What Is The Ideal Basement Humidity Level to Prevent Mold?

what is the ideal finished and unfinished basement humidity level

Last Updated on February 20, 2021 by Kimberly Crawford

Every homeowner knows that the basement is the most humid place in the house. This is so because it is underground, and has few to no windows, and is surrounded by concrete. 

Your basement is the haven of molds because of the adequate amount of humidity in the area. A dry basement does not mean it is free of mold and mildew. The fungi may already be growing underneath carpets, furniture, or behind walls. 

A finished or unfinished basement will always have molds or mildew because of humidity. This means the temperature in your basement is affected by whether it is hot or cold outside. A leaking pipe or slab can cause increased moisture and humidity in your basement

It is, however, common for a basement to have moisture problems that are not properly treated. 

what is ideal basement humidity

What should Basement Humidity be?

High and low levels of humidity can cause serious repercussions causing your basement to be a less comfortable area. Levels of humidity can also affect the welfare of the house. 

Finished or unfinished basements should maintain an ideal humidity level of 30% – 50%. These figures, however, may change depending on the climate in your area. 

Even without a hygrometer (moisture meter), you will be able to know if your basement has moisture problems. Whether the humidity level in your basement is high or low, you will feel varying sensations even when still in the stairs of your basement. 

Basement Humidity Level in Summer

While the ideal humidity in your basement during summer is 50%, actual humidity depends on the climate of your location. The levels of humidity in your basement depend on the temperature outside. 

If it is hot and dry during the summer in your area, levels of humidity in your basement will be higher than average. The humid and hotter air outside during summer can enter your basement and increase the levels of humidity to around 60%. 

On the other hand, levels of humidity may be higher than what is normal with the presence of monsoon rains.  

As a homeowner, you need to bring back the levels of humidity in your basement to between 30% and 50%. If you are not able to, there will be a buildup of bacteria, mold, and mildew in your basement. 

Basement Humidity Level in Winter

The cold air outside during winter can drop the levels of humidity in your basement. The relative humidity in your basement may drop to below 50%. The low levels of humidity may have negative impacts on your health causing you to have dry skin, nosebleeds, and prone to illnesses common during winter. 

The icy conditions outside may cause ice to form in the ventilation ducts and window sills of your basement. You may need a dehumidifier to help adjust the humidity levels in your basement. 

Causes of High humidity in your Basement

mold moisture on the wall
Mold and moisture on the house wall

Basements often have poor insulation and allow the outside temperature to affect its level of humidity. Other than differences in indoor and outdoor temperatures, other factors may also cause your basement to have high humidity? 

  • A crack foundation 
  • Leaking pipes 
  • Leaking exhaust vents 
  • Defective gutter spouts

A damp basement is uncomfortable, gives out a bad smell, and may also make your basement prone to the growth of bacteria, mold, and mildew. Humid basements may also cause structural damage to your house.

Signs that your Basement has Excess Moisture

Discovering that your basement has been penetrated with moisture is not as simple as seeing standing water. There are some signs you need to watch out for to determine moisture is present so you can make some repairs. 

1. Water Stains

water leaks
Water leak in a wall due to damaged pipes

A moist basement may show brown or yellow stains starting on its interior walls and floors. Any discoloration or even water crawling down the walls are signs that something is wrong. 

2. Excess Condensation in Windows

If your basement has excess condensation, water tends to bead on the inside portion of the windows. 

3. Mold and Mildew

Mold and mildew are disastrous effects of having damp a basement. Green, yellow, brown, black, or in whatever color, mold, and mildew spell a lot of trouble for your basement. 

4. Stinky Smell

An unpleasant smell in your basement, especially if the air feels humid and damp means your basement is accumulating water. This may ruin the stuff you have in the basement and may spread to other parts of your home.

5. Concrete Spalling

Peeling, flaking, pooping off, or blistering on the face of a stone, brick, or concrete happen when water enters and leaves deposits of salt. This shows that there is seepage in your basement. 

6. Rotting

Water entering your basement may show in the deterioration of wood and carpets. Rotting may also show in joists, headers, and columns in your basement. 

Any of these signs are clear indications that your basement has excess moisture. 

Effects of Basement Humidity Issues

measure moisture

Poor quality of indoor air is the major effect of basement humidity. This can lead to many serious repercussions. 

Growth of Mold and Mildew

The presence of mold and mildew can present serious threats to your health. It may also compromise the structural integrity of your house. Mold and mildew have the capacity of deteriorating paper, wood, and carpets. 

