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What's That Smell? Identifying Crawl Space Problems with Your Nose

An old soda can in a dirt crawl space

Garbage, wet dirt, and other debris in a crawl space can cause unpleasant smells inside a home. (Image credit: Healthy Spaces)

“My crawl space stinks” is a common complaint from homeowners who have an unsealed crawl space.

If you’ve noticed a musty smell in your home and can’t figure out where it’s coming from, the answer could lie underneath your home - inside the crawl space. A crawl space provides a perfect spot for unwanted critters to live and die (yikes!). It can also be a breeding ground for mold.

The first step in making your home smell better is identifying what’s inside the crawl space that’s causing the foul odor.

What’s in the crawl space?

Whether you just moved into a new house or you have lived in your home for years, now is a good time to look in the crawl space to see what’s in there, if you haven’t already. Some things will be obvious while others might require some detective work (cue image of Sherlock Holmes).

Trash & Old Stored Items

There might be old paint cans or trash left behind by contractors or the previous homeowners. The bottom line: Check for junk that shouldn’t be there.

Dead Critters

Crawl spaces are ideal homes for mice, snakes, and other animals that like warm, damp places. A crawl space provides shelter from the cold and rain. Sometimes pests will die inside the crawl space, and when they do, the decaying produces a foul smell.

Rodent Droppings & Urine

Feces and urine left by mice in the crawl space can get into the air vents, spreading diseases that can make you and your family members sick.


A musty smell inside your home could be caused by mold inside the crawl space. Crawl space moisture creates conditions that are ideal for mold and mildew. When air from the crawl space makes its way into the upper levels of the home, so do mold spores and other harmful bacteria. Exposure to mold spores can aggravate allergies and asthma.


A sewage backup in the crawl space will cause an extremely foul odor. When the main sewer line clogs, it can cause the water to back up in the pipe and spill into the crawl space. A sewage backup can lead to serious damage, such as mold growth and damage to wooden support posts. The contaminated soil can release toxic fumes into the air which can enter your upstairs living area and make you sick. If you're dealing with a sewage leak, contact a disaster restoration company to handle the cleanup.

Organic Matter

The soil in a dirt crawl space contains organic matter, such as leaves and manure that decay and emit odors. If the crawl space is unsealed, this smell can eventually make its way into the upstairs living space.

How does air (and smells) from the crawl space get inside my home?

Studies have proven that as much as half of the air you breathe on the first floor of your home comes from the crawl space. If you spray paint inside the crawl space you will smell it upstairs.

Crawl space air gets upstairs one of two ways:

  1. The stack effect draws air from the crawl space upward into the upper floors of the home. As warm air rises, it leaks out of the upper levels and new air must replace the air that escaped. And some of this air comes from the crawl space - through holes around wires and pipes, joints in floorboards, and through duct chases.
  2. Ducts in the crawl space provide a direct pathway for air from the crawl space to mix with the air upstairs. Leaky return ducts suck damp, smelly, mold air from the crawl space into the duct system and blow it back into the upper floors of the home.

Venting the Crawl Space

We’re all familiar with the idea of going outside and “getting fresh air.” But in a crawl space, letting fresh air in is a bad practice. Instead of “airing out” the crawl space and letting odors escape,
ventilating a crawl space actually lets in warm, humid air in the summer and cold air in the winter. When warm air from outside comes in through the vents, it makes wood surfaces and fiberglass insulation damp. Mold loves to grow on damp organic materials.

Problems in the crawl space affect much more than just the quality of the air in your home. To learn more, read “5 Ways Your Crawl Space Can Affect Your Health."

Is your crawl space too small for you to do a detailed inventory of odor-causing culprits? Or maybe just the thought of coming nose-to-nose with an unidentified carcass makes you cringe. If either one of these scenarios is true, the best bet is to hire an expert who deals with crawl spaces to identify the source of the smells and help make your crawl space clean and healthy. Contact Basement Systems to
find a crawl space contractor in your area.

About the author

Kristina McGovern
Content Specialist
After nearly a decade writing about home improvement, Kristina realizes the importance of having a dry, clean crawl space. Born and raised in Connecticut, she has made it her mission to find good pizza in the South. She enjoys spending time on her 13-acre property with her husband (and high school sweetheart), energetic toddler and rescued Labrador mix.

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