Sewage or Septic Odors from Blocked Plumbing Vents
PLUMBING VENT BLOCKAGE ODORS - CONTENTS: causes of blocked plumbing vents & resulting smells & odors in and around buildings; why do some plumbing vents get blocked in freezing weather? Effects of snow cover on plumbing system vents & odors. Plumbing drain trap siphonage, odors, noises due to clogged plumbing vents.
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Clogged or blocked plumbing vents as a cause of sewer or septic system odors:
Diagnose odors traced to clogged, frozen or snow-covered plumbing vents. This article describes the causes of blocked plumbing vents & resulting smells & odors in and around buildings; why do some plumbing vents get blocked in freezing weather? Effects of snow cover on plumbing system vents & odors. Plumbing drain trap siphonage, odors, noises due to clogged plumbing vents.
Plumbing Vent Blockage Problems as a Source of Building Smells, Septic or Sewage Odors
What's different in cold weather that could cause indoor sewer gas odors only during freezing weather?
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An under-sized plumbing vent (less than 2" diameter or too short above the roof line) can become blocked by frost in the vent line above the roof, blocked by snow cover, or have its gases blown down to a lower level by cold or varying air movement. If it's a plumbing vent diameter problem in a freezing climate, you'll see the vent basically blocked by frost above the roof line.
Too-short plumbing vents: Look also for short plumbing vent stacks above the roof line - they can be covered and blocked by snow.
If in cold weather a plumbing vent pipe is frosting up, sewer gases may vent backwards out through building drains. In that case, even re-priming building drain traps won't prevent sewer gas entry as flushing a toilet or running a nearby drain can siphon water out of a nearby trap. [Illustration provided courtesy Carson Dunlop Associates.]
A thoughtful reader, Jill Elwert, suggested insulating the vent piping to try to delay vent pipe blockage by freezing moisture. We are afraid that even if you insulate the vent line in a cold attic, it'll freeze above the roof surface outdoors. You could try it but if that proves the problem, ultimately you'll want to have a plumber or handyman install a 2" or larger diameter vent from the attic floor up through the roof.
Diagnose frozen or snow-covered plumbing vent lines:
Noisy drains only in freezing weather: Look for a clue of blocked vents (from freezing moisture) by listening for a glub glub sound at nearby drains, say when flushing a toilet or emptying a bathtub.
Poor drainage only in freezing weather: Another blocked vent line symptom might be poor drainage that occurs only in freezing weather.
Rooftop inspection for frozen or snow-covered plumbing vents: WATCH OUT! don't try going on an icy, wet, high, steep, or snow-covered roof. But if the roof is safely accessible, or you can get visual access, perhaps from a higher elevation, or some safe location with binoculars, see if you see frost build-up in the plumbing vent.
Priming the plumbing trap (where sewage odors are most observed) by pouring water into it may stop the sewer gas odor, but if the plumbing vent is blocked, the trap is likely to lose its prime and the odors will return.
Inspect for small diameter plumbing vents above the roof line or in the attic - just a simple visual inspection can tell you where to look first for frozen, blocked plumbing vents. Start with the smallest diameter vents, especially if the plumbing vent is one that vents a place where lots of hot (steamy) water is run such as a vent for a clothes washer, kitchen sink, or shower.
Reader Question: 16 Feb 2015 rose said: do I need to dig out the septic vents that are snow-covered?
I hear about the need to clear vents in the house in this snow, but can't find anything about when the septic vent pipes are buried in snow -- do those need to be dug out?
Reply: frost blocked or snow-covered vents can cause dangerous sewer gas backups
My OPINION is that the answer is ... it depends.
On what your sewer piping connects to and where you live.
For example: North Dakota State University has advised that in deep-snow-winter weather, blocked sewer vents can cause a [dangerous in my opinion] sewer gas backup in homes that can "make people sick" (sewer gas is also explosive). - see "Clogged vents can lead to sewer gas backup, which can make you or your family ill.", Roxanne Johnson, Water Quality Associate, (2011), - ag.ndsu.edu
Johnson also notes that deep snow on a roof can block the roof vents of the plumbing system too; indeed I've published photos of that condition here at InspectApedia.
