Why Your Crawl Space Smells Like Sewage (and What to Do About It)

There’s no place like home—until it smells like sewage. If your crawl space is emitting less-than-pleasant odors lately, it could be a sign of a big problem. Learn common reasons your crawl space smells like sewage and what you should do about it.

2 Reasons Your Crawl Space Might Smell Like Sewage

Odors in your home are never welcome—unless they’re freshly baked cookies or puppy breath. If your crawl space smells like sewage, it could be due to a couple of different reasons, but both warrant a visit from a professional as soon as possible.

1. You've Had a Sewage Backup

If you have a clog in the main sewer line, the water will back up in the pipe and eventually overflow. And because your pipes are located in the crawl space, that's where the overflow will end up. Look for warning signs of a main sewer line clog as well, like water backing up in your toilet or sink and low water pressure.

2. Your Crawl Space Isn't Properly Sealed

It's important to encapsulate or seal your crawl space from the outset. This prevents air from your crawl space from entering the living portions of your home, which makes the air healthier and prevents exposure to toxic conditions like fumes from sewage.

How Much Does It Cost to Fix Sewage in Your Crawl Space?

The average cost to clean or repair a crawl space is $6,000, although the typical price range is anywhere between $1,500 to $15,000.

Generally, crawl space jobs on the low end of price are for areas that just need a little cleanup. If you've had a sewage backup, you're looking at the mid to higher end of the price spectrum.

10 Additional Reasons Your Crawl Space Might Smell

Not quite sure if what you’re smelling is sewage? Keep in mind that mold, mildew, and fungus are frequent fliers in crawl spaces that come with their own smells you could possibly mistake for sewage.

Here’s a look at 10 additional reasons your crawl space might smell:

1. Leaking or cracked sewer pipe in subfloor under bathroom, in the crawl space joists, or in the ground after the drain line goes underground

2. Leaking toilet wax seal

3. Cleanout left open or leaking

4. Other water accumulation in the crawl space from leaking water pipe or surface/groundwater infiltration resulting in stagnant water, which after enough time (think stagnant pond), can smell much like sewage as it goes anaerobic

5. Water or sewer pipe leak in subfloor, or leaking wax ring, causing mildew/mold/fungal growth in the subfloor

6. Chronic high humidity in crawl space leading to mildew/mold/fungal growth in subfloor

7. Decay/fungal growth of wood piers or columns (or blocking/cribbing for them), which are supporting house rotting at the ground contact

8. With large colonies, some insect colonies can smell similar to sewer gas

9. Dead animal in crawl space

10. Stagnant sump pump

What to Do About Smells in Your Crawl Space

No matter the smell, this is almost certainly a job for a professional, and possibly multiple contractors. You may need a plumber to fix the sewage line that caused the problem to begin with, someone to clean up all the sewage that spilled, and finally a crawl space encapsulation pro to seal the space. 

You’ll want to hire a pro to diagnose the source of the smell, whether it’s mold or sewage (or anything else), so you can find out the suggested solution. Contact a crawl space encapsulation professional in your area to get a consultation and a quote so you can determine the best way to move forward with taking care of your problem.