Urban areas stand at the forefront of global energy consumption and carbon emissions, underscoring the imperative for innovative solutions to foster sustainable urban development. Among these, Positive Energy Districts (PEDs) have emerged as a promising concept, offering a multifaceted approach to not only mitigate urban energy consumption and climate impacts but also serve as pioneering models for larger urban areas and regional contexts. However, a critical gap exists in the availability of tools tailored for incorporating environmental considerations, particularly during the early stages of PED design. In this context the objectives of the work are: i) the validation of the TREE (Tool for Retrofitting Energy Efficient Buildings) PED tool and ii) the assessment of the potential for reaching the target of PED within a district case-study in the Bucharest area in Romania. This tool integrates dynamic simulation results and environmental life – cycle oriented considerations to offer a robust framework for guiding early PED design decisions. The Bucharest Sector Six area, comprising 443 residential buildings constructed between 1963 and 1984 and covering a total of 3.05 million square meters, presents an intriguing case study, characterized by its expansive residential infrastructure and diverse urban landscape. The analysis performed through the TREE PED tool includes energy efficiency solutions and renewable based generation systems feasibility studies aimed at paving the way for the achievement of the PED level with the case-study district. Findings suggest that the aforementioned solutions could potentially satisfy up to 70% of the district's combined heat and electricity needs. However, the research underscores that further concerted efforts, such as the integration of renewable energy systems in public areas, are indispensable to fully unlock and capitalize on the district's potential