Renovation is a general solution for reducing building stock emissions and energy consumption. While technical competence and digital tools exist, the renovation process is hindered by various barriers, particularly for non-expert renovation initiators (e.g., apartment building association representatives, building managers). This study proposes a knowledge-based configuration expert system (KBCES) concept as a solution to support non-experts in early-stage deep renovation planning. Using the Design Science Research (DSR) methodology, a system architecture and prototype Renokratt were developed and evaluated for typical Estonian apartment buildings. Renokratt was tested in a lab environment with results indicating that it can effectively support early-stage renovation planning, provided further development. The evaluation highlighted the importance of reliable building data. The study concludes that KBCES can bridge the gap between expert knowledge and end-user needs, improving the quality and pace of renovation planning while supporting broader climate goals.