How to Add a Half Bathroom to Your Home

Adding a half bathroom requires running plumbing lines to your chosen location, installing a toilet and sink, and ensuring proper ventilation. Most projects take 3-7 days and cost $3,000-$8,000 depending on location and finishes.

1. Scout for Plumbing Access First. Look for spaces at least 3 feet by 5 feet, ideally near existing plumbing. Under stairs, converted closets, or areas adjacent to kitchens work well. Ensure the space has access to main water lines and can connect to the main drain stack. Check ceiling height requirements - you need at least 7 feet of clearance.
2. Map the Water Highway. Map out how you'll run supply lines for hot and cold water from the nearest source. Plan the drain line route to connect to the main stack or existing drain. The toilet drain needs a 3-inch line with proper slope, while the sink needs a 2-inch drain. Keep runs as short and direct as possible to minimize costs.
3. Get the Green Light. Pull permits for plumbing and electrical work through your local building department. Schedule rough-in inspections for when plumbing and electrical are installed but walls are still open. Plan final inspections after everything is complete. Most municipalities require licensed plumbers for new bathroom installations.
4. Frame and Wire Safe. Build walls to enclose the bathroom if needed, ensuring proper door swing clearance. Install electrical rough-in including GFCI outlets, light switches, and exhaust fan wiring. Place outlets away from water sources and install a dedicated 20-amp circuit if required by local code.
5. Connect the Water Lines. Install supply lines for hot and cold water, typically using PEX or copper pipes. Run the drain lines with proper slope toward the main stack. Install shut-off valves for easy maintenance. Pressure test all connections before covering with drywall. This step typically requires a licensed plumber.
6. Close Walls and Add Air. Hang and finish drywall around all plumbing and electrical rough-ins. Install an exhaust fan rated for the room size - typically 50-80 CFM for a half bath. Ensure the fan vents to the exterior, not into an attic space. Prime and paint walls with bathroom-appropriate paint.
7. Set Fixtures Straight. Install water-resistant flooring like tile, luxury vinyl, or sealed concrete. Set the toilet first, ensuring it's level and properly sealed to prevent leaks. Install the sink and faucet, connecting supply lines and drain. Add trim work around the base and any decorative elements.
8. Polish and Test Everything. Install light fixtures, mirror, toilet paper holder, and towel bar. Add door hardware and ensure the door opens outward if space is tight. Test all plumbing connections for leaks and verify the exhaust fan operates properly. Clean thoroughly and stock with basic supplies.