Why Does My Basement Smell Like Sewer When It Rains?

Have no idea what causes this sewer-like odor? Read on to find out

If you have ever noticed that your basement smells like sewage after rain, you might be both worried about this and curious about the possible reasons. How dangerous is it? And is it dangerous at all? Where does this sewer odor come from? How to get rid of it and how to prevent it?

These are all the questions we will try to answer today. Read this article to learn about the possible sewer smell sources in your house, as well as about the most common and effective ways of dealing with them.

Also, we will explain how you can prevent this sewer odor from developing and spreading around your basement and home.

What Makes Your Basement Smell Like Sewer When It Rains?

If you regularly notice that your basement develops an unpleasant sewer smell when or after it rains, there are a few causes of this odor.

Why does the basement smell like sewage
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Luckily, most of them can easily be fixed to get rid of this rotten smell!

How to get rid of the smell in the sewer
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Horrible Smell Coming From Basement Sewer Drain - How To Fix ItHorrible Smell Coming From Basement Sewer Drain – How To Fix It

 

You May Have a Dried-Up Drain

The most common source of sewer smells in your basement is a dried-up drain. See, basement floor drains use a special trap that contains a small amount of water. This trap is used to hold smells inside the sewer lines.

Until the water is there and it’s in a liquid form, everything is fine and all the odors are captured within. But if the trap dries out, all the smells creep up into the basement and end up in the rest of the rooms around the house.

You May Have a Dried Up Drain
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You May Have Problems With Your Basement Vents or Pumps

There is one more thing that can make your basement smell like a sewer. It often develops if you have problems with your sump pump, ejector pump, basement toilet, water heater, or vents.

To avoid this issue, make sure you perform regular maintenance and check each of these pieces of equipment in time. If the smell of rotten eggs remains and gets stronger even after the maintenance routine, then you may have found the problem!

Air Pressure And Gravity Might Be the Core Issue!

Yes, the problem may come from the most unexpected place! It’s not always a malfunctioning part of your drain or vent that causes your basement to smell like sewage. When it rains (especially if it rains heavily or frequently), sewer gas often creeps out of the floor drain, causing the entire house to smell like rotten eggs!

This happens because air pressure changes during the rain. As a result, the air becomes heavy and falls. Naturally, the sewage smell reacts by rising from the drain pipe.

An unpleasant rotten egg smell can also come from your sewer system after a large rainstorm. In this case, the unpleasant odor of sewage gas is forced upwards by water being pulled down the lines by gravity.

Air Pressure And Gravity Might Be the Core Issue!
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Why Your Basement Smells Like Sewage When It’s Cold Outside?

Sewage smells can develop and spread not only when it’s raining outside. Quite many homeowners report having this odor in their basement and even in the rooms upstairs during the winter months or on cold rainless days. But why does it happen when it’s cold outside and there is no rain?

Well, homeowners often forget (or don’t know at all) that sewage smells tend to increase in cold weather and during the winter months! It happens for a number of reasons:

  • Ice can crack your drain lines and cause this odor to rise from the plumbing vent
  • Small animals can make homes in your sewer pipe in winter, blocking the line and causing a foul odor that starts spreading around the home
  • Sewer odors may develop and distribute due to the frozen systems

So, as you can see now, there are quite many different reasons for your basement smelling like rotten eggs! And it’s not always a malfunctioning drain or clogged pipes.

So in order to figure out what exactly makes your basement smell foul, we’d recommend you inspect it, starting from your basement, and try to spot anything that might be the possible culprit. When you know for sure what you are dealing with, it’s easier for you to decide how to cope with it.

Why Your Basement Smells Like Sewage When It’s Cold Outside
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How to Get Rid Of Sewage Smell In Your Basement After Rain?

If your house smells like sewage after rain, your first move would be to find the reasons for this. And the next step would be to fix it as soon as possible to get rid of that odor.

How to Fix a 'Smelly' Basement - Dealing with Sewer Odor and SmellsHow to Fix a ‘Smelly’ Basement – Dealing with Sewer Odor and Smells

The good news is that it’s pretty easy to get rid of a basement sewer odor. You probably won’t even have to call a professional plumber in most cases!

You simply need to follow a few easy steps that we will describe below, and your home will be smelling normal again in no time:

  • Find the source of the smell using your nose and find where the odor is the strongest in your basement
  • Check the water trap and refill it with fresh water, adding a tablespoon of bleach and cooking oil. It will help evaporate the smell
  • Clean the cleanout plug and retighten it to make sure it is airtight and produces no foul odors
  • If your basement has a toilet, the problem could be with the wax ring seal and toilet flange. You need to check that none of them is leaking
  • Make sure you have no broken pipes since they can cause water damage and be the source of a nasty stink!
  • Check for a broken and/or cracked drain pipe as well

With these simple steps, you will be able to eliminate the sewage smell in your house and basement after rain easily.

How to Get Rid Of Sewage Smell In Your Basement After Rain
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Is Exposure to Sewer Gas Dangerous For My Health?

If you can sense a sewage smell in your house or basement each time when it rains, you might start wondering how dangerous this odor can be. This is why “is sewer smell dangerous?” is the most frequently asked question from homeowners.

