Environmental Benefits from the Reuse of Building Parts and Materials from the Swiss Building Stock

Abstract

Reusing building components promises environmental benefits as it reduces construction waste, preserves resources and saves greenhouse gas emissions. Therefore, this paper investigates the potential of reusing building parts and materials in order to calculate the environmental impact with reference to the building stock in Switzerland and ultimately raise awareness of this alternative construction method in the context of sustainability and climate protection.
To analyse the environmental benefits, a case study of a typical multi-family house (MFH) as timber construction, built in two different ways is presented: Either it is built from scratch as it is common today or it is constructed with reused building materials. Biogenic materials are identified as the materials with the greatest environmental benefit for reuse in this case. These two different construction approaches in combination with three end of life variants serve as a basis for compiling multiple scenarios. For comparison purposes, the same MFH is also under consideration if it is constructed in reinforced concrete according to the current state of the art. It is considered "business as usual construction".

A life cycle assessment (LCA) is then carried using the Ecoinvent database to calculate the global warming potential (GWP100a). The results show that timber construction causes much lower CO2 emissions compared to the business as usual construction. Precisely, the MFH constructed with mainly reinforced concrete is responsible for almost three times more kg CO2 eq. than the timber construction. It is also found that the processes involving reuse hardly emit any greenhouse gas emissions, in fact they save production emissions. Finally, it is also found that energy recovery from the heat of incineration plants contributes significantly to reducing the GWP compared to when the residual energy of the waste materials is not used further. A sensitivity analysis is then carried out to verify the reliability of the results.
Furthermore, a dynamic life cycle assessment (DLCA) is performed in order to take also time dependent factors and biogenic carbon into account. It is modelled how the GWP develops for the Swiss building stock during several life cycles for different construction cases for a time horizon of 500 years. Growing biomass captures CO2 and stores it as carbon in its cells. When the biomass in form of trees is then processed and integrated into buildings as components, it is possible to offset emissions from the construction process. As a result, a temporary carbon sink can be established. It is found that the moreoften biogenic materials are reused in successive cycles, the larger the carbon sink will be and the lower the net emissions of GHG until the end of the considered time horizon.
The results presented in this thesis from the LCA and the DLCA undoubtedly show the benefits of reusing, but also limitations are pointed out. Nevertheless, there is great potential for reducing emissions from the construction industry and the opportunity to store CO2 in the form of carbon in the Swiss building stock.