Room by room

• Open every cabinet under a sink and feel for damp, staining, or a musty smell.
• Look behind and beside toilets where slow leaks hide against the baseboard.
• Check window frames and sills for condensation rings and dark speckling.
• Walk the basement or crawlspace looking for chalky salt lines and damp corners.
• Pull the AC drip pan and check for standing water or slime.
• Keep a cheap humidity gauge on each floor and hold readings below 50%.

Humidity rule: keep every floor under 50% RH. Above that, mold has everything it needs.

• Water that sits somewhere it shouldn't stalls the whole room — resolve moisture before decorating.