Concept studies and feasibility study for serial facade refurbishment of WBS 70 buildings

Background

The prefabricated housing type "Wohnungsbauserie 70" (WBS 70) was built in large numbers in the GDR in the 1970s to 1990s and still characterises many urban residential districts in eastern Germany today. In the meantime, however, this type of building has considerable energy and structural deficits, which are increasingly coming into focus against the backdrop of rising energy requirements, growing climate protection targets and social responsibility for affordable housing.

Serial refurbishment, in which industrially prefabricated façade systems are used, has the potential to implement refurbishment processes in a cost-efficient, time-saving and quality-assured manner. However, the transferability of such solutions to existing buildings such as the WBS 70 has not yet been sufficiently investigated in technical, economic and organisational terms.

Against this background, the work is intended to make a contribution to the further development of economical and sustainable refurbishment strategies in multi-storey residential buildings and thus shed light on a current topic at the interface of construction, climate protection and urban development.

Main part

This paper begins by examining the history and construction of the building and analysing the energy-related condition of the building envelope in the existing building stock. On this basis, four refurbishment concepts for the façade refurbishment of WBS 70 buildings are developed and the respective advantages and disadvantages are compared. The refurbishment variants are a conventional variant, in which a thermal insulation composite system is applied to the existing façade, and three serial refurbishment variants. The serial façade refurbishment variants include

• Variant 1: A prefabricated ventilated rainscreen façade (VHF) is subsequently applied to the existing façade
• Variant 2: The three-layer exterior wall is completely removed and replaced with a new prefabricated façade element
• Variant 3: The weather protection layer with core insulation is removed and a new prefabricated façade element is installed on the remaining load-bearing layer

For all concepts, the legal requirements and the requirements for obtaining subsidies as part of the federal subsidy for efficient buildings were taken into account. An energy and life cycle assessment of the different variants was then carried out using the Solarcomputer software on the basis of a five-storey WBS-70 residential building in Potsdam-Schlaatz. Finally, a cost calculation according to DIN 276 for a WBS-70 building was used to compare all the refurbishment options presented with regard to their economic efficiency.

Results

The analysis showed that the technical and logistical costs vary greatly depending on the variant and therefore depend on the objective and scope of the energy-efficient refurbishment. The energy and life cycle assessment also showed that the energy efficiency of an existing building can be increased by structural measures alone, but that an even greater improvement can be achieved in combination with regenerative heat generators. This has an impact on both CO₂ emissions and the associated CO₂ costs, thus reducing the building's operating costs in the long term. The economic comparison shows that the refurbishment variants with increased energy requirements and the installation of regenerative heat generators using subsidies result in lower construction costs overall than the variants that fulfil the legal requirements. A technical upgrade with regenerative heat generators would therefore be a sustainable and economical solution in the long term as part of an energy-efficient refurbishment.