Photograph of a loose, improperly installed, slanted plumbing vent above the building roof Backdrafting Sewage or Septic Odor FAQs

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Backdrafting sewage odor Q&A:

Questions & answers about the causes of & cures for sewage odors in buildings that are traced to backdrafting or draft control problems.

This article series discusses the role of back drafting in buildings, exhaust fans, or other building air movement in causing sewer gas or septic odors (and other building smells and odors). This article is part of our series SEWER GAS ODORS that helps track down and cure the source of sewer gas or septic smells in buildings.

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Back-Drafting Sewer Gas Odor FAQs

Bathroom ceiling vent fan, heater, light combination (C) Daniel Friedman

Questions & answers about the relationship between backdrafting and odors in buildings, posted originally at BACKDRAFTING & SEWER/SEPTIC ODORS

On 2017-06-02 by (mod) re: sewage odors in rainy weather after vent system modified


we need to get an accurate diagnosis of the cause of the odor before any fix can be attempted.

This article may help you prepare to talk with a plumber: SEWER GAS ODORS in COLD / WET WEATHER as there we also discuss odors related to conditions that occur in rain or wet weather.

On 2017-06-02 by Sabrina

I just had my bathroom done and they had to repipe the pipe from the toilet to the stack. So now it raining outside and I'm getting a sewage odor inside my house thats really strong smell. I call the plumber who did it, but can not get a answer. what do I do?

On 2017-05-04 by (mod) re: find the odor source before trying a remedy.


You want first to find the odor source. For example if there's been a water leak you'll need to find and fix the leak as well as to remove moldy drywall or insulation. Links at the end of this article suggest where to start.

On 2017-05-04 by Sharon

It really smells in the laundry room but eventually gets all through the house. What can I do to remedy this

On 2017-03-28 by (mod) - re: odors ever since a flood


As you say there were no odor problems before your area was flooded I suspect that a drain line or septic component has been blocked or partly blocked by sediment or mud brought in by the flooding. Perhaps a vent as clogged too.

On 2017-03-28 by Brian

Ever since our area had a flood every time it rains our basement gets the smell of sewer in our basement, not sure we're to start but is starting to get worse .

On 2017-03-26 by (mod) - re: sewage leaks under a home?

I'd look for a sewer line leak under or near the home, perhaps asking a plumber with a sewer line camera to inspect both the drain piping and the vent piping.

On 2017-03-26 by Greg

Whenever it rains, or we have a Springtime thaw, we have sewer gas smell in the basement of our home. We are connected to the city water system. Would sure like to know how to fix this problem.

On 2017-03-06 by (mod) - re: odors traced to dry plumbing traps

Yes a dry trap can be a source of plumbing odors. If the bath fixtures aren't to be used for a time just pour some clear mineral oil to fill the trap(s).

Water wouldn't evaporate out of a trap in just a few hours, but improper or clogged venting might cause it to siphon out of traps when other fixtures are being drained.

On 2017-03-05 by Holly

The closet was next to a downstairs bathroom and a shower that was hardly ever used. Plumbers I spoke to suggested the water in the shower trap could have evaporated and I was smelling methane gas due to upstairs bath use. I poured a gallon of water in the shower drain downstairs and then used the upstairs bathroom extensively and then had no smell! No smell for a week. However it rained really badly last night, the bath was used this morning.

The smell in the closet was back. I poured more water into the shower drain downstairs - half an hour later, no smell. Articles I've read suggest that water can be sucked out of a p trap if the vent is blocked. Would you suggest that's my problem? I'm assuming rain triggers this due to rainfall going into the roof pipe and if it's blocked not draining, causing more of block and not allowing the gas to vent?

On 2017-02-25 by (mod) - re: skunk smells

Holly skunk smells are quite distinctive, though there might be some mold or other odor sources that are similar. I'd look for leaks and I'd inspect the floor framing for mold.

On 2017-02-23 by Holly

I have a two storey townhome and there is a strong skunk odour in the first level closet underneath our stairs that only occurs when it has rained outside in combination with the bathtub upstairs being run. It is very strong but goes away after a day of the bath not being used.