Recently, in New York, dealing with deep snow and ice dam leaks on a flat roof, we had what seems to me a clever solution: having to make an emergency "repair' by adding a heat tape to a leaky roof we just stuck an extra length of the heating tape cable into the rooftop plumbing vent stack. That small amount of heat won't damage the plastic piping of the vent, and the heat can avoid a frost-blocked plumbing vent that can occur in freezing weather whether there is deep snow cover or not.
Freezing weather can cause a complete blockage of a plumbing vent stack by frost that forms inside the portion of the vent that extends outdoors above the roof, or by deep snow cover that completely covers a short plumbing vent.
For example steam from long showers moves up the vent pipe where it freezes in the pipe section extending above the building roof.
The absence of venting (missing or blocked) causes plumbing trap siphonage and loss of water in building traps. (Water flowing down a drain line without a nearby supply of makeup air to follow the water creates a vacuum that pulls water out of nearby plumbing traps. Flushing a toilet can siphon out a nearby sink or tub trap.)
What happens when the water seal is lost from a plumbing trap?
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When the water seal is lost from a plumbing trap sewer gases can back up out of that fixture and not just smell bad. Sewer gases contain methane which is an explosive gas - possibly quite dangerous. In addition to occasional methane gas explosions inside buildings, I've had a report of an outdoor septic tank explosion too when an owner built a brush fire atop the tank.
In sum, dry plumbing traps are caused by evaporation at an unused fixture, leaks at the trap, or siphonage due to improper plumbing vent line installation. Dry traps can leak smelly or dangerous sewer gases into a building.
Check for dry plumbing traps, particularly at un-used basement or lower floor fixtures and at floor drains which might be connected to the sewer line. "Dry trap" means that there is no water in the trap bend or weir.
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raw sewage odors in very cold weather
I read your article and I would like to explain my problem to see if I have come up with the problem. I live in Cheyenne Wyoming and when it is very cold (below 25 degrees Far.) we get a very strong raw sewage odor from our basement bathroom. I have narrowed it down to the bathtub. We did not finish the basement, it was finished when we moved in. The odor was not disclosed to us when we moved in 3 years ago and this winter it is worse but it is colder. We have smelled it every winter since we moved in. Now tonight I decided to try an experiment. I closed the drain on the tub and put water in the tub and this seemed to fix the problem. So my opinion is that they did not put a "P" trap on the tub. So what do you think?
I do not smell the odor from the sink, the toilet, or the floor drains.
Thank you - John 12/6/11
There may be a corroded leaky P-trap that thus doesn't maintain its water seal. Try pouring water into the trap and inspect with a good light to see if it remains in the drain; Unfortunately some demo and digging may be in order to fix this odor source.
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Herb Reed County Extension Director, Agricultural and Natural Resources Educator, Calvert County Maryland - private email to DF 9/5/2006 adding comments about odors and partial blockages.
Onsite Wastewater Disposal, R. J. Perkins;
Quoting from Amazon: This practical book, co-published with the National Environmental Health Association,
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Onsite Wastewater Treatment Systems, Bennette D. Burks, Mary Margaret Minnis, Hogarth House 1994 - one of the best septic system books around, suffering a bit from small fonts and a weak index. While it contains some material more technical than needed by homeowners, Burks/Minnis book on onsite wastewater treatment systems a very useful reference for both property owners and septic system designers.
