10.3 Key UPC Definitions and Referenced Standards (UPC Chapters 2 and 17; WA Definition Amendments)
Key Takeaways
The UPC defines a trap arm as the portion of a fixture drain between the trap and the vent, and the trap seal as the vertical distance between the crown weir and the top dip of the trap.
Developed length is measured along the centerline of the pipe and fittings (UPC Chapter 2).
A stack vent is the extension of a soil or waste stack above its highest horizontal drain; a vent stack is a separate vertical vent that circulates air to and from the drainage system.
Washington defines hot water as water at 100°F or more and includes water heaters and medical gas systems within the property lines in the plumbing system definition (WA 210.0, 218.0).
Standards in UPC Table 1701.1 are mandatory where required by code sections; for example ASSE 1013 covers RP assemblies and ASSE 1016 covers shower and tub-shower valves.
Why Definitions Matter
Code language is precise. "Building drain" and "building sewer" are different pipes. That difference matters in Washington, where building sewer rules are deleted (Section 6.4). Likewise, a "vent stack" and a "stack vent" are different pipes. Many Part 1 questions are answered by knowing the definition.
Drainage and Vent Definitions (UPC Chapter 2)
| Term | Definition in brief |
|---|---|
| Building drain | The lowest drainage piping inside the building walls, carrying discharge to the building sewer, which begins 2 feet outside the wall |
| Building sewer | Horizontal piping from the end of the building drain to a public or private sewer or other point of disposal |
| Drainage system | All piping within public or private premises conveying sewage, storm water, or liquid wastes to a legal point of disposal; not the public sewer or treatment plant |
| Fixture drain | The drain from a fixture's trap to its junction with any other drain |
| Trap arm | The portion of a fixture drain between the trap and the vent |
| Trap | A fitting or device that provides a liquid seal against the back passage of air, without materially affecting flow |
| Trap seal | The vertical distance between the crown weir and the top dip of the trap |
| Crown weir (trap weir) | The lowest point in the cross-section of the horizontal waterway at the exit of the trap |
| Horizontal branch | A drain extending laterally from a stack or building drain, receiving one or more fixture drains |
| Stack | The vertical main of soil, waste, or vent piping extending through one or more stories |
| Soil pipe | Conveys water closet, urinal, clinical sink, or similar discharge |
| Waste pipe | Conveys only liquid waste, free of fecal matter |
| Branch interval | A length of stack corresponding generally to a story height, but not less than 8 feet, within which one floor's branches connect |
| Developed length | Length measured along the centerline of pipe and fittings |
| Grade | The slope or fall of a pipe, usually expressed as a fraction of an inch or a percentage per foot |
| Offset | A combination of elbows or bends that moves one pipe section out of line but parallel to the other |
| Stack vent | The extension of a soil or waste stack above the highest horizontal drain connected to it |
| Vent stack | A vertical vent pipe installed primarily to circulate air to and from any part of the drainage system |
| Continuous vent | A vertical vent that continues the drain it connects to |
| Individual vent | Vents one fixture trap, connecting above the fixture or terminating outdoors |
| Relief vent | Mainly provides air circulation between drainage and vent systems, or acts as an auxiliary vent |
| Yoke vent | Connects upward from a soil or waste stack to a vent stack to prevent pressure changes in the stacks |
| Wet vent | A vent that also serves as a drain |
| Dry vent | A vent that carries no sewage or waste |
| Combination waste and vent system | Waste piping that horizontally wet vents sinks or floor drains through an oversized common waste and vent pipe |
Water and Backflow Definitions
| Term | Definition in brief |
|---|---|
| Building supply | Pipe carrying potable water from the meter or source to the building or point of use on the lot |
| Fixture branch | Water pipe between the fixture supply pipe and the water distribution pipe |
| Fixture supply | Water pipe connecting the fixture with the fixture branch |
| Air gap, water distribution | Unobstructed vertical distance through free atmosphere from the lowest potable outlet to the flood-level rim |
| Air gap, drainage | Same concept for a pipe or fixture conveying waste, measured to the receptor's flood-level rim |
| Air break | A physical separation, which may be a low inlet into the indirect waste receptor |
| Flood-level rim | The top edge of a receptor from which water overflows |
| Critical level | The marked point on a backflow device that sets its minimum height above the flood-level rim. With no marking, the bottom of the device |
| Roof washer | A device diverting initial rainfall away from a cistern, also called a first-flush device |
Washington Definition Amendments (WAC 51-56-0200)
- 205.0 Certified backflow assembly tester: certified by the Department of Health under chapter 246-292 WAC to inspect, test, maintain, and repair assemblies, devices, and air gaps (maintenance and repair in compliance with chapter 18.106 RCW).
