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Occupancy Load Cal vs. proposed occupancy load

A

ArchMuse

Member
Joined
Jan 31, 2013
Messages
24
Location
Illinois
This is my first time trying this forum...and I hope it's not my last. Here is the question.

When calculating the occupancy load of a restaurant the total occupancy is a lot higher then the numbers of seat. The calculation is around 400 person, where as the total seating is around 190. So should 400 person be used when determining all design aspect of the building (i.e. parking, heating/cooling loads, plumbing fixture counts, emergency exits, etc.) even though 190 person is the proposed max occupancy load?
 
That is a BIG jump from 190 to 400. Something is wrong...

Is there a area for Standing?

Dancing? waiting? Entertainment?

Whos to say they don't add seats later...
 
mark handler said:
That is a BIG jump from 190 to 400. Something is wrong...Is there a area for Standing?

Dancing? waiting? Entertainment?

Whos to say they don't add seats later...
Click to expand...
net circulation: 1389 SF / 7 sf per person = 198 --- seats could be added in here in the future but very unlikely

net seating area: 4378 sf / 15 sf per person = 291 --- 10 very large tables that only 10 seats

net bar seating area: 387 / 7 sf per person = 55 ---- not sure I calculated this correct but error on the side of caution. I used the entire bar area including behind the bar and bar storage. only 10 seats at on bar and 8 at the second bar

net kitchen area: 1343 / 200 sf per person = 6 ---- again, unlikely seats will be added.

Total occupancy load is 550. This space will not hold 550 persons comfortably with dynamics of the restaurant. 190 + 25 employees = 215 is the proposed occupancy.

I've seen permit plans submitted to our AHJ that show allowable occupancy load with similar calcs and then below it says proposed occupancy load with low numbers (sometime much lower). I'm trying to figure out how the proposed occupancy load is calculated - is it based on furniture layout or a design judgement? Maybe it's not allowed and our AHJ doesn't really review the plan?
 
From 2009 ibc and commentary

1004.7 Fixed seating. For areas having fixed seats and aisles, the occupant load shall be determined by the number of fixed seats installed therein. The occupant load for areas in which fixed seating is not installed, such as waiting spaces and wheelchair spaces, shall be determined in accordance with Section 1004.1.1 and added to the number of fixed seats.

For areas having fixed seating without dividing arms, the occupant load shall not be less than the number of seats based on one person for each 18 inches (457 mm) of seating length.

The occupant load of seating booths shall be based on one person for each 24 inches (610 mm) of booth seat length measured at the backrest of the seating booth.

The occupant load in an area with fixed seats is readily determined. In spaces with a combination of fixed and loose seating, the occupant load is determined by a combination of the occupant density number from Table 1004.1.1 and a count of the fixed seats.

For bleachers, booths and other seating facilities without dividing arms, the occupant load is simply based on the number of people that can be accommodated in the length of the seat. Measured at the hips, an average person occupies about 18 inches (457 mm) on a bench. In a booth, additional space is necessary for "elbow room" while eating. In a circular or curved booth or bench, the measurement should be taken just a few inches from the back of the seat, which is where a person's hips would be located (see Figure 1004.7).

Some assembly spaces may have areas for standing or waiting. For example, some large sports stadiums have "standing room only" areas that they use for sell-out games. The Globe Theater in England has standing room in an area at the front of the theater. This section is not intended to assign an occupant load to the typical circulation aisles in an assembly space. Occupant load for wheelchair spaces should be based on the number of wheelchairs and companion seats that the space was designed for. As specified in Section 1004.9, if the wheelchair spaces may also be utilized for standing space, the occupant load must be determined by the worst-case scenario.
 
Any other area in the dining,,, make sure you are taking out the kitchen , storage and

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

This area is intended to be only the room areas that are used for specific occupancy purposes and does not include circulation areas, such as corridors or stairways, and service and utility spaces, such as toilet rooms and mechanical and electrical equipment rooms. Floor area, net and gross, is utilized in Table 1004.1.1 to determine occupant load for a space.
 
I don't know what you are calling "net circulation"....I would allow a reduction on the area of the means of egress paths that should not be blocked or occupied.....I would also give a reduction behind the bar and the storage should use a lower multiplier (300?).....But might not let you count just the 8 seats at the bar.....Never seen people 3 deep at the bar?
 
