DC Plumber cheat sheet

DC adopts the International Plumbing Code as the DC Plumbing Code; the DC Construction Codes Supplement contains local amendments that override the model text where they conflict.

Permits are required for new plumbing, alterations, replacements, and repairs except minor work such as stopping leaks, clearing stoppages, or replacing exposed fixture fittings.

A permit expires if work does not start within 180 days of issuance or if work is suspended or abandoned for 180 days; extensions must be requested in writing.

Inspections follow a sequence: rough-in (before concealment), underground, and final. Concealed work must be inspected before covering or the contractor must expose it for re-inspection.

Plumbing work in DC must be performed by a licensed master or journeyman plumber; a master plumber holds the license and a journeyman works under a master.

Appeals of code interpretations go to the DC Board of Appeals and Review; code officials may grant alternative materials or methods if equivalent in safety and performance.

The code sets minimum fixture clearances: 15 inches from a wall or partition to the centerline of a water closet, and 30 inches minimum width for the fixture space.

Local amendments commonly tighten requirements for backflow protection, lead-free materials, and water conservation beyond the model code minimums.

Water weighs 62.4 lb per cubic foot; one cubic foot equals 7.48 gallons, and one gallon weighs 8.34 lb.

Static pressure equals 0.433 psi per foot of elevation (2.31 feet of head per psi); pressure increases 0.433 psi for every foot of depth below the source.

A water column of 1 psi corresponds to 2.31 feet of height; a 10-foot column produces about 4.33 psi.

Flow rate through a pipe relates to velocity by Q = A × V; doubling diameter quadruples cross-sectional area and roughly quarters velocity at the same flow.

Drainage pipes flow by gravity at partial capacity; design slope is typically 1/4 inch per foot for pipes 2 1/2 inches and smaller and 1/8 inch per foot for 3 inches and larger.

A trap seal is 2 to 4 inches deep; the trap seal depth is measured from the trap weir to the top of the trap dip.

Vent stacks relieve pressure differences; a vent's job is to protect the trap seal by equalizing pressure on both sides of the trap.

Water hammer is controlled by arrestors or air chambers placed near quick-closing valves; thermal expansion in a closed system requires an expansion tank.

Potable water pipe must be lead-free: the wetted surface of pipe, fittings, and solder may not exceed a weighted average of 0.25 percent lead.

Solder for potable water is lead-free tin-antimony or tin-copper; 50/50 tin-lead solder is prohibited on potable systems.

PVC and CPVC are joined with solvent cement matched to the pipe; ABS uses ABS cement; never mix cement types across materials.

Copper tube is designated by type: K (thickest, underground), L (standard), M (thin wall, above ground, not for underground).

Cast iron soil pipe is joined with hub-and-spigot or no-hub couplings; no-hub couplings require a torque wrench set to the manufacturer's value.

PEX is joined by crimp, clamp, or expansion fittings; each fitting system must be used with its matching tool and manufacturer-approved components.

Water closets are rated in gallons per flush; DC follows the federal 1.6 gpf maximum for tank-type toilets, and urinals are limited to 1.0 gpf.

Fixtures must bear the certification mark of an approved testing agency such as ASME, CSA, or IAPMO.

Minimum residual pressure is 8 psi at a fixture outlet under flow, 15 psi at a sink faucet, and 20 psi at a flushometer valve.

Static pressure above 80 psi requires a pressure-reducing valve; the valve must be installed with a strainer and be accessible.

Sizing uses fixture units from tables; a 3/4-inch service typically serves a single-family dwelling while larger demands require calculated sizing.

Hot water distribution should keep the hot source close to fixtures; long runs require recirculation or a demand-initiated pump to limit wait time and waste.

A water service must be protected against backflow by an approved device, and a thermal expansion tank is required on a closed system with a backflow preventer or PRV.

Pipe support spacing depends on material: copper horizontal runs are supported about every 6 feet for 1-inch and smaller, plastic per manufacturer and code table.

Water supply lines must be protected from freezing; in DC, bury depth and insulation must account for the local frost line.

Shutoff valves are required on the fixture supply to each water heater, and a full-open valve on the cold inlet to the water heater.

Every fixture except a listed exception must have a trap; a trap must be liquid-sealed and protected from siphonage, backpressure, and evaporation.

A vent must rise vertically at least 6 inches above the fixture's flood-level rim before offsetting horizontally.