- 210.0 Hot water: water at 100°F or more. The unamended UPC uses 120°F.
- 211.0 Insanitary (2015 amendment): includes a trap that does not keep its seal, an opening without a trap, a fixture without enough water to stay clean, a defective fixture or pipe, an unvented trap, and any cross-connection that could let foreign matter into domestic water.
- 218.0 Plumbing system: includes potable water, building supply and distribution pipes, alternate and rainwater systems, fixtures and traps, drainage and vent piping, and building drains within the property lines, plus potable water treating equipment, medical gas and medical vacuum systems, and water heaters. No certification is required for installing a plumbing system within the property lines and outside a building.
- 225.0 Water/wastewater utility: a public or private entity, including a water purveyor as defined in chapter 246-290 WAC, that treats or delivers reclaimed or potable water.
Referenced Standards (UPC Chapter 17)
Section 1701.1: the standards in Table 1701.1 are for design, testing, and installation of materials and devices, and are mandatory where required by code sections. Standard numbers you should recognize:
| Standard | Subject |
|---|---|
| ASSE 1001 | Atmospheric vacuum breakers |
| ASSE 1002 | Antisiphon fill valves (ballcocks) |
| ASSE 1010 | Water hammer arresters (also PDI-WH 201) |
| ASSE 1011 | Hose connection vacuum breakers |
| ASSE 1013 | Reduced pressure principle assemblies |
| ASSE 1015 | Double check valve assemblies |
| ASSE 1016 | Shower and tub-shower control valves |
| ASSE 1018 and 1044 | Trap seal primers |
| ASSE 1020 and 1056 | Pressure and spill-resistant vacuum breakers |
| ASSE 1037 | Flushometers |
| ASSE 1047 and 1048 | RP and DC detector fire assemblies |
| ASSE 1060 | Outdoor enclosures for backflow assemblies |
| ASSE 1061 | Push-fit fittings |
| ASSE 1069 | Gang shower mixing valves |
| ASSE 1070 | Temperature-limiting devices |
| ASSE 1079 | Dielectric unions |
| ASME A112.1.2 | Air gaps |
| ASME A112.18.1 / CSA B125.1 | Faucets and fixture fittings |
| ASME A112.19.2 / CSA B45.1 | Ceramic fixtures |
| ASTM B88 | Copper water tube |
| ASTM B813 and B828 | Soldering flux and soldering practice |
| ASTM C564 | Gaskets for cast-iron soil pipe |
| CISPI 301 and 310 | Hubless cast-iron pipe and couplings |
| NSF 14 | Plastic piping components |
| NSF 61 | Drinking water system components |
| NSF 350 | On-site treated nonpotable water systems |
What is the portion of a fixture drain between the trap and the vent called in the UPC?
Continuous waste
Horizontal branch
Fixture branch
Trap arm
What is the difference between a stack vent and a vent stack?
A stack vent is horizontal and a vent stack is vertical
A vent stack may carry waste; a stack vent may not
They are two names for the same pipe
A stack vent is the extension of a soil or waste stack above its highest horizontal drain; a vent stack is a separate vertical vent pipe that provides air circulation to and from the drainage system
Under Washington's amendment to UPC definition 218.0, installing plumbing that is within the property lines but outside a building requires what certification?
No certification is required
A residential service certificate
A backflow specialty certificate
A journey level certificate
Sections you finish are checked off in the contents.