Mold in Wyoming: the driest case, and the thinnest rulebook

Wyoming's four NOAA stations report 52 to 60 percent annual mean relative humidity, with Sheridan highest at 60 and Lander lowest at 52. Precipitation runs 12.2 to 15.4 inches at these stations, against a statewide long-term average NOAA puts at 15.9 inches, and long-term station totals across the state range from 5.51 inches in the north central region to 32.82 inches in Yellowstone. The calculated annual mean dew point is 29 to 32 F. This is a semiarid, high-elevation state, and outdoor air here does not wet indoor surfaces.

The monthly shape confirms it. Relative humidity peaks in January and December at 62 percent and bottoms out in August at 44 percent, which is the reverse of a humid state's calendar and is a cold-air artifact rather than a moisture increase. The morning mean never exceeds 68 percent in any month. There is no season in Wyoming when the air alone will grow mold indoors.

The disaster record says the same thing. Of 32 billion-dollar weather disasters affecting Wyoming from 1980 to 2024, 11 were drought, 11 were severe storm and 9 were wildfire, and not one was a flood. Where outdoor water does arrive suddenly, it arrives from snowmelt: NOAA singles out Chinook winds, the warm dry downslope winds off the eastern slope of the Continental Divide, which produce large winter temperature jumps that melt snow rapidly and can cause flooding. Total annual precipitation and the count of one-inch extreme precipitation events have both been trending upward since 2000. So the Wyoming mold conversation is about pipes, appliances, roofs under snow load, and the occasional Chinook thaw, not about the weather.

Wyoming against the national picture

Relative humidity figures are the mean of the morning and afternoon observations NOAA publishes for each first-order station, rounded to whole percent. Dew point is calculated from the NOAA normal mean temperature and that mean relative humidity using the Magnus formula, so treat it as a derived figure rather than a published one.

Every station on this table is dry, and the ranking barely matters. Eight points separate the wettest from the driest, and all four are well below the level at which ambient humidity wets an indoor surface. In a humid state you can reasonably ask whether growth came from the air. In Wyoming you cannot. When mold appears here, water came from somewhere specific, and finding it is the whole job.

What this table cannot show is elevation. NOAA's long-term station record for the state ranges from 5.51 inches in the north central region to 32.82 inches in Yellowstone, a sixfold spread these four airport stations do not capture. A cabin at 8,000 feet in the Tetons under heavy snow load has a roof and ice-dam problem that Lander does not. Read this table as describing Wyoming's populated basins. Neighboring reports for Colorado, Montana, Idaho and Utah cover the same mountain-west mechanism.

EPA and CDC name the same core genera everywhere, but in a semiarid state the mix skews toward species that exploit one specific wet spot rather than general dampness.

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.

No Wyoming agency publishes a mold remediation price schedule, and Wyoming publishes no state mold guidance at all. There is no Department of Health mold page. The most substantive mold document produced by any Wyoming public institution is a five-page fact sheet from the University of Wyoming's Risk Management and Safety office, and it is candid that there is no accepted national standard for mold contamination. Teton County publishes an indoor air quality page that names mold as a home air pollutant, and that is close to the extent of it.

In a dry state, the cost that matters most is diagnosis, and it is usually cheap relative to what it saves. Because ambient humidity cannot be the explanation here, a remediator who cannot tell you where the water came from has not finished the assessment. Pay for the moisture meter survey, the look inside the wall, the check of the supply lines and the appliance connections. A quote that starts at demolition without a source is a quote for something that will recur.

The second driver is remoteness, and Wyoming has the least population of any state. Restoration equipment and crews cluster around Cheyenne, Casper and Jackson, and a job in a small town can carry meaningful travel and mobilization. Ask about it explicitly rather than being surprised by it on the invoice.

The third is that the state licenses nothing here, so bids differ in scope as much as in price. Get an itemized written scope from each bidder. Our national mold remediation cost guide covers the drivers that move a quote in any market, and the cost estimator lets you scope your own job first.

On insurance: a sudden and accidental discharge such as a burst supply line during a cold snap is normally the covered event, and in a state with Wyoming's winters that is the common claim. Long-term seepage is usually excluded, and many policies cap mold remediation at a fixed sublimit even when the water event is covered. Take coverage questions to the Wyoming Department of Insurance, and read our guide to homeowners insurance and mold.

Wyoming does not license, certify or register mold assessors or mold remediators, and it does not license general contractors either. The Wyoming Business Council, a state agency, states it plainly: "Contractor licensing (except electrical) is not done by the state of Wyoming. Rather, the option to license contractors is deferred to the local jurisdiction where the construction activity is to take place."

The Department of Workforce Services publishes the official list of licensed occupations in Wyoming, roughly 95 of them from acupuncturists to water well drilling contractors, and the only construction trade on it is electrician. There is no mold assessor entry, no mold remediator entry and no general contractor entry. That list is the positive proof rather than an absence of evidence, and it is worth looking at yourself.

So the licensing question in Wyoming is a municipal question. A mold remediation firm is regulated by the city or town where the work happens, and the Business Council points contractors to the Wyoming Association of Municipalities member list to find the right local office. Before you sign, call your city or town clerk and ask what contractor licensing they require, then confirm the company holds it. Do not accept a license number without knowing which body issued it.

