This paper introduces methodologies and optimal strategies to reduce the energy consumption of the building sector with the aim to reduce global energy usage of a given .region or country. Many efforts are underway to develop investment strategies for large-scale energy retrofits and stricter energy design standards for existing and future buildings. This paper presents a study that informs these strategies in a novel way. It introduces support for the cost-optimized retrofits of existing, and design improvements of new buildings in Turkey with the aim to offer recommendations to individual building owners as well as guidance to the market. Three building types, apartment, single-family house and office are analyzed with a novel optimization approach. The energy performance of each type is simulated in five different climate regions of Turkey and four different vintages. For each vintage, the building is modelled corresponding to local Turkish regulations that applied at the time of construction. Optimum results are produced for different goals in terms of energy saving targets. The optimization results reveal that a 50% energy saving target is attainable for the retrofit and a 40% energy saving target is attainable for new design improvements for each building type in all climate regions.