Uniform Plumbing Code Explained
What each Uniform Plumbing Code section says and what it means for real work. Not every Valley city uses the UPC (some adopt the IPC), so check your city's hub for the code it enforces. Short excerpts only; the full text is IAPMO's.
Water Heaters
Water Heaters in every city- Model CodeUpdated Jul 2026UPC 506: Combustion Air for Gas Water HeatersUPC Section 506 sets how much fresh air a gas water heater's burner gets and where that air comes from. A small closet is a confined space and needs sized free-air openings, high and low, to outside or an adjacent room so the burner does not starve, soot, or backdraft.
- Model CodeUpdated Jul 2026UPC 510: Venting Gas Water Heaters (Category I Flues)UPC Section 510 sets how a natural-draft gas water heater's flue and vent are sized so the exhaust leaves the building instead of spilling back inside. Nearby sections control the draft hood, the vent connector, and how the heater shares a vent with another appliance.
- Model CodeUpdated Oct 2026UPC Section 507: Water Heater Installation RequirementsUPC Section 507 sets the general installation rules for a water heater: it must be accessible for service, anchored against movement, and placed where a code official allows it. These rules sit alongside the separate requirements for relief-valve discharge, clearances, and drain pans that also govern a safe install.
- Model CodeUpdated Jul 2026UPC Section 608: Water Heater Relief Valve and Discharge Pipe RulesUPC Section 608 requires every water heater to have a temperature and pressure relief valve and a discharge pipe that carries released hot water to a safe place. The pipe must run downhill, stay full size, carry no valve or cap, and end near the floor so nobody is scalded.
- Model CodeUpdated Jul 2026UPC Water Heater Drain Pan: When One Is Required and How It DrainsPlumbing code requires a drain pan under a water heater where a leak or tank failure could damage the building, such as an attic, an upper floor, or over finished space. The pan catches leaking water and a pan drain carries it to a safe spot, so a slow leak does not flood the area below.
Gas Lines
Gas Lines in every city- Model CodeUpdated Oct 2026UPC 1208: Approved Fuel Gas Piping MaterialsUPC Section 1208 lists which materials are approved for fuel gas piping and how they may be joined. Steel and iron, copper where the gas allows, corrugated stainless steel tubing (CSST), aluminum alloy, and polyethylene (PE) for buried service each have their own limits and joining methods.
- Model CodeUpdated Jul 2026UPC 1210: Installing Fuel Gas PipingUPC Section 1210 sets how fuel gas piping is physically installed. It covers underground and concealed pipe, corrosion and impact protection, pipe turns, sediment traps, prohibited locations, and where each manual shutoff valve must sit.
- Model CodeUpdated Jul 2026UPC 1211-1212: Gas Appliance Connections and Shutoff ValvesUPC Sections 1211 and 1212 set how a gas appliance is joined to the house gas line. Each appliance needs an accessible manual shutoff valve close to it, an approved connector, and a sediment trap that keeps dirt out of the burner.
- Model CodeUpdated Jul 2026UPC 1213: Testing and Inspection of Fuel Gas PipingUPC Section 1213 makes new fuel gas piping prove it is leak-free before any gas flows. The plumber pressure-tests the line with air or another non-flammable gas, an inspector checks it, and the line is purged before appliances are connected.
- Model CodeUpdated Jul 2026UPC 1215: Sizing Fuel Gas PipingUPC Section 1215 sets how a plumber sizes fuel gas piping. The pipe has to be big enough to feed every appliance at the same time. The size is based on the total appliance demand in BTU per hour, the length of the run, and the type of gas.
Backflow Prevention
Backflow Prevention in every cityWater Supply and Pipes
Water Supply and Pipes in every city- Model CodeUpdated Jul 2026UPC 606: Where Shutoff Valves Are RequiredUPC Section 606 sets where the water supply system needs valves. The main building supply needs a full-way valve so the whole structure can be shut off in one place. Each dwelling unit in a multi-unit building gets its own control valve. The section also covers valves for groups of fixtures, where a check valve is required, and a draindown valve.
- Model CodeUpdated Oct 2026UPC 609: Water Piping Installation and TestingUPC Section 609 covers potable water piping installation, support, protection and testing before concealment. The adopted code and pipe manufacturer determine the permitted test method; compressed-air testing is not a universal alternative. Never use compressed air or gas to test PVC pipe or fittings.
