Little Rock humidity and mold: a month-by-month calendar

Mold needs moisture, and in Little Rock the moisture usually comes out of the air. The useful number isn't the humidity on the weather app, it's the dew point: the temperature at which the air's water condenses onto a surface. Any surface in or under your house that's cooler than the outdoor dew point (an air-conditioning duct, a floor joist over cool dirt, a cold-water pipe) will get wet if that air reaches it. Here is what the official numbers say about when that happens in Little Rock, and what to do about it each season.

The numbers: Little Rock, 1991–2020 normals

From NOAA's National Centers for Environmental Information 1991–2020 climate normals for Little Rock's Adams Field airport station (hourly normals, monthly normals). Temperature and dew point are monthly averages of the hourly normals; relative humidity is calculated from them.

Three things stand out. Humidity is high all year: the monthly average never drops below about 63%, and early mornings sit in the 80s from April through October. Dew points from June through August average 68–71°F, and NOAA's 90th-percentile July dew point is about 75°F, so the muggiest tenth of July hours are wetter still. And the wettest months for rain are March through May and again in November and December, which is when crawl spaces flood from below.

What that means for your house

The EPA recommends keeping indoor relative humidity below 60 percent, ideally between 30 and 50 percent. Outdoor air in Little Rock averages above that every month of the year, so whatever outside air gets into a crawl space, attic or house brings moisture with it.

• Summer dew points are above duct temperature. Air-conditioning ducts carry air that's typically in the 50s °F. With the outdoor dew point near 70°F from June through August, any duct or boot in a vented crawl space or attic that isn't sealed and insulated will sweat, and drip onto insulation and subfloor.
• Cool ground under a vented crawl space. Soil under the house stays cooler than summer air. When humid outside air comes in through the vents, it cools and its relative humidity climbs toward 100%. That's why many Little Rock crawl spaces are wettest in July, not January.
• Spring and late-fall rain. Five inches a month in March through May (and again in December) is when downspouts, grading and clay soil decide whether water ends up under the house.

Season by season

January–February: check the attic

Dew points are low (low to mid 30s °F), so outdoor air is dry. The risk shifts to the attic: warm, moist house air leaking through ceiling gaps or bath fans vented into the attic can condense on cold roof sheathing. Look for frost or dark staining on the underside of the roof, and make sure bath and kitchen fans vent outdoors. See crawl space and attic mold.

March–April: water season

The rainiest stretch of the year. Walk the house during a heavy rain: downspouts should discharge well away from the foundation, and the ground should slope away. Look in the crawl space a day after a big storm for standing water or wet soil. Fix water now, before the humid months start.

May–September: the condensation season

Dew points climb into the 60s in May and hover near 70°F through summer, with average morning humidity of 86–88%. This is when musty smells show up and duct sweating starts. Keep the AC running steadily rather than shutting it off for long stretches, keep indoor humidity under 60%, and put a cheap hygrometer in the crawl space in July. If it reads in the 70s or 80s for days, read crawl space dehumidifiers: when you need one and how to size it.

October–December: dry it out and look

Dew points fall back toward the 40s and 50s by November. It's a good time for a crawl space inspection: summer's damage (wet insulation, staining on joists, sagging duct wrap) is still visible, and work under the house is more pleasant. Rain picks up again in November and December, so recheck drainage.

Dehumidifier and AC settings that fit Little Rock

• Indoors: aim for 30–50% relative humidity, and under 60% at most, per the EPA. A hygrometer in the main living area and one in the crawl space tell you whether you're there.
• Sealed crawl space: a crawl-space dehumidifier set to hold under 60% (many owners set 50–55%) through May to September. In a vented crawl space, a dehumidifier mostly dries outdoor air; fix the vents, ground cover and water first.
• Oversized AC: an air conditioner that cools the house quickly and shuts off removes little moisture. If the house feels clammy at 74°F in July, ask an HVAC contractor about the unit's size and fan settings.

Already seeing growth? Drier air stops new mold; it doesn't remove what's there. See mold remediation in Little Rock, or call and we'll connect you with a local mold professional.