Basement Sewage Cleanup

Cross-section of a house with a basement where sewage rises through the floor drain, with a backwater valve on the line to the sewer main

Why basements take the hit

Wastewater exits at the lowest open point in a plumbing system. In a home with a basement, that is usually a floor drain, basement toilet or shower, or laundry drain. When the main line is restricted, the basement fills while upstairs fixtures still seem to work.

If your home is built over a crawl space instead, see crawl space sewage cleanup.

Signs of a basement sewage problem

Water or sewage rising from the floor drain, especially after laundry or showers upstairs.
Sewer odor in the basement that comes and goes.
A dry floor-drain trap letting sewer gas into the space.
Staining or efflorescence around the drain or along the base of walls.
A basement toilet or shower that gurgles when upstairs fixtures run.

Finished vs. unfinished basements

Unfinished basements

Bare concrete floors and walls can usually be cleaned and disinfected. Stored items in cardboard boxes, fabric and paper that touched sewage are typically discarded; hard plastic and metal items can be cleaned.

Finished basements

Carpet and pad, drywall, baseboard, insulation, and particleboard furniture or built-ins that were soaked are usually removed. Laminate and vinyl plank floors often trap sewage underneath and need to be lifted. Wall cavities are opened to dry and disinfect framing.

The basement cleanup process

Confirm the source is stopped — usually by having the main line cleared.
Check utilities. Furnaces, water heaters and electrical panels in basements are inspected for water contact.
Extract standing sewage and dispose of it properly.
Remove contaminated flooring, drywall and contents.
Clean and disinfect concrete, framing and fixtures.
Dry with dehumidifiers and air movers until moisture readings are normal.
Deodorize and filter the air before reconstruction.

Furnaces, water heaters and electrical in basements

Mechanical equipment often sits in basements. If sewage reached a furnace, water heater, softener or electrical panel, have it inspected by a qualified technician before use. Ductwork on the basement floor or in contact with sewage may need cleaning or replacement.

Contents stored in basements

Basements are often used for storage. Cardboard boxes, paper, fabric and upholstered furniture that soaked up sewage are usually discarded. Hard plastic bins, metal shelving and glass can usually be cleaned and disinfected. Photographs, important documents and heirlooms may be worth setting aside for a specialist to evaluate.

Reducing future basement backups

Ask a licensed plumber whether a backwater valve is appropriate for your home.
Pour water into rarely-used floor drains every few weeks so the trap does not dry out.
Store items in the basement on shelves and in plastic bins, off the floor.
Have the main line camera-inspected after a backup to find the cause.

Basements in Boise and the valley

Older neighborhoods in Boise, such as the North End and East End, include many homes with full or partial basements, often with older clay or cast-iron drain lines. Some newer homes around Meridian and Eagle have daylight basements on sloped lots. See the Boise sewage cleanup page for more on older homes.

Sump pumps vs. sewage ejector pumps

These two pumps are often confused. A sump pump removes groundwater that collects in a pit around the foundation; it is not connected to sewage. A sewage ejector pump serves basement bathrooms and laundry that sit below the level of the sewer line, lifting wastewater up into the building drain.

When an ejector pump fails — from a stuck float, a burned-out motor, a power outage or wipes jamming the impeller — the basin fills and sewage backs out of the basement toilet, shower or floor drain. If your basement bathroom backs up while the rest of the house drains normally, the ejector pump is a likely cause, and a plumber should check it before the bathroom is used again.

Daylight basements and walk-outs

On sloped lots, part of the lower level may be at grade with doors to the yard. These spaces often have finished living areas and bedrooms. Because the lower floor is still the lowest part of the plumbing, it is where backups appear first — and carpet, drywall and furniture in finished spaces raise the stakes for fast extraction.

Odor after a basement backup

Basements trap odor because they have little natural airflow. If a sewer smell lingers after cleanup, likely sources are wet material left behind a wall or under flooring, contamination in a floor-drain trap or ejector basin, or ductwork that pulled contaminated air. Finding and removing the source works; masking sprays and air fresheners do not.

Frequently asked questions

Why does my basement floor drain back up when I do laundry?

The washing machine sends a large volume of water down the drain at once. If the main line is partly blocked, that water cannot get past and comes up at the lowest drain — the basement floor drain.

Can basement drywall be saved after sewage?

Drywall that wicked up sewage is generally removed, typically at least 12–24 inches above the highest wet line, so the framing behind it can be cleaned and dried.

Why does my basement smell like sewer even without a backup?

A common cause is a floor drain trap that has dried out, letting sewer gas in. Pouring water into the drain refills the trap. If the odor continues, there may be a cracked pipe or a failed seal.