The Analysis of the EDGE Certiﬁcation System on Residential Complexes to Improve Sustainability and Affordability

: In this paper, the characteristics of the Excellence in Design for Greater Efﬁciencies (EDGE) green building certiﬁcation system in terms of the scope of certiﬁcation, and environmental and social strategies focused on 6024 units in the 17 EDGE-certiﬁed residential buildings in South Africa was investigated. This research analyzed the efﬁciency of energy, water, embodied energy in materials, and annual CO 2 emissions and their contribution to solving housing issues in the given context. This research revealed that the design of EDGE-certiﬁed buildings focuses on the “efﬁciency ﬁrst” approach and reduced energy and water demand more than on-site energy production. In energy-saving strategies, energy-saving solutions are three times (69.2%) higher than energy-generating solutions (23.1%). The results on resource savings showed that, on average, embodied energy in materials (54%) is the most reduced resource, followed by water (31%) and energy (29.7%). The statistical analysis indicated that there is no statistically signiﬁcant correlation between energy, water, embodied energy in materials, and CO 2 savings with ﬂoor areas of the buildings. In addition, this research highlighted how EDGE certiﬁcation has positively contributed to solving South Africa’s resource shortage and affordable housing problems.


Introduction
Throughout history, the building sector has been facing economic, social, and technical problems caused by misuse of available resources, climate change, and overpopulation [1]. Particularly, excessive energy consumption, CO 2 emissions, and water shortage have become global issues [2]. Consequently, buildings have been negatively criticized for playing a big role in environmental pollution. According to the International Energy Agency (IEA) in 2018, the building and construction sector recorded 36% of global final energy use and 39% of energy-related CO 2 [3]. To address this international issue, a lot of institutions and countries have introduced building certification systems, which are being used to study the consumption of energy and other resources from the planning stage to the demolition stage using the life cycle analysis method and the assessment of the built environment [4]. In addition, the importance of the indoor environment including thermal, air, lighting, and acoustic, and the value of post-occupancy for a better quality of life, occupant health, and productivity has been highlighted [5][6][7][8]. The built environment industry has grown significantly to reach enhanced energy efficiency, environmental impact, building management, and user satisfaction over the past few decades [4].
According to a study conducted by the US Environmental Protection Agency (EPA) on Americans, an average person spends 93% of their life indoors and 87% inside buildings [9]. Out of 24 h, more than 12.7 h per day is spent sleeping and living at home [10]. For this reason, residential building quality holds a significant role and directly impacts everyone. Nevertheless, due to the increase in population, especially in major cities all over the world, the housing problem and its affordability remain a big issue in society [11]. In 2018, an Table 1. Overview of certification criteria of different certification systems [16][17][18][19][20][21][22].

