To fully assess the amount of CO2 emissions and costs from the building, life cycle assessment and life cycle cost analysis can be performed. The advantage of these methodologies is the assessment of a building during the whole life cycle from the material extraction through the building operation to the end of life. However, to be able to perform such an assessment, a lot of information is required for a long period of building lifetime, which in Switzerland is set to 60 years. For instance, such information includes the unknown replacement of time and cost of the future materials, such as windows and insulation, the future evolution of climate, the future emissions and costs of the electricity due to the phase out of nuclear reactors in Switzerland. It is also unclear, which heating set points would be set by the residents, which can significantly affect the overall heating consumption.

Due to all these factors, it is often difficult to precisely estimate the benefits of the performed renovation. In our work, we accounted for all the uncertain factors and identify the robust, cost-effective and climate-friendly renovation solution for Swiss buildings.

Our result show that best solutions are the opposite as the current practice.

Usually, a deep renovation with the conventional materials and windows replacement is suggested. And the heating system can be kept as it is, as it requires additional investments and does not add energy savings. Such a renovation solution decreases the amount of released CO2 due to the energy savings, however it is counter-balanced by the increased amount of CO2 required for conventional materials production.

We show that the most impactful part of building renovation is the replacement of the fossil-based heating system to the low carbon source such as heat pump or wood pellets. By just replacing the system without building insulation, we significantly decrease the amount of CO2 emissions and reach the target recommended by the standards.

Another outcome of our study shows that in case building insulation is applied, only biobased materials should be used as they require small amount of CO2 for production, they also provide insulation properties comparable to the conventional materials and can store carbon, which is not possible in case of conventional materials. Moreover, due to the hygrothermal properties of bio-based materials, a better thermal comfort for the residents is achieved specially during summer heat waves.