Sewer backups can occur for many reasons.
In our experience, the most common cause of sewer backups is an issue with your personal sewer or drain system. Tree roots, for example, can make their way into your sewer lateral pipe and interfere with the movement of waste. This makes it difficult for solids to pass through, so they often don’t. Instead, the solids clump together into a sewer lateral blockage.
When your waste can’t go out the proper path due to a blockage, it will find another place to go. This is usually another drain, usually a floor drain in the basement.
Other common reasons include broken sewer lines, collapsed sewer lines, cracked sewer lines, and much more.
All that being said, sewage backups can also be a return from the sewerage system. If there is a blockage in the sewerage pipes or too much water has entered the sewer system at once, all the sewage will find somewhere else to escape.
Unfortunately, this is usually the nearest, lowest drains – which could be in your basement.