Printed from the blog of Lori Greene, AHC/CDC, CCPR, FDAI
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Email: lori_greene@allegion.com, Blog: www.idighardware.com or www.ihatehardware.com


Jul 08 2014

Decoded: Calculating the Occupant Load (September 2014)

Category: DHI,EgressLori @ 12:16 am Comments (34)
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This post was printed in the September 2014 issue of Doors & Hardware

[Click here to download the reprint of this article.]

Fixed Seating

For Assembly occupancies with fixed seating, the quantity of seats is added to the occupant load of any additional occupiable spaces to determine the total occupant load.

Many code requirements are dependent upon the occupant load of the room or space in question.  For example, the International Building Code (IBC) requires panic hardware for doors equipped with a lock or latch, which serve Assembly or Educational occupancies with an occupant load of 50 or more (the occupant load limit for NFPA 101 – The Life Safety Code is 100 or more).

In order to apply the code requirements correctly, it is sometimes necessary to calculate the occupant load of a room or space.  The IBC defines Occupant Load as:  “The number of persons for which the means of egress of a building or portion thereof is designed,” and NFPA 101 defines it as: “The total number of persons that might occupy a building or portion thereof at any one time.”

To calculate the occupant load, the first step is to calculate the area of the space in question by multiplying the length times the width – typically measured within the interior faces of the walls.  For example, if a classroom measures 30 feet by 40 feet, the nominal area is 1,200 square feet (30’ x 40’ = 1200 SF).

Less Concentrated or Unconcentrated

When an Assembly occupancy includes tables and chairs, it is typically considered a less concentrated or unconcentrated use, with an occupant load factor of 15 net square feet per person.

The next step is to divide the area by the occupant load factor, which varies depending on the use of the space.  This factor establishes the amount of square footage per occupant; a warehouse would have a lower occupant load and more square footage per occupant, while a nightclub would have a much more dense occupant load and less square footage per person.

In the 2012 and 2015 editions of the IBC, the occupant load factor is found in Table 1004.1.2 – Maximum Floor Area Allowances per Occupant.  In the 2012 and 2015 editions of NFPA 101, it is Table 7.3.1.2 – Occupant Load Factor.  The factors vary depending on which code is being used, so you must consult the code in effect for the project location.  The factors included in these tables are indicative of typical occupant densities for each use.

For classrooms, both the IBC and NFPA 101 list an occupant load factor of 20 net square feet per person.  Factors are based on either gross or net floor area.

  • Gross floor area is measured within the inside surface of the walls, and includes all occupiable and nonoccupiable spaces. Bathrooms, closets, electrical/mechanical rooms, and other nonoccupiable spaces are not subtracted from the gross floor area.
  • When an occupant load factor is based on the net floor area, the calculation is based on the actual occupied area. Nonoccupiable spaces like corridors, stairs, bathrooms, electrical/mechanical rooms, closets, and fixed equipment are subtracted from the total area to determine the net floor area.
Concentrated

Concentrated use in an Assembly occupancy may include chairs that are not fixed, and the occupant load factor is 7 net square feet per person.

To calculate the net floor area of the classroom used in our example, you would take the gross area (1200 square feet) and subtract any nonoccupiable space.  For example, let’s subtract 80 square feet for a classroom storage closet, leaving us with a net floor area of 1,120 square feet.  We would then divide the net area (1,120 square feet) by the occupant load factor from the table (classrooms = 20 net square feet per person), to calculate an occupant load of 56 occupants.  If the prevailing code was a recent edition of the IBC, this load would trigger the requirement for panic hardware (as well as two exits and outswinging doors).  If NFPA 101 was used, panic hardware would not be required for this occupant load.

For Assembly occupancies with fixed seating, the seats are counted to determine the occupant load.  Seating for benches without dividing arms (for example, bleachers) is calculated at 18 linear inches of seating length per person.  Additional occupiable space (for example, a waiting area) is calculated using the occupant load factor for that space, which is then added to the number of fixed seats.

Several additional occupant load factors are listed for Assembly occupancies without fixed seating.  Unconcentrated or less concentrated use (15 net square feet per person) may have tables and chairs, concentrated use may be set up with chairs only (7 net square feet per person), and standing space is addressed by the IBC with an occupant load factor of 5 net square feet per person.

Standing Space

According to the International Building Code (IBC) standing space is calculated using an occupant load factor of 5 net square feet per person.

Once you are able to calculate the occupant load, you can determine the applicable code requirements for doors serving that space, including how many egress doors are needed, and whether they are required to swing in the direction of egress.  This calculation and the posted occupant load limit required for some occupancy types will also help to prevent unsafe occupant loads if properly enforced.  The Authority Having Jurisdiction (AHJ) should be consulted for any questions regarding occupant load.

