Basement Plumbing - How to Install Plumbing in a Basement

Basement Plumbing
How to Install Plumbing in a Basement
DIY Basement Plumbing just got a whole lot easier!


Basements in many newer homes are built with basic plumbing drains and vent stacks built into the basement. This is commonly called stub-outs or stubs. If you see pvc plumbing pipes that look like they just go into the basement floor and lead nowhere, you may already have basic stubs for plumbing. Stub-out plumbing in a basement could include drains for a toilet, tub and shower drains as well as a bathroom sink drain and a vent stack for the future basement bathroom. Don't worry if you don't know which pipe is for plumbing. We will go over some basic plumbing terms on this page. Pictures and video of basement plumbing will also be included at the bottom of this page as well as links to other helpful plumbing resources for your basement.

If you have an older home or a basement where plumbing stub-outs were not included during construction, you can still add whatever plumbing fixtures you need and tie them into the existing home plumbing. Installing a bathroom with toilet or a shower will require you to break up the concrete to run drain lines and you may have to install an ejector pump to drain the waste. Most important is to have a plan before you start. Draw your plumbing layout and fixtures on the basement floor with chalk, Make a blueprint or whatever you have to do to figure out where the basement plumbing will go.

When installing plumbing it is important to know what codes your area requires. You can usually get this information by calling your local building dept. You may need a licensed plumber to check your work and also to be present during rough-in or final plumbing inspections. Requirements can vary for different areas so be sure you know what is required in your basement before you start.

100 Hot Tools

How Basement Plumbing Works

You will find 2 types of plumbing sub-systems in your basement. The supply system brings water into your basement and supplies water to each fixture you install. The drain waste vent system carries away wastewater, sewage and sewer gasses. Plumbing follows the laws of gravity and pressure. In other words it will always flow downhill unless pressure is applied to move it upstairs. The water that comes into your basement is under pressure and this is called the plumbing supply. When you turn on a sink, flush a toilet or take a shower the water you just used is turned into waste and as it goes down the drain it is no longer under pressure and enters the drain-waste part of your plumbing system.

The main water line coming into your house is the supply line. The supply line will connect to every fixture that requires water in your house and in your basement. The main sewer line that takes all water out of your house after it is used is part of the drain waste plumbing. Once you understand these 2 simple jobs that plumbing does, you should be able to trace your supply and drain waste lines in your basement. Most plumbing pipes in your basement will be visible. You should be able to find the main water valve or inlet where water enters your house. This is cold water and you can follow this pipe to your water heater which is usually in your basement. Cold water goes in and hot water comes out. Now you will have 2 pipes which supply hot and cold water to your house. These supply pipes will usually be made of copper but they could also be galvanized or plastic.

Rough Plumbing


A single supply pipe brings water into the house. This pipe is usually 3/4" to 1.5" inches in diameter and made of copper. After the water meter this pipe may branch off to feed outside faucets, water softeners or other fixtures in your home that need cold water only. The cold water supply pipe goes into your water heater and another pipe comes out of the water heater with hot water. Now you have hot and cold supply lines which run thru your basement and branch off to supply hot and cold water as needed to your entire house. These copper lines may be reduced down to 3/4" or 1/2" You may have several shut off valves in your home near the water meter, near the hot water tank and under individual sinks. When adding plumbing fixtures to your basement, you will want to know where these shut off valves are located and which ones you will need to shut off in order to add basement plumbing fixtures.

Drain Waste Vent

The Drain Waste Vent (DWV) part of your plumbing system carries waste out of your house to a city sewer system or a septic tank. Drain lines rely on gravity to move waste. Check your basement to determine where the DWV pipes exit your home. If the main DWV exits above your basement floor, you may need to install an ejector pump before you can add a bathroom in the basement. The DWV system also includes vent pipes which allow air to enter the drainpipes so wastewater will flow out properly. Examine the pipes in your basement and watch this video before you get started to help you understand the system better.

Installing New Plumbing

Installing new plumbing will require you to tie into both the existing Supply lines and the DWV in your home. You should have a good understanding of plumbing before you attempt this. If you are not a licensed plumber you should at least have a plumber on speed dial in case you get in over your head. Also check out our selection of plumbing videos listed to the left. We have picked out a that may help you with new plumbing installations for your basement. Plumbers say you only need to know three things about plumbing: Hot's on the left, Cold's on the right and Sewage doesn't run uphill!

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. Stub-Out: Short lengths of pipe installed during rough-in to which fixtures and drains will eventually be installed. basement_stub_in (572K) . Stub-Out: Short lengths of pipe installed during rough-in to which fixtures and drains will eventually be installed.