Are home mold test kits accurate?

Most hardware store kits are settle plates: a dish of growth medium that you leave open in a room for an hour, then cover and wait a few days. Spores from the air land on it and grow. The EPA notes that molds are found in virtually every environment, indoors and outdoors. So the dish growing something is the expected result, not a finding.

A kit cannot answer the questions that matter. It does not compare your indoor air with the outdoor air on the same day. It does not find the wet material that the mold is growing on. It does not show whether growth is inside a wall cavity, under carpet pad, or behind a basement finish. No federal standard exists for how many spores are acceptable, so there is no number to compare a kit result against.

The EPA also states that if mold growth is visible, sampling is usually not necessary. The useful question is where the moisture is. A professional mold inspection answers it with a moisture meter, a thermal camera and photos, and writes down what was found and where. When a lab result is needed, for example for a buyer, a landlord or an adjuster, an air sample goes to an independent lab with an outdoor sample taken for comparison.

If you smell a musty odor or see spots and want to know what is behind them, start with the moisture. Find the wet area first, then decide whether a lab sample adds anything.