Differences in Plumbing Codes Happens Often

Plumbing codes are different, but that does not necessarily mean they are wrong

Differences in Plumbing Codes Happens Often

Example A

For the past 28 years I have either been learning plumbing code or teaching it. I know what you’re thinking: “He needs to get a life,” but honestly, I enjoy it. It has become a large part of who I am.

I served a four-year plumbing apprenticeship here in Wisconsin. Class was a day away from the hands-on work in the field and an intense day of learning. I had a great instructor by the name of John W. Kollman III. He instilled the importance of what it was to be a plumber to me. He inspired me and gave me a true understanding of how “the plumber protects the health of the nation.”

The code training I received served me well. Shortly after passing my journeyman plumber’s exam, I started teaching evening classes to plumbing apprentices and journeymen. The first class I taught? Well of course, plumbing code review! I like to think I found my knack when it came to teaching code. Eventually I became a full-time plumbing apprenticeship instructor.

For 20 years I worked in the classroom grooming tomorrow’s next plumber. I found ways to present complex and, sometimes, mind-bending methods to my students in a way that made the most sense to them. It took a lot of work to first understand how the code was developed and what the intention or the “why” was about a specific code topic. But as I always told my students, once you understand the why, the “how” comes easy.

Flash forward to the second week of October 2020. I wrote and passed the master plumbers exam for another state. Now, just so you understand, and do not jump to conclusions, I don’t run around the United States taking plumbing exams for fun! I took this exam to assist my www.iwsh.org team with an upcoming project in 2021. IWSH — or the International Water, Sanitation and Hygiene Foundation — is a foundation that harnesses the skills and expertise of water industry professionals, organizations and manufacturers to support critical water, sanitation and hygiene initiatives worldwide. In order for my team and I to legally perform plumbing in this state, I needed to show competence of the applicable code.

Here is where I truly had to relearn plumbing. You would think plumbing should be an internationally recognized process where for a lack of better words, plumbing is plumbing. But that is far from the case, which I quickly learned. Some of you reading this today probably subscribe to a social media network that relates to plumbing and I’m sure you can relate to what I’m saying. How many times have you seen another plumber post a picture of their work/craftsmanship on social media only to have 2 million comments either blasting that person for shotty work, or posting “That’s not legal!” or “You can’t do it that way, it will never work!”

I can certainly relate to the above and many times rolled my eyes at some of these installations saying the exact same things. But let me tell you, I’m not as quick to do so after my recent studies. Let me give you an example of what I’m talking about.

Here are three venting systems from three different codes: 

All three are referred to as “horizontal wet vents” by their respective codes but you can easily see that they are not all the same.

Example A has a dry vent extending from the lavatory. In this code it states that the drain from a lavatory or lavatories which are either provided with individual vents or a common vent may serve as the wet vent for not more than two bathtubs or showers and not more than two water closets. All fixtures must be located in a nonpublic bathroom group only. The dry vent size is 1.5 inches and may not exceed 150 feet in developed length based on drainage fixture units of the fixtures being vented (DFU). The wet vent is required to be a minimum of 2 inches and cannot exceed 4 DFU.

Example B, from another code, indicates that the horizontal wet vent begins at the connection of the required dry vent connection and extends downstream to the last horizontally connected wet vented fixture drain. The required dry vent shall be an individual or common vent for any (public or nonpublic) bathroom group fixture except for an emergency floor drain and not more than one fixture may connect upstream from the dry vent connection to the horizontal. Again, the dry vent is 1.5 inches but is based on the vent being half the diameter of the drain served. It also goes on to state that in the event that the dry vent exceeds 40 feet, the entire vent would increase one nominal pipe size. The wet vent portion of the system is sized via a table based on the total DFU discharging into the wet vent.

Example C was taken from yet another code. While still being classified as a horizontal wet vent system, that code indicates that the dry vent connection to the wet vent shall be an individual vent for the bidet, shower or bathtub. One or two vented lavatory(s) shall be permitted to serve as a wet vent for a bathroom group (public or nonpublic). Only one wet-vented fixture drain or trap arm shall discharge upstream of the dry-vented fixture drain connection. Notice this time that the dry vent above the lavatory is 2 inches since there is a water closet in the system. The dry vent is permitted to be 120 feet in length provided not more than 40 feet is installed horizontally.

Each system is a legal horizontal wet vent, yet I would say that you probably thought somewhere along the line while looking at them, “That’s not legal!” or “You can’t do it that way, it will never work!” Oh, and don’t even get me started on permitted point of vent distances (aka vent to trap), we’ll save that one for another article!

Each system works. Each system is installed every day around the country. The moral of the story is, plumbing codes are different, but not necessarily wrong.  


Randy Lorge is a third-generation plumber and the director of workforce training and development for the International Association of Plumbing and Mechanical Officials (IAPMO). Lorge is also a member of the planning team for the International Water, Sanitation and Hygiene Foundation (IWSH). This 501(c) (3) foundation has completed water and sanitation projects for those less fortunate in India, South Africa, Indonesia and, more recent, the United States. He enjoys time with his family and spending as much time as possible in his deer stand. To contact Lorge, email editor@plumbermag.com.


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