Energy efficiency in the building stock is a substantial contributor to infrastructure sustainability. In Latvia, buildings’ thermal energy use for space heating accounts for 80% of total building energy use in the cold season. Therefore, reducing thermal energy consumption for space heating needs through the implementation of energy efficiency measures, enforcement of local building codes and regulations can ultimately lead to cost savings for building owners and stakeholders. The present PhD thesis introduces a methodology of evaluating thermal energy saving potential in the long run across residential, public, and industrial building stock under various thermal energy consumption compliance scenarios. These scenarios were developed based on three different building code protocols with a 10-year forecast analysis. Evaluation of the proposed building code implementation practices and their feasibility in Latvian building stock is discussed for these buildings with regards to their long-term thermal energy savings potential. This doctoral thesis is written in English and contains introduction, 10 chapters, conclusions, references, 28 figures and 27 tables for a total of 104 pages. Bibliography lists 121 reference.