Work still in progress. Site is not finished.
The exact ordinance (Verordnung zur Berechnung der Wohnfläche) you can find here: https://www.gesetze-im-internet.de/woflv/index.html. The ordinance says: - area under the sloping roof, if it has a height of less than one meter, is not to be calculated to the square meters. - area under the sloping roof, if it has a height of fewer than two meters but a minimum of one meter is to be calculated as half the square meters. - area under the sloping roof, if it has a height of a minimum of two meters, is to be entirely calculated to the square meters. All information is supplied without guarantee.