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I'll take a gander that perhaps the calculation is counting the maximum from the types of occupancy (mixed for instance) with the number of exits, water closets, square footage, etc. The proposed occupant load is what is determined that will be the allowable maximum from the calculations and to be posted.
 
We have allowed a lower "proposed occupancy" and posted this on the occupant load sign. It is mostly used to get a cheaper price for the sporing events they want to simulcast. Exits and restrooms and ventilation are all calculated on the allowable number.
 
rkeyteck said:
net circulation: 1389 SF / 7 sf per person = 198 --- seats could be added in here in the future but very unlikely net seating area: 4378 sf / 15 sf per person = 291 --- 10 very large tables that only 10 seats

net bar seating area: 387 / 7 sf per person = 55 ---- not sure I calculated this correct but error on the side of caution. I used the entire bar area including behind the bar and bar storage. only 10 seats at on bar and 8 at the second bar

net kitchen area: 1343 / 200 sf per person = 6 ---- again, unlikely seats will be added.

Total occupancy load is 550. This space will not hold 550 persons comfortably with dynamics of the restaurant. 190 + 25 employees = 215 is the proposed occupancy.

I've seen permit plans submitted to our AHJ that show allowable occupancy load with similar calcs and then below it says proposed occupancy load with low numbers (sometime much lower). I'm trying to figure out how the proposed occupancy load is calculated - is it based on furniture layout or a design judgement? Maybe it's not allowed and our AHJ doesn't really review the plan?
Click to expand...
Can you post a simple floor plan???
 
north star said:
* & *FWIW, ...the listed screen name is " rkeytek ". :mrgreen:

* & *
Click to expand...
Hay what do you expect from someone in a secret basement in the middle of the dessert????
 
cda said:
Yes you can count seats
Click to expand...
BUT, only if it is "Fixed Seating" which, per the definition in Chapt. 2, is seats that are secured in place. Movable tables and chairs does not meet the definition of fixed seating, and, therefore, has to be calculated at 1 person per 15 sq.ft. net. (per Table 1004.1.2)

Also, per 1004.1, the means of egress must be designed for the occupant load determined by the prescriptive methods in Section 1004. The occupant load can be increased in accordance with 1004.2, but cannot be less than the prescriptive calculated occupant load.

The Life Safety Code (NFPA 101) Handbook has a very good description of this concept: "The normal occupant load is not necessarily a suitable criterion, because the greatest hazard can occur when an unusually large crowd is present, which is a condition often difficult for authorities having jurisdiction to control by regulatory measures. The principle of this Code is to provide means of egress for the maximum probable number of occupants, rather than to attempt to limit occupants to a number commensurate with available means of egress."

Restaurants always have several different areas in which occupant loads are calculated differently - movable table/chair seating is calculated at one person per 15 sq.ft. net (subtraction only fixed building features, not aisles or other open areas); booths are calculated at one person per 18 inches of bench length; kitchens and bar service areas are calculated at 200 sq.ft. gross area, and the waiting area (if provided) is calculated at one person per 5 sq.ft. net. Granted, this method will usually produce a number higher than the anticipated occupant load, but, per 1004.1, it's the number that is required to be used when determining means of egress.
 
IJHumberson said:
BUT, only if it is "Fixed Seating" which, per the definition in Chapt. 2, is seats that are secured in place. Movable tables and chairs does not meet the definition of fixed seating, and, therefore, has to be calculated at 1 person per 15 sq.ft. net. (per Table 1004.1.2)Also, per 1004.1, the means of egress must be designed for the occupant load determined by the prescriptive methods in Section 1004. The occupant load can be increased in accordance with 1004.2, but cannot be less than the prescriptive calculated occupant load.

The Life Safety Code (NFPA 101) Handbook has a very good description of this concept: "The normal occupant load is not necessarily a suitable criterion, because the greatest hazard can occur when an unusually large crowd is present, which is a condition often difficult for authorities having jurisdiction to control by regulatory measures. The principle of this Code is to provide means of egress for the maximum probable number of occupants, rather than to attempt to limit occupants to a number commensurate with available means of egress."

