Issue link: https://hi.iaq.net/i/630729
Moisture, Mold and Mildew 143 be the location where condensation first occurs, if the relative humidity at the surface reaches 100%. It is important to understand this when trying to understand why mold is growing on one patch of wall or only along the wall-ceiling joint. It is likely that the surface of the wall is cooler than the room air because there is a void in the insulation or because wind is blowing through cracks in the exterior of the building. FIGURE C-2: Relationship of Temperature, Relative Humidity, and Moisture in the Air A relative humidity reading taken in a room will only give an accurate indication of the actual amount of moisture present if a temperature reading is taken at the same time. The chart below shows that air at 70°F and 40% RH contains approximately 0.006 pounds of moisture per pound of dry air (as indicated by the bold line), while air that is at 50°F and 40% RH contains approximately 0.003 pounds of moisture per pound of dry air (as indicated by the dashed line). Although both are at 40% RH, the 70°F air contains roughly twice as much moisture as the 50°F air. SOURCE: Adapted from Psychometric Chart from ASHRAE Fundamentals, 1981 TAKING STEPS TO REDUCE MOISTURE Mold and mildew growth can be reduced where relative humidities near surfaces can be maintained below the dew point. This can be accomplished by reducing the moisture content (vapor pressure) of the air, increasing air movement at the surface, or increasing the air temperature (either the general space temperature or the tempera- ture at building surfaces).