How deep is my house sewer line?

Author: Lilliana Okuneva II  |  Last update: Monday, August 4, 2025

The sewer pipe(s) that leave your house and flushes everything into the sewer main can be anywhere from four-feet to ten-feet under ground depending on if you have a basement or your house is built on a slab. Some sewer pipes are installed deeper than that.

How do you find out how deep your sewer line is?

Contact Your City's Engineering Department

You could also contact someone in your city's zoning office. In most cases, you'll be able to know where your sewer line is and how deep it's buried. Depending on the city you reside in, you could even get a copy of various helpful documents, like your property map.

How far down is a sewer line on a house?

Sewer lines come in a variety of depths. They can range in depth from 12″ to 30″ and can be as deep as 6+ ft. Often, it's only a matter of the environment and climate.

How deep does a residential sewer line have to be?

Residential sewer line pipe depths range from as shallow as 18 to 30 inches in depth or 5 to 6 feet deep. However, in colder climates where freezes occur, you often see sewer line depths ranging from 4 to 8 feet deep. This ensures the pipes are below the freeze line.

How deep to dig for a 4 inch drain pipe?

The trench should be about 18 inches deep and 9 to 12 inches wide.

How Your Home Plumbing Works (From Start to Finish) | GOT2LEARN

How much drop does a sewer line need?

But do you know the proper slope? The ideal slope of any drain line is ¼ inch per foot of pipe. In other words, for every foot the pipe travels horizontally, it should be dropping ¼ inch vertically.

How do I know where my sewer line runs?

Dial 811

Probably the most convenient method, you can dial 811 in the United States. This national hotline connects you to your local utility company, allowing you to request that utility professionals come to your property and mark the location of various underground utilities, including your sewer lines.

How deep should a sewer line be under a slab?

Believe it or not, plumbing pipes under a slab house foundation is typically 12 to 24 inches deep. The pipes are installed into trenches and then buried before the rebar, wire mesh, and concrete slab are poured.

How far down are house water lines buried?

Your water line must be buried at least 12 inches below the frost line to meet local code requirements. However, a minimum depth of 6 inches below the frost line is often recommended for extra security against freezing.

How many sewer lines does a house have?

Not in most homes. Ordinarily, you have one sewer line that is intended to primarily carry what's known as “black” water; water from the toilets into either the city sanitary sewer system or into your own septic tank.

How do I find the plumbing diagram for my house?

Get a Residential Plumbing Diagram from the County Clerk

This local government professional typically has access to your neighborhood's plumbing diagram and can send it your way to help you find the main sewer line.

What is the correct fall for sewer pipe?

Pipes must slope slightly downhill to drain properly. The standard slope is anywhere from ¼ inch to 3 inches per foot depending on the use. An accurate calculation is essential for properly functioning plumbing.

How much does it cost to fix a clogged sewer line?

You will likely pay around $350 to $650 to have a plumber unclog a main sewer line unless you have complications like serious damage to the line.

How many sewer cleanouts does a house have?

Many homes have two clean-outs (see below). One is near the foundation of the house and the second is at or near the property line. First, check the clean-out next to the house to see if it has water in it. If it doesn't contain any water, then you know the blockage is somewhere in the house plumbing.

What size is my main sewer line?

The most common sewer pipe size is four inches in diameter, but there are also six and eight-inch pipes available, which are also sometimes referred to as concrete storm sewer pipe sizes.

How deep should a sewage drain be?

In general, pipe runs made of blue MDPE should be buried at least 750mm below finished ground level. In addition, they should be positioned 350mm from other pipes and utilities. Alternatively, they can be buried in a trench that is at least 300mm wide and as deep as the pipe itself.

Does sewer pipe go under footing?

Yes, your main water line can definitely (and usually does) run underneath the footing. Your sewer line also usually needs to run under the footings to allow for downward slope from any plumbing drains in the basement to the sewer main.

How do I test my main sewer line?

Test Balls for Drainage Lines

To start the process, make sure your main line sewer cleanout is clear of debris and liquid. Next, insert the test ball and inflate it so that it blocks the main line. Fill the sewer system with water and observe the water level for 15-20 minutes.

What does the main sewer line look like?

You may spot a 3 to 4-inch diameter pipe peeking out of the slab floor of the basement. The sewer drain pipe could be made of plastic or cast iron; it might be copper or brass in rare cases. The stub-out will have a screw-in plug coupled with a square-head lug on it, representing your access to the main drain.

How to unclog main sewer line?

Your step-by-step guide: How to clear a main sewer line clog
  1. Step 1: Loosen the cap on the drain pipe. ...
  2. Step 2: Open the cap and let the buildup drain out. ...
  3. Step 3: Feed the auger cable into the drain pipe. ...
  4. Step 4: Run the auger until the clog is clear—and beyond. ...
  5. Step 5: Hose down the pipe and auger cable.

How much drop do you need for sewer?

Pitch on a sewer line for a building or home

In the cases of a 6″ sewer line the minimum recommended pitch on a sewer line is 1/4″ per foot, or about one foot for a fifty-foot run.

What is the average depth of a sewer line?

Ask “How deep are residential sewer lines buried?” and you're likely to get a quicker answer than anywhere else you might look. On average, trenches should be around 12-24 inches-deep, and wide enough to house your pipe comfortably before filling it in with soil and sod.

How much does it fall for a 3 inch sewer line?

Two-percent slope is required for 21/2-inch (64 mm) diameter and smaller pipe, and 1-percent slope is required for 3-inch (76 mm) diameter and larger pipe. Drainage pipe can always be installed with greater slopes.

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