Chicago's humid summers turn basements, bathrooms, and garden units into mold and mildew hot spots. Here's how to clean it safely and keep it from coming back.
When people picture Chicago property problems, they think of frozen pipes and road salt. But summer is quietly the busiest season for mold and mildew. Warm air off the lake holds a tremendous amount of moisture, and on a humid July week the relative humidity inside an un-air-conditioned hallway or garden unit can sit above 70% for days at a time. Mold needs three things to grow: moisture, a food source, and time. Chicago's older housing stock supplies all three. The plaster, wood trim, and paper-faced drywall in a Logan Square two-flat or a Rogers Park courtyard building are food. The humidity is the moisture. And in a busy leasing summer, small problems sit unnoticed between showings. By the time a tenant calls, what started as a patch of mildew on a bathroom ceiling has spread behind the baseboards.
The two terms get used interchangeably, but the difference matters for how you clean. Mildew is a surface fungus, usually gray or white, that grows flat on damp surfaces like grout, windowsills, and painted walls. It wipes away with the right cleaner and rarely damages the material underneath. Mold is more aggressive. It appears fuzzy or slimy, often black, green, or orange, and it digs into porous materials such as drywall, ceiling tiles, and wood. Mold that has penetrated a surface cannot simply be wiped off, and scrubbing it dry can release spores into the air. If you can see discoloration spreading across more than roughly ten square feet, or if it keeps returning after cleaning, you are likely dealing with a moisture source that has to be fixed before any cleaning will hold.
Certain spaces show up again and again across the buildings we service. Garden and basement units lead the list. Below-grade walls in an Andersonville greystone stay cool, so warm summer air condenses against them, and tenants often block the only vents with furniture. Bathrooms without working exhaust fans are next, especially in vintage Hyde Park apartments where the original ventilation was a single painted-shut window. Then come laundry rooms, the backs of closets on north-facing exterior walls, and the area around window air-conditioning units, where condensate drips onto sills and drywall. Common areas matter too. A shared basement storage room or a back stairwell in an Evanston walk-up can grow mildew along the baseboards all summer without a single tenant reporting it, because no one lives there to notice the smell.
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