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Plumbing codes: IPC, UPC and IRC

Entry in Sizes, codes and marks · Updated · Written by the Know Your Pipes editors from the sources listed under References

The UPC vs IPC question is about two competing model plumbing codes: the Uniform Plumbing Code (UPC), published by IAPMO, and the International Plumbing Code (IPC), published by the International Code Council (ICC). A third ICC code, the International Residential Code (IRC), has its own plumbing chapters for houses.

A model code is not law by itself. It becomes enforceable when a state, county or city adopts it, often with local amendments, so the code that applies to a house is whatever that jurisdiction's building department has adopted.

1 The three codes

The ICC revises its codes every three years through what it calls a governmental consensus process, and states that the IPC is in use or adopted in 37 states, the District of Columbia, New York City, Puerto Rico and Guam, covering about 257 million people, or 76% of the US population[1]. The IPC is written to correlate with the other 14 International Codes[1].

The UPC was introduced in Los Angeles in 1928 and formally published as the Uniform Plumbing Code in 1945[2]. IAPMO develops it under ANSI-accredited consensus procedures on a three-year cycle, and the 2024 edition, published in May 2023, was the eighth developed that way[2]. IAPMO names Los Angeles, Houston, Minneapolis, Seattle and Portland among the cities that use it[3].

The IRC sets minimum rules for one- and two-family dwellings of three stories or less and gathers structural, plumbing, mechanical, fuel gas, energy and electrical rules in one book[5]. In the 2024 IRC, Part VII Plumbing runs from Chapter 25 to Chapter 33[4].

IPC, UPC and IRC compared
CodePublisherCoversCurrent editionPlumbing content
IPCICCAll building types2024[1]Whole code
UPCIAPMOHomes and commercial buildings in one book[3]2024[2]Whole code
IRCICCOne- and two-family dwellings, up to three stories[5]2024[4]Chapters 25–33[4]

2 2024 IRC plumbing chapters

The plumbing part of the 2024 IRC is organized as follows[4]: Chapter 25, Plumbing Administration; 26, General Plumbing Requirements; 27, Plumbing Fixtures; 28, Water Heaters; 29, Water Supply and Distribution; 30, Sanitary Drainage; 31, Vents; 32, Traps; and 33, Storm Drainage. Gas piping sits in a separate part, Chapter 24, Fuel Gas[4].

3 How the codes differ

On many basics the codes agree. The 2024 IRC (Section P2609.3) and the 2024 UPC (Section 301.2.3) both require plastic pipe and fittings to meet NSF/ANSI 14, and the 2024 IPC and IRC both require water distribution pipe to conform to NSF/ANSI/CAN 61[6]. Details differ. The 2024 IPC, Section 603.1, sets a 3/4 inch minimum for the water service[6]. The 2024 UPC, Section 604.13, bars PEX and several other plastic tubings from the first 18 inches of piping connected to a water heater[6]. The ICC lists features of the IPC it says differ from other model codes, such as not requiring indirect waste lines to be vented to the atmosphere[1].

Other model codes exist; the 2024 National Standard Plumbing Code is one[6]. Because codes are adopted and amended locally, a rule seen in one code may not apply in a given town. Code-specific details appear in entries such as pipe sizing basics and sanitary tees and wyes.

See also

  • PVC Schedule 40 pipeWhite rigid PVC pipe made to ASTM D1785; used for cold-water pressure lines outside the house and, when dual-marked, for drains.
  • Push-fit fittingsFittings that seal by pushing tube into an O-ring and locking device; covered by ASSE 1061 for PEX, copper, CPVC and PE-RT.
  • Sanitary tees and wyesHow sanitary tees, wyes and combination wyes differ, and which drain direction changes each fitting is allowed to make.
  • Copper pipe types K, L and MThe three wall grades of copper water tube under ASTM B88, how to tell them apart and where each is normally used.
  • Burst pipe: first stepsThe order of priorities when a water pipe bursts: water off at the main, electricity safety, then a licensed plumber.
  • Black steel gas pipeThreaded Schedule 40 steel pipe with a dark finish, long used for natural gas and propane piping inside buildings.

References

  1. International Code Council, "The 2024 International Plumbing Code: Why It Should Be In Your Future" (December 2024) — iccsafe.org
  2. IAPMO, "IAPMO Publishes 2024 Editions of Uniform Plumbing Code, Uniform Mechanical Code" (May 1, 2023) — iapmo.org
  3. IAPMO, "Uniform Plumbing Code" — iapmo.org
  4. International Code Council, "2024 IRC Code and Commentary, Volume 2: Table of Contents" (2025) — shop.iccsafe.org
  5. Pacific Northwest National Laboratory, Building America Solution Center, "International Residential Code (IRC)" (2024) — basc.pnnl.gov
  6. Plastics Pipe Institute and Plastic Pipe and Fittings Association, "PEX Plumbing Distribution Systems Design and Installation Guide, Third Edition, Chapter 4: Code Acceptance" (2026) — plasticpipe.org