How much does bathroom plumbing cost?

Toilet replacement: $200-$700 installed. Faucet replacement: $150-$600. Full rough-in (new bathroom): $1,500-$4,000. Remodel with fixture relocation: $3,000-$8,000. Moving a toilet or shower is the most expensive change because it requires moving drains (in the slab or subfloor). Keeping fixtures in their original locations saves thousands.

Can I do my own bathroom plumbing?

Simple projects (toilet replacement, faucet swap, supply line connections) are straightforward DIY. Rough-in work (running new drain lines, venting, supply lines) requires plumbing knowledge and permits in most areas. Improper venting causes slow drains and sewer gas leaks. DWV (drain-waste-vent) work is where most DIY mistakes happen — consider hiring a plumber for drain work.

What size pipe is used for bathroom plumbing?

Supply lines: 1/2-inch PEX or copper for individual fixtures, 3/4-inch for main lines. Drains: 3-inch or 4-inch for toilet, 2-inch for shower, 1-1/2 inch for sink. Vents: 1-1/2 inch or 2-inch (must be at least half the diameter of the drain it serves). These are standard residential sizes per most plumbing codes.

What is the rough-in distance for a toilet?

12 inches from the center of the drain to the finished wall (not the framing — the finished wall after drywall). This is the standard rough-in. Some toilets are designed for 10-inch or 14-inch rough-ins (for older homes or special situations). Always measure before buying a new toilet.

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Home Improvement

Bathroom Plumbing Guide: Fixtures, Rough-In, Venting & Costs

Lumberama Editorial Team, Plumbing & Bathroom Remodeling Specialists Jun 10, 2026 15 min read

Bathroom Plumbing Overview

Bathroom plumbing consists of two systems: supply (hot and cold water delivered under pressure to fixtures) and drain-waste-vent (DWV — gravity-fed drains carrying wastewater away, plus vent pipes that allow air in to prevent siphoning of traps). Understanding both systems is essential whether you're remodeling a bathroom or building new.

Supply Lines

PEX (cross-linked polyethylene): The modern standard. Flexible, easy to install, freeze-resistant, color-coded (red for hot, blue for cold). Connects with crimp, clamp, or push-fit fittings. PEX has largely replaced copper in residential construction. 1/2-inch for individual fixtures, 3/4-inch for main lines.

Copper: The traditional choice. Durable (50+ year lifespan), rigid, requires soldering (sweating) for connections. More expensive than PEX in both material and labor. Still preferred in some commercial and high-end applications.

CPVC: Plastic pipe rated for hot water. Cheaper than copper but more brittle than PEX. Glued connections (no special tools). Being phased out in favor of PEX in most markets.

Drain-Waste-Vent (DWV)

PVC (Schedule 40): The standard drain pipe material. Lightweight, inexpensive, easy to cut and glue. White pipe. Used for all drain and vent lines in most residential construction.

ABS: Similar to PVC but black. Common in Western states and Canada. Cannot be directly connected to PVC (requires a transition fitting).

Cast iron: Found in older homes. Extremely durable and quiet (dampens water flow noise). Heavy and requires special tools to cut and connect. Being replaced with PVC in remodels.

Rough-In Dimensions

Toilet: 12-inch rough-in (center of drain to finished wall) is standard. 10-inch and 14-inch rough-ins exist but are less common. The toilet supply line is typically 6 inches left of center, 6 inches above the floor. Drain size: 3-inch (minimum) or 4-inch.

Sink: Drain at 18–20 inches above finished floor (center of drain pipe). Supply lines at 20–22 inches above floor, 4 inches apart (hot on left, cold on right). Drain size: 1-1/2 inch.

Shower: Drain at center of shower floor (or offset per design). Shower valve rough-in: 48 inches above floor (adjustable). Showerhead: 78–80 inches above floor. Drain size: 2-inch.

Bathtub: Drain at tub waste outlet (determined by tub model). Tub spout: 4 inches above tub rim. Valve: 28–32 inches above floor. Drain size: 1-1/2 inch (tub) connecting to 2-inch (branch drain).

Venting

Every drain fixture needs a vent pipe. Venting allows air into the drain system so water flows freely (without a vent, draining water creates a vacuum that siphons the trap, allowing sewer gas into the room). Vent pipes connect to the drain near each fixture and run upward to exit through the roof.

Vent types: Individual vent (one vent per fixture — simplest), wet vent (a single vent serves multiple fixtures — common in bathrooms where the sink drain vents the toilet), and AAV (Air Admittance Valve — a mechanical valve that opens to admit air when negative pressure occurs — allowed by most codes in specific situations, can't replace all vents).

Common Projects

Toilet replacement: A 1–2 hour DIY project. Shut off water, disconnect supply, remove bolts, lift old toilet, install new wax ring (or wax-free seal), set new toilet, reconnect. $150–$500 for the toilet + $0–$200 for installation.

Faucet replacement: 30–60 minute DIY project. Shut off supply valves, disconnect supply lines, remove old faucet, install new faucet, reconnect. $100–$500 for the faucet.

Full bathroom rough-in (new construction): $1,500–$4,000 for plumbing rough-in of a new bathroom (supply lines, drains, and vents for toilet, sink, and shower/tub). Requires permits and inspection.