Introduction
The decarbonisation of the built environment is a crucial step towards meeting the Paris climate agreement. In the Netherlands, this decarbonisation is incentivised with the BENG and a mandatory minimum EPC label C for all office buildings. While energy improvement measures (EIMs) are widely adopted to reduce operational carbon, their environmental payback, meaning the time needed to offset the embodied carbon introduced during retrofitting, remains under-researched, particularly for small office buildings.

Aim and methods
This study investigates the environmental payback time of common EIMs in retrofitting small office buildings (100, 200 and 500m²) in the Dutch context. A simulation-based experimental approach was used, modelling four scenarios: baseline, hybrid, full-electric, and full-electric with PV panels across the three building sizes. Operational energy use and emissions were calculated using Vabi Elements software, while embodied carbon was assessed through the Whole Life Carbon Assessment (WLCA) framework using the input from the Ökobaudat EPD/LCA database.

Results
Results show energy reductions between 56% and 78%, depending on retrofit depth, with smaller buildings exhibiting proportionally higher savings. However, operational carbon reductions were not always proportional in relation to the energy reduction, due to the carbon intensity of grid electricity. Embodied carbon varied greatly, especially between biobased and conventional materials, and was also significantly influenced by the PV system. Payback times ranged from less than 1 year (in the 500m² biobased retrofits) to over 6 years (in small 100m² conventional+ PV scenario).

Conclusion
This research confirms that, despite variability, all retrofits examined achieved environmental payback well within the lifespan of the implemented measures. The findings underscore the importance of material choice and highlight the growing value of biobased solutions. They also suggest that hybrid systems, in light of the payback times, can offer a better solution as long as the electricity grid is not decarbonising rapidly and there is no access to renewable energy. These insights ultimately support informed, lifecycle-based retrofit decision-making.