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Why does my house smell like sewer?

By the PlumbingRepairCost editors · Last updated 2026-10-05 · How we source these figures

Caution

When a sewer smell means leave

If it could be natural gas: sewer gas and the odorant in natural gas can both smell like rotten eggs (Illinois Department of Public Health; Fire Department of the City of New York (FDNY)). If you cannot tell which it is, the New York City Fire Department’s instruction is to leave the house and call 911 from a safe distance, without switching lights or appliances on or off (FDNY).
If the smell is strong: Wisconsin’s health department says that if you believe there are high concentrations of sewer gas in an enclosed space, evacuate the building and call the fire department, and avoid creating an ignition source such as a spark from an appliance, a match, or a lighter. If you have headaches, dizziness, drowsiness, or nausea and suspect sewer gas, it says to see a doctor (Wisconsin Department of Health Services).
If you feel ill or the smell suddenly fades while you are still in the room: Illinois’ health department says that at higher levels hydrogen sulfide can overwhelm the nose so you can no longer smell it (Illinois Department of Public Health). Get to fresh air.
If sewage is backing up, keep children and pets out of the area, and wear rubber gloves and eye protection for any cleanup (Washington State Department of Health).

The short answer

Sewer gas is a mix of gases from decaying waste, including hydrogen sulfide and methane. Wisconsin’s health department says it can enter a home through a floor drain, a leaking or blocked roof vent, or foundation cracks when the gases are in the soil (Wisconsin DHS). Illinois points to dry traps in sewer drains (Illinois DPH). Finding where the smell is strongest is the first step.

What people usually report

A rotten egg or sewage smell in a basement, a guest bathroom, or a laundry room, sometimes only after the house has been closed up, on windy or cold days, or after a fixture has gone unused for weeks.

What official sources say the causes can include

Dry traps. Sewer drains with dry traps can let hydrogen sulfide into the home (Illinois Department of Public Health). NDSU Extension names basement floor drains and rarely used sinks, showers, and tubs (North Dakota State University Extension).
The roof vent. A leaking or blocked plumbing roof vent is a way in (Wisconsin Department of Health Services), and clogged vents can lead to sewer gas backup (North Dakota State University Extension). In cold weather, moisture in sewer gas can freeze at the top of the vent (North Dakota State University Extension).
Foundation cracks. Where the gases are in soil next to the house, they can enter through cracks in the foundation (Wisconsin Department of Health Services).

What the health departments say about exposure

Wisconsin says exposure to low levels of hydrogen sulfide can cause eye and respiratory irritation, dizziness, drowsiness, headaches, and nausea, and that extremely high concentrations can cause loss of consciousness and death (Wisconsin Department of Health Services). Illinois says you can smell hydrogen sulfide at lower levels than may cause health effects, so smelling it does not always mean it will make you sick (Illinois Department of Public Health). These are general statements, not an assessment of your home; a strong or persistent smell is a reason to act.

How to find out

Find where it is strongest. Check floor drains and rarely used bathrooms first.
Refill the traps. Wisconsin suggests flushing floor and sink drains with water so traps do not dry out (Wisconsin Department of Health Services), and NDSU suggests doing it every three to four weeks for rarely used drains (North Dakota State University Extension).
Note when it happens. A smell tied to cold weather, wind, or a particular fixture draining helps a plumber check the vent and seals.

If drains are also gurgling or slow, see gurgling drains. If the smell is in water from the tap rather than the air, see water that smells like sewage.

Local help

Who to contact

For a strong smell, the fire department (911) comes first, as Wisconsin’s guidance says. Your gas utility handles anything that might be natural gas. For a public sewer problem outside the house, call your sewer utility; its number is on your bill.

For work on the pipes and fixtures inside your home, hire a licensed plumber and confirm the license before work starts. Our guide to choosing a plumber covers what to ask. License lookups for the areas our city pages cover:

Elsewhere, search your state’s plumbing or contractor licensing board. Some cities issue plumbing licenses themselves.

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Common questions

Sewer smell questions

Is a sewage smell in the house harmful?

The Illinois Department of Public Health says you can smell hydrogen sulfide at lower levels than may cause health effects, so smelling it does not always mean it will make you sick, but at higher levels the nose can be overwhelmed so you cannot smell it. Wisconsin’s health department says low levels can cause eye and respiratory irritation among other symptoms, and that methane and hydrogen sulfide in sewer gas are both flammable. For high concentrations it says to evacuate and call the fire department.

Why does my house smell like sewage even though nothing is clogged?

Health departments and extension services point first to dry traps. The Illinois Department of Public Health says sewer drains with dry traps can let hydrogen sulfide into the home, and NDSU Extension names basement floor drains and drains of rarely used fixtures. Wisconsin also lists a leaking or blocked plumbing roof vent and, where gases are in the soil, cracks in the foundation.

Why does the sewer smell come and go?

A trap that dries out slowly, a fixture used only now and then, or a vent that frosts over in cold weather can all make a smell that appears and fades. NDSU Extension describes moisture in sewer gas freezing at the top of the roof vent in winter, and suggests running water into rarely used drains every three to four weeks.

How do I fix the sewer smell in my house?

Wisconsin’s health department suggests locating where the gas is getting in and trying simple fixes such as adding water to floor drains, and occasionally checking the roof plumbing vent for debris like leaves or bird nests. If the smell persists or you cannot find the source, a licensed plumber can check the traps and vents. A smell you cannot tell from natural gas should be treated as gas: leave and call 911 from outside.

Sources and limits

Fire Department of the City of New York (FDNY), Natural Gas Safety: If you think you smell gas or suspect a gas leak. Checked 2026-10-05.
Wisconsin Department of Health Services, Air: Sewer Gas. Checked 2026-10-05.
Illinois Department of Public Health, Hydrogen Sulfide Gas (fact sheet). Checked 2026-10-05.
North Dakota State University Extension, Prevent Sewer Gas Backup. Checked 2026-10-05.
North Dakota State University Extension, Check Your Sewer Vents. Checked 2026-10-05.
Washington State Department of Health, Sewage Spills: Cleaning Them Up. Checked 2026-10-05.

This page summarizes guidance published by the agencies and organizations listed above. It is general information, not a diagnosis of your home or your water. Guidance can change, so check the linked source, your water utility, or your local health department before acting on it. PlumbingRepairCost is not affiliated with any agency named here. Spotted an error? Email hello@plumbingrepaircost.com and we will check it against the source.