The Uniform Plumbing Code requires a floor drain to have a trap, to be sized for the water it must carry, and to keep its trap seal so sewer gas cannot rise. Because floor drains sit unused for long stretches, code addresses drying-out with trap primers or approved seal devices.
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 floor drain is the drain set into the floor of a garage, laundry room, utility room, or commercial kitchen. Its job is to carry away water that ends up on the floor, from a spill, a leak, or an overflow. Simple as it looks, the Uniform Plumbing Code sets real requirements for how a floor drain is built, because a bad one lets sewer gas into the room.
What the code requires
Three requirements carry most of the weight: a trap, the right size, and a protected seal. The code states the core rule:
Each floor drain shall be provided with a trap, and the drain shall be sized in accordance with the fixture it serves.
First, every floor drain must have a trap, the U-shaped bend that holds a plug of water to block sewer gas. Second, it has to be sized for the water it might carry, so it can drain the area fast enough without overflowing. A drain in a room that could see a large spill needs to be larger than one in a small utility closet. Third, and specific to floor drains, the code addresses the trap seal. Floor drains often sit unused for weeks, and the water in the trap can slowly evaporate and let sewer gas in. To prevent that, code calls for a way to keep the seal, such as a trap primer that feeds a little water to the trap, or an approved trap-seal device.
When this comes into play
This governs any floor drain that is installed or replaced. Picture a laundry-room floor drain that no one has used in months: without a trap primer or a topped-up seal, its trap dries out and the room starts to smell like sewer gas even though nothing is leaking. Code requires the drain to be trapped and to have a way to keep that trap wet, precisely so that does not happen. An inspector checks for the trap and, where required, the primer.
What this means for you
If a floor drain in your home smells of sewer gas, the most common cause is a dried-out trap, and the simplest fix is to pour a bucket of water down it to refill the seal. If the smell keeps coming back, the drain may lack a working trap primer, which is a code-level fix covered by UPC 1007 trap seal protection. For when a floor drain backs up instead of smelling, see floor drain backing up, and to tell one drain type from another, see floor sink vs floor drain vs mop sink. Keeping the trap wet is the key, since the whole system depends on that plug of water.
Full text and source
The UPC floor-drain rules are part of the Uniform Plumbing Code, published and copyrighted by IAPMO. The excerpt above reflects the requirements as adopted; Phoenix enforces the 2024 UPC with local amendments, so verify the current sizing and trap-seal rules and section numbers. Read the floor-drain rules on UpCodes, or confirm local amendments through the City of Phoenix: phoenix.gov/pdd.
Keep Reading
- UPC 1003: Which Fixture Traps Are Allowed (and Banned)
- UPC Section 1101: Storm Drainage and Roof Runoff
- UPC Section 603: Cross-Connection Control and Backflow Protection
- UPC 705: Joints and Connections in Drainage Piping
- Why is my floor drain backing up?
- What's the difference between a floor sink, floor drain, and mop sink?