[z2]

I've had success using my nose and a cheap $15 moisture meter against walls and ceilings. In my case I was already pretty sure the moisture came from the roof when it rained so went looking right after rainstorms. This was after also running a dehumidifier in a formerly damp basement.

If a home has an active mold problem, it probably has an active water or moisture problem. What mold remediation people sometimes do as well is use an IR camera to try to find unusually cold (thus damp areas).

[Aurornis]

> If a home has an active mold problem, it probably has an active water or moisture problem.

Mold can't grow or spread without moisture, so a moisture problem is a necessary prerequisite for a mold problem.

So focusing on fixing any moisture problems is a great place to start. Feeling around walls and baseboards or climbing up into the attic in the hours and days after a big rainstorm is one way to get started without any equipment investment. Air circulation also helps dry things out, so make sure every space has some openings for air exchange.

[DANmode]

> or spread

Not explicitly true - dry spores get anywhere dust does.

Whether they become active growth or not is a different question.

[HPsquared]

Infrared thermometer is also good to survey a room and look for cold spots which are associated with moisture (condensation and/or structural dampness increasing thermal transfer). A thermal camera even moreso (but more expensive).

[tdeck]

I've seen situations where experts put different colored water soluble dye on different spots outside the house, so that when it leaks through you can determine the source. Presumably that's within reach for an individual as well.

[taneq]

The IR camera idea is clever, usually we use them to find hot spots. Gonna try this next time I suspect we have a leak.

[_blk]

Yup, look at anything with temps below the dew point and badly vented areas below (condensation follows gravity)

[DANmode]

or unusually warm!

(When your shower is improperly installed, for instance)