Mold by state: All 51 US Mold Reports
Mold is a local problem with a national vocabulary. The humidity a house sits in, the storms that soak it, the license a remediator needs and the notice a tenant has to give all change at the state line. Pick your state below.
Every report in this index carries the same four things: the NOAA humidity record for the weather stations in that state, the water events that actually wet homes there, the rule on who may legally perform mold remediation, and the statute a renter's mold complaint runs through.
The humidity column is the mean of the morning and afternoon relative humidity NOAA publishes for each first-order station in the state, so a range means the state spans different climates rather than that the number is fuzzy. Texas runs from 38 percent at El Paso to 76 percent on the Gulf. Oregon runs from 58 percent at Pendleton to 80 percent at Astoria. One state, two completely different mold problems.
Humidity is only half the picture. Six jurisdictions license or certify mold professionals directly: Texas, Florida, New York, Louisiana and Washington, DC license both assessors and remediators, and New Hampshire requires a national certification for anyone paid to perform residential mold assessment while leaving remediation unlicensed. A few more regulate the work without licensing it. Virginia makes it a Consumer Protection Act violation to sell residential mold remediation without a recognized certification, Kentucky requires remediation companies to follow standards its Attorney General sets, Connecticut requires residential mold remediators to register as home improvement contractors, and Illinois has a registration act on the books that its own health department says is not yet in force. Everywhere else the work falls under general contractor licensing or under nothing at all, which puts the credential check on the homeowner. Each state report says which situation you are in and links the agency page it was checked against.
New England
| State | Mean RH range | Humidity band | What drives mold there |
|---|---|---|---|
| Connecticut | 64 to 67% | Moderate | Coastal Long Island Sound humidity meets an old, heavily basemented housing stock, so summer condensation on cool foundation walls is the default failure. |
| Maine | 68 to 70% | Humid | Long cold winters push moisture out through the envelope, and coastal fog keeps Portland's morning humidity near 78 percent even when the annual mean looks tame. |
| Massachusetts | 64 to 66% | Moderate | Triple-deckers and pre-war basements plus a 72 to 75 percent morning humidity mean the mold story is condensation, not rainfall. |
| New Hampshire | 66% | Moderate | Concord's 80 percent morning humidity against a 53 percent afternoon reading is the biggest daily swing in New England, and that swing is what wets a cold surface. |
| Rhode Island | 65% | Moderate | The densest rental stock in New England sits under 48 inches of annual rain, so landlord notice rules matter here more than the climate does. |
| Vermont | 67% | Moderate | Deep-winter interior moisture and ice damming drive the problem, with Burlington's humidity peaking in December rather than August. |
Mid-Atlantic
| State | Mean RH range | Humidity band | What drives mold there |
|---|---|---|---|
| New Jersey | 62 to 68% | Humid | Two climates in one small state: an Atlantic City coastal profile near 68 percent and a Newark urban profile near 62 percent, with flood-prone shore towns in between. |
| New York | 62 to 72% | Humid | Binghamton and Buffalo run near 72 percent while Manhattan sits at 62 percent, so upstate is a humidity story and the city is a building-systems story. |
| Pennsylvania | 65 to 71% | Humid | Lake Erie humidity at 71 percent in the northwest, drier Philadelphia at 65 percent, and a very old housing stock the whole way across. |
South Atlantic
| State | Mean RH range | Humidity band | What drives mold there |
|---|---|---|---|
| Delaware | 66% | Moderate | One NOAA station, a 78 percent morning mean, and a coastal plain water table that puts crawl spaces close to saturation. |
| Washington, DC | 64 to 66% | Moderate | A humid subtropical summer, a dense rental market, rowhouse basements below grade, and a licensing rule that covers mold work directly. |
| Florida | 72 to 74% | Very humid | The highest sustained dew points in the country, hurricane landfalls, and air conditioning running most of the year. |
| Georgia | 68 to 70% | Humid | Savannah's coastal humidity, Atlanta's clay soil and crawl-space housing stock, and a long warm season for growth. |
| Maryland | 65% | Moderate | Chesapeake Bay humidity, a 77 percent morning mean, and a rowhouse and split-level stock with basements below the water table. |
| North Carolina | 66 to 74% | Very humid | Cape Hatteras at 74 percent against Charlotte at 66 percent, with crawl spaces and hurricane rainfall as the two recurring mechanisms. |
| South Carolina | 67% | Moderate | Coastal storm surge and a humid interior, with morning humidity in the low 80s statewide. |
| Virginia | 64 to 68% | Humid | Tidewater humidity near Norfolk at 68 percent, mountain condensation to the west, and crawl spaces across most of the state. |
| West Virginia | 70 to 72% | Humid | Elkins posts an 86 percent morning mean, the highest in the mid-Atlantic, and mountain flash flooding does the rest. |
East South Central
| State | Mean RH range | Humidity band | What drives mold there |
|---|---|---|---|
| Alabama | 70 to 72% | Humid | Mobile runs an 87 percent morning humidity, Gulf storms land regularly, and slab-on-grade construction traps what gets in. |
