There could be a variety of reasons for a sewer gas smell in the basement of a home. It’s important to note that sewer gas can be dangerous as it contains methane, hydrogen sulfide and other harmful gases, so it’s recommended to contact a plumber to diagnose the problem and fix it as soon as possible.
Causes of sewer gas smell in the basement

A blocked or broken sewer line: If there is a blockage or break in the sewer line, gas can escape and make its way into the home through the basement. This can be caused by a variety of factors such as debris, tree roots, or ground shifting. To determine if this is the cause of the smell, the sewer line can be inspected using a camera. If a blockage is found, it will need to be cleared, and if there is a break in the line, it will need to be repaired or replaced. A plumber will be able to diagnose the problem and recommend the appropriate course of action.
A dry P-trap: A P-trap is a plumbing component that is designed to prevent sewer gas from entering the home. It’s a U-shaped pipe that holds a small amount of water, which creates a barrier between the sewer gas and the home. If the P-trap is dry, it may not be functioning properly and could be allowing gas to escape. This can happen if the P-trap is not used often, or if the water in it evaporates. A dry P-trap can be fixed by running water through the drain or by pouring water into it. A plumber can also check if the P-trap is properly installed and recommend any necessary repairs.
Cracks in the foundation: If there are cracks in the foundation, they could be allowing sewer gas to enter the home. This can happen due to age of the house, foundation settlement, or water damage. The cracks should be sealed as soon as possible to prevent the gas from entering the home. A plumber can identify the location of the cracks and recommend a solution, which can range from simple sealants to more extensive foundation repair work.
Vent pipe issues: The vent pipes on a plumbing system allow air to enter the system and prevent a vacuum from forming. If the vent pipe is blocked or damaged, it can cause sewer gas to back up into the home. This can happen due to the accumulation of debris, or if the pipe is not properly sealed. The vent pipe should be inspected and cleaned if necessary, or repaired or replaced if it’s damaged. A plumber can determine if the vent pipe is blocked or damaged and recommend the necessary repairs.
An issue with the septic system: if you have a septic system and the tank is not working properly, it can cause the gas to come into the basement. This can happen if the tank is full and need to be pumped out, or if there is a malfunction in the system. Septic systems should be inspected and serviced regularly to ensure that they are functioning properly. If a septic system is found to be the cause of the smell, a plumber or septic professional will be able to diagnose the problem and recommend the necessary repairs or maintenance.
Other possible causes: A gas leak from the main line or a gas appliance such as a water heater or furnace, or a rotting food in the garbage disposer can also cause the smell. You can also check if your basement has proper ventilation. If there is not enough ventilation, the sewer gas will not have a way to escape, which can cause the smell to linger. In this case, you can install vents or a ventilation fan to help improve air flow in the basement.
What to do about sewer gas smell in the basement
In summary, a sewer gas smell in the basement of a home can be caused by a variety of factors, including a blocked or broken sewer line, a dry P-trap, cracks in the foundation, vent pipe issues, or an issue with the septic system. It’s important to address the problem as soon as possible to prevent the gas from entering the home and potentially causing health issues. A plumber should be contacted to diagnose the problem and make the necessary repairs. The plumber will be able to determine the cause of the smell and recommend the appropriate course of action. They will also be able to repair or replace any damaged or broken components, and ensure that the sewer line, P-trap, vent pipes, and septic system are functioning properly. Additionally, you may want to install a carbon monoxide detector in the basement to ensure that the gas levels are safe.
If you’re looking for help finding the cause of and eliminating sewer gas smell in the basement of your home, please don’t hesitate to call us. We’re top rated local plumbers for reasons. This is what we do. We’re available anytime you need, 24 hours a day, 7 days a week, even nights and weekends for emergency calls and questions. Call us anytime at 626.448.6455