What Causes Sewer Gas Smell in the Basement?

If you’re noticing a strong, foul odor in your basement that smells like sewage or rotten eggs, it could be sewer gas — and it’s not something to take lightly.

At CPR – Complete Pipe Repair, we help homeowners throughout Troy, Dayton, and the Miami Valley track down the source of these smells and fix them for good. Here’s what causes the odor and how we make it go away.

What Is Sewer Gas?

Sewer gas is a mixture of gases produced by decomposing waste. It often includes:

• Methane
• Hydrogen sulfide
• Ammonia

Not only does it smell bad, but in high concentrations, it can also be hazardous to your health, especially in poorly ventilated basements.

Most Common Causes of Basement Sewer Odors

1. Dry Floor Drain or Trap
The P-trap may have dried out if your basement has a floor drain or an unused fixture. That water barrier blocks gas from entering the home. If it evaporates, odors come through.

Fix: Run water into unused drains monthly or pour mineral oil to slow evaporation.

2. Cracked or Broken Sewer Line
A damaged or collapsed pipe beneath your home can leak sewage and gas into the soil, seeping through the foundation or sump pit.

We often confirm this with a video inspection.

3. Clogged or Venting Issues
If your plumbing vent is blocked (often on the roof), gas can’t escape and is forced back into the home through the drains. You might also hear gurgling from fixtures.

4. Failed Sewer Cleanout Cap
If your sewer cleanout in the basement is damaged or not properly sealed, sewer gases can leak right into the room.

5. Root Intrusion or Line Collapse
Roots growing into your sewer line can break the pipe or cause standing wastewater, releasing odors.

We treat these issues with CIPP lining or trenchless repair to fix the problem without excavation.

Don’t Try to Mask the Smell

Air fresheners won’t stop methane or hydrogen sulfide. If you smell sewer gas, it’s time for a professional inspection—especially if you also notice slow drains, bubbling toilets, or damp spots in your basement.

Local Help You Can Trust

We’ve helped homeowners in Dayton, Piqua, Greenville, and Vandalia track down the source and fix the issue without mess or pressure.

Schedule Your Inspection Today

If your basement smells like sewer gas, don’t wait for it to worsen. Call CPR (937) 703-1811 to schedule a no-dig inspection and fix the problem.