| Kentucky | 68 to 71% | Humid | Ohio River valley humidity, 48 to 52 inches of rain, and a large stock of finished basements in the flood plain. |
| Mississippi | 72 to 74% | Very humid | The highest morning humidity readings in the country outside the Gulf Coast proper, with Jackson at 90 percent. |
| Tennessee | 68 to 70% | Humid | Three river valleys, 51 to 55 inches of rain, and crawl spaces that stay damp from March through October. |
West South Central
| State | Mean RH range | Humidity band | What drives mold there |
|---|---|---|---|
| Arkansas | 70% | Humid | An 85 percent morning humidity, Mississippi delta flooding, and 47 to 50 inches of rain a year. |
| Louisiana | 72 to 76% | Very humid | The wettest and most hurricane-exposed state in the country, with a 90 percent morning humidity at Lake Charles. |
| Oklahoma | 68% | Humid | A 50 F mean dew point, spring hail and tornado roof damage, and flash flooding along the Arkansas River. |
| Texas | 38 to 76% | Very humid | The widest humidity spread of any state, from 76 percent at Galveston to 38 percent at El Paso, and a mold program that licenses assessors and remediators separately. |
East North Central
| State | Mean RH range | Humidity band | What drives mold there |
|---|---|---|---|
| Illinois | 70 to 72% | Humid | Chicago's lake-effect humidity, a December peak rather than a summer one, and basements everywhere. |
| Indiana | 70 to 72% | Humid | An 83 percent morning mean at Fort Wayne, a sump-pump housing stock, and Ohio River flooding at the southern end. |
| Michigan | 70 to 74% | Very humid | Surrounded by the Great Lakes, humidity peaks in December, and Sault Ste. Marie posts an 84 percent morning mean. |
| Ohio | 69 to 72% | Humid | Consistent high-60s to low-70s humidity year-round with no dry season, and finished basements as the default risk. |
| Wisconsin | 71 to 73% | Very humid | Green Bay and Madison run 83 percent mornings, and the deep freeze pushes interior moisture into cold wall cavities. |
West North Central
| State | Mean RH range | Humidity band | What drives mold there |
|---|---|---|---|
| Iowa | 70 to 73% | Very humid | Waterloo's 84 percent morning mean, Mississippi and Cedar River flooding, and a farmhouse basement stock that predates vapor barriers. |
| Kansas | 60 to 70% | Humid | A 10-point humidity gradient from Topeka to Goodland, plus hail and flash flooding that opens the envelope. |
| Minnesota | 69 to 74% | Very humid | Rochester at 74 percent, International Falls at 72, and a heating season long enough that interior moisture has nowhere to go. |
| Missouri | 70 to 72% | Humid | Columbia at 72 percent, two major river confluences, and a long history of federally declared flood events. |
| Nebraska | 60 to 70% | Humid | Omaha at 70 percent against Scottsbluff at 60, with Missouri River flooding at the eastern edge. |
| North Dakota | 70 to 73% | Very humid | Grand Forks posts an 83 percent morning mean, and Red River spring flooding is the state's defining water event. |
| South Dakota | 60 to 72% | Humid | Huron at 72 percent versus Rapid City at 60, a genuine split between the eastern prairie and the western hills. |
Mountain West
| State | Mean RH range | Humidity band | What drives mold there |
|---|---|---|---|
| Arizona | 34 to 52% | Dry | Phoenix at 34 percent makes mold a plumbing-failure story, except in Flagstaff at 52 percent where snowmelt changes the math. |
| Colorado | 46 to 54% | Dry | A 46 to 54 percent range statewide, so mold follows supply lines, ice dams and burn-scar flooding rather than the weather. |
| Idaho | 53 to 58% | Dry | Lewiston at 58 percent, a December humidity peak, and crawl spaces under a cold-climate building stock. |
| Montana | 54 to 66% | Moderate | Kalispell at 66 percent against Billings at 54, with the western valleys holding moisture the plains never see. |
| Nevada | 28 to 50% | Very dry | Las Vegas at 28 percent is the driest reading in the country, which makes every Nevada mold case a water-intrusion case. |
| New Mexico | 41 to 51% | Very dry | A 41 to 51 percent range, monsoon-season flash flooding, and evaporative coolers that add moisture indoors on purpose. |
| Utah | 53% | Dry | Salt Lake City at 53 percent, a January humidity peak, and a valley inversion that keeps winter air damp at ground level. |
| Wyoming | 52 to 60% | Dry | The state runs 52 to 60 percent, so mold arrives with a burst pipe, an ice dam, or a roof that failed under snow load. |
Pacific
| State | Mean RH range | Humidity band | What drives mold there |
|---|---|---|---|
| Alaska | 65 to 79% | Very humid | Juneau at 79 percent and Annette Island at 104 inches of rain, against Fairbanks at 65 percent and deep-cold condensation. |
| California | 56 to 78% | Very humid | San Francisco at 78 percent versus Fresno at 56, marine layer on one side and irrigation-valley heat on the other. |
| Hawaii | 65 to 74% | Very humid | Hilo takes 120 inches of rain a year and the state's dew point never drops below the mid 60s, so drying is the whole game. |
| Oregon | 58 to 80% | Very humid | Astoria at 80 percent and 70 inches of rain against Pendleton at 58 percent, split by the Cascades. |
| Washington | 58 to 82% | Very humid | Quillayute at 82 percent and 101 inches of rain, Yakima at 58 percent and 8 inches, in the same state. |
How to read the humidity band
The band names what the column measures: annual mean relative humidity at that state's NOAA stations. It is not a mold forecast. A very dry state with a slab leak has a mold problem, and a very humid state with a tight envelope and a working dehumidifier may not.