Item EDGE BREEAM LEED DGNB HQE CASBEE G-SEED
Technical quality ------ However, there are relatively fewer certified green buildings in Africa compared to other continents. Despite LEED being the most certified green building certification system in the world, for example, the list of top 10 countries with the most LEED-certified projects (US excluded) does not include any African country [23]. In particular, Sub-Saharan countries need building certification in order to overcome their continuous building problems. Therefore, green building certification systems should be actively introduced to improve both the economy and the quality of life. The certification system of Excellence in Design for Greater Efficiencies (EDGE) focuses on the major problems in not only developed countries but also developing countries, especially Africa, where it helps to build resource-efficient buildings [24].
The EDGE building certification system was established in 2014 by the International Finance Corporation (IFC). The Green Buildings Council of South Africa (GBCSA) exclusively provides EDGE certification for homes in South Africa [25]. EDGE helps calculate costs, focuses on resource (energy, water, embodied energy in materials) efficiency, saves time through a streamlined process, and provides bioclimatic modeling [26]. EDGE-certified building types include educational facilities, residential buildings, accommodation facilities, medical facilities, light industry, office buildings, and retail and warehouses [27].
This study intends to examine EDGE in South Africa through its application in residential buildings. EDGE's main purpose is to ensure that a building has successfully met goals to reduce the building's negative impact on the environment by supporting the design and construction of sustainable buildings and providing a validating certificate. In addition, EDGE has been adopted in South Africa toward solving housing shortages and energy problems [24].
Growing demand for housing and scarcity of resources such as water and electricity are major problems [28]. South Africa is known to have high mortgage rates of about 10% [29,30]. According to Statistics South Africa in 2017, the unemployment rate in South Africa was 27.7% [31]. This means there are many people who cannot afford a good home. EDGE was introduced in South Africa to solve the country's problems while providing green buildings. Certified buildings have minimal operating costs and low rental fees. In addition, low utility bills and rents have reduced the economic burden and encouraged residents to use their remaining deposits as an opportunity to invest in health and education [30]. South Africa's GDP growth has declined from 1.49% in 2018 to −6.43% in 2020, which increased to 4.91% in 2021 [32]. To overcome this decline, residential buildings have received more attention than any other type of building. Through that, it was possible to find solutions to water and energy shortages and other related crises. So, new measures were taken including the introduction of the EDGE building certification system in South Africa [24]. IFC's EDGE certification system was launched in South Africa with the aim of focusing on the residential real estate sector. The certification system includes the EDGE app, innovative software designed to help home builders track and regulate the financial viability of their projects [33]. This free app allows officials and developers to assess the costs and advantages of strategies related to carbon reduction [34]. Despite the falling market prices in South Africa, housing demand is still high. A total of 86% of the market was estimated to be residential complexes as the new target to solve the housing shortage problem [28]. The green investment fund was distributed to utilities and materials such as heating and cooling, ventilation, energysaving technologies, photovoltaics, green walls, glazing and windows, water-efficient technologies, and so forth.
According to National Geographic, only 3% of the water on earth is freshwater and only 1.2% of the freshwater is potable water [35]. With less water consumption in buildings with EDGE certification, other South African residents can have better access to water. South Africa consumes 65 L/person/day more than the world's average water consumption [36]. In addition, South Africa is expected to have water scarcity in 2025 and a water deficit of 17% by 2030. This water challenge will be aggravated by existing climate change. EDGE certification is the solution needed for South African residential complexes to reduce water consumption. An elevated carbon footprint is the main culprit of global warming. To combat global warming, it is important to reduce CO 2 emissions, consume less energy, recycle, use fuel/energy efficient devices, and so on.

Methodology
The aim of this paper is to explore characteristics of the EDGE certification system through its application in residential complexes located in South Africa. This paper particularly focused on the 6024 units in 17 residential complexes as shown in Table 2 which received EDGE certificate from 1 July 2017 until 19 June 2022. The characteristics analysis of buildings was performed based on (1) the features of the environmental technical strategies applied in 17 residential complexes, (2) the buildings' energy, water, and embodied energy in materials savings and annual CO 2 savings, and (3) solution to housing issues and accommodation capacity based on housing units. Building-related data from the EDGE website were examined as a given priority and supplementary data from the buildings' real estate developers [37,38]. Each data collected at the preliminary through final stage of certification includes certification level, building's location, photos, floor area (m 2 ), the savings on energy, water, and embodied energy in materials, annual CO 2 savings, and technical solutions to save energy, water, and materials. Table 2 summarizes the main features of 17 EDGE-certified residential complexes. In this study, we used correlation and regression analysis to find the relationship between energy, water, embodied energy in materials, CO 2 savings, and floor area using the SPSS program [39].

EDGE Environmental Strategies in 17 Residential Complexes
EDGE's representative environmental strategy is improving energy efficiency. A total of 6024 units in 17 EDGE residential complexes have shown technical solutions that reduce energy consumption and thus occupants pay less in utility fees. The strategies include window-to-wall ratio (WWR), openings, green roofs, air filtration systems, energy-efficient artificial lighting, elevators, ceiling fans, and air exchange system to reduce indoor and outdoor temperature differences. General cleaning, washing, toilet flushing, equipment, water for heating, ventilation, and air conditioning (HVAC) kitchen, swimming pool, rainwater collection, and water recycling were considered in various ways for water management. Insulation materials, structural members of buildings (beams, floor slabs, interior and exterior walls, roofs), multi-pane glass, and low-E glass were mainly applied as materials [26,41].

