Plumbing Rough-In for Kitchen Renovation
With electrical in place, it's time to install your kitchen's plumbing infrastructure. This phase involves running water supply lines and drain pipes to all fixture and appliance locations. Whether you're keeping your sink in the same spot or moving it across the room, proper planning and execution prevent leaks and drainage problems.
Quick Summary
Time needed
1-2 days
Cost
$1,500-3,000
Difficulty
Hire a Pro
Why Plumbing Rough-In Matters
Kitchen plumbing rough-in is where functionality meets code compliance. Get it wrong and you'll have slow drains, low water pressure, leaks behind walls, or failed inspections. Get it right and your kitchen will have reliable water delivery, fast drainage, and no surprises.
Critical Consideration: Drain lines must have proper slope (1/4 inch per foot minimum) and adequate venting to work correctly. This isn't flexible—physics and plumbing code require it. A licensed plumber knows how to route drains properly even in challenging situations.
This phase also locks in your layout decisions. Once drains are installed and inspected, moving fixture locations becomes expensive. Make sure you're committed to your final kitchen design before plumbing rough-in begins.
Planning Your Plumbing Layout
1. Confirm All Fixture Locations
Your plumber needs exact locations for every water-using fixture and appliance. This includes obvious items like the sink, plus less obvious ones like ice makers and pot fillers.
What Needs Plumbing Connections:
- •Kitchen sink (hot, cold, drain)
- •Dishwasher (hot water, drain, possibly electric)
- •Refrigerator with ice maker (cold water line)
- •Garbage disposal (drain connection, electric)
- •Pot filler if included (hot water line)
- •Additional sinks in island/bar area
- •Instant hot water dispenser if desired
2. Understand Drain Requirements
Drains are more complex than supply lines because they rely on gravity and proper venting. Your plumber will design a system that meets code while working with your existing drain stack and vent locations.
Drain Line Sizing
- • Kitchen sink drain: 1.5 inch minimum, 2 inch preferred
- • Dishwasher drain: 3/4 inch to 1 inch
- • Disposal connection: Must match sink drain size
- • Branch drain to main stack: Usually 2-3 inches
- • Vent pipes: 1.5 to 2 inches typically
Slope and Venting Rules
- • Minimum slope: 1/4 inch per foot of horizontal run
- • Maximum slope: Avoid too steep (can cause problems)
- • All drains must be vented to atmosphere
- • Dishwasher needs air gap or high loop
- • Island sinks require special venting considerations
- • P-traps required at all fixture drains
3. Plan Water Supply Routes
Supply lines are more forgiving than drains—they're pressurized so they don't need slope. But they still need proper sizing, support, and shut-off valves at each fixture.
Pro tip: Install individual shut-off valves for every fixture and appliance. This lets you service or replace items without shutting off water to the entire kitchen. Quality quarter-turn ball valves are worth the small extra cost.
The Rough-In Process
Install Drain Lines First
Experienced plumbers install drains before supply lines because drains are larger, less flexible in routing, and must be positioned precisely. They'll work from the main drain stack out to each fixture location.
Drain Installation Steps:
- • Cut into existing drain stack if needed
- • Run branch drains with proper slope to fixture locations
- • Install P-traps at fixture locations
- • Add cleanouts at accessible locations
- • Install vent pipes connecting to vent stack or through roof
- • Test all drains with water to verify proper flow
Run Water Supply Lines
After drains are in place, your plumber runs hot and cold supply lines to each location. Modern kitchens often use PEX piping, which is flexible, reliable, and easier to install than copper.
Supply Line Installation:
- • Tap into existing hot and cold supply lines
- • Run lines to all fixture and appliance locations
- • Install shut-off valves at each location
- • Secure lines properly to studs/joists
- • Protect lines from damage with nail plates
- • Stub out at correct heights for each fixture type
- • Cap all lines and pressure test before closing walls
PEX Piping
Modern choice, flexible, fewer connections, resistant to freezing, easy to route through framing.
Most common for residential renovations
Copper Piping
Traditional choice, very durable, heat resistant, requires soldering skills, more expensive.
Still used in some applications
Pressure Test and Inspect
Before walls close up, your plumber will pressure test supply lines and test drain flow. This catches any leaks or issues while they're still easy to fix.
Testing Process:
- • Pressure test supply lines (usually to 80+ PSI)
- • Leave under pressure for several hours
- • Check all connections for leaks
- • Run water through drains to verify flow and slope
- • Check for any leaks at drain connections
- • Verify vents are properly connected and open
- • Take photos of completed rough-in before covering
Special Plumbing Considerations
Moving the Sink Location
Moving your sink to a different wall or adding an island sink significantly increases plumbing complexity. Drains need proper slope to the main stack, which may require creative routing or even floor trenching.
Cost impact: Moving a sink typically adds $500-1,500 to plumbing costs. Island sinks are particularly challenging due to venting requirements. Discuss feasibility and costs with your plumber early in planning.
Adding a Pot Filler
Pot fillers are convenient but require running a water line to your range/cooktop area, often through walls or ceilings. They need a shut-off valve and proper support since they extend from the wall.
Installation note: Pot fillers only need cold water (or hot if you prefer). They don't drain, so there's no drain installation. Budget $200-400 extra for the supply line during rough-in.
Water Filtration Systems
If you plan to add under-sink water filtration or a reverse osmosis system, mention this during rough-in. While these are typically installed during finish plumbing, knowing your plans helps the plumber position supply lines optimally.
Planning tip: RO systems need a drain connection for waste water. If you want the filtered water dispenser at the sink rather than a separate faucet, plan for this in your faucet selection.
Frequently Asked Questions
Should I hire a plumber or DIY the plumbing rough-in?
Hiring a licensed plumber is strongly recommended for kitchen plumbing work. Kitchens require proper drain slope, venting, water pressure, and code compliance. Mistakes can cause leaks, water damage, mold, and failed inspections. While basic plumbing can be DIY, the cost of professional work ($1,500-2,500) provides expertise, code knowledge, warranties, and peace of mind.
What size water lines should be used in a kitchen?
Kitchen water supply lines are typically 1/2-inch diameter for individual fixtures (sink, dishwasher) and 3/4-inch for main supply lines. Ice maker lines are often 1/4-inch. Drain lines vary: sink drains are 1.5 inches minimum (often 2 inches), dishwasher drains are 3/4 to 1 inch, and the main drain stack is 3 inches or larger. Your plumber will size appropriately based on code and fixture requirements.
Do I need a vent for every kitchen drain?
Yes, all kitchen drains must be properly vented per plumbing code to prevent siphoning, allow air into the drain system, and ensure proper drainage. The sink typically ties into a vent stack, while dishwashers often use an air gap or high loop. Your plumber will design the venting system based on your layout and existing plumbing. Proper venting is critical for inspection approval.
Can I move my sink to a different wall?
Yes, but it increases plumbing complexity and cost. Moving a sink requires rerouting drain lines (which need proper slope), extending water supply lines, and potentially adding new venting. If you're moving the sink to an island, venting becomes more complex. Moving a sink typically adds $500-1,500 to plumbing costs depending on distance and complexity. Plan this early so your plumber can budget time and materials.
How long does plumbing rough-in take?
A professional plumber typically completes kitchen plumbing rough-in in 1-2 days for a standard kitchen. Complex kitchens with relocated sinks, pot fillers, multiple islands, or significant rerouting may take 3-4 days. The work includes running drain lines, water supply lines, installing shut-offs, and pressure testing. Schedule your rough inspection right after plumbing completion.
Ready for the Next Step?
With plumbing complete, it's time to address any HVAC adjustments needed for your new kitchen layout.