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Why Does My Crawl Space Smell Like a Sewer? (3 Causes)

Why Does My Crawl Space Smell Like a Sewer? (3 Causes)

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Building your home requires putting thought into even the smallest details. One example is the crawl space.

Having one of those in your home has its pros and cons. However, if you don’t plan carefully, that little space may be more than you bargained for.

Say you’re enjoying a delicious meal with your loved ones. Then, suddenly, you’re hit with a foul odor. Your heart sinks once you finally realize where the stench is coming from, which makes you wonder, “Why does my crawl space smell like sewer?”

If this sounds familiar, then you’ve come to the right place. We have just the answers you’re looking for.

What’s the Purpose of a Crawl Space?

A crawl space is like a basement but with better air circulation. The vertical clearance is also significantly less in a crawl space, hence, the name.

Homeowners usually install crawl spaces for two reasons:


Building a house can be a costly investment. The silver lining is that having a crawl space lowers some of the expenses because it removes the need for a concrete slab to level the ground underneath the house.


Crawl spaces serve as an area for the installation of piping for your sewer distribution, water lines, and HVAC unit. Then, if there are any problems, they’re easier to find.

Why Does My Crawl Space Smell Like a Sewer?

Crawl spaces can give rise to a myriad of odors, none of which are pleasant. Take a look.

1 – Sewage Backup

The main reason your crawl space smells like a sewer could be a clogged sewer line. This is usually caused by the inability of wastewater to flow down the line.

Unfortunately, the crawl space is the one place it can overflow to. If left unchecked, it can cause serious problems, like mold and bacterial growth.

Moreover, large amounts of wastewater overflow may ruin the integrity of the framework on your house.

2 – Pipe Leaks or Cracks

Smells can also come from cracks and leaks in the pipes, causing wastewater to accumulate in the crawl space. Over time, this build-up can cause the same problems as a sewage backup.

Sewer gas is also a cause for concern. This is because sewers contain a mixture of gases, including ammonia and methane from urine and feces.

The good news is that the liquid in the lines prevents these gases from escaping into your homes. However, cracked pipes cause the lines to dry out, which poses a higher risk of exposure and severe health problems.

3 – A Combination of Things

Your crawl space is also home to a few other foul-smelling elements. Combined, they can be the reason for that sewer-like smell.

This mix can include urine, feces, organic matter, decaying materials, as well as other unfavorable things you might see in the sewer.

There may also be other things aggravating the stench even more. So, you may need to ask yourself these questions:

Are My Vapor Barriers Ineffective?

Too much moisture is undesirable in crawl spaces. Installation of vapor barriers addresses this problem. Just ensure getting the correct type and material to avoid having additional odor issues.

Remove previously installed vapor barriers, if any, to eliminate the risk of mold and bacterial growth on top of your existing dilemma.

Why Does My Crawl Space Smell Like Cat Urine?

Cat urine contains ammonia, which is a type of sewer gas with a distinctive off-putting odor. It’s also extremely harmful when inhaled for extended periods.

Yet, the smell is familiar to cats. It signals to them that this is a safe place. Once they get that sense of familiarity, they’ll likely urinate in your crawl space, exacerbating the sewer smell even more.

How to Keep Your Crawl Space from Smelling

Seek professional help for more serious problems and tedious work. However, it pays to know a little DIY to help keep your crawl space from smelling like a sewer.

Clean Drains and Sewer Lines

If you have clogged lines, get a plumber to get the job done, or you can do it yourself if you’re up for it. Pouring hot water into your drains also helps remove possible blockages like oil and grease build-up.

Remove Excessive Water

Moisture is your enemy when it comes to crawl spaces. This is an area that gets a lot of airflow, pipe leaks, sewage backup, and even flooding.

Yet, the good news is that there’s an easy fix to this problem. All you have to do is install a vapor barrier to encapsulate the crawl space and minimize moisture.

However, you’ll still need to use a pump in the event the area is flooded or there are leaks or a sewage backup.

Clean and Air Out the Space

Schedule time to clean the space. Also, use this time to check for signs of mold, mildew, and other things that may cause unwanted odors.

While at it, open up to allow for proper ventilation. Letting that fresh air in will help reduce the musty smell.

Use Odor Eliminators

Baking soda, vinegar, and coal are all cheap and readily available materials that help minimize odors. Scatter them around your crawling space and leave them to work their magic.

Final Thoughts

“Why does my crawl space smell like a sewer?” may be a common question for homeowners. Luckily, our handy guide has got you covered.

Crawl spaces allow for ease of locating troublesome pipes and lines. However, they can also become problematic if not maintained properly.

They can give off harsh odors due to sewage backup and moisture build-up. Both these factors are prime causes of mold and bacterial growth.

So, keep in mind that you’ll need to regularly clean and aerate the space to keep it from smelling. This reduces moisture buildup and eliminates foul odors, so your crawl space always smells nice and fresh.


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