According to sustainable development strategy, the Egyptian government objective is reducing the energy consumption and greenhouse gas emissions by 14% and 10% respectively by 2030. So, the national trend and the target of this phase is reducing the energy consumption in the buildings sector by applying the Net Zero Energy Building (NZEB) strategies to the new buildings and refurbishment the existing buildings to reduce the demand and apply on-site generation to reach NZEB target. This study starts with the analysis of the current situation of an exemplary existing administrative building in Cairo, Egypt. Consequently, the economic feasibility of converting exemplary existing administrative to be nearly and Net ZEB is analyzed. Generally speaking, the guideline to achieve this has three steps; (1) reducing the energy consumption by suggesting retrofitting strategies, (2) implementing energy efficiency technologies, (3) installing energy generation systems. OpenStudio as a cross-platform collection of software tools used to build the model where it is simulated by EnergyPlus as an energy modeling engine. The energy consumption is validated by comparing it with the real energy consumption of the existing building. The study analyzes the energy consumption including space heating, cooling, ventilation, lighting and appliances. The aforementioned guideline is applied by suggesting retrofitting strategy, implementing energy efficiency technologies instead of an existing one (11.925% Energy reduction), then installing photovoltaic solar system as a renewable energy system (29.45% Energy reduction). The economic feasibility is evaluated. The research completes with a possible energy saving by applying nearly and net ZEB guidelines to the existing administration buildings. The final conclusion of the study is a method that merges both retrofitting the building and installing renewable energy systems that suit the Egyptian situation and possible to convert the existing administration buildings to nearly and net ZEB.