Finding the source of a sewer smell in Salem homes

Every drain in your house connects to the sewer, and the only things keeping that air out of your rooms are water-filled traps, sealed joints and a vent pipe that carries gas up through the roof. When one of those fails, the smell is your first clue. It can drift a few feet or travel through a wall cavity, so the room where you notice it is not always the room with the problem.

Some causes take seconds to fix, like a guest shower drain that dried out. Others hide under the house, where a broken joint lets gas and sometimes wastewater into the crawlspace. We work from the easy checks to the deeper tests, so you do not pay for smoke and camera work a cup of water would have solved.

Dry traps and other quick causes of sewer odor

A trap holds a few inches of water that blocks gas from the sewer. In a basement floor drain, a guest bath or a laundry standpipe that rarely gets used, that water slowly evaporates until the seal is gone. Running water into each unused drain is the first thing we try.

Loose or missing cleanout caps are another common source. A cap knocked loose in the crawlspace, or left off after an earlier cleaning, gives sewer gas a direct way out, and the smell rises through the subfloor and into the rooms above.

Wax rings, vents and hidden pipe failures

A toilet sits on a wax ring that seals it to the drain flange. If the toilet rocks, or the ring has slumped over the years, gas leaks out at the base and you smell it most right after a flush. Resetting the toilet on a new ring usually ends it.

A cracked vent in an attic or wall, or a joint that pulled apart when the house settled, can release gas inside the building. Under the floor, a broken drain joint or rotted cast iron lets gas and moisture into the crawlspace, which often shows up as a smell near floor registers.

How a smoke test finds a gas leak in the pipes

When the simple checks come up clean, we use a smoke test. We seal off the system at the roof vent or a cleanout and blow a dense, low-odor test smoke into the drain lines under light pressure. Wherever a pipe is cracked or a seal has failed, smoke leaks out and shows us the spot.

We watch the rooms, the crawlspace and the roof while the smoke runs. A camera then gives us a close look inside any suspect pipe, so we know whether the fix is a new coupling, a short section or a bigger repair.

• Smoke escaping at a toilet base means a failed seal
• Smoke in a wall cavity points to a cracked vent or drain
• Smoke in the crawlspace shows a broken joint or a loose cap

Why a strong sewer smell should be checked soon

A faint whiff from a dry trap is mostly a nuisance. A strong, steady sewer smell with no obvious cause is different. It can mean a drain pipe is open under the house, letting sewage soak into the crawlspace soil and raising moisture right where your floor framing sits.

Sewer gas also carries small amounts of hydrogen sulfide and methane. In a typical house the amounts are low, but a smell that keeps getting worse should be checked within days, not left for months. If the odor seems more like natural gas than sewage, leave the house and call the gas utility.