What humidity should a basement be? Keep it between 30% and 50%, and never let it stay above 60%. That range keeps mold, musty smells and wood rot out of your basement.
Basements in Georgia have challenges in remaining dry. High summer dew points are persistent for many months, while the red clay in the soil keeps water around the foundation walls for a long time even after rain. Below, you will discover how to monitor your basement’s humidity and what it means.
What Is the Ideal Basement Humidity Level?
An ideal humidity level for the basement should be between 30% and 50%. The relative humidity level measures how much water is present in the air in relation to its capacity.
Indoor humidity levels should not be above 60% but should ideally range between 30% and 50%, according to the Environmental Protection Agency (EPA). Don’t strive for 60%.
| Basement humidity | What it means | What happens |
| Below 30% | Too dry | Wood trim and flooring shrink and crack. Rare in a basement. |
| 30% to 50% | Ideal | Mold and dust mites have a hard time growing. This is your target. |
| 50% to 60% | Watch it | A faint musty smell starts. Look for a water source. |
| Above 60% | Mold risk | Mold, wood rot and rust start. Bring it down now. |
Humidity in finished basements needs to be within 30%-50%. The distinction here lies in the response of the materials: when humidity becomes too high, they absorb moisture quickly and can develop mold.
How Does Basement Humidity Change in Summer and Winter?
Basement humidity spikes in summer and drops in winter, but keeping track of what humidity a basement should ideally be- between 30% and 50% year-round prevents mold and damp air.
Basement Humidity in Summer
The main issue caused by basement humidity in the summer months is of concern to many Georgia residents. The warm and humid air from outside finds its way into the house through the doors, windows, and cracks around the rim joist. The walls of the basement remain cool – usually between 60 degrees.
As the humid air contacts a cool wall surface, it cools, and the humidity becomes higher, causing moisture formation. This is called condensation in basement walls, and in July, it does not necessarily indicate leakage.
This is a simple test we conduct in our inspections. Walls which show sweating in July but remain dry after rains in January are cases of condensation. Walls which become wet every time after rain, regardless of the season, are indicative of a water penetration problem.
Basement Humidity in Winter
Humidity in the basement during winter usually drops automatically. The cold air outside contains little moisture, and the heat dries out the air. Humidity levels in the 30s range are common between December and February.
If your basement’s humidity is below 30%, you should turn off the dehumidifier or set it higher. In most North Georgia homes, the dehumidifier does not need to run all through the winter.
How Do You Measure Basement Humidity?
The most convenient way for homeowners who want to learn how to measure humidity in basement spaces is by using a digital hygrometer. Here is the right way to do it:
- Position the device in the center of the room at the approximate waist level.
- Avoid positioning the hygrometer near the walls, the sump pit, the dryer vent, and the dehumidifier.
- Record the readings once daily for an entire week. One reading a day for one day is not enough.
- Make another measurement during the month of July, when the readings are higher.
If all readings are within 30-50%, your basement is okay. If you have readings of 60% or higher for more than two days in a row, continue recording.
What Are the Signs of High Humidity in a Basement?
High humidity in a basement leaves clues you can see and smell, even without a hygrometer. Most basements we inspect show two or three of these at once.
- Condensation on basement walls and on cold water pipes, especially in summer
- Musty odor that gets stronger after rain. Our guide on musty smell after rain covers this sign in detail.
- White, chalky powder on block or concrete walls, called efflorescence
- Mold or mildew spots on walls, wood framing, boxes or stored items
- Peeling or bubbling paint on basement walls
- Rust on tools, shelving, the water heater base or the washer
- Soft, damp cardboard boxes that never feel fully dry
How Do You Reduce Humidity in a Basement?
If you want to know how to reduce humidity in a basement, start with the water, not the air. A dehumidifier pulls moisture out of the air. It does nothing to stop new water from coming in.
Fix Water Sources First
- Clean gutters and extend downspouts at least six feet from the house.