Images: Shutterstock

 

34 Responses to “Decoded: Calculating the Occupant Load (September 2014)”

  1. Beth says:

    Wow, this is a tremendously helpful article, I wish it had been written about five years ago when I needed it!

  2. ~ Becky says:

    Thanks! I was discussing net vs. gross and also assembly with a potential client. It’s much easier to point them here than to dig out the IBC and wade through it.

  3. John Thompson says:

    I read every readily comprehensible word, and I still have not a tiny clue why all the many persons associated are allowing s e v e n Oxacans to live in the one bed. Apt. Next to my one bed. Apt.Crap! They’re mean!

  4. Faizal says:

    Hi…anybody can help me to culculate human load for stage 24ft x 18ft. How many person can be on stage in 1 time. We use a-frame scaffolding and wooden platform. Thanks

    • Lori says:

      Hi Faizal –

      For a stage, the IBC and IFC use an occupant load factor of 15 net square feet per person. If the entire area of your stage is occupiable, the area is 432 square feet (24 x 18) – then divide by 15 net square feet per person to get an occupant load of 29 people.

      – Lori

  5. Faizal says:

    Can i know what is IBC and IFC? also i want to know what is 15net? Thanks

    • Lori says:

      The IBC is the International Building Code and the IFC is the International Fire Code. I don’t know which codes are used in your area, but these are widely-used so they will at least give you an idea of the occupant load. Each type of occupancy has a certain occupant load factor, as I mentioned in the article, and the occupant load factor for stages is 15 net square feet per person.

      – Lori

  6. Mike says:

    Great article thanks. My county uses the 2006 IBC. According to section two, the business I am opening is classified as amusement, so an A-3 assembly. However, it says if the occupant load is <50, then consider yourself a Business (zoned B). I have a 3000 sf space, but we never expect to have more than 50 people. Can we just impose our own maximum occupancy maximum of 49 people to be considered a business, or do we have to do (3000 sf. – nonoccupiable)/5 sf. pp. for standing space = ~2500/5 = 500 people, which would make us not only an A-3 but also subject to many more codes?

    • Lori says:

      Hi Mike –

      Sorry for the delay – I’ve been traveling and my inbox got out of control. The final answer to your question will be up to the local code official, but I have not seen AHJs allow this very often – especially for new occupancies. They might let you use the unconcentrated use factor of 15 which would still put you over the 49-person limit, but would reduce the number of required exits.

      – Lori

  7. Edward says:

    How does one calculate the increased occupancy load? I am trying to calculate for a retail space which is 100% covered by an Automatic sprinkler system, and I’ve heard that this should allow for increased occupancy, but I cannot find any information saying this in IBC.

    Have you heard of this?

    Thanks!!!

    • Lori says:

      Hi Edward –

      I found this in the 2015 IBC:

      1004.2 Increased occupant load. The occupant load permitted in any building, or portion thereof, is permitted to be increased from that number established for the occupancies in Table 1004.1.2, provided that all other requirements of the code are met based on such modified number and the occupant load does not exceed one occupant per 7 square feet (0.65 m2) of occupiable floor space. Where required by the building official, an approved aisle, seating or fixed equipment diagram substantiating any increase in occupant load shall be submitted. Where required by the building official, such diagram shall be posted.

      Here’s what the Commentary says:
      An increased occupant load is permitted above that developed by using Table 1004.1.2, for example, by utilizing the actual occupant load. However, if the occupant load exceeds that which is determined in accordance with Section 1004.1.2, the building official has the authority to require aisle, seating and equipment diagrams to confirm that all occupants have access to an exit, the exits provide sufficient capacity for all occupants and compliance with this section is attained. The maximum area of 7 square feet (0.65 m2) per occupant should allow for sufficient occupant movement in actual fire situations. This is not a conflict with the standing space provisions of 5 square feet (0.46 m2) net in accordance with Table 1004.1.2. Standing space is typically limited to a portion of a larger area, such as the area immediately in front of the bar or the waiting area in a restaurant, while the rest of the dining area would use 15 square feet (1.4 m2) net per occupant.

      – Lori

  8. Josie says:

    Hi Lori, this is a really wonderful article. I was wondering when do we use the gross floor area for calculation and when do we use the net floor area? Also, if my project is in San Francisco, where can I see if they follow CBC or NFPA?

    • Lori says:

      Hi Josie –

      In NFPA 101, the table referenced in the article shows some factors as “net”…for those you’d use the net area. For the other factors you would use the gross area – At the bottom of the table there is a footnote: All factors are expressed in gross area unless marked ‘net.’

      In the IBC table, either gross or net is listed for each occupant load factor.

