Sewer Gas Smell in Your Encino or Sherman Oaks Home: Causes and How to Fix It

Published April 30, 2026 • BBC Rooter & Plumbing • Northridge, CA

You walk into your bathroom, laundry room, or kitchen and catch it — that unmistakable rotten-egg odor. It might come and go. It might be strongest in the morning or after nobody has been home for a few days. Either way, if your Encino or Sherman Oaks home smells like sewage, the cause is almost always sewer gas leaking into your living space through a failed seal, a cracked pipe, or a blocked sewer main.

Sewer gas is not just unpleasant — it can be a health hazard. It contains hydrogen sulfide, methane, and ammonia, among other compounds. At the concentrations you typically encounter indoors the risk is mostly headaches, nausea, and eye irritation, but the smell is your early-warning system that something in your sewer or drain system has failed and needs attention before it gets worse.

As a sewer and drain specialist serving the entire San Fernando Valley, BBC Rooter diagnoses and fixes sewer gas problems at their source every week. Here are the most common causes we see in Encino, Sherman Oaks, and surrounding neighborhoods — and what it takes to fix each one.

1. Dried-Out P-Traps: The Most Common (and Easiest) Cause

Every drain in your house — sinks, showers, floor drains, washing machine standpipes — has a P-trap: that curved section of pipe directly below the drain opening. The trap holds a small plug of water that blocks sewer gas from rising up through the pipe and into your home. It is the single most important gas barrier in your plumbing system.

When a drain goes unused for weeks or months, the water in the trap evaporates. With no water seal, sewer gas has a straight path into the room. This is extremely common in guest bathrooms, basement floor drains, and laundry drains in Encino and Sherman Oaks homes where certain fixtures see little use.

The fix is simple: run water in every drain you have not used recently. Two to three cups is enough to refill the trap. If the smell disappears within an hour, a dry P-trap was your problem. Make a habit of running water in unused drains once a month to prevent it from happening again.

2. Cracked or Broken Sewer Line Under the House

Many homes in Encino and Sherman Oaks were built in the 1950s through 1970s with clay or cast iron sewer laterals. After 50 to 70 years in the ground, those pipes crack, separate at joints, or corrode through entirely. When a sewer pipe breaks under the slab or in the crawlspace, raw sewer gas escapes into the soil and migrates upward into the home through foundation cracks, utility penetrations, and expansion joints.

This type of sewer gas leak is persistent — it does not go away by running water in drains because the leak is not at a trap. The odor may be strongest near the center of the house or wherever the main sewer line runs beneath the foundation. You might also notice damp spots on the slab, unexplained mold, or patches of unusually green grass in the yard above the sewer line path.

Diagnosing a cracked sewer line requires a sewer camera inspection. BBC Rooter runs a high-definition camera through the line to identify the exact location, depth, and severity of the break. Depending on what the camera reveals, repair options include trenchless pipe lining (CIPP) for cracks and joint separations, pipe bursting for severely damaged sections, or targeted excavation when trenchless methods are not feasible.

3. Offset or Bellied Sewer Pipe

Even when a sewer pipe has not cracked, ground movement can push pipe sections out of alignment (an offset) or create a low spot where the pipe sags (a belly). Both conditions trap waste, water, and debris in the line. The trapped material decomposes, generating concentrated sewer gas that can back-pressure through drain traps — especially at night when water usage drops and trap seals are weakest.

Bellied and offset pipes are common in the hillside neighborhoods of Sherman Oaks and the expansive-clay soil zones of Encino. The shifting soil slowly displaces pipes over decades. A camera inspection reveals the exact location, and the fix typically involves relining the affected section or, in severe cases, excavating and re-grading the pipe to restore proper slope.

4. Failed Wax Ring or Toilet Seal

The wax ring between the base of your toilet and the sewer flange creates a gas-tight and water-tight seal. Over time — especially in homes with slight foundation settling — the wax compresses, cracks, or shifts, breaking the seal. Sewer gas seeps out from under the toilet base, often noticed as a persistent sewage smell in the bathroom that does not respond to cleaning.

A failed wax ring is a straightforward repair, but the smell it creates is identical to much more serious sewer line problems. If you notice a sewer odor concentrated around the base of a toilet, it is worth checking the wax seal first. However, if the toilet rocks or moves when you sit on it, the underlying flange may also need repair to prevent recurring failures.

5. Blocked Vent Stack

Your home's plumbing vent stack runs from the sewer system up through the roof, allowing sewer gas to escape safely outdoors and maintaining air pressure balance in the drain system. When the vent gets blocked — by leaves, bird nests, tennis balls, or even accumulated debris — sewer gas cannot exit through the roof and instead gets pushed back into the house through drain traps.

A blocked vent also causes gurgling sounds when you flush toilets or run sinks, and slow drainage throughout the house. If you notice the sewer smell plus gurgling drains, the vent is a strong suspect. Clearing the blockage from the roof restores normal venting and eliminates the gas problem.

