Cold-weather-related sewer or septic system odors:

This article describes how to diagnose and correct sewer gas or septic odors (and other building smells and odors with focus on diagnosing odor sources and causes in cold weather.

This article on diagnosing sewer gas or septic odors is a special cold-weather edition of our more general advice on finding and curing sewage odor problems.

Here we focus on sewage or septic odor problems that occur during cold weather or wet weather. We also discuss causes and cures for sewer gas odors related to wet or cold weather. We include questions & Answers on tracking down cool weather and night time sewer gas / septic tank smells.

Sewer Gas Odor Tracking by Site Location and Season or Weather

Article Series Contents

• SEWER GAS ODORS in COLD / WET WEATHER
• SEWER GAS ODOR COLD / WET WEATHER FAQs
• PLUMBING VENT BLOCKAGE ODORS
• TRACK DOWN COLD WEATHER SEWER ODORS
• SEWAGE ODOR SOURCE LOCATION

Where on the property are odors strongest?

you may be able to point to a waste line, building exit piping, leaks at a septic tank, drainfield failure, or even a neighbor's septic system problem.

• Downdrafts causing odors?
  
  Cold weather can cause downdrafts from a building plumbing vent stack - if this is the case the odors would probably vary by wind conditions and would probably subside as the day warms up; look for nearby plumbing stacks above the area of odor.
• Frozen septic systems causing odors?
  
  If a septic system is backing up due to a failed (or frozen solid) drainfield, sewer gases may be pushed back into the home even before there is an actual sewage backup (this is unusual but possible. usually a sewage backup is not far off.)
  
  If the system is clogged, such as a clogged waste line, blocked septic tank inlet or outlet line or baffle (in the tank), or failed drainfield, and if the system is in common daily use by one or more people, you'd expect that the system would soon backup, forcing drains to back up with sewage, starting at the lowest drain in the building - look there.
• Long persistent odors?
  
   If odors have persisted for some time, and no drains are backing up, it's unlikely that the septic system drain field is blocked. Still if the septic system is in failure, such as a failed drainfield, one common failure mode is that septic effluent is coming to the surface - which will mean outside smells.

Look for a wet area, possibly covered by snow in northern climates - kick the snow aside in a grid pattern over the septic system components (don't' fall into a collapsing septic system - it can be fatal).

Look for areas where snow has melted to a thinner cover. This can occur in a normal system (bacterial action in the soil over the septic system and warm septic effluent carry heat out of the septic tank). But it can also be a clue of sewage effluent coming to the surface. Check such areas for effluent.

If a waste line is blocked or partly blocked and the odors are near the house,

such as at the house wall at the waste line exit point, effluent could be running along the buried pipe but outside it, having leaked from a damaged pipe at the wall, between the wall and the septic tank, or at the tank itself there could be an effluent leak where the line enters the tank, or at the tank cleanout top cover (which would indicate a blocked tank outlet or blocked drainfield).

Effluent will follow a buried pipe because it runs in a trench dug in the soil

the pipe and backfill in the trench are less solidly packed than in the surrounding soil - the trench acts as a conduit to bring sewage effluent to the house if the trench is filling with liquid.

Broken pipe leaks may be mistaken for ground water leaks:

At left we show a broken sewer pipe found by lifting a section of sidewalk in a soft smelly area of the yard.

At a different property where basement paneling was removed following "a history of basement water entry from 'rising ground water' (according to the basement de-watering company)" a company had installed an expensive interior trench and drain system and sump pump to pump the "ground water" away.

We saw an inverted "vee" of leak stains on the basemen wall extending from below the main waste line where it exited the building.

It was obvious that the water entry had been not from rising ground water but from a broken leaking waste line outside the wall. Sure enough, our septic dye appeared in the new basement trench and drain system in just a few minutes.

The basement de-watering system had not been needed at this home, and the owner still needed to have the broken waste line excavated and repaired.

Look for leaks at a waste line,

perhaps first by having a plumber snake the line from inside the building to see if s/he feels evidence of a broken or collapsing or damaged pipe between the house and the septic tank.

See SEWER LINE REPLACEMENT (includes How to Find Distance to Drain Blockage)

If the drain field is saturated or blocked, expect to find abnormally high sewage level in the septic tank, possibly even backing up and flowing out when the tank is opened, and possibly also evident at the distribution box.

See SEPTIC TANK INSPECTION PROCEDURE

 

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

How do I fix a winter sewer smell in my house

Every winter for the past 7 years I have a sewer smell in my house. I don’t know if it’s a coincidence but it started the winter after we remodeled the outside of our house.

