According to the EU targets on decarbonizing the heating sector as well as improving energy efficiency in the built environment, the economics of energy efficiency improvements and the respective measures are of high importance to understand the scenario outcomes and analyses in this work package. The aim of this deliverable is to provide an overview of efficiency potentials for the built environment and at which costs these potentials can be achieved. To do so, we analyse on the single building level different building types (e.g., single-family houses or multi-family houses) with different building age and building status (e.g., refurbished or non-refurbished) and the potential measures to improve energy efficiency. In the build environment, insulating the building envelope or improving the energetic quality of windows are the most common measures to improve the energy efficiency and reduce heat losses. For each set of building typologies, the measures can vary in terms of refurbishment depth and quality. Based on the potential technical solutions of improving the building envelope, the related costs for such measures have an impact on investors decision if they are implemented or not. To improve on the quality of the results also gathered within the HRE4 project, we have conducted an extensive literature review on published cost data on building refurbishment measures. Based on these costs, one can calculate the overall cost curves for the respective measures. By integrating different sources for refurbishment costs in the analysis, one must keep in mind the often-diverging cost parameters for different countries which are considered in the referenced publications. With our dataset we are integrating these differences into one platform and are providing an extensive overview of assumed costs for different refurbishment measures in the built environment.