Diagnosing and Curing Sewer or Septic Odors Caused by Building Drains
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Sewer or septic gases and odors traced to building drain or vent piping defects: this article describes how to diagnose, find, and cure odors in buildings caused by leaks or other defects in the building drains or sewer line - leaks that make sewage smells or sewer gas smells or "gas odors" in buildings
with a focus on homes with a private onsite septic tank but including tips for owners whose home is connected to a sewer system as well.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Building Drain & Sewer Line Defects Can Release Sewer Gases & Odors Indoors
Watch out: Because sewer gas contains
methane gas (CH4) there is a risk of an explosion hazard or even fatal asphyxiation.
Sewer gases also probably contain hydrogen sulfide gas (H2S) In addition some writers opine that there are possible
health hazards from sewer gas exposure, such as a bacterial infection of the sinuses (which can occur due to any sinus irritation).
 Sewer gas source: check for a cap left off of a sewer line cleanout:
Our client is pointing out an open sewer line in the basement of a home she was purchasing. The cap had been left off of a cleanout port where main waste line exited the building.
We suspected more trouble than just an open drain cleanout permitting sewer gases to leak into the basement.
Because this "work" appeared to have just been performed, right before our property inspection, we wondered if someone had been asked to attempt to clear a blocked connection between the building sewer line and the community sewer (or private septic system). |
See Building drain odor source for more details about odors coming from plumbing drains - clues that may be more likely to appear in cool or cold weather. Also see our broad-scope article on diagnosis and cure of sewer gas and septic odors: Sewer Gas Odors diagnosing, finding, and curing septic tank and sewer line smells. Also see ODORS & SMELLS DIAGNOSIS & CURE for procedures to diagnose and cure all kinds of odors in and around buildings.
What makes the smell in sewer gas? Sewer gases are more than an obnoxious odor. They are also explosive and they may carry bacterial or pathogenic hazards too. Depending on the sewer gas source and other factors such as humidity and building
and weather conditions, mold spores may also be present in sewer gases. We discuss plumbing vents as sources of sewer gas odors separately at Plumbing Vent Defects.
We discuss plumbing fixtures, such as loose toilets, as sources of sewer gas odors separately at PLUMBING FIXTURE TRAPS. Also see CLOGGED DRAIN DIAGNOSIS & REPAIR, Drain Noises (gurgling drains means bad vent piping or clogged drains).
 Sewer Gas Source: inspect the building drains and gas lines for leaks:
Plumbing drains and traps may smell regardless, as they are usually a reservoir for organic debris.
Remember that a building drain can be leaking inside of a wall or ceiling cavity without showing up as a wet spot or mold.
But if you notice a sewer gas smell particularly at one or more plumbing drains, the fixture may not be properly vented.
If the plumbing fixture or drain "gurgles" or makes funny noises when it is draining, or if you hear gurgling noises at some fixtures, say a sink or tub when nearby fixtures are draining, we would certainly suspect that the fixture is not well vented or may not be vented at all. |
If you suspect that odors are due to a problem with the building drains but you cannot find a drain line leak nor an open drain cleanout cover, take a look at CLOGGED DRAIN DIAGNOSIS & REPAIR.
The sewer gas odor may be coming not from a wet building drain (discussed just above) but from the dry or vent portion of a building's drain-waste-vent system. We discuss plumbing vents as sources of sewer gas odors separately at Plumbing Vent Defects.
Other Sources of Sulphur Odors & Sewer Gas Smells in buildings may Include Chinese Drywall
CHINESE DRYWALL HAZARDS discusses Chinese drywall odors, sulphur smells, and corrosive outgassing hazards in buildings. Major costs to remove this product, repair or replace electrical wiring, plumbing, and HVAC components may be involved, and there may be immediate safety hazards due to damaged smoke detectors or carbon monoxide detectors in buildings where Chinese drywall outgassing has caused damage.
 Hidden plumbing vent pipe leaks septic gas into building: Plumbing vents are used to direct sewer or septic tank gases safely above the building.
But on occasion we trace a sewer or septic gas odor to a hidden leak in a drain or vent line passing through building walls or ceilings.
At left our photo illustrates how hidden vent piping leaks may be lurking in an old building, a new building, or in one that has been renovated.
When the installer needed to extend the plumbing vent and drain line to an upper floor of this 1920's home, s/he simply broke open a cast iron vent pipe that was in a lower floor bathroom. There the "plumber" jammed a plastic ABS drain line into the open cast iron waste or vent pipe.
Our pen points out that this connection was certainly not sealed, and that sewer gases or septic gases were readily passing up the vent and/or drain line, into the building walls, and into the occupied spaces.
See more plumbing vent problems detailed at PLUMBING VENT DEFECTS & NOISES and at SEWER GAS ODORS in COLD WEATHER
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Frequently Asked Questions (FAQs) about plumbing drain odors
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- Thanks to Slade Franklin
for the reminder that a leaky wax ring at a toilet can lead to septic odors in bathrooms. 11/2007
- Thanks to J.V. (privacy protected) for the reminder to make a detailed inspection of the plumbing vent system when sewer gas odors are present. 07/2008
- Thanks to Roger Hankey & Cheryll Brown, www.hankeyandbrown.com, ASHI home inspectors in Minnesota, for the deteriorated transite pipe gas flue vent photograph and comments. Mr. Hankey is a past chairman of the ASHI Technical Committee, serves as co-chairman of ASHI legislative committee, and has served in other ASHI professional and leadership roles. 7/2007
- Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
- Cold Weather Septic Odors or Sewage Odor Diagnosis for additional odor tracing and cure advice focused on sewer gas odor tracking in cold or wet weather.
- Drain Noises: may indicate defective or clogged plumbing: how to diagnose and cure drain sounds
- A Toxic Gas Testing Sampling Plan for Residential Indoor Air Investigations
- Pennsylvania State Fact Sheets relating to domestic wastewater treatment systems include
- Pennsylvania State Wastewater Treatment Fact Sheet SW-161, Septic System Failure: Diagnosis and Treatment
- Pennsylvania State Wastewater Treatment Fact Sheet SW-162, The Soil Media and the Percolation Test
- Pennsylvania State Wastewater Treatment Fact Sheet SW-l64, Mound Systems for Wastewater Treatment
- Pennsylvania State Wastewater Treatment Fact Sheet SW-165, Septic Tank-Soil Absorption Systems
- Document Sources used for this web page include but are not limited to: Agricultural Fact Sheet #SW-161 "Septic Tank Pumping," by Paul D. Robillard and Kelli S. Martin. Penn State College of Agriculture - Cooperative Extension, edited and annotated by Dan Friedman (Thanks: to Bob Mackey for proofreading the original source material.)
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Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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