There are no signs of moisture. The three roof vents were replaced 3 weeks ago as there was cracking and one was leaking. However the smell still persists. When it was -10, -20 here there was never a smell even if it snowed. I have consulted with a roofer and a restoration company and no one knows how to fix it or the source. Do you have any suggestions?

On 2017-02-08 by (mod) - re: when toi inspect the septic tank and plumbing in tracking down an odor

OK then I think the next step is a competent septic system inspection, including conditions in the tank, such as evidence of blockage, sewage passing over baffles, damaged baffles, or improper sewer piping venting.

On 2017-02-08 by Donna

We're in the dry season, we haven't had any rain in months. I wish we did.

On 2017-02-08 by (mod)

Sounds as if your sewer pipe or septic tank are flooding with rainwater.

On 2017-02-08 by Donna

We purchased a home in sw florida 2 years ago . Before the closing the previous owners had a new septic tank installed, no problems everything is great. About 2 months ago i've noticed a poop smell comes in the front bathroom window when it's open. I never had this problem before. When I close the window it goes away. All the drains work good . There is a vent on the roof, close to the window. I don't understand why it now smells.

On 2017-02-07 by Randy

I have a house built in 1960 and when it rains hard or get more that couple inches of rain, I get a pretty strong sewer smell for a day or two. I have a septic system and leachbed.Could someone give me an idea of where the smell is coming from?

On 2017-02-02 by William

I happened to find this site when I was searching for any available information about sewer odors in home. I hope my questions are posted appropriately. We recently moved into a small townhouse down at south Florida. There is constantly a sewer odor that comes from the kitchen.

I located the source is inside the side wall against which dishwasher and sink are positioned. When I pull away the appliances or open the cabinet below the sink, I could smell strong odors passing through the gap between the drywall and floor. This air&odor movement becomes more pronounced when the AC is on.

Feels like the air with odor is sucked out from inside the wall. At the same time, at the bathroom on the second floor, a 1 square feet hole was made a few weeks back due to a replacement of faucet fixture. I noticed the same strong odor inside the hole.

This wall and the wall in the kitchen are connected, I believe. Another fact is that the temperature went down below 74 F for the whole last week. The odor disappeared completely. When the temperature raises yesterday above 74 F, the odor comes back again. How should I deal with this odor issue? Thanks for your assistance.

On 2017-01-25 by John

I have a slight smell of sewer gas in my master bathroom. This is usually when it is rainy/foggy. I have no vent in the bathroom. I believe all the traps are good. I have no gurgling or slow drainage. Am I wrong and a trap is bad? Would there be an atmospheric issue? The smell seems to come from the toilet and not any other drain. Would the toilet wax seal be leaky or eroded?

On 2016-12-27 by (mod) - re: stormdrain overloads may back up into sewer system

Perhaps an overloaded storm drain was backing up into your sewer line, slowing drainage.

On 2016-12-27 by Chris

During a storm Sunday night, my main bathroom had a minor sewer smell (noticeable but not enough to chase us out of the house). It seemed to come from the bottom of the toilet, that's where it smelled most. So I closed the door and turned off our furnace.

After the storm, once the smell dissipated, it's been fine for two days. This hasn't happened before that I know of. There is no fan in any of the bathrooms. No leaks around the bottom of the toilet. I'm on city sewer. Any ideas?

On 2016-10-27 by (mod)

Sewage odor from the water supply piping is not likely to be due to sewage gas backdrafting - more likely there's a contaminant, bacterial or sulphur in the water system, water heater, or well. Search for SULPHUR ODOR DIAGNOSIS to read details.

On 2016-10-27 by CJ

We purchased a home built in 1969 and it has a septic. When we turn the bathroom taps on - sometimes the taps leak out a sewage smell or unpleasant order. Wondered if there is an underlying issue.

