Rough In Plumbing

A closet flange sticking up through sub-flooring.

Just like it sounds, to rough in plumbing is essentially the rough draft to a later more finalized plumbing installation. Like a rough draft, the job is incomplete at this stage, but unlike a rough draft, changes or alterations to the layout are not expected at this stage.

The point is simply to get the basic plumbing skeleton in place. This way, while the rough in plumbing work pends inspection from a professional who will ensure things are up to code and eventually issue a building permit, the other stages of construction or remodeling can move forward without the pipes of a fully finished plumbing system getting in the way and causing obstructions.

Here’s a step by step outline of a rough in toilet installation. Bear in mind that each situation is slightly different, so this will only provide a basic outline and list of considerations.

DISCLAIMER: Even with a step-by-step outline, plumbing work of this caliber can be difficult and can require a high level of understanding or expertise. This, coupled with the fact that this project puts you inside of a largely unfinished structure, means that safety is also a concern. In many cases, calling in a professional may be worth it. Especially since rough in plumbing is just a stepping stone to the larger plumbing installation.

Step 1 - Find and Mark Your Key Locations

Determine where the toilet is going to be positioned and mark its center on the wall. Measure 13 1/2 inches outward from that center point, and then, on the floor, make another mark at this distance. This is where the closet flange will be located. Also known as a toilet flange, it will eventually serve two purposes. It will mount the toilet to floor and connect the toilet’s drain to a larger drain pipe.

Take the actual flange and center on top of the mark on the floor. Trace a line around the outside of it so that you have a circular shape on the floor.

Step 2 - Cut out the Drain Hole

Cut out the marked, circular section of floor and position the flange in the hole with the edges resting solidly on the floor. Ensure the two elongated slots are on the sides (your toilet bowl bolts onto the flange using these two slots) and screw the flange to the floor.

Since the toilet flange needs to be perfectly flush, no pun intended, with the finished floor, you may need to place shims under the flange before bolting it to the floor if you’re eventually going to be using a raised floor, such as ceramic tile, in your bathroom.

Step 3 - Install Drain Piping

Drain components will include traps or pipes that intentionally curve downward and then back up in order to trap small amounts of water to act as a seal for sewage gas, as well as vents to prevent any negative air pressure from occurring that could suck the water out of the trap.

Both the drain pipes and the vent components will be installed underneath the floor. Keep in mind that during true rough in work, no finishes like floors or even walls installed, so getting under the floor should not pose much difficulty.

Drainage Flow

You want to direct the flow of the drain towards the main waste stack. To achieve this directionality, use a 3-inch long 90 degree turn fitting and run it into a 3"x3"x2" Y fitting, positioning it so the 2-inch lead can be piped back to the main vent pipe.

Continue the 3-inch piping all the way to the main waste stack and connect into it with a 3-inch Y fitting.

Step 4 - Install the Supply Line

To install the water supply line, take your line and run it from the designated water supply directly up through the floor or inside the wall so that it comes out near the side of the toilet tank that has the water supply link fixture.

Position a “T” fitting on top of the supply line, with the water line going into the bottom of the “T,” the middle outlet of the “T" facing out through the wall, and the top of the “T” extending up in behind the wall.

Step 5 – Finishing Touches

Attach an 8-inch section of pipe extending through the wall to supply the toilet and attach a piece of pipe (about 12 inches long) onto this up pointing "T" side. Solder or attach cap fitting to this section to create an air chamber that will prevent "water hammer."

Now that the plumbing is roughed in, you can finish the rest of the bathroom, get approval from an inspector, move forward with the toilet install, and hook it up to the drain and supply lines.

Additional Tips

Drain Slope

The ideal slope for a drain is 1/4 inch for each foot long. Too little slope means water and solids may not drain, while too much slope could cause the water to drain away too fast, leaving solids behind and clogging your pipes.

Vent Angles

Proper angles on vent pipes are necessary. Vents need to angle upward at a 45 degree angle or more away from level to ensure they won’t ever fill with water. A vent filled with water obviously can’t work.


Accessible cleanouts are required. No matter how well a system is designed and built, clogs can occur, and you need to be able to easily open up the drain and clean it out manually. Local plumbing codes specify where cleanouts are required in a plumbing system.

Comfort Room

People need space. For someone to comfortably use a toilet, maintain a minimum of 15 inches of space from the center of a toilet to a wall or vanity on either side, as well as 18 inches between the front of a toilet and its facing wall.