The German government has committed to reducing the primary energy demand of buildings by 80% by 2050. Achieving this reduction will require foremost efficiency improvements, with a first milestone of a 20% reduction in heat demand levels by 2020. Given that about 80% of today’s building stock will remain in place beyond 2050, thermal retrofit of this existing building stock is essential. This report focusses on implications in order to achieve the reduction of primary energy demand.