Why Does a Sewer Smell Come and Go?
What each option costs
| Option | Job | Low | High |
|---|---|---|---|
| Repair | Drain Cleaning | $100 | $400 |
| Replace | Sewer Line Repair | $1,100 | $5,800 |
Common reasons
- A dry trap in a rarely used drain, sink or floor drain. Pittsburgh's lab safety manual says lab odors are frequently traced to these.
- An exhaust fan that pulls gas in through a dry trap. Pittsburgh's guideline describes this with lab exhaust, and a home bath or kitchen fan could act the same way. That last step is our inference.
- A leaking or blocked roof vent, per Wisconsin's health department.
- Cracks in the foundation or leaks in a wall, also from Wisconsin.
What to try first
- Follow your nose to find the room. Wisconsin suggests this.
- Pour water into unused drains. Wisconsin says to flush floor and sink drains with water. Pittsburgh's lab guideline uses a quart once a week or month, which isn't a home rule.
- Note when it happens: after rain, with a fan on, or at certain times. It helps your plumber.
When to call
If adding water doesn't fix it, call a licensed plumber. Wisconsin says a leak behind a wall may need one. Roof vents involve climbing, so we'd leave those to a pro too. If you feel dizzy or sick, or the smell is strong in an enclosed space, leave, avoid sparks and flames, and call the fire department, as Wisconsin says. If it smells like natural gas, leave and call your gas utility or 911 from outside.
Don't trust the fading smell
Illinois and Wisconsin both warn that high levels can overwhelm your sense of smell. So a smell that goes away isn't proof the gas has gone.
Sewer Smell in House? Causes and What to Do
Common questions
Why does sewer smell get worse at night?
Is it dangerous if it comes and goes?
Related questions
- Are GFCI Outlets Required in a Garage?
- Can a Breaker Go Bad Without Tripping?
- Can a Light Switch Cause a Breaker to Trip?
- Can a Roof Leak Be Fixed From the Inside?
- Can a Water Heater Leak Carbon Monoxide?
- Can Breakers Trip for No Reason?
- Can Garage Door Springs Kill You?
- Can GFCI Outlets Go Bad?
Last verified 2026-11-04
- University of Pittsburgh Safety Manual: Dry sink traps (guideline 03-010, for labs, reviewed 2020, not a home rule) — Sewer odors traced to dry traps or unused drains; water seal; exhaust systems can draw gas in; a quart of water weekly or monthly.
- Wisconsin Department of Health Services: Sewer gas — Sources: dry floor drain traps, roof vents, foundation cracks, wall leaks; follow the odor; hire a plumber for wall leaks; high-level response.
- Illinois Department of Public Health: Hydrogen sulfide gas — Faulty plumbing and dry traps; high levels can overwhelm smell.
- Public Service Commission of Wisconsin: Natural gas consumer safety — If you smell gas, leave immediately and call the gas utility's emergency number or 911 from a safe distance outdoors; odor described as rotten eggs, sulfur or garlic.
General information, not professional advice. Conditions, codes and prices vary. Turn off power, gas or water before any work, and hire a licensed professional when in doubt. Cost figures are our estimates, not quotes.