  The residential sector is responsible for approximately 20 percent of the
world's energy-related greenhouse gas emissions. In order to improve this
reality, it is essential to help and support the leading actor in this scene,
the homeowner. In general, buildings are complex objects as each home may have
very particular parameters: different materials (windows, walls, types of
roofs, etc.), uses, and habits. No two cases are identical. In this paper, we
addressed this problem by proposing a method to obtain estimates of energy and
carbon savings resulting from a class of retrofit projects and housing
profiles. We applied our formulas to conduct a case study of the London
residential sector, supported by the publicly available Energy Performance
Certificates (EPC) dataset. As a result of a multi-project renovation of a
house, including loft insulation, double-glazed windows, and energy-efficient
lighting (LED), we found that the average family in the Greater London area
could save approximately 9 MWh in energy consumption, 1,700 kgCO$_2$ in carbon
emissions and more than GBP 800 on the energy bills, over a year, in contrast
to a cost of around GBP 9,000 (or a return on investment of 11 years). In
another example, applying the method to calculate what is needed to install
heat pumps in each house in London, a total of GBP 16.9 billion would be spent,
leading to savings of GBP 450 million per year (return on investment of 37
years). Finally, an overall upgrade to loft insulation would cost London
households GBP 1.4 billion, generating GBP 290 million in annual savings (a
5-year return on investment).
