A Deep energy retrofit (abbreviated as DER) can be broadly categorized as an energy conservation measure in an existing building also leading to an overall improvement in the building performance. While there is no exact definition for a deep energy retrofit, it can be defined as a whole-building analysis and construction process, that aims at achieving on-site energy use minimization in a building by 50% or more compared to the baseline energy use (calculated using utility bills analysis) making use of existing technologies, materials and construction practices. Such a retrofit reaps multifold (energy and non-energy) benefits beyond energy cost savings, unlike conventional energy retrofit. It may also involve remodeling the building to achieve a harmony in energy, indoor air quality, durability, and thermal comfort. An integrated project delivery method is recommended for a deep energy retrofit project. An over-time approach in a deep energy retrofitting project provides a solution to the large upfront costs problem in all-at-once execution of the project. Climate Change 82% of final energy consumption in buildings was supplied by fossil fuels in 2015 The energy-related emissionsaccount for the environmental impact due to a building. The Global Status Report 2017 prepared by the International Energy Agency (IEA) for the Global Alliance for Buildings and Construction (GABC) highlights the significance of the buildings and construction sector in global energy consumption and related emissions again. Deep energy retrofitting in existing building stocks is critical to achieve the global climate goals laid down in the Paris Agreement. Deep energy retrofits vs. Conventional energy retrofits Conventional energy retrofits focus on isolated system upgrades (i.e. lighting and HVAC equipment). These retrofits are generally simple and fast, but they often miss opportunity for saving more energy cost-effectively. Deep energy retrofits require a systems-thinking approach than the traditional approach followed for a conventional retrofit – home weatherization or typical home performance upgrade. Systems thinking approach is a step ahead of traditional analysis by evaluating the interactions between the different isolated components in the building. For example, Home Performance with ENERGY STAR offers a comprehensive, whole-house approach to improving your home's energy efficiency, comfort and safety while helping to reduce the energy costs only by up to 20%. In addition to the efficiency measures taken for a building, a deep energy retrofit requires occupants’ proactive role in energy conservation. This approach must take into account all the energy uses in the home, as well as