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Basement humidity, musty smells and mold in Northern Virginia
Northern Virginia summers push basement humidity up. How to keep a lower level fresh, what the EPA says about humidity and mold, and when to call a pro.
By Northern Virginia Housekeeping · 6 min read · Updated
If your basement smells musty by July, you are in good company. Our summers are hot and humid, and the basement is the coolest, dampest part of most homes. The fix is mostly about moisture, not cleaning products. Below: how to keep a lower level fresh, what EPA guidance says about humidity and mold, and where a cleaner's job ends and a mold professional's begins.
Why basements here get musty
- Humid air meets cool walls. In summer, warm, damp air finds its way into the basement. The concrete walls and floor stay cool because they sit in the ground. Like a cold glass on a hot day, those surfaces collect moisture.
- Soil and storms. Basement walls sit against soil. After a heavy summer storm, water can collect around the foundation and find its way in.
- Still air. Lower levels often have closed doors, storage rooms and less airflow than the floors above.
- Everyday moisture. A laundry room, a spare shower or a home gym all add water to the air.
A finished lower level needs more attention, not less, whether it is in an older McLean or Vienna house or a newer Brambleton build. Carpet, drywall and upholstered furniture hold onto moisture in a way bare concrete does not.
A musty smell is worth taking seriously. The EPA notes that you may suspect hidden mold if a building smells moldy but you cannot see the source.
The number to watch: indoor humidity
The EPA advises keeping indoor relative humidity below 60 percent, and ideally between 30 and 50 percent. You cannot judge that by feel. A small humidity meter, sometimes called a hygrometer, is inexpensive and sold at many hardware stores. Put one in the main basement room and check it through the summer.
Dehumidifier basics
A dehumidifier is the main tool for a humid basement. To get the most from one:
- Size it for the space. Use the label and the maker's guidance to match it to your basement's size and how damp it gets.
- Set it at 50 percent or a little below. That keeps you inside the EPA's ideal range.
- Drain it continuously if you can. A hose to a floor drain or a sump pit means no bucket to empty. If you use the bucket, empty it often and wash it now and then, since standing water turns slimy.
- Clean the filter. Follow the manual. A clogged filter makes the machine work harder for less.
- Give it room. Keep it away from walls and furniture so air can move around it.
- Close the windows. On humid days, keep basement windows and doors shut while it runs. Otherwise you are trying to dry the outdoors.
Your air conditioning also pulls moisture out of the air. The EPA lists both air conditioners and dehumidifiers as ways to bring indoor humidity down.
Stop moisture at the source
A dehumidifier treats the air. These steps deal with where the water comes from. Most of them come straight from EPA guidance:
- Keep gutters clean and in good repair, and point downspouts away from the house
- Make sure the ground slopes away from the foundation
- Fix leaky pipes and fixtures as soon as you find them
- Dry any wet area within 24 to 48 hours
- Vent the clothes dryer to the outside
- Run the bathroom fan when you shower
- Keep the air conditioning drip pan clean and the drain line flowing. Your HVAC technician can check both at a tune-up
- Avoid carpet on concrete floors that get wet or often show condensation
Many homes in Great Falls sit on large, wooded lots. If yours does, check the window wells for leaves in late fall and after big storms. A clogged window well can hold water against the glass.
Cleaning habits that keep a basement fresh
- Vacuum carpets, rugs and upholstery on a regular schedule
- Store things in lidded plastic bins, up off the floor, instead of cardboard boxes. Paper, cardboard and fabric give mold something to grow on once they stay damp
- Wash and dry the bedding in a lower-level guest room before it sits unused for months
- Clean the spare bathroom on the same schedule as the others. Everyday mildew on tile, grout and caulk comes off with a detergent cleaner and a brush. Dry the surface afterward
- Do not leave wet laundry in the washer. If you have a front-loader, leave the door open after use so the seal can dry
- Do not cover a musty smell with air fresheners. Find the source
Never mix bleach with ammonia, or with any cleaner that contains ammonia. The EPA warns that the mix can produce toxic fumes. Read every label before you combine anything.
When to call a mold professional
The EPA's guidance draws a few clear lines. It says you can usually handle a patch smaller than about 10 square feet yourself. That is roughly 3 feet by 3 feet. Consider an experienced professional when:
- The mold covers more than about 10 square feet, or there has been a lot of water damage
- The water was sewage or other contaminated water, such as a backed-up drain
- You smell mold but cannot find it. Hidden mold can release spores when it is disturbed, for example when you peel back wallpaper
- You suspect mold in your heating and cooling system. The EPA advises against running the system if you know or suspect it is contaminated
- Anyone in the home has health concerns. The EPA suggests talking to a health professional before any cleanup starts
Two more rules from the same guidance. Absorbent materials that get moldy, like ceiling tiles and carpet, may need to be thrown away. And do not paint or caulk over mold. Clean it up and dry the surface first.
If you hire a contractor, ask for references and ask about their experience cleaning up mold.
What a house cleaner can and cannot do
A house cleaner keeps a basement clean, which makes moisture problems easier to spot and less likely to take hold. That is a real job, but it is not mold remediation.
What a cleaner can do
- Dust, vacuum and mop the lower level on a regular schedule
- Clean the basement bathroom: the toilet, the sink, the tub or shower and the floor
- Wipe windowsills, baseboards and hard surfaces
- Change the bedding in a lower-level guest room
- Tell you about a new musty smell, a water stain or a damp corner. A team that cleans your home every visit is more likely to notice what has changed
What a cleaner cannot do
- Remove mold from drywall, carpet, insulation or ceiling tiles
- Clean up after a flood or a sewage backup
- Test for mold, or search for hidden mold
- Clean air ducts or HVAC equipment
- Fix leaks, grading or waterproofing
Our terms put mold on the short list of things we do not clean. If your team finds mold, they will stop and tell you where it is, so you can call a mold professional.
Keep the humidity in range and keep water away from the foundation. Then clean the lower level on the same schedule as the rest of the house. Many musty basements need nothing more. The ones that do need a specialist, not a stronger cleaner.
How we can help
Discuss accessible lower-level rooms and routine surface-cleaning needs as part of a deep clean or recurring clean. Cleaning does not fix a moisture source or replace specialist mold work. We review the scope, price and availability personally before confirming a visit. The quote request collects no money or card.