On 2016-10-14 by Beth

We have lived in our home 19 yrs. We live high on a hill in rural area and have a septic tank. When it is really foggy, there is a sewage smell that comes in around our back door into our utility room. You can also smell it inside the door at the fuse box panel. My husband thinks its caused by the barometric pressure? the smell is only there in the evenings. Can I get your opinion.

On 2016-08-19 by (mod) - re: sewage smell from tub spout

Tub faucet? Really Barbara? That'd be a problem in the water supply, not drain/waste/venting. Check for a bad water heater anode or bacterial contamination; test the water.

On 2016-08-18 by Barbara

We recently moved to a house with a beautiful finished basement; kitchenette with sink, bathroom with sink, toilet and jetted tub. The remodeling is most likely 6 to 8 years old. There is a sewer smell that comes every week or so from the bathroom.

more specifically, from the tub faucet, it seems to me. I thought it was a dry trap at first and it went away eventually after I ran the water in the tub. However, even when I run water daily in the sinks, as well as flush the toilet daily, the smell keeps returning.

A local plumber capped a pipe that was left from where the washer used to be. The smell still returns. He says if he comes back he would pull the toilet to replace the seal, but I am sure the smell comes from the tub. Since we go away for three months in the Winter, I have to get this issue resolved. it dangerous since we have a gas fireplace with a pilot light in the basement?

On 2016-06-03 by (mod) - re: new house with septic tank and drywell makes the house smell when we flood-irrigate our land

Anon: we welcome your questions as it helps us see what information or clarification is needed at - working together makes us smarter.

I am rather worried about your septic system design and location, from what you say. If you located the septic tank and/or drainfield in an area that you are flooding, you are ruining the drainfield, preventing it from operating properly, contaminating the environment, and are at risk of backing up sewage into your home. Adding dirt atop the tank won't fix a case of the drainfield flooding.

Search for FLOODED SEPTIC SYSTEMS, REPAIR where we discuss what to do when a septic system has been flooded due to area flooding from a hurricane or other storm causing high floodwaters.

You will need

- to keep surface runoff directed away from the drainfield
- never to flood the drainfield area nor septic tank area
- assure that you have at least 24" between the bottom of your soakbed or drainfield trenches and the seasonal high water table in the soils below.

If you don't have those things you may need to redesign the system, perhaps going to a septic mound or raised bed septic.

On 2016-06-03 by Anonymous

I hope it is ok to ask this question here, I'm not getting any help elsewhere! We recently built a new house with a septic tank and dry well. Everytime we flood irrigate our land, the entire house inside and out smells terribly of septic.

This was never a problem with our previous house/septic on this property that we tore down for the new construction. We've contacted the company who put in the septic tank and they put more dirt on top of the septic tank and said the smell will go away. It has now been 6 months and we are still getting the smell.

Today's smell is so strong it has given me a pounding headache. Is this even safe? Is there something the company or we should be doing? Thank you for your assistance.

On 2016-05-16 by (mod)

Anon, please see detailed procedures found at InspectApedia by searching for WATER TREATMENT EQUIPMENT DISINFECTION and found at

On 2016-05-15 by Anonymous

Per your suggestion how do you do shock treatment to hot water heater?

On 2016-05-15 by (mod) re: check for methane odors coming from a well: gas and explosion hazards


Check with your local well drillers and water testing lab as in some areas methane gas can occur right in the incoming water supply.
Odors in hot water can also stem from a bacterial contamination in the water heater - usually solved by shock treatment disinfection of the water heater tank.

Check below the washer for an oil leak - or water leak - as you may have a failing component. Also search for WASHING MACHINE REPAIR

On 2016-05-15 by Anonymous

Have methane gas smell coming from washer intermittently. The smell usually starts after the water is pumped in. If washer is not used, the smell is not present. Washer is new. There is also a vibrating noise from the intake pump area. Any suggestions on how to fix problem?

On 2016-02-21 by (mod) re: how to track dow a hard-to-find smell when it rains

Lauren perhaps someone with a very sensitive sense of smell, or an expert armed with a combustible gas analyzer such as a broad-spectrum detecting TIF8800 could inspect the property to try to trace the odor to its strongest point.

