How to Rough-In Plumbing for a Bathroom Renovation

Roughing-in plumbing represents the skeleton of your bathroom, setting the stage for every fixture you plan to install. This is the moment where the hidden network of pipes must be perfectly pitched, secured, and pressure-tested, as these lines will become inaccessible once the drywall goes up. A job done well means your shower drains quickly, your toilet flushes reliably, and your vanity faucets deliver hot and cold water without rattling or leaks. Precision is your greatest asset here. You are working within the constraints of your floor joists and wall studs, meaning you need a clear plan for your drainage slopes and supply pipe routing. It is not just about putting pipes in holes; it is about respecting the integrity of the building's framing while meeting local code requirements for venting and pipe size. Focus on the geometry of the flow, and the rest of the project will follow.

  1. Map and Drill for Precision. Mark the exact center lines for your toilet, shower drain, and vanity sink on the subfloor. Drill holes through the studs and joists for your piping, ensuring you leave enough room for protective nail plates to prevent future punctures.
  2. Pitch the Drains Right. Lay your main 3-inch drain line for the toilet and 2-inch lines for the shower and sink. Maintain a consistent downward slope of 1/4 inch per foot to ensure proper drainage.
  3. Vent to Atmosphere Now. Connect your drain lines to a vertical vent pipe that terminates through the roof. This equalizes air pressure in the pipes, preventing the P-traps from being siphoned dry.
  4. Route Supply Lines Clean. Route your 1/2-inch PEX or copper supply lines from the main manifold to each fixture location. Secure the pipes to the framing using plastic pipe straps to eliminate vibration and noise.
  5. Square the Valve Perfectly. Mount the shower mixing valve securely to a block of wood spanning two studs. Install brass drop ears for the vanity and showerhead to provide a rigid mounting point for the finished trim.
  6. Pressurize and Hold Steady. Cap off all open ends and pressurize the supply lines with air or water to check for leaks. Monitor the gauge for at least one hour to ensure the system holds pressure.