There are 3 main sources of moisture in your home; the first being air leaks. Air can leak into the home through walls, roofs and floors and have damaging effects on a house. Uncontrolled airflow through the shell not only carries moisture into framing cavities, causing mold and rot, but it can also account for a huge portion of a home’s energy use and can cause indoor-air-quality problems. In a leaky house, large volumes of air – driven by exhaust fans, the stack effect, and wind – can blow through the floor, walls, and ceiling.
The second source of moisture is diffusion through materials. This is a process by which vapor spreads or moves through permeable materials caused by a difference in water vapor pressure. An example of this is when the soil becomes saturated and that moisture enters the crawl space through the walls by vapor diffusion. Installing a vapor barrier or vapor diffusion retarder can help reduce the rate at which the water vapor can move through a material.
The final source is internally generated moisture. A family of four can add, on average, up to 25 pints of water to the air simply by washing dishes, taking showers, cooking, and breathing. Adding 4 pints of water to the air in a house at 70°F and 30% RH can boost the RH to 50%. Eight pints can boost RH to 70%.
There’s a great article on the Building Science Corporation website which has additional information on this subject. Here’s a quick link Air Leaks How They Waste Energy and Rot Homes.
Next week we will be sharing the top 10 signs of high moisture. See you then.