EDGE Certification Process
EDGE's certification process consists of a total of six steps, and all steps must be completed before a certificate is granted. First, the applicant uses the EDGE web-based software to register general information for the project. Second, the applicant registers for the project and pays the applicable fees. Third, the applicant selects an EDGE auditor from the provided list. Fourth, the applicant uses the EDGE app to collect and submit all relevant documents and then pays a certification fee after submitting the application. Fifth, the EDGE auditor and GBCI (Green Business Certification Inc., Washington, DC, USA) review the submitted application of the project in detail. Sixth, if all previous processes are successfully completed, EDGE certification is granted to the project. EDGE Advanced is awarded only if the project achieves at least 40% of the projected energy savings and at least 20% of the projected water savings. After receiving EDGE certification, EDGE Zero Carbon certification may be pursued. This process is not mandatory and can only be carried out by projects granted EDGE Advanced [42]. Table 3 summarizes the characteristics of the EDGE certification system. Table 3. Summarized characteristics of EDGE certification system.

Aspects Information
Country [40] More than 140 countries Active in 35  Building type [27] Educational facilities, Residential complexes, hospitality facilities, medical centers, light industries, offices, retail, and warehouses (Only Residential complexes in South Africa). Table 3. Cont.

Aspects Information
Certification standard [16] 20% reduction in operational energy consumption, embedded energy, embodied energy Consideration for calculation [43] Building type, occupant use [27] Homes, hotels, offices, hospitals, retail, education Use "quick method" under EN 15193 S energy requirements-installed lighting power, annualized usage Water demand [43] Fresh water, recycled water, rainwater harvested => water "savings"

EDGE Zero Carbon Certification
There are three levels of EDGE certification; Level 1: EDGE Certified, LEVEL 2: EDGE Advanced, and LEVEL 3: EDGE Zero Carbon [16]. EDGE Advanced projects are eligible for EDGE Zero Carbon certification under the conditions of 20% water and embodied energy savings, 40% energy savings, and 100% energy savings through renewable or carbon offsets [27,41,43]. There are three requirements in total. First, the building must be one of the building types mentioned by the EDGE, such as educational facilities, residential buildings (homes), accommodation facilities, medical facilities, light industry, office buildings, and retail and warehouses. Second, the normal building occupancy rate must be at least 75%. Finally, only EDGE Advanced certified buildings can apply [27,41,43]. Requirements, timing, and renewal of each level are presented in Table 4.

Environmental Technical Strategies
In this paper, we analyzed (1) the features of the environmental technical strategies applied in 6024 units in 17 residential complexes, (2) the buildings' energy, water, and embodied energy in materials savings, and annual CO 2 savings, and (3) solution to housing issues and accommodation capacity based on housing units. Due to overpopulation in big cities, housing shortages are frequent. The results of this study showed that 70.6% of residential complexes with EDGE certification are located in major cities such as Cape Town and Johannesburg, and 23.5% in cities or towns that are close to a major city.
The energy, water, and materials technical solutions of the 17 residential complexes are shown in Tables Table 5. The table also shows the percentage of buildings that have the corresponding solutions depending on which part or location of the building it is installed. Energy technical solutions were divided into three major parts: energy-saving solutions (69.2%), energy-generating solutions (23.1%), and energy measurement (7.7%).
Buildings' design focused more on "efficiency first" and energy and water demand reduction than on-site energy generation. All energy-saving strategies were designed and installed during construction. Consequently, the building user has little to no extra work to do other than use the given environment well. Energy-saving solutions comprise lighting controls, reflective paint, an energy-saving lighting system, reduced window-towall ratio, low-E coated glass, external shading devices, roof and external wall insulation, and ventilation. Energy-generating solutions consist of solar photovoltaics and solar hot water collectors. In energy use solutions there is a heat pump (hot water generation) and in energy measurement, there are smart electricity meters. All buildings had a reduced window-to-wall ratio (gross glazing area (m 2 )/gross exterior wall area (m 2 ). In particular, buildings are designed to prevent thermal bridging where heat and energy leak, especially shown in Belhar Gardens [34]. Smart meters record a monthly energy footprint and show energy consumption, which helps residents save on utility bills [41,45]. Reduced wall-towall ratio, natural ventilation, insulated roofs, and walls optimized energy efficiency and saved electricity bills. [46].

