This article contains wording that promotes the subject in a subjective manner without imparting real information.(July 2022)
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. 
DERs are projects that create new, valuable assets from existing residences, by bringing homes into alignment with the expectations of the 21st century— Brennan and Less 
82% of final energy consumption in buildings was supplied by fossil fuels in 2015.  The energy-related CO2 emissions account 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. 
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 the activities of the occupants. Deep energy retrofit projects are an evidence to the fact that technology is available to set the thresholds of energy savings to a limit much higher than that achieved by a conventional retrofits.
Deep energy retrofits achieve much greater energy efficiency by taking a whole-building approach, addressing many systems at once. It is most economical and convenient to take this approach on buildings with overall poor efficiency performance, with multiple systems nearing the end of useful life, and perhaps other reasons. 
Deep energy retrofits and conventional energy retrofits both undertake different approaches and lead to varied outcomes. In scenarios where capital improvements are being looked forward to in an existing project deep energy retrofit is certainly an upper hand decision to create the most value out of investments in the long term. Deep energy retrofits can be well-timed to reap maximum benefits in such situations. 
The overall success of the deep energy retrofit project also depends upon the inclusion of occupants in all the phases of the project. The phases include – project recruitment, project planning and during the use. Occupant behavior requires the project to focus on building owners’ needs and wants as much as the technical specifications. This ascertains actual performance, cost-effectiveness, willingness to progress from a design to an actual implementation, and occupant satisfaction.  Also, evidence suggests that our building simulation models can become more accurate for a given house when we include actual operational information, such as thermostat set-points, appliance usage, etc. (Ingle et al., 2012). 
Over-time retrofit is the implementation of a retrofit project which is planned in a step-by-step manner at intervals of time within a stipulated duration. Such an approach is usually sought for deep energy retrofits over an all-at-once approach to reduce the burden of large upfront costs and break it down into chunks of timely investments. Thus, an over-time retrofit can at times be a more viable option than a conventional deep energy when there are capital constraints. Research in the United Kingdom has demonstrated that retrofits carried out over-time can achieve levels of home performance equal to those achieved by all-at-once DERs (Fawcett, 2013; Fawcett, Killip, & Janda, 2014)    and select projects have been successful in the United States. (Less & Walker, 2014).  The pros and cons of an Over-time Retrofit are compared as follows (Less & Walker, 2015): 
|Potential benefits||Potential downsides|
|Less perceived disruption, because it is spread out over-time.||More numerous small disruptions.|
|More likely that occupants can continue to inhabit their home continuously, |
without any need for alternative accommodations.
|Difficult to finance traditionally.|
|Costs are spread over-time, allowing owners to build up savings between phases.||Costs may be higher, due to repeated fees and fixed costs, such as |
permitting, inspection and construction labor.
|Introduce occupants to the benefits of energy upgrades, thus feeding |
their desire for further improvements and refinements.
|Possible need to reinvest in measures that are inadequately addressed, |
due to a lack of careful and detailed planning.
|More aligned with making incremental deep green improvements, |
as maintenance and equipment replacement require.
|Lower aggregate energy savings and reduction in environmental footprint.|
|Over-time process can inform occupants of the effects of their |
behaviors, and the potential for behavior modification to reduce
both energy use and project costs (through use of human effort
rather than technology to achieve savings)
|Difficult for occupants to delay the gratification of investing in glamorous |
efficiency measures (such as solar PV or windows), by first investing
in the invisibles (insulation and airsealing).
It is important to note that, for example, an overtime retrofit project could be able to stipulate the occupants' need over the time but could perform sub-optimal technically. It could also prove to be costlier. There's a lack of tools to execute over-time projects efficiently. 
Detailed planning must be inculcated from the very beginning. It is recommended to include post-occupancy evaluation at each stage of implementation to deal with modifications required in future stages. Home performance should be tracked at each stage either using utility bills or feedback devices. This helps in achieving the set-target for energy consumption. It must be kept in mind to implement building envelope and passive design elements before making major HVAC and technology investments. This will help to reduce the load parameters for HVAC design. The technology investments should also come later to have an innovation advantage. Over-time retrofits, thus can be guided by these strategies to overcome the challenges and achieve success. 
