Building stock is one of the crucial energy consumers in Europe. The majority of the European residential and public buildings were constructed after the Second World War. The external building envelope of these buildings has very poor thermal insulation properties with regards to modern requirements. There are several well known building retrofitting technologies such as rendered and double facades. These retrofitting technologies require large amount of on-site human working mounts. However, there might be significant limitations in mounting processes of the unclassified buildings such as prisons, military buildings and other buildings with specific safety requirements. In scope of this article the benefits of modular retrofitting solutions are taken into consideration. The paper presents the results of the architectural project development specifics as well as selection of the optimal modular pane layout, integration of existing communication and modular panels junctions solutions. This paper is prepared in the scope of work done within the European Regional Development Fund project “NEARLY ZERO ENERGY SOLUTIONS FOR UNCLASSIFIED BUILDINGS”.