In standard analyses of Swiss energy and climate policies, the speed and extent of energy efficiency improvements (EEI) are usually assumed to be unaffected, even by policies designed to foster innovation. This project introduces endogenous EEI and barriers to retrofitting in the housing sector. In order to achieve this, we explain how Swiss building stock has evolved and how retrofitting decisions and heating system improvements may reduce energy consumption. We use a two-step model to illustrate how homeowners take decisions about retrofitting, then we consider several scenarios. Our results showed that in order to achieve deep decarbonisation in the building sector, a number of different economic instruments need to be used simultaneously.