How to stop mold and high humidity ruining a basement
Basement humidity hitting around 80% creates a persistent musty smell and mold growth on furniture, fabrics, and cardboard boxes. This excess moisture risks spreading mold spores throughout the rest of the house, threatening stored items and equipment.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
How to stop mold and high humidity ruining a basement
- 1Using a dehumidifier with a condensate pumpDid this help you?
- 2Creating air vents to the exterior on ground level to force airflowDid this help you?
- 3Spraying surfaces with bleach to temporarily kill moldDid this help you?
- 4Running a dehumidifier constantlyDid this help you?
- 5Spraying mold remover like RMR multiple timesDid this help you?
- 6Removing damaged or moldy framingDid this help you?
- 7Opening basement windows and using a fanDid this help you?
- 8Keeping connected HVAC systems turned offDid this help you?
- 9Using a dehumidifierDid this help you?
- 10Installing a U.V.C light in the air handlerDid this help you?
- 11Adding a vent in the return to circulate airDid this help you?
- 12Replacing flexible plastic duct with insulated metal ductingDid this help you?
- 13Shortening duct length and routing more directly to eliminate traps and bendsDid this help you?
- 14Upgrading to a modern exhaust fan supporting larger diameter ductsDid this help you?
- 15Running a dehumidifier continuously 24/7Did this help you?
- 16Connecting a drain hose to a sump pump or floor drain to avoid manual emptyingDid this help you?
- 17Extending gutters and downspouts away from the foundationDid this help you?
- 18Installing a heat-pump water heater to help dehumidify the spaceDid this help you?
- 19Improving basement ventilation and checking exterior drainageDid this help you?
- 20Buying mold control from the hardware storeDid this help you?
- 21Opening up the ceiling patch to inspect with a flashlightDid this help you?
- 22Checking room humidity and outside wallsDid this help you?
- 23Putting on a respirator, cutting out drywall carefully, and bagging itDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“I’ve been running a dehumidifier constantly, but 1: it makes it really hot down there, and 2: I have to empty it twice a day or it shuts its and humidity goes right back up and 3: my new smart electric meter shows the humidifier is like 30% of my electric bill.”source ↗
“oh i feel this in my bones, my basement is basically a swamp creature's dream home”source ↗
“Humidity is around 80%, and there's a persistent musty smell. What appears to be mold keeps developing on old furniture, fabrics, cardboard boxes, chairs and even some cables.”source ↗
“A spore test in the basement showed an amplification over the outside of Aspergillus/Penicillium of 1273 counts per cubic meter near the cold room and 796 in the rest of the basement.”source ↗
“While the rest of the house showed an acceptable spores count, isn't it possible for the spores to spread through the house from the basement?”source ↗
“West Coast FL upstairs Air Handler closet sweating plenum (humid control issue) and mold growing.”source ↗
“Mold has been like this for a bit and there is no issues inside duct work have tested around house but not sure what to do getting all kinds of conflicting information.”source ↗
“What's best way to control the humidity issue and clean this up?”source ↗
“We’ve noticed too high humidity in our bathroom and we’re not sure if it’s because of the bathroom exhaust fan needing replaced due to a weak motor, how the ducts are set up, or something else.”source ↗
“Additionally we noticed some microbial growth in the attic rafters that were getting remediated, and we’re not sure if the duct work is contributing to it or if it’s more of an attic/roof venting issue.”source ↗
“Just discovered a water leak/mold in my basement. Concrete ceiling. I don't know what to do and my wife is 8 months pregnant.”source ↗
Where this came up
People with this problem also raised
- 4Do I need crawlspace encapsulation for high humidity?
- 8Why are my metal floor vents sweating and growing mold?
- 4Dealing with severe mold in a rental when management won't act
- 6Why is there condensation and damp spots on walls only on laundry days?
- 2What to do about mold in an apartment HVAC system
- 16How to clean mold under water damaged flooring without DIY experience