How plumbing codes are written, adopted and amended

Maya Chen started the second level of her plumbing apprenticeship in the same place she finished the first: Kingsway Tower, the 12-story residential building over two parking levels in Columbus where Northbridge Mechanical holds the plumbing contract. The rough-in was done on most floors, the risers were tested, and the finishing crews were setting fixtures on the lower floors. On her first morning back, Luis Ferreira put a thick binder on the gang box in front of her and opened it to a page covered in small print and numbers. "Up to now you learned how to install things," he said. "This level is about why. Every pipe size, slope, vent and valve you put in this building is there because a code says so. You need to be able to find the rule yourself, read it properly, and show an inspector where it is."

This course is the first of two on the plumbing code. PLB-110, PLB-120 and PLB-130 taught the materials, the drainage and venting system and the water supply system, and they mentioned code rules as they went. PLB-210 turns the code itself into the subject: where it comes from, how it is organized, how to read a requirement, and how its main parts apply to real work. The examples use the International Plumbing Code and the Ohio Plumbing Code, because Kingsway Tower is in Ohio, with comparisons to the Uniform Plumbing Code used in several western states. The skills carry over to any state.

The first lesson answers a question many apprentices never ask: where does the code come from, and who decides what it says? Knowing the answer explains why the book in Luis's binder is not quite the same as the one a plumber uses two provinces or states away, why the rules change every few years, and why an inspector sometimes asks for something the national book does not mention.

Why plumbing has a code at all

Plumbing codes exist because bad plumbing makes people sick. In the nineteenth century, cities in Europe and North America grew faster than their water and sewer systems, and outbreaks of cholera and typhoid spread through contaminated water. Engineers and public health officials learned that clean water, proper drainage, trap seals, venting and the separation of drinking water from waste were the difference between a healthy city and an epidemic. The first plumbing regulations were written by cities to stop the worst practices: wells next to cesspools, drains without traps, and drinking water pipes cross-connected to sewers.

Over time, cities found that writing and updating their own plumbing rules was expensive and led to confusion. A plumber working in two neighboring towns could face two different rule books. Manufacturers had to make products to many local standards. That pressure led to model codes: a single, carefully written code that many governments could adopt as their own, with local changes where needed.

Every rule in a modern plumbing code still traces back to one of a small number of purposes. Luis put it simply for Maya: protect health, protect safety, protect the building and its neighbors, and make sure the system can be used and maintained. When a rule seems fussy, asking which of those purposes it serves usually explains it.

• Health: keep drinking water safe, carry waste away completely, and keep sewer gases out of the building.
• Safety: prevent scalds, explosions of water heaters, injuries from broken fixtures and falls caused by leaks.
• Protection of the building: prevent water damage, freezing, structural damage from cutting and notching, and fires spread through openings.
• Function and access: make sure fixtures work, systems can be cleaned out and tested, and people with disabilities can use the facilities.

Model codes and the codes that are law

A model code is a document written by a code body so that governments can adopt it. On its own, a model code is not law. It becomes law only when a government with authority over construction adopts it, usually by referencing it in a regulation or by-law, sometimes with amendments. The version that is actually enforced on a job site is the adopted code, not the model.

In the United States, there are two widely used model plumbing codes. The International Plumbing Code, or IPC, is published by the International Code Council, the same body that publishes the International Building Code and the International Residential Code. The Uniform Plumbing Code, or UPC, is published by the International Association of Plumbing and Mechanical Officials, known as IAPMO. Construction is mostly regulated by the states and local governments, so neither model code is law until a state, county or city adopts it.

Ohio adopts the IPC with Ohio amendments as the Ohio Plumbing Code, a rule of the Ohio Board of Building Standards in the Ohio Administrative Code. The current Ohio Plumbing Code is based on the 2021 IPC and took effect on March 1, 2024. It applies to commercial buildings, which include large residential buildings such as Kingsway Tower; one-, two- and three-family dwellings fall under the Residential Code of Ohio instead. The City of Columbus enforces the state code through its building department.

Who writes the code

The IPC is written through the ICC's governmental consensus process. Anyone can submit a code change proposal. Proposals are heard at public committee action hearings, where a committee of code officials, contractors, engineers and industry representatives recommends approval, approval as modified, or disapproval. Anyone can then submit public comments, and the final decision is made by the ICC's governmental members, who are code officials working for governments. The UPC uses an ANSI-accredited consensus process run by IAPMO, in which technical committees vote on proposals and the membership acts on them. Both processes are slow on purpose, because a code change affects every building built afterward.

This matters to an apprentice for a practical reason. When something in the code does not make sense, or a new product does not fit the rules, there is a way to change it. Many code changes start with an experienced plumber or inspector who noticed a problem in the field and wrote a proposal. Luis had once helped his union's code committee prepare a proposal on cleanout access, and he still remembered how long it took.

Editions and code cycles

Both US model codes are updated on a three-year cycle. Recent IPC editions are 2018, 2021 and 2024, and the UPC follows the same years. A new model edition does not change the law anywhere until a government adopts it, and adoption can lag by several years. Ohio's current plumbing code is based on the 2021 IPC, even though the 2024 IPC has been published, and some jurisdictions in other states are still using editions older than that.