Water Saving Strategy
Of all the three groups of technical solutions, water had the least number of strategies. Water strategies focused on controlling water flow in the bathroom and kitchen. Low-flow fixtures were installed for the purpose of water consumption and decreasing energy. When they are used, water usage reduction is expected to be more than 50% [47]. A total of 88.2% of buildings had low-flow faucets in kitchen sinks, low-flow showerheads, and dual-flush water closets installed. Dual-flush toilets are known to be more environmentally friendly and more water-saving than single-flush toilets. Water technical solutions are shown in Table 6 below.

Material Use and Saving Strategy
There are different strategies used on different components of a building such as a floor, internal and external walls, and roof. Solid dense concrete blocks were the highest with 64.7% on externals and 58.8% on internals. On average, 11.7% of buildings have recycled existing slabs, roofs, internal and external walls, and flooring frames. Material technical solutions are shown in Table 7 below.
In particular, the Tygerberg 3 Student Residence building at Stellenbosch University used lightweight steel construction instead of bricks and mortar, 90% of the steel structure was recycled, and no water was needed during the construction process, which means that it is carbon neutral. Its construction time was reduced by 40%, building costs up to 13%, and construction waste from between 25% to less than 0.1% of building bulk [48]. In Fourleaf Estate, the community is required to do recycling [49].

Environmental Improvement
Buildings with EDGE certification conserve and protect natural resources. Each project creates a base case at the design stage based on assumptions. The assumptions are made by using national or local building performance codes, market studies, and data collection about actual buildings in the country where the project is based. A project selects technical measures to reduce corresponding resource consumption. A building satisfies the EDGE standards by proving that the difference in consumption between the base case and the improved case is above the required value [43]. Figures 1-4 represent energy savings (%), water savings (%), embodied energy in materials savings (%), and total annual CO 2 savings (ton), respectively, of the 17 buildings. South African residential complexes with EDGE certification had an average of 29.7% energy savings, 31% water savings and 54% embodied energy in material savings. All buildings with EDGE certification had a total of 5979.41 tons of CO 2 savings annually. Generally, the total number of savings (energy, water, and embodied energy in materials) increased from 2017 to 2020 with a slight decline in between. None of the seventeen buildings had EDGE Zero Carbon Certification and only two of them have achieved LEVEL2: EDGE ADVANCED. Even though residential complexes comprised more than 73% of all EDGE-certified buildings in South Africa, they occupy only 33.3% of all LEVEL2: EDGE ADVANCED achievers. EDGE Zero Carbon level is harder to achieve compared to other levels. For this reason, only three of all buildings with EDGE certification reached the EDGE Zero Carbon level.

Energy Savings
Given 17 residential complexes, on average, the total energy is saved by 29.7% compared to the base case which does not have an EDGE certification system in South Africa. Urbika Apartments had the highest energy savings with 53%, followed by Belhar Gardens with 41%. Waterfall Park and Terenure had the lowest savings of 21%. Even though Terenure had the lowest in energy savings, its high savings in "embodied energy in materials" made it come fourth in the overall ranking, even before the highest energy saver, Urbika Apartments. Figure 1 shows the energy savings of each building.
Due to the fact that South Africa's climate is warm, a reduced WWR minimizes the heat gain from windows and keeps the indoor air cool. Consequently, residents can save money from summer cooling and sometimes from winter heating. One-third of the electricity used in Tygerberg 3 Student Residence was produced by solar photovoltaics and its 25 units do not need air conditioning or space heating to achieve thermal comfort [48].

Water Savings
Water use reduction is important due to its scarcity in big cities such as Cape Town. Water has been restricted in 2018 and there is a severe water shortage caused by drought [50]. This caused water to become the most expensive utility bill for residents in cities such as Johannesburg [47]. On average, buildings saved 31% of water. Similar to energy savings, only one building had more than 50% savings. Devland Gardens had the most saving with 51% followed by Erand Creek with 40%. The Village (Clubview), Southgate Ridge, and Terenure came last with only 24% savings. Figure 2 shows the water savings for each building.

Embodied Energy in Materials Savings
The less embodied energy in materials a project has, the more sustainable the construction is, and the lower the carbon footprint emitted from the project [51]. In general, 17 buildings had the highest savings in embodied energy in materials. On average, buildings saved 54% of embodied energy in materials. Southgate Ridge had the highest with 94%, followed by Terenure with 92%. Fourleaf Estate had the lowest savings, with 35%. The lowest savings in "embodied energy in materials" was higher than the average of both energy and water savings. Embodied energy can be reduced when materials such as hollow core precast floor slabs, micro concrete tiling on roofs, and core brick walls are used in construction [47,52]. Figure 3 shows embodied energy in the materials savings of each building.

