What is relative humidity, and how does it affect mold growth?
The amount of water that can dissolve in a given volume of air is dependent on the temperature. Absolutely dry air has a relative humidity of 0%; completely saturated air has a relative humidity of 100%. When a constant volume of air and dissolved water is cooled, the relative humidity goes up. When the temperature has dropped to a point where the relative humidity is 100%, water will condense to a liquid in the air itself or onto surfaces with a temperature below the dew point (defined as the temperature at which a given volume of air reaches 100% relative humidity). Ideally, the relative humidity indoors should be between 35 and 55%. If the relative humidity is too low, your skin will dry out and static electricity will increase. If the relative humidity is too high, condensation will occur on cool surfaces (such as windows, air conditioning vents, and on floor joists and beams in crawlspaces). This condensation provides the moisture necessary for mold growth.