Restaurant and Commercial Kitchen Gross vs Net (CBC)

[roxas]

Hi,

Working through a code study on a restaurant remodel and was curious about gross area calculations in a commercial kitchen as required by CBC 1004.5. The kitchen itself has walls separating areas of prep and dishwash and offices.

As a gross area, they would need to be calculated as per the definition below, although the definition really seems to be more about the gross building, not gross spaces.

FLOOR AREA, GROSS. The floor area within the inside perimeter of the exterior walls of the building (emphasis mine, on "building" not "space") under consideration, exclusive of vent shafts and courts, without deduction for corridors, stairways, ramps, closets, the thickness of interior walls, columns or other features. The floor area of a building, or portion thereof, not provided with surrounding exterior walls shall be the usable area under the horizontal projection of the roof or floor above. The gross floor area shall not include shafts with no openings or interior courts. (Weird that is isolates shafts but not walls)

In the past I have normally calculated each room in a kitchen as gross, but am on the cusp of an occupancy issue and I don't want to get burned if I have to add up all the walls and poche spaces. Similarly, at a front of house bar, where does the gross perimeter end? At the back side of the die wall between the staff and customer, or at the back (kitchen side) edge of that bartop? There seems to be a gray area here. I never count the bar surface in my net A-2 calcs, but do I need to include it in my gross kitchen calcs?

For the restaurant front of house (A-2 Occ), I have seen many cases where movable tables aren't counted, but chairs are. And other cases where the access aisles or circulation are not counted and times when they are. Is there anything definitive on this? I have tried to look elsewhere online, but I have only seen the the basics, and nothing delving into this type of specificity.

FWIW, I am actually that close on my numbers, but I also just want this particular line of thinking verified with smarter folks than myself, for now and the future. Thanks!

 

[mtlogcabin]

[BE] OCCUPANT LOAD. The number of persons for which the means of egress of a building or portion thereof is designed.

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

Without an actual floor plan, I would use the entire dining floor are as net.
This would include the aisles IMHO.

Gross would be employee work areas.

 

[Yankee Chronicler]

Restaurant seating is calculated based on net seating area. Table and chairs are NOT deducted. From the 2021 IBC Commentary:

The net floor area permits the exclusion of certain
spaces that would be included in the gross floor area. The
net floor area is intended to apply to the actual occupied
floor areas. The area used for permanent building components,
such as shafts, fixed equipment, thicknesses of
walls, corridors, stairways, toilet rooms, mechanical rooms
and closets, is not included in net floor area. For example,
consider a restaurant dining area with dimensions, measured
from the inside of the enclosing walls, of 80 feet by
60 feet (24 384 mm by 18 288 mm) (see Commentary
Figure 1004.5). Within the restaurant area is a 6-inch (152
mm) privacy wall running the length of the room [80 feet by
0.5 feet = 40 square feet (3.7 m2)], a fireplace [40 square
feet (3.7 m2)] and a cloak room [60 square feet (5.6 m2)].
Each of these areas is deducted from the restaurant area,
resulting in a net floor area of 4,660 square feet (433 m2).
Since the restaurant intends to have unconcentrated seating
that involves loose tables and chairs, the resulting
occupant load is 311 persons (4,660 divided by 15). As the
definition of “Floor area, net” indicates, certain spaces are
to be excluded from the gross floor area to derive the net
floor area. The key point in this definition is that the net
floor area is to include the actual occupied area and does
not include spaces uncharacteristic of that occupancy.

As to the kitchen areas, the occupancy load factor for commercial kitchens is based on gross square foot area. So for that I would draw an outline around the overall kitchen area, to the inside face of the surrounding walls. And walls within that outline are ignored, and the area they occupy is included in the gross square footage.

Also, remember that the occupant load is the occupant load as calculated based on Table 1004.5, or the actual occupant load, whichever is greater. So if you have a restaurant dining are that calculates out to 48 occupants but the restaurant really crammed in the tables and they have seating for 54 occupants -- the occupant load is 54, not 48. In most cases this isn't a problem with regard to number of exits or exit capacity, but it often triggers a requirement for additional plumbing fixtures.