- Model CodeUpdated Oct 2026UPC Section 313: How Often a Pipe Must Be SupportedUPC 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.
- Model CodeUpdated Jul 2026UPC Section 604: Approved Materials for Water PipeUPC Section 604 lists which pipe materials are approved for a building's water service line and interior water distribution. Only listed materials rated for potable water and pressure may be used, such as copper, PEX, CPVC, and approved plastics, each installed by the rules for that material.
- Model CodeUpdated Oct 2026UPC Section 720: The Required Gap Between Water and Sewer LinesUPC Section 720 requires a water service line to stay at least 10 feet horizontally from a building sewer or septic line. When that gap is not possible, the water line must sit on a solid shelf at least 12 inches above the sewer, so a sewer leak cannot reach the drinking water.
- Model CodeUpdated Jul 2026UPC Water Supply Pipe Sizing: How Code Sizes Your Water LinesThe Uniform Plumbing Code sizes water supply pipe so every fixture gets enough flow and pressure at once. It counts each fixture's demand in water supply fixture units, adds them up for a line, and factors in pipe length and available pressure to set the minimum pipe diameter.
Drains, Traps and Vents
Drains, Traps and Vents in every city- Model CodeUpdated Jul 2026UPC 1003: Which Fixture Traps Are Allowed (and Banned)UPC Section 1003 describes which fixture traps are approved and which are banned. The standard P-trap is allowed. S-traps, bell traps, drum traps, and traps with moving or hidden parts are prohibited. Each fixture gets one approved trap, and double-trapping is not allowed.
- Model CodeUpdated Jul 2026UPC 705: Joints and Connections in Drainage PipingUPC Section 705 sets the approved ways to join drain, waste, and vent piping for each material. That includes solvent-welded ABS and PVC, no-hub cast iron, and soldered copper. It also bans joints that are prone to leak.
- Model CodeUpdated Jul 2026UPC 706: Changes of Direction in Drainage PipingUPC Section 706 controls how a drain line turns corners. Every change of direction has to use an approved fitting with the right sweep. Tight fittings are only allowed where a horizontal line drops into a vertical stack. Turns that stay horizontal or flatten out at the base of a stack need gentle long-sweep fittings so waste keeps moving and does not clog.
- Model CodeUpdated Oct 2026UPC 712: Testing Drain, Waste and Vent PipingNew drain, waste and vent piping must pass the applicable leak test before it is covered. Test method, pressure or water head, duration and inspection requirements depend on the adopted code, local amendments and manufacturer instructions. Charlotte Pipe prohibits compressed-air or gas testing of ABS, CPVC and PVC pipe and fittings.
- Model CodeUpdated Jul 2026UPC 905: How Vent Pipes Must Be Graded and ConnectedUPC Section 905 sets how a vent pipe must slope and where it may tie back in. A vent has to grade back toward the drain so no water pools inside it, and it must reconnect above the flood level of the fixture so waste can never rise into a dry vent.
- Model CodeUpdated Jul 2026UPC 907: Vent Stacks and Relief VentsUPC 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.
- Model CodeUpdated Jul 2026UPC 908: Wet Venting a Bathroom GroupUPC Section 908 allows wet venting, a method where one drain pipe also vents the other fixtures in a bathroom group. The drain doubles as the vent for the upstream fixtures, so the group needs far less vent pipe.
- Model CodeUpdated Jul 2026UPC 909: Island Fixture (Loop) VentingUPC Section 909.0 covers special venting for island fixtures like a kitchen island sink that has no wall behind it. The vent rises to drainboard height, loops over, and drops to a foot vent below the floor. A cleanout must be provided so the loop can be rodded clear.
- Model CodeUpdated Jul 2026UPC 910: Combination Waste and Vent SystemsUPC Section 910 lets one oversized horizontal drain carry both the waste and the air for certain fixtures. It is used where a normal vent is hard to run, like a floor drain in the middle of a room or an island sink. The drain is sized larger than usual so air moves freely above the flowing water and vents the fixtures.
- Model CodeUpdated Jul 2026UPC Floor Drain Requirements: Traps, Size, and Keeping the SealThe 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.
- Model CodeUpdated Jul 2026UPC Section 1101: Storm Drainage and Roof RunoffUPC Section 1101 governs how rainwater is carried off roofs and paved areas. It requires storm drainage to be kept fully separate from the sanitary sewer, and it sizes roof drains, gutters, and leaders based on the roof area and local rainfall so heavy rain drains without flooding.
