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Sewer Smell in the House? Common Causes in Westminster, CO
Start with the fixtures you rarely use. A dry trap is the most common cause of a sewer smell, and it takes thirty seconds to fix. If the smell persists, the cause is a pipe or a vent.
By the Westminster Plumbing Co. team ·
Check the dry traps first
Every drain has a curved section called a trap that holds water and blocks sewer gas. A floor drain in the basement, a guest bath shower or a rarely used sink can dry out. Pour a quart of water down each one and the smell may stop.
Floor drains need a periodic refill. A little mineral oil on top slows evaporation. Westminster's utility lists a dry trap as one of the causes of a sewer odor in a basement or a room.
Damaged pipes
A cracked or separated drain pipe inside a wall or under a slab lets gas escape. The smell may be stronger in one room and worse after a long run of water. A camera inspection finds the break.
Outside the house, a damaged lateral can smell in the yard. A sunken spot or lush grass over the line is a clue.
Blocked or broken vents
Drains rely on a vent pipe through the roof. A blocked vent lets pressure build, which pulls water from traps and pushes gas into the house. Gurgling drains are another sign.
Nests, leaves or ice in the vent cause it. A plumber can clear the vent and check the connections.
Where the smell points
The location and timing of the smell narrows the cause.
| Where you smell it | Likely cause | Next step |
|---|---|---|
| Basement floor drain | A dry trap | Pour water into the drain |
| Guest bath or rarely used sink | A dry trap | Run water and add a little oil |
| Around a toilet base | A failed wax ring | Reset the toilet with a new seal |
| Throughout the house, with gurgling | A blocked vent or a main line problem | Call for a vent check and a camera |
Toilets and seals
A toilet that rocks has a failed wax ring or a loose flange. Sewer gas leaks around the base, often with a faint odor and a damp floor.
The fix is to reset the toilet with a new seal. It is a short job, and it prevents rot in the subfloor.
Is it dangerous?
Sewer gas contains hydrogen sulfide and methane. In small amounts it is unpleasant. In larger amounts in a closed space it can be a health hazard, and methane is flammable. A strong or lasting smell is a reason to ventilate the house and call.
The city notes that sewer gas is a health and safety concern and recommends a licensed plumber when the smell continues.
When to call a plumber
Call if the smell does not go away after refilling traps, if more than one drain gurgles or if the smell comes with a backup. A plumber can smoke-test the drain system or run a camera through the lateral.
If you smell gas, as in natural gas, go outside before anything else and contact 911 or the gas utility. That is a separate emergency.
Tracing the smell room by room
Walk through the house with your nose and note where the odor is strongest. A smell that is strongest at one drain suggests a dry or failing trap there. A smell that follows you across several rooms points toward a vent or a leak in the drain system.
Pour a quart of water down every rarely used drain, including floor drains and the tub in a guest bath. Wait an hour and check again. If the smell fades, the trap was dry, and running the fixture monthly will prevent a repeat.
What a plumber checks
A professional looks at the vent stack on the roof for blockages, inspects the visible drain pipes for leaks and may run a camera down the main line. Smoke testing can reveal cracks that release gas into walls without leaving any stain.
Sewer gas is mostly an annoyance in small amounts, yet persistent odors should not be ignored. They mean a seal is broken somewhere, and the same break may leak water over time. Fixing it early costs less than repairing damage from a slow leak.
Odors that need faster action
A smell with gurgling drains, water backing up in a tub or standing water in a basement drain suggests the main line is partly blocked. Stop running water, since each load adds to the problem, and call for clearing and a camera check.
A smell that comes with a rotten egg odor strongest near gas appliances may be natural gas, not sewer gas. Step outside and ring the gas utility. If you are unsure which smell you have, treat it as gas first.
Mold-like smells that follow a sewer odor can mean a slow leak in a drain line inside a wall. A plumber can pressure test the line and find the damaged section before it ruins drywall.
Simple habits that prevent odors
Run water in seldom-used sinks, tubs and floor drains once a month. A little cooking oil on top of the water in a floor drain slows evaporation and keeps the trap sealed between uses.
Keep drain screens clean and avoid pouring grease down the sink. Grease coats pipe walls and produces odors as it breaks down. Collect it in a can and throw it away with the trash.
Common questions
Answers about sewer smell
The floor drain trap may be dry. Pour water into the drain and see if the smell fades. If not, a pipe or vent may be at fault.
Yes. A blocked vent lets pressure siphon traps dry and pushes gas back into the house.
Natural gas has a rotten-egg odor added deliberately. Sewer gas smells more like decay. If unsure, treat it as natural gas and leave first.
Not always, but it can. A camera inspection shows whether the lateral is damaged.
Related services
Sewer Line Repair
Mend a cracked, root-choked or bellied lateral, either as a spot fix or a longer section.
Drain Cleaning & Unclogging
Open clogged kitchen, bath, laundry and main drains, then find out why the stoppage came back.
Keep reading
Tree roots in your sewer line
Roots enter a sewer lateral through tiny cracks and joints. Learn the signs, the options and how to protect the line.
Basement floor drain backing up
A floor drain that bubbles or fills is usually the first sign of a blocked main line. Here is what to do and how to tell groundwater from sewage.
Toilet won't flush: what to check
A toilet that will not flush has a short list of causes. Check the tank, the clog and the bigger line before you call.
Odor that never fades?
Phone in and describe where it is strongest and when it began. The dispatcher then matches you with a nearby contractor.