Clarification on IPC Minimum Water Closets

[rookieplumber]

I'm studying for a plumber exam and found a practice test with no tech support so I have to ask others for some clarification on a question. This is somewhat new to me and I dig this forum.

This practice question says the office building has occupancy of 400 total. 200 men, 200 women. The answer explanation used the 400 occupancy and Table 403.1 in the #2 classification to reach the number 9 total water closets.



I computed my answer of 10 water closets like this: I included IPC 403.1.1 because I thought that meant I would divide the total occupancy of 400 in half, so 200 men need 2 water closets for the first 50, and 3 more for the remaining 150, total 5. Then 200 women also need 5 water closets for a total of 5. Grand total 10 water closets. Urinal substitution per 424.2 didn't enter the equation so I ignored that. But that's the wrong answer. I see how they got 9 but I need to clarify my process.



My question is this: when I look at Table 403.1 and there is no vertical line separating men and women, like there is no line in the men/women box for business classifications and the ratio calculation just covers both sexes....then does that mean that each bathroom will actually be a single room with just a single water closet and a single lavatory opposed to a group bathroom with 5 water closets in individual stalls? Maybe that's a design question, but I'm looking for a clue why the fixture calculation is sex segregated in some but not others, and why the question did not divide 400 occupancy in half.



likewise, In theaters and assembly buildings there is a line between the men and women columns so that means those are group bathrooms that will be segregated by sex? And if a total occupancy of a Theater (#1) is say, 2000, then I would divide that into 1000 Male, 1000 Female...and have 8 Men's Water Closets in a group bathroom and 15 Female water closets in another group bathroom?

I've definitely seen sex segregated group bathrooms in office buildings so I'm confused by this calculation. If the building needs 9 water closets does that mean 5 toilets for women in a group bathroom and 4 for men in another group bathroom, or does that mean 9 separate small rooms with 1 water closet each? What is the significance of the line separating Male and Female? The answer is probably right in the code book but I'm not seeing it so thanks if you can point me in the right direction.

 

[Sifu]

The question asks for the minimum, which I have normally computed the way you did it. However, if using all single user toilet rooms, identified by for use by either gender, then you get one less. so that is the minimum number. I see this from time to time, but never for 9 single user toilet rooms. When this first started to happen I had DP's try to have it both ways. They would compute based on one gender (200=5), then claim that since either gender could use them that is all they need. My take is you can do it either way, and take the lesser number, but it rarely presents a reduction, and if so it is minimal. My guess is that the question is doing it the same way. The 2021 IPC added a paragraph to 403.1.2 that says the total number is permitted to be based on the required number of separate facilities or on the aggregate of any combination of single user facilities. I THINK this codifies the approach I describe, but as usual the writers of the code did not take in to account my limited ability at interpreting their words.

 

[brokenkeys]

Unfortunately, all of the study guides/ test prep I've worked with over the years have had at least one error, some have had many (looking at you ARE study guides).

403.1 tells you to split for gender first and then multiply the ratio. 403.2 tells you when you have to provide separate facilities for each sex. If your count is low enough you can provide a couple unisex restrooms, but cross one of the thresholds and you have to separate.

 

[rookieplumber]

Interesting. Oh, the study guides and online test prep are FULL of errors. I mean, $300 for a "course" and it was hardly worth any money at all. They finally gave me my money back because nearly every question was contradicted or incomplete. I truly think these are clever computer kids with zero trade code experience who are using Artificial Intelligence programs to scan all the code books online and generate a lame practice exam. How else could they offer 50 different trade exams?

But the Artificial Intelligence is limited and it will generate a question based on one code number without realizing that 2 numbers away there is an exception that makes the question itself incomplete or the answer wrong. And the editors don't have any experience in the trade so they just accept the answer until someone with trade experience actually tries to answer the question and realizes it's all contradicted by other codes. Never mind simple typos and data entry mistakes that confuse the student.

My advice is to look at your local library for an online free test prep because it might as well be free if it's full of mistakes.

This costly test prep managed to ignore the entire Chapter 14 section of the IPC so I go to a different free test prep and it asked me about soil percolation tests and greywater disposal and seepage trenches and I had not seen 1 previous question about that. And it asked me about Tables in the appendix that I hadn't looked at.