Very humid is 73 percent and up, Humid is 68 to 72, Moderate is 62 to 67, Dry is 52 to 61, and Very dry is under 52. EPA generally advises keeping indoor relative humidity between 30 and 50 percent where possible, so every band on this page sits above that outdoors, which is why ventilation choices matter more in some states than others.
Morning humidity, which each state report shows separately, is the number that usually decides whether a cold surface sweats overnight. Several states with an unremarkable annual mean run morning readings in the mid 80s, and that is where the growth starts.
Frequently asked questions
Which states require a license to do mold remediation?
Six jurisdictions, and it is worth knowing which. Texas, Florida, New York, Louisiana and Washington, DC license mold assessors and mold remediators as separate credentials, and each publishes a way to verify a company before you sign. New Hampshire is a half case: since 2016 it has been unlawful there to perform residential mold assessment for pay without a national third-party certification, while remediation stays unlicensed. Several states regulate the work without licensing it, including Virginia, Kentucky and Connecticut, and Illinois has an enacted registration act that its own health department says does not bind anyone until the rulemaking is adopted. Everywhere else there is no mold credential at all, so the check falls to you: IICRC certification, ANSI/IICRC S520 compliance, and a firm that does not both assess and remediate. The licensing section of each state report names the rule and links the page it was verified against.
Is there a federal mold standard?
No. There is no federal law setting a permissible level of mold in a home, and no federal agency certifies mold inspectors or remediators. EPA publishes guidance rather than a limit, HUD publishes healthy-housing guidance for the properties it touches, and OSHA covers worker protection during the work. The practical standard the industry uses is ANSI/IICRC S520, which is a private consensus standard, not a regulation. That gap is exactly why state rules and state health department guidance carry so much weight.
Does a humid state always mean more mold?
No, and this is the most common mistake. Humidity sets the baseline, but the events that soak building materials matter more. A burst supply line in Nevada wets drywall exactly as thoroughly as a wet August in Mississippi, and EPA guidance treats porous material that stays wet past 24 to 48 hours as at risk either way. What high outdoor humidity does change is how hard it is to dry that material out afterward, and whether an unoccupied basement drifts above 60 percent on its own.
Which states set a square-footage threshold for professional mold work?
The licensing states mostly do, and the number varies. Texas requires a licensed assessor and remediator at 25 contiguous square feet or more. Florida and New York set their thresholds above 10 square feet. Washington, DC allows an unlicensed person to clean less than ten affected square feet and requires a licensed remediation professional at or above that. Louisiana keys its licensing requirement to job value rather than area. Several states with no licensing at all still publish 10 square feet as a rule of thumb for calling a professional, including Vermont, Idaho and Montana, which is roughly a three foot by three foot patch. Below the line the work is generally yours to do with proper protective equipment; above it, get help.
Do landlords have to fix mold?
In most states the duty exists but arrives through general habitability law rather than a mold statute. The landlord has to keep the unit fit to live in and repair conditions that materially affect health or safety, and serious mold from a leak they will not fix usually qualifies. The trigger is almost always written notice from a tenant who is current on rent, followed by a set number of days to act. A handful of states go further with a mold-specific disclosure or remediation duty. Each state report names the statute and links it on the state's own code site.
What does mold remediation cost, state by state?
No state agency publishes a price schedule, so any state-by-state cost table you see online is built from contractor marketing rather than from a public record. What the state does change is the shape of the bill. In states that separate assessment from remediation you get two invoices from two firms by law. In states with no mold licensing you are paying for a credential check you have to do yourself. Our national mold remediation cost guide covers the drivers that actually move the number, and every state report explains the local ones.
How were the humidity numbers on this page calculated?
They come from NOAA NCEI Comparative Climatic Data, which publishes the mean morning and mean afternoon relative humidity for each first-order weather station by month and for the year. The figure shown is the mean of those two values, rounded to whole percent, and the range spans the stations NOAA reports for that state. Dew point on the individual state reports is calculated from the NOAA 1991 to 2020 normal mean temperature and that mean relative humidity, and it is marked as calculated everywhere it appears.
Think your home has a mold problem?
Use guided photo prompts across 19 rooms. AI-assisted visual screening result with variable processing time. The app does not replace a licensed inspection.
Get Early Access