Dew point and the risk of condensation and mould on your walls and windows.
How this works
Dew point uses the Magnus formula: g = ln(RH/100) + 17.62 T / (243.12 + T), dew point = 243.12 g / (17.62 – g). We estimate the cold wall surface from indoor and outdoor temperature and insulation. Mould grows when the surface stays above about 80% humidity, and water forms at the dew point.
Questions people ask
How do I use the Mould and Condensation Risk tool?
Fill in the fields, starting with “Room temperature”, “Room humidity” and “Outdoor temperature”, and change any other options that match your home. The answer, a drawing and practical tips update as you type, and the Copy link button saves your numbers in a link you can share.
Is the Mould and Condensation Risk tool free?
Yes. The Mould and Condensation Risk tool is free, with no sign-up, and works on phones, tablets and computers. The results are estimates to help you plan, so check with a qualified professional before structural, electrical, gas or plumbing work.