How to Determine the Measure of Relative Humidity in a Building Enclosure

Relative humidity is a measure of the moisture in the air relative to the maximum amount of moisture that the air can hold. Hot air holds more moisture than cold air, so the absolute amount of moisture in a warm room will read as a lower relative humidity than that same amount of moisture in a cold room. The best way to determine the amount of relative humidity in a building enclosure is with a hygrometer. This small, inexpensive device is available at most home improvement centers.

• 1

  Place the hygrometer in the building enclosure. Do not place the hygrometer near a drafty doorway, radiator, chimney or any other device or aperture that expels cold or warm air.

• 2

  Check the hygrometer's reading in two hours. It takes a hygrometer roughly this long to produce an accurate reading of the relative humidity in the room.

• 3

  Recheck the hygrometer in another two hours. If the reading has not changed, this is the relative humidity in the room.