Have you ever walked into your office, restaurant, or retail space and caught a whiff of that unmistakable sewer odor? A sewer smell in a commercial building is more than just unpleasant—it can disrupt daily operations, drive away customers, and signal that something’s off in your plumbing system.
Unlike residential setups, commercial plumbing systems are much larger and more complex. They handle higher traffic, multiple restrooms, commercial kitchens, floor drains, and even low-use zones that don’t get regular water flow. All these factors make commercial plumbing odors more common and often trickier to diagnose.
In this post, we’ll cover:
- The most common causes of sewer smells in commercial buildings
- How to identify where the odor is coming from
- Practical steps to prevent and maintain your plumbing system
- When it’s time to bring in professional help
By understanding what’s behind these unpleasant smells, you can take proactive steps to protect your property, your team, and your business’s reputation.
Table of Contents
Understanding Sewer Smells in Commercial Buildings
When we talk about a “sewer smell,” we’re typically referring to gases like hydrogen sulfide (which smells like rotten eggs) and methane, both byproducts of wastewater decomposition. In small amounts, these gases are unpleasant. In larger concentrations, they can become a safety concern and affect indoor air quality (IAQ).
Commercial plumbing systems are especially vulnerable because they handle:
- Higher flow volumes and waste loads
- Dozens of connected fixtures across multiple floors
- Floor drains, grease traps, and low-use drain lines
- Multiple vent and stack systems
Unlike residential setups, commercial systems often include floor drains in mechanical rooms, kitchens, and maintenance zones that may go unused for weeks. These unused drains can dry out, allowing gas to escape into occupied areas.
Beyond smell and complaints, sewer gases can corrode metals and pose IAQ risks for employees and visitors. Early identification and maintenance are key to keeping your commercial drainage system functioning safely.
Common Causes of Sewer Smell in Commercial Spaces
Sewer odors rarely come from a single source. Often, multiple minor issues combine, especially in older or high-traffic properties. Here are the most frequent culprits behind sewer gas odor in commercial spaces:
Dry or Evaporated Traps (Floor Drains, Seldom-Used Fixtures)
Every drain has a U-shaped pipe called a trap. It holds a small amount of water that acts as a seal to block sewer gases. In seldom-used drains, the water can evaporate over time, breaking the seal and allowing odor to rise through the floor or fixture.
Areas like storage rooms, mop sinks, or mechanical closets are common problem zones. To resolve the smell, regularly pour water into these drains or install trap primers to maintain the water seal.
Blocked or Clogged Drain or Sewer Lines (Grease, Debris, Roots)
Blockages are one of the most common and disruptive causes of sewer odor. Grease buildup from kitchens, debris from restrooms, or root intrusion in older systems can slow wastewater flow. As waste stagnates, gases accumulate and escape through nearby fixtures.
Regular commercial drain cleaning and hydro jetting services can keep lines clear and prevent clogs from developing into odor-causing backups.
Damaged, Cracked, or Deteriorated Sewer Lines
Over time, commercial sewer lines can crack or deteriorate due to corrosion, ground movement, or simple aging. Even small fractures allow gases and wastewater to leak beneath floors or behind walls, creating stubborn odors that don’t go away with cleaning.
Because these systems are often buried or hidden, the first visible clue may be the smell itself—or slow drains across multiple restrooms or floors. When this happens, a professional trenchless pipe repair service can inspect and rehabilitate damaged pipes without disrupting business operations.
Improper or Obstructed Venting Systems
Vent stacks are the unsung heroes of any drainage system. They equalize air pressure in plumbing lines and release gases safely outdoors. If a vent is blocked by either debris, nesting animals, or roof damage, those gases have nowhere to go except back into the building.
In commercial properties, these vents often connect through mechanical penthouses or rooftop assemblies, where blockages can easily go unnoticed. Periodic inspection and maintenance are essential to prevent vent stack problems in commercial buildings.
Faulty Seals & Poor Fixture Installation
Sometimes the issue is as minor as a loose toilet flange or a missing clean-out cap. These small gaps create direct openings for sewer gases to escape into occupied spaces. Poorly installed fixtures, especially in large restrooms or retrofitted spaces, can amplify the issue.
Facility teams should regularly check that every clean-out cap, toilet base, and drain seal is tight, properly sealed, and free of deterioration. These small maintenance tasks can save hours of troubleshooting later.
Increased Load from Food Service, Grease Traps & Shared Systems
Restaurants, cafeterias, and mixed-use commercial spaces often share drainage networks with other tenants. When grease traps are neglected, the buildup doesn’t just cause slow drains—it can emit a foul, rancid odor throughout the building.
Implementing a consistent maintenance schedule and scheduling grease trap repair and replacement when needed will help reduce odor complaints and prevent plumbing blockages in shared systems.
