How do you know if you have mold in your house?
You usually know by sight or smell. Mold grows where something stays damp, so the first clue is often a past leak, a humid basement or a bathroom that never dries out. Here are the signs worth taking seriously:
- Spots or fuzz in black, green, gray or white on drywall, ceilings, wood, grout or fabric.
- Stains and discoloration that keep coming back after you clean, often in a ring around a past leak.
- Peeling or bubbling paint and soft or warped drywall, especially low on basement walls.
- A musty smell that is stronger in one room, closet or cabinet.
- Condensation on windows, pipes or walls that shows the air is too humid. The EPA recommends keeping indoor humidity below 60 percent, ideally between 30 and 50 percent.
- A history of water: a burst pipe, roof leak, flooded basement or sewer backup that was not dried out fast. The EPA says water-damaged areas should be dried within 24 to 48 hours to prevent mold growth.
What does mold smell like in a house?
Mold smells musty and earthy, a lot like damp cardboard, wet socks or an old cellar. Your nose is one of the best detectors you have. The EPA points out that a building that smells moldy may have hidden mold, even when you cannot see any. If a smell gets stronger when you open a cabinet, lift a rug or stand near one wall, that is where to look first.
Where does mold hide in a house?
Mold hides wherever water collects and air does not move. The EPA lists the back side of drywall, wallpaper and paneling, the underside of carpet and pad, the inside of walls around leaking pipes, ductwork and roof materials above ceiling tiles as common hidden spots. In Northern Virginia homes, start with these:
- Basements and crawlspaces. Block foundation walls, carpet on slab floors and the bottom of finished walls. Our guide to mold in the basement covers this in detail.
- Under kitchen and bathroom sinks. Slow drips at supply lines and drain joints.
- Ceilings below bathrooms and the attic. A stain on the ceiling is often the only sign of a leak above. See water leaking from the ceiling.
- Attics. Bath fans that vent into the attic instead of outside, and roof leaks around flashing.
- Around the washer, water heater and HVAC unit. Leaks and condensation lines that drip unnoticed.
- Window sills and outside-wall corners. Cold surfaces where condensation forms in winter.
Do not tear into walls to look. Disturbing moldy drywall or wallpaper can release spores into the air, which is why the EPA calls for protective equipment during that kind of work.
Do you need a mold test?
Often you do not. The EPA says that in most cases, if visible mold growth is present, sampling is unnecessary. There are also no EPA or other federal limits for mold or mold spores, so a number on a lab report cannot tell you your home passes or fails a federal standard. Testing is most useful in a few situations:
- You smell mold but cannot find it, and you need to narrow down where it is.
- You want to compare indoor air to outdoor air after a water event.
- A buyer, seller, landlord or insurer asks for documentation.
- Mold was removed and you want to check that the area was cleaned well. The EPA notes surface sampling can help with this.
The EPA also says sampling should be done by professionals with experience designing sampling plans and reading results, and that samples should be analyzed using methods recommended by groups like the American Industrial Hygiene Association.
What are the types of mold tests?
There are three common types of mold samples. Each answers a different question.
| Test type | How it works | What it can tell you |
|---|---|---|
| Air sample | A pump pulls a set amount of air through a collection cassette, indoors and outdoors | How indoor spore levels and types compare to outside air |
| Surface sample | Tape lift or swab from a stain or surface | What is growing on that spot, or if a cleaned area still has residue |
| Bulk sample | A small piece of drywall, carpet or insulation goes to a lab | If mold is growing inside a material |
None of these tests replaces a careful look at moisture. A test can confirm mold is there. Only a moisture investigation tells you why it is there, and the EPA is clear that the key to mold control is moisture control.
Are DIY mold test kits worth it?
Usually not. Most store kits are a dish you leave open for a while, then send off or watch for growth. Mold spores are in nearly all indoor and outdoor air, so a kit that grows something is not telling you much. Most kits do not compare indoor air to outdoor air, measure how much mold is present, or show where it is coming from.
| Question | DIY kit | Professional inspection |
|---|---|---|
| Is there mold in the air? | Almost always yes | Yes, with an outdoor comparison |
| Where is it coming from? | No | Visual check, moisture readings, targeted samples |
| How big is the problem? | No | Yes, which drives the removal plan |
| What caused it? | No | Yes, by finding the moisture source |
How do you read mold test results?
Read them as a comparison, not a pass or fail. With air samples, the usual question is if indoor levels and mold types look like the outdoor sample taken the same day. The EPA describes indoor mold types and concentrations that resemble outdoor levels as one sign that cleanup is complete. Indoor counts that are much higher than outdoors, or mold types that show up indoors but not outside, point to a source inside the house. Ask whoever took the samples to walk you through the report and tell you what they think is causing it.
What should you do if you find mold?
- Find and fix the water. Leaks, condensation, high humidity or a past flood. Mold comes back if the moisture stays.
- Size it up. The EPA says a homeowner can usually clean up a moldy area of less than about 10 square feet. Larger areas call for the EPA remediation guidance or a professional.
- Do not paint over it. The EPA says not to paint or caulk moldy surfaces.
- Plan to remove it, not only kill it. The EPA does not recommend routine use of bleach and other biocides, and notes that dead mold can still cause allergic reactions.
- Call for help with anything bigger. Our mold inspection and testing finds what you have and how far it goes, and mold remediation removes it. Read what mold remediation involves to know what to expect.
If you are selling, see mold disclosure in Virginia. If the mold followed a leak, read does homeowners insurance cover mold before you start cleanup, and take photos first.
Who inspects for mold in Virginia?
Virginia does not currently license mold inspectors or remediators, as far as we can confirm. The state created a license for both in 2011 and repealed it in 2012. In 2025 the General Assembly passed HB 2195, which asked the Department of Professional and Occupational Regulation to study if licensing or certification should come back. Until that changes, ask any inspector how they will find the moisture source, what samples they plan to take and why, and who will analyze them.