Basements have changed a lot over its history in housing—not in structure, but in purpose. While these underground floors used to be relegated to long-term storage only (think wine cellars), modern basements have become living spaces in their own right, now just as useful as the floors built above ground.

But many basements share a particular problem that upper floors rarely do: that unmistakably musty “old house” smell.

What Is That Smell, Anyway?

There are really only two culprits when one talks about irritating basement odors: mold and mildew. More specifically, the odor comes from the spores that these fungi release regularly, which float through the air and take root wherever they land, growing to form new patches of their own to continue the cycle. 

All forms of mold and mildew thrive in cool, dark, and humid places. And if you haven’t already noticed, these three qualities just so happen to be the exact conditions you will find in a typical basement.

Is Mold and Mildew That Big of a Deal?

Absolutely. Even if you can tolerate the smell (or, at least, try to), mold and mildew can cause all manner of other problems that will force you to take action one way or another.

For one, these fungi like to spread across the surfaces on which they grow, leaving glaring and unsightly stains if left unchecked. They are particularly fond of organic materials like wood and cotton—anyone who’s ever reopened a box of old clothes will know exactly what this looks like.

Arguably the more pressing issue here is the fact that mold and mildew can cause actual health problems in people who are sensitive to their spores. Breathing in moldy air might cause coughing, irritation in the eyes and nose, and difficulty breathing in more severe cases. 

So, how do we get rid of it?

Step 1: Identify the Source

In order to fight these fungi, we will first need to find them.

Now, what’s important to note here is that mold and mildew don’t need to be visible to us in order to produce a smell. After all, they can grow anywhere with enough moisture, and this includes the space and structures behind the walls themselves. 

As such, fixing your mold problem is less a matter of killing the actual fungi and more a matter of eliminating the conditions that allow them to grow in the first place. For the purposes of this guide, we will be focusing on moisture, as it is one of the main ingredients for mold and mildew growth.

One of the telltale signs of mold growth is their stains, so try to look for those first. You are more likely to find them in crevices like the corners of walls and floors. 

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If this fails, you should try to seek out any points of excess moisture such as cold spots or water stains, which can often be traced back to a leak in a pipe or through a window if the basement partially sticks out above ground. 

Step 2: Eliminate the Odor

Once you’ve determined the source of the mold, it’s time to get to cleaning. Hopefully the mold patches as you find them are just that; any additional problems you might have found like water buildup might be best left to professionals. Thankfully, the cleaning process isn’t too difficult, although it might be a bit tedious. 

First off, prepare a batch of cleaning fluid, which could either be alcohol, dilute ammonia and bleach, vinegar and baking soda, or an off-the-shelf option. Your cleaning fluid will be your best friend when removing those mold stains. 

Once all the mold from the room has been cleaned out, getting rid of the odor is just a simple matter of aerating the room until it’s dry, then removing the smell of the cleaning fluid as needed with baking soda or some other deodorizer.

Step 3: Prevent Regrowth.

As we touched on earlier, the key to solving a mold and mildew problem is to remove the ingredients that allow it to grow in the first place. Hence, our third and last step involves preventive measures to keep the basement clean and fungus-free.

There are several ways of going about this, which will depend on how your basement is structured and what items you already have stored there. We’ve summarized a few of the most important parts you need to tackle in the list below:

  • Fix leaks. Mold thrives on moisture, so plugging up any sources of excess moisture will help prevent it from building up in the basement. Leaky pipes should be fixed immediately and any condensation could be covered up with foam pipe insulation. If your basement has any above-ground windows, redoing the seals will also help keep water from leaking in.
  • Rework storage solutions. Basements tend to be used as storage areas, which means that you probably have some objects there stored in cardboard boxes. These are the perfect breeding grounds for mold and mildew, so they should be thrown out as soon as possible and replaced with plastic storage bins, which are practically immune to mold growth. 
  • Clean stored items. Even if your basement is mold-free at this point, mold can still spread from the items you keep there. Make sure to properly clean out any items you plan to store in your basement long-term, particularly clothes and furniture as these tend to be the starting points for future mold growth. 
  • Get a dehumidifier. Finally, you would want to have a dehumidifier installed in your basement to properly and effectively curb moisture in the air—and in turn, the growth of mold and mildew. You don’t have to get the most advanced model; it just has to be powerful enough to keep your basement’s relative humidity or RH to 50% or below. For reference, most species of mold and mildew start to grow at an RH of 55% to 60%, and tends to spread faster when the RH reaches 80%.
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Matt Greenfield

Matt Greenfield is an experienced writer specializing in home improvement topics. He has a passion for educating and empowering homeowners to make informed decisions about their properties. Matt's writing focuses on a range of topics, including windows, flooring, HVAC, and construction materials. With a background in construction and home renovation, Matt is well-versed in the latest trends and techniques in the industry. His articles offer practical advice and expert insights that help readers tackle their home improvement projects with confidence. Whether you're a DIY enthusiast or a seasoned professional, Matt's writing is sure to provide valuable guidance and inspiration.

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