From 2008, an energy label is mandatory for the sale and rental of a home, with a few exceptions. The energy label for houses gives an indication of how energy efficient a home is with classes and colors. From 1st of January 2015, compliance with having an energy label for the transfer of ownership will be monitored.
In the case of a home without a definitive energy label, the Inspectorate for the Living Environment and Transport (ILT) can impose a penalty on the seller. This can be a fine up to € 410,- or a penalty order with the obligation to still apply for a label. This legal obligation can not be excluded in a purchase agreement. More information can be found on the website of the national government.