Mold Smell in the House: How to Find Where It Is Coming From

Can you smell mold in your house?

Yes. A mold smell in your house is often the first sign of growth, long before you see a single spot. The EPA's page What Does Mold Smell Like? explains that molds give off gases called microbial volatile organic compounds, or mVOCs, which cause the musty odor. The EPA says a moldy odor suggests mold is growing and should be investigated.

Most people describe it as musty, earthy, damp or like an old basement. Some say it smells like wet cardboard or dirty laundry left in the washer. It tends to be strongest in closed-up rooms, first thing in the morning and on rainy days.

The smell often shows up before any visible sign. In A Brief Guide to Mold, Moisture and Your Home, the EPA says you may suspect hidden mold if a building smells moldy but you cannot see the source. It names places like the back side of drywall, wallpaper and paneling. That is why the smell is worth chasing down instead of covering up.

This guide is about tracking a moldy smell anywhere in the house. If the odor is new, faint and you are not sure it is mold at all, our guide on how to test for mold in your house walks through your testing options.

Start with the complete guide: mold in your house, how to spot it, test it and get rid of it.

How do you find where a mold smell is coming from?

You find the source by following the smell to its strongest point, then looking for the water that feeds it. UGA Extension's Mold and Moisture Home Inspection Checklist, reviewed in 2023, says that anywhere you smell a musty, earthy odor or see excess moisture, there is potential for mold growth.

1. Reset your nose. Turn off plug-in air fresheners, candles and wax melts for a day or two. They do not remove the odor, but they make it much harder to tell which room is worse. Then step outside for a few minutes before each round of sniffing.
2. Close doors and go room by room. Keep each room shut for a few hours, then open the door and take a breath. The room that hits you first is your starting point.
3. Get low and get close. Smell baseboards, closet corners, under sinks and behind furniture on outside walls. Mold odor is usually strongest within a few feet of the growth.
4. Check every water line. UGA's checklist says to check for leaks around sinks, tubs, the refrigerator, dishwasher and showers, plus water heater and washing machine lines.
5. Measure humidity. A simple hygrometer tells you a lot. The EPA says to keep indoor humidity below 60 percent, ideally 30 to 50 percent. The CDC says no higher than 50 percent, all day long.
6. Look below and above. Open the crawl space or basement door and the attic hatch. Damp soil, wet insulation and stained wood point to the source.
7. Compare the vents. Smell the air coming out of a supply vent, then the air in the room with the system off. If the vent smells worse, the odor is coming from the HVAC system or ductwork.

Write down where and when the smell is worst. A pattern like "only the guest bath, only after rain" narrows things down fast. A professional inspection uses that same information, plus moisture readings, to pin the source.

Where do mold smells usually come from?

Most mold smells come from a small number of wet spots: slow leaks, damp crawl spaces or basements, wet carpet pad, and the HVAC system. The EPA's mold guide says it is impossible to get rid of all mold spores indoors, so the goal is finding and fixing the moisture that lets them grow.

If a ceiling below a bathroom smells musty, it is often the same moisture problem we cover in our guide to mold on the bathroom ceiling.

In a lot of North Atlanta homes we inspect, the smell people chase upstairs actually starts below the floor. Georgia's red clay holds water, many crawl spaces have torn or missing vapor barriers, and that damp air works its way up into living space. UGA's checklist says a crawl space should have, at a minimum, a 6 to 8 mil plastic vapor barrier covering the soil. When it does not, crawl space encapsulation is usually the long-term fix.

Why does my room smell stale or damp?

A room smells stale when damp air sits still, so moisture collects in carpet, fabric and wall corners and starts to grow mildew. The EPA's Mold Cleanup in Your Home page notes that places that are often or always damp can be hard to keep free of mold, and closed guest rooms, closets and lower levels get the least air movement in the house.

Guest bedrooms with the door shut and the vent closed are classic. So are closets on outside walls, where a cold wall surface gathers condensation behind hanging clothes. Rooms over a crawl space or garage often smell worse than the rest of the house too.

Start simple. Open the vent, leave the door open and run a fan for a few days. If the room still smells damp with good airflow and normal humidity, the moisture is coming from somewhere specific, and it is time to look harder.

Cumming homes have their own version of this. Cumming is the county seat and the only incorporated city in Forsyth County, and it sits near Lake Lanier, which Buford Dam created in the 1950s. Homes with basements and lower levels, which sit partly below ground, tend to run damper than the floors above. If a downstairs room in your home smells musty, start there. We offer mold testing in Cumming with same-day appointments available.

Will a mildew smell eventually go away?

No. A mildew smell will not go away on its own as long as the moisture behind it is still there. The EPA says it is important to dry water-damaged areas and items within 24 to 48 hours to prevent mold growth. Past that window, growth keeps producing odor until you remove it and dry the area.

How to get rid of a damp smell for good

• Fix the water first. Repair the leak, clear the clogged drain line or correct the drainage outside.
• Dry everything. Fans and a dehumidifier bring the area down to normal humidity. For a real leak, our water damage mitigation team handles extraction, drying and moisture checks.
• Clean or remove what grew. The EPA says to scrub mold off hard surfaces with detergent and water. Absorbent materials like carpet and ceiling tiles may need to be thrown away.
• Deal with the air system. If the vents carry the odor, our duct sanitizing and odor removal cleans the system and treats it with an EPA-registered sanitizer and deodorizer.
• Keep humidity down. Georgia summers run humid for months. Holding the house at 45 to 50 percent keeps the smell from coming back.

When should you call a professional about a mold smell?

Call when you smell mold but cannot find it, when it follows a leak or flood, or when people in the house feel worse at home. The EPA links mVOC exposure to headaches, nasal irritation, dizziness, fatigue and nausea. The CDC adds that mold can cause a stuffy nose, coughing, wheezing, burning eyes or a skin rash.

The air at home adds up. In its Report on the Environment, the EPA says Americans spend about 90 percent of their time indoors, where some pollutants are often 2 to 5 times higher than typical outdoor levels.

Fresh Cleaning Solutions is IICRC and NADCA certified and has served Gwinnett, Forsyth, North Fulton and the surrounding area since 2016. Our mold testing and inspection tells you what is growing and where the moisture is coming from, so you fix the right thing the first time. We are open 24 hours, 7 days a week, with flat rates quoted up front, no hidden fees.

Smelling mold but cannot find it? Call (678) 609-8713 or book a free estimate and we will track it down.