Mold in a dry climate
The National Weather Service describes Reno's high-desert setting, and the air outside is often dry. That doesn't make homes immune to mold. Mold inside a house grows where water is: a slow leak in a wall, a burst pipe that wasn't dried completely, snowmelt in a crawlspace, condensation on cold surfaces, or a bathroom without proper ventilation. Dry outdoor air can help a house dry after a leak, but water trapped inside wall cavities, under flooring and in insulation still needs to be found and dried.
Frozen pipes and hidden leaks
Reno winters are cold; Washoe County's residential design criteria use a 17°F winter design temperature, and NOAA's engineering weather data for the Reno airport records about 123 freeze-thaw cycles a year. Frozen pipes that split inside walls can leak for days before anyone notices, especially if the family is away. After any burst pipe, make sure the wall cavity, insulation and subfloor are dried professionally and checked with moisture meters, not just the visible surfaces. A musty smell weeks later is a sign that something stayed wet.
Winter condensation
In winter, warm, moist indoor air meeting cold surfaces condenses. Windows, exterior wall corners, closets on outside walls, and attic sheathing are common spots. Showers, cooking and drying laundry indoors add moisture. Exhaust fans that vent outdoors, good insulation and air sealing, and keeping furniture slightly away from exterior walls help. If you run a humidifier for comfort in dry winter air, monitor indoor humidity so it doesn't climb high enough to cause condensation.
Attics and ice dams
Ice dams at the eaves can push meltwater under shingles and into the attic and walls. Bathroom fans venting into the attic add moisture that condenses on cold sheathing. Check the attic in late winter for frost, damp insulation or dark staining on the underside of the roof.
Crawlspaces and snowmelt
Snowmelt and spring runoff can collect in crawlspaces. A vapor barrier over crawlspace soil, good drainage and adequate ventilation reduce moisture. If insulation hanging from the subfloor is wet, it should be removed, the area dried, and the cause fixed.
Evaporative coolers
Some Reno homes use evaporative coolers, which add moisture to indoor air. They work best in dry weather. A leaking cooler, or running one when outdoor humidity is high, can raise indoor humidity and contribute to mold. Maintain coolers each season and watch for leaks around the unit and ducts.
Before you hire
Ask Reno mold contractors what moisture source they've found, how they'll contain the work area, what they'll remove and clean, how they'll confirm the job is complete, and whether they recommend independent clearance testing. Look up the contractor with the Nevada State Contractors Board.
Basements
Reno-area basements can take on water during snowmelt. Finished basements hide moisture behind carpet and drywall, so check the bottom of exterior walls each spring and fix water entry before it becomes a mold problem.