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25 Moldiest and Most Humid Cities in the U.S.

Mold and humidity often go hand in hand. Does that mean the most humid cities in America are also the worst cities for mold allergies? Let’s look at the data about the worst cities for mold and humidity.


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What Does High Humidity Even Mean?

Relative humidity measures the moisture in the air as a percentage of its total holding capacity. A 50 percent humidity measurement means the moisture in the air is half of its maximum capacity.

Humidity can make a hot day feel even hotter, and this effect can be explained by the science of how the body reacts with the environment.

Sweating is the body’s natural air conditioner and as moisture evaporates from the skin, the body cools down. However, if a city reaches the upper limits of 100 percent relative humidity, the air is saturated and cannot hold any more water. This means perspiration stays on the skin rather than evaporating into the air.

This result is that the higher the humidity, the less the body can cool itself through sweat evaporation.

Relative humidity between 30 and 50 percent is typically the most comfortable range for people. Interestingly, buildings have similar preferences. The EPA recommends indoor humidity levels should be kept between 30 and 50 percent to stop the growth of mold and discourage pests such as cockroaches and dust mites.

Additionally, humidity levels ranging from 55-60% and above can contribute to problems like mold growth and wood rot. Mold growth can contribute to unhealthy conditions and affect structural integrity, and wood rot can significantly impact the stability of your underlying structures. Rotting wood supports like floor joists in crawl spaces can lead to sagging and uneven floors, and fail to properly support these above floors. When you get in touch with your local Groundworks crawl space experts, we will test the air and the moisture of the wood during our inspections so you know what you’re dealing with in your crawl space.

Because ground moisture typically leads to indoor humidity problems, the most effective home dehumidification is usually in the basement or crawl space. By properly sealing and dehumidifying these lower levels, the effects can be felt throughout the house because of air’s natural upward circulation.

Which Cities Have the Highest Humidity?

There’s a good reason why we tend to associate humidity with cities in southern states such as Florida and Louisiana.

Large bodies of water tend to cause more humidity because evaporation adds water to the air. Plus, warmer water evaporates more quickly, and so warmer cities near water are more apt to have high levels of humidity.

Using data from the National Oceanic and Atmospheric Administration (NOAA), we identify the cities with the highest average relative humidity, based on morning humidity measurements.

25 Most Humid Cities in the United States

  1. Port Arthur, TX — 90% humidity
  2. Lake Charles, LA — 90% humidity
  3. Brownsville, TX — 90% humidity
  4. Victoria, TX — 90% humidity
  5. Jackson, MS — 90% humidity
  6. Meridian, MS — 90% humidity
  7. Quillayute, WA — 89% humidity
  8. Corpus Christi, TX — 89% humidity
  9. Baton Rouge, LA — 89% humidity
  10. Houston, TX — 89% humidity
  11. Gainesville, FL — 89% humidity
  12. Saint Paul Island, AK — 88% humidity
  13. Olympia, WA — 88% humidity
  14. Jacksonville, FL — 88% humidity
  15. Fort Myers, FL — 88% humidity
  16. Orlando, FL — 88% humidity
  17. Tallahassee, FL — 88% humidity
  18. Cold Bay, AK — 87% humidity
  19. San Francisco, CA — 87% humidity
  20. New Orleans, LA — 87% humidity
  21. Daytona Beach, FL — 87% humidity
  22. Shreveport, LA — 87% humidity
  23. Mobile, AL — 87% humidity
  24. Montgomery, AL — 87% humidity
  25. Asheville, NC — 87% humidity

What Cities Have the Most Mold?

Mold is naturally found everywhere, but it grows most prolifically in damp areas with high humidity. In part, this means the cities with the highest humidity could also have high levels of mold. However, that’s only part of the story.

To measure mold, we first need to divide potential environments into indoors and outdoors. Even though the mold spores themselves may not be different, mold needs specific conditions to grow, and differences can occur between the environments.

For example, in a cold, wintry city, there are likely to be minimal outdoor mold spores. However, if a house in that setting has high humidity in the basement or crawl space, the warm, damp environment can create the ideal conditions for indoor mold growth.

When it comes to outdoor mold in the U.S., the growth of airborne mold spores is typically related to regional climate. Areas with high humidity, heavy precipitation, and low winds could see the worst problems. The peak is usually around July for the warmer states. For the cooler states, mold spores peak around October as piles of damp leaves and debris accumulate.

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How Is Indoor Mold Growth Different?

Indoor mold can be especially damaging to one’s health and property. Mold allergy sufferers may even be prone to asthma attacks because of the duration of mold exposure.

Researchers have found that when it comes to indoor mold, “It is primarily the homes’ internal and external structural integrity that controls moisture and mold growth,” said one analysis by researchers at the Environmental Protection Agency (EPA) and the Department of Housing and Urban Development (HUD).

The EPA and the NY Academy of Medicine sampled air quality in homes across the country. They found indoor moldy conditions have less to do with geography than a home’s water problems or moisture conditions.

water and moisture problems can cause indoor mold

The research compared different home conditions based on the level of mold. Using the Environmental Relative Moldiness Index (ERMI), a home in the lowest quartile for mold had 24 percent of respondents say they had water damage and 11 percent say they have a musty smell. In contrast, homes in the highest quartile of mold had 34 percent of respondents with water problems and 24 percent say they have a musty smell.

Controlling mold starts with managing indoor humidity. However, all building situations are different. A free inspection from your local Groundworks basement waterproofing and foundation repair experts can help you determine if the best solution is to improve drainage, add a vapor barrier, install a sump pump, or add a dehumidifier to your basement or crawl space. Contact us today for a free inspection and estimate.