I guess some study prep is better than none and if I find a mistake then it helps me engage with the text even just to realize the editors are wrong. But it's hardly worth money to proofread someone's incorrect test prep. They should pay me.

I'm guessing this minimum bathroom chart is not meant to be a guide to architecture or how to realize the bathrooms. It's just a start. The building needs 9 water closets minimum. How those are realized is not part of the chart. Group bathrooms, unisex bathrooms, a mixture...that's a different topic. The line separating the MALE/FEMALE column perhaps indicates there is, or isn't, some wiggle room for unisex bathrooms or at least there is no need to calculate the minimum by splitting the number in half. Just take total occupancy and use the ratio given.

 

[rookieplumber]

I got another practice question about this topic that confirms what brokenkeys wrote.
Separating facilities is 2021 IPC 403.2
That line between MALE/FEMALE in the Table 403.1 just simplifies the calculation.
403.2 is what determines the thresholds
Because the business/office has a 400 person occupancy that exceeds exception #4 there will definitely be separate facilities. 5 Female, 4 Male wc. How they are arranged is another topic.

 

[rookieplumber]

super annoying. I get a very similar practice question and it explains the right answer using the exact process that got me the wrong answer in the other question.






It divides sexes and then computes the ratio from the divided number instead of just going with 70 total employees and 190 total visitors and 40 residents.
The Table does not separate MALE/FEMALE so I just used 190 total visitors. 1 w/c for the first 75 and 2 more for the remaining 115 for a grand total of 3. But nooooo. that's wrong. In this case I'm supposed to divide 190 into 95 Male and 95 Female and reach 4 total water closets.

What this teach me is to divide the total occupancy in half by sex and then compute the ratio TWICE using the same calculation in the table, instead of taking total unisex occupancy and computing the ratio ONCE with the calculation, which will always leave me short a toilet or two. Jeeez. Why the office building occupancy was not divided is a mystery.

 

[rookieplumber]

I want to do a public service announcement for the Plumbing Code Essentials and the Plumbing Commentary/Code edition found at iccsafe.org. You get a 14 day free trial of both of these plus a study guide and flash cards access and they are about $4 a month if you want to subscribe after that over at codes.iccsafe.org. I would not waste any money on the private exam prep programs I've found online. They are full of errors and they barely seem to understand what they are talking about, while the study guide and code essentials and commentary require lots of reading and the tests are more basic, but they are completely correct and well explained.

I struggled visualizing some of the details when only using the code book but the commentary basically explains and illustrates everything better than any study guide I've read. The diagrams leave nothing to the imagination. Especially helpful illustrating building drains and stacks and fixture drains/branches.

This sample problem I found in the Commentary portion of the IPC answers my question about when occupancy # is divided in half by gender. The answer is ALWAYS. Always divide the number in half by gender. The line that separates the MALE/FEMALE water closet column in the Assembly classifications doesn't mean anything except to remind you there is a different ratio per gender. The study guide question I found in post#1 that just took a total occupancy and applied the ratio to the total # is wrong. Even if the bathroom is a single use room, you should still reach the final minimum fixtures by applying the ratios to both genders. Assembly classifications have different ratios for MALE/FEMALE because:

"The buildings or spaces having these use descriptions have historically had numerous situations where there were long lines (queues) of females waiting to use toilet facilities while male facilities had very short or no lines. The reasons for this include the following:

1. 1.For a variety of social and physical reasons, women generally take a longer period of time to use the facilities.
2. 2.Women somewhat outnumber men in the general population and this becomes especially evident in large groups of people.
3. 3.Women, in general, tend to use the facilities more frequently."

And in assembly classifications this difference in bathroom use is most obvious causing long lines so they get different ratios. "The potty parity" The other classifications don't have big problems with lines so they get the same ratio, but will often be a group bathroom separated by gender.

Only when the occupancy gets an exception specified in IPC: 403.2 do bathrooms become single-use rooms.












The Business will have group bathrooms, the library will also have group bathrooms but the storage-use building will probably have 2 single use non-gender bathrooms because that will satisfy 403.1.2 code about single use facilities counting toward the required number. It is noteworthy that they do not round up the subtotal fractions until the last stage because that would start to increase fixtures beyond the maximum.