 

[steveray]

I might be the wrong person to ask as I try to be reasonable...What number are you bumping up against?

 

[arwat23]

In the past I have normally calculated each room in a kitchen as gross, but am on the cusp of an occupancy issue and I don't want to get burned if I have to add up all the walls and poche spaces. Similarly, at a front of house bar, where does the gross perimeter end? At the back side of the die wall between the staff and customer, or at the back (kitchen side) edge of that bartop? There seems to be a gray area here. I never count the bar surface in my net A-2 calcs, but do I need to include it in my gross kitchen calcs?

To me, there are two options for calculating the occupancy for gross areas. Either combine all gross areas that are physically connected and have the same function together (eg, all individual office and that share walls with each other) OR each room separately, measuring from the centerline of interior walls. Regardless of the method used, interior walls WILL BE included in the area calculations. No way around that since code demands it.

When a gross function butts up against a net function, I usually measure to the centerline of the wall for gross and face of wall for net. For casework / counters that separate net and gross functions, I usually have gross end either at the furthest point of the work surface or, if there's no well defined worksurface, I measure to the same location I measure the net area to (same boundary line basically, if that makes sense). There is grey area in that regard, but no jurisdiction has called me out on this yet.

For the restaurant front of house (A-2 Occ), I have seen many cases where movable tables aren't counted, but chairs are. And other cases where the access aisles or circulation are not counted and times when they are. Is there anything definitive on this? I have tried to look elsewhere online, but I have only seen the the basics, and nothing delving into this type of specificity.

I've personally never seen this, at least in California. In my experience, unless the furniture or fixture is fixed in place (like a bar counter), you must include the area in occupancy calcs. I've been called out by a plan reviewer for not including a movable conference table in my Net occupancy calculations. I would assume the same would apply to restaurants since the function is the same / similar.

As for circulation space, it depends on the design. If you have a totally open floor plan where tables and chairs can be freely moved to any location, I'd say you can't remove any "circulation" areas from area calcs since there is no specifically defined circulation path. For all the Fire Department knows, the restaurant may remove or add tables and chairs that completely change the circulation area after the project is completed. If there was, say, a path of travel that was defined by pony walls or railings (a boundary that is permanent and fixed in place), that well-defined space could, arguably, be removed from net occupancy calcs. The local Fire Marshal should be able to give you guidance on what they would consider "circulation" for your specific design, but I've never run into issues using this method.

 

[roxas]

I might be the wrong person to ask as I try to be reasonable...What number are you bumping up against?

If I calculate interior walls inside the kitchen spaces, I may jump up to 50 occupants

 

[Yankee Chronicler]

If I calculate interior walls inside the kitchen spaces, I may jump up to 50 occupants

Well, then, the occupant load may exceed 50. It is what it is. The code says gross square foot area for commercial kitchens. That's what is.

 

[arwat23]

If I calculate interior walls inside the kitchen spaces, I may jump up to 50 occupants

I gotta ask, how big is this kitchen? A 200 Gross occupant load factor (table 1004.5) shouldn't cause the occupancy to jump up that much just by including some interior walls. Or is it already close to 50 occupants but that extra few from the interior walls pushes you too far?

 

[steveray]

In the past I have normally calculated each room in a kitchen as gross, but am on the cusp of an occupancy issue and I don't want to get burned if I have to add up all the walls and poche spaces. Similarly, at a front of house bar, where does the gross perimeter end? At the back side of the die wall between the staff and customer, or at the back (kitchen side) edge of that bartop? There seems to be a gray area here. I never count the bar surface in my net A-2 calcs, but do I need to include it in my gross kitchen calcs?

soooo...to help this at times, I would allow most of the ancillary spaces to be done in one lump of 200 gross....and not worry about room by room "rounded up". When it is more complicated egress with corridors and convergence, I like to see room by room for accumulated OL for hardware and door swing, etc....

So again, is it change of use or upgrading the egress components you are concerned with?