Mold doesn't need a disaster. In East Tennessee, ordinary weather supplies plenty of moisture, and a house only has to hold onto some of it to grow mildew in a closet, on window frames or under the floor. Knowing the local climate and the humidity number to aim for prevents a lot of remediation bills.
The climate you're working with
- Rain: the 1991-2020 normal at Knoxville is 51.93 inches a year (NWS Morristown). That's spread across the year rather than packed into one season.
- Heat: the city averages 34 days a year at or above 90 degrees over its period of record, which means long stretches of air conditioning and cold ductwork.
- Humidity: NOAA's climate summary for Tennessee describes summers across most of the state as warm and humid, fed by moist air from the Gulf of Mexico (NOAA).
- Trend: the same summary notes that 2016 to 2020 was the wettest five-year stretch on record statewide, and that spring precipitation is projected to rise further by midcentury.
Knoxville sits in the Great Valley of East Tennessee, which NOAA describes as sloping from about 1,500 feet in the north to 700 feet in the south, between the Cumberland Plateau and the Smoky Mountains. NOAA also notes temperatures drop about 3 degrees for every 1,000 feet of elevation, so homes up toward Gatlinburg run cooler than those on the valley floor.
The number to watch: 30 to 50 percent
EPA recommends keeping indoor relative humidity below 60 percent, ideally between 30 and 50 percent. A basic humidity meter costs about $10 to $50 at a hardware store (EPA). Put one in the main living area and another in a basement or near the crawl space hatch, and check them through a July week. If they sit above 60 percent with the air conditioning running, something is letting moisture in or not taking it out.
Say what you found and where, and we will hand you to a mold remediation company that covers your end of the valley. (865) 417-9186
Where moisture hides in local houses
- Crawl spaces: humid summer air condenses on cool joists and ducts. See crawl space mold.
- Bathrooms: showers without a working exhaust fan vented outdoors leave moisture in walls and ceilings.
- Window frames: condensation on glass and sills in cool months. EPA treats condensation as a sign of high humidity.
- Laundry rooms: EPA advises venting clothes dryers to the outside.
- Basement walls: gutters that overflow or downspouts that empty beside the house keep soil wet against the foundation, and that water works its way through block.
- Attics: bath fans dumping into the attic instead of through the roof, or roof leaks that go unnoticed for months.
Cheap fixes before expensive ones
- Clean gutters and extend downspouts so water lands several feet from the foundation.
- Make sure bath and kitchen fans actually vent outdoors, and run them.
- Get a properly sized air conditioner serviced; one that cools fast without running long may not dehumidify well.
- Run a dehumidifier in a basement that tests high, and empty or drain it. The dehumidifier size calculator shows how many pints a day the space needs.
- Replace torn or missing plastic on the crawl space floor.
If humidity stays high after the easy fixes, or you've already got growth larger than about 10 square feet, it's time for professional remediation.
FAQ
What humidity level stops mold?
EPA recommends keeping indoor relative humidity below 60 percent and ideally between 30 and 50 percent. Mold can still grow on any surface that stays wet from a leak, regardless of room humidity.
Does air conditioning reduce humidity?
It does remove moisture as it cools, which is one reason Knoxville homes feel better with it running. An oversized or poorly maintained system may not run long enough to dry the air well, so a separate dehumidifier sometimes helps.
Why does my house smell musty only in summer?
Summer is when humid outdoor air meets cool surfaces under and inside the house, especially in a vented crawl space, and that condensation feeds mold growth. The smell often fades in winter and comes back when the humidity does.