Kitchen Plumbing Rough-In: Dimensions, Pipe Sizes, and Layout

A kitchen plumbing rough-in sets the drain, vent, and supply lines for the sink, dishwasher, disposal, and ice maker before the cabinets and wall close up. The working numbers anchor the whole job: a drain stub around 18 inches above the floor, 1/2-inch supplies a few inches above it, a 1.5 to 2-inch drain, and a 1.5-inch vent. Hit these and the finish hookups drop in clean.

What does a kitchen plumbing rough-in include?

A kitchen rough-in is the stage where you run and secure every pipe inside the framing, then cap and pressure-test it, with no fixtures attached. It covers one drain and vent for the sink, 1/2-inch hot and cold supplies, the dishwasher and disposal tie-ins under the sink, and a 1/4-inch water line for a refrigerator ice maker.

Every dimension is measured to the finished floor and finished wall, not to the subfloor or bare studs. Add the thickness of flooring and drywall before you commit a stub location, or the sink drain can land an inch off once the kitchen is finished.

The kitchen runs simpler than a full bath because it has one main fixture group at the sink. If you are new to reading these layouts, our guide to residential plumbing diagrams shows how supply, drain, and vent lines stack across a house. This page zooms in on the kitchen group.

What are the standard kitchen rough-in dimensions?

The table below gives the working numbers for a standard kitchen: pipe size and the rough-in height or offset for the sink drain, supplies, dishwasher, disposal, ice maker, and vent. These reflect common International Plumbing Code (IPC) and Uniform Plumbing Code (UPC) practice, but fixture spec sheets and local code override them, so verify before you cut.

AFF means “above finished floor.” A single 1/2-inch supply usually branches off a 3/4-inch trunk line, and the ice maker taps a 1/4-inch line off the cold supply. Set the drain to one side of the cabinet, commonly 8 inches off the sink center, so the disposal and trap have room to hang without fighting each other.

What pipe sizes does kitchen plumbing use?

Kitchen pipe sizing follows the fixture load, which is light because one sink dominates the group. The sink drains through 1.5-inch pipe at minimum, often 2-inch with a disposal or long run. The vent is 1.5 inches or larger. Supplies are 1/2-inch hot and cold, and the ice maker taps a 1/4-inch line.

The 1.5-inch drain and P-trap match the numbers you see under any sink, and the same trap-and-vent logic covers kitchen sink plumbing at the finish stage. Step the drain up to 2 inches when the branch carries a disposal, a double bowl, or a trap arm that runs long back to the stack.

Supply pipe is commonly 1/2-inch PEX or copper at the sink, teeing down to 3/8-inch risers at the shutoff valves. PEX has taken over most new kitchen rough-ins because it flexes through the cabinet base with fewer fittings and resists freeze bursts better than rigid copper on an outside wall.

Horizontal drain runs pitch at 1/4 inch per foot back toward the stack. Under-slope it and grease and food solids settle in the line and clog it early, which is the most common kitchen drain failure.

How do you rough in the dishwasher, disposal, and ice maker?

These three appliances share the sink group but connect differently. The disposal hangs under one bowl and discharges into the trap. The dishwasher drains through a hose that ties to the disposal or a branch tailpiece, protected by a high loop or air gap. The ice maker runs a 1/4-inch line to a shutoff box behind the fridge.

The dishwasher drain hose needs siphon protection so dirty sink water cannot back-feed the machine. A high loop straps the hose up under the counter before it drops to the connection. An air gap is a fitting mounted at the countertop, and code requires it in California, Washington, Minnesota, and Hawaii. One or the other is mandatory.

The disposal takes the dishwasher inlet on its side, and a new disposal ships with that inlet plug still in place, so knock it out before you connect the hose. On a double bowl with no disposal, the dishwasher ties into a branch tailpiece instead. The disposal itself needs a dedicated switched outlet, so rough in the electrical to match.

The ice maker is the smallest run. Set a recessed outlet box on the wall behind the refrigerator with its top around 18 inches above the floor, feed it a 1/4-inch line off the cold supply, and cap it with a quarter-turn valve. A saddle valve is quick but a known leak point, so a soldered or push-fit tee is the better tap.

What order do you rough in kitchen plumbing?

Rough-in runs largest pipe to smallest, drains before supplies. Locking in the drain and vent path first means the sloped waste line and vent claim their space in the wall, then the flexible half-inch supplies route around them. Working in this order avoids tearing out a supply run to fit a drain that had nowhere else to go.

