Retrofitting measures in old buildings aimed at reducing energy consumption has become a widespread subject and an urgent matter to counteract the effects of climate change and GHGs emissions. The globe has reaffirmed its agreement taken in COP21 to reduce emissions in COP26. The building sector is one of the culprits with a 70 % future energy consumption forecasted by 2050 i.e., the year certain countries aim to carbon neutral (e.g., Sweden). An old building with a severe problem of energy leakage has been studied under the influence of multiple parameters such as building orientation, shading systems, location, Low-E film and an alternative energy supply (GHP). The original building’s EnU amounted to 194.5 kWh/m2•yr; the parameters were applied and orientation of 90⁰ worked best, if the building was being designed, contrary to this case. However, energy reductions, compared to the base model, were actually achieved with the application of Low-E (5%) films and when substituting the heating demand with a GHP (57.5%), LEF-GHP reached (59.2%) and a corresponding decrease in CO2 emissions. Thermal comfort was best achieved with models that had the highest energy consumption such as LEF and ES making it counterproductive in fulfilling the aim of reducing GHG footprint of Rådhuset. The economic feasibility study showed that the installation of a GHP with at least the COP of 4.0 would lead to a shorter payback period than solely applying LEF. A tailored solution of a change in the energy source such as electrified heat supply from renewables combined with LEFs would reduce the energy and emission impact of any building; this would help the building sector reach the envisioned goal of carbon neutrality in 2050.