Correct Level of Humidity in a Basement

Causes

• Humidity builds up in basements due to a lack of air circulation. Most basements have small or no windows and also tend to be filled up with clutter and are rarely used. All of this leads to a lack of air circulation which might dissipate the humidity to other areas. Opening your basement door for a couple of hours while running a fan in the room can help improve the air circulation in your basement and decrease the humidity.

Best Level

• Humidity in your basement needs to remain below 45 percent in the winter. Above 45 percent can lead to mold and mildew problems. In the summer, when humidity levels are higher, the humidity should be kept at or below 65 percent. Low humidity is not usually a problem in basements, especially if they are not used. Typically, you want to keep the humidity above 30 percent. You should check the humidity levels in your basement every couple of months to ensure it remains at the proper level.

Monitoring Humidity

• You can measure the level of humidity in your basement using a hygrometer; use a digital or electronic hygrometer versus a mechanical hygrometer. Mechanical hygrometers are often inaccurate and may be off by as much as 20 percent. You can calibrate or check your hygrometer by mixing 1/2 cup of water with 1/4 cup of table salt. Place the water in a cup, set it inside a clear plastic bag with your hygrometer and leave it at room temperature. Check the meter after 12 hours. It should read 75 percent relative humidity.

Decreasing Humidity Levels

• Besides increasing air circulation, you can also decrease the humidity levels in your basement by decreasing temperature or by using a dehumidifier. Cool air holds less moisture than warm air, which is why winters are drier than summers. Running an air conditioner in your basement is one way to decrease the humidity, but a dehumidifier is a more efficient method. Dehumidifiers are good at removing humidity from warm areas that are between 60 to 80 degrees Fahrenheit. Below 60 degrees they are not as efficient but will still work.