Oborishte is an older, mixed-use district of Bulgaria’s capital Sofia, with around 36,000 inhabitants. Though the fast growing city is in need of living space for its inhabitants, the existing building stock is deteriorating. Demolishing the buildings and replacing them with new housing blocks is rarely an option due to complicated ownership structures and the poor financial situation of the residents.

The CONCERTO programme offered the possibility of improving conditions not only just for a single flat, but for a whole multi-family building, where the multiple owners agreed on the goals and collaborated. The Oborishte retrofitting project consists of three separate multi-family apartment blocks that were built between 1932 and 1957, as well as the refurbishment and the extension of a kindergarten. The refurbishment package included insulation and double glazing in accordance with the requirements for new buildings; the ventilation systems were also replaced by more efficient ones.

The main source of heat is still, as was the case before the retrofitting, the district heating network although smart control systems were applied during the programme which have resulted in additional savings. All in all, the energy saving for heating achieved by the retrofitting measures was estimated to be 68%. Besides the above mentioned measures, the production of domestic hot water was also decoupled and solar collectors were mounted on the roofs of the buildings – an uncommon approach in Bulgaria.

Energy savings of at least 10 % was the target for domestic hot water preparation. Thanks to the refurbishment, the apartments are much more energy-efficient and more comfortable when compared to other multi-family apartment buildings, leading to a higher quality of life for the residents in this part of Sofia. The experiences of the refurbishment in Oborishte are of great value for similar projects in Bulgaria and other countries. The comprehensive approach also included the residents who have organised themselves into homeowners’ associations. The thorough programme of external insulation and window renewal led to its success.