For the mold work itself the whole check is yours. Ask for IICRC certification and ask whether the job will follow ANSI/IICRC S520, the industry consensus standard. Ask whether the same firm is doing the assessment and the remediation. Ask for daily moisture readings by material. And above all in this climate, ask them to tell you where the water came from before they tell you what the work costs, because in a state with a 30 F mean dew point, a remediation without a diagnosis is a remediation that will be repeated.

Wyoming has no mold-specific statute. A mold complaint runs through Wyo. Stat. Ann. §§ 1-21-1202 and 1-21-1203. Section 1-21-1202(a) requires every owner renting a residential rental unit to maintain it in a safe and sanitary condition fit for human habitation, with operational electrical, heating and plumbing and hot and cold running water. Section 1-21-1203(a) adds that the owner shall not rent a unit unless it is reasonably safe, sanitary and fit for human occupancy, shall maintain common areas, and shall maintain electrical, plumbing, heating and hot and cold water.

The notice mechanism is unusually specific and it is easy to get wrong. Under § 1-21-1203(b), a renter who is current on rent and has reasonable cause supported by evidence must advise the owner in writing, must specify the remedial action requested, and must serve it by certified mail. Within a reasonable time the owner must either begin correcting the condition or dispute the claim in writing. Miss the certified mail step and you have not started the process the statute describes.

If nothing happens, § 1-21-1206(b) provides a second notice. The renter serves a "notice to repair or correct condition" that recites the first notice and states the owner has three days to begin reasonable corrective action before suit. The renter may then sue in circuit court for costs, damages and affirmative relief, including an order to make repairs or termination of the lease.

Two limits are worth knowing before you start. Section 1-21-1203(d) lets the owner refuse to repair and terminate the lease with 10 to 20 days' notice if the repair costs are unreasonable against the rent charged, which is a real risk on a large remediation in a low-rent unit. And § 1-21-1203(e) says the owner is not liable under this article for claims of mental suffering or anguish, so the damages available are property and cost damages rather than distress. Send the first notice properly, by certified mail, with the remedial action specified. Our landlord letter generator produces that notice, and our guide to mold and apartment rights covers the general playbook.

General information, not legal advice. For your situation, talk to a Wyoming attorney, a legal aid office, or your local tenant council.

In the driest state in this report, everything comes down to finding indoor water fast. Three moves cover most of it.

A. Treat every mold spot as a leak until you have proven otherwise

At a 29 to 32 F calculated mean dew point and under 16 inches of rain, Wyoming air does not grow mold on a wall. If growth appears, something is wet: a supply line in an exterior wall that froze and split, a water heater, an ice maker line, a washing machine hose, a dishwasher, a slow toilet supply, or a roof penetration. Shut off every fixture and watch the water meter for 30 minutes. If it moves, you have a leak and finding it is the job. Cleaning the surface without finding the source in a dry climate is the clearest possible waste of money.

B. Winterize against the burst pipe, which is the state's main mold event

Wyoming's mold problems overwhelmingly begin with a freeze. Insulate supply lines in exterior walls, in crawl spaces and in unheated garages. Disconnect and drain hose bibs before the first hard freeze. Know where the main shutoff is and make sure everyone in the house does. If you leave a property empty in winter, either keep the heat on above 55 F or drain the system properly, because a split line in an empty house runs for days. Check the washing machine hoses while you are at it, since burst hoses are one of the most common household water events anywhere.

C. Manage winter interior humidity, and watch the Chinook thaw

Wyoming's relative humidity peaks in December and January because the air is cold, not because it is wet. Indoors that means the moisture that matters is the moisture you make, and it condenses on very cold glass. Target roughly 30 to 35 percent indoor relative humidity in the cold months and run exhaust fans. Separately, NOAA identifies Chinook winds as a Wyoming flood mechanism: warm downslope winds that melt snow rapidly. After a big thaw, check the roof for ice dam evidence, check the foundation perimeter, and look in the basement or crawl space within 48 hours. Our indoor humidity calculator shows measured relative humidity plus calculated dew point.

Monthly mean relative humidity across Wyoming's four NOAA stations. The winter peak is a cold-air artifact, and the August low of 44 percent is the lowest monthly reading in this report.

December and January read highest and mean the least. The daily mean reaches 62 percent while the calculated dew point sits near 30 F, so the air holds almost no water. What the winter does produce is condensation on cold single-pane and older double-pane glass from interior moisture, and burst supply lines during hard freezes. Both are indoor problems with indoor fixes.

July and August are the driest months in this report at 44 to 46 percent. That is the window for any work needing a dry structure: opening a wall, drying a crawl space, replacing subfloor. The ambient air is doing the drying for you, which is a genuine advantage over a humid state.

Spring is the snowmelt window, and Chinooks can move it. NOAA identifies Chinook winds as a Wyoming flood mechanism because they produce large winter temperature jumps that melt snow rapidly. A February thaw can put meltwater against a foundation that is still frozen. Walk the perimeter after any big warm-up rather than waiting for April. The mold risk by ZIP tool gives you the local read.

Wyoming has no state health department mold page, and that is a finding rather than a gap in this list. The most useful documents come from the university and from one county.

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