On 2016-02-20 by Lauren

We moved into our home 3 years ago and had inspections, plumbing companies and sewage companies out to try to find what is causing the sewage smell in our house. No one can determine it and no company had figured it out. We live in a split level house and the downstairs often smells from a heavy rain and then it leaks upstairs to the rest of the house (mainly through the floor vent of the upstairs bathroom).

Downstairs there are no sinks or toilets, no dry traps. The drain field was replaced, the septic tank has been cleaned...we even had the house reinsulated and somehow it's still getting in the house. The main sewer line, which is downstairs has been checked for clogs and cracks

We even had the old iron plumbing down there replaced with PVC. We are at a roadblock! The only thing I can think of is something is underground from that main sewer line to the tank outside.

But that would be 10,000 or more dollars to dig up that. Don't even know if it's possible since it goes under the house? Please help!

On 2016-02-12 by (mod) re: dry traps and odors

Open or dry plumbing traps, improper or missing or inadequate drain line venting, or a sewage backup into the septic tank from a clogged or overloaded drainfield may be at fault

On 2016-02-12 by john

we added a septic next door and connected the sewer drain to our drain field for our main house. ever since that we get sewer gas odor in our main house. can you comment please as to what may be causing this.

On 2015-09-14 by (mod) re: how to isolate causes of backdraft odors

You might try isolating the backdrafting problem by looking at the conditions that cause it:

- exhaust fans
- strong indoor updrafts of air leaking upwards and out, typically through a roof venting system

And using a combustible gas analyzer might be a good way to sniff around for sewer gases at possible outlets such as loose toilets;

I doubt that sewer gases are actually by passing a water-filled plumbing trap - the physics of gases and water argue against that hypothesis; if air were moving through the water you ought to hear bubbles; besides it's easy enough to check by listening (flush a toilet and listen for gurgling drains), inspect visually for dry traps, try closing off suspect fixture drains).

On 2015-09-14 by Daisy

We've been having problems with our bungalow for quite some time. Mainly with damp and sewage smell.
Currently our main concern is the sickening sweet smell (cough, sinus irritation,sleepless nights, sweating, depression, tiredness etc). We believed that the smell was coming from the sewage system.
as our bungalow shares the sewage system with two neighboring building and one owned by the landlord. Our bungalow is the last on the system and about 20m away from the main manhole. So he called the plumber, who has done quite a lot of work; checked all the piping, seals and added extra vent, everything was cleaned, flushed etc.. Well it didn't help. Sickening smell is still present.
Our plumber is puzzled and so are we.

The more we read this site, the more it seems that there is a problem with the back drafting. The bathroom is windowless and single room HR unit and another one in the open plan room. HRs probably make situation worse. We were advised to install HRs because they will help to reduce the damp and the smell in the property. Interesting is that sometimes you get used of the smell and you only notice it when entering the building.

Also there is a strong smell of urine in the toilet bowl which was well inspected by a plumber and cleaned by us dozen times with white vinegar, soda bicarbonate, bleach, cleaning tablets... Somehow the smell by pass the water in the U traps. Is it possible that the smell can by pass the water? What should we do?

On 2015-09-07 by (mod) re: is it normal for the house to smell after a new septic tank is installed

No it's not normal; it sounds as if your home had a sewage backup that was not properly cleaned or perhaps there is a plumbing or vent defect in the system.

On 2015-09-07 by sandy

After having my septic tank replaced a month ago, my house still smells like septic. Is this normal, and if so, how long until the order is gone?

Question: septic smells in my Houston Texas apartment

(July 21, 2011) ru by douglass said:
I live in brand new apts., it is on city water and sewer. The residents and I get the septic like smell everyday at 7pm until morning. The manager says its because so many units are sitting vacant. I might add they are on a seperate well system for garden watering.

The city of houston has tested the water even though it smells hideous they say it passes for drinking. After living on well water and use of septic system w/drainage fields, I can't help but say this smells like septic. Its in all of the water including shower! what gives?


