Energy upgrading of existing collective housing with environmental and economic criteria: financial accessibility gap in cost-optimal energy retrofit of a ten-storey residential building in Athens, Greece.

The collective housing buildings developed during the construction boom of the 1970s and 1980s form the bulk of the contemporary urban fabric of Athens, Greece, the majority of which lack any intrinsic capacity of thermal protection. At the same time, unprecedented economic factors during the last decade depleted the disposable income of large parts of the population and threatened households’ ability to maintain conditions of thermal comfort. This original research focuses on a ten-storey collective housing unit of multiple owners, part of a larger 1972 complex, located in central Peristeri, one of the most densely populated areas at the west of the city-centre of Athens. Cost-optimality methodology was employed to compare the energy assessment of the current condition of the building and 15 energy retrofit scenarios consisting of four fundamental measures and all their possible combinations. This calculated the annual needs in primary energy and the total cost per square meter over a period of 15 years. A users’ questionnaire was employed as an additional methodological tool and a focus group of residents established their willingness to undergo a hypothetical energy retrofit of their residence and the amount of disposable income that each resident would be willing to dedicate to cover its costs. Findings demonstrate that although primary energy consumption could be reduced significantly from the current condition levels, self-funding is not sufficient to cover most of the energy retrofit scenarios’ initial investment costs, including the cost-optimal scenario, even if a common investment amount could be agreed among the multiple residents. This indicates the financial accessibility gap between sustainable retrofit of the existing collective housing stock and current household income.