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How to inspect the plumbing vent system to find leaks and sewer gas or septic gas odor sources How to prevent or cure sewer gas odors from septic systems, building plumbing, & other causes Sewer gas smell Septic gas smell diagnosis - plumbing checklist

This page describes how to examine the building's plumbing vent system piping and connections in order to diagnose, find, and cure odors in buildings including septic or sewage or sewer gas smells that may appear indoors or outside. We describe how to track down and correct these "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. What makes the smell in sewer gas? Sewer gases are more than an obnoxious odor. Also see Plumbing Vent Definitions, Types. Our page top sketch of a plumbing stack vent and other sketches included below are provided courtesy of Carson Dunlop.

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). 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. Also see Wet Weather or Cold Weather Septic Odors or Sewage Odor Diagnosis & Repair Guide for additional odor tracing and cure advice for odors occurring during wet or cold weather.

Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author. Technical review by industry experts has been performed and is ongoing - reviewers welcomed and are listed at "References." © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Plumbing Vent Piping Defects May Release Sewer Gas Odors Indoors

• Install proper and complete drain-waste-vent (DWV) piping in the building: sometimes a building drain system has inadequate or missing plumbing vents. The first photo just below below shows our client observing a very questionable plumbing vent on a new house. The vent is so far from vertical that we wondered if it had been connected to anything inside, and even if it was, we took this detail to suggest work by someone who lacked proper training - so we were alert for other plumbing defects in the building.

• Plumbing vents which have been accidentally closed off or blocked: some plumbing vents include a screen which can slide down, closing off the vent and causing sewer gas backups in the building. We've also found plumbing bents blocked by wasps nests, birds, and once even a frog. Our photos above show how we simply raised the screen back up to open an old sheet-metal vent.
• Leaking plumbing vent system piping: check that all of the pipe connections in the building's plumbing vent system have been properly made and sealed. Particularly with plastic piping it's possible for an installer to push vent pipe sections together while forgetting the glue.
  
  Because the vent is passing only gas, no one notices that it's leaking until there is an odor complaint, the pipe falls apart (which may never happen), or there is a sewer gas explosion. An experienced plumber may spot a loose vent piping correction quickly, especially in an attic or basement. It helps if you've already traced the sewer gas smell to its strongest location.
  
  Pressure test the vent piping or drain piping systems: It is also possible to perform a pressure test of the vent piping system or the drain piping system - a procedure which will diagnose for sure whether or not the plumbing vent system is leaking sewer gas. A plumber installs seals at appropriate locations and pressurizes the piping to check for leaks. [Thanks to J.V. for this detail.]
• Missing plumbing vents: I've seen systems with no vents at all - which often leads to sewer gases reentering the building through sink and shower traps.
• 
  Plumbing vents which are too short in their above-roof projection can be blocked by snow and ice in freezing climates.
• Plumbing vents which are blocked by ice freezing inside the vent line: in freezing weather if a lot of water vapor is passing up the vent line, for example from long steamy showers or perhaps from a hot water fixture left running or leaking into the drain system, frost can form in the vent piping where it passes through a cold attic and outside. When the frost becomes heavy enough it can block the plumbing vent system completely.
  
  In freezing climates, check that a plumbing vent is not being blocked by frost or by snow-cover. Waste line sounds heard in piping or at plumbing fixtures, such as "drain gurgling" or "glub glub" sounds, or similar noises may indicate defective or clogged plumbing, We discuss how to diagnose and cure drain sounds at Plumbing Drain Noises. . Also see Wet Weather or Cold Weather Septic Odors or Sewage Odor Diagnosis & Repair Guide

• Plumbing vent distances to fixtures: Plumbing codes require that plumbing vent lines be installed sufficiently close to plumbing fixtures to vent those drains (typically 5' or less) and that the vent system conducts any sewer gases outside and above the building (not in the attic).
• House Traps and Sewer Gases: Some residential plumbers like to install a trap in the main house sewer line at the point where the line exits the house wall to head for the septic tank. Such traps may protect copper waste lines from corrosive sewer gases. They also may prevent gases from a septic tank from passing back up the waste line and up the house plumbing vent stack.

Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

SEWER GAS ODORS
  First Steps for Sewer Gas Odors
  Dangerous Conditions
  Tracking Odors to Source
  Plumbing Vent Definitions, Types
  Plumbing Vent Defects
  Plumbing Fixtures or Traps
  Building Drain & Sewer Line
  Septic System or Sewer Piping
  Cure Odors in Septic Systems
  Site, Weather, or Failing Neighbors
  Other Causes of Odors from a Septic System
  Tests for Indoor Sewer Gas
SEWER GAS ODORS in COLD WEATHER

Technical Reviewers & References

Particular thanks are due to experts and also consumers who read these articles and suggest corrections, changes, and additions to the material. Content suggestions, technical corrections and content critique are invited for any of the content at our website.

• Daniel Friedman - InspectAPedia.com ^TM Website Author/Editor
• Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• Critique, contributions wanted: Contact Us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

More expert information on this topic

More Information on Building Diagnostic Inspections and Repairs

• 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


• The Septic System Information Website home page for this topic
• Septic Systems Inspection, Testing, & Maintenance- online textbook. Detailed how to inspect, maintain, repair information
• The Home Buyer's Guide to Septic Systems
• Septic Tank Pumping Guide: When, Why, How to pump the septic tank
• Home & Outdoor Living Water Requirements
• Septic Tank Capacity vs Usage in Daily Gallons of Wastewater Flow, calculating required septic tank size, calculating septic tank volume from size measurements
• How Big Should the Leach Field Be? - table of soil percolation rate vs. field size
• Septic System Drainfield Absorption System Biomat Formation - what leads to drain field clogging and expensive drainfield repairs
• Table of Required Septic & Well Clearances: Distances Between Septic System & Wells, Streams, Trees, etc.
• 
  What is a Septic System An Engineer's View - Types of treatment tanks, adsorption systems, pumps, and other special equipment are discussed in some further detail in this text
  Components of a Septic System- the Basic Parts of a Conventional Septic Tank and Leachfield, a chapter in the Home Buyers Guide to Septic Systems
  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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