Ruby , back in the article starting at SEWER GAS ODORS you'll see some first steps in odor diagnosis.

First: be sure that the odor is coming from your water, not from some outside source around the building.

Second, if the odor is for sure in the water we won't pursue a plumbing drain waste vent problem diagnosis for now.

Third: if the odor is in both cold and hot water than it's likely that it's a water source problem and some treatment may be required for the building's water supply. Do other buildings in the area have smelly water? Is it the incoming water from the city that's smelly or is it local to your building.

An example of a local building water odor source would be bad sacrificial anodes in hot water heaters or bacterial contamination in water heaters both of which can give a sulphur or rotten egg smell to hot water.

Question: horrible sewer smell in the house comes and goes

(Jan 17, 2012) Susie said:

We just had the septic lines from our 1920s home replaced. Ever since, we have had a horrible sewer smell in the house that comes and goes. We have narrowed the source to be under the sitting room floor, where there happens to be the pipe from the upstairs bath that was unusable until the new septic tie-in.

Investigation has proven there are not sewage leaks under the house, and observing sewage flow through the clean-out valve shows there isn't a blockage in the pipe. We might have more of a problem if it's windy or if the heat is running oftne, but it's hard to tell. No smell is detected around any of the interior plumbing. Help!


Sounds to me as if there is a plumbing drain waste or vent line leak. If you're pretty confident of the odor's source as you describe, it's worth opening the ceiling below the toilet and drains in the floor above to inspect and repair.

Question: mildewy odor from drains

(Apr 14, 2012) Pam said:
I have a mildewy odor in the house coming from the drains in the sinks and shower. I know this because I have kept the drains closed (when not in use) for several days at a time and the odors have disappeared in the house. We have a septic tank. The odors started about 4 years ago - we have owned the property since 2001, lived fulltime since 2006. Any advice will help...thanks


Pam see SEPTIC SYSTEM ODORS for help in tracking down these smells

Question: odors coming from roof vents

(May 29, 2012) Sharon King said:
We have just recently noticed an odor coming from a roof vent from our mechanical sewer system. We've also noticed the odor in a guest bath. Not sure if they are related. The sewer systems seems to be working fine. Not sure why all of a sudden there is an odor.

(Aug 22, 2012) Jon said:
How do you eliminate septic odors coming from the stack vent pipe ? I have no odors in the house, any time you are down wind of the stack pipe, you can smell the odor ??? The pipe is about 6 feet above the roof


Odors at a roof vent would be normal as the vent is releasing sewer gases from the drain system. On occasion a downdraft or odd site and roof conditions and shapes can send roof vent odors down towards a building window or even to ground level. But odors in an individual bathroom might first be checked by

1. cleaning all surfaces to remove any confusing odor sources
2. checking for loose or leaky drain connections at the sink
3. replace the toilet wax ring seal
4. check for slow or blocked drain or vent

Question: best steps to take to track down building odors

(July 21, 2012) M Braver said:

We have lived in our 100 year old house on septic system for 12 years. Six or seven months ago started getting bad sewer odor in our only bathroom. It comes and goes, is worse in wet weather, and occurs in warm and cold weather, and whether or not we are running the whole house fan.

There is no exhaust fan in the bathroom. Plumber has checked traps in tub, sink, replaced toilet seal, checked roof vent with water from a hose, pumped septic tank, and is now installing some kind of baffle in our septic tank. Our wood-burning stove is very old. We'll see about sealing it better, but aside from that, should we focus on drains first, or vent pipe. Trying to avoid tearing up any more than we need to. Thanks for your help.

(Aug 4, 2012) Laurie Whitaker said:
We have lived in our 50 year old house for 10 years. When we leave for a week or more we return to an odor that is located in one bedroom/bathroom of our house that is unbearable. At first we assumed it was an animal that had crawled in the floor joists or between the walls and couldn't get out.

But it happen's EVERY time we leave. We have had a plumber come over to check to P traps in this bathroom with no luck.

