Residential New Construction Plumbing

The takeoff starts with the floor plan, the fixture schedule, and the site plan. Fixture count sets the size of the water service and the drain, the site plan shows where the meter and the sewer tap or the septic tank sit, and the elevations say how much fall there is between the house and the connection point.

This is also where the expensive problems get caught. A freestanding tub in the middle of a slab, a kitchen island sink, a laundry moved to the second floor, and a bathroom added over a garage all change the groundwork. Sorting them out on paper costs a phone call. Sorting them out after the concrete truck leaves costs a saw cut.

Sand drains fast and holds a trench wall poorly, and on a lot near the bay or the coast the water table can sit close to the surface. Trenches get bedded and backfilled so the pipe keeps its slope after the ground settles, and drain lines are supported where they turn up through the slab instead of resting on loose fill.

Before the pour every stub-up is capped, braced, and sleeved where it passes the vapor barrier, and the locations are checked against the framing plan one more time. Concrete does not forgive a toilet drain that ends up four inches off its wall. After the slab is poured the crew comes back for the wall and ceiling rough-in, and the water heater location, hose bib count, and outdoor shower get confirmed while the walls are still open.

Drain, waste, and vent piping is tested with water before anything covers it. The system is capped and filled so the joints hold a standing column of water, which is the hydrostatic plumbing test the inspector comes out to see, and the water lines get a plumbing pressure test that has to hold while the joints are checked. Nothing is buried, poured over, or covered with drywall until that test has been witnessed.

The work is inspected in phases: the underground and slab rough-in before the pour, the top-out once the walls and ceilings are piped and before insulation and drywall, and the trim-out after the fixtures are set. The local building department sets the exact test method and how long the system has to hold, so each inspection is booked with them rather than assuming one county calls it the same way as the next.

On a custom home the fixture selections arrive late and change more than once. Freestanding tubs, wall-mounted faucets, multi-head showers, pot fillers, outdoor showers, and a pool bath all carry rough-in dimensions that have to be known before the walls close, so we ask for model numbers rather than pictures. Where a selection is still open, the wall stays open too, and that connection waits until the model number is in hand.

Spec homes run the other way. The plan repeats, the fixture package is fixed, and the value is in hitting the same rough-in the same way on every lot so the builder can pour, frame, and drywall on a predictable rhythm. Builders running several houses at once can have them scheduled together.

Send the plans, the fixture schedule, the lot address, and the date you expect to be ready for underground. The quote comes back tied to that plan, and the crew is booked for all three phases instead of one visit at a time. If the pour date moves, say so as early as you can and the slot moves with it.

Owner-builders get the same process with more explanation. Expect to hear which decisions have a deadline attached, which ones can wait until trim, and what the plumbing side of the final walkthrough covers before the certificate of occupancy.