Why Tulsa houses grow mold: weather, water and age

Mold needs three things: spores (always present indoors and out), something to eat (wood, paper-faced drywall, dust, carpet backing), and moisture. The first two you can't do much about. The third is where Tulsa's climate, its housing and its history come in. This page pulls the official numbers together so you can see when and where trouble tends to start.

Dew point: the number that matters

Relative humidity changes with temperature all day long, so it's a slippery number. Dew point is steadier: it's the temperature at which the moisture in the air turns to water on a surface. When the outdoor dew point is higher than the temperature of something in your house, and that air reaches it, the surface gets wet. Here are NOAA's 1991–2020 normals for Tulsa International Airport (hourly normals, monthly normals), averaged by month:

Annual rainfall at the airport averages about 41 inches. In July, NOAA's 90th-percentile dew point is about 74°F, so the stickiest tenth of July hours carry even more water.

What that means inside the house

• June through August: outdoor dew points near 67–69°F mean anything kept colder than that, like AC supply ducts, registers, cold-water pipes, and the back of a closet against an air-conditioned wall, can collect condensation when humid air leaks to it. Attic ducts with torn insulation and a dripping condensate line are classic summer mold spots. EPA recommends insulating cold surfaces and keeping AC drip pans clean and drain lines flowing.
• April and May: the wettest stretch of the year. May alone averages nearly six inches. This is when roof leaks, gutter overflows and water against the foundation show up.
• Winter: outdoor air is dry, but cooking, showers and unvented appliances can still push indoor humidity up against cold exterior walls and windows. EPA advises venting dryers and stoves outside where possible.

The goal EPA gives is indoor humidity under 60 percent, ideally 30 to 50. An inexpensive hygrometer tells you where you stand.

The housing

In the Census Bureau's American Community Survey (2020–2024), the median home in the city of Tulsa was built in 1973, older than the Oklahoma median of 1980 and well older than Broken Arrow (1994) or Owasso (2001) (Census Reporter). Houses that age often still have original supply lines, older roofs and windows, and ductwork that has been patched more than replaced. Tulsa is also close to half rentals (about 48 percent of occupied homes), which matters for who fixes what; see mold in rentals.

The water history

The 1984 Memorial Day flash flood, the 1986 Arkansas River flood that crested at 25.21 feet at Tulsa, and the 2019 Keystone Dam releases are covered on our page about mold after a flood or leak. Tulsa's drainage work since then earned it FEMA's top flood-management rating, but heavy local rain still finds its way into houses every spring.

If the numbers above line up with what you're seeing at home, start with an inspection to find the moisture, or go back to the Tulsa mold removal overview.

Good questions

What is the most humid time of year in Tulsa?

By dew point, July, at about 69°F on average in NOAA's 1991-2020 normals for Tulsa International Airport, with June and August close behind.

Should I run a dehumidifier in my Tulsa house?

If a hygrometer shows indoor humidity regularly above 60 percent, EPA's guidance is to bring it down, and a dehumidifier is one way. Fixing air leaks, venting bathrooms and kitchens outside, and having your AC checked can help too.