Deep energy retrofit across the European building stock would require decades during which boundary condi-tions will change. This study identifies a range of retrofit pathways, using a dynamic stock model, a bottom-up energy model and an optimization model for different climate scenarios. We consider 1.1 million different retrofit options in the Swiss residential building stock for different economic/environmental objectives until 2060. Despite the replacement of old by new buildings, energy demand and greenhouse gas (GHG) emissions in the reference scenario without deep energy retrofitting are likely to decrease by only about 25%, while ac-counting for investments of 2–3 billion CHF/a. Partial energy retrofitting or an investment-minimized pathway are neither cost-effective nor sufficient to get close to the net zero targets. In contrast, the highest GHG-saving pathway leads to very high emission reduction of 90%, but requires investment cost of 9 billion CHF/a, which leads to specific cost of 180 CHF/t CO2eq. The cost-optimal pathway shows moderate trade-offs for in-vestment cost and could reach GHG savings of 77% with specific cost of 􀀁 140 CHF/t CO2eq. Hence, early and deep energy retrofit is cost-effective and allows deep GHG emission reductions by making full use of the syn-ergies between GHG and cost savings.