- Model CodeUpdated Oct 2026UPC Section 707: Where Drain Cleanouts Are RequiredUPC Section 707 requires access points, called cleanouts, on a building's drain system so a plumber can clear a clog. Code calls for cleanouts near where the drain leaves the house, at each long horizontal run, and at sharp changes of direction, sized to match the pipe.
- Model CodeUpdated Oct 2026UPC Section 708: How Much Slope a Drain Pipe NeedsUPC 708.1 starts at 1/4 inch per foot for building drains and other horizontal drainage piping. Building drains 4 inches and larger may use 1/8 inch per foot where the baseline is impractical because of sewer depth, structural features or building arrangement, with prior approval from the authority having jurisdiction.
- Model CodeUpdated Jul 2026UPC Section 710: When Phoenix Code Requires a Backwater ValveUPC Section 710 requires a backwater valve on any drain line serving a fixture whose flood-level rim sits below the elevation of the next upstream public-sewer manhole cover. That valve blocks sewage from backing into the building when the main surcharges. Fixtures above that line must never drain through the valve.
- Model CodeUpdated Jul 2026UPC Section 807: Indirect Waste and the Air BreakUPC Section 807 requires certain equipment, like a dishwasher, ice maker, or food-prep sink, to drain indirectly rather than being hard-piped to the sewer. The waste line ends above a receptor with an air gap or air break, so sewer water can never back up into food or clean equipment.
- Model CodeUpdated Jul 2026UPC Section 906: Where a Plumbing Vent Can TerminateUPC Section 906 controls where a plumbing vent pipe can end so sewer gas leaves safely and cannot re-enter the building. A vent through the roof must rise a set height above the roof and stay a set distance from any door, window, or air intake.
- Model CodeUpdated Jul 2026UPC Table 1002.2: Maximum Trap Arm Length by Pipe SizeUPC Table 1002.2 caps how far a fixture's trap can sit from its vent, so the vent can break suction before it siphons the trap seal dry. The limit rises with pipe size: 30 inches for 1-1/4 inch pipe up to 10 feet for 4 inch pipe. Self-siphoning fixtures like toilets are exempt.
Fixtures
Fixtures in every city- Model CodeUpdated Oct 2026UPC 804.1: Clothes Washer Standpipe and Drain RequirementsUPC 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.
- Model CodeUpdated Jul 2026UPC Section 408: The Minimum Shower Size Phoenix Code RequiresUPC Section 408 requires a shower compartment to have at least 1,024 square inches of finished interior floor area and enough room to fit a 30-inch circle. That size must hold up to 70 inches above the drain. Phoenix enforces this figure under the 2024 UPC.
Commercial Plumbing
Commercial Plumbing in every city- Model CodeUpdated Jul 2026UPC 1007: Trap Seal Protection for Floor DrainsUPC Section 1007 covers trap seal protection for floor drains. A seldom-used floor drain can dry out as its trap water evaporates, which lets sewer gas into the building. The fix is an automatic trap seal primer that adds water to the trap, or a barrier-type device. These must meet ASSE 1018, ASSE 1044, or ASSE 1072.
- Model CodeUpdated Oct 2026UPC 422: How Many Plumbing Fixtures a Building Must HaveUPC Section 422 and Table 422.1 set the fewest plumbing fixtures a commercial building must have. The count runs off the occupant load and the occupancy group, so a busy restaurant needs more toilets, sinks, and drinking fountains per person than a quiet office. Separate facilities for each sex are generally required above a set occupant load.
- Model CodeUpdated Jul 2026UPC 803: Indirect Waste PipingUPC Section 803 covers indirect waste piping, the drain line that empties over an open receptor through an air gap or air break. Ice machines, coolers, food-prep sinks, and similar equipment must discharge this way, never straight to the sewer. The code also limits how long the pipe may run.
- Model CodeUpdated Jul 2026UPC Grease Interceptor Sizing: How Code Sizes a Grease TrapPlumbing code sizes a grease interceptor from the fixtures that drain into it, so it is large enough to trap fats, oils, and grease before they reach the sewer. Sizing uses the drainage load and flow of the connected sinks and equipment, with a minimum size for gravity interceptors serving a commercial kitchen.
Water Treatment
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