Updated 2026-09-04
Both are model codes. Neither governs anything until a jurisdiction adopts it, and adoption comes with amendments. The useful question is not which is better — it is which one your authority having jurisdiction adopted, in which edition, with what changed.
Best overall
Whichever your AHJ adopted
There is no better code, only the adopted one. Everything else on this page is context for that answer.
Best for a plan set
Cite the edition and section
"IPC 2021 §704.1" survives a change of inspector. "Code slope" does not.
Best first move
Ask two questions
Which code and edition, and where is the local amendment sheet published.
Neither code is federal and neither is universal. Adoption is decided state by state and sometimes jurisdiction by jurisdiction, and a state may write its own code derived from one of them with its own section numbering. The only authoritative answer is your authority having jurisdiction (AHJ).
| Factor | IPC | UPC |
|---|---|---|
| Publisher | International Code Council | IAPMO |
| Cycle | Three years | Three years |
| Rough geography | East, much of the centre and south | West and parts of the midwest |
| Fixture unit schedule | Its own values | Different values for several fixtures |
| Supply sizing | Appendix E method plus tables | Its own tables |
| Wet venting | Permitted for a bathroom group under stated conditions | Permitted, different conditions |
| AAVs | Recognised, subject to local amendment | Historically restricted |
| Companion codes | IRC, IFGC, IMC | UMC, USHGC |
Adoption maps go stale
Sits in the ICC family alongside the IRC, IFGC and IMC, so a residential job under the IRC uses plumbing provisions written to match. Fixture unit values and the supply sizing appendix are its own, and its wet-venting provisions are the ones most residential bathrooms in IPC territory are built to.
Published by IAPMO with the UMC as its mechanical companion. Its fixture unit schedule differs from the IPC's for several fixtures, which means a total computed on one is not submittable to the other. Historically stricter on air admittance valves.
The practical consequence for a plan set: fixture unit totals, supply sizes and vent arrangements are code-specific. Compute them on the adopted code, cite the section, and the review is short.
Both codes agree on the physics, and most of what you do every day is common ground. Drainage runs downhill at a minimum slope by size. Traps need vents within a limited distance. Potable water needs backflow protection matched to the hazard. A closed system needs thermal expansion control. Relief valves need a discharge that cannot be blocked.
The differences are in the numbers, the tables and the permitted arrangements — not in the principles. A plumber who understands why a trap arm is limited will pass either inspection once they read the right table.
Two questions before any calculation