If you are building a house in Australia, particularly in a cold temperate climate in some southern parts of Australia, you need to start thinking about putting in mechanical ventilation to prevent the build up of water vapour and mould. Last year, CSIRO published a study that showed the average airtightness of a new building is now 6.8 ACH@50Pa. Which is very close to 5 ACH@Pa, the point at which mechanical ventilation is required. This is down from a national average of 15.5 ACH@50Pa in 2016 #mould#airTightness#BuildingScience