Residential Plumbing Rough-In: DWV, Supply, and Pressure Tests
What inspectors look for at rough — and what gets a redo.
Plumbing rough-in is the inspection gate before drywall closes the walls. Get it wrong and you're cutting drywall in week 32 of an eight-month project. This article covers the California Plumbing Code's standard rough-in requirements, common correction items, and how to read a plumbing isometric.
DWV (Drain, Waste, Vent) layout
Every plumbing fixture needs a trap, a drain, and a vent. Vents prevent siphoning of the trap seal. Wet venting is allowed in most CA jurisdictions under CPC 908.1; air admittance valves (AAVs) are limited (most jurisdictions reject them on primary plumbing, allow on islands). Slope drains 1/4-inch per foot for 3-inch and smaller pipe.
Water supply distribution
PEX-A is now the dominant supply material in California (post-2016 code amendments). Copper remains common in high-end. CPVC is rare and rejected by some jurisdictions. Minimum sizing per CPC 610 — most code-checks fail when an undersized branch line can't supply two fixtures at 8 gpm.
Pressure testing
DWV: 10-foot column of water held for 15 minutes (or 5 psi air, per inspector preference). Supply: 100 psi air or working pressure plus 50 psi water, held for the inspection. Fail = cut into the wall to find the leak.
Common correction items
Missing nail plates at supply lines within 1¼ inch of stud edge (CPC 312.9). Insufficient slope on 2-inch lavatory drains. Vent terminations within 4 ft of operable openings. Strapping at intervals greater than 4 ft on copper, 32 inches on PEX.
Hot water and recirculation
California's HCD recommends point-of-use heat-pump water heaters or central tankless with demand-controlled recirc. Title 24 requires recirculation pumps to be demand-controlled (push-button or motion sensor activation), not constantly running.
Authoritative sources
- 2022 California Plumbing Code (Title 24, Part 5) — California Building Standards Commission
- IAPMO Uniform Plumbing Code reference — International Association of Plumbing and Mechanical Officials
More from the library
- Residential Structural Engineering 101 for California Owners — Load paths, shear walls, and why your remodel needs an engineer's stamp.
- California Title 24 Energy Compliance: A Plain-English Guide — Why your remodel needs a HERS rater and what the energy compliance form really says.
- Seismic Retrofit Basics for California Single-Family Homes — Cripple walls, sill bolting, and the Earthquake Brace + Bolt grant program.