Deep energy retrofit project has different phases governing them – pre-panning, project planning, construction, test out. The beacon for the design and construction process in deep energy retrofit projects is a set of defined project needs, opportunities, goals and objectives. This completely determines the overall project. Walker et al. provide design and construction process guidance which can be followed flexibly in deep energy retrofit projects in residential homes. 
|1.1||Establish and clarify the project needs, opportunities, goals and objectives.|
|1.2||Establish a performance baseline|
|1.2.1||Perform home inspection and energy audit|
|1.2.2||Identify Healthy Homes health and safety issues|
|1.2.3||Establish energy baseline using utility bill analysis|
|1.3||Develop project goals and performance metrics|
|1.3.1||Establish an annual performance target or energy reduction goal.|
|1.3.2||Establish metrics to be used in assessing progress towards project goals|
|1.3.3||Establish non-energy goals of the project|
|2||Project Planning Phase|
|2.1||The design team|
|2.1.1||Assemble qualified and trusted team|
|22.214.171.124||Plan all aspects of the project as if it were new construction|
|126.96.36.199||Systems integrated approaches|
|188.8.131.52||Design to the energy reduction goal or target|
|184.108.40.206||An integrated project delivery method|
|220.127.116.11||Use energy models|
|3.1||Plan product procurement for a DER as you would any remodel|
|3.2||Be prepared for unexpected issues to arise|
|3.3||Provide quality assurance wherever possible|
|4.1||Verify installation and performance of retrofit measures|
|4.2||Commission all building systems|
|5.1||Provide post-occupancy performance feedback to occupants.|
|5.2||Encourage occupants to make acceptable behavioral adjustments|
|5.3||Guide occupants using short-term usage targets|
Cluett and Amann (2014) found the most commonly implemented efficiency measures in the US for residential buildings. They are broadly listed as follows: 
The deep energy retrofit specifications for various elements vary from climate to climate zones.
A Level III energy audit, as defined by ASHRAE, is required in order to complete a commercial building deep energy retrofit. Also known as an investment grade audit, this type of energy audit features analysis of the interactions between efficiency strategies and their life cycle cost.  Upon selection and implementation of measures, the energy savings are verified using the International Performance Measurement and Verification Protocol. 
Deep energy retrofits make use of energy modeling tools that integrate with an organization's pro forma or other financial decision making mechanisms. Smartphone technologies have simplified the retrofit process as a number of audit and retrofit tools have appeared over the last 5 years to speed up retrofits and maximize efficiency in the field.
A building that has undergone a deep energy retrofit is well positioned for a green building rating such as LEED.
There have been a number of studies done to determine and quantify the benefits afforded to owners, tenants, and various other stakeholders from the successful completion of deep energy retrofits.    The following tabulation by the Rocky Mountain Institute lays the efficiency measures undertaken in a deep energy retrofit project in correspondence to the building performance improvements and therefore, the quantifiable and non-quantifiable values generated from implementation of such a project. 
|Sr No.||Deep Energy Retrofit Efficiency Measure||Building Performance||Value|
|1||Envelope||Thermal comfort |
Indoor air Quality
rating or score
Views to the
|Reduction in cost|
|2||Passive Design||Revenue Growth|
|3||Electric Lighting||Improved Reputation |
|4||Plug Loads & Misc.||Compliance with |
|5||Heating, Cooling, & Ventilating||Reduced Risk to |
A paradigm shift is needed to achieve the motive of climate change mitigation through retrofitting. This shift is underpinned by a greater need to propagate behavioral change rather than just the technology implementation. The framework should move from a project focus outlook towards an understanding of a larger scale execution that includes social awareness and interests. Hence, the need for laying down large scale retrofitting programs that support the idea of cities as active sites to inculcate newer technologies. 
