International Plumbing Code basics
Updated 2026-09-04 · 11 min read
What the IPC is, and is not
The International Plumbing Code is a model code published by the International Code Council. On its own it governs nothing. It becomes law only when a state or a local jurisdiction adopts it, and adoption almost always comes with amendments. That is why two towns can both say "we're IPC" and disagree about a detail.
The other model code is the Uniform Plumbing Code, published by IAPMO. Roughly speaking the IPC dominates the east and much of the centre, the UPC the west, and several states write their own from one or the other. The comparison page covers where the two actually diverge on a house.
Never write "code says" without a section
How adoption actually works
A model code is published on a three-year cycle. A state legislature or a building department adopts an edition, sometimes years after publication, and attaches local amendments. Your jurisdiction might be on the 2021 edition, the 2018 edition, or a state code derived from one of them with its own numbering.
The practical consequence: before you size or submit anything, ask the authority having jurisdiction (AHJ) which edition is adopted and whether there is an amendment sheet. It is one phone call and it is the difference between a plan review and a plan rejection.
The sections a house job touches
| Chapter | Covers | When you meet it |
|---|---|---|
| 1 | Administration | Permits, inspections, who may do the work |
| 3 | General regulations | Support intervals, sleeves, protection of pipe |
| 4 | Fixtures | Clearances, minimum fixture counts |
| 5 | Water heaters | Installation, relief valve and discharge |
| 6 | Water supply and distribution | Sizing, materials, backflow, pressure |
| 7 | Sanitary drainage | Slope, drain sizing, cleanouts |
| 8 | Indirect and special waste | Air gaps, appliance discharge |
| 9 | Vents | Trap arms, wet venting, terminations |
| 10 | Traps and interceptors | Trap seals, grease interceptors |
| 11 | Storm drainage | Roof drains, sizing by rainfall |
Four numbers from those chapters carry most residential jobs: 704.1 minimum drain slope, 909.1 trap arm to vent, 604.8 pressure-reducing valve above 80 psi, and 607.3 thermal expansion control on a closed system.
How to read a code clause
- 1
Find the section, not a summary
Read the clause itself. Summaries drop the exceptions, and the exceptions are where the job usually lives.
- 2
Read the exceptions
They are printed immediately after and they are part of the requirement. IPC 909.1's exception for self-siphoning fixtures is a whole design freedom.
- 3
Follow the table reference
Most sizing clauses point at a table. The clause is the rule; the table is the number.
- 4
Check for a local amendment
Amendments override. A jurisdiction can be stricter than the model code and frequently is.
Where to read it
The ICC publishes the code text and sells the printed volumes; the digital versions are searchable by section number, which is how you should be using them. Several commercial services republish the adopted text state by state with the local amendments folded in, which is worth the subscription if you work across jurisdictions.
Whatever you use, cite the edition when you write a number down. A drawing note that says "slope per IPC 2021 Table 704.1" survives a change of inspector; one that says "code slope" does not.