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.
| Month | Avg temp | Avg dew point | Avg humidity | 6 a.m. | 3 p.m. | Rain (in) |
|---|---|---|---|---|---|---|
| January | 42°F | 32°F | 67% | 79% | 50% | 3.50 |
| February | 46°F | 34°F | 65% | 79% | 48% | 3.97 |
| March | 54°F | 41°F | 63% | 79% | 46% | 4.96 |
| April | 63°F | 50°F | 65% | 84% | 47% | 5.59 |
| May | 71°F | 60°F | 70% | 87% | 52% | 5.08 |
| June | 79°F | 68°F | 71% | 87% | 52% | 3.55 |
| July | 82°F | 71°F | 70% | 87% | 51% | 3.33 |
| August | 81°F | 70°F | 70% | 88% | 49% | 3.16 |
| September | 75°F | 63°F | 68% | 86% | 47% | 3.01 |
| October | 63°F | 52°F | 69% | 86% | 46% | 4.47 |
| November | 52°F | 42°F | 69% | 83% | 48% | 4.72 |
| December | 44°F | 35°F | 70% | 81% | 53% | 5.08 |
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.
Musty smell, a leak, or mold you can see? Call us and tell us what you're finding.
(501) 476-2521Season 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. If a spring storm does put water inside, the first 48 hours decide whether mold follows; see water damage restoration in Little Rock for what drying should involve.
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.
Does a dehumidifier help with mold?
Yes, for the part of the problem that comes out of the air, which in Little Rock is most of it. A dehumidifier pulls the room's humidity down so the next round of growth never gets started. It does not remove mold that is already there: dried-out mold is still on the drywall or joist, and EPA's advice is still to clean it up and fix the water source (how existing growth is removed).
Sizing. ENERGY STAR's buying guidance sizes a portable unit by the room and how damp it is, and says it's better to oversize than undersize:
| What the room is like | Room under 2,000 sq ft | Over 2,000 sq ft |
|---|---|---|
| Damp feel, musty odor that comes and goes (50 to 75% humidity) | 20 to 30 pints/day | 30+ |
| Always feels and smells damp, damp spots on walls or floors (75 to 90%) | 25 to 40 | 40+ |
| Walls or floor sweat, seepage (90 to 100%) | 30 to 50 | 50+ |
Those are the newer ratings; units sold before 2020 were tested warmer and list bigger numbers for the same machine (ENERGY STAR on the change).
Where to put it in a Little Rock house. In a house over a crawl space or slab, with no basement, the usual spots are a closed-up back bedroom on an exterior wall, a utility or laundry room, or a bathroom without a working fan. ENERGY STAR says to keep doors and windows closed while it runs and, unless the unit blows out the top, keep it away from walls and furniture. A bucket unit shuts off when full, which means a summer full of overnight shutoffs if nobody empties it; one with a hose fitting can drain to a floor drain or sump instead. A unit in a room that drops below about 65°F can frost its coils.
Whole-house versus one room. ENERGY STAR says a whole-home dehumidifier tied into the ducts makes the most sense in a humid climate, with central air, in a fairly well sealed house that reads above 55% throughout. That describes plenty of Central Arkansas houses from June through September. Under the floor is a different machine and a different job: see crawl space dehumidifiers.
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 how mold remediation removes existing growth, or call us.
Common questions
What is the most humid month in Little Rock?
By dew point, July (about 71°F on average in NOAA's 1991–2020 normals), with June and August close behind. By average relative humidity, May through August all run about 70–71%, with early-morning humidity in the high 80s.
What humidity should I keep my house at in Little Rock?
The EPA recommends below 60 percent, ideally 30 to 50 percent. Little Rock's outdoor air averages above that every month, so the AC and, where needed, a dehumidifier do the work.
Why is my crawl space wetter in summer than winter?
Summer outdoor air in Little Rock has a dew point near 70°F. When it flows into a vented crawl space and touches cooler soil, joists and AC ducts, the moisture condenses. In winter the outdoor air is much drier.
Can I link to this calendar?
Yes. Home inspectors, HVAC companies, realtors and neighborhood groups are welcome to link to this page; it stays free.