Total Annual CO 2 Savings
The purpose is to reduce the total CO 2 footprint that a project could have emitted into the atmosphere. Carbon reduction or removal is calculated in one metric ton (ton) of CO 2 or equivalent greenhouse gas (GHG). CO 2 emissions of the improved case and the carbon offset's value are compared to determine the percentage of the total offset. There are no restrictions on the kind and origin of carbon offsets. This can be from renewable energy, energy efficiency improvements, methane (CH 4 ) and CO 2 capture and storing, or forest restoration and conservation. On average, buildings saved 351.73 tons of CO 2 . The savings range from 40 to 1318.4 tons per year where there was a significant gap in CO 2 savings among buildings. Celebration Retirement Village had the highest annual CO 2 savings with 1318.4 tons, followed by Urbika Apartments with 893.44 tons. Tygerberg 3 Student Residence had the lowest savings of only 40 tons. Figure 4 shows the total annual savings of each building.  Figure 6 shows a moderate correlation.

Statistical Analysis of Relationship between Energy, Water, and CO 2 Savings and Floor Area
The results of the relationship of energy, water, embodied energy in materials, and CO 2 savings with floor areas show that there is no strong correlation as shown in Table 8. There was a low positive correlation between the energy savings and floor area; a moderate positive correlation between water savings and floor area; a low positive correlation between embodied energy in materials savings and floor area; and a very low positive (negligible) correlation between the CO 2 savings and floor area.

Solution to Housing Issues and Accommodation Capacity
The critical housing issues in South Africa can be characterized by the lack ofxs quality and affordability [12]. Only 20.4% of urban households can afford a house with their financial capacity [12]. EDGE supports affordability and its projects are increasing in many African countries, including South Africa [53]. Given our data, the results of this research show that EDGE-certified buildings helped to solve some concurrent issues in residential complexes offering (1) a high capacity to accommodate many people, (2) affordability, (3) utility fee saving, and (4) improved quality of life. The average number of housing units is 376. Tygerberg 3 Student Residence is excluded as there was a lack of information. Devland Gardens had the highest with 870 units, followed by Celebration Retirement Village with 774 units and Belhar Gardens with 630 units. Zevenwacht Lifestyle Estate had the lowest of 95, which is almost four times lower than the average. Based only on the number of units, buildings with numbers of housing units are more likely to solve the housing shortage because they can accommodate a large number of people. However, considering that the buildings have a mix of one, two, and three bedrooms in one unit, it is impossible to determine which one can accommodate more people. Figure 9 shows the number of housing units each residential building possesses. A total of 76.5% of all the 17 EDGE-certified buildings are recognized by EDGE as affordable housing. Furthermore, the majority of developers of 17 EDGE-certified buildings are interested in affordability. A total of 47% of the buildings are developed by International Housing Solutions (IHS), a South African real estate developer which focuses on developing affordable green housing [46,54,55]. In addition, 17.6% are developed by Transcend Residential Property Fund (TPF) which invests in affordable housing [51]. Central Developments Property Group also develops affordable housing; however, its EDGE-certified building, Celebration Retirement Village focuses more on providing good retirement space than affordability [56]. The Social Housing Regulatory Authority (SHRA) granted full accreditation to Devland Gardens for providing affordable housing in Johannesburg [47]. Table 9 shows the affordable buildings and their developers. EDGE-certified buildings have helped the affordability. The Madulammoho Housing Association (MHA), for example, the owner of Belhar Gardens, has played a big role by providing low-cost housing even students can live in. A total of 70% of Belhar Garden units are reserved for households that earn between USD 216 and USD 432 monthly income. The rest is for those with a combined household income that is less than 216 USD [50]. Similarly, Waterfall Park offers two-bedroom, one-bath and two-bedroom, two-bath homes with rent between USD 365 and USD 389 [55]. The affordability of the buildings has caused high competition between buyers and renters. For instance, The Village (Clubview) has a high demand for its units where the properties are between USD 340 and USD 424 because of its ideal location and high quality in addition to the affordability [46]. The 17 buildings with EDGE certification not only solve housing affordability but also provide a quality life to their residents. Projects are situated in a good location where occupants can find work opportunities, access to public transport, educational facilities, and other amenities in the vicinity [45]. Celebration Retirement Village's community is involved in contributing to environmental sustainability such as reducing their carbon footprint despite their old age. The building gives a convenient and safe environment to the retired. Residents can access amenities including a hair salon, restaurant, library, and swimming pool within the perimeter of the project [56]. Zevenwacht Lifestyle Estate, another retirement building with EDGE certification prioritizes the health of its retired residents where there are healthcare centers and assisted living suites. Residents can also enjoy outdoor activities such as hiking trails in nearby mountains [52].

