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Why Do I Have a Musty Basement Smell?

The reason for the musty basement smell can be elusive at first, largely because most people never experience this smell outside of the basement. There are typically three main things that have to happen for a musty-smelling basement.

Organic Material 

The first necessity is some kind of organic material. This can come from just about anywhere; wood, which many homes use for at least part of the floor joists, is an organic material. Many insulations also count as organic material, and if you don’t take good care of your basement, it’s possible the insulation could come out of the walls and ceiling.

Although you can clean up some of this organic material, like the fallen insulation and anything else that has fallen into the basement in some way, you can’t get rid of all of it. If you have wood as part of your foundation, for example, you’re never going to be able to get rid of the organic material in your basement. The good news is that this is only one part of the equation.

High Relative Humidity 

The next necessary thing is high relative humidity. Relative humidity is a measure of how much moisture is in the air proportionate to how much moisture that air could hold maximum. For example, if the air is at 70% humidity, that means the air is currently saturated with 70% of the moisture it could hold at the most.

This is an important measurement because once air gets to 100%, that means it’s as saturated with moisture as it can possibly be. If the air goes over 100%, that excess moisture has to go somewhere, and most commonly it comes out as condensation on a cool surface. High relative humidity is a necessary part of the equation because it’s the only way you’ll be able to get the next part.


Most of the time, when you’re smelling a “musty smell,” the majority of that smell is just mold. Mold forms when organic material and high relative humidity come together. Mold typically requires a relative humidity level of at least 60%, but beware: even if the rest of your basement has a relatively low humidity level, mold can grow on and around water spots, including condensation spots.

Mold is typically recognized as a danger to humans. Although it’s very rarely toxic, it can certainly cause allergic reactions and respiratory problems, which can be frustrating and upsetting to anyone who doesn’t know why it’s happening. This mold might not kill you or even seriously harm you, but it will have a dramatic impact on your quality of life.

This is the most important reason that if you smell a musty smell in your basement, you need to seek help from a basement waterproofing expert immediately. Mold isn’t something you should just leave to its own devices. If you can remove it from your basement, you’ll be more well-positioned to fix any problems you were experiencing due to mold.