Energy Upgrade of Existing Buildings to nearly Zero Energy Consumption ones; Embodied Energy Considerations Eleftheria Alexandri 1 , Stavroula Malamouli 2 , Anthi Prinou 3 1 Lecturer, Open University of Greece, Em. Mpenaki 152, 114 73 Athens, Greece, +30 6997023595, el_alexandri@yahoo.gr 2 MSc student, Open University of Greece, Mavrokordatou 15, 38221 Volos, Greece, +30 6976555451, skm@malamoulis.com 3 MSc student, Open University of Greece, Gorgopotamou 15, Argyroupoli, 16451 Athens, Greece, +30 6945333430, anthiprinou@gmail.com Key words: Building retrofitting, Zero CO 2 emissions buildings, Embodied energy payback period Concise synopsis As nearly Zero Energy Buildings (nZEB) are a mandatory requirement of EU legislation for new buildings (Directive 2010/31/EU), this paper explores the possibility of transforming existing buildings into nZEB ones. The available energy upgrade techniques are explored in three buildings in Greece, taking into consideration their embodied energy, so as to evaluate whether these techniques can pay back the energy consumed for the materials and components production during the rest of the buildings’ lives. Conclusions are drawn on which techniques are the most appropriate ones, taking into consideration energy savings in relation to the embodied energy payback period. Abstract The aim of this work is to define whether, for the mild climatic zone B of Greece, urban non-residential buildings can be easily transformed into zero energy buildings and pay back the embodied energy of the applied technologies, within the buildings’ life span. Two existing buildings are chosen; a historical, uninsulated building, which is going to be used as an office building in the city of Volos and an insulated nursery in the area of Elliniko, Argyroupoli, both in climatic zone B. Data is collected on the technical characteristics of both buildings. Their energy consumption and the energy savings for energy upgrade scenarios that make up to transforming these buildings into nZEB are calculated with the software TRNSYS 16. Embodied energy is estimated according to respective bibliography. Its payback period is calculated with