What I've come to realize is that perhaps it is a smell that is 'stirred up' enough while we live here (although I have a fierce nose....truly) so when we leave it settles and then upon return we smell it. It get's worse and worse for the first day back and then over 2 or 3 days dissipates.


(Aug 5, 2012) (mod) said:
Laurie, On this page at Continue reading we provide an INDEX to RELATED ARTICLES that includes a live link to

that will suggest a series of steps useful for tracking down the odor you describe.

Question: more sewer gas smell track-down problems

(Nov 29, 2012) jim said:

We have a 60 year old home with a septic system. We have lived in this home for 17 years and NEVER had any sewer gas odors.

This last summer I replaced a back door with a more efficient sliding door, had the roof replaced and now when we open our fireplace flue we get a strong lingering sewer gas smell in our first floor laundry room seemingly from the trap on our laundry tub?

I am just am trying to understand why over the last 17 years when doing this we have never had the problem?? Any help is appreciated.

(Nov 29, 2012) TAnderson said:

We just started to notice a sewer like/ gas smell on the left side of our house on the second and third floors. We bought the house in June and have only noticed a similar smell once before but only in the master bathroom, never throughout the house. I was worried it was the chimney because we just started using the fireplace with the cold weather.

There don't seem to be any obvious leaks, just the smell. Should I call a plumber? Is the smell dangerous to my health? I'm 9 months pregnant and concerned. Thanks.


T. Anderson,

You might want to try the diagnostic links(Found in INDEX to RELATED ARTICLES at our Continue Reading suggestions at the end of this article) for


Also, check that the roofer didn't close off ot modify the plumbing vent

Question: septic odor when use kitchen or bath exhaust fans

(Sept 30, 2014) JBrooker said:

When we turn on our kitchen or bathroom exhaust fans for an extended period of time we get a septic odor. The odor seems to emanate from somewhere around our upstairs guest bathroom. The kitchen is almost directly below that bathroom and when the kitchen fan is on the smell comes out one of the kitchen pot lights (but is also mild in the bathroom). The house is very tight and does have a mechanical ventilation system in addition to the exhaust fans.

The smell also seems to be stronger in the winter and can be eliminated by cracking a window when operating the fan. It is not present at all when the exhaust fans are off. Is this odor caused by a leak in the pipe or back drafting, or both? What can be done about it?

Also, the odor does not appear to be coming from any of the drains in that bathroom and the traps have all been kept wet. If anything, the smell also seemed a bit stronger under the sink where the pipe comes through the wall (which is directly above the pot light). That being said, the smell was also noticeable when standing in that bathroom, which lead me to believe that it was coming from somewhere higher up than the sink (but I couldn't pinpoint where)

The pipe on the roof did not appear to be covered in snow or impeded in any way last winter when the smell was strongest. Thanks

oh, the plumbing vent comes out of the house on the opposite side of this bathroom and is proper diameter. And there is no glub glub or gurgle sound from the drains ever. Thanks again.



I'd be looking for a missing plumbing vent, blocked vent, leaky vent piping that backdraft into the house when there is negative pressure created by a vent fan or any other source.

Question: Georgia septic tank and basement smell when it rains

25 Feb 2015 Tfin said:

We have a septic tank system and a basement (in GA). In the past several years, since we had our septic tank replaced, when it rains heavily (summer or winter) or the ground is saturated and cold, a sewage smell emanates from the basement.

The strongest smell can be found up against the wall where the main water valve is (which is the wall closest to where the septic tank is located. No smells come from any vents; none are out in the yard, and there is no squishy ground. Any one have an idea as to what it could be? Who is the right person to call--a plumber or the septic guy?



There are two articles above at More Reading that should help you diagnose this complaint:
Before calling anyone you might want to see



SEWER GAS ODORS in COLD / WET WEATHER (which also includes wet weather)

Let me know if questions remain or if you need more help after looking at those guides.


Continue reading at BACKDRAFTING & SEWER/SEPTIC ODORS - home, or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.





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