The sub-block sits between a private unit and a communal block, fulfilling many of the inhabitants infrastructural needs internally. Minimal interventions on the ground floor preserve the walls as space defining elements, resulting in both a continuity of the social structure and a solid base for the physical intervention. Due to the very random arrangement of these concrete and brick walls, the vertical extension consists of a wooden frame construction, adapting to each specific structural situation. Each sub-block accommodates one new building with drinking water collection facilities, providing the other sub-block units with fresh water. Waste water is dealt with in a similar fashion, where one unit houses a purifying system, treating all sub-block waste water.