Kitchen Sink Plumbing Rough-In Guide

Kitchen plumbing rough-in has gotten complicated with all the drain sizing, vent requirements, and code specifications flying around. As someone who has roughed in plumbing for every kitchen layout, I learned everything there is to know about getting pipe positions right. Today, I will share it all with you.

Key Components

Probably should have led with this section, honestly—understanding each element matters:

• Drain Lines: Carry used water away from sink
• Supply Lines: Bring fresh water to sink
• Vent Pipes: Allow air for proper drainage
• P-Trap: Prevents sewer gas from entering home
• Shut-Off Valves: Control water flow for maintenance

Drain Line Positioning

That’s what makes proper positioning endearing to us plumbers—it prevents future problems:

• Drain line typically 18-20 inches above floor
• Center with sink position for efficient flow
• P-trap at right height for under-sink fixtures

Water Supply Lines

• Hot and cold lines 10-12 inches above floor
• Position 2-4 inches left and right of center drain
• Correct spacing ensures repair access and avoids cabinet interference
• Flexible copper or plastic tubing allows maneuvering

Vent Pipes

Vent pipes maintain air pressure and allow smooth wastewater flow. Install with upward slope to avoid water accumulation. Position within 5-7 feet of P-trap for efficient ventilation.

Shut-Off Valves

Install on hot and cold lines just above floor level. Compression valves offer easy DIY installation. Soldered valves provide permanent professional solution.

Electrical Considerations

For garbage disposals and dishwashers, plan outlets at least 6 inches above counter. Ensure disposal wiring is grounded. All electrical must comply with local codes.

Checking for Leaks

Turn on water supply and run for several minutes before sealing walls. Check P-trap and shut-off valves for moisture signs.

Code Compliance

Follow local building codes for pipe diameter, component spacing, and materials. Consult National Plumbing Code or local guidelines. Non-compliance can result in fines or rework.