Because of the lag, a plumber has to know which edition applies to a given job. The rule is that a building is normally built to the code in force when the permit was applied for, even if a newer code takes effect while the building is under construction. A large project like Kingsway Tower can take three years to build, and the code edition is fixed by the permit date. Transition periods are common: a government announces a new code, sets an effective date, and allows permits applied for within a set time to use either the old or the new code.

Amendments: why local codes differ

Governments that adopt a model code often change parts of it. These changes are called amendments, and they are why the code in force in one place can differ from the model and from the code next door. Amendments usually fall into a few groups.

• Climate and geography: deeper frost protection in cold regions, different rules for areas with expansive soils or earthquakes.
• Local practice and history: a city that has always required cast iron in tall buildings, or that bans a material after failures.
• Water supply conditions: rules for high city pressure, hard water or private wells.
• Administrative matters: who issues permits, who may do plumbing work, what licenses are required and how inspections are booked.
• Policy goals: water conservation, energy efficiency, accessibility or lead reduction that go beyond the model.

The Ohio Plumbing Code amends the IPC in a number of places, many of them administrative, such as the rules on who enforces the code and how. Columbus enforces the state code but also has its own city rules that affect plumbing, such as Division of Water rules on service connections, meters and backflow prevention, and sewer rules on grease interceptors and what may be discharged to the sewer. In other states, cities and counties are often allowed to amend the plumbing code themselves, so the code in one city can differ from the code in the next.

Luis gave Maya a rule she would hear many times: the code is the minimum. An engineer's specification can require more than the code, a city by-law can add rules, and the owner can ask for better materials. What nobody can do is build to less than the code without an approved alternative. When the drawings, the specification and the code disagree, the stricter requirement usually governs, and the question goes to the engineer or the inspector before the work goes in.

Codes, standards and listings

The plumbing code does not try to describe every product. Instead, it refers to standards: documents that describe how a pipe, fitting, valve or fixture must be made and tested. When the code says a material must conform to a particular standard, it brings that standard into the code. The code tells you what to use and where; the standard tells the manufacturer how to make it.

Most plumbing product standards referenced by the IPC and UPC are published by ASTM International, ASME, NSF International, the American Society of Sanitary Engineering (ASSE), CSA Group and other bodies. For example, plastic drainage pipe, copper tube, backflow preventers and water heaters each have their own standards. A product is shown to meet a standard by listing or certification: an accredited agency tests the product, and the product carries the agency's mark. The inspector looks for the mark.

Maya had already seen these marks printed along PVC drain pipe and stamped on copper fittings. Now she understood why Luis rejected a box of cheap fittings from an online seller: they had no certification mark, so there was no proof they met the referenced standard, and the inspector would have been right to fail them.

The program below is the kind of quick check a foreman might run on a materials list: it compares each item's certification marks against what the job requires and flags anything missing.

# Check a materials list for the certification marks the job requires
required = {"pvc dwv pipe": "ASTM D2665", "copper tube type l": "ASTM B88",
            "rp backflow preventer": "ASSE 1013", "pex tubing": "ASTM F876"}
delivered = [("pvc dwv pipe", ["ASTM D2665"]), ("copper tube type l", ["ASTM B88"]),
             ("rp backflow preventer", []), ("pex tubing", ["ASTM F876", "NSF 61"])]

for item, marks in delivered:
    need = required[item]
    status = "ok" if need in marks else "REJECT: no " + need + " mark"
    print(f"{item:24s} {status}")

pvc dwv pipe             ok
copper tube type l       ok
rp backflow preventer    REJECT: no ASSE 1013 mark
pex tubing               ok

The example standard numbers in the program are typical of what appears on a specification, but always take the actual standard from the code and the project specification, not from memory.

Who enforces the code

In Ohio, the Board of Building Standards adopts the code and certifies local building departments to enforce it. In Columbus, the city's Building and Zoning Services department issues permits and inspects commercial plumbing work. Where a local department is not certified for a type of work, the state provides enforcement. Day-to-day enforcement is almost always local.

The official who interprets and enforces the code is often called the authority having jurisdiction. When the code is unclear, that person's interpretation governs on their jobs. Interpretations can differ between jurisdictions, which is one more reason to ask early rather than guess. A good working relationship with inspectors, based on knowing the code and building neatly, saves time on every job. Lesson 11 covers permits and inspections in detail.

Licensing and who may do plumbing work

Codes set the technical rules; other laws set who may do the work. In Columbus, plumbing work must be done by or under a licensed journeyperson plumber, and commercial plumbing contractors in Ohio must hold a state contractor's license from the Ohio Construction Industry Licensing Board. Maya's apprenticeship is registered, and her work is supervised by Luis, who holds his journeyperson license. Designers of plumbing systems in large buildings are usually professional engineers.

Doing plumbing work without the right qualifications can bring fines, stop-work orders and insurance problems, and work done by unqualified people may have to be torn out and redone. For an apprentice, the rule is to work within the scope your supervisor assigns and to keep your logbook current.