Skip to content
Burst pipe or backup? Close the main valve, then call.A plumber answers (365) 363-2754Call now
Ajax Plumbing Company Ajax PlumbingCompany · Durham Region
Kitchen sink full of dishes by a window
Kitchen sink full of dishes by a window

Sewer gas downstairs

A sewage smell in the basement, traced to its source

Sewer gas has a sharp, unmistakable smell. In most basements it is getting in through a gap in a seal, and the gap is usually easy to find.

  • A dry floor-drain bend nobody has topped up since spring
  • A wax ring under a basement toilet that has flattened or shifted
  • A loose or missing cleanout cap on the main stack
  • A cracked ABS fitting or a split cast-iron hub behind drywall
Call a plumber now(365) 363-2754A plumber answers the phone
  • Licensed & insureddetails on request
  • A plumber answersnot a call centre
  • See the problem firstthen choose the fix
  • Ajax · Pickering · WhitbyDurham Region

At a glance

Symptom
Sewer gas downstairs
First move
Refill the floor drain trap

Where sewer gas gets in

The drain system is meant to be gas-tight from the fixtures to the street. A smell in the basement means one of the seals in that chain has failed. In finished Ajax basements we usually trace it to one of a handful of spots, most of them within a few metres of the furnace room.

The common culprits

  • A dry floor-drain bend nobody has topped up since spring
  • A wax ring under a basement toilet that has flattened or shifted
  • A loose or missing cleanout cap on the main stack
  • A cracked ABS fitting or a split cast-iron hub behind drywall
  • A sump pit that also receives laundry water and has no sealed lid
  • A backwater valve flap held open by debris

The checks to do first

  1. Tip a pail into the floor grate, followed by a tablespoon of mineral oil to slow evaporation.
  2. Rock the basement toilet gently. Any movement at the base points at the wax ring and flange.
  3. Find the cleanout on the stack near the front wall and check that the cap is tight.
  4. Sniff along exposed pipes with the furnace fan off. Gas is strongest near the leak.

How we find and fix it

When the easy checks do not settle it, we run a smoke test: the drain system is sealed at the roof vent, harmless theatrical smoke is pushed in, and it shows up wherever a joint is open. From there the repair is specific. A wax ring and closet bolts get replaced, a flange gets a repair ring if it has cracked, a cleanout gets a new threaded plug, and a failed fitting is cut out and rebuilt with new ABS and solvent cement. Cast iron with a split hub is replaced in sections with no-hub couplings.

Local tip

Durham Region and the Town of Ajax have both encouraged backwater valves in flood-prone basements. A valve that has not been opened and cleaned in years can hold sewage and smell. Check the current program terms before any upgrade work.

When to call straight away

If the smell comes with a rotten-egg note near a gas appliance, that may be natural gas rather than sewer gas. Leave the house and phone the gas utility from outside. For a sewage smell with water coming up a drain, call the shop line.

Questions we hear on the phone

Is sewer gas harmful?

In the small amounts a dry trap lets in, it is mostly unpleasant, but it should not be ignored. Larger exposures in a closed basement are a health concern.

How often should a floor drain be topped up?

Every few weeks for a drain that never gets water, or fit a trap seal primer or insert.

Call now(365) 363-2754