Mold in Louisiana: what the numbers actually say

Louisiana sits on the northern rim of the Gulf of Mexico, a body of water that pumps warm moist air into the state every month of the year. According to NOAA National Weather Service climatological normals for 1991 to 2020, every major Louisiana metro posts an annual average relative humidity above 73 percent. That is roughly ten points higher than the U.S. national average and well above the 50 percent indoor-RH threshold EPA flags as the upper safe bound for household humidity.

Annual average dew points across the state run 61 F to 65 F, compared with a U.S. national average near 50 F. Dew point is the more honest moisture metric because it does not move with temperature. A 65 F dew point means the air is fully saturated the moment any surface, wall cavity, or coil drops to 65 F. In a Louisiana summer where night air sits in the upper 70s, the difference between the dew point and the dew point of an air-conditioned wall cavity is small enough that condensation is routine.

Louisiana is also America’s most frequently hit hurricane state per unit coastline, according to the NOAA National Hurricane Center landfall database. The state has absorbed more than 60 tropical storm or hurricane landfalls since 1851. FEMA disaster declarations for flooding events specifically, including non-tropical rainfall events, exceed most other U.S. states. Each of those events resets the bulk-water clock: EPA guidance says porous materials that stay wet longer than 24 to 48 hours are considered at risk of mold colonization.

Louisiana vs U.S. average

Why New Orleans tops the ranking. Three independent factors compound. First, humidity: Louis Armstrong International reports the highest annual average RH of any Louisiana reporting station. Second, geography: large portions of Orleans Parish sit below sea level behind levees, which means saturated soil is the default state and foundation moisture wicks into walls year-round. Third, housing stock: the New Orleans core is dominated by century-old shotgun and creole cottage housing with cellulose-heavy materials (plaster with wood lath, cypress sills, cotton-backed insulation) that retain water long enough for colonization. Every post-1965 major hurricane (Betsy, Camille, Katrina, Ida) produced documented widespread post-event mold.

Why Shreveport is the lowest in the state but still “high”. North Louisiana sees drier air masses from the Texas interior more often than south Louisiana, which pulls the annual RH average down four points. The trade-off is older housing stock with less modern vapor barriers and HVAC systems that are frequently undersized. When outdoor dew points do spike into July and August, indoor RH catches up fast. Shreveport still beats the national average for days above 70 percent RH.

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

Species information is general and informational. Health responses vary. Consult a 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 account for most of the mold risk reduction available to a Louisiana homeowner. Each maps to an existing free Mold Scanner AI tool.

A. Run a hurricane-season checklist every June

Before the storm (by June 1): Roof inspection, gutter clear, service HVAC, inventory removable content above flood line, verify flood insurance policy active (NFIP requires a 30-day waiting period). First 48 hours after landfall: Remove standing water, open windows only when outdoor RH is lower than indoor, run any operational AC or generator-powered dehumidifier, photograph all damage for insurance. First 7 days: Cut out wet drywall a foot above the visible water line, remove saturated insulation and carpet padding, dry framing with air movers, log moisture-meter readings daily. Materials that still read above 16 percent moisture content after 72 hours of drying should be removed.

B. Keep indoor RH below 50 percent year-round

Use a hygrometer in each living zone. Add portable dehumidification in any room above 55 percent. EPA guidance: 30 to 50 percent indoor relative humidity. For Louisiana, target 45 to 50 percent given the outdoor load.

C. Scan quarterly, especially after storms

Louisiana’s four high-risk quarters are June (hurricane season start), September (peak hurricane season), January (cold-surface condensation on AC off days), and April (spring rain plus HVAC switchover).

Monthly average RH across the five reporting stations, expressed as percent of the year the indoor growth threshold is routinely exceeded. Based on NOAA NWS climatological normals 1991–2020.

Every month of the year, Louisiana’s average RH sits at or above 73 percent. There is no dry season. Mold risk is continuous; hurricane events are accelerants, not the only cause.

Louisiana has no state-level mold disclosure or remediation licensing statute. 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.