Sewer Smell Inside the House?
Here's What's Causing It

A sewer gas smell inside the house is unpleasant but usually traceable to one of a handful of common causes — most of which are relatively simple fixes once you find the source. Here's how to narrow it down.

A Dried-Out P-Trap

Every drain has a P-trap — a curved section of pipe that holds standing water to block sewer gas from coming back up through the drain. If a drain isn't used often (a guest bathroom, a floor drain, a rarely used laundry sink), that water can evaporate, breaking the seal and letting gas through. Running water down the drain for a minute usually resolves this immediately, confirming it as the cause.

A Venting Problem

Plumbing vents let sewer gas escape safely through the roof rather than back into the house. A blocked vent (sometimes from debris, a bird's nest, or ice in winter) can force gas back through drains instead. This is more likely if the smell is intermittent and seems to correlate with weather or wind direction.

A Cracked or Loose Drain Line

If the smell is persistent and not tied to a specific dry trap, a cracked drain pipe or a loose connection — sometimes behind a wall or under a floor — could be releasing sewer gas continuously. This is harder to pinpoint without a camera inspection but is a real possibility if simpler causes have been ruled out.

Sewer Gas Is Worth Taking Seriously

Sewer gas contains methane and hydrogen sulfide, and while brief low-level exposure isn't typically dangerous, prolonged exposure in a poorly ventilated space isn't something to ignore either. If the smell is strong, persistent, or you can't identify the source, it's worth having it professionally diagnosed rather than living with it.

Frequently Asked Questions