The developed length of a fixture trap arm is limited by pipe size: 42 inches for 1 1/2-inch, 60 inches for 2-inch, and 72 inches for 3-inch pipe.

A building drain is the lowest piping that receives soil and waste inside the building; it becomes the building sewer 30 inches outside the building wall.

Cleanouts are required at the base of each stack, at the building sewer, at changes of direction over 45 degrees, and every 100 feet of horizontal drain.

Vent terminals must extend at least 6 inches above the roof and be at least 10 feet from a window, door, or air intake, or 2 feet above it.

A wet vent may serve a lavatory and water closet in a bathroom group where allowed; the wet-vented pipe must be sized per the vent tables.

Horizontal drainage pipe changes from vertical to horizontal with a long-turn fitting or a combination wye and eighth-bend to keep flow smooth.

Water heaters require a temperature and pressure relief valve with a discharge pipe that terminates within 6 inches of the floor and does not connect to the drainage system.

A T&P relief valve is rated by Btu input and must match or exceed the heater's rating; the discharge pipe must be the same size as the valve outlet.

Gas-fired water heaters need a draft hood or draft control and a flue sized to the appliance; the vent connector must slope upward to the chimney.

Water heater drain pans are required where leakage would cause damage; the pan must have a drain to an approved location.

A water closet must be set level with a wax ring or approved gasket and secured with a closet flange; the flange must be anchored to the floor.

Fixture fittings such as faucets must be installed with access for repair; shower valves must have anti-scald protection limiting hot water temperature.

Temperature of hot water delivered to fixtures should be limited to 110°F at public lavatories and bathtubs to prevent scalding.

Floor drains require a trap primer where the trap could evaporate; primer connections must be protected against backflow.

Gas piping must be sized per the code's tables based on Btu input, length of run, and specific gravity of the gas; natural gas is about 0.60 specific gravity.

Gas pipe must be supported at intervals per code and protected from physical damage; exposed piping must be at least 6 inches above grade.

A shutoff valve is required within 6 feet of the appliance and must be accessible; a union or approved disconnect must be provided for removal.

Gas piping must be tested with air or inert gas at a pressure of at least 1 1/2 times the working pressure, but not less than 3 psi, for the required duration.

Combustion air must be provided to gas appliances; confined spaces require two openings sized per the code or a direct-vent arrangement.

A sediment trap must be installed downstream of the appliance shutoff valve, and the appliance connector must be listed and not concealed.

Gas-fired appliances must be vented to the outdoors; a vent connector must not be smaller than the appliance draft hood outlet.

Leak detection uses soap solution, never an open flame; a gas odorant is added to natural gas so leaks are detectable.

A cross-connection is any actual or potential connection between potable water and a source of contamination; it must be eliminated or protected by an approved backflow preventer.

An air gap is the best protection; it must be at least twice the diameter of the supply pipe and never less than 1 inch above the flood-level rim.

A reduced pressure zone (RPZ) assembly provides protection against both backsiphonage and backpressure and requires annual testing and certification.

A double check valve assembly protects against backpressure and backsiphonage for low-hazard connections, but not against contaminants that are toxic.

A pressure vacuum breaker protects against backsiphonage only and must be installed at least 12 inches above the highest downstream outlet.

A hose bibb vacuum breaker is required on sill cocks where a hose can be attached; it protects against backsiphonage at the fixture.

Backflow preventers must be tested at installation and annually by a certified tester; test reports are submitted to the water authority.

Irrigation systems, boilers, and chemical injection systems require an approved backflow assembly matched to the hazard level.

Before trenching, call 811 for utility locates; trenches 5 feet or deeper require protective systems such as shoring, sloping, or a trench box.

Confined spaces require atmospheric testing and a permit before entry; gas-fired equipment must never be operated in an unvented enclosed space.

Soldering requires fire watch and a fire extinguisher; remove combustibles and use a heat shield when working near framing.

Personal protective equipment for plumbing includes safety glasses, gloves, hearing protection, and a respirator when cutting cast iron or working with solvent cement.

Solvent cement and primers are flammable and must be used with ventilation; store in a closed container away from ignition sources.

Hand tools include a pipe wrench, tubing cutter, and flaring tool; a pipe wrench is directional and must be pulled toward the user for control.

Lockout/tagout applies when servicing equipment with energy sources; isolate and tag before repair of pumps or water heaters.

Job-site housekeeping prevents slips and falls; keep walkways clear and secure ladders at a 4:1 ratio of height to base distance.