USA Expert Plumbing

Sewer backup in the basement: what to do first

By USA Expert Plumbing Editorial Team. Updated . 2 min read.

Short answer

Stop using water anywhere in the house so you do not add to the backup, keep people and pets away, and avoid touching the sewage. Turn off power to the basement only if you can do it without standing in water. Call a plumber or drain service to clear the line, and a water damage company for cleanup. Photograph everything for insurance.

In this guide
  1. First steps
  2. Common causes
  3. Clearing the line
  4. Cleanup
  5. Insurance
  6. Prevent the next one
  7. What cleanup costs depend on
  8. Questions to ask the plumber

A sewer backup usually shows up first at the lowest drain in the house, often a basement floor drain or shower. Sewage carries bacteria and viruses, so safety comes first.

First steps

  1. Stop running water, flushing toilets, and using the washer or dishwasher.
  2. Keep children and pets away from the area.
  3. Do not wade into sewage. If you must go near it, wear waterproof boots and gloves.
  4. If water is near outlets or appliances, turn off power only from a dry location.
  5. Call a plumber or drain cleaning company to clear the main line.
  6. Photograph the damage before cleanup.

Common causes

  • A clog in the main sewer line from grease, wipes or roots
  • A collapsed or sagging sewer line
  • Heavy rain overwhelming a city sewer
  • A failed septic system, for homes on septic

Clearing the line

A plumber usually snakes or jets the main line through a cleanout, then may run a camera to find the cause. See our drain cleaning cost, sewer camera inspection cost and sewer line replacement cost guides for typical prices.

Cleanup

Sewage-soaked carpet, drywall and insulation usually need to be removed, and hard surfaces disinfected. Many homeowners hire a professional water damage company for this. Open windows for ventilation and wash thoroughly after any contact.

Insurance

Standard homeowners policies often exclude sewer backups. Coverage usually requires a separate water or sewer backup endorsement. Check your policy, and consider adding it if you have a finished basement.

Prevent the next one

  • Keep wipes, grease and paper towels out of drains.
  • Have roots cleared on a schedule if they are a recurring problem.
  • Ask a plumber about a backwater valve, which can stop city sewer water from flowing back into the house.

What cleanup costs depend on

  • How much of the basement was affected and for how long
  • Whether carpet, drywall, insulation or furniture must be discarded
  • Whether the basement is finished
  • Whether the main line needs more than cleaning, such as a spot repair or replacement

Questions to ask the plumber

  • Where exactly was the blockage, and what caused it?
  • Can I see the camera footage?
  • Is the line damaged, or was it only a clog?
  • Would a backwater valve or a cleanout make sense for this house?

Common questions

Is sewage in the basement dangerous?

Yes. It can carry bacteria and viruses. Avoid contact, wear protective gear, and consider professional cleanup.

Does homeowners insurance cover sewer backup?

Often not by default. It usually requires a sewer or water backup endorsement.

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