      – Lori

    • Lori says:

      Sorry – I forgot to answer your other question. I found the list of San Francisco codes here: http://sfdbi.org/codes. There’s also a link to the San Francisco fire code on the SF-Fire page: http://sf-fire.org/division-fire-prevention-and-investigation.

      – Lori

  9. Chuck says:

    Hi Lori,
    Was wondering if you could help me occupancy load for a 4000sqf nightclub. Bar&drink rail 183 sq.ft. Booths 167sqft. Tables 1814sqft , pool table 76sqft and Isle space 90sqft.

    I used 7sqft for bar and 7sqft for booths and tables I used 15sqft And pool table I used 5sqft and for Isle space I used 5sqft. I’m not sure if I’m using the correct square footage per person for the Tables and pool table. Can u help? Thanks

    • Lori says:

      Hi Chuck –

      If you can send me a floor plan I will take a look. lori.greene@allegion.com

      The load of the booths can be calculated using 18″ of seat per person. The area of the pool table can be subtracted from the gross area to find the net area. The 5-SF factor is usually used for the dance floor or an area that will be really congested.

      – Lori

  10. Jason says:

    I have a question about calculating occupant load in regard to bathroom requirements. When calculating either gross on a new, unfinished space, do you include the space taken by planned walls or do you simply use interior dimensions of the empty shell?

    • Lori says:

      Hi Jason –

      I believe the measurements are taken inside of the walls. Some occupant load calculations use a “net” figure, in which case you can subtract other uninhabitable areas like closets and fixed furniture.

      – Lori

  11. Gilbert says:

    In a business setting it lists the occupancy load at 100 sqft/person. I have a room full of 8’x8′ cubicles that equate to 64 sqft/person. How can I determine how many cubicles I can fit in an open floor plan?

    • Lori says:

      Hi Gilbert –

      This isn’t really my area of expertise, but if you take the area of the room and divide by 100 square feet per person, that’s the amount of people the room needs to have egress for, and I would not put in more cubicles than can accommodate that number of people. There are other considerations like width of circulation spaces, length of dead ends, and travel distance to the exits.

      – Lori

  12. Clay says:

    I ran into an occupancy issue and I think maybe you could help.

    There has been a request to add some seating to a room in an art center but I need to figure out if code will permit more seating to be added. Essentially I am trying to find out how much square footage is required per seat. I have researched under the NFPA and IBC codes, but they both only list number of occupants/square foot as “use number of fixed seats”. The room is classified a Group-B Assembly. Where do you think I could look to find the amount of fixed seats allowed per square foot?

    Thanks

    • Lori says:

      Hi Clay –

      I don’t know of a required amount of square footage per seat. If you have an open art center and want to add fixed seating to a portion of it, I would add the number of seats to the calculated occupant load of the rest of the space, and then make sure you have enough doors to accommodate that occupant load.

      – Lori

  13. vaibhav says:

    Hi Lori,
    This article has really helped me a lot.
    I am from india We use NBC here,
    in occupant load table it states that area should be 10m2 for an business occupany , can u tell me why 10m2 is used ??

    • Lori says:

      I’m not familiar with the NBC, but the area of 10 square meters is consistent with the International Building Code which uses the occupant load factor of 100 square feet per person for business areas. When you divide the area of the space by this factor, you will find the occupant load of the space.

      – Lori

  14. pleiades says:

    Hi Lori,

    Is occupant load related to minimum area sq ft? If you know how many persons is going to use the room then you can compute the area of the room. Is that correct?

    And how about guests in an office? Are they considered or not?

    • Lori says:

      The occupant load is based on the area of the room and an occupant load factor. For business areas, the occupant load factor shown in the IBC is 100 gross square feet per person. For an individual office that is 10′ x 10′, the occupant load is 1 person.

      – Lori

  15. Kevin says:

    Regarding the gross vs. net topic for concentrated/unconcentrated in assembly spaces. If I have a dining arrangement with tables and chairs, do I need to deduct the square footage of the dining tables to determine the net available square footage or would I just deduct any staging and other things (not the dining table/chairs) to determine the net available square footage?

    • Lori says:

      Hi Kevin –

      You don’t have to deduct the square footage of the tables. The tables and chairs are already taken into consideration because the occupant load factor for an assembly space with tables and chairs is 15 square feet per person and an assembly space without tables and chairs is 7 square feet per person. The space will be calculated to have a higher occupant load without the tables and chairs.

      – Lori

      • Kevin says:

        Understood. Would things like portable stages, static displays etc. need to be deducted from the available square footage?

        • Lori says:

          Not usually, if they are temporary items that may be there when the room is set up a certain way, but may not be there when setting up for a different event.

          – Lori

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