2025 Volume 13 Issue 2 Pages 57-71
Buildings are a substantial contributor to climate change. Accordingly, several high-performing building concepts have emerged, including low-energy buildings, zero-carbon buildings (ZCBs), nearly zero-carbon buildings (nZCBs), and sustainable buildings, applicable to both new constructions and retrofitting. Traditional retrofitting strategy applied in a mixed-use building only consider the structural envelope, lighting and HVAC systems, without much focus on the type of function housed inside the building. Understanding the impact of vertical functional zoning is crucial for developing targeted retrofit strategies that optimize energy efficiency and reduce carbon footprints in mixed-use buildings. The objective of this study is to investigate and identify strategies for achieving low-to-net zero emissions during the façade retrofitting process of existing mixed-use buildings in Abu Dhabi. In this research, a methodology combining qualitative analysis and simulation modelling has been chosen to effectively address the objectives and subject matter. The initial phase involves conducting a thorough literature review, specifically focusing on the methods and techniques used in retrofitting mixed-use buildings to achieve the transition from low to net-zero carbon concept. Additionally, the study explores the influence of vertical zoning parameters on the energy consumption and carbon emissions using Building Information Modelling (BIM) application within the context of façade retrofitting. Research results indicate that the type, order and height of functions within the mixed-use building significantly impact the annual energy consumption and total cost. Whereas, carbon emissions are mainly impacted by the order of function. This endeavour necessitates the development of appropriate design specifications considering the vertical zoning parameters, a comprehensive understanding of intervention sequencing, and the implementation of innovative practices.
The World Green Building Council’s global initiative, Advancing Net Zero, aims to ensure that all buildings achieve zero carbon emissions by 20250. As part of this initiative, Green Building Councils worldwide, including the Emirates Green Building Council, have introduced certification programs, specialized training and demonstration projects to promote net-zero carbon buildings.
In the UAE, sustainable development is a national priority, driven by policies and regulations addressing the fast-paced growth of the construction sector. Buildings account for 70-80% of the country’s electricity consumption, making energy efficiency a critical focus (Majd Fayyad, 2017). Estidama Pearl Rating System (PRS) have been implemented from 2010 to improve the performance of both new and existing buildings (SAS International, 2010). Retrofitting existing buildings and enhancing energy efficiency through targeted modification has become a key approach (Tan, Liu et al., 2018). These efforts align with the global movement toward low-carbon buildings, which integrate passive design strategies, high performance envelopes and energy efficient systems (Champ, 2022; Meziani and AlRifai, 2023).
Urbanisation in Abu Dhabi has transformed the city into a modern metropolis characterised by rapid development and modernization, witnessing planned development projects that are transforming the city from deserts to modern urban neighbourhoods (Elessawy, 2021). One of Abu Dhabi’s greatest challenges is developing its growing population alongside its urbanization. Higher population densities in urban areas call for optimal use of land and preservation of space for infrastructure development, recreational green spaces, biodiversity, and ecosystem services within city centres (Zhan and Li, 2024). Mixed-use buildings have emerged as a solution to these challenges (LaSalle, 2008). A mixed-use project is defined as a real estate development with planned integration of some combination of retail, office, residential, hotel, recreation or other functions that are pedestrian oriented (Olmer, 2006). A successful mixed-use building is one that houses several planned uses and public functions. Such a project might include offices, houses, hotels, retail outlets, cultural amenities, and sometimes even industrial functions. It is like a miniature city within the urban fabric, where people live, work, meet, relax, eat, and shop. The key feature of a mixed-use building (in any city) is that it brings back space in the city, thereby enhancing its livability and walkability (Mouada, Zemmouri et al., 2019).
Multi-family and high-rise buildings make up most of the housing in cities, while single-family homes are more common in sprawling and rural areas (Schoenfeld, n.d.). Mixed-used building typology found in the urban centres of Abu Dhabi can be categorized into three types based on their construction period. The first type, built in the 1980s and 1990s, formed the identity of the capital in the past. The second type includes buildings constructed at the turn of the second millennium. The third type, built from 2011 to the present day, incorporates advanced construction technologies and sustainable design principles mandated by the government and local municipalities. A study by Min Lin on the energy consumption of the mixed-use buildings in Abu Dhabi, identifies several building characteristics that influence the operational energy consumption. The most significant parameters among the identified ones are the glazing type, function (residential, commercial, offices, institutional, restaurants etc), chiller condition and AC cleanliness (Lin, Afshari et al., 2018).
