How to Install Residential Drain Sewer Lines

In a typical installation, a lateral is the piping connecting a house to the municipal branch or main sewer line under the street. Pipes usually of 4 inches are installed below the frost line in trenches that are sloped properly. The slope is a key factor in how well the pipe drains by the force of gravity. The following five steps comprise the basic installation process of a sewer lateral. Local code authorities oversee all installation details and must approve any installation through several inspections.

Estimating Elevations

Sewer pipe installation has two main steps. First, determine the distance the pipe needs to go and the elevation of each end. An installation of a sewer pipe into a home begins where the common drain exits at the foundation. At a connection known as a tap, where the line connects to the city branch or main, it then slopes downwards. Elevations can be measured and laid out with laser levels, GPS, or traditional surveying equipment. 

Slope Calculation

In order to calculate the initial slope, initial elevation and pipe length are used. When you subtract from the elevation starting point, you get the total change in elevation. The slope of the pipe is determined by dividing the drop by the total run (length).

So the total drop is 2 feet if the pipe reaches a depth of 6 feet and a depth of 4 feet starts at a house that is 4 feet deep. If the pipe run is 80 feet, the slope will be:

2/80 equals 0.025 or 2.5 percent.

There is a minimum drop or slope requirement of 2 percent or 2 feet per 100 feet of a run for laterals in most areas. Although the slope needs to be in compliance with the local codes, in reality, it may be a little steeper than this target. Too steep slopes can cause liquids to run faster than solids, causing clogs. Too shallow slopes don’t generate enough speed to drain properly.

Make a trench and lay the bedding

In order to prevent unnecessary disturbance of the soil, lateral trenching must be done very carefully. To reduce settling, disturbed soils should be firmly compacted. There are several different ways to make trenches narrower, and this requires precise knowledge of the pipe location. Sometimes larger trenches are needed.

Ideally, the trench’s bottom should be smooth and compacted, with the slope following the desired trajectory. The trench is typically lined with bedding material, such as sand, in order to provide continuous support for the pipe. Sand slopes easily, while soil does not, so fine-tuning of the slope can be achieved before pipe installation.

Put the pipe in place

Installers typically install sewer pipe section-by-section, typically starting at the base of the pipe and working up to the top elevation. Today’s drain pipes usually consist of PVC and are attached with a gasket or with solvent glue. Local codes specify the various types and sizes of pipe, including the standard pipe size which is four inches. 

A small amount of gravity will work to prevent leaks at the pipe joints so that the bell (female) end will face uphill. Typically, one or two cleanouts are required at the house end so that the pipe can be monitored or cleaned with a sewer auger. In general, the connection to the city main follows the city’s specifications. 

Fill the trench with backfill.

In order to finish the sewer lateral installation job, the trench must be backfilled after it passes the final inspection. The backfill procedure typically begins with a layer of sand protecting the pipe and eliminating any voids that may exist around it. Afterward, the trench is filled with earth, which is added one layer at a time. Each layer is compacted strictly to prevent settling in the future.

Installation of a warning tape on top of the first layer of compacted soil is a good idea, sometimes necessary. The pipe marking will alert crews to its presence so that no damage will occur during excavating operations near it.

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