The growth of mold and mildew, more importantly, increases the risk of you and your family developing respiratory diseases and allergies. 

Musty Smells

Musty smells in your basement due to excess moisture makes it difficult to open or close windows and doors. The musty smell may also leak throughout your home. 

Flooring Problems

Mold and mildew may be difficult to remove from the wood flooring of your basement and from stored carpets. 

Toilet Tanks and Pipes Issues

Condensation due to humid weather may affect your toilet tanks and pipes leading to issues with mold and mildew.

Related: Is a Tankless Toilet Right for your Home? – Price, Pros and Cons, Problems, Installation

Wall Issues

Walls may be soggy and can be a breeding ground for the growth of mold and mildew. Paint on the walls may peel, bubble, and blister when humid conditions exist in your basement. 

Stored Items

Your basement stores most of the things you no longer need. Excess humidity can damage these items. 

The problems caused by excess humidity in your basement can leak out and affect your entire home. 

Related: Basement Leaks Where The Wall Meets The Floor

What is Relative Humidity (RH)?

Relative humidity (RH) is expressed in percentages. It refers to the ratio between the current absolute humidity and the highest absolute humidity possible based on the temperature of the air.  

In relation to water damage in your home, relative humidity refers to the water vapor in the air of a specific area against the maximum amount needed at the present temperature. The relative humidity is expressed in percentages. 

In other words, relative humidity measures the amount of moisture in the air in relation to the ideal moisture in the air before condensation. 

Low RH

Low RH means humidity levels dropping to as low as 10% or anything below 30% during extreme cold. A comfortable humidity level is about 40%. Low RH can cause dry lips, skin, and hair, chapping and itching, and itchiness of the nose and throats, and respiratory problems.

Low RH in your home can cause damage to your furniture and flooring including separation of wood flooring, shrinkage, and warping of the wood. The edges of wallpaper may peel and drawers in furniture may also loosen. 

High RH

Humidity levels above 50% are considered high RH. Molds, mildew, and fungi infestations are the main effects of high humidity. Molds and mildew can damage concrete and wood. Molds and mildew can also have serious effects on your health. Black mold can even cause death.

High RH also causes termite colonies to thrive because wood rots in a humid environment. Termites also bring with them health risks. They may also compromise the structural integrity of your home. 

Ideal RH

An ideal RH should for comfort and health be between 30% to 50%. 

Depending upon the function of your basement (storage, recreation, furnished living, wine cellar, etc.), high humidity can have a negative impact on your health, possessions, and home. Low humidity can likewise have the same effects. 

How to Remove Humidity from Basements

To remove humidity from your basements and keep it at ideal levels means you need to get rid of moisture in the air. A dehumidifier, an electrical device that can maintain ideal levels of humidity, can be used to prevent damages caused by too high or too low humidity in your basement.

A dehumidifier is a good solution to remove humidity in your basement while you work on permanently fixing the cause of humidity issues. The dehumidifier should be positioned in the dampest area of your basement.  

How to Get Rid of Humidity in Basements without a Dehumidifier

You are aware of humidity issues in your basement but you are not willing to invest in a dehumidifier. Well, there are ways you can get rid of humidity even without a dehumidifier. Here are some of the ways:

Use Plants

peace lily

Some plants such as a Peace Lily can deal with moisture issues in your basement. The leaves of this plant remove moisture from the air in your basement. This plant will also work well in your basement because it only needs little sunlight to grow and survive. 

Related: Basement lighting ideas

Install Exhaust Fans in your Kitchen and Bathrooms

Using exhaust fans in your kitchen and bathroom can control steam. Steam from your kitchen and bathrooms is one of the causes of high humidity in your basement. 

Related: Basement bathroom ideas for low ceiling

Repair Leaks

Leaks in your house are sources of moisture that can affect the humidity in your basement. Leak pipes cause moisture to go down to your basement causing dampness and wet areas. 

Fix Leaks in your Ductwork

 Leaks in the ducts of your HVAC can affect the humidity in your basement because it allows moisture to seep out. Fixing the leaks will prevent moisture from getting into your basement. 

Inspect your Sump Pump

The sump pump is often found in your basement. It should always be in perfect condition so it can pump water away from your house. 

Keep Gutters Clean

Gutters work to keep water out of your house. Clogged gutters, though, allows external water to enter your basement. 


Humidity in your basement should be maintained at ideal levels of between 30% to 50%. The growth of molds and mildew are two of the most adverse effects of your basement having too high or too low humidity. 

You can choose to have a dehumidifier or do some maintenance works in your home to keep humidity in your basement at ideal levels