Indoor Humidity Levels

• An indoor relative humidity level that is considered ideal is difficult to estimate, since humidity relies on so many disparate factors. But at the most basic level, the US Department of Energy recommends an indoor relative humidity between 30 and 50 percent for the house generally. Maintaining relative humidity between these percentages will stave off problems such as mold and mildew growth and aggravated symptoms in asthmatics and those with chronic breathing conditions.
  
  

Basement Humidity Levels

• Controlling humidity levels in the basement is critical since a basement is more likely to suffer moisture problems than other rooms in the home. Dripping plumbing, leaking air conditioning equipment, damaged water heaters, leaking toilets from a bathroom above the basement, and even water vapor seeping upwards from moist soil below the basement can all cause an increase in relative humidity in the basement and create problems. Homeowners should aim to keep basement humidity levels between the ideal 30 to 50 percent range, just as in other rooms in the home ((though relative humidity can reach up to 65 percent in the summer months without creating moisture problems). But homeowners will likely need to measure humidity in the basement more often than in other rooms in the home, given the higher likelihood of humidity and moisture problems in the basement.
  
  

Signs of Excessive Moisture

• High humidity is most easily diagnosed by measuring the relative humidity inside the basement with an electronic hygrometer. But to confirm a humidity problem in the basement, look for other clear signs of high humidity in the basement. Check basement walls and floors for any dampness. If your basement is carpeted, check the carpet and, if possible, the padding underneath the carpet for any dampness, mold or mildew growth. Check for any water stains or peeling paint inside the basement as well. All these, either individually or collectively, can indicate that humidity levels in your basement are too high and could cause problems.
  
  

Controlling Humidity in the Basement

• Controlling high humidity in any room in the home begins with identifying the source of the high humidity; any leaks, cracks, or other problems that could introduce excess moisture into the basement should be repaired at once by a professional. If there does not appear to be a leak or other source of excess moisture, an electronic dehumidifier can be placed in the basement and operated according to the manufacturer's instructions. Ventilate the basement as much as possible to replace stagnant, damp air with moving, dry air. Continue to measure relative humidity in the basement to confirm a drop in humidity levels.