Sewer Gas Smell in a Minneapolis Apartment? Why We Suspect the Vent Stack

A property manager asked us to look at a second-floor unit in an apartment building in Minneapolis's Whittier neighborhood. The tenant had reported a sewer gas smell between her bathroom and her bedroom, and it was bad enough that she had left the living room window open all night to air the place out. That's not a complaint you can sit on, for the tenant or for the building.

Here is how we diagnosed it, what we think is going on, and what to check first if a tenant in one of your buildings reports the same thing.

How sewer gas is supposed to stay out

Every sink, tub, and toilet has a trap, a bend in the drain that holds a small amount of water. That water is the seal that keeps sewer gas in the pipes and out of the room.

The other half of the system is the vent. Vent pipes connect to the drains inside the walls and run up through the roof. They let air into the drain system so water flows freely and doesn't siphon the traps dry, and they carry sewer gas up and out above the building.

When a vent is blocked or broken, both halves start to fail. Drains slow down and gurgle, traps can get pulled dry, and sewer gas that should be leaving through the roof can collect in the pipes or escape through a crack inside the wall.

The test we ran

We filled the bathroom sink, then let it drain with the faucet still running while covering the overflow opening with a finger. With the overflow covered, the drain can't pull in air from the sink side, so it has to rely on the vent to move air as the water goes down. On a healthy system, the sink drains steadily. This one struggled to drain and acted air-locked, as if the drain couldn't get the air it needed.

We ran the same test on the bathtub and got the same result, though it wasn't as severe. Two fixtures in the same bathroom acting the same way points away from a simple clog in one drain and toward the vent they rely on.

Why we're looking at the whole stack, not just one unit

In many apartment buildings, units stacked directly above one another share the same vertical drain and vent pipe, called the stack. A problem in that stack can show up in any unit on the line, not just the one that called.

Our working diagnosis is that the vent stack serving this line of units is either clogged or compromised:

• Clogged. Debris such as leaves or nesting material can collect at the vent opening on the roof or build up inside the pipe. In a Minnesota winter, frost can also build up at a vent opening and close it off.
• Compromised. Older vent piping, especially cast iron and galvanized steel, can rust through, rot out, or crack after decades inside a wall. A break like that lets sewer gas leak straight into the unit, which could explain why the smell was strongest between the bathroom and the bedroom.

We went upstairs to ask the tenants in the unit above whether they were noticing the same thing, but no one was home. Whether other units on the stack have symptoms is one of the questions we still want answered.

Next step: a camera down the vent stack from the roof

Rather than guess and start opening walls, we've recommended a camera inspection of the vent stack, run from the vent opening on the roof down through the pipe. The camera will show whether the vent is blocked with debris or whether the pipe itself is cracked or rotted out, and if it is damaged, exactly where.

That answer decides the fix. A blockage can usually be cleared from the roof. A failed section of pipe is a plumbing repair at one specific spot, and the footage tells the property manager where that spot is and why, before anyone cuts drywall.

A sewer smell checklist for property managers

Sewer gas is more than unpleasant. It can cause headaches and nausea, and no tenant should have to leave a window open in a Minnesota fall to get through the night. If a tenant reports a sewer smell, here is what we'd check, in this order:

• Rule out natural gas first. Sewer gas and natural gas can both smell like rotten eggs. If there is any chance it's natural gas, have everyone leave and call the gas utility or 911 from outside.
• Run water in drains that don't get used. Floor drains, spare tubs, and fixtures in vacant units dry out. An empty trap is the most common cause of a sewer smell and the easiest one to fix.
• Note where the smell is strongest. A smell concentrated in one room or along one wall points to the drain or vent piping behind it.
• Ask the units above and below. If neighbors on the same stack notice it too, the problem is probably in the stack, not in one unit.
• Watch for slow, gurgling drains. Drains that struggle or gurgle in a unit that smells like sewer gas are a classic sign of a vent problem.
• Get a camera on it before opening walls. The footage shows whether you're looking at a cleaning or a repair, and it gives you something concrete to share with the owner.

Good access makes for a faster diagnosis

One more note for property managers: this visit went quickly because access was set up before we arrived. The work order told us where to park, how to get into the building, and where to find the unit keys, and the tenant left a note describing what she'd been dealing with. Clear access instructions and a short note from the tenant save a return trip and get the diagnosis done on the first visit.

Sewer smell in one of your buildings?

Lucky Dog Sewer & Drain works with property managers across Minneapolis and the western suburbs on drain, sewer, and vent problems in multifamily buildings. We diagnose before we quote, document what we find with photos and camera footage, and price the work flat before we start, so you have what you need to take to the owner. Learn more about our commercial drain and sewer services, or contact us to get a technician out to your property.

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