Despite their advantages, mixed-use buildings present unique challenges for retrofitting to achieve net-zero carbon emissions. Traditional retrofitting approaches often overlook the complexities of vertical zoning, the arrangement of functions across different floors and its impact on energy usage and carbon emissions.
Hypothesis for this research is that the vertical zoning of a mixed-use building has an impact on the building’s energy consumption and carbon emissions. This research investigates the role of vertical zoning in retrofitting mixed-use buildings in Abu Dhabi to achieve low-to-net-zero carbon emissions. Specifically, it explores how the order of functions (residential, commercial etc) and the floor heights (number of floors) of each function within a building influence its carbon footprint and energy consumption. The study also aims to identify the challenges associated with retrofitting mixed-use buildings, focusing on strategies that optimize vertical zoning to minimize emissions.
Net Zero Carbon building (ZCB) concept refers to buildings that are on the path to Net Zero carbon emissions in their construction, operational or embodied energy phases. The carbon emissions associated with its product and construction stages up to practical completion are zero or negative, achieved using offsets or the net export of on-site renewable energy. A representation of net emissions is provided in Figure 1.
There are different categories of ZCBs like Energy Efficient, Zero Energy, Energy Positive, Net Zero Operational Carbon or Net Zero Whole life Carbon. ZCBs are achievable through energy efficiency measures, on-site production of renewable energy, export of off-site renewable energy, reducing emissions or offsetting for the residual emissions. An illustration of different Zero Carbon Buildings is provided in Figure 2.
Carbon dioxide equivalents (CO2e), or the amount of CO2 emissions with an equivalent global warming potential (GWP) over 100 years, are the climate metrics used in the assessment of emissions according to their impact on global climate. The time horizon (100 years or 20 years etc) impacts the GWP of different emissions; for example, methane and other kinds of refrigerants have a short life span but a large heat-trapping capacity. It is recommended that projects assess emissions using 20-year GWP values.
The carbon impacts of the product and construction stages of a building can be significant, sometimes accounting for half of a new building’s whole life carbon impacts. Addressing these carbon impacts initially can provide a staged approach for tackling whole life carbon impacts in the future. Developers aiming for net zero carbon retrofit or construction should also design the building to enable net zero carbon operation (Twinn, Desai et al., 2019).
Zero carbon retrofittingSustainable or green retrofit refers to the process of upgrading the fabric, systems, or controls of an existing building to improve its overall energy performance. According to the U.S. Green Building Council (USGBC), a sustainable retrofit involves making improvements to an existing building with the goal of enhancing its energy and environmental performance, reducing water usage, improving occupant comfort, using natural light, noise reduction, and improving indoor air quality. To achieve sustainable retrofitting, it is essential to consider both thermal comfort and indoor air quality, regardless of the specific methods used to complete the green retrofit (Eiz, Mushtaha et al., 2021; Financial Times, 2023). Given these definitions and explanations, the green or sustainable retrofit can enhance the energy performance of the existing building, satisfying all the services inside the building and improving the indoor environment quality of the building (Zhou, Z., Zhang et al., 2016).
Concept of Zero-energy, Zero-carbon retrofit strategies are considered as effective methods for reducing operational energy and environmental impacts through lower emissions. Integrating energy generation and conservation measures is crucial in achieving net-zero energy buildings, ensuring that the energy needs of the buildings are met sustainably by combining on-site renewable energy sources with advanced energy conservation strategies (Lou and Hsieh, 2024). Moreover, maintaining a balance between operational energy and embodied energy through effective Life Cycle assessment (LCA) and Life Cycle Costing (LCC) is vital to promote overall efficiency and environmental responsiveness. Several studies have analysed design strategies and material impacts on ZCB renovation through comprehensive life cycle assessments and suggests that the future studies should focus more on formulating integrated packages of specific retrofitting strategies (Weerasinghe, Darko et al., 2024).
