UPC Section 907 sets when a tall or busy drainage stack needs its own vent stack and relief vents. A vent stack runs beside the soil stack to keep air pressure near normal, and relief vents cross-connect the two so falling water cannot pull trap seals dry on upper floors.
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.
Tall drainage stacks move a lot of water. When water rushes down a stack, it pushes and pulls air. Those pressure swings can suck the water out of a trap and let sewer gas in. UPC Section 907 sets when a tall or busy stack needs its own vent stack and relief vents to protect the trap seals.
What Section 907 covers
Section 907 is titled "Vent Stacks and Relief Vents." It deals with venting for tall drainage stacks, the kind found in multi-story and commercial buildings. A short house drain does not swing pressure much. A stack that drops several floors does. The code steps in where that pressure could break a trap seal.
The section has a subsection titled "907.1 Drainage Stack." It ties the venting to the size and height of the drainage stack it serves. The taller and busier the stack, the more venting it needs.
Vent stack vs relief vent
A vent stack is a vertical vent pipe that runs alongside a drainage or soil stack. It gives air a path so the pressure stays near normal as water falls. Without it, air gets trapped or pulled hard, and traps lose their seal.
A relief vent is a cross connection between the drainage stack and the vent stack. It ties the two together at set points, often at every few floors. It relieves the pressure that builds up on a tall stack. Together, the vent stack and the relief vents keep the air balanced from top to bottom.
The exact sizing, spacing, and connection points come from the code and its tables, so they are described here, not quoted.
When this comes into play
This section is a commercial and multi-story rule. Picture a three-story office or an apartment building with bathrooms stacked floor over floor. The main soil stack carries waste from all of them. On its own, it would swing pressure and gurgle. A parallel vent stack with relief vents fixes that. A single-story house rarely needs one.
If upper-floor fixtures gurgle, glug, or lose their trap water, stack venting may be the reason. This is different from a clog. It is an air problem, not a blockage. See why is my toilet gurgling and sewer gas smell in a commercial building.
How it fits with the other vent rules
Section 907 is one of several venting methods in Chapter 9. Nearby, a heading titled "905.0 Vent Pipe Grades and Connections" covers how a vent is graded and tied in. A heading titled "906.1 Roof Termination" covers where a vent ends above the roof. Note that the code has no Section 904. The chapter jumps from 903 to 905. Section 907 is the real home for stack venting.
What this means for you
If a tall building gurgles or smells of sewer gas on upper floors, the fix is often in the venting, not the drain. See our pages on UPC 905 vent grade and connections and UPC 906 vent termination. For a related method, see UPC 908 wet venting. Because stack sizing is a design job, a licensed plumber should lay out the vent stack and relief vents.
Full text and source
Section 907 is part of the Uniform Plumbing Code, published and copyrighted by IAPMO. The up.codes viewer shows the section headings, so the headings above are quoted and the rules are paraphrased, not copied. The exact stack sizes, spacing, and connection points live in the code text and its tables. Phoenix enforces the 2024 UPC with local amendments, so confirm the current numbers. Read Chapter 9 on UpCodes or the official 2024 UPC, and check local amendments at phoenix.gov/pdd.