Septic Tank/Soil-Absorption Systems: How to Operate & Maintain [ copy on file as /septic/Septic_Operation_USDA.pdf ] - , Equipment Tips, U.S. Department of Agriculture, 8271 1302, 7100 Engineering, 2300 Recreation, September 1982, web search 08/28/2010, original source: http://www.fs.fed.us/t-d/pubs/pdfimage/82711302.pdf
Builder's Guide to Wells and Septic Systems, Woodson, R. Dodge: $ 24.95; MCGRAW HILL B; TP;
Quoting from Amazon's description: For the homebuilder, one mistake in estimating or installing wells and septic systems can cost thousands of dollars. This comprehensive guide filled with case studies can prevent that. Master plumber R. Dodge Woodson packs this reader-friendly guide with guidance and information, including details on new techniques and materials that can economize and expedite jobs and advice on how to avoid mistakes in both estimating and construction. Chapters cover virtually every aspect of wells and septic systems, including on-site evaluations; site limitations; bidding; soil studies, septic designs, and code-related issues; drilled and dug wells, gravel and pipe, chamber-type, and gravity septic systems; pump stations; common problems with well installation; and remedies for poor septic situations. Woodson also discusses ways to increase profits by avoiding cost overruns.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Advanced Onsite Wastewater Systems Technologies, Anish R. Jantrania, Mark A. Gross. Anish Jantrania, Ph.D., P.E., M.B.A., is a Consulting Engineer, in Mechanicsville VA, 804-550-0389 (2006). Outstanding technical reference especially on alternative septic system design alternatives. Written for designers and engineers, this book is not at all easy going for homeowners but is a text I recommend for professionals--DF.
Country Plumbing: Living with a Septic System, Hartigan, Gerry: $ 9.95; ALAN C HOOD & TP;
Quoting an Amazon reviewer's comment, with which we agree--DF:This book is informative as far as it goes and might be most useful for someone with an older system. But it was written in the early 1980s. A lot has changed since then. In particular, the book doesn't cover any of the newer systems that are used more and more nowadays in some parts of the country -- sand mounds, aeration systems, lagoons, etc.
Septic System Owner's Manual, Lloyd Kahn, Blair Allen, Julie Jones, Shelter Publications, 2000 $14.95 U.S. - easy to understand, well illustrated, one of the best practical references around on septic design basics including some advanced systems; a little short on safety and maintenance. Both new and used (low priced copies are available, and we think the authors are working on an updated edition--DF.
Quoting from one of several Amazon reviews: The basics of septic systems, from underground systems and failures to what the owner can do to promote and maintain a healthy system, is revealed in an excellent guide essential for any who reside on a septic system. Rural residents receive a primer on not only the basics; but how to conduct period inspections and what to do when things go wrong. History also figures into the fine coverage.
US EPA Onsite Wastewater Treatment Systems Manual Top Reference: US EPA's Design Manual for Onsite Wastewater Treatment and Disposal, 1980, available from the US EPA, the US GPO Superintendent of Documents (Pueblo CO), and from the National Small Flows Clearinghouse. Original source http://www.epa.gov/ORD/NRMRL/Pubs/625R00008/625R00008.htm
Water Wells and Septic Systems Handbook, R. Dodge Woodson. This book is in the upper price range, but is worth the cost for serious septic installers and designers.
Quoting Amazon: Each year, thousands upon thousands of Americans install water wells and septic systems on their properties. But with a maze of codes governing their use along with a host of design requirements that ensure their functionality where can someone turn for comprehensive, one-stop guidance? Enter the Water Wells and Septic Systems Handbook from McGraw-Hill.
Written in language any property owner can understand yet detailed enough for professionals and technical students this easy-to-use volume delivers the latest techniques and code requirements for designing, building, rehabilitating, and maintaining private water wells and septic systems. Bolstered by a wealth of informative charts, tables, and illustrations, this book delivers:
* Current construction, maintenance, and repair methods
* New International Private Sewage Disposal Code
* Up-to-date standards from the American Water Works Association
Wells and Septic Systems, Alth, Max and Charlet, Rev. by S. Blackwell Duncan, $ 18.95; Tab Books 1992. We have found this text very useful for conventional well and septic systems design and maintenance --DF.
Quoting an Amazon description:Here's all the information you need to build a well or septic system yourself - and save a lot of time, money, and frustration. S. Blackwell Duncan has thoroughly revised and updated this second edition of Wells and Septic Systems to conform to current codes and requirements. He also has expanded this national bestseller to include new material on well and septic installation, water storage and distribution, water treatment, ecological considerations, and septic systems for problem building sites.
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