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What Causes Mildew in a Crawl Space?

What Causes Mildew in a Crawl Space?
What Causes Mildew in a Crawl Space?
Looking for information about mildew in a crawl space? If so, you’ve landed on the right page. In this article, we will go over what causes mildew in a crawl space, how to get rid of it, prevent it, and more.
You don’t want mildew in a crawl space for various reasons, including the fact that a certain percentage of air in your home’s crawl space flows up and into the living area. Mildew in a crawl space can also encourage wood rot which will eat away at the beams and joists in the crawl space, eventually affecting the structural integrity of your home.

Is Mildew the Same as Mold?

Is mildew the same as mold? Pretty much. Although people use the terms “mold” and “mildew” interchangeably, mildew is actually a type of mold. So, the title of this article could have been “What causes mold in a crawl space?” and it would contain the same information. This article will use both “mildew” and “mold.” Just remember that we’re talking about the same thing.

What Causes Mildew in a Crawl Space?

Mildew in a crawl space is caused by a wet, humid environment. Moisture in a crawl space creates the perfect petri dish for mildew to start growing. This probably isn’t a surprise to anyone reading this. When things get wet, they can quickly get moldy. But, what causes excess moisture in a crawl space? Here are a few culprits:
  • Damp soil – If the soil in the crawl space is damp, the air in the crawl space will be damp. This encourages mold growth. Now you need to answer the question: why is the soil damp? Leaking pipes? A recent flood? Is your yard improperly graded? See The Importance Of Proper Foundation Drainage Around Your Home for more information.
  • Cracked foundation wall – If your foundation wall is cracked, it could be allowing water in the soil around the foundation to seep into the crawl space.
  • High water table – This is another cause of damp soil in the crawl space.
  • Recent flood – This one should be obvious.
  • Open vents – Open vents allow warmer, humid air to enter the crawl space and condense on cooler surfaces, including the wooden structures in the crawl space. Mold likes to feed on wood.
Without these moisture sources, the ability of mold to form and grow in the crawl space is significantly reduced. So, the key to preventing mildew in a crawl space is controlling moisture. We’ll talk more about how to do this in just a bit.

Can Mildew in a Crawl Space Cause Health Problems?

Yes, mildew in the crawl space can cause health problems because some of the air in your home’s crawl space flows up and into your home’s living area via the stack effect. If that air is full of mold spores, people living in the home could have trouble with asthma, allergies, and other respiratory problems. This is why you don’t want mildew in a crawl space. What goes on in the crawl space doesn’t stay in the crawl space.
the stack effect Epp Foundation Repair

Can Crawl Space Mildew Cause Foundation Trouble?

Yes, mildew in a crawl space can cause foundation trouble because it encourages wood rot which weakens the wood structures in the crawl space. Mildew in a crawl space means there’s moisture in the crawl space, and moisture encourages wood-eating pests like termites. 

Signs Your Home’s Crawl Space Has Mildew 

You might have a problem with mildew in your crawl space if…
  • Your home smells musty – This could be because your crawl space is full of mildew. Due to the stack effect, some of the air in the crawl space enters your home’s living area.
  • People living in the home have allergies, asthma, or other respiratory issues – This could happen if the air in the crawl space is full of mold spores.
  • There’s mold on the baseboards or floor above the crawl space – The mold that started in the crawl space could be spreading.
  • The floor above the crawl space is warped – This could be a sign there’s excess moisture in the crawl space.
While we don’t recommend that you enter your home’s crawl space, you could open the entrance to the crawl space and peek inside using a flashlight. Do you see any wood rot or visible mold anywhere? Is the soil damp?

Permanently Get Rid of Mildew in a Crawl Space via a Drain Tile System and Encapsulation

Since mildew in a crawl space is caused by excess moisture, you can prevent mildew from forming by keeping the crawl space dry. The best way to do that is by installing a drain tile system. A drain tile system works by preventing excess water from building up in the soil around the foundation. A drain tile system can be installed in both basements and crawl spaces. For more information, see What is Drain Tile? 
After the drain tile system is in place, you can start thinking about crawl space encapsulation. Encapsulation covers the floor and walls of the crawl space. It completely seals off the crawl space’s dirt floor. When you add a dehumidifier, you have a clean, dry area beneath your home that you could even use to store things like holiday decorations, tools, etc. For more information on crawl space encapsulation, see Is Crawl Space Encapsulation Worth It? Yes!
Of course, before installing a drain tile system followed by crawl space encapsulation, you’ll need to have any existing mold in the crawl space removed. For this, you can contact a company in your area that specializes in mold remediation. Once the mold is gone, you can contact a foundation repair contractor with experience in drain tile installation and crawl space encapsulation.
crawl space

Other Ways To Prevent Mildew in a Crawl Space

There are some other things you can do as well to prevent excess water from building up in the soil around your home’s foundation:
  • Install a dehumidifier in your crawl space to keep the moisture level down.
  • Regrade your yard, if necessary – Your yard should slope away from your home so that water doesn’t drain toward the foundation.
  • Clean your gutters regularly – Clogged gutters can cause water to spill over the side of your home and into the soil around the foundation.
  • Install downspout extensions – If your downspouts are short, they’ll release water too close to the foundation. Extensions are inexpensive and channel water away from the foundation before releasing it.
  • Install an underground downspout with a pop-up emitter – Water flows from the gutter into the underground downspout and toward a pop-up emitter situated in your yard 10 feet or so from the foundation. When the pop-up emitter is full, it pops up and releases the water away from the foundation.
  • Don’t plant shrubs, flowers, and trees next to the foundation – You don’t want to add more water to the soil around the foundation.
  • Make sure you don’t have any leaking pipes 
If you think you might have mildew in the crawl space underneath your home and you’re in our service area in Nebraska, Iowa, Kansas, and Missouri, contact us today for an inspection and repair estimate.


Dave Epp

Dave is the President at Epp Foundation Repair with over 27 years of experience in the industry. Dave has worked on thousands of foundation, basement, concrete, and crawl space repair projects since 1993. Dave is involved in several civic and church organizations and enjoys coaching youth sports, mainly football, golfing, and elk hunting.



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