Restaurants always have several different areas in which occupant loads are calculated differently - movable table/chair seating is calculated at one person per 15 sq.ft. net (subtraction only fixed building features, not aisles or other open areas); booths are calculated at one person per 18 inches of bench length; kitchens and bar service areas are calculated at 200 sq.ft. gross area, and the waiting area (if provided) is calculated at one person per 5 sq.ft. net. Granted, this method will usually produce a number higher than the anticipated occupant load, but, per 1004.1, it's the number that is required to be used when determining means of egress.
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Providing means of egress that is designed using the occupancy loads per 1004.1 is understandable. I'm having a difficult time with exterior parking, plumbing fixtures and HVAC loads. Using occupancy per 1004.1, IMO will provide a bad design for these other elements (parking, fixtures, and HVAC loads).

I didn't calculate the bar at 200 SF/person plus I have several other eating bars that should probably be calculated at 200 SF/person (server side). This will lower my total occupancy load.
 
= = + = =

If the calculated Occ. Load [ i.e. - a higher occupant number ] is used for MOE,

and all that is associated with it, ...how can a lower number be used for Parking,

...HVAC loads, ...plbg. fixtures, etc. ? :confused:

= = + = =
 
The questions about plumbing fixtures and parking always comes up, but that's a whole different question that I usually reply to the designer that the plumbing code might have more guidance on fixture counts and where they base their occupant loads, and the parking goes by the planning people for most jurisdictions. I think that, since the IBC says that the means of egress has to be based on the occupant calculations per that chapter, there really isn't any basis that would require the other aspects (plumbing counts and parking counts) to have to be tied to that - it's up to the AHJ to decide.

Also, for the bar area at 200 sq.ft. per person, I was meaning the service/bartender areas, not the patron areas. We (Montgomery County, MD) used to require the bar areas to be calculated at 1 person per 9 inches of bar length and then the open areas at one person per 15 sq.ft. - that will produce a really high number such as is typical at St. Patrick's Day or other similar 'holidays'.
 
= = + = =



The plbg. fixtures count also comes out of the Building Code.

See Ch. 29, ...Table 2902.1 & Section 2902.1.......It's the same

from the IPC.

I am not sure that different Occ. Loads can be used !

= = + = =
 
rkeyteck - It's a good idea to list the applicable codes and versions (year) when posting. This can help to alleviate confusion between code cycles as well as state amended codes.

In my area, parking is determined by the municipality's zoning code, egress is per the 2009 IBC, and minimum ventilation rates are per the 2009 IMC. Actual heating and cooling loads are outside the scope of the IMC, I think.

The IMC ventilation rate table has its own default occupant load for the room / space, which may be different than the building code's occupant load for egress.

From the 2009 IMC, there is an exception in Section 403.3 Outdoor airflow rate (listed below) that you could possibly use to justify a lower occupant load than that calculated per the IBC and even the IMC ventilation rate table.

Exception: The occupant load is not required to be determined based on the estimated maximum occupant load rate indicated in Table 403.3 where approved statistical data document the accuracy of an alternate anticipated occupant density.
 
Assembly spaces without fixed seating are either standing space, concentrated space (chairs only), or unconcentrated space (tables and chairs). There s no 'circulation space', net or otherwise. Backbar and storage areas are left out of 'net' floor area. Booths are measured at the bench back.
 
north star said:
= = + = =If the calculated Occ. Load [ i.e. - a higher occupant number ] is used for MOE,

and all that is associated with it, ...how can a lower number be used for Parking,

...HVAC loads, ...plbg. fixtures, etc. ? :confused:

= = + = =
Click to expand...
Because the building code allows it when you do not have fixed seating in an assembly use. 1004.1 is called "Design Occupant Load"

1004.1.2 Areas without fixed seating.

The number of occupants shall be computed at the rate of one occupant per unit of area as prescribed in Table 1004.1.2. For areas without fixed seating, the occupant load shall not be less than that number determined by dividing the floor area under consideration by the occupant load factor assigned to the function of the space as set forth in Table 1004.1.2. Where an intended function is not listed in Table 1004.1.2, the building official shall establish a function based on a listed function that most nearly resembles the intended function.

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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