In my diploma thesis I present a proposal for improving the energetic efficiency of a thermally non-insulated and highly energy-consuming two apartment house. The proposal is based on a technical and cost-related analysis of the renovation and thermal insulation of the house envelope. The thermal insulation of the house envelope consists of windows and doors substitution, façade thermal insulation and roof thermal insulation based on Eco Fund requirements and on the economical thickness of thermal insulation layer which represents an upgrade of the PURES-2 2010 regulations. In addition, I present ways for reducing or eliminating thermal bridges effects with the use of common thermal insulation products and the vacuum thermal insulation. Furthermore, based on pre-calculations and informative calculations I provide a) an overview of the costs related to each of the activities for renovating and thermally insulating the house under study and b) an estimation of the grant to be refunded based on the requirements of the Eco Fund public call. These calculations form the basis for estimating overall expenses of the renovation and thermal insulation investment. In this regard, I also summarize all procedures that have to be undertaken to get the grant. Based on calculations and electric energy prices I also provide an overview of annual heating savings in energy and money consumption and I evaluate investment criteria which serve to assess the economic rational to renovate and thermally insulate the house envelope. To assess the influence of improved energetic efficiency on a two apartment house price I conducted a survey among residents in Slovenia and an analysis of the prices of comparable two apartment houses. Based on the analysis results of both I conclude that the impact of thermal insulation of house envelope on house price is higher than the renovation and thermal insulation investment.