"Buildings will also be particularly affected by the effects of climate change: storms, flooding and seepages, reduced durability of some building materials and increased risk of structure damage or collapse (e.g. from severe storms) could all decrease building lifetime, while increasing health-related risks such as deteriorating indoor climate." (The GABC Global Roadmap) 
From the industrial revolution, fast forward to a few centuries later. We have come far ahead with global warming and climate change. To counter the global temperature-rise problem, a decision was reached at the Paris agreement in 2015, wherein member nations pledged to maintain temperatures below 2℃, compared to pre-industrial levels.
The Global Status Report 2017 underscores the importance and potential of deep energy retrofitting among other solutions in achieving climate mitigation goals. Deep energy retrofitting is one of the solutions for cutting down the carbon footprint of buildings.
The report found out that buildings & the construction industry together accounted for 36% of global final energy use & 39% of energy-related CO2 emissions. It calls to action for a 30% improvement, by 2030, in energy-use intensity (i.e. energy use per square meter) of the building sector, as compared to the 2015 levels, to achieve the Paris agreement goals successfully.
Though a growing number of countries have laid down policies to buildings energy performance improvements but a rapidly growing buildings sector, especially in developing countries, has offset those improvements. The Report states that the efficiency improvements, including building envelope measures, represent nearly 2400 EJ in cumulative energy offsets to 2060 – more than all the final energy consumed by the global buildings sector over the last 20 years. 
It asserts that an aggressive scaling up of deep building energy renovations of the existing global stock is one of the important steps ahead. It points out to refer to Global Alliance for Buildings and Construction (GABC) Global Roadmap for building sector towards sustainability. 
The GABC Global Roadmap sets up to 'accelerate the improvement of existing buildings’ performance' towards energy-efficient, zero GHG emissions and resilient buildings well before the end of the century taking the following steps globally:
An analysis for 50% dip in energy consumption & carbon emissions by the US by 2050 translates to comprehensive energy efficiency retrofits in more than half the existing buildings (Nadel 2016). 
The policy framework for retrofitting in USA is directed at state and local levels. These efforts are supported by the national government. Hundreds of such programs exist, right from the basic energy audits, provision of financial rebates, to comprehensive ones that aim to optimize the entire house.
Carine et al. summarize the below-listed elements present mostly in the best programs: 
The Home Performance with Energy Star program is run by many bodies in the US, with the aid of the US Department of Energy. This project reports an average cost of $3500 per home retrofitted, with a distribution of 57%, 14%, 29% to homeowner incentives, contractor incentives, & administrative costs respectively. 
In the commercial domain, the Energy Star Program by EPA aims to reduce the carbon footprint of buildings. According to this initiative, owners benchmark their buildings on a scale of 1–100. Those scoring 75 & above receive 'Energy Star' designation; while the others are encouraged to follow upgradation strategies for a better performance. Nearly 500,000 properties, representing about half of US commercial building floor area has been benchmarked as of 2016, with a grand total 29,500 buildings receiving the 'Energy Star' rating to that point. 
The retrofitting industry is steadily on the rise. Some major obstacles in its path include as found by Carine et al.: 
The Empire State Building is undergoing a deep energy retrofit process that is projected to be completed in 2013. Upon completion, the project team, consisting of representatives from Johnson Controls, Rocky Mountain Institute, Clinton Climate Initiative, Jones Lang LaSalle, and NYSERDA will have achieved an annual energy use reduction of 38% and $4.4 million. 
A notable achievement of the project is that instead of replacing the chillers as originally planned, the design team were able to first reduce the building's required cooling capacity by 1600 tons, allowing for a chiller retrofit instead of replacement which would have been $17.3 million more in capital costs.
The City-County Building recently underwent a deep energy retrofit process that is projected to be completed in September 2011. Upon completion, the project team, consisting of representatives from the Indianapolis Marion County Building Authority, Indianapolis Office of Sustainability, Rocky Mountain Institute, and Performance Services will have achieved an annual energy reduction of 46% and $750,000 annual energy savings.
A business case study by The Rockfeller Foundation sizes the potential of retrofitting market in the USA. Retrofitting offers a burgeoning business market for entrepreneurs, engineers, investors in the USA. It offers a $279 billion investment opportunity. The residential sector, followed by commercial and institutional sectors, offers the largest business impact. Scaling up retrofitting efforts can create 3.3 billion direct and indirect cumulative job years in the United States. 
