Keep indoor relative humidity between 30% and 50% and mold cannot establish itself. Above 60% it becomes likely over weeks; above 70% it grows within days on anything organic. But the room reading is only half the story — mold grows where surfaces are cold enough to reach the dew point, which is why a house at 55% can still grow mold behind a north wall. These guides cover target levels by room and season, how to measure properly, and the twelve ways to bring humidity down.
August 28, 2026
August 28, 2026
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