It required action. The rain came into the roof. The energy consumption was too high.
The idea was to keep the appeal of this 1929 Siedlungshaus. With limited interventions get out as much as possible but damage the look and feel of the house as little as possible. E.g. one of the main measures was to keep the original Kastenfenster in the house. No real trade-off to the energy saving ambitions.
One of the main targets was to create additional space for additional family members. This was achieved by building a dormer/gaupe in the roof. Definitely a serious intervention in the old structure, but gaining another 40m2 existing surface area which became inhabitable.