How Would I Calculate The Plumbing Fixtures and Occupant Load In An Office Building

[arwat23]

I'm analyzing the existing OL and plumbing fixture count for an existing office building to determine compliance with current plumbing code. I can get the OL for each suite no problem. The issue I'm having is determining how to assign that to the plumbing fixtures in the building.

This is a single-story office building. If all the fixtures were in common restrooms (outside of suites, usable by anyone), this would be easy - take the building OL and make sure there's enough fixtures for that. However, a majority of the restrooms are within suites, with very few in the common restrooms.

I have two designers proposing different ways of determining if there's enough fixtures in the building:

1. Take the total OL for the building and apply it to all the restrooms regardless of where they are. This would consider that all restrooms are usable by anyone in the building, which would lower the number of required fixtures.

2. Take the OL of each suite, subtract the occupants that the fixtures within the suite can serve, add all remaining occupants from each suite that don't have any fixtures, then subtract these remaining occupants that the common fixtures server. For example, let's say a suite has an OL of 120. 60 men, 60 women. The following numbers are from the UPC. 2 WC for men (51-100) and 4 WC for women (51-100) are required. The suite has one WC for men and 2 for women. That would cover up to 50 men (1-50) and 30 women (16-30). So there are 10 men and 30 women who don't have any plumbing fixtures. The common restrooms have 1 WC for each, which would then cover the remaining men, but would only cover 15 women. So there's still 15 women that aren't accounted for in the fixture count.


My gut is telling me that option 2 is the "correct" way to calculate this. After all, someone in suite 105 won't have access to the restrooms in suite 102. However, I can't seem to justify that in code, and option 1 significantly lowers the required fixture count. Any advice?

 

[Yankee Chronicler]

Option number 1 doesn't work, for the reasons you propose.

Don't forget that for Business occupancies the occupant load is based on gross square foot area. If there are corridors in the building -- they get counted.

Oops! You're in California. In my corner of the world, we use the same IBC occupant load for both egress and for plumbing fixtures. Does the UPC use the same occupant load for plumbing as for egress, or does your plumbing code calculate occupant load for plumbing differently than for egress?

 

[walker.t]

Any advice?

Yes, follow your gut. Option 1 is not going to work because there’s no way to guarantee that the “overflow” facilities in another suite will be available when needed.

For Option 2, you are providing the minimum number of facilities required based on your occupant load, restrooms in common areas will be available when needed but some occupants might have to take a walk if they don’t want to wait for the restroom in their unit to become available.

So there's still 15 women that aren't accounted for in the fixture count

New facilities would have to be added.

 

[arwat23]

Oops! You're in California. In my corner of the world, we use the same IBC occupant load for both egress and for plumbing fixtures. Does the UPC use the same occupant load for plumbing as for egress, or does your plumbing code calculate occupant load for plumbing differently than for egress?

For most projects, we use the OL calculated in IBC for egress to determine the fixture count. The only time we don't is for state projects, OSHPD projects (hospitals), and campsites.

 

[Joe.B]

I think the plumbing fixture count based on Ch. 10 occupant load shouldn't be an absolute, I think it should just be a starting point. For means of egress sizing, absolutely a life safety minimum. Plumbing fixtures? Not so much. The designer should be able to take some liberties in the design and not waste clients' money and/or environmental resources. If you follow the strict occupant load you could often still end up with too many or not enough fixtures.

One hang-up people get into is "code is the minimum, you can go more restrictive, but not less." In most situations that's a clear-cut adage that you can rely on. In the case of plumbing fixtures, one could argue that having fewer plumbing fixtures is more restrictive and therefore should be allowed. Personally, I would allow a design with fewer fixtures than strictly required by code, provided there is documented justification.

Waiting in line to get out of a burning building, not okay. Waiting in line for the bathroom, I call that okay.

 

[arwat23]

If you follow the strict occupant load you could often still end up with too many or not enough fixtures.

I agree, to an extent. Most of the projects I work on are healthcare of office TIs, and most of my clients want all or most of the required restrooms within their suite, spread out as unisex rooms. My approach is, usually, to provide the number of WCs code calls for, while ignoring the urinal requirement. All of these restrooms are single-user, so the urinal isn't really serving much of a purpose other than water efficiency and taking up additional space. Even then, they'll not be used very often. On top of what, most of my clients have received complaints from employees and guests when a urinal is included, saying that women tend to feel uncomfortable or that the room is meant just for men if there's a visible urinal. No jurisdiction has forced me to put urinals in unisex restrooms, and the few times I was called out on that, they allowed it after I explained my reasoning.

