Verify the instrument
Place a second hygrometer nearby for several hours. Large disagreement means the sensors—not necessarily the building—need investigation.
Log the weather
Record RH and temperature at the same time each day for a week, including after rain. Note odors, condensation and equipment runtime.
Act on persistent conditions
Repeated readings above 60 percent, condensation or musty odors justify investigating water sources, the air boundary and humidity control.