Rooms located below-grade or partially below-grade (below ground level) can easily become contaminated with mold growth, because basements often experience water-leakage events and floods. But mold can also grow in conditions of elevated relative humidity, which often develop in below-grade spaces. (This is also true of houses that are built on a slab, where the lower level is partially below grade.) Most molds found in basements are commonly called mildew and are plant-like organisms that grow along surfaces and that require food and moisture. Paper, leather, cardboard, and even dust can support mold growth. It’s impossible to remove all foods for mold from an environment, but you can minimize moisture, which will prevent mold growth.

Breathing in living or dead mold spores can cause health symptoms, so you don’t want mold to remain in spaces where you live or work.If your house has a basement family room, playroom, exercise area, or office, you may spend a lot of time down there. Adults who exercise in such spaces and children who play on moldy basement carpeting can disturb and breathe in huge concentrations of mold spores – an unhealthy situation.

With very few exceptions, mold does not degrade wood, but wood-decaying fungi may be present if you’ve had a basement flood and the wood remained soaking wet and exposed to air (all fungi need oxygen from the air). If you see rotten or soft wood or even mushrooms, a contractor should evaluate the space, as structural repairs may be needed.

Mold can grow in barely visible colonies on acoustical ceiling tiles and unpainted drywall surfaces, especially in corners and the lower few feet of walls that cover the foundation. Mold also grows on the invisible dust trapped in carpeting and in concealed fiberglass ceiling and wall insulation, and on the solid furniture surfaces that face the cooler floor or walls. This furniture can include built-in bookcases, cabinets, benches, chairs, tables, and couches.

Any of this mold growth can cause the musty odors associated with some finished basement spaces, but sometimes, a basement can be full of mold growth that has little or no odor.

Basement spaces get moldy because there’s too much moisture present in either the liquid form (water) or vapor form (humidity). The moisture can come from the exterior because of poor drainage and grading, or because humid exterior air is flowing into the basement. Moisture can also come from plumbing leaks and floods, as well as overflowing mechanical equipment and appliances.