Short answer: most sewer smells in a house are a dry trap. Every drain holds a plug of water that blocks sewer gas, and a drain nobody uses loses that water over a few weeks. Pour a jug of water down every unused drain first. If the smell goes away, that was it. If it returns to the same spot, or comes with gurgling and slow drains, the cause is further out.
People search this when the smell is strong enough to notice but not strong enough to tell where it is coming from. Start with the simplest causes and work outward, because most of them cost nothing to rule out.
Causes inside the house
- A trap that dried out. The most common cause. A guest bathroom, a basement floor drain, or a utility sink nobody uses. Pour a jug of water down it.
- A failed wax ring under a toilet. A toilet that rocks slightly, or a smell worst at its base, usually means the seal to the floor has gone. That is a plumber's afternoon.
- A blocked or frozen vent. The stack through the roof lets the system breathe. Blocked by a nest, ice or debris, drains siphon their own traps dry, so the smell moves around the house after every big drain. Gurgling is the tell.
- A basement floor drain without its primer. Some floor drains are fed by a small line that keeps the trap full. When it fails the trap dries out on a schedule, which is why the smell seems seasonal.
Causes outside the house
Three signs point at the sewer line rather than a fixture indoors: the smell comes with gurgling drains or slow emptying, it gets worse after heavy rain, or it is strongest outdoors along the line and near the foundation. Wet ground pushes sewer gas toward the easiest opening, which is often a basement, so a smell that tracks the weather is a reasonable hint that gas is escaping underground.
The outside causes we see most are:
- A cracked or offset lateral. The pipe from the house to the main can crack, shift at a joint, or separate, letting gas into the soil.
- Roots in the line. Roots enter at joints and hold solids, and slow drains usually come first.
- A belly in the run. A settled section holds standing waste, smells, and is why a line that has been cleared twice still misbehaves.
- An abandoned line that was never capped. Old laterals, a removed outbuilding, or a septic tank taken out of service and left open to the house drain. More common on older properties than people expect.
A camera inspection is the test that settles it. With us it runs $200 to $800, driven mostly by how much line there is and whether there is a usable cleanout. It either shows a crack, roots, a belly or a separation, or it shows a sound pipe and tells you the cause is inside. Our camera inspection page explains the process.
Is sewer gas a health concern?
In most cases a sewer smell is an irritant rather than a hazard. The exception is a strong, persistent smell in an enclosed space such as a closed basement or crawl space, which is worth ventilating and taking seriously. If anyone has headaches or nausea that clear when they leave the house, leave the house and get medical advice.
Common questions
Why does my house smell like sewer? Most often a drain that has dried out. Water in each trap blocks sewer gas, and an unused drain loses it to evaporation. Pour water down every unused drain, including basement floor drains, and wait a day.
How do I know if the smell is my sewer line and not something inside? Gurgling drains, a smell that worsens after rain, or a smell strongest outdoors along the line all point outside. A smell confined to one room, especially at a toilet base or an unused drain, is almost always inside.
Do you fix the smell? We fix the outside causes: the lateral, roots, a bellied or collapsed run, and an abandoned line that was never capped. Traps, wax rings, vents and anything inside the wall are a plumber's work, and we will say so rather than sell you a dig. When a job needs both, we bring in a licensed plumber.
Is sewer gas dangerous? Usually an irritant, not a hazard. Ventilate any enclosed space with a persistent smell, and if anyone has symptoms that clear outdoors, get out and seek medical advice.
Still not sure how this applies to your property? That is what a free on-site estimate is for. Call 862-268-2510 or tell us what is going on, and we will give you a straight answer, including when the answer is that you do not need us.
