Why is there mold in my house?

A musty or damp odor can indicate mold or another moisture problem, even when growth is not visible. Mold releases spores into the air, and mold can grow on damp materials. CDC/NIOSH treats musty odors and visual inspection as more reliable than air sampling. If a room smells musty, look for leaks, standing water, water stains and condensation, and check the areas you cannot see, such as behind drywall and under carpet.

Trust the smell and go looking for moisture. Indoor mold growth can usually be seen or smelled, and in most cases the presence of visible growth or a musty odor is enough to act on without sampling. Check behind and under furniture, inside closets and cabinets, around AC air handlers and drain pans, under sinks, and along exterior walls. A moisture meter may help identify elevated moisture in building materials. Fix the source, dry the area and clean any growth you find.

Yes. Impermeable vinyl wall covering over gypsum board can trap moisture and cause hidden mold in hot-humid climates, and it often shows as pinkish-to-yellowish staining on the vinyl while the gypsum board behind it becomes soft or mushy. Florida also sees hidden growth where humid outdoor air is pulled into slightly depressurized wall cavities and condenses on the cold interior surface. If vinyl-covered walls stain or the drywall feels soft, treat it as a moisture investigation.

Rain exposes a path that may already exist: a roof or window leak, a crack in the building envelope, or water running toward the foundation instead of away from it. If you notice a musty odor after rain, check for leaks and damp materials, including hidden areas. EPA advises fixing building-envelope leaks as soon as possible and watching for condensation and wet spots, plus cleaning gutters and grading the ground away from the foundation. Trace the water before cleaning anything.

Yes. Hidden mold may be on the underside of carpets and pads, which stay wet long after the surface feels dry. Porous moldy materials such as carpet may have to be thrown away because mold grows into crevices and can be hard or impossible to remove completely. EPA recommends drying carpet and backing within 24 to 48 hours using water extraction, dehumidification and fans. If the material stayed wet longer, inspect it and determine whether it can be cleaned and dried thoroughly; the missed window alone does not decide whether it must be replaced.