Cost effectiveness can be achieved when the annual energy cost savings can equal or exceed the annual loan costs. Their perfect balance is referred as neutral net-monthly costs. Cost effectiveness could be a key driver in decision making related to deep energy retrofit projects. 
A study by Less et al. (2015) found that: 
Less et al. (2015) found that on average, the U.S. deep energy retrofits were cash-flow neutral on a monthly basis. However, variability was large, with some projects substantially reducing net-monthly costs and others substantially increasing net-costs. Questionable cost-effectiveness is thus, seen as a barrier to widespread of deep energy retrofits.  This forms the basis to think of economic value of deep energy retrofit in larger context.
Although many modeling tools are available to assess home energy savings, the inaccuracy of their predictions (compared to actual energy use measurements) limits their usefulness (Osser, Neuhauser, and Ueno 2012).  Cluett et al. point that the pilot programs should monitor actual energy savings to evaluate project impact and help calibrate estimation tools.  This is important to track, evaluate and verify reality-based energy performance metrics.
Weatherization or weatherproofing is the practice of protecting a building and its interior from the elements, particularly from sunlight, precipitation, and wind, and of modifying a building to reduce energy consumption and optimize energy efficiency.
Energy conservation is the effort to reduce wasteful energy consumption by using fewer energy services. This can be done by using energy more effectively or changing one's behavior to use less service. Energy conservation can be achieved through efficient energy use, which has a number of advantages, including a reduction in greenhouse gas emissions and a smaller carbon footprint, as well as cost, water, and energy savings.
Green building refers to both a structure and the application of processes that are environmentally responsible and resource-efficient throughout a building's life-cycle: from planning to design, construction, operation, maintenance, renovation, and demolition. This requires close cooperation of the contractor, the architects, the engineers, and the client at all project stages. The Green Building practice expands and complements the classical building design concerns of economy, utility, durability, and comfort. Green building also refers to saving resources to the maximum extent, including energy saving, land saving, water saving, material saving, etc., during the whole life cycle of the building, protecting the environment and reducing pollution, providing people with healthy, comfortable and efficient use of space, and being in harmony with nature Buildings that live in harmony. Green building technology focuses on low consumption, high efficiency, economy, environmental protection, integration and optimization.’
Superinsulation is an approach to building design, construction, and retrofitting that dramatically reduces heat loss by using much higher levels of insulation and airtightness than normal. Superinsulation is one of the ancestors of the passive house approach.
A Zero Energy Building (ZEB), also known as a Net Zero Energy (NZE) building, is a building with net zero energy consumption, meaning the total amount of energy used by the building on an annual basis is equal to the amount of renewable energy created on the site or in other definitions by renewable energy sources offsite, using technology such as heat pumps, high efficiency windows and insulation, and solar panels.
Domestic housing in the United Kingdom presents a possible opportunity for achieving the 20% overall cut in UK greenhouse gas emissions targeted by the Government for 2010. However, the process of achieving that drop is proving problematic given the very wide range of age and condition of the UK housing stock.
Retrofitting is the addition of new technology or features to older systems. Retrofits can happen for a number of reasons, for example with big capital expenditures like naval vessels, military equipment or manufacturing plants, businesses or governments may retrofit in order to reduce the need to replace a system entirely. Other retrofits may be due to changing codes or requirements, such as seismic retrofit which are designed strengthening older buildings in order to make them earthquake-resistant.
An energy audit is an inspection survey and an analysis of energy flows for energy conservation in a building. It may include a process or system to reduce the amount of energy input into the system without negatively affecting the output. In commercial and industrial real estate, an energy audit is the first step in identifying opportunities to reduce energy expense and carbon footprint.
An energy service company (ESCO) is a company that provides a broad range of energy solutions including designs and implementation of energy savings projects, retrofitting, energy conservation, energy infrastructure outsourcing, power generation, energy supply, and risk management.