Discussions
The EDGE has played a critical role in the development of sustainable architecture and the building industry in improving the quality of buildings, especially in developing countries including South Africa. However, given the seventeen projects with EDGE certification, only three buildings have reached the EDGE Zero Carbon level and none of them are in South Africa. Therefore, buildings are encouraged to have EDGE Zero Carbon Certification as it helps reduce the environmental impact caused by the building industry. Moreover, EDGE should encourage building developers to focus and invest not only in quality but also affordability that ordinary citizens can use. It is important to remember that not all green buildings are certified, and all buildings should aim for sustainability. As the world is facing an environmental crisis, it is crucial to revise the impact of the built environment on our natural environment and its contribution to protecting it. A small daily improvement in resource efficiency produces a long-term, positive and tangible impact on humans and the environment. Large buildings use more resources, which negatively impacts the environment and the economy more than smaller buildings. On the other hand, a small percentage of resource-saving can result in bigger savings. Therefore, EDGE should regulate and give detailed guidelines on savings based on the size of the project. EDGE has fewer areas of focus compared to other certification systems. As a result, it should be expanded to other areas such as indoor environmental quality, transport, waste management, ecology management, sustainable sites, local environment, among others. More aspects conditioned to certify will provide better quality buildings.
In future studies, we considered that it is necessary to expand the application cases of various certification systems and facilities to not only residential but also other building types such as office buildings and medical facilities to conduct a broad and in-depth analysis including the post-occupancy evaluation and life cycle analysis. In future research, we will also study the correlation between social economic status, WWR, and location with energy and water consumption.

Conclusions
Through this study, characteristic analysis of the EDGE certification system was conducted by focusing on 6024 units in 17 residential complexes. This study highlights that EDGE tackles South African housing issues and improves building performance through its certification. Thus, the purpose of EDGE in South Africa reflects the country's big issues with residential complexes. In particular, it measures energy savings, water savings, embodied energy in materials, and total CO 2 savings (annually) for each building at both the preliminary and final EDGE Certification stages. Based on the results of this study, energy and water "efficiency first" solutions were prioritized over on-site energy generation during the design of buildings. The average savings for 17 EDGE-certified residential buildings from August 2017 to June 2022 are as follows: energy (29.7%), water savings (31%), embodied energy in materials (54%), and total annual CO 2 savings (351.73 t). All buildings reduced energy consumption through a reduced WWR. Buildings installed low-flow plumbing fixtures such as faucets and showerheads. A total of 88.2% of buildings had low-flow faucets in kitchen sinks, low-flow showerheads, and dual-flush water closets installed. Consequently, water usage was expected to be reduced to more than 50%. In materials used on buildings, solid concrete blocks were installed in 64.7% of all buildings. Buildings with outdoor energy-saving lighting systems and smart electricity meters equally accounted for equally 58.8% of all cases. Among all technical solutions, energy-saving solutions were the most used accounting for 69.2% of all technical strategies, followed by energy-generating solutions (23.1%). Lastly, energy measurement accounted for only 7.7%. According to the statistical analysis, there is no statistically significant relationship between energy, water, embodied energy in materials, and CO 2 savings with floor areas.
Author Contributions: Introduction, research background, data collection, original draft preparation, D.I.; review, editing, supervision, J.P. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.

Acknowledgments:
The authors would like to thank the members of Humans, Environment and Architecture Lab (HEAL) at Ewha Womans University for providing research advice during various stages of the paper preparation.

Conflicts of Interest:
The authors declare no conflict of interest.