6. Main Sewer Line Blockage Building Pressure

A partial blockage in the main sewer line — from root intrusion, grease accumulation, or debris buildup — restricts flow and creates back-pressure in the system. That pressure pushes sewer gas backward through trap seals, particularly at the lowest drains in the house. You might notice the smell worsens after heavy water use (multiple showers, laundry, dishwasher running simultaneously) as the partial blockage creates more turbulence and gas release.

Root intrusion is the leading cause of main line blockages in the San Fernando Valley. Mature ficus, magnolia, and pepper trees — which are everywhere in Encino and Sherman Oaks — send roots directly into aging clay pipe joints. BBC Rooter clears root blockages with hydrojetting and then cameras the line to assess whether the pipe needs lining or replacement to prevent the roots from returning.

How BBC Rooter Diagnoses Sewer Gas Problems

Because sewer gas can enter a home through multiple pathways simultaneously, a systematic approach matters. When BBC Rooter responds to a sewer gas call in Encino, Sherman Oaks, or anywhere in the Valley, the process follows a consistent diagnostic sequence:

1. Trap check — every accessible drain is checked for water level. Dry traps are refilled to eliminate the simplest cause first.
2. Visual inspection — toilet bases, cleanout caps, and exposed drain connections are checked for obvious seal failures or missing caps.
3. Sewer camera inspection — a high-definition camera is run through the main sewer line from the cleanout. This reveals cracks, offsets, bellies, root intrusion, and any structural issue generating gas below grade.
4. Smoke testing (when needed) — non-toxic smoke is introduced into the sewer system. It exits at any break in the system — cracked pipes, dry traps, failed seals, damaged vent connections — making the gas entry point visible.

This approach identifies the root cause on the first visit rather than guessing. Every BBC Rooter diagnostic includes recorded camera footage so you can see exactly what is happening inside your sewer line.

Why Sewer Gas Problems Get Worse if You Wait

It is tempting to ignore a faint sewer smell, especially when it seems to come and go. But the underlying causes — cracked pipes, root intrusion, bellied lines — are progressive. A hairline crack in a clay lateral becomes a full separation within months. Roots that have found a joint opening grow rapidly, especially during the Valley's rainy season. A bellied section collects more debris with every flush, accelerating the blockage.

Beyond the structural damage, persistent sewer gas exposure affects indoor air quality. Hydrogen sulfide at even low concentrations causes fatigue, headaches, and respiratory irritation. If anyone in your household has been experiencing unexplained symptoms like these, a sewer gas leak is worth investigating.

Encino and Sherman Oaks: Why These Neighborhoods See More Sewer Gas Issues

Several factors make Encino and Sherman Oaks particularly prone to sewer gas complaints. The housing stock is predominantly 1950s through 1970s construction with original clay and cast iron sewer laterals now well past their expected lifespan. The mature tree canopy — while beautiful — means aggressive root systems are constantly seeking moisture in aging pipe joints. And the hillside terrain in parts of Sherman Oaks creates soil movement that shifts and stresses underground pipes over decades.

BBC Rooter has been diagnosing and repairing sewer lines across these neighborhoods for years. The combination of local soil knowledge, tree-root expertise, and trenchless repair capability means most sewer gas problems can be resolved with minimal disruption to your property and landscaping.

Frequently Asked Questions About Sewer Gas Smells

Is sewer gas dangerous to breathe?

Yes. Sewer gas contains hydrogen sulfide, methane, and ammonia. At the low concentrations typically encountered indoors, it causes headaches, nausea, and irritation. At high concentrations — possible with a major sewer break in a confined space — hydrogen sulfide can cause loss of consciousness. Methane is also flammable. If you smell strong sewage odors, ventilate the area and call a licensed sewer specialist.

Why does my house smell like sewage at night or in the morning?

Sewer gas odors that fluctuate — especially overnight — usually point to a dried-out P-trap, a partial main line blockage creating pressure changes, or temperature-driven gas movement through cracked pipes. Cooler nighttime temperatures can push sewer gas through cracks that remain sealed during warmer daytime hours. A sewer camera inspection identifies the exact source.

How do plumbers find where sewer gas is coming from?

A sewer specialist uses camera inspection and smoke testing. The camera reveals structural damage inside the pipe — cracks, offsets, bellied sections, root intrusion. Smoke testing pushes non-toxic smoke through the system; it exits at any failed seal, dry trap, or pipe break, making the entry point visible. BBC Rooter includes camera inspection on every diagnostic visit.

Can a cracked sewer line cause a gas smell in my house?

Yes. A cracked, offset, or separated sewer pipe allows gas to escape into surrounding soil. That gas migrates upward through foundation cracks, utility penetrations, and the soil itself, entering the home. This is especially common in older Encino and Sherman Oaks homes with aging clay or cast iron sewer laterals.

BBC Rooter & Plumbing • CSLB License #720343 • 8635 Yolanda Ave #6, Northridge, CA 91324 • Serving Encino, Sherman Oaks, Tarzana, Van Nuys, Woodland Hills, and the entire San Fernando Valley. See our FAQ page for more answers to common sewer and drain questions.