refer to IBC which does not consider toilet rooms to be occupiable space, therefore you would include the square footage of toilet rooms in gross occupancy classifications and not net classificiations.

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    Michael Ermann

    Breton this is a fantastic response
    Would you write me at ermann@amber-Book.com? I want to (digitally) meet you— Michael Ermann, Amber book creator

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    Natalie Hamshaw

    Breton, 

    I really appreciate the response.

    That is what I thought I understood from reading the IBC. The Building Code Illustrated page that threw me off me off regarding assembly assignments is this one:

     

    Thank you for clearing up the lobby/ toilet question, as well as the 10% accessory question. 

    My question regarding toilets on a floor with both spaces that use 'net' and 'gross' assignments, arose from reading this (also Building Codes Illustrated): 

    I was uncertain if this interpretation aligns with the PA exam's requirements. 

    Again, I really appreciate you taking the time to assist with some of my confusion. 

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    Breton Smith

    Somebody else should chime in, but in my opinion that is a sketchy floor plan given in Codes Illustrated. It appears the accessory assembly spaces (conference room and seating area) are more than 10% of the floor if we assume the entire floor plate is shown. Cocktail napkin math puts it at 37% of the floor dedicated to accessory use, but if this were simply a plan enlargement of a much larger floorplan, it might be acceptable. Nothing is said or implied about the whitespace around the drawing. It could be that the oversimplified plan is violating one aspect of IBC in order to demonstrate the aspect of cumulative occupant loads; the author probably just wants you to grasp that the net area of each space is analyzed separately based on accessory uses.

    Regarding that second snippet, again someone else should chime in but my opinion is that it's a typo and they meant to say "we recommend that the toilet rooms be treated as a part of the gross area occupant load and thus they may be excluded from occupied floor area calculations per the definitions references in 1002..."

    IBC 2015 Chapter 2 Section 202 Definitions clearly states:

    "FLOOR AREA, NET. The actual occupied area not including unoccupied accessory areas such as corridors, stairways, ramps, toilet rooms, mechanical rooms, and closets."

    Clearly the toilet rooms are excluded from the definition of net areas which means, since they are still within the footprint of the exterior wall, you should treat them as gross area.

    I don't grasp why they are couching that whole snippet you provided with "We recommend..." as the verbiage in IBC is pretty cut-and-dry. Maybe someone else can chime in.

    I have never factored toilets into net floor area in practice.

     

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    Natalie Hamshaw

    Ok, thank you!

    I think I understand how I am supposed to solve these problems even if I don't understand Building Code Illustrated's example. Even if it was part of a larger floor plan, the assembly spaces are for less than 50 people and so would be classed as Occupancy B not Assembly as they've shown. 

    I think they did mean 'net' because they are telling you that you can therefore exclude the toilet room area from any calculations. However I'm not sure I would do that in an exam. Assigning to the gross area if they share the bathrooms, as you said, seems more logical than excluding that area. 

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    Gang Chen (Edited )

    Very good discussion.

    In real practice, Table 1004.5 is often used together with Table 2902.1 to determine number of plumbing fixtures needed.

    I’d not be surprised to see an ARE exam question or even a case study that tests a candidate’s ability to do the same.

    Here are the free ICC links to these two tables:

    https://codes.iccsafe.org/content/IBC2018P3/chapter-10-means-of-egress#IBC2018P3_Ch10_Sec1004

    https://codes.iccsafe.org/content/IBC2018P3/chapter-29-plumbing-systems

    Gang Chen, Author, Architect, LEED AP BD+C (GreenExamEducation.com)

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    James Willis

    I have to disagree w/ Breton.  When calculating the occupancy load, you use the "function" of the space, not its occupancy classification, so the conference room would be an assembly space.

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    Matthew Hurst (Edited )

    This is an old post but I will comment anyway.

    James is correct - The occupancy load is different from the occupancy classification. These are two separate concepts but are closely related. An Occupancy load can affect a building's Occupancy type but the Occupancy type does not affect the space's Occupancy Load. Applying Chapter 3 to occupancy loads is not correct. The page snippit included by Natalie is correct.

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    Breton Smith

    Regarding James Willis comment, I don't understand what part of my comments he disagrees with, or what part of my comment he is "correcting"... but anyway both James and Matthew Hurst are correct, you have two tasks to accomplish, 1. determine the occupancy classification and 2. determine the occupant load (based on the "function")

    As they point out, the function of the space determines the occupant load and the calculation is straightforward. The sketch from BCI is correct in that regard.

    That said

    You as the architect can always bring IBC 1004.5 Exception to your AHJ. For example, a business with ~10 occupants based on floor area has a conference room with an occupant load of 49 occupants based on floor area. It is in your interest to use the exception with the AHJ. Reducing the occupant load will save you money and effort in other areas of the code...

    Exception: Where approved by the building official, the actual number of occupants for whom each occupied space, floor or building is designed, although less than those determined by calculation, shall be permitted to be used in the determination of the design occupant load.

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