Yes, a sewer backup can happen in a house without a basement. When the main line is blocked, wastewater rises out of the lowest drain in the home, which is often a first-floor shower, tub, or toilet.
Where the Backup Shows Up
Water always looks for the lowest exit. In a slab or crawl space home, that is usually a ground-floor tub or shower drain, since they sit lower than sinks. Toilets on the lowest floor are another common spot. You may also see water near an outdoor cleanout, or notice the toilet water level rising when other fixtures drain.
Warning Signs
- Water rising in the tub when the toilet is flushed
- Gurgling from drains when the washing machine empties
- Slow drains in every bathroom at once
- Sewer smells near ground-floor drains
- A toilet that bubbles or will not flush fully
What Causes It
The causes are the same as in homes with basements: grease and wipes in the main line, tree roots, a sagging or broken pipe, or a public sewer that is overloaded during heavy rain. In crawl space homes, a broken pipe under the house can also leak sewage into the crawl space, where it may go unnoticed for a while.
Steps When the Lowest Drain Overflows
Stop using all water in the house. Keep people and pets away from any backed-up water. Do not use chemical drain cleaners. If neighbors are having the same issue, contact your local sewer authority, since the public line may be involved.
If you notice a sewer smell coming from below the floor, have the crawl space checked. Wear protection and avoid entering it if there is standing sewage.
When drains throughout the house back up, clearing the main line and finding the cause is the next step. For homes on slabs or crawl spaces, you can ask a plumber about where the line runs by calling (833) 603-1840.