During the heating season the average American home (unhumidified) may have a relative humidity (RH) as low as 13%. Amazingly, that is about one-half of the average RH in the Sahara Desert. The amount of humidity required in a home is dependent to a certain extent on the way it is constructed. A well insulated house with vapor barriers in walls, ceilings and slabs and properly fitting storm doors and windows may need only three gallons of additional moisture per day to maintain the proper relative humidity. A house of similar size but loosely constructed might require five times as much moisture in the same period.