Energy has become an essential requirement for human activity and survival in the 21st century. Of all the key sectors around the world, the building construction and operation sector has been recognised as one of the largest energy consumers, globally. With the unprecedented fluctuations in fossil fuel prices on the global market, most energy-dependent countries are increasingly devising strategies and regulations to minimise their energy consumption, especially consumption involving buildings. One strategy that has been adopted and implemented globally in the last few decades is the Zero Energy Buildings (ZEB) approach. However, Jordan is a country that is yet to implement the ZEB strategy. The ZEB strategy could be particularly relevant for the case of Jordan, considering that residential and commercial buildings consume approximately half of the energy produced in the country. Yet, 96% of the country’s energy generation is still dependent on fossil fuels that are imported. Therefore, this study aimed to study the possibly of developing a sustainable and comfortable ZEB reference retrofit that can be implemented on Jordan’s existing buildings. Energy simulations using the Integrated Environmental Solutions Virtual Environment (IESVE) software tool were run to study and identify the optimal strategies and create a retrofit manual for existing buildings, for use as a guide for comfortable ZEB implementation in Jordan, by considering the various factors that affect energy consumption in buildings. The study found that changing the type of windows in existing buildings would lead to the highest energy reductions and also improve thermal comfortability. Utilising a green roof would also improve the thermal comfortability in the building space, while also achieving a slight reduction in the energy consumption. In terms of the building’s systems and operations, Light Emitting Diode (LED) lighting utilisation could result in a 15% reduction in the building’s annual energy consumption. The study established that while the set-point temperature controls the number of hours that achieve thermal comfort in the building, it is the occupancy behaviour that has the highest impact on energy consumption and human comfort inside the building space. In general, this study established that retrofitting an existing building in Jordan to run as a nZEB is achievable. In terms of energy consumption, the optimal result can be achieved by using 10 cm Polyurethane Boards (PUR) for additional insulation on the walls and roof, adopting LED lighting, and utilising a solar water heater and an air source heat pump to provide the building with domestic hot water. This would result in a reduction in annual energy consumption of about 48%, and photovoltaic cells could then be used to cover the rest of the energy demands of the building. Overall, the optimal case in terms of thermal comfort operation would implement the same measures described above, but with a set-point temperature of 21.1 ℃ for cooling and 20 ℃ for heating, along with a green roof for roof insulation. This would increase thermal comfortability by 11% in terms of the average number of hours that achieve the acceptable PMV range on ASHRAE 55.