- Make sure the soil slopes away from the foundation. Poor yard drainage sends water straight toward your basement walls.
- Seal wall cracks and gaps around pipes. See our checklist for water leaking into the basement from outside.
- Test your sump pump before storm season by pouring a bucket of water into the pit.
Run a Dehumidifier
Once you get the water under control, all that is left is to run the dehumidifier. This is recommended from May through September in Georgia. Make sure that you have a dehumidifier sized for your basement.
Seal and Insulate Cold Surfaces
Cold surfaces cause condensation. Insulate your cold water pipes using foam pipe insulation. Seal the gaps where the rim joist is and insulate it using rigid foam board.
Improve Airflow, but Keep Windows Shut in Summer
Moving air helps damp corners dry out, so run a fan or keep interior doors open. Opening basement windows during a Georgia summer makes the problem worse, though. Outdoor air in July carries far more water than the air in your basement. Save open windows for cool, dry days in spring and fall.
For a full list of year-round habits that keep your basement dry, see our maintenance guide.
What Should You Set Your Basement Dehumidifier At?
The optimal level for the best dehumidifier setting for the basement should be set at 45 percent or 50 percent. This remains within the recommended range but is just under the 60 percent maximum limit.
If your question concerns setting the dehumidifier at an even lower level, avoid going any lower than 40 percent. The lower you go, the more energy is consumed unnecessarily.
- Use continuous drain: Run a hose to a floor drain or the sump pit, or add a condensate pump. A bucket fills fast in summer, and a full bucket shuts the unit off.
- Clean the filter every month: during summer. A clogged filter cuts how much water the unit pulls out.
- Watch how it runs: A healthy unit cycles on and off. One that never stops is telling you something (see the next section).
Crawl spaces follow different targets and sizing rules. If your home has one, read our guide to crawl space humidity and dehumidifiers.
When Does High Humidity Mean a Water Problem?
An always-running dehumidifier that is not hitting its set point is a definite red flag. This isn’t due to high humidity. Water is seeping through the wall or floor faster than the machine can dehumidify it.
There are other signs to watch out for too. Humidity levels increase during every storm. The drain bucket is filling up quickly during storms. Wet patches are forming at the wall-floor interface. These are all signs of basement water problems, which cannot be handled by a dehumidifier alone.
The solution is drainage, crack repair, or waterproofing. It’s what we do every week in North Georgia.
Frequently Asked Questions About Basement Humidity
Is 60% humidity too high for a basement?
Yes. 60 percent is the ceiling point, not the safe point. At 60 percent and higher, mold will start developing after a few days. The desired range is 30 percent to 50 percent.
Should I run a dehumidifier in my basement all year?
Generally no. In Georgia, basements require dehumidifiers from late spring until early fall. During the winter, basements tend to have less than 50 percent humidity naturally. Look into your hygrometer; turn your dehumidifier off once the readings drop under 50 percent.
Why is my basement humid when it isn’t raining?
During summer, the air contains much moisture. Moist air enters the basement and gets cooled down by cold walls, thus increasing the humidity and causing condensation. Laundry, an improperly vented dryer, and open windows contribute.
Does a finished basement need a lower humidity level?
Not necessarily. The range is still 30 percent to 50 percent. However, finished basements have more to lose. Drywall, carpets, and furniture absorb moisture easily; hence, maintain a consistent humidity level and remove any moisture sources immediately.
Get a Free Basement Moisture Inspection
If your basement moisture levels are consistently over 60%, or you are unsure what humidity a basement should be in your home, or your dehumidifier is running all the time, allow us to look into that. Tri-State Waterproofing has been protecting North Georgia basements from moisture since 2000. Our services include moisture testing, source identification, and a clear explanation of your options.
We serve Gainesville, Woodstock and communities across North Georgia. Call (770) 869-7888 or schedule your free basement waterproofing inspection today.
