The challenge when expanding it was to update the structure, materials and details for the present day. The structural and energy requirements, which had risen sharply, were to be integrated. The construction site for the extension was chosen in order to retain the existing public access to the lake. The comb-like structure on the west side is continued in harmony with the existing layout, thereby establishing a scale reference to the adjacent residential development. The courtyards serve as retention areas for the natural drainage of rainwater and are designed as themed courtyards.
As in the existing building, the construction of the extension is based on a continuous expansion grid of 1.2 m. This also applies to building services (e.g. floor tanks, ventilation outlets) meaning that office space can be easily converted if necessary. The offices have an axis width of 4.8 m and can be used flexibly as double or single offices with a meeting area. In order to avoid the need for chemical wood protection, the exterior supports and wooden braces were made of larch glulam (existing: spruce).
The façade was designed as a post-and-beam façade with spruce glulam profiles and aluminum cover shells (no maintenance coatings required). Composite building materials were avoided as far as possible during planning. Sustainability The extension, with disabled access, continues the architectural concept of the building envelope, but with a modern and highly insulated facade with triple glazing and external solar protection. A hygiene ventilation system is provided. The extracted air is drawn in centrally via overflow elements in the corridor walls.
The extracted air overflow from the offices is "reused" for conditioning the adjoining rooms (cooling or heating) free of charge, before the air in turn generates solar gains under the roof and feeds this energy back into the supply air via the heat recovery of the air conditioning systems. Heating and cooling are provided by component activation of the reinforced concrete composite ceiling (14 cm, Holorib system), which rests on larch glulam beams. Empty conduits for LED lighting and electrical installations were also installed in the ceiling (subsequent installations are possible via inspection openings).
The 250kWp photovoltaic system on the roof supplies a groundwater heat pump, which in turn enables CO2-free heat generation. The electricity produced by the PV system exceeds the district office's own needs, so that electricity can be fed into the grid. Therefore, the legal energy-saving requirements have been exceeded and a KfW 55 efficiency building has been realised.