1. Mark the sink centerline on the floor and studs, measured to finished surfaces, and set the base cabinet layout.
2. Tie into the stack and run the branch drain to the sink at 1/4-inch-per-foot slope, drain stub at 16 to 20 in AFF.
3. Set the P-trap arm location, offset about 8 inches from center opposite where the disposal will hang.
4. Run the vent up from the drain, above the flood-level rim, and tie it into the vent stack.
5. Route the 1/2-inch hot and cold supplies to their stubs at 20 to 23 in AFF, 8 inches apart, and cap with stops.
6. Tee off the cold supply for the 1/4-inch ice maker line and set the outlet box behind the fridge.
7. Cap all stubs, then air-test or water-test the drain and vent and pressure-test the supply before inspection.

Once the rough-in passes and the cabinets go in, you set the trap, disposal, and valves and install the sink to finish the group. Get the drain height and trap offset right at rough-in and the finish stage takes an afternoon.

How does a kitchen rough-in layout look?

Picture the sink wall in cross-section: one drain stub low in the wall, two supply stubs a few inches above it, and a vent running straight up. Everything else, the disposal, dishwasher hose, and trap, connects inside the base cabinet after the walls close. The layout is compact because a single fixture group carries the whole kitchen.

From left to right on the sink wall, the drain sits centered or offset about 8 inches, the hot supply on the right and cold on the left flank it a few inches higher, and the vent climbs off the drain fitting up into the ceiling. The ice maker box sits on its own, on the wall behind the refrigerator location, well away from the sink.

The kitchen shares the drains-first, supplies-second logic with a bathroom plumbing rough-in, but the numbers differ: no 12-inch toilet flange, no tub, and one drain instead of three or four. The kitchen trades those for the disposal and dishwasher tie-ins that a bathroom never has.

What are the most common kitchen rough-in mistakes?

Most failed kitchen rough-ins trace back to a few repeat errors, and each is cheaper to fix before the cabinets go in than after. The pattern is usually a stub set to framing instead of finished surfaces, a drain too high for a deep sink, or a dishwasher hose with no siphon protection. Catch these before you call for inspection.

• Setting the drain stub too high, so a deep or undermount sink leaves no room for the disposal and trap below.
• Centering the drain on the cabinet, then finding the disposal and trap crowd each other with no offset.
• Skipping the dishwasher high loop or air gap, which fails inspection and lets sink water back-feed the machine.
• Under-sloping the branch drain below 1/4 inch per foot, so grease and food solids settle and clog the line.
• Tapping the ice maker with a saddle valve, a slow leak that shows up months later behind the fridge.
• Forgetting the vent or tying it below the flood rim, which siphons the trap dry and vents sewer gas.

Frequently asked questions

What is the standard rough-in height for a kitchen sink drain?

The kitchen sink drain stub roughs in about 16 to 20 inches above the finished floor, with 18 inches the common target for a standard 36-inch base cabinet. That height leaves room for a garbage disposal and a P-trap under the basin. Deep or undermount sinks sit lower, so drop the stub a few inches and confirm the fixture spec sheet first.

What size drain pipe does a kitchen sink need?

A kitchen sink drains through 1.5-inch pipe at minimum, and many plumbers run 2-inch when the branch also carries a disposal or a long trap arm. The trap is 1.5 inches. Under IPC a kitchen sink counts as 2 drainage fixture units, so 1.5-inch handles the load, but local code and a food-waste disposer can push it to 2 inches.

Does a dishwasher need an air gap or is a high loop enough?

It depends on where you live. A high loop, the drain hose strapped up under the counter before it drops to the disposal, satisfies most jurisdictions. California, Washington, Minnesota, and Hawaii require a countertop air gap fitting instead. Both break siphoning so dirty sink water cannot back-feed the dishwasher. Check your local code before you pick one.

How high should kitchen sink supply lines be?

Rough in the hot and cold supply stubs about 20 to 23 inches above the finished floor, roughly 2 to 3 inches above the drain, spaced 8 inches apart on center and centered under the sink. Each line is 1/2-inch, capped with a shutoff valve. Keep them clear of the disposal and trap so the connections stay easy to reach.

Do you need a vent for a kitchen sink?

Yes. Every kitchen sink drain needs a vent so the trap cannot siphon dry and leak sewer gas into the room. The vent is 1.5 inches at minimum and often 2 inches where it serves the branch, tied in above the flood-level rim of the sink. An island sink with no wall behind it usually needs a loop vent or an air admittance valve where code allows.

Do you need a permit to rough in kitchen plumbing?

In most areas, yes. Adding or moving drain, vent, or supply pipe for a kitchen almost always requires a plumbing permit and a rough-in inspection before the walls and cabinets close. A straight fixture swap on existing connections often does not. Permit fees commonly run 50 to 500 dollars, and rules vary by state and local code, so ask your building department first.

Last reviewed: September 2026.