Simple tests first

Many Mayfair basements were finished decades after the house was built, often over bare slabs with no vapor barrier.

  1. Fill every trap

    Run water into each floor drain and unused fixture.

  2. Wait and smell

    Check again after ten minutes and an hour.

  3. Use water in sequence

    Run laundry or a shower and watch for smell.

  4. Record

    Write down results next to the time.

Why older plumbing is a suspect

Older houses can have older pipe materials and venting arrangements, and a house that has been remodeled may have vents that no longer connect as intended. A drain that is dry or a vent that is blocked can let gas into the basement.

A smell that appears when water runs is almost always connected to the drain system. A smell that appears only in humid air more often relates to moisture. Telling these apart is the first job.

Seasonal use matters too. A utility sink or floor drain used only in summer will dry out in winter, and the smell returns when the heating season begins and air moves through the house differently.

Some households put a small amount of mineral oil or a trap seal product over trap water to slow evaporation. Ask a plumber whether that suits your fixtures before trying it.

Take care with chemical drain products. They do not fix a dry trap or a vent problem and may damage older pipes.

Notice the order of events. If the smell begins within a minute or two of running water, think drains and traps. If it builds over hours with humid weather, think moisture.

Finally, remember that more than one cause can be present at once. A dry trap may explain a sour smell on some days while damp materials explain a musty one on others, so retest after each fix.

Terms

Trap
The curved part of a drain that holds water to block gas.
Vent
A pipe that lets air into the drain system.
Cleanout
An access point for clearing a drain.

Questions for a plumber

  1. Which fixtures are vented and where do the vents end?
  2. What is the material of the main drain?
  3. Is a camera look appropriate?
  4. What would you check first and why?
Map of Mayfair. It shows an area, not an office or a job site.

Common questions

Should I run a camera immediately?

Usually not. Do traps and vents first.

Is a sewer smell dangerous?

Sewer gas can be harmful in strong concentrations. If the smell is strong or you feel unwell, ventilate and seek professional help.

Will pouring bleach help?

It does not fix a dry trap or a vent problem and can harm pipes.

General information for Hilltop, not a quote or professional advice. In an emergency, call 911.