Desirable Humidity Levels Return to top The human body is comfortable when relative humidity ranges between 20 and 60 percent. In your home, an average relative humidity of 35 to 40 percent is appropriate when the outside temperature is 20?F or above. However, during cold weather, higher humidity ranges may cause structural damage because of condensation on windows and on the inside of exterior walls. As outdoor temperatures fall, condensation problems inside may develop.
The construction of a home also influences how much humidity is desirable. Tightly constructed buildings with properly installed vapor barriers and tight fitting doors and windows retain more heat and moisture. This is where mechanical ventilation becomes important. If a home does not have the proper mechanical ventilation, excess water vapor can move through walls and ceilings, causing wet insulation, peeling paint, and mold on walls and woodwork.
A vapor barrier protects walls from condensation.
The following table shows recommended indoor humidity levels in relation to outdoor temperatures.
Outside temperature (0?F) Recommended relative humidity +20? and above 35% to 40% +10? 30% 0? 25% -10? 20% -20? 15%