The diffusion of energy-efficient building technologies is crucial for decarbonizing the building sector. However, many of these technologies diffuse slowly despite being economically superior compared to carbon-intensive alternatives. This study analyzes how combinations of different policies can effectively close this energy-efficiency gap. Applying an agent-based model that represents construction planning in Switzerland between 1995-2015, we ex-post evaluate the impact of four policies – financial incentives, mandatory building energy codes, voluntary energy labels, information campaigns – on the diffusion of three technologies – heat pumps, comfort ventilation, low-e glazing. Results indicate type and timing of policy combinations as key for successful technology diffusion.