Green Building Design Strategies for Residential Areas in Informal Settlements of Developing Countries

Abstract

Informal settlements, urban areas with substandard housing conditions and inadequate infrastructure, are increasing in Africa’s sub-Saharan cities, fueled by rapid urbanization, economic challenges, and high housing prices. However, developers often ignore the green building (GB) concept when upgrading housing conditions for these communities. This study aims to investigate GB design strategies specifically for residential structures in Akabahizi to identify and propose practical strategies suitable for informal settlements such as Akabahizi and to develop sustainable housing solutions that enhance environmental quality and meet the needs of residents. Simulation software and combined qualitative and quantitative data collection techniques, including field surveys, interviews, and assessments of existing building conditions, constitute the methodology used in this study. The focus was on the influence of climatic factors, including temperature, precipitation, and wind, on design choices, particularly GB design and current residential buildings in Akabahizi. Based on the survey, 82.5% of residents support the GB concept, 87.4% recognize the importance of GB for community well-being, and 97.1% recognize the benefits of integrating energy-efficient technology for residents’ well-being. Questionnaire findings were considered in decision-making for the design of the new proposed structure to address challenges in the area. Optimized energy efficiency, daylight access, and thermal comfort resulting from courtyard design support GB design incorporating a courtyard as a robust and culturally relevant sustainable design framework tailored for Akabahizi. The courtyard provides green space that promotes social interaction, improves air quality, and delivers natural cooling elements that are essential for residential housing. The proposed new design, with green roof and renewable energy devices, improved material usage, and natural ventilation elements, outperformed the existing one in terms of lower levels of carbon emission for environmental protection. In conclusion, a collaborative effort is needed among various stakeholders, including architects, urban planners, and educational institutions, to promote and implement sustainable building practices. The study suggests that enhancing awareness, offering training opportunities, and empowering local professionals and residents alike can pave the way for improved living conditions and sustainable urban development in Akabahizi and similar informal settlements.

1. Introduction

Green building (GB) is a comprehensive approach to planning, designing, building, operating, and maintaining structures to minimize adverse effects on the environment and maximize positive impacts on human health and the natural world [1]. GB is a sustainable approach used in residential contexts to minimize problems associated with informal settlements by optimizing the use of resources, including electricity, water, and materials [2,3]. GB strategies are based on principles that guarantee the efficient utilization of resources over an extended period with consideration of future generations, namely water conservation, the utilization of renewable sources for energy efficiency, and providing a sustainable and conducive living environment for informal settlements [4,5].

Informal settlements, commonly referred to as slums, represent a significant global issue, affecting approximately 800 million people, particularly in the Global South [6], with projections indicating that this number is likely to reach 2 billion by 2030 [7]. These communities often emerge in metropolitan areas where residents typically do not have legal ownership of land or housing, resulting in unstable living conditions [8]. In many settlements around the world, residents lack effective strategies for managing rainwater and greywater, leading to frequent flooding during the rainy season and further deterioration of quality of life [9].

GBs incorporate innovative technologies and design strategies to minimize environmental impact and promote sustainability, including energy-efficient heating, ventilation, and air conditioning (HVAC) systems; sustainable building materials; and smart building management systems [10,11]. The GB concept provides improved indoor environmental quality [12] by minimizing indoor air toxicity (CO₂, CO, PM_2.5) and improving indoor air quality [13,14,15], regulating heat for thermal comfort [16,17,18], maximizing the use of more natural light than artificial light to enhance visual comfort [19,20,21], and minimizing the effects of high noise levels to improve acoustic comfort [22,23,24]. All these factors make the indoor environment more comfortable for occupants. The GB concept is becoming popular because of growing environmental awareness and the need for sustainability [12,25]. Countries such as the United States (US), Canada, and Europe are at the forefront of global adoption, with cities such as Singapore, Hong Kong, and Tokyo also advocating for GB practices [12].

