A considerable share of the existing buildings in Europe has low energy performance and are expected to last at least for the next 50 years. The operation of these buildings causes high atmospheric greenhouse gases emissions, besides low thermal comfort for occupants. In Sweden, most of the existing buildings are residential, consisting of multi- and single-family houses. Large final energy savings can be achieved by integrating energy efficient measures (EEMs) to the thermal envelopes of these buildings. However, it is often a challenge to achieve a considerable energy savings and realize cost effectiveness simultaneously. This study investigates the effect of carbon taxes implementation on the cost effectiveness of EEMs applied to an existing multi-apartment building in southern Sweden. It explores the implications of different additional insulation thicknesses for exterior walls and roof, and high-performance windows and doors, for the final energy use and carbon dioxide (CO2) emissions of the building. The final energy savings of the EEMs are estimated through dynamic energy balance simulations and the CO2 emissions are calculated considering the full energy chains. The cost effectiveness of the EEMs are analyzed with and without carbon abatement costs considering the investment costs and associated net present value of costs savings of the EEMs. The results show that replacing the existing windows give the highest final energy savings, reducing the building’s space heating demand by 23 %. The cost optimal analysis without carbon abatement costs shows that all the analyzed thicknesses of roof insulation and high-performance windows are cost effective. Considering the carbon abatement costs altered the cost effectiveness of the EEMs, with exterior walls as well as ground floor insulations and door replacement becoming cost effective for certain thicknesses and U-values, respectively.