OR Plumber cheat sheet

Water column pressure: 1 psi = 2.31 ft of water head; conversely 1 ft of head = 0.433 psi.

Fixture unit (FU) is a measure of probable drainage load, not a volume; 1 FU ≈ 1 gpm of drainage flow for sizing purposes.

Minimum practical slope for horizontal drainage pipe is 1/4 in per ft (2%) for pipe 3 in and smaller; 1/8 in per ft is allowed for 4 in and larger where the code permits.

Flow rate formula: Q = A × V; for a full circular pipe, Q (gpm) ≈ 0.0408 × d² (in) × V (ft/s).

Thermal expansion of water is roughly 4% by volume over a 40°F to 140°F rise; closed systems need an expansion tank or relief provision.

Standard atmospheric pressure at sea level is 14.7 psi; a perfect vacuum gauge reads 29.92 in Hg.

Copper tube type K is heaviest wall (underground), L is standard above-ground, M is lightest and often limited to exposed interior work.

Water weighs 62.4 lb per cubic ft; a cubic ft contains 7.48 gallons.

Water closet flush volumes: 1.6 gpf standard since 1994; 1.28 gpf and 1.0 gpf high-efficiency models are common; Oregon follows the federal 1.6 gpf maximum.

Fixture trap seal depth is 2 in minimum and 4 in maximum; the trap weir must be below the fixture outlet.

Each fixture trap requires a vent unless it is a listed combination waste-and-vent or a code-recognized exception.

Air gap is the only backflow protection recognized for high-hazard, non-pressure connections; a 1 in minimum air gap is typical for most fixtures.

A lavatory drain is 1-1/4 in minimum; a water closet drain is 3 in; a bathtub drain is 1-1/2 in.

Floor drains require a trap primer or a trap seal protection device where the trap is subject to evaporation.

Shower valves must be pressure-balancing or thermostatic, with a maximum outlet temperature limit (typically 120°F) to prevent scalding.

Fixture clearances: water closet centerline at least 15 in from side walls and 21 in in front of the bowl.

Minimum static pressure at a fixture is typically 8 psi for flush tanks and 15 psi for flushometer valves; maximum 80 psi requires a pressure-reducing valve.

Developed length includes pipe run plus equivalent lengths for fittings; a 90° elbow is often counted as 5–10 equivalent ft depending on size.

Sizing uses the fixture-unit method with the Hunter curves; convert FU to gpm, then select pipe size for the allowable velocity and pressure loss.

Recommended maximum velocity is 8 ft/s in cold water and 5 ft/s in hot water to limit noise and erosion.

Backflow prevention: an RPZ assembly is required for high-hazard, cross-connection-prone services such as irrigation and boiler feed.

Hot water distribution should maintain 110°F at fixtures; recirculation or heat-traced lines reduce wait time and waste.

Water service line size is determined by the building supply demand in FU plus the meter and street pressure; a 1 in service is common for a single-family dwelling.

Thermal expansion control: install a closed-system expansion tank downstream of the pressure-reducing valve or backflow preventer.

Building drain is the lowest pipe receiving soil and waste inside the building; it extends to the building sewer, which begins 5 ft outside the foundation (Oregon terminology).

Vent stack sizing: a 1-1/2 in vent handles up to 8 FU; 2 in up to 24 FU; 3 in up to 48 FU (typical code table values - verify against the current Oregon table).

A wet vent may serve a limited number of fixtures on the same floor; the wet-vented branch must be sized per the code and connect to a dry vent above.

Horizontal drainage pipe must have cleanouts at intervals not exceeding 100 ft and at each change of direction greater than 45° in the building drain.

Trap arm length is limited to 5 ft for a 1-1/4 in trap arm and 6 ft for 1-1/2 in, with the vent connection at the trap weir.

A backwater valve is required where the building drain is below the level of the next upstream manhole or where the sewer can surcharge.

Vent terminal must extend at least 6 in above the roof and be at least 10 ft from an operable window or air intake.

Stack vent (also called a vent stack extension) is the continuation of a soil or waste stack above the highest fixture branch.

Oregon adopts the Oregon Plumbing Specialty Code (OPSC), based on the Uniform Plumbing Code (UPC), administered by the Oregon Building Codes Division (BCD).

Plumbing work in Oregon requires a licensed plumber; a plumbing contractor license is separate from the individual journeyman or master plumber license.

Permits are required for new plumbing, alterations, and replacement of water heaters, fixtures, and drain lines; minor repairs may be exempt per OPSC.

The Oregon BCD issues licenses and administers continuing education; journeyman plumbers must complete continuing education hours per renewal cycle.

Inspections are performed by local jurisdictions or the state; the plumber must request inspection before concealing work.

Oregon requires backflow assembly testers to be certified and assemblies to be tested annually where required.

Water heater installation in Oregon must include a temperature-and-pressure relief valve piped to within 6 in of the floor or to a safe discharge point.

Oregon seismic requirements include strapping water heaters with two straps, one in the upper third and one in the lower third, and anchoring the base.