The bathroom is a major source of moisture within a home—showering, soaking in the bathtub, running water in the lavatory, water evaporating from the toilet bowl, towels drying. In a new bathroom, many building products such as grout, joint compounds, plaster, and latex paints also contain water. These products dry and cure, and water vapor is released.

Even in a very dry climate, excess moisture inside a building structure can lead to serious problems.

Prevention of moisture problems within the bathroom is part of the designer’s responsibility. The designer needs to consider problems that might occur throughout the home due to moisture gener­ated in the bathroom. The designer’s goal should be to make it as easy as possible to control moisture in the bathroom, and to minimize the potential for problems from moisture that is not controlled.

Excess moisture is a potential problem for both the building and the people who live in it. Excess moisture in building materials leads to structural problems, such as peeling paint, rusting metal, and deterioration of joists and framing. Damp building materials tend to attract dirt and therefore require more cleaning and maintenance.

Damp spaces make good environments for the growth of many biological pollutants. Bacteria and viruses thrive, as do pests from dust mites to cockroaches. Wet building materials can also harbor mold, which leads to further structural damage. Mold can be a health threat. In addition, mold growing on interior finish materials smells bad and is ugly.

Подпись: Moisture Basics Water vapor is present in the air in varying amounts, depending on the temperature. The warmer the air, the more water vapor it will hold. Humidity describes how much water vapor there is in air. Relative humidity, expressed as a percent, can be explained by the following formula: Amount of water vapor in the air maximum amount of water vapor air can x 100 = relative humidity hold at that temperature Note that the temperature of the air is important to understanding relative humidity. For example, on a winter’s day, when the temperature is 20 degrees Fahrenheit (-7 degrees Celsius) and the relative humidity is 70 percent, the air will actually be much drier, and have less moisture, than on a summer’s day, when the temperature is 85 degrees Fahrenheit (21 degrees Celsius) and the humidity is 70 percent. Condensation, the opposite of evaporation, occurs when water vapor returns to a liquid state. As air cools, it can no longer hold as much water vapor, so the water condenses into a liquid. The temperature at which condensation occurs is referred to as the dew point. Most everyone is familiar with the experience of taking a warm shower and then finding that water has condensed onto the cooler surface of the bathroom mirror.

The cycle of water evaporating and condensing in a bathroom can lead to moisture problems. A bathroom tends to be warmer than other parts of the home, which is desirable as it increases the comfort level when someone is naked or wet. However, because they are warmer, bathrooms tend to have higher humidity.

Many bathroom activities, such as showers and baths, further increase the temperature of the air as well as the moisture level. However, materials and surfaces in the bathroom tend to be cooler

Подпись: FIGURE 3.12 AS warm, moist air moves through a wall, condensation will occur when the air is cooled to the dew point temperature. Rendered in 20-20 by Michael Brgoch, CKD

than the air—which leads to condensation. In addition, when the user finishes showering or bath­ing, the room tends to cool down, leading to more condensation.

Wet materials result in increased maintenance, and eventually, deterioration. This is especially true of any that are absorbent and stay damp, such as drywall and textiles.