In the Field · Part 4
Daily-use code: drainage slope, venting, water sizing, cleanouts, trap arms, and fixture units, with the section for each
The exam taught the code chapter by chapter. The field uses about a dozen numbers from it every day, and an inspector checks the same dozen on every rough. This lesson is those numbers, in the order a plumber meets them on a job, each with the 2025 California Plumbing Code section that governs it: how much a drain has to fall, where cleanouts go, how long a trap arm can be, how big a drain and a vent must be for the fixtures on them, where the vent can come out of the roof, and how to size supply piping by fixture units. It is written to be read once and then kept on the phone.
What the full lesson covers
- Drainage falls 1/4 inch per foot (2 percent); 1/8 inch per foot is allowed only for 4-inch and larger building drains and only when the inspector approves it first (CPC 708.1).
- Cleanouts: at the upper end of every horizontal drain, every 100 feet, and wherever the aggregate change of direction exceeds 135 degrees; watertight and gastight (707.3, 707.4).
- Trap arms run from the trap weir to the vent: at least two pipe diameters, and no more than 30 inches for 1-1/4, 42 for 1-1/2, 60 for 2, 72 for 3, 120 for 4 inch; a water closet may be up to 6 feet from its vent (Table 1002.2).
- Size drains and vents by fixture units from Table 702.1 against Table 703.2: a 2-inch horizontal drain carries 8 DFU, a 3-inch 35, a 4-inch 216; a lavatory is 1, a tub 2, a kitchen sink 2, a washer standpipe 3, a 1.6 gpf toilet 3.
- Vents terminate at least 6 inches above the roof and 1 foot from a vertical surface, 10 feet from or 3 feet above any openable window, door, or air intake (906.1, 906.2). Supply is sized by water supply fixture units (Table 610.3) with a regulator required above 80 psi static (608.2).
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More lessons in The Field: Method, Code, and Cases
- 1The diagnostic method: verify, isolate, cheapest test first, cause not symptom, the options ladder, document
- 2Permits: when one is required, what is exempt, pulling it online, the inspection sequence, what inspectors look for, and handling corrections
- 3Daily-use code: drainage slope, venting, water sizing, cleanouts, trap arms, and fixture units, with the section for eachYou are here
- 4Gas piping in practice: sizing, CSST bonding, the pressure test, appliance connectors and shutoffs, sediment traps, and seismic shutoff valves
- 5Water heaters I: tank. Seismic strapping, the T&P discharge line, expansion tanks, sediment traps, pans, venting, and the garage rules
- 6Water heaters II: tankless and heat pump. Gas sizing, venting, condensate, the 2025 Energy Code direction, and where the gas-ban ordinances stand
- 7Sewer and drain I: the camera, the locator, hydro-jetting vs. cabling, and when each is the right tool
- 8Sewer and drain II: trenchless vs. open trench, whose lateral it is (it varies by city), backwater valves, and point-of-sale lateral ordinances
- 9Case: the hissing line. The meter test, the supply leak that fed the roots, the lateral to the city tap, and the contract and permit trail
- 10Leak detection: slab leaks, acoustic and pressure methods, thermal imaging, and repipe vs. reroute
- 11Low pressure: the PRV, galvanized pipe, and the sequence that finds which one it is
- 12Sewer gas: trap seals, trap primers, vents, and the sequence that finds the smell
- 13Water treatment: where softeners are restricted in California, filtration, pressure regulators, and thermal expansion
- 14Fixtures and conservation: CALGreen flow rates, SB 407 retrofit-on-alteration and disclosure-on-sale, 1.28 gpf, and the ADA basics a plumber needs
- 15Materials and methods: PEX vs. copper vs. CPVC, ABS vs. PVC (it is regional), cast iron, and the transitions that fail
- 16Commercial basics: grease interceptors, the backflow program, and the tester certification that opens a second line of work
- 17Cal/OSHA for a small shop: the IIPP every employer must have, heat illness prevention, trenching and the 5-foot permit, confined space, silica, and ladders
- 18Environmental rules: EPA lead-safe certification for any pre-1978 home, asbestos and transite pipe, and stormwater
- 19Job-site craft: sequencing with the other trades, protecting the home, and the punch list that ends the job
- 20Case: the water heater that failed inspection twice
- 21Case: the gas leak call. The protocol, and the walk-away
- 22Case: the "customer doesn't want a permit" job
- 23Template: the job-site checklist, from the truck to the walk-through
- 24Template: the pre-inspection checklist by stage. Underground, rough, water heater final, gas, and trim
- 25Template: the Injury and Illness Prevention Program starter for a plumbing shop of one to five
- 26Template: the Heat Illness Prevention Plan for a plumbing shop, outdoor and indoor
- 27Template: the customer options sheet (good / better / best) with the cost band, the permit path, and the code trail on each rung