Mold in Georgia: what the numbers actually say

Georgia pulls moist air from two directions: the Gulf of Mexico to the southwest and the Atlantic to the east. NOAA National Weather Service climatological normals for 1991 to 2020 put annual average relative humidity for the major metros roughly between 68 and 73 percent. The national average sits near 65. From late May through September, dew points south of the fall line hold above 70 F for weeks at a time, which keeps homes in the growth zone EPA flags for common household molds. You can check your own area with our mold risk by ZIP tool.

Then there’s the rain. Atlanta averages about 50 inches a year, more than Seattle, and most of it lands in hard thunderstorm bursts rather than drizzle. Those bursts find torn shingles, lifted flashing, clogged gutters, and window seals. EPA guidance says porous materials that stay wet longer than 24 to 48 hours are at risk of mold colonization, so every summer downpour starts a clock somewhere.

The third factor sits under the floor. A large share of Georgia housing, from pre-war bungalows in Macon to 1970s and 1980s subdivisions around Atlanta, stands on vented crawl spaces over red clay that drains slowly. In summer, humid outdoor air flows through the vents, cools against shaded soil, framing, and ductwork, and condenses. That’s why so many Georgia mold cases start on floor joists and subfloor that nobody looks at for years.

The coast adds an occasional storm accelerant. Hurricane Matthew (2016) and Hurricane Irma (2017) both pushed surge and flooding into coastal Georgia. Hurricane Michael (2018) was still a major hurricane when it crossed into southwest Georgia, and Hurricane Helene (2024) cut a damage corridor from Valdosta to Augusta. Compared with Louisiana’s 60+ landfalls, Georgia’s storm count is modest. Humidity, rainfall, and crawl spaces do most of the work here.

Georgia vs U.S. average

Why Savannah tops the ranking. Three factors compound. First, humidity: coastal Georgia posts the state’s highest annual RH, and morning readings near the river regularly run into the high 80s. Second, housing: the historic district is packed with homes more than a century old, full of heart pine, plaster on wood lath, and vented crawl spaces under raised floors. Those cellulose-heavy materials hold water long enough for colonization. Third, storms: the metro evacuated for Matthew in 2016 and took surge flooding from Irma in 2017, and each event resets the 24-to-48-hour wet-materials clock EPA warns about.

Why Atlanta still makes the list. Atlanta sits over 1,000 feet up with drier air than the coast, so people assume mold is a coastal problem. The metro’s risk comes from water hitting the house, not air alone: roughly 50 inches of rain a year in hard bursts, red clay that sheds water toward foundations, and the state’s biggest inventory of vented crawl spaces and below-grade basements. A crawl space that stays damp all summer can keep the subfloor above it wet enough to grow mold without a single visible leak, and that growth can spread out of sight inside walls before anyone smells it.

Every EPA indoor air quality guide lists the same core species for warm humid climates. Georgia homes concentrate five of them.

Species information is general and informational. Health responses vary. See a licensed physician for symptom evaluation. Species sources: EPA Mold Remediation in Schools and Commercial Buildings, EPA A Brief Guide to Mold Moisture and Your Home, CDC National Center for Environmental Health guidance.

Three actions cover most of the mold risk reduction available to a Georgia homeowner. Each maps to a free Mold Scanner AI tool or guide.

A. Dry out the crawl space first

Most Georgia mold stories start under the floor, so start there. Twice a year, look for standing water, damp clay, white fuzz on joists, or a musty smell at the vents. Cover exposed soil with 6-mil plastic sheeting, lapped and taped, get downspouts discharging well away from the foundation, and fix grading that slopes toward the house. If the space stays damp all summer, a sealed crawl space with a dedicated dehumidifier is the durable fix. Our crawl space guide walks the full inspection, and an ERMI dust test can help show whether crawl-space spores are reaching the living space. If you find growth, start with our guide to getting rid of mold. For anything bigger than about 10 square feet, EPA’s threshold, hire a qualified mold remediation professional (one who follows the IICRC S520 standard; ACAC or RIA credentials and state licenses count too).

B. Keep indoor RH below 50 percent

EPA guidance is 30 to 50 percent indoor relative humidity. For Georgia summers, 45 to 50 percent is the practical target. Put a hygrometer in each living zone, run your readings through the Indoor Humidity Context Calculator, and add a dehumidifier in any basement or room over a crawl space that reads above 55 percent in July.

C. Start the clock after every storm

Georgia’s storm story is mostly thunderstorms: hail-torn shingles, wind-lifted flashing, gutters dumping water into walls. After any roof leak or flooding, run the storm damage mold timer and work the post-flood checklist, because the 24-to-48-hour window EPA describes goes fast. Coastal homeowners should treat the June 1 to November 30 hurricane season the way Savannah does: roof and gutter inspection by late May, and a dry-out plan ready before the first named storm.

Monthly average outdoor RH for Georgia, approximate statewide averages built from NOAA NWS climatological normals for 1991 to 2020. Unlike the Gulf Coast, Georgia has a real seasonal swing: spring runs driest, late summer peaks.

The April dip is real but shallow. Even Georgia’s driest months average above 60 percent outdoors, and July through September keeps crawl spaces and closed rooms in the growth zone. Mold season never fully closes here, it slows down. Our prevention guide covers the year-round routine.

Georgia has no widely known state-level mold licensing program; verify current rules with the state health department. The agencies below are the authoritative starting points.

Every source chip on this page points here. Agency and statute pages first, then the federal technical references.