Retrofit strategies for mixed-use buildingsBuilding typologies are key to understanding and achieving energy performance requirements in buildings and is crucial to identify the most suitable energy-efficient and energy conservation measures. The primary role of building typology is to identify the suitable energy efficiency techniques for existing buildings while quantifying potential energy savings and carbon emissions reduction from refurbishment measures (Imani, Dawood et al., 2023). Several challenges remain in applying building typology to energy performance optimisation. However, there is a notable lack of published research and guidelines specifically addressing retrofit strategies tailored to the unique challenges and requirements of mixed-use buildings. Existing retrofitting strategies of mixed-used buildings, as demonstrated in case studies like The Cultural Foundation in the UAE (CEBRA, 2016), Sidwell Friends Middle School in the USA (LAF, 2018)\ and Birmingham Zero Carbon House in the UK (Jankovic and Christophers, 2022), as discussed in the review paper by (St Clair, 2009), often overlook the diversity of functions within these buildings. Specifically, they do not account for the vertical zoning of functions or height (number of floors) assigned to each function. Consequently, these retrofits may fall short in achieving significant carbon emission reductions and cannot be deemed fully sustainable. A summary of the findings from these case studies is presented in Table 1.
| Case study name and buiding location | The Cultural Foundation (UAE) | Sidwell Friends Middle School (USA) | Birmingham Zero Carbon House (UK) |
|---|---|---|---|
| Concept | Moving towards sustainability | Carbon neutral building | ZCB |
| Retrofitting methods | Local materials and native plants. Water is a natural focal point in the design of the Al Hosn landscape, and photo-sensors and occupancy sensors. | Recycle wastewater, recycled materials, low chemical emissions, photo-sensors and occupancy sensors, and high-performance operable windows, skylights. | The roof is positioned for solar panel installation, supplying renewable energy. High-quality natural light permeates through roof-lights and openings with mirrored linings. |
| Renovation | Offers a range of services and has been extended upwards to optimize natural lighting and ventilation. | The existing building was renovated, and new classrooms extension were constucted. | The scheme redevelops a two-bedroom Victorian house to provide four bedrooms plus a studio loft space. |
| Building envelope | The design maximizes access to daylight and views through passive design strategies. | Exterior sunscreens on the façade, and light-shelf transmits daylight deep into the building. | On-site renewable energy (PV), solar thermal, and biomass. |
| Awareness about ZCB | N.A. | Within the curriculum for students. | Social awareness. |
Source: By authors. Retrieved from CEBRA (2016), St Clair (2009), LAF (2018) and Jankovic and Christophers (2022).
This study focuses on developing envelope retrofitting strategies to be applied for achieving low to net zero emission in mixed-use buildings which constitute a major part of Downtown Abu Dhabi. The cost and energy involved can be immense while retrofitting, hence the need to implement applications of low emissions becomes paramount and necessitates the development of an appropriate design specification, a clear understanding of the sequencing of interventions, and innovative thinking and practices. The methodology employed in this research is a combination of qualitative and simulation approaches, which are appropriate for the objectives and topic of the study.
The research methodology adopted in this study is illustrated in Figure 3. Literature reviews analysed the methods and techniques used for retrofitting buildings with low carbon concepts. Interviews with leading contracting and design consultants’ offices have been conducted to gain insight on the ongoing modernization of Abu Dhabi, background of mixed-use buildings and their role in the capital, also to serve as a foundation for subsequent observation and documentation. In addition to observing the current situation of mixed-use buildings (mainly mid-rise and high-rise), the physical, structural, and architectural modifications made to the buildings to accommodate low to net zero carbon concept have been carefully noted. Interviews and physical observation were done due to the unavailability of research reports on the retrofitting efforts of mixed-use buildings in Abu Dhabi. Initial phase of research helped to explore the existing methods and techniques adopted in the retrofit of mixed-use buildings in its journey towards low to net zero carbon building. However, gaps were identified in the methods and a research hypothesis was formulated in an effort to explore the impact of vertical zoning on the energy consumption and emissions of mixed-use building retrofits.
Case study buildingThe case study building selected for simulating the low-carbon retrofit strategies is a mixed-use high-rise building located in Abu Dhabi, UAE. Constructed in the late 1990s and retrofitted in 2023, the building was designed by Dar Al-Zein. With a total area of 17,800 sq.m, the structure consists of 22 floors, including a basement. The ground floor and basement house retail spaces and utility areas, while the mezzanine floor is dedicated to office use. The first through nineteenth floors are allocated for residential apartments. This diverse functional distribution makes the building an ideal candidate for exploring the impact of vertical zoning and floor heights on energy efficiency and carbon emissions. Details of the Case Study building is provided in Figure 4 and Table 2.