What does sewer gas include
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At this point, you need to understand that the smell itself poses no danger. What is indeed dangerous is the gas that has this smell. So the answer to the question is yes — breathing sewer gas is not healthy. And in fact, this gas can be quite dangerous.

See, in fact, sewer gas is a combination of various gases and compounds. This combination includes:

While sewer gas may not be dangerous in small amounts, some of the gases it consists of can cause high-level toxicity when inhaled in large amounts!

For example, hydrogen sulfide can be toxic to the oxygen systems of the body. In high amounts, this compound can also cause adverse symptoms, organ damage, and sometimes even death.

Ammonia is another component of sewer gases. It is a common compound used in different cleaning chemicals and products. And even exposure to low levels of ammonia can lead to eye, nose, and/or throat irritation. At higher levels of exposure, this compound can damage your organs or even be lethal!

As for methane and carbon dioxide, both compounds are relatively non-toxic and harmless to humans compared to their more dangerous “colleagues”. However, methane can become extremely flammable if it’s collected in large amounts!

Ammonia is also highly flammable, which is why you can understand now that sewer gas can be a serious fire hazard if you have a lot of it in your home!

Is Exposure to Sewer Gas Dangerous For My Health
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How Do I Know I’m Exposed? The Symptoms of Exposure to Sewer Gas?

Since sewer gas can be very dangerous, you need to know how to define it’s already in your house. The very first sign is a foul odor that reminds of rotten eggs or sewage. But if there is no smell, it doesn’t mean there is no gas indoors!

So depending on the concentration of sewer gas in your basement or house, you may experience different symptoms, including:

  1. Headaches
  2. Lightheadedness
  3. Nausea
  4. Vomiting
  5. Fatigue
  6. Dizziness
  7. Poor concentration
  8. Poor memory

If there is a massive sewer gas leak in your home, this can be noticed by much more serious symptoms, such as:

  1. Loss of smell
  2. Mouth, throat and lung irritation
  3. Eye irritation
  4. Pink eye
  5. Seizures
  6. Coma
  7. Death

This is why, if you can smell sewer gas in your home, take action immediately even if the odor is weak. It will help you keep yourself and your family safe and sound.

How Do I Know I’m Exposed The Symptoms of Exposure to Sewer Gas
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How to Prevent Sewer Smell in Your House When It Rains?

When your basement smells after rain, you need to act quickly and luckily, now you know what to do. But anyway, it’s better to know how to prevent the odor rather than deal with it later. This is why we have prepared three preventative measures you can take to avoid sewer gas leakage and prevent the unpleasant odor:

Make Sure Water Is In The Sewer Traps

As you know, dried-up sewer traps can be the source of this foul smell in your basement. This is why you need to make sure they stay at the correct water level all the time. It will help you avoid dried-out water barriers.

A good way to prevent the sewer traps from drying out is to pour a few tablespoons of vegetable oil on top of the water. Oil will slow down evaporation, keeping the trap moist.

Make Sure Water Is In The Sewer Traps
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Remember to Clean Out Your Drains Regularly

Clogged drains often become another cause for smelly basements. To avoid clogs, you should regularly clean them by removing the drain stoppers and cleaning out all the debris. If you have a pipe waste cleaner, you can make the process way faster: just stick it down the drain and pull out all the debris.

If you don’t have a pipe waste cleaner, you can simply make a small hook at the end of a wire and remove debris with its help. For sure, if the drain is badly clogged, you will have to repeat this procedure a few times. In the end, always flush the drain with 4-5 gallons of boiling water and replace the stopper.

Check Your Toilet! It Should Not Be Loose

A loose toilet is not only the cause of leakage onto the floor. It can also let sewer gases escape inside your home! This is why you should have your toilets regularly checked. Make sure there are no loose joints or bolts. Like this, you will know for sure there is no way for the odor to accumulate in your home.

So now you know why your house may smell like a sewer. We explained what may cause this odor and what you should do in order to get rid of it safely and quickly.

Also, you are now aware of the possible dangers sewer gases may pose. And with the tips and recommendations for preventing this issue, you will be able to keep your house free from foul odors.

Check Your Toilet! It Should Not Be Loose
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Frequently Asked Questions

⭐Is sewer smell itself dangerous?

The smell means that there’s sewer gas in the air which means that there is a potential health hazard.

⭐When shall I call a specialist plumber if I have sewer smell in my house/basement?

You should never attempt to fix the issue yourself due to the potentially hazardous nature of the problem. Once you sense this odor, it is best to call a specialist plumbing company to deal with it.

⭐Is it possible that sewage smell will go away on its own?

The sewer smell may not go away on its own. Instead, it may lead to a serious problem that might require professional plumbing repair.

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Melinda worked as an art consultant and Home Designer for eight years in total. As an art consultant, she was first employed in a local art gallery in San Francisco where she was responsible for picking the most suitable artwork for her clients depending on their goals and budget. At this job, Melinda showed herself as a confident specialist and a true art lover with exceptional taste and artistic sense. Melinda is a passionate author of Housekeeping Bay and we are really happy that she is our Expert.
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