Renovate or replace – Finding the optimal decision for buildings considering cumulative CO₂ emissions

Abstract

To reduce emissions from the building sector, a key question is which strategy is most effective for minimizing the CO₂ impact of the existing building stock. Is it better to renovate a building, or to rebuild it in a very energy efficient manner? In a joint research effort we developed a framework to assess cumulative CO2 emissions throughout the lifecycle of a building. The framework is based on a building energy simulation tool to assess operational emissions together with a lifecycle assessment framework to study environmental impacts and benefits associated with material and systems used during the construction or renovation process of buildings. The approach was applied on various typical buildings in Germany, including single and multifamily houses, where we examined various scenarios of renovation and building replacement options. The aim of this analysis is to evaluate the trade-off between costs, emissions and energy consumption of the buildings during a time span of 25 years. The approach consists of an analysis of relevant data sources, modelling of the geometry and constructions which are then used by both the building simulation and the life cycle assessment tool. A rigorous scenario analysis has been performed to evaluate life cycle costs, emissions and energy consumption for both retrofitting and replacement buildings. Results show that the lowest CO2 emissions during the lifetime of the analyzed single-family house can be achieved with a sustainable replacement building by using a heat pump coupled with PV under the condition of reusing the materials as much as possible, so that carbon remains stored in the wooden materials. Interestingly, the application of small renovation measures, such as replacing the windows, doors and replacing the natural gas-based heating system by a heat pump is on the edge for achieving the 2°C CO2 emissions target at much lower costs.