Autodesk REVIT was used to create a 3D model of the mixed-use building case study, Insight and Green Building Studio (flexible cloud-based service that allows to run building performance simulations to optimize energy efficiency and emissions) was used for building simulations; which will serve as the basis for the consequent analysis. REVIT is a leading Building Information Modelling (BIM) software, allowing for accurate representation of the energy usage and CO2 emissions of the case study building. It has the ability to be integrated with other building performance analysis tools for detailed simulations of energy consumption, daylighting and thermal performance, which are crucial for achieving zero carbon target (Arenas and Shafique, 2024).
| Location | Abu Dhabi, UAE |
|---|---|
| Construction Year | The late nineties |
| Retrofit Year | 2023 |
| Architect | Dar Al-Zein |
| Total area | 17,800 M² |
| Number of floors | G+22 (inculding basement) |
| Use/Function |
Ground floor and basement (retails and utility) Mezzanine floor (offices) 1st -19th floor (residential) |
Source: By authors. Retrieved from architect and contractor firms.
Energy efficiency and carbon emissions of a mixed-use high-rise building is demonstrated to be better than those of single-use high rise buildings as a result of the different operational schedules and comfort requirements. Floor area proportions of different functions and its vertical zoning components can also influence its energy efficiency (Zhou, Y., Li et al., 2016). Different scenarios were created and simulated in REVIT to verify if the function type, function order and height ratio of function affect the CO2 emissions and energy usage in a mixed-use building. The three scenarios created for further simulation and analysis is given in Table 3. The first Scenario compares the energy consumption and carbon emissions of a single-use high rise residential building with that of the existing retrofitted mixed-use building. The second scenario is created to study the influence of the order of function within a mixed-use building. Here, the energy consumption and emissions of the existing retrofitted mixed-use building is compared with another mixed-use case where the order of function is varied keeping the height of each function a constant. In the third scenario, the height ratio of each function within the mixed-use building is varied keeping a fixed order of function.
Table 3 lists the evaluation parameters and simulated carbon emissions, Energy Use Intensity (EUI) and Energy cost of all scenarios.
| Parameter | Unit | Scenario 1 | Scenario 2 | Scenario 3 | Scenario 4A | Scenario 4B |
|---|---|---|---|---|---|---|
| Carbon Emission | kgCO2 | 436477 | 436477 | 475577 | 237488 | 260026 |
| EUI | Mj/m2/yr | 1095 | 1381 | 1020 | 1400 | 1081 |
| Electric Annual Cost | $ | 414084 | 519865 | 425390 | 227209 | 208797 |
| Fuel Annual Cost | $ | 26915 | 34556 | 14728 | 13941 | 9337 |
| Energy Annual Cost | $ | 440999 | 554421 | 440118 | 241150 | 218135 |
| Electric Annual Energy | kWh | 4409842 | 5536366 | 4530249 | 2419691 | 2223615 |
| Fuel Annual Energy | kWh | 3623515 | 4652228 | 1982782 | 1876807 | 1257060 |
| Floor Area | m2 | 17798 | 17798 | 17926 | 8005 | 8561 |
Energy Use Intensity (EUI) of all five simulated cases as shown in Figure 5, highlights variations based on the function, order of function and height of function in the energy consumption of a mixed-use high-rise building. While comparing the EUI of scenario 1 and 2, there is a significant variation in the EUI when the high-rise is of mixed-use or single-use typology. Comparing the EUI of scenario 3, 4A and 4B shows that the vertical order of functions also have a notable influence on the EUIs, suggesting that the envelope requirements of various functions have to be considered while proposing envelope retrofit strategies
Figure 6 and Figure 7 shows the comparison of Scenario one and two, where the energy consumption and cost of the existing retrofitted mixed-use high-rise building is compared to that of a single-use high-rise residential building. The annual electrical and fuel consumption is higher in single-use high-rise residential building compared to the existing mixed-use case. This high energy use intensity is mainly dependent on the type of function within the building. For example, residential flats operating 24/7 typically consume more energy than offices with fixed working hours, resulting in higher energy consumption and more emissions. It can also be inferred that the type of function affects the annual cost, reinforcing the concept that the retrofitting strategies for mixed-use buildings should carefully consider the requirements and design aspects of functional zones.
Figure 8 and Figure 9 shows the comparison of simulation results from scenario one (existing case) and scenario three where the order of function within the mixed-use building is varied. The results verify that function composition in mixed-use buildings don’t notably affect the annual electrical cost and consumption. However, from Figure 4 it is evident that parameter has significant influence on the building's emissions. Placing offices or open space functions on upper floors can increase embodied carbon emissions due to direct heat gain, suggesting the use of Low-E glass and window shades. Interestingly, this arrangement can also reduce annual fuel costs and consumption.