I would argue that waiting to use bathroom in an office is a no-no. In a assembly place? Sure. But an office? Nah. That's wasted productivity, could make people late for meetings, etc. (speaking from experience on the latter one). Just my opinion though. If a client wants less and can prove that less would be sufficient, I'll try to convince the AHJ to allow it.

 

[walker.t]

I think the plumbing fixture count based on Ch. 10 occupant load shouldn't be an absolute, I think it should just be a starting point. For means of egress sizing, absolutely a life safety minimum. Plumbing fixtures? Not so much.

You might find this commentary interesting:

2018 IBC Illustrated Handbook commentary on 2902.1 Minimum Number of Fixtures (partial quote)
When determining the proper occupant load to be utilized in calculating plumbing fixture count, there is no specific methodology referenced. However, because the only provisions in the IBC addressing occupant load calculation are found in Chapter 10, it is typically assumed that the approach established in Section 1004 for the means of egress should be used for plumbing fixture count…

It should be noted that the building official also has the authority established in the exception to Section 1004.5 to base the occupant load on the actual number of occupants anticipated, rather than the calculated number. Although the use of this exception is typically inappropriate for egress and fire-safety purposes, it is commonly applied for plumbing fixture count.

Personally, I would allow a design with fewer fixtures than strictly required by code,

My local zoning department and building department are in two separate buildings, I’ve used the public restrooms in both buildings during normal business hours, I think maybe only a couple of times there was one other guy in the room, yet they have like five toilets and lavatories, definitely overkill.

 

[Joe.B]

You might find this commentary interesting:

Yes, interesting. Also, validating. (Not that I needed it.)

I think it's also worth noting that while CA did make the switch over to IBC model codes for building and fire, our plumbing (and mechanical) codes still utilize the uniform model codes. I just pulled the 1995 California Plumbing Code off our shelf, it says:

411.0 Plumbing Fixtures Required
Each building shall be provided with sanitary facilities as prescribed by the local or state department having jurisdiction. In the absence of local requirements, a recommended list of minimum facilities for various occupancies is given in Appendix C of this Code.

Appendix C resembles Table 422.1. It references "the total occupant load shall be determined by minimum exiting requirements" so that's consistent, but I find it interesting that they call it a recommended list.

 

[Yikes]

arwat23, here's the excerpts from the CPC regarding existing installations. If the original building was an office and the new building is an office, it looks like there is a mechanism under which the AHJ can determine that the existing plumbing system can remain.

102.2 Existing Installations​

Plumbing systems lawfully in existence at the time of the adoption of this code shall be permitted to have their use, maintenance, or repair continued where the use, maintenance, or repair is in accordance with the original design and location and no hazard to life, health, or property has been created by such plumbing system.

102.3 Maintenance​

The plumbing and drainage system, both existing and new, of a premise under the Authority Having Jurisdiction shall be maintained in a sanitary and safe operating condition. Devices or safeguards required by this code shall be maintained in accordance with the code edition under which installed.

The owner or the owner's designated agent shall be responsible for maintenance of plumbing systems. To determine compliance with this subsection, the Authority Having Jurisdiction shall be permitted to cause a plumbing system to be reinspected.

102.4 Additions, Alterations, Renovations, or Repairs​

Additions, alterations, renovations or repairs shall conform to that required for a new system without requiring the existing plumbing system to be in accordance with the requirements of this code. Additions, alterations, renovations, or repairs shall not cause an existing system to become unsafe, insanitary, or overloaded.

Additions, alterations, renovations, or repairs to existing plumbing installations shall comply with the provisions for new construction unless such deviations are found to be necessary and are first approved by the Authority Having Jurisdiction.

102.4.1 Building Sewers and Drains​

Existing building sewers and building drains shall be permitted to be used in connection with new buildings or new plumbing and drainage work where they are found on examination and test to be in accordance with the requirements governing new work, and the proper Authority Having Jurisdiction shall notify the owner to make changes necessary to be in accordance with this code. No building, or part thereof, shall be erected or placed over a part of a drainage system that is constructed of materials other than those approved elsewhere in this code for use under or within a building.

102.4.2 Openings​

Openings into a drainage or vent system, excepting those openings to which plumbing fixtures are properly connected or which constitute vent terminals, shall be permanently plugged or capped in an approved manner, using the appropriate materials in accordance with this code.

102.5 Health and Safety​

Where compliance with the provisions of this code fails to eliminate or alleviate a nuisance, or other dangerous or insanitary condition that involves health or safety hazards, the owner or the owner's agent shall install such additional plumbing and drainage facilities or shall make such repairs or alterations as ordered by the Authority Having Jurisdiction.

102.6 Changes in Building Occupancy​

Plumbing systems that are a part of a building or structure undergoing a change in use or occupancy, as defined in the building code, shall be in accordance with the requirements of this code that are applicable to the new use or occupancy.