6 Reasons Your Crawl Space Smells Like Sewage and How to Fix It

There’s no place like home—until it smells like sewage. Troubleshooting a stinky crawl space isn’t exactly the most fun part of homeownership, but it gets a lot easier if you know what to look for. Everything from pests and leaky pipes to the condition of your sump pump or encapsulation can play a role. This guide will show you why your crawl space smells like sewage and how to fix it.

1. Clogs In Your Drainage System

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. 

How to Fix It

The kind of clog that makes your crawl space smell is usually deeper in your plumbing system, so you’ll need to hire a pro who can snake or hydrojet your sewer line. 

2. Problems with Ventilation or Encapsulation 

When your crawl space isn’t properly sealed, it can let in outside elements. Any moisture that enters can be a problem, because it encourages mold and bacteria growth. This can create a musty smell, especially when organic material like leaves start to decompose. 

Even if your space is sealed, odors can get trapped in your crawl space without proper ventilation. They may rise into your home. 

How to Fix It

You have two options. You can encapsulate your crawl space and/or install crawl space ventilation. This prevents air from the crawl space from entering the living areas of your home and generally improves your indoor air quality. 

3. Damaged Sewer Lines

Broken sewer lines are one of the biggest causes of sewage smells in a crawl space. Sewer lines can corrode, crack, or fall victim to tree roots. Depending on where the break is, it can leak waste or sewer gasses into your crawl space, and the smell may permeate your home.

How to Fix It

There are a few sewer line repair options depending on the type of damage, but you’ll need to hire a pro for this type of extensive repair.

4. Pests 

Unfortunately, sometimes small animals get stuck inside crawl spaces. This can cause a lot of bad odors, from the smell of feces and urine to the smell of a dead critter. 

How to Fix It

To get rid of the smell, get rid of the pests and clean up your crawl space. You’ll also want to take steps to prevent pests from entering your crawl space in the future. A local pest control specialist can help. 

5. Dry or Malfunctioning P-Traps

The P-trap is an essential part of your drainage system that holds a small amount of water. This water acts like a barrier and prevents sewer gasses from entering your home. Sometimes a P-trap malfunctions or dries out. Depending on the location, that could cause a sewage smell under your house.

How to Fix It

Running water for 20 minutes can refill a dry trap, but if the trap is damaged or malfunctioning, you’ll need to bring in a pro to fix it.

6. Stagnant Water In Your Sump Pump

Not everyone has a sump pump in their crawl space, but if you do, it can occasionally fail. Even if it’s working perfectly, water can become stagnant during a dry spell. This standing water is prime real estate for mold and bacteria—and it can start to smell pretty funky depending on how long the dry spell lasts. 

How to Fix It

If it’s been dry, you can pour a diluted bleach solution into the pit. Use a cup of bleach per gallon of water. If it has rained and your sump pump won’t activate, you’ll need to hire a sump pump repair pro to fix the issue.

When to Call a Pro

If you don’t know what’s making your crawl space smell like sewage, it’s a good idea to hire a professional. You won’t be able to fix a sewer line clog or break on your own. The most common causes require a knowledgeable plumber. 

After repairs, you may need to clean out your crawl space to get rid of the smell—especially if there are pests, mold, sewage, or standing water. For most homeowners, crawl space cleaning costs $2,000 to $6,000 on top of any repairs. If you want to encapsulate your space to prevent future issues, hire a local crawl space encapsulator or a basement waterproofing pro near you.