New construction plumbing: stages, costs, and hiring a plumber

By Panyala · Last updated October 26, 2026 · How we write and review guides

Plumbing for a new house is usually done in three stages: underground (or under-slab), rough-in, and finish (trim-out), with an inspection after the first two before anything gets covered up. Bids are typically priced per project from your plans, and they vary with the number of fixtures, pipe materials, and whether the home is on city water and sewer or a well and septic.

Disclosure: FreePlumbingEstimates.net connects homeowners with independent local contractors. We are not a contractor. How it works.

The three stages of new construction plumbing

1. Underground or under-slab

Before a concrete slab is poured (or before a basement floor goes in), the plumber installs the drain lines and sometimes water lines that run beneath it, plus the building sewer that leads to the street or septic system. Lines are tested, often by filling them with water, and inspected before concrete covers them. Mistakes at this stage are expensive to fix later, so the layout has to match the plans exactly.

2. Rough-in (top-out)

After framing, the plumber runs supply lines and drain-waste-vent (DWV) piping through the walls, floors, and ceilings, sets tub and shower bases that have to go in before the walls, and stubs out pipes where fixtures will go. The system is pressure tested and inspected before insulation and drywall go up.

3. Finish (trim-out)

Once walls, flooring, and cabinets are in, the plumber installs toilets, sinks, faucets, shower trim, the water heater, and appliance connections, then tests everything. A final plumbing inspection usually happens around this time.

Key decisions that affect the plumbing

Pipe materials

• PEX: flexible plastic tubing common for water supply in new homes. It installs quickly with fewer fittings and is often less expensive to install.
• Copper: long-established, durable, and more expensive in both materials and labor.
• CPVC: rigid plastic supply pipe used in some regions.
• PVC or ABS: common for drain, waste, and vent lines, depending on local code.

Local codes determine which materials are allowed. Your plumber can explain what's typical in your area.

Water heater

Tank or tankless, gas, electric, or heat pump. This affects venting, gas line sizing, electrical work, and where the heater can go. A central location shortens the wait for hot water.

Fixture count and layout

Every bathroom, sink, and appliance adds pipe and labor. Stacking bathrooms above each other and grouping wet rooms shortens runs and can lower cost.

Water and sewer source

City water and sewer require tap and connection fees in many areas. A rural build may need a well and a septic system, which are usually separate contracts. If you're building on septic, use our septic tank size calculator early and talk to your health department about permits and soil testing. Building small? See septic systems for tiny houses.

Extras worth planning now

• Shut-off valves at every fixture and a manifold system for PEX
• Rough-ins for a future bathroom in the basement
• Gas lines for a range, dryer, grill, or fireplace
• Outdoor hose bibs on several sides of the house, ideally frost-free in cold climates
• A water treatment or softener loop if you're on a well
• Floor drains and a laundry pan where a leak could cause damage

What affects the cost of new construction plumbing

• Number of bathrooms and fixtures
• Pipe materials and fixture quality (and whether fixtures are in the plumber's bid or supplied by you)
• House layout, number of stories, and slab vs basement vs crawlspace
• Distance to the water and sewer connections
• Permit and inspection fees in your area
• Local labor rates and how busy plumbers are

Prices vary too much by region and design to give a meaningful national number. Getting several bids based on the same plans is the reliable way to know what your project should cost.

How to get and compare new construction plumbing bids

1. Send the same plans and fixture schedule to every plumber. Note which fixtures you're supplying.
2. Ask what's included: underground, rough-in, finish, water heater, gas piping, sewer or septic connection, permits, and inspections.
3. Ask about exclusions: excavation, trenching to the street, concrete cutting, or appliance installation.
4. Confirm license and insurance and check them with your state.
5. Ask how change orders are priced if you add a fixture or move a bathroom.
6. Agree on a payment schedule tied to stages, for example after each passed inspection.
7. Get the warranty in writing, on both workmanship and equipment.

Finding a new construction plumber near you

Plumbers who focus on new construction often work closely with local builders, so ask your general contractor, local supply houses, and your building department for names. You can also request estimates through our form. We'll pass your project to independent local plumbers who may be a fit, and they'll contact you to discuss the plans.