Damp (structural) - Humidity

Humidity

Humidity occurs in indoor environments due to building related causes. Porous walls, rising damp, and leaks in the building are determinants for structural dampness due to elevated humidity levels. The construction of the building can also lead to humidity and unwanted moisture in the indoor environment. Wet materials, such as lumber stored unprotected outdoors before construction, can lead to increased humidity indoors for up to the second year of occupancy in the building. Most commonly in residences, elevated relative humidity is produced by poor drainage systems. This leads to dampness in substructures such as crawlspaces and basements. The dampness results in vaporization where water vapor is transmitted into the building's interiors. Water vapor may enter the building through supply air ducts in building slabs and circulated by warm forced air. Water vapor can also enter a building through leaky return air ducts in homes with crawlspaces.

Human occupancy adds a significant amount of humidity to the indoor environment. Personal activity as basic as breathing and perspiration add moisture to an indoor space. Cooking and showering raise humidity levels in the indoor environment, which directly affects the structural dampness of a home. Aspects of the home can also increase the humidity of a space. Items such as aquariums, indoor swimming pools, hot tubs, and even indoor plants add to the humidity of an indoor space. All of these attributes can increase the humidity of a home beyond its recommended thirty to fifty percent.

Humidity levels in an indoor environment need to be accounted for based upon season and temperature. If humidity levels do not agree with the time of the year and the temperature during seasons, mold infestation and deterioration of the building will occur due to moisture. An acceptable humidity level in indoor spaces ranges from twenty to sixty percent year round. However, levels less than twenty percent in the winter and levels higher than sixty percent in the summer are deemed unacceptable for indoor air quality. Structural dampness is likely to occur as well as an increase of health risks associated with moisture damage.