How to Diagnose the Source of the Odor in a Commercial Building
Locating the source of a sewer gas leak in a large building can feel like detective work. The key is to take a systematic approach:
1. Map the Odor’s Location and Pattern
Note where the smell is strongest and when it occurs. Certain areas (such as restrooms or kitchens) may experience odor only during specific times of day or system use.
2. Review Building Plumbing Drawings
Identify the locations of all traps, vent stacks, clean-outs, and floor drains. Comparing drawings to real-world layouts can help pinpoint overlooked problem zones.
3. Inspect Seldom-Used Drains and Fixtures
Inspect roof vents for debris, bird nests, or ice blockage. Ensure they’re located well away from HVAC intakes that might draw in exhaust gases.
4. Check Vent Outlets and Roof Assemblies
Inspect roof vents for debris, bird nests, or ice blockage. Ensure they’re located well away from HVAC intakes that might draw in exhaust gases.
5. Use Diagnostic Tools
Professionals can employ pressure or differential tests, smoke tests for vent leaks, and sewer camera inspections to detect cracked lines or leaks beneath the surface
A routine sewer line inspection can reveal these issues before they become major odor problems or air quality concerns.
Seeing These Signs?
Don’t ignore the warning signs. Contact HVAC professional today!
Preventive Maintenance & Best Practices for Commercial Buildings
Preventing sewer smells in commercial spaces isn’t just about fixing what’s broken—it’s about maintaining what works. Regular plumbing maintenance and awareness can prevent most odor issues before they ever start.
Below are the best practices every facility manager should integrate into their maintenance checklist:
Schedule Regular Inspections of Floor Drains and Seldom-Used Fixtures
Floor drains in storage rooms, janitor closets, and other low-traffic areas are prime culprits for dry traps. Include them in weekly walkthroughs to ensure water is present in each trap. If your facility has trap primers, test them to make sure they automatically refill the traps as designed.
Implement a Grease Trap Program in Food Service Areas
Commercial kitchens generate high volumes of fats, oils, and grease (FOG). Without proper care, these materials congeal in drain lines, leading to odors and costly backups. Establish a consistent grease trap repair and replacement schedule, train kitchen staff on proper disposal practices, and use drain strainers to capture solids before they enter the system.
Perform Regular Sewer Line Cleaning and Camera Inspections
High-volume commercial drainage systems benefit from periodic hydro jetting services to remove built-up grease, scale, and sediment. Combining jetting with routine camera inspections helps catch potential leaks or obstructions before they cause widespread odors.
Training and Collaboration Between Facility Managers and Occupants
Occupants can be the first to notice subtle odor changes. Encourage staff to report smells promptly and record the date, time, and location. Facility managers can then trace these reports against maintenance logs to identify recurring trouble spots. Collaboration turns casual observations into early warning systems.
Vent System Maintenance
Because vent stacks are often on the roof, they’re easy to forget—but critical to system balance. Regular roof inspections can catch blockages or corrosion before they restrict airflow. Always ensure that vent outlets are clear and not located directly below HVAC air intakes, which could pull sewer gases back inside.
Seal All Clean-Out Caps and Fixture Seals
Loose toilet bases or open clean-out caps are small details that can lead to big odor problems. Verify that all caps are tightened and that seals around toilets and floor fixtures are intact. Minor re-sealing now can prevent major odor complaints later.
Monitor HVAC Systems and Indoor Air Quality
Your HVAC system influences air movement throughout the building. Ensure air returns or intakes are not pulling in exhaust from plumbing vents. Integrate IAQ monitoring to detect abnormal gas levels or pollutants. For complex systems, consider consulting professionals specializing in commercial HVAC repair and installation for balanced ventilation and cleaner air circulation.
Safety Considerations & When to Act Immediately
Not every sewer smell is an emergency—but in a commercial setting, ignoring it can quickly turn into one. Strong, persistent odors may be signs of system failure or a dangerous gas buildup.
Here are key red flags facility teams should never ignore:
- Widespread odor affecting multiple zones or floors
- Smells are present during off-hours when plumbing use is low
- Occupant complaints of nausea, dizziness, or headaches
- Odor near mechanical rooms or basements (where gases can accumulate)
- Suspected methane buildup—remember, methane is both odorless and flammable
If these issues arise:
- Evacuate the affected area immediately if gas concentration is suspected.
- Contact a licensed commercial specialist for gas detection and system inspection.
- Increase ventilation temporarily and isolate problem drains until professionals arrive.
Contact Andrew’s for Sewer Smell Solutions
Sewer smells in commercial buildings are more than unpleasant—they’re often warning signs that your plumbing deeper needs attention. Whether caused by dry traps, clogged lines, or damaged venting systems, these odors typically point to maintenance gaps that can be solved with proactive care.
By prioritizing routine inspections, grease management, and sewer line maintenance, facility managers can prevent sewer odors and keep tenants and employees comfortable year-round.
If you’re dealing with consistent commercial plumbing odors or you suspect a gas leak, don’t wait for it to worsen. At Andrew’s, we offer a full suite of commercial mechanical, plumbing, and construction services.