Figure 10 and Figure 11 illustrates the results from scenario four where the height ratio of function within the mixed-use building is varied to compare the changes in energy consumption and emissions. The results clearly demonstrates that the height ratio significantly impact the energy consumption, energy use intensity and emissions; whereas changes in the total cost are minor.
The results from all three scenarios show that the type of function, the order and height ratio considerably impact the carbon emissions of mixed-use buildings. While retrofitting the exterior envelope of a mixed-use building, it is crucial to consider the building’s function. Focusing solely on the interior and structure envelope, including maintenance, lighting, and HVAC systems, tends to lower the annual cost. However, when both façades treatment and interior functions of the building are considered, the annual cost increases. Considering the functions of a mixed-use building in retrofitting costs more, but the cost can be reduced by installing PV panels on the building’s top roof.
When modifying the functional order within mixed-use buildings, architects should consider balancing public and semi-public functions with private ones and noisy functions with quiet spaces. This can help to create a more harmonious and comfortable environment for the building’s occupants. For example, placing noisy functions such as restaurants or entertainment venues away from quiet spaces such as residential units or offices can help to reduce noise pollution and improve the overall liveability of the building. Additionally, providing a mix of public and semi-public spaces can help to foster a sense of community and encourage social interaction among the building’s occupants.
It is worth mentioning that single-use buildings frequently have additional yearly electricity and fuel consumption compared to retrofitted mixed-use buildings depending on the building’s use. Moreover, changing the height of function composition in mixed-use buildings affects the annual cost and energy consumption. Also, the arrangement of functions in a mixed-use building does not affect the annual energy cost of the building, provided that the height of the function is not changed. Research also proposes that shifting the functional order within a mixed-use building can affect carbon emissions. Verification of energy consumption and cost data from the real case study is proposed in future research endeavour. Retrofitting is an asset that might require additional costs and more energy consumption in stages of this process, yet, retrofitting naturally occurs every 15~20 years for buildings in Abu Dhabi.
The energy consumption and emissions of mixed-use buildings are significantly influenced by specific function they house. Residential areas typically have energy usage patterns driven by occupancy behaviours and vary throughout the day and night. Commercial spaces like offices and retail stores have fixed working hours and their energy usage pattern is different, same is the case of institutional buildings. The interplay of these diverse functions within a single building can lead to complex energy consumption and emissions. The paper identifies vertical zoning of functions within a mixed-use high-rise building, as an important parameter that has significant impact on the energy consumption and carbon emissions. The paper offers valuable insights for stakeholders proposing façade retrofit strategies in Abu Dhabi.
By the end of the research, the authors propose:
The study hypothesizes that the vertical zoning of functions within a mixed-use high-rise building, significantly impact its energy consumption and carbon emissions. A mixed-use building in Abu Dhabi was selected as a case study and involved energy simulations in REVIT to evaluate the performance under various retrofit scenarios. In conclusion, this research underscores the importance of tailored retrofit strategies for mixed-use buildings to achieve low-to-net zero carbon emissions. By focusing on the selected case study of a mixed-use building, the study demonstrates how vertical zoning, defined by the arrangement and height of different functions within the building, plays a significant role in determining energy efficiency and caron emissions. The findings highlight the need for retrofitting approaches that consider the unique energy demands and operation characteristics of each function, rather than applying generalised strategies. Addressing these nuances can not only optimize energy performance but also significantly contribute to the UAE’s broader sustainability goals. This research provides framework for future retrofitting project in mixed-use buildings, emphasizing the potential for more effective and sustainable outcomes through function-specific strategies.
Conceptualization: Dr. Rim Meziani, Dr. Mohamed Elkaftangui, and Asmaa Mohamed; Methodology: Dr. Rim Meziani and Dr. Mohamed Elkaftangui.; Software: Asmaa Mohamed; Investigation: Dr. Rim Meziani and Dr. Mohamed Elkaftangui; Data curation: Dr. Mohamed Elkaftangui; Writing-original draft preparation: Dr. Rim Meziani; Writing-review and editing: Dr. Rim Meziani, Dr. Mohamed Elkaftangui, Dr. Joshima VM and Asmaa Mohamed. All authors have read and agreed to the published version of the manuscript.
The authors declare that they have no conflicts of interest regarding the publication of the paper.
