Below 60 percent
The EPA advises: "If possible, keep indoor humidity below 60 percent (ideally between 30 and 50 percent) relative humidity." An inexpensive hygrometer from a hardware store tells you where your house sits.
Moisture, Mold and the Pine Belt Climate
Humidity and Mold in the Pine Belt
Hattiesburg gets nearly sixty inches of rain in a normal year and spends most of the summer above 90 F. Mold does not need a flood here. It needs a damp corner and a little time.
Why houses in Forrest, Lamar and Jones counties grow mold, the numbers the EPA uses, what you can clean yourself, and when it is time to call for help.
Found a patch bigger than a door?
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Most mold calls we take in the Pine Belt do not start with a disaster. They start with a musty closet, a dark ring on a bathroom ceiling, or a spot behind a dresser that nobody moved all summer. Mold spores are in every house. What decides whether they grow is moisture, and the climate here supplies a lot of it.
This page explains where that moisture comes from in a typical south Mississippi house, what the federal guidance actually says, and a short list of things worth checking on a dry Saturday.
The Climate Is Part of the House
Rain, heat and long humid seasons, measured at the Hattiesburg airport.
The National Centers for Environmental Information publishes thirty year climate normals for the Hattiesburg airport station. For 1991 to 2020 the station averages 58.91 inches of precipitation a year. The rain is spread across the calendar rather than packed into one season, so walls, roofs and crawlspaces rarely get a long dry spell to recover.
| Measure at Hattiesburg | Normal, 1991 to 2020 |
|---|---|
| Rain in a year | 58.91 inches |
| Wettest month | June, 5.85 inches |
| Normal July high | 91.6 F |
| Normal August high | 91.8 F |
| Summer days at 90 F or hotter | about 70 |
Heat matters as much as rain. Warm air carries more water vapor, and when that air meets something cooler, like an air conditioned wall, a cold water pipe or the underside of a floor above a cooled room, the vapor condenses. A house can stay damp in places without a single leak. Mississippi State University Extension builds its healthy housing module on mold and moisture control around the same idea: understand the conditions that cause growth, then control the moisture.
What the EPA Numbers Mean
Three figures do most of the work.
Within 24 to 48 hours
The EPA says to dry wet areas and items within 24 to 48 hours to prevent mold growth. After a leak, that window is the difference between drying and removing. The first hour guide covers what to do while it is open.
About 10 square feet
The EPA says that for a moldy area of less than about 10 square feet, "in most cases, you can handle the job yourself." Above that, larger areas or significant water damage call for professional help.
Ten square feet is roughly a three by three foot patch. It is a rule of thumb for surface mold you can see, not a measure of what may be behind it. A small patch on drywall can be the visible edge of a wet wall cavity.
Where Moisture Hides in a Pine Belt House
Four places we check first on almost every mold call.
Crawlspaces and raised floors
Some older houses in the region sit on piers or over a crawlspace. Ground moisture rises into that space, and on a hot day the humid air under the house meets the cooled floor above. Wet insulation hanging from the joists, a musty smell in the rooms above and cupping in hardwood floors are the usual signs. The older homes page covers what else to expect under a house built before 1980.
Attics
A small roof leak can soak insulation for months before a ceiling stain shows. Attics also collect bathroom and dryer exhaust when a vent was run into the attic instead of outside. The EPA’s advice is to vent moisture producing appliances such as clothes dryers "to the outside where possible."
Air conditioning and condensate lines
An air conditioner pulls a great deal of water out of the air on a Mississippi summer day, and that water has to drain somewhere. When the drain line clogs, the pan overflows into a closet, a ceiling or the subfloor. The EPA says to "Keep air conditioning drip pans clean and the drain lines unobstructed and flowing properly." If your air handler is in the attic, a float switch on the pan is worth asking your HVAC contractor about.
Bathrooms, laundry and kitchens
Daily moisture with poor ventilation. Run the bath fan during and after a shower, and make sure it actually vents outside.
A note on paint
Painting over mold changes how it looks, not what caused it. Unless the moisture source is fixed, it comes back, often in the same spot by the next summer.
What a Professional Does Differently
The goal is to remove the growth and the reason it grew.
When mold covers more than a small area, follows a water loss, or sits in a crawlspace or duct, the work changes. Our technicians start by finding and measuring the moisture, because removal without drying is temporary. Then:
Contain the area
Plastic sheeting and negative air pressure keep spores from moving into clean rooms while work goes on.
Remove what cannot be cleaned
Porous materials with growth, such as drywall, insulation and carpet pad, are cut out and bagged. Framing and other hard surfaces are cleaned.
Dry the structure
Dehumidifiers and air movers bring the wood and wall cavities down to a dry reading, logged each day.
Confirm and rebuild
Once the area is dry and clean, the same team can put the walls and floors back.
The EPA also warns against running a central air system you know or suspect is contaminated with mold, because it can spread spores through the house. More on the service itself is on our mold remediation page.
A Dry Saturday Checklist
An hour or two, twice a year, catches most problems early.
- Put a hygrometer in the main living area and one in a back bedroom; aim for under 60 percent.
- Pour a cup of water into the air conditioner condensate line access and confirm it drains outside.
- Look at the drip pan under the indoor unit for standing water or rust.
- Shine a flashlight into the attic around vent pipes, the chimney and roof valleys.
- Check that the bathroom fan and dryer vent end outside, not in the attic.
- Look under sinks and behind the toilet and washer for stains or soft spots.
- If you have a crawlspace, check for standing water, sagging insulation and a musty smell.
- Clear gutters and make sure downspouts carry water away from the foundation.
- Pull furniture a few inches away from exterior walls in closed rooms.
Questions About Mold in the Pine Belt
Should I have the house tested for mold?
If you can see it, you already know it is there. The EPA’s guidance centers on fixing the moisture and cleaning what you can see. Testing can help in specific cases, such as when a smell has no visible source, but it does not replace finding the water.
Will a dehumidifier fix a damp crawlspace?
Sometimes it is part of the fix. A crawlspace usually needs the water source handled first: grading, gutters, a ground vapor barrier and repaired plumbing. A dehumidifier without those is working against the ground under the house.
Is mold after a flood or a sewer backup different?
Yes. The EPA says that if the damage came from sewage or other contaminated water, you should call a professional with experience in contaminated water. That kind of loss has its own page, when drains back up.
Sources for this page
- NOAA NCEI, annual and seasonal normals for Hattiesburg, 1991 to 2020, annual rain and summer days at 90 F or hotter.
- NOAA NCEI, monthly normals for Hattiesburg, 1991 to 2020, monthly rain and summer highs.
- U.S. EPA, a brief guide to mold, moisture and your home, indoor humidity, the drying window, drip pans and venting.
- U.S. EPA, mold cleanup in your home, the 10 square foot guidance, contaminated water and running the HVAC system.
- Mississippi State University Extension, mold and moisture control, the extension’s healthy housing module on mold and moisture control.
Mold You Would Rather Not Touch?
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