3. How to rehabilitate existing buildings?

It's not just new buildings that can be certified as "passive buildings". The process can be extended to older buildings if the economic balance sheet shows that the project is profitable, with an ROI of less than twenty years, for example. However, it would be pointless to attempt this renovation on a building facing due north and/or in the shadow of other buildings. The list of difficulties (and the impossibility of meeting the above labelling criteria) is not exhaustive. To take account of these difficulties, another label called EnerPHit has been developed. Some requirements have been relaxed, and the main criteria are as follows.

• The heating requirement must be less than 25 kWh/m ² /year.

• Primary energy demand must be less than 120 kWh/m ^...