What Causes A Sewer To Backup?

Sewer backups can cause tremendous damage to the interior of a building. Unfortunately, building sewers are often not maintained by private property owners until a disaster strikes. Out of sight, out of mind, is a typical approach to building sewer maintenance and operation by many. Knowing the cause of sewer backups will keep building sewers flowing and free of debris.

What are the biggest contributors to sewers backups in private properties?


Roots from trees and shrubbery are drawn to the water inside sewer pipes. When the tree roots reach an opening in a pipe the roots will grow into the pipe to reach the nutrients and moisture inside. After the roots reach the inside of the pipe they will continue to grow, causing a blockage and preventing solids to move in the pipe. Root removal is a maintenance issue.

Engineering Sewer Info

Fats, Oils and Grease (FOG)  

Fats, Oils and Grease (FOG) occur when cooking fats are poured down the drain and coat the inside of the pipes. These products harden and stick to the inside of the sewer pipes, which build up and may eventually cause a blockage in the sewer pipe.

Engineering 3 Sewer grease

“Flushable” Wipe and cloth-like products

Cleaning wipes, baby wipes, and other wipes that are described as “disposable” or “flushable” generally do not dissolve when flushed the way toilet paper does. Instead, they accumulate in sewer pipes causing clogs and backups. 

Engineering 3 Sewer Paper Buildup

Objects not meant to be flushed

Your toilet is not a trash can. Examples of what people flush that should not be flushed include:

  • Aquarium gravel or kitty litter
  • Sanitary napkins
  • Rags 
  • Cotton swabs or other products
  • Sponges
  • Toys
  • Disposable toilet brushes
  • Plastic or rubber items of any kind
  • Food wrappers

The only thing that should be flushed down the toilet besides human waste is toilet paper.  Flushing any of the products listed above can lead to a building sewer to back up.

 Deteriorated pipe material and structure failure

The first sewers in Nashua were constructed about 1870 and were connected to houses built around that time or even earlier.  In most cases, the building sewer pipe is as old as the building.   Sewer pipes collapse due to shifting soil, settling, or changes on the ground above. Deterioration of the material of an older pipe can cause the pipe to crack, break or collapse. 

Building sewers were first constructed of clay or unreinforced concrete. Starting about the 1940s, new pipe materials known as Bermico, transite, and asbestos cement began being introduced for building sewers. These materials have been known to deteriorate faster than other pipe materials like clay or reinforced concrete.  Since about 1980, building sewers have been generally constructed of a type of plastic pipe known as PVC.  Knowing the age of your property and pipe material can assist in making a decision about repairing or replacing the building sewer.

Deteriorated pipe or pipe that is shown to have collapsed may need to be repaired or replaced.

 Building sewers need maintenance

Like your roof, siding, windows, and large appliances, your building sewers require maintenance.  Know the age of your property because that is likely the age of your building sewer.  Stop the backup before it happens. If you have slow moving water after a flush, maintenance of your building sewer may be needed.  Call a plumber that specializes in maintaining building sewers.   

 How to avoid building sewer backups?  

Taking these simple steps can help keep the flow going, and prevent costly overflows and damage. 

  • Remove vegetation near your building sewer. 
  • Do not flush any paper like product down your toilet other than toilet paper.
  • Gather fats, oils and grease in a container to be thrown away.  Do not put down the drain.