Water rots almost all building materials, causes mold to grow and ruins the ability of most insulations to function. Great green framing lumber, surrounded by green insulation will only serve to grow a great crop of mold and will decay into rubble if water is allowed to intrude. In Selecting Building Materials , we provided details on how to flash windows, doors, porches, chimneys and other key areas of the exterior walls and roof to ensure your home remains a place of dreams, not nightmares.
The basements and crawlspaces of homes are commonly places we avoid because of their musty odors, mold and dampness. A clue for you: when you smell a musty odor, what you smell is mold. As with spoiled meat, our noses are acutely tuned to that smell through thousands of years of exposure and self-preservation, and we very rarely mistake it for any other odor. Building science has proved through a million blower door tests that the basement, attic, garage and crawlspace air are intimately connected to our living spaces. Some people try to tell themselves that those bad things are down there and not in here. If only that were true; but it isn’t. The air in these connected areas moves into your home easily through HVAC ducts that run through these areas, the plumbing and electrical penetrations that connect them, hollow interior wall cavities, utility chases and floor framing. Even if you don’t have a mold allergy, your wooden framing is going to suffer structural rot and decay if it is exposed to high moisture levels.
Humidity Control
Humidity control should be the first defense against indoor contaminants from mold, mildew and dust mites. At relative humidity levels over 50 percent, dust mite populations flourish, leaving unseen masses of dust mite waste that creates havoc for humans sensitive to that respiratory contaminant. Mold grows on surfaces above 60 percent relative humidity during the cooling season and in building cavities where humid air collides with cooler surfaces and condenses. All of these activities may go unseen but not undetected by sensitive noses. And again, our lungs are the doorway to our bloodstreams. Many HVAC systems now come with humidity-sensing thermostats (thermidistats) that cause the air handler to operate when unacceptable humidity levels are detected. Air conditioners function as dehumidifiers, so running them helps to bring humidity back to tolerable and healthy levels. Best practice is to have whole-house humidity control systems analysis recommend systems designed specifically to address these concerns.
In some very cold regions, humidity control includes the use of a whole-house humidifier. If you live in an area with long periods of very low relative humidity, these devices can add to your comfort. But a word of caution is needed here. When indoor relative humidity levels reach 30 percent or above during the heating season, the danger of condensation forming on cold surfaces increases greatly. This condensation can occur around windows, on basement walls and other cool surfaces. The resulting mold growth and possible decay can be very harmful to your family’s health and to the durability of your home. If you find even slight dampness forming in cool areas, lower the indoor humidity level until the condensation stops. It is also very important to remember to turn off your humidifier when warmer and more humid spring weather returns.
