How Many "Johns" You Need

Bathroom, Restroom, Loo, Lav, John, Throne, Privy, Powder Room. It doesn't matter what you call it but what does matter is that when you need it, you NEED it, and you DON’T want to have to wait in line for it. When we design buildings, how do we know how many johns to install? To help you understand how we come to that answer, here is a brief -and by no means complete- explanation.

It's not the number of bathrooms that we try to determine but the number of plumbing fixtures that are required. This includes water closets (toilets), lavatories (sinks), drinking fountains, and service sinks (mop sinks). A little historical detour here: Back in days passed (the mid-1800s), a toilet was installed in a small room in the home. Many times a home was retrofitted for indoor plumbing, and the toilet was installed in an existing closet, ergo, water closet. In the process of designing a building, we refer to various standards or codes to help guide safety, structural stability, also durability. There are quite a few of these codes, which I won't bore you with, but two resources that we are required to use in determining the number of plumbing fixtures are the IPC (International Plumbing Code) and the IBC (International Building code).

In chapter 29 of the IBC is table 2902.1; see the table below. This holds the information that could help expedite some of those too-long bathroom lines by helping us to know just how many plumbing fixtures are really needed.

Table 2902.1 from the 2018 International Building Code, Chapter 29 Plumbing systems

Determining how many plumbing fixtures will be needed in a facility starts by looking at the use (Description) of the facility. Once you have decided how the facility will be used, take the number of occupants (if you haven't read our post on Occupant Load Calculations: "What Is Occupancy?" click here) and divide by two (male and female). This is the number used to determine how many water closets (toilets), lavatories (sinks), and other fixtures will be required.

Let's look at an example of a simple office building (Business or B Occupancy); see Ex.1 at right. Let's say we calculate the occupant load at 200 total occupants. Looking again at Table 2902.1, we see that for each male and female occupant load, we use the calculation of: 1 WC, or water closet, per 25 occupants up to the first 50 occupants, and 1 WC per 50 for the remainder exceeding 50. For our example here, this means we would be required to provide 3 toilets for each of the men's and the women's restrooms. The IPC does allow for up to 50% of the WC’s in men's restrooms to be replaced with urinals. Looking at the same table, you can also see that three lavatories, one drinking fountain, and one service sink would also be required.

Additionally, when you look at some of the various Assembly Occupancies in that same Table, you’ll notice that the requirements for WC’s and lavatories are different from men to women. This is based on what some like to call "potty parity." The reason? These occupancies have historically long lines of females waiting to use toilet facilities while male facilities have almost no lines. If you have been to a large concert venue, chances are you have witnessed this firsthand. There isn’t an exact science to determine the ideal number of bathroom fixtures, but hopefully, this can get us close, and you can get back to the party/concert/dinner and not spend your time standing in line with your legs crossed.

All Information was obtained from 2018 International Building code

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