Efficient energy use, sometimes simply called energy efficiency, is the process of reducing the amount of energy required to provide products and services. For example, insulating a building allows it to use less heating and cooling energy to achieve and maintain a thermal comfort. Installing light-emitting diode bulbs, fluorescent lighting, or natural skylight windows reduces the amount of energy required to attain the same level of illumination compared to using traditional incandescent light bulbs. Improvements in energy efficiency are generally achieved by adopting a more efficient technology or production process or by application of commonly accepted methods to reduce energy losses.
High-performance buildings are those which deliver a relatively higher level of energy-efficiency performance or greenhouse-gas reduction than what is required by building codes or other regulations. Architects, designers, and builders typically design and build high-performance buildings using a range of established strategies, techniques, tools, and materials to ensure that, upon completion, the building will consume a minimal amount of energy for heating, cooling, illumination, and ventilation during operation.
The United States Department of Energy's State Energy Program (SEP) provides grants to states and directs funding to state energy offices from technology programs in Office of Energy Efficiency and Renewable Energy. States use grants to address their energy priorities and program funding to adopt emerging renewable energy and energy efficiency technologies. Started in 2010, the program "is the only program administered by the U.S. Department of Energy (DOE) that provides cost-shared resources directly to the states for allocation by the governor-designated State Energy Office for use in energy efficiency and clean energy innovation, development, and demonstration activities.”
Energy Management Software (EMS) is a general term and category referring to a variety of energy-related software applications which may provide utility bill tracking, real-time metering, building HVAC and lighting control systems, building simulation and modeling, carbon and sustainability reporting, IT equipment management, demand response, and/or energy audits. Managing energy can require a system of systems approach.
A green retrofit is any refurbishment of an existing building that aims to reduce the carbon emissions and environmental impact of the building. This can include improving the energy efficiency of the HVAC and other mechanical systems, increasing the quality of insulation in the building envelope, implementing sustainable energy generation, and aiming to improve occupant comfort and health.
The Energy efficiency implementation industry branch comprises firms which retrofit or replace inefficient equipment with more efficient parts or equipment, with the goal of reducing energy consumption and GHG emissions. Retrofitting enhances existing equipment by increasing operational energy efficiency at a lower cost. As a comparison, complete replacement of equipment may be more costly, but can reduce the implementation complexity. The common goal is to save kilowatts (kW) and kilowatt hours (kWh). The difference between these two measurements is that one is a power rating (kW) and the other is a measurement of energy actually consumed (kWh).
ISO 50001Energy management systems - Requirements with guidance for use, is an international standard created by the International Organization for Standardization (ISO). It supports organizations in all sectors to use energy more efficiently through the development of an energy Management System. The standard specifies the requirements for establishing, implementing, maintaining and improving an energy management system, whose purpose is to enable an organization to follow a systematic approach in achieving continual improvement of energy performance, including energy efficiency, energy security, energy use and consumption.
Sustainable refurbishment describes working on existing buildings to improve their environmental performance using sustainable methods and materials. A refurbishment or retrofit is defined as: “any work to a building over and above maintenance to change its capacity, function or performance’ in other words, any intervention to adjust, reuse, or upgrade a building to suit new conditions or requirements” . Refurbishment can be done to a part of a building, an entire building, or a campus . Sustainable refurbishment takes this a step further to modify the existing building to perform better in terms of its environmental impact and its occupants' environment.
Public plans for energy efficient refurbishment are put in place by states to encourage building owners to renovate their properties in a way that increases their energy performance. As financing represents the most important obstacle to this type of renovation, the plans favour financial incentives in the form of loans or grants. Various institutions can be involved in the process, such as ministries, banks, firms, or energy services companies (ESCOs).
The International Energy Agency Energy in Buildings and Communities Programme, formerly known as the Energy in Buildings and Community Systems Programme (ECBCS), is one of the International Energy Agency's Technology Collaboration Programmes (TCPs). The Programme "carries out research and development activities toward near-zero energy and carbon emissions in the built environment".
Energiesprong is a program that originated in the Netherlands that introduced and retrofitted houses that satisfy energy efficient standards. It has since been implemented in the United Kingdom, the United States, France, and Canada. The program typically consists of snapping a shell of panels to the outside of a building to increase its thermal efficiency.