The reduction of energy consumption in the existing building stock is a crucial element of the Swiss Energy Strategy 2050 in view of the fact that the built environment accounts for more than 44% of the final energy use in Switzerland. It is therefore necessary to characterise the Swiss building stock and in particular the residential sector at an appropriate degree of detail, distinguishing between various types of buildings (archetypes) and building elements in order to identify the untapped potential for energy retrofit. In this paper, the current thermal performance and retrofit state of the Swiss residential building stock is examined based on approximately 10,400 Cantonal Building Energy Certificates issued for individual buildings across the country. The statistical analysis of the certificates allows to estimate a thermal performance level of archetype buildings and their respective building elements as well as of the heating systems. For this purpose, we develop a method allowing to obtain typical U-Values for original and retrofitted buildings from the total U-Value distributions. Our results indicate that approximately 75% of all building elements do not yet reach the thermal performance of buildings constructed in the last 15 years. In order to reach current low-energy building standards (MINERGIE P), the U-Values of building elements constructed prior to 1990 would have to be reduced by a factor of three to more than six, from 0.5–1 W/(m²K) to 0.15 W/(m²K); windows would require an improvement by at least a factor of two, from 2.5–2 to 0.9 W/(m²K). With regard to heat supply, 50% of the surface area is still heated by inefficient and CO2-intensive oil-fired boilers. The results of this study hence confirm the high potential for thermal retrofit in the Swiss residential building stock.