**5. Conclusions**

This study investigated the trade-off between a reduced operational carbon reduction and added embodied carbon emissions of eight deep energy retrofit projects. The analysis of the case buildings demonstrated that the current practice, which focuses solely on an operational energy use reduction, may not result in the most sustainable solution if the embodied energy and related carbon emissions are not carefully counted. Moreover, using the proposed sustainability index, integrating both operational carbon and embodied carbon, we found that the large operating energy reduction can be offset by the added embodied energy, and the renovated building with the lowest EUI can be less sustainable than buildings with higher EUIs. In addition, this study revealed that the sustainability score varies based on stakeholders' perspectives. If embodied carbon emissions are not included in the consideration of energy retrofit planning, it is impossible for building owners to reduce the additional emissions once the renovation is finished. Consequently, addressing embodied carbon emissions should go hand in hand with deep operating energy retrofit initiatives to achieve a comprehensive sustainable result. In the future, we recommend that embodied carbon be included in building codes and regulations and that it be used together with EUI to measure the effectiveness of a building energy retrofit.

**Funding:** This research was funded by Finland Fulbright Foundation and the APC was funded by Faculty of Architecture, Civil Engineering and Applied Arts, University of Technology.

**Institutional Review Board Statement:** No Institutional Review Board required for this study.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data available on request due to restrictions eg privacy or ethical. The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy of the project owners.

**Acknowledgments:** I thank School of Architecture, Planning and Preservation at University of Maryland, Faculty of Built Environment, Tampere University and VTT Technical Research Centre of Finland for their support.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

