Overview
- After showering in a bathroom with a window, keep the door closed and open the window wide for about five to ten minutes so moist air vents directly outside.
- Aim for 40–60% relative humidity in living rooms as the Umweltbundesamt recommends, and consider keeping winter humidity lower in poorly insulated homes to reduce risk.
- Watch for local surface danger: mould can grow on cold walls or corners once surface humidity reaches about 70–80%, even if the room air seems fine.
- Windowless bathrooms need properly sized mechanical exhaust (standards like DIN 18017-3 reference about 40 or 60 m³/h); dehumidifiers help short-term but do not fix cold surfaces or heat-loss problems.
- Use simple tools correctly—a hygrometer in the room centre and an infrared thermometer for surface checks—and treat the DIN 4108-2 ~12.6 °C example as a technical benchmark that needs context and multiple readings before judging a construction defect.