Main characteristics. The buildings constructed before 1920, also referred to as “pre-revolutionary” (Figure 1, 2), are presumably represented by low-storied buildings (1-2 floors), though sometimes they can have up to 8 floors. Apartments in such buildings had no space norms and had their distinctiveness, though their space did not exceed 100–120 m². Floor height − from 3 to 4 m.

Figure 1 − 2-storied pre-revolution building

 Figure 2 − 5-storied pre-revolution building

The interfloor overlappings in such buildings were made of wooden, metal or reinforced concrete floor beams.

The building envelope was usually constructed of bricks, or was of a combined type with use of the local materials (including wooden frames).

Wooden windows.

The roofs are mostly pitched, with wooden roof frame: hipped or Italian roof^[1].

The heating systems of such buildings have been also completely reconstructed by today (modern individual or district heating), because many low-storied buildings constructed before the 1920’s had individual stove heating. The heating devices installed in the process of operation are generally sectional and tube-type radiators or heating system registers. The situation with the hot water supply systems that were reconstructed or completely installed during the period of mass connection to the district boiler houses is similar. When individual heating and hot water supply systems were installed, gas-fired water heaters were popular.

Energy saving measures. For this type of building, it is possible to use almost the full range of EE measures due to the significant aging of the construction elements of these buildings over their life period. Accordingly, these buildings require technical surveys and capital renovation or restoration.

One advantage of such buildings is their permanent nature and the significant thickness of the outer bearing walls. They were usually made of 640 mm and thicker bricks.

Therefore, the recommended measures include:

• Roof insulation – unless the building is an architectural monument;
• Insulation of attic floor, combined floor structure or pitched roof with polyurethane foam;
• Partial or complete reconstruction of the roofing before insulating the attic floor; 
• Insulation of the floor or basement floor; 
• Heat insulation of basements, foundations and pedestals;
• Replacement of old windows with modern plastic or metal-plastic windows; 
• Installation of window ventilators;
• Heat insulation or replacement of entrance doors – if possible (if the doors are not of historical and cultural value);
• Arrangement of a single or double ante-room (if there is space);
• Installation of door closers;
• Installation of reflectors (screens) behind radiators;
• Insulation of pipelines in the heating systems;
• Insulation of pipelines in the hot water supply (HWS) system; 
• Installation of automated HW supply unit (other measures in the engineering networks are rather costly and not so efficient in view of the insignificant heated space of the majority of this type buildings);
• Replacement of indoor lighting incandescent lamps (also in common areas) with modern energy efficient lamps;
• Installation of astro timers^[1] in the lighting system for common areas;
• Installation of motion sensors in the lighting system for common areas;
• Installation of gas meters. Optimization of work of the building internal gas supply system.