- Press Release
Study Ranks America’s 50 Moldiest Cities Using Climate and Housing Data
Analysis combines rainfall, humidity, home age, and flood exposure across major U.S. metros
A new nationwide study has identified the 50 most mold-prone cities in the United States by analyzing environmental conditions and housing characteristics that contribute to long-term indoor mold growth.
The analysis evaluated more than 200 major U.S. cities using six quantitative metrics, including average annual rainfall, average relative humidity, number of high-humidity days, median home age, flood risk scores, and storm exposure frequency. Each city was assigned a composite mold risk score based on how strongly these factors correlate with documented mold growth conditions.
According to the data, cities in the Southeast dominated the rankings, accounting for 32 of the top 50 moldiest cities nationwide. These cities experienced sustained relative humidity levels above 70 percent, annual rainfall exceeding 50 inches, and a higher concentration of homes built before 1980, a period when modern moisture control standards were less common.
Key findings from the study include:
64 percent of the top 50 mold-prone cities are located in the Southeast
Cities ranking in the top 10 experience an average of 190 or more high-humidity days per year
Homes built before 1980 showed a 41 percent higher mold risk score compared to newer construction
Cities with flood risk scores above 7 out of 10 were 2.3 times more likely to rank in the top 25
Annual rainfall above 55 inches correlated with consistently higher mold exposure risk
Newer homes in high-humidity regions still showed elevated mold risk when relative humidity exceeded 65 percent for extended periods
Researchers found that mold risk is rarely driven by a single event. Instead, the data shows that prolonged moisture exposure over time plays a larger role than isolated flooding incidents. High humidity, repeated storm activity, aging building materials, and insufficient ventilation were identified as the most influential factors contributing to elevated mold risk scores.
The study also found that flood risk compounds existing moisture issues. Cities with both high rainfall and above-average flood risk were significantly more likely to experience recurring indoor moisture problems, increasing the likelihood of mold growth even after remediation efforts.
The full dataset includes city-by-city rankings, individual mold risk scores, and a detailed breakdown of how each environmental and housing factor contributed to the final results. The study also outlines broader regional trends homeowners can use to better understand mold exposure risks in their area.
The complete study, rankings, and methodology are available at: “America’s 50 Moldiest Cities” study
For Immediate Release
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