Specimen 05Attic mold
Attic mold after storms, coolers and AC drains
Attic mold in Las Vegas homes nearly always traces back to one of three things, a roof leak in a monsoon storm, a dripping evaporative cooler, or an AC drain that backed up.
ReadingsThe numbers behind this page
Normal yearly rainfall at the airport.
Extra moisture and higher than average humidity.
Evaporative cooling's rank among consumptive water uses.
Rain is rare, which is the problem
A normal year at the airport brings 3.99 inches of rain1. A roof can go many months without being tested. Then the monsoon arrives. The Weather Service says it pushes extra moisture into the Mojave Desert in July and August and brings higher than average humidity2, and the flood control district says July through September bring sudden downpours even on sunny days4. A flashing that failed in the spring finds out in one afternoon.
The cooler on the roof
SNWA says evaporative cooling is the second largest consumptive use of water in Southern Nevada3. A cooler that runs all summer is a water appliance sitting on your roof. A cracked pan, a stuck float or a split feed line drips onto the deck, and the first sign inside is a stain on the ceiling below.
The air handler in the attic
With a normal of 79 days at or above 100 degrees5, an AC pulls a lot of water out of the air. That water drains through a pan and a line. EPA says to keep drip pans clean and drain lines open and flowing6. When the line clogs, the pan overflows onto the ceiling drywall and the insulation around it.
What comes out and what stays
Wet insulation is porous, and EPA says porous materials may have to be thrown away if moldy7. Roof sheathing and framing are wood. Surface growth on solid wood can often be cleaned and dried8, while soft or rotted wood gets replaced. Ceiling drywall that stayed wet goes. EPA's drying window is 24 to 48 hours9.
What you get when you call
Tell us where the stain is and when it showed up. If it lines up with a storm, a cooler or the air handler, that is where we start. Call or text (702) 728-4493.
CutawayWhere to look first
Attic and roof. Most attic mold starts with water from above. A monsoon storm or a tired roof lets rain in, and an attic can stay damp long after the sky clears.
Q and AQuestions people ask
Q01Why is there mold in my attic if it barely rains here?
Because a roof can go months untested, then a monsoon storm finds the gap. The Weather Service says the monsoon brings extra moisture in July and August2.
Q02Can a swamp cooler cause mold?
A leaking cooler is a steady water source, and EPA says the key to mold control is moisture control10.
Q03Can my AC cause attic mold?
Yes, when the drain line clogs and the pan overflows. EPA says to keep drip pans clean and drain lines flowing6.
Q04Does moldy attic insulation need to be replaced?
Usually. It is porous, and EPA says porous materials may have to be thrown away7.
Q05Is attic mold dangerous if I never go up there?
Air moves between the attic and the house, and if ducts run through it EPA warns that a moldy system can spread mold11.
Q06What does attic mold look like?
Dark spotting on the underside of the roof deck, stains around nails, and matted or stained insulation near a leak.
Q07How fast should I dry a wet attic?
EPA says within 24 to 48 hours to prevent mold growth9.
Q08When is monsoon season in Las Vegas?
Q09Do I need a permit to fix attic mold damage?
In the City of Las Vegas, opening walls or doing plumbing or mechanical work beyond routine maintenance generally needs a permit13. Ask the city or county before framing work.
Q10Should I wear a mask to look in the attic?
For any cleanup CDC says an N95 respirator at a minimum, plus goggles and gloves14.
IndexOther service sheets
References
- NOAA NCEI 1991-2020 annual normals, Las Vegas airport. ncei.noaa.gov/access/services/data/v1?dataset=normals-annualseason..., checked October 27, 2026.
- NWS Las Vegas, Climate of Las Vegas. weather.gov/vef/ClimateofLasVegas, checked October 27, 2026.
- SNWA Conservation Initiatives. snwa.com/water-resources/conservation-initiatives/index.html, checked October 27, 2026.
- Regional Flood Control District, Flash Flood Safety. regionalflood.org/programs_and_services/public_information/flash_f..., checked October 27, 2026.
- NOAA NCEI 1991-2020 annual normals, Las Vegas airport. ncei.noaa.gov/access/services/data/v1?dataset=normals-annualseason..., checked October 27, 2026.
- A Brief Guide to Mold, Moisture and Your Home, US EPA. epa.gov/mold/brief-guide-mold-moisture-and-your-home, checked October 27, 2026.
- A Brief Guide to Mold, Moisture and Your Home, US EPA. epa.gov/mold/brief-guide-mold-moisture-and-your-home, checked October 27, 2026.
- A Brief Guide to Mold, Moisture and Your Home, US EPA. epa.gov/mold/brief-guide-mold-moisture-and-your-home, checked October 27, 2026.
- A Brief Guide to Mold, Moisture and Your Home, US EPA. epa.gov/mold/brief-guide-mold-moisture-and-your-home, checked October 27, 2026.
- A Brief Guide to Mold, Moisture and Your Home, US EPA. epa.gov/mold/brief-guide-mold-moisture-and-your-home, checked October 27, 2026.
- A Brief Guide to Mold, Moisture and Your Home, US EPA. epa.gov/mold/brief-guide-mold-moisture-and-your-home, checked October 27, 2026.
- NWS Las Vegas, Climate of Las Vegas. weather.gov/vef/ClimateofLasVegas, checked October 27, 2026.
- City of Las Vegas, When Do I Need a Permit? A Homeowner's Guide. files.lasvegasnevada.gov/building-safety/Forms/General/WHEN-DO-I-N..., checked October 27, 2026.
- Homeowners and Renters Guide to Mold Cleanup After Disasters, Mold, CDC. cdc.gov/mold-health/communication-resources/guide-to-mold-cleanup...., checked October 27, 2026.