Installing new plumbing pipes and fixtures requires some preparation. Your first step should be to rough in new fixtures by figuring out their location and how they will connect to plumbing pipes. Find out how to rough-in plumbing so you can do repairs yourself or install new fixtures.


It is crucial to make sure all pipes and fixtures are properly aligned when installing new plumbing. If you are building a home or upgrading your plumbing system, your first step should be to rough in the main water supply and drain pipes. Here is what you need to know about how to rough-in plumbing.

Plumbing 101

plumbing 101

You should be familiar with the main components of your plumbing system before getting started with repairs or installation. The rough-in requirements will vary depending on the kind of pipes you are working with. Keep in mind that the measurements between pipes and floors correspond to the finished floor height and not to the subfloor height.

The wastewater system of your home will typically use larger pipes. These pipes need to be angled down so wastewater can properly drain. You need to have at least a 1/4” drop per foot on a pipe that runs horizontally.
Your wastewater system will be connected to smaller drain pipes for all your fixtures, including your sinks, toilet, bathtub, or shower. The main component of your wastewater system is the drain stack, which is connected to the main sewer drain at the bottom and a vent at the top.

In addition to this main vent stack, each fixture should have a P-trap to prevent sewer gas from backing up. Toilets already have a built-in P-trap, but you will need to account for a P-trap when roughing in other fixtures such as sinks, bathtubs, and showers.

Water supply pipes are typically installed after the waste pipes because they are thinner. After the main water pipe or trunk line enters your home, it will split in two. One of these pipes is the cold water supply for your different fixtures, and the other pipe will bring cold water to your water heater.

Check your local building code to find out more about plumbing and rough-in requirements. Some requirements are standards, but you might need to follow local ordinances for your pipe layout, pipe dimensions, or venting requirements.

How To Rough-In Plumbing

man checking faucet

When learning how to rough-in plumbing, there are a few steps to take before installing new plumbing pipes or fixtures:

Check the specs of the new fixtures, preferably before you purchase them. Make sure they will fit in your kitchen or bathroom.

Figure out where the new fixtures will go. Take existing pipes and clearance into consideration.
If you need to install new pipes, figure out where they will connect to the main water supply lines or wastewater system.

If you need to install new pipes, measure everything carefully and submit a diagram of the changes to your local building department if needed.

How To Rough-In A Sink

running faucet

Sinks should be installed approximately 31” above the floor. There should be at least 21” of free space in front of the sink. Start by figuring out the exact location and height of the new sink you want to install.

You can then measure where the drain pipe will be. The drain pipe fitting should be between 16 and 20” above the floor. Make sure you leave enough room for the P-trap that will be directly under the sink bowl. You should leave at least 12” under the lowest point of the sink bowl so the P-trap can fit.

You should use a two-inch pipe for the drain pipe. This pipe will be connected to the nearest waste line thanks to a sanitary tee. Remember that all drain pipes need to have a slight drop.

You should also add a stub-out on top of the sanitary tee. You can use a 12” pipe and glue a cap on top of it.

You will also need to connect the drain pipe to the main vent stack. You can add a vertical vent to the sink drain pipe and have it connect to the main vent stack.

The water supply line fittings should be located two or three inches above the drain pipe fitting. Place one water supply line fitting four inches to the left of the drain pipe and the other one four inches to the right.

The water supply lines will probably be ½” pipes that will be connected to a nearby ¾” pipe. The slope doesn’t matter since water supply lines are pressurized.

Once you have established the correct location for the water supply lines and installed the pipes, you can use drop-ear elbow fittings to attach the water lines to the framing of the new sink and connect the water supply lines to the faucet.

How To Rough-In A Bathtub Or Shower

bathtub

You need to be familiar with the specs of the new bathtub or shower you want to install. Most bathtubs have a faucet that is 18” high, while showers typically have a valve that is 42” above the floor.

The shower head should be between 72 and 80” from the floor, but you can adjust the height of the shower head as needed.

Determine where the new bathtub or shower will go. You should have 18” of clearance on at least one side of this fixture.

You can install the bathtub or shower first if you can easily access the drain of the new fixture once it is in place, for instance from the basement. Otherwise, you should start by installing the drain.

The location and diameter of the drain will vary from one fixture to another. Check the specs of your fixture to find out where the drain is. If there is an existing hole in the subfloor, measure its location and keep these specs in mind when shopping for a new fixture.

The drain pipe will either be a two-inch pipe or a one-and-a-half-inch pipe. You will need to connect a P-trap underneath your shower or bathtub.

Drill a hole in the subfloor, install the drain pipe and P-trap, and connect this pipe to a nearby drain pipe while being mindful of the slope. You can then add a vent on the sanitary tee used to connect the drain pipe of your new fixture to the main sewer system and connect this vent to the main vent stack.

If you1.70 are installing a bathtub, there will be a discharge hole that prevents the bathtub from overflowing. It should be between 10 and 14” from the floor. You will need to connect this discharge hole to the drain pipe with a sanitary tee.

You can then move on to connect water supply lines to the shower valve or bathtub faucet. Imagine that there is an imaginary line running in the middle of the new fixture. The water supply line fixtures should be located 4” the right and 4” to the left of this line.

You can finish the installation by connecting the shower valve to the shower head.

How To Rough-In A Toilet

clean bathroom

Part of learning how to rough-in plumbing is roughing in a toilet, which is easier since the P-trap is already built into the toilet. You will also have only one water supply line to connect.

Determine the dimensions and location of your new toilet first. Check your local building codes for clearance requirements. You will need at least 15” of clearance in front of the toilet and on both sides.

Toilets require a three-inch drain pipe. The drain of the toilet is called the flange. The flange of your toilet will have a diameter of 3,” and the center of the flange should be 12” away from the back wall.

Connect the 3” drain pipe to a drainage pipe with a diameter of at least 3” with a sanitary tee. You should place a vent on top of this sanitary tee with a diameter of at least 1 ½.”

Most toilets are designed to have a flange that is 12” away from the back wall, but you can find models with a flange that will be 10 or 14” away from the back wall. Older homes sometimes have flange openings that aren’t 12” away from the back wall. This is something you should measure before purchasing a new toilet.

The water supply line of your new toilet should be a ½” pipe. You can have this supply line come through the back wall or out of the floor depending on what is convenient.

Having the water supply line come out of the back wall is the most common solution. The fitting should be at least 6” above the floor. Don’t hesitate to place the fitting a little higher so it can clear the floor trim.

The water supply line fitting should be located 6” to the left of the center of the flange. If you decide to have the water supply line come out of the floor, all you have to do is install the fitting 6” to the left of the center of the flange.

These are the dimensions you need to keep in mind when roughing in plumbing. Don’t forget to check your local building code to find out about additional requirements, and take the time to measure new fixtures and figure out where existing plumbing pipes are before you install anything.

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