In Sub-Saharan Africa, around 75 percent of urban dwellers live in informal settlements [26]. This reality reflects urban poverty, where substandard housing, insecure land tenure, and insufficient access to social services are common [27]. Rwanda’s capital, Kigali, serves as a prime example of how rapid urbanization has fueled the growth of informal communities such as Akabahizi village in the Nyarugenge district. Residents face numerous challenges, including inadequate housing, limited access to vital amenities, and heightened risks from environmental factors such as flooding [28,29]. As the population grows, the demand for housing also increases, leading to the expansion of informal settlements that often lack proper planning and infrastructure [29]. Many homes in Akabahizi are built using substandard materials and construction methods, with inadequate housing and poor drainage systems (Figure S1). Akabahizi village is a settlement in the central area of Kigali city, characterized by a substantial population of 7392 inhabitants, and the growing demand for adequate housing in this village is driven by natural population growth occurring at the rate of approximately 2.4% per year [30,31].

1.1. Traditional Informal Building in Akabahizi Cell

As depicted in Figure 1, the traditional buildings of the Akabahizi village in the Gitega Sector (Figure 1a,b) realistically illustrate the community’s economic limitations and traditions. Historically, residences in the area have been built with locally produced materials, including mud bricks and clay, supplemented by corrugated iron sheets for roofing. These materials are economical and easily accessible, making them practical options for the community. Traditional informal buildings in Akabahizi are often characterized by a rectangular shape, a single front entrance, and limited windows, frequently comprising only one near the door or none whatsoever (Figures S1 and S2). The roofs, constructed from corrugated iron sheets, are economical and easy to install, typically featuring a flat design with a slight pitch to facilitate rainwater drainage. This roofing material has drawbacks; it is prone to rust and corrosion over time, raising considerable durability concerns [32]. The living conditions in Akabahizi village are marked by informal housing that causes congestion [31]. The situation has been intensified by inadequate urban planning, leading to the emergence of settlements that developed spontaneously without formal regulations.

The elevated population density has led to substandard living conditions and limited privacy for inhabitants. Fundamental infrastructure, including sanitation facilities, roadways, and drainage systems, is either inadequately developed or entirely absent [31,33]. This deficiency could precipitate substantial problems concerning waste management and raise the danger of hazards such as flooding and landslides during the rainy season [34]. Land use in Akabahizi village is often complex, incorporating both residential and commercial activities. The lack of zoning laws has caused land use disputes and further increased congestion [35].

Numerous structures have been erected without compliance with established planning or building codes, leading to a disordered housing landscape lacking organization [33]. The economic condition of families significantly influences home development within the neighborhood [36]. Residences are generally constructed using the economic means of the inhabitants; hence, numerous residences consist of merely a single room, and the dimensions and number of rooms fluctuate according to familial size and financial capacity [37]. The majority of residences are single-story buildings constructed from indigenous materials, which highlights the informal characteristics of these communities and the limited availability of green spaces in the town [38].

1.2. The Design of the Courtyard of a Traditional Informal Building

The design of the courtyard spaces in the housing of Akabahizi village typically reflects a communal, multifunctional approach and the informal nature of the area [39]. Many homes in Akabahizi village have courtyards arranged in central formation and serve as communal spaces for social interactions. Most of these courtyards act as the heart of the community and foster a sense of cooperation among residents [40]. The pathways connecting individual residences to the courtyard are informal, constructed from temporary materials, and lack standardization, with many varying in width and condition [41]. Overcrowded spaces characterize the courtyards of the housing in Akabahizi village because of the high population density in the area, which limits their effectiveness as communal spaces and causes an increase in space-use conflicts [41,42]. Ultimately, the overcrowding of the courtyards has led to a lack of green spaces and the development of an urban heat island effect in this region, along with associated problems [36]. The poor arrangement of Akabahizi courtyards resulting from unplanned development contributes to numerous challenges, including the community’s vulnerability to climate change and poor living conditions [43]. Therefore, there is a need to upgrade these settlements by focusing on integrating GB strategies in Akabahizi village, enhancing access to services, and promoting sustainable practices to improve living conditions for local communities [2].

1.3. Challenges in Achieving Sustainable GB in Akabahizi

The challenges affecting sustainable GB are multifaceted, primarily resulting from high population density and unregulated urban expansion [12]. These challenges include limited land availability and environmental sensitivity. The increasing population density of Akabahizi village has resulted in encroachment on environmentally sensitive areas, including steep slopes, floodplains, and wetlands [44]. This unplanned expansion raises the risk of natural disasters such as landslides and flooding and disturