Mold inspection in California: how the air test works and why inspectors say “moisture”
A dark stain and a musty smell are not enough to say a house has mold — and saying it without proof can end in a lawsuit. Here is how air and surface sampling works, what the lab tells you, and what to ask for when the report flags moisture.
Why the inspector writes “moisture,” not “mold”
On a general inspection, the inspector can attest to what he measures or sees: moisture, with a meter, and stains or signs of water intrusion. Saying a stain is mold — a fungus, with different species and different risks — takes a lab analysis.
Inspector Aguiar explains the risk: if the buyer’s inspector writes “there’s mold,” the seller may order a lab air test, and if it comes back normal, whoever made the claim without proof is exposed to a lawsuit.
“I have to stay away from the word mold. I have to say there’s moisture here.” — inspector Aguiar
How a mold inspection works
The specialized mold inspection follows the industry’s usual method:
- Indoor air samples: a device draws in a set volume of air and traps the particles in a cassette. Samples are taken in the dampest rooms — bathrooms, kitchen, laundry — or wherever there is a concern. Aguiar usually takes three or four.
- An outdoor air sample, as the baseline: fungal spores are naturally present outside. What matters is the comparison — inside, the concentration and types should not be very different from outside.
- A surface sample (swab or tape lift) when there is a visible stain to identify.
- The lab: samples go out for analysis, and the report lists the types of fungus found and their concentration, compared with the outdoor sample.
The lab analyzes; the inspector samples and explains
Aguiar notes that the inspector does not need to be a microbiologist, because the lab does the analysis. The inspector’s job is to take the samples properly, in the right places, and explain the result.
What California law says
California passed the Toxic Mold Protection Act in 2001, asking the Department of Public Health (CDPH) to evaluate exposure limits and standards. To date there is no legal limit for airborne spores in a home and no specific state license for mold inspectors. The official guidance is practical: if there is visible growth or a musty smell, the priority is to find and fix the moisture source and remove affected material.
Mold is also part of the seller’s disclosure duty: known problems, including water intrusion and water damage, must be reported.
Hidden moisture
Aguiar has found houses, some recently remodeled, where someone covered up a damp area for the sale — and the house had a strong musty smell. The key point: mold is a consequence. Without fixing the leak, the poor ventilation or the water intrusion, cleaning does not solve it.
The risk is higher in homes near the beach, where the salt air keeps humidity high, in properties closed up for a long time, and under the floor of houses with a crawl space.
What to do when the report flags moisture
- Ask for the exact location and the meter reading in the report.
- Find the cause: a plumber for a leak, a roofer for water intrusion, a check of bathroom and attic ventilation.
- Consider a mold test when there is a smell, widespread staining or someone in the family with asthma, allergies or a weakened immune system.
- Use the contingency window to negotiate fixing the cause and remediation by a specialized company.
- Ask for documentation of the work and, if possible, a new test after remediation.
- After you move in, ventilate, run the bathroom fan and keep indoor humidity under control.
This article is for general information and does not replace medical advice or an evaluation by remediation professionals.