We had a steeper pitch roof put on and I’m wondering if the smell is coming from a downdraft on the vent. The smell is strongest in an entrance closet closest to one of the bathrooms and to the outside part of the house.

My husband always fixed things, but he was diagnosed with cancer at the end of the remodel and passed away four years later.

I have no idea who to even call, but I’d love to fix this problem. I know it’s not an LP gas leak because the smell started to smell before I turned on my heat this year. Any help is greatly appreciated. - On 2022-10-16 by Debbie -

Reply by InspectApedia (Editor) - steps to diagnose sewer smell in my house in winter, but after remodelling

@Debbie,

Particularly in winter, when, if my surmise is accurate, your home's windows are closed, if you smell sewer gas indoors, the problem is not so likely to be due to roof pitch and outdoor wind conditions that might cause an outdoor down-draft of odors from the rooftop plumbing vent.

But as you'll read above on this page, the colder temperatures of winter can explain why some odors appear only in cold weather.

For example, if there were a leaky plumbing vent connection in the walls of your home (in that entry closet wall?) it might be that only in winter when outdoor air is cold, might rising sewer gases in the vent system spill out of a leaky joint rather than rising by convection and exiting at the rooftop.

A clue in your question is that the odor started after a remodel job. So here are some specific diagnostic questions:

1. Did the remodeling job add to or move or change any plumbing fixtures, drain piping or vent piping?
2. Did the painter or drywall contractor flush paint or drywall debris down a drain when cleaning up after their work?
3. What else changed in or at your home during the remodeling?
   

A plumber can pressure test your drain and vent system for leaks, but before going to that expense I'd first check the more-obvious sewer gas smell sources like a loose toilet, bad toilet wax ring (are odors strong if someone, on hands and knees, sniffs near the base of the toilet?), or from a dry plumbing trap in that nearby bathroom (does the odor dissipate if you run some water into each of the traps?).

Watch out: don't assume that there could be no fuel gas leak just because you have not yet turned on your heat.

Fuel gas leaks (LP or natural gas) can be present anywhere in the gas piping system, and might be noticeable only in cold weather when the building is less ventilated.

Bad smell in one bathroom after shower is used

We have a horrible smell like dirty diapers and almost hurts a bit to breathe that happens after the shower is used in one bathroom and only during cold weather.

The smell completely disappears during spring and summer and didn't start up again until we started needing to turn on the heat (like when it hit below 60 degrees outside but not freezing temps.)We can smell it coming from the shower drain but we also sometimes smell it in other areas likely the wall behind the toilets.

The master bathroom is on the other side of this bathroom and has a window that we have to keep open at all times during winter or smells back up in there too.

We've tried everything so far: septic pump, adding vents to plumbing in basement, putting hose down vent pipe on roof to wash out anything that might be in there (black water backed up in sinks, is that a clue?), adding sweet air filter to vent pipe (made it worse so we took it off), vinegar/baking soda down all the drains, draino in case of clogged pipes.

The house was built in 1967 and does not have PVC. We're on a septic and well. Looking for any possible solutions and I'm scared it may be a damaged vent pipe in the walls. - On 2021-11-29 by Melissa -

Reply by Inspectapedia Com Moderator - inspection of the sewer piping and vent piping using a sewer line camera

@Melissa,

I suspect that the drain or vent for that bathroom has been plugged or is leaking.

An inspection of the sewer piping and vent piping using a sewer line camera might be worthwhile and also a review of the buildings leak history to address the question of whether there could be mold contamination in a wall floor or ceiling cavity

On 2021-10-25 by Jeremy - Plumber can't figure out cause of intermittent sewage odors in bathrooms

Hello,
We just built a new house this year and we have had intermittent sewage smells in the bathrooms that our plumber has been unable to figure out. The plumbing passed inspection and the pressure test.

We run water in all the drains once a week to ensure traps have water. It started in our master toilet shortly after we moved in and was strong when it rained. They replaced a gasket on toilet and that seemed to fix it for a bit. It then moved to our half bath located on main floor.

They then replaced and reset every gasket in every toilet in the house. The smell then seemed to come in the morning time from about 7 am till noon. The plumbers then inspected our propane lines for any small leaks. Found small ones but that also did not fix the problem permanently.

Now the smell is on the 2nd floor bathroom and I have not been able to find anything that drives the smell (ie rain, cold etc). I am out of ideas as is the plumber. Thought maybe I'd give this forum a try since I am losing my mind lol. Thanks!

On 2021-10-25 by inspectapedia.com.moderator - moving around odor source - try a rooftop wind deflector on plumbing vent?

@Jeremy,

I agree that a moving around odor source is difficult to diagnose.

You might look for causes of building air currents and door transport in your home such as is air conditioning or heating duct system that can pick up an order from one place and transported to another.

That can account for a remote and undetected odor source.

You might also check to be sure that the odors are only indoors and not outdoors. Outdoors you might look at site conditions including wind direction and downdrafts from the rooftop plumbing vents.

If a pressure test on the Beltline found no leaks then it's probably not worth any invasive inspecting methods such as cutting up on a wall or ceiling to check the routing of the vent line.

You're on site people respond to look for other odor sources as well, ones that may have nothing to do with the plumbing system.

Sometimes a sensitive gas detection instrument can help pinpoint an order source.

On 2021-10-25 by Jeremy

@inspectapedia.com.moderator, Thanks for the quick response! You mentioned a wind-operated elbow that keep vends open facing down wind in another response. We have lots of wind out here on the farm, so I was wondering if you could tell me what kind of fitting that was or where we could buy one? Thanks!

On 2021-10-25 by inspectapedia.com.moderator

@Anonymous,

Look for a high-wind cap for plumbing vents or a plumbing vent wind diverter; an example is made by Camco, their "Camco Cyclone Plumbing Vent " often used on RV plumbing system vents and shown below.

Also see products like the OdorHog sewer vent or plumbing vent cap claiming to prevent odorous downdrafts from rooftop plumbing vents;

You'll see that the manufacturers of ALL of these outdoor efforts to stop downdrafting sewer gas odors from an outdoor or rooftop plumbing vent take care to warn you that these products address outdoor sewer gas odors, not in door sewage or sewer gas odors.

On 2021-10-27 by Jeremy

@inspectapedia.com.moderator, we just purchased on amazon. I will let you know if we see improvement. Thanks!

On 2021-10-27 by inspectapedia.com.moderator

@Jeremy

Great, that will help other readers.

About tracking down indoor odors, the rooftop vent is not a likely source unless

- it is not properly plumbed, sealed, connected as it passes up through the building

or

- there are downdrafts of outdoor air containing sewer gas that also leak into the building interior

But a deflector or other plumbing vent device (such as an odor filter) can reduce outdoor odors of downdrafting sewer gases.

 

On 2021-10-04 by Michelle Dolloff - Bathroom closest to lagoon septic smells bad

We have a lagoon and our bathroom closest to it has sewer smell recently. Could it be because of the lagoon if so what do we need to do?

On 2021-10-04 by inspectapedia.com.moderator - is lagoon cause of sewer smell

@Michelle Dolloff,

First, be sure you've reviewed the lagoon septic system maintenance requirements found

at LAGOON SEPTIC MAINTENANCE 

since a failing lagoon septic OR a backup of wastewater from that septic system could cause odor problems.

It would be helpful to know what country, state, city you are in as weather and climate can make a difference. If the smell is a new problem and the lagoon has always been there, it may be from another source.

Also, if a sewer gas odor seems specific to just one area in the home one could suspect a clogged drain, inadequate vent piping, or a loose toilet or leaky vent line or leaky drain line.

We list several possible sources to review and rule out if possible at this page:

TRACK DOWN HARD-TO-FIND SEWER GAS ODORS IN BUILDINGS

Plumbing Vent Blockage Problems as a Source of Building Smells, Septic or Sewage Odors

This topic has moved to PLUMBING VENT BLOCKAGE ODORS - separate article

PlumbingTrap Siphonage, Dry Plumbing Traps, Sewer Gas Leaks & Freezing Weather-Related Plumbing Vent Problems

This discussion is now at TRAP SIPHONAGE & SEWER GAS

How to Find & Fix Sources of Septic Odors that Occur in Cold Weather

This topic moved to TRACK DOWN COLD WEATHER SEWER ODORS - separate article

Tips for Tracking Down Hard-to-Find Sewer Gas Odors in buildings

Please see SEWAGE ODOR SOURCE LOCATION - other Sources of Sewer Gas or Methane Gas Odors in buildings

...

Continue reading at SEWER GAS ODOR REMEDIES or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see SEWER GAS ODOR COLD / WET WEATHER FAQs - questions & answers posted originally at this page

Or see these

Recommended Articles

• SEWAGE PUMP ODORS
  
• SEWER GAS ODORS - home
• SEWER GAS ODORS in COLD / WET WEATHER
• SEWER GAS ODOR REMEDIES
• SEWER / SEPTIC PIPE CAMERAS
• SITE WEATHER or NEIGHBOR'S SEWER ODORS
• TRACK SEPTIC ODORS to SOURCE
• TRACK SEWER ODOR by WEATHER
• WET WEATHER SEWER ODORS

Suggested citation for this web page

SEWER GAS ODORS in COLD / WET WEATHER at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to DRAIN SEPTIC SEWER PIPES

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