Plumbing: The Rules the Exam Asks For

The building drain is the lowest piping of a drainage system. It receives the discharge from the soil, waste, and other drainage pipes inside the building's walls and carries it to the building sewer, which begins 2 feet outside the building wall.

Plumbing Code § 204.0

A stack is the vertical main of soil, waste, or vent piping that runs through one or more stories. A stack vent is the extension of a soil or waste stack above the highest horizontal drain connected to that stack.

Plumbing Code § 221.0

Every fixture trap has a protecting vent. The trap arm's developed length, from the trap weir to the inner edge of the vent, may not exceed Table 1002.2 for its pipe size, and may never be less than two pipe diameters. The maximums are 30 inches for 1-1/4-inch pipe, 42 for 1-1/2, 60 for 2, 72 for 3, and 120 for 4 inches and larger. Trap arms keep a 1/4-inch-per-foot slope. A water closet's trap-to-vent length, from the face of the flange, may not exceed 6 feet. Horizontally wet-vented tubs and showers are limited to 6 feet for 1-1/2-inch drains and 8 feet for 2-inch drains.

Plumbing Code § 1002.2

A trap seal is the vertical distance between the crown weir and the top dip of the trap. The crown weir is the lowest point of the horizontal waterway where it leaves the trap; the top dip is the highest point of the trap's inside bend at the bottom. The water held between them is what blocks sewer gas.

Plumbing Code § 222.0

Each fixture trap holds a liquid seal of at least 2 inches and not more than 4 inches, unless the Authority Having Jurisdiction finds a deeper seal necessary. Traps are set true to their liquid seals and protected from freezing where necessary.

Plumbing Code § 1005.1

A shower compartment's finished interior must be at least 1,024 square inches and able to hold a 30-inch circle. The size is measured at the top of the threshold and held to 70 inches above the drain outlet, with only valves, showerheads, soap dishes, shelves, and grab bars allowed to protrude. Fold-down seats in accessible showers may enter the circle. Two exceptions: showers built to Chapter 11A of the Building Code, and receptors at least 30 inches wide and 60 inches long.

Plumbing Code § 408.7

A shower receptor is tested for watertightness by filling it with water at least 2 inches deep for at least 15 minutes. Where there is no threshold, a temporary 2-inch barrier is built for the test. The test plug is placed so that both the upper and under sides of the subpan take the test where it clamps to the drain.

Plumbing Code § 408.8.5

PVC solvent-cement joints start clean and dry: cut the pipe square, deburr it, and clean both surfaces of dirt, moisture, oil, and foreign material. Apply purple primer complying with ASTM F656 to the pipe and fitting surfaces until they soften. Apply solvent cement complying with ASTM D2564 to all joint surfaces, and make the joint while both the socket and the pipe are still wet with cement. Hold the joint in place, undisturbed, for 1 minute after assembly. Under the HCD provisions, primer and cement are low-VOC products.

Plumbing Code § 705.6.2

Up to eight floor-outlet water closets, showers, bathtubs, or floor drains on one horizontal branch may be circuit vented. Each trap arm connects horizontally to the branch, within the trap-arm table's limits. From the most downstream trap arm to the most upstream one, the branch counts as both a drain and a vent. Back-outlet and wall-hung water closets may be circuit vented only where no floor-outlet fixture shares the branch.

Plumbing Code § 911.1

A circuit vent is sized from Table 703.2 by the number of circuit-vented fixtures on the branch, but is never smaller than 2 inches. It connects to the horizontal branch on the vertical, between the two most upstream trap arms, and it may not receive any soil or waste. Where several circuit vents are interconnected, each is sized on its own and the pipe joining them is sized from Table 703.2.

Plumbing Code § 911.2

Where a system includes a chemical injector, or provisions for chemical injection, the potable water supply is protected by a reduced-pressure principle backflow prevention assembly, an RP.

Plumbing Code § 603.5.6.3

The discharge pipe from a temperature or pressure relief valve has no valves, obstructions, or means of isolation. It is at least the size of the valve outlet and discharges full size, pointing down, to the flood level of the area receiving it. Its material is rated for the system's operating temperature or complies with ASME A112.4.1. It discharges by gravity through an air gap into the drainage system, or outside the building with the end between 6 inches and 2 feet above the ground, pointing down. It may not cause injury or structural damage, may not be trapped or subject to freezing, may not have a threaded end, may not discharge into the water heater pan, and must end where it is readily observable.

Plumbing Code § 608.5

When a section or the whole hot and cold water supply is complete, it is tested with water or air. A water test is at or above the working pressure; an air test is at least 50 psi. Plastic pipe is not tested with air, except PEX, PP, or PE-RT tube where the manufacturer's instructions permit it. The system must hold the test pressure with no evidence of leakage for at least 15 minutes.

Plumbing Code § 609.4

New or repaired potable water piping is disinfected before use where the Authority Having Jurisdiction requires it. Unless the health authority prescribes a method, the code's is: flush with clean potable water until it appears at the outlets; fill with a chlorine solution of at least 50 parts per million and let it stand 24 hours, or at least 200 parts per million for 3 hours; then flush until the chlorine residual matches the flushing water. The procedure is repeated where a bacteriological examination shows contamination.

Plumbing Code § 609.10

Water heaters are anchored or strapped to resist horizontal displacement in an earthquake. Strapping goes at points within the upper third and the lower third of the heater's height. At the lower point, the strap stays at least 4 inches above the controls. Health and Safety Code Section 19211(a) applies the duty to all new and replacement water heaters, and to all existing residential water heaters.

Plumbing Code § 507.2

Plumbing, drainage, and venting piping is tested with water or air, except that plastic pipe is not tested with air. The Authority Having Jurisdiction may require cleanouts and similar fittings removed to confirm the pressure reached every part of the system. After the fixtures are set and their traps filled with water, the system is submitted to a final test.

Plumbing Code § 712.1

The water test covers the drainage and vent system as a whole or in sections. For the whole system, every opening but the highest is closed tight and the system is filled to overflow. In sections, every opening but the section's highest is plugged and the section is filled, and no section is tested with less than a 10-foot head of water. Each successive section includes at least the upper 10 feet of the section before it, so every joint except the top 10 feet of the system sees a 10-foot head. The water stays in for at least 15 minutes before inspection starts, and the system must be tight at all points.

Plumbing Code § 712.2

Water pressure changes 0.433 psi for every foot of elevation. The pressure lost lifting water to a fixture is 0.433 times the height in feet, and the pressure at the fixture is the supply pressure minus that loss, before friction. Example: a fixture 30 feet above the meter loses 30 × 0.433 = 12.99, about 13 psi.

Standard trade practice

A drain's invert is the inside bottom of the pipe. Slope gives the FALL, not the depth: fall in inches equals the slope in inches per foot times the run in feet. Only where the ground is level along the run does the far end's depth below grade equal the starting depth plus the fall. Example on level ground: a drain 18 inches down at 1/4 inch per foot over 80 feet falls 0.25 × 80 = 20 inches, to 38 inches down.

Standard trade practice