UPC Section 804.1 sets the height limits for a clothes washer standpipe. The standpipe must extend at least 18 inches and no more than 30 inches above its trap. The trap must be roughed in 6 to 18 inches above the floor, never below it. Each standpipe needs its own trap.
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.
A clothes washer pumps out a big slug of water fast. That water needs somewhere safe to go. The drain uses a standpipe, a vertical pipe with a trap that the washer hose empties into. UPC Section 804.1 sets how tall that standpipe can be and where its trap has to sit. Get the heights wrong and the washer can drain slowly, back up, or siphon its own trap dry.
What this section says
Section 804.1 covers standpipe receptors, the pipe a clothes washer drains into. The washer hose hooks over the top and discharges through an air break. That means the hose sits loosely inside the pipe and is not sealed to it. The open gap keeps drain water from being pushed back into the machine. The code sets two height limits.
The first limit controls the standpipe itself:
No standpipe receptor for a clothes washer shall extend more than 30 inches (762 mm), or not less than 18 inches (457 mm) above its trap weir.
So the top of the standpipe must sit at least 18 inches and no more than 30 inches above the trap. The second limit controls the trap:
No trap for a clothes washer standpipe receptor shall be installed below the floor, but shall be roughed in not less than 6 inches (152 mm) and not more than 18 inches (457 mm) above the floor.
The trap cannot hide under the slab. It has to sit 6 to 18 inches above the floor where you can reach it. Every clothes washer standpipe needs its own trap. The trap holds a water seal that blocks sewer gas from rising into the room.
When this comes into play
These numbers matter at rough-in, before the wall closes. Picture a laundry box being set into a new wall. The plumber fixes the trap about 12 inches off the floor, then runs the standpipe up so its top lands roughly 24 inches above the trap. That keeps both heights inside the code range. If the standpipe is too short, the fast washer discharge can overflow the top. If it is too tall, the long column of water can pull the trap seal down and let odors in. An inspector checks these heights during the plumbing rough-in.
What this means for you
If your washer drains slowly or the standpipe spits water onto the floor, the standpipe height or trap may be wrong, not just clogged. See why a washing machine drain overflows for the common causes, and how often to replace washing machine hoses while you are back there. A standpipe is an indirect waste connection, the same air-break idea covered in UPC 807. The trap is what protects your trap seal. Because fixing a bad standpipe means opening the wall, it is far cheaper to set the heights right at rough-in than to redo them later.
Full text and source
UPC Section 804.1 is part of the Uniform Plumbing Code. IAPMO publishes and holds the copyright on it. The excerpts above reflect the rule as adopted; Phoenix enforces the 2024 UPC with local amendments. Read the current section on UpCodes, or confirm local amendments through the City of Phoenix Planning & Development Department: phoenix.gov/pdd.
Keep Reading
- UPC Section 408: The Minimum Shower Size Phoenix Code Requires
- UPC 1003: Which Fixture Traps Are Allowed (and Banned)
- UPC 1007: Trap Seal Protection for Floor Drains
- UPC Section 1101: Storm Drainage and Roof Runoff
- Why does my washing machine drain overflow?
- How often should I replace my washing machine hoses?