The world faces global warming and climate changebecause of natural destruction and pollution; we use the resources faster than they replenish. As the buildings we live in and within are responsible for 35% of total energy consumption and carbon emissions globally, a sustainable strategy is needed to protect the planet we live on, and Passivehus is one of the solutions that provide a range of comfort but using less energy for heating and cooling. This report aims to show the process of designing a Passivehus to meet net zero energy demands by using London as the project site. To achieve the standard of Passivehus and building energy performance, climate analysis of the site was critical, and the analysis will include temperature, humidity, and wind in different seasons. Furthermore, the calculations for U-Value, Airtightness, Services, Ventilation, Energy efficiency, and the consideration of the material, insulation, and window performance will be explained. After that, three renewable technologies will have to be applied to the design to meet 100% of the building's energy demand, and the financial feasibility of a simple payback period and reducing carbon emissions calculation will sum up the design. Additionally, we will do adaptability testing to the design proposal by changing the PHPP climate data and then highlighting the need to allow the building to perform. Through these detailed analyses, calculations, and research, this report will present the role of an energy-efficient building in mitigating climate change and achieving a sustainable building.