ICC P3 key terms

The official or agency responsible for enforcing the plumbing code, including reviewing plans, issuing permits, inspecting work, and approving materials and methods. The AHJ interprets code requirements and grants approval where compliance is demonstrated.

A written authorization issued by the AHJ before plumbing work starts. It defines the scope of work, triggers the required inspections, and allows installed work to be tracked and checked for code compliance.

Drawings, specifications, and calculations submitted to the AHJ that describe the proposed plumbing system, including fixture layout, pipe sizes, riser diagrams, and equipment data, so the design can be reviewed before construction begins.

Equipment or materials included in a list published by an approved testing agency that performs periodic inspection of production, and bearing that agency's mark. Listing is evidence that the item complies with a recognized standard.

An inspection performed after piping is installed but before it is covered, concealed, or backfilled. The inspector verifies pipe size, slope, support, joints, venting, and required tests before concealment is allowed.

A unit expressing the probable drainage load of a fixture based on its discharge rate and duration. One fixture unit represents roughly 1 cubic foot per minute (about 7.5 gallons per minute) of flow; fixture units are used to size drains and vents.

An unobstructed vertical distance through free atmosphere between a water outlet and the flood level rim of the receptor it discharges into. It is the most reliable backflow protection; the gap must be at least twice the effective opening and never less than 1 inch.

An assembly or device that prevents reversal of water flow that could contaminate the potable supply. Types include air gaps, vacuum breakers, double check valves, and reduced-pressure principle assemblies, chosen according to the degree of hazard.

A backflow preventer with an air inlet that opens when internal pressure drops to atmosphere, breaking a siphon. It must be installed on the discharge side of the last control valve and at least 6 inches above the highest outlet served.

The column of water retained in the dip of a P-trap that blocks sewer gas from entering the building. Seal depth must be at least 2 inches and not more than 4 inches, and is preserved by proper venting and trap primers.

The edge of a receptacle from which water overflows, such as the top of a fixture or the rim of a floor drain receptor. It is the reference elevation for setting air gaps and vacuum breaker heights and for judging fixture flooding.

A self-closing device on a water heater that opens at a set temperature and pressure to prevent tank rupture. It is typically rated at 210 degrees F and 150 psi, or the tank's working pressure if lower.

A tank containing a compressed air charge that absorbs the volume increase of water as it is heated in a closed system, preventing excessive pressure buildup and repeated relief valve discharge.

A corrosion-resistant pan placed beneath a water heater installed where leakage would cause damage. It must be at least 1.5 inches deep, have a drain outlet, and drain by gravity to an approved location.

An appliance that heats potable water and supplies it to the plumbing system. It may be storage type, instantaneous type, or a combination, and must be listed, installed per the manufacturer's instructions, and protected against over-temperature and over-pressure.

The pipe that carries discharge from a water heater relief valve to a safe place. It must be full size, drain by gravity, contain no traps or valves, and terminate with an air gap where discharge can be seen.

The pipe that carries water from the public main or other source to the building, ending where it enters the building or at the meter. It is sized from fixture units and available pressure, and is typically at least 3/4 inch for a one-family dwelling.

A device installed in a water line to lower incoming pressure to a usable level, typically required where street pressure exceeds 80 psi. It protects fixtures and appliances and creates a closed system requiring thermal expansion relief.

A device with a trapped air chamber or piston that absorbs the shock wave produced when a valve closes quickly, preventing banging noise and pipe damage. It is installed near quick-closing valves and appliances.

Piping inside a building that carries potable water from the service or source to fixtures and equipment. It is sized by fixture units and developed length so that minimum residual pressure is maintained at each outlet.

The total length of pipe measured along its centerline, including all offsets, bends, and fittings. It is used with fixture unit tables to size water piping and to estimate friction loss and pressure drop.

A measure of the probable demand a fixture places on the water supply system, reflecting its flow rate and how often it is used. Code table values are summed to size the service, mains, and branches.

The portion of a fixture drain between the trap weir and the vent connection. Its length and fall are limited so the trap is not siphoned; the fall of the trap arm may not exceed one pipe diameter.

The lowest horizontal piping of a drainage system, receiving soil and waste from inside the building. It extends from the building to a point 30 inches outside the wall, where it becomes the building sewer.

The pipe that carries sewage from the building drain to the public sewer or private disposal system, beginning 30 inches outside the building wall. It is uniformly sloped and provided with cleanouts at required locations.

An accessible fitting with a removable plug that allows a drain to be rodded or cleared of blockages. Cleanouts are required at the end of horizontal drains, at changes in direction, on long runs, and near the building sewer.

The downward pitch of horizontal drainage pipe, expressed in inches per foot, that moves solids and liquid by gravity. Typical values are 1/4 inch per foot for small pipe and 1/8 inch per foot for larger sizes.

A plumbing appurtenance that separates and retains fats, oils, and grease from kitchen waste before effluent enters the drainage system. It must be sized to the fixture load, accessible for cleaning, and periodically pumped.

A device installed on a drainage line to stop sewage from backing up into a building from a public sewer or other lower source. It is required where fixtures are subject to backflow and is installed per the manufacturer's instructions.

A vertical vent pipe installed mainly to provide air circulation and relieve pressure in a drainage stack. It connects the drainage stack to outdoor air or to the stack vent through the arrangement shown in the code.

The extension of a soil or waste stack above the highest horizontal drain connected to it, terminating in open air. It vents the stack itself and protects the trap seals of fixtures discharging into it.

A pipe that serves at the same time as a drain for one or more fixtures and as a vent for other fixtures. It must be sized and arranged so that waste flow does not choke off the vent path, within code limits.

A one-way valve that admits air into the drainage system to equalize pressure and protect trap seals but does not allow sewer gas to escape. It must be listed, remain accessible, and be installed above the fixture flood level rim.

A fitting installed in a roof that collects rainwater and directs it into a leader. Roof drains must be sized for the design rainfall, fitted with strainers, and connected to the primary or secondary roof drainage system.

A backup system that carries rainwater off a roof when primary drains are blocked or overloaded. It may consist of additional roof drains, scuppers, or overflow openings set above the low point of the primary drains.

A pipe or tube that carries rainwater from a roof drain or gutter to the storm drainage system. Leaders are sized for the rainfall load and must discharge to an approved location such as grade, a storm drain, or a dry well.

Piping, tubing, and fittings that convey fuel gas from the point of delivery to gas utilization equipment. It must be sized for the connected load, supported, protected from damage, and pressure tested for leaks before being placed in service.

A drip leg of pipe installed downstream of the gas shutoff valve and as close as practical to the appliance inlet, where dirt, scale, and moisture collect so they do not reach the burner controls.

A device that reduces and holds gas pressure delivered to appliances at a steady level. Vented regulators must vent to a safe outdoor location where required, and appliance regulators are set to the manufacturer's manifold pressure.

Air supplied to a fuel-burning appliance for burning fuel and for dilution. It may come from indoor volume at 50 cubic feet per 1,000 Btu/hr of total input in the space, or from outdoors through sized openings.

Wastewater from bathtubs, showers, lavatories, and laundry that excludes toilet and kitchen waste. It may be collected, treated, and reused for flushing or irrigation where permitted by the code and the local authority.