UPC Section 313 sets how often plumbing pipe must be held up by hangers or supports so it cannot sag, strain its joints, or trap water. The required spacing depends on the pipe material and whether the run is horizontal or vertical, with softer materials like PEX needing more frequent support.
The Uniform Plumbing Code is published and copyrighted by IAPMO. This page explains the section in our own words with a short excerpt only. Read the full official text at the source.
Pipe is heavy when it is full of water, and it does not hold itself up. If a run is not supported often enough, it sags between its supports. On a drain line, a sag creates a low spot that traps water and waste and clogs. On any line, sagging strains the joints and can pull a fitting apart over time. UPC Section 313 sets how often pipe has to be held up so none of that happens.
What this section says
The rule ties support spacing to two things: the pipe material and whether the run is horizontal or vertical. Stiffer materials can span farther between supports; softer or more flexible ones need supports closer together. The code frames the requirement this way:
Piping shall be supported at intervals prescribed by the code to ensure adequate support of the pipe and to maintain alignment and prevent sagging.
In practice that means a rigid material like cast iron or steel can run several feet between hangers, while a flexible material like PEX needs support at much shorter intervals, often every few feet, because it will bow under its own weight. Copper falls in between. The code publishes a table of the maximum spacing for each material in both the horizontal and vertical direction. Supports also have to be made of a material that will not corrode the pipe or cut into it, and they must let the pipe expand and contract with temperature changes rather than pinching it in place.
When this comes into play
This section governs how any pipe run is hung, in new work and remodels alike. Picture a repipe that switches an old house to PEX: the flexible tubing has to be strapped far more often than the rigid pipe it replaced, or it will droop between joists and, on drain lines, form bellies that hold water. An inspector checks support spacing before walls close, because a sag hidden inside a wall or ceiling is expensive to fix later.
What this means for you
If a drain in your home runs slow no matter how often it is cleared, an unsupported sag, called a belly, may be trapping water in the line. That is a support-and-slope problem rather than a clog. For the material-by-material spacing table, see pipe hanger and support spacing. A whole-house repipe is a common time this comes up, since flexible PEX needs strapping far more often than the rigid pipe it replaces. Because correcting a belly means re-hanging the pipe, proper support at installation is far cheaper than a repair later.
Full text and source
UPC Section 313 is part of the Uniform Plumbing Code. IAPMO publishes and holds the copyright on it. The excerpt above reflects the rule as adopted; Phoenix enforces the 2024 UPC with local amendments, so verify the current spacing tables and section numbers. Read the support rules on UpCodes, or confirm local amendments through the City of Phoenix: phoenix.gov/pdd.
Keep Reading
- UPC Section 604: Approved Materials for Water Pipe
- UPC Water Supply Pipe Sizing: How Code Sizes Your Water Lines
- UPC 1003: Which Fixture Traps Are Allowed (and Banned)
- UPC 1007: Trap Seal Protection for Floor Drains
- How often do plumbing pipes need to be supported?
- PEX vs CPVC pipe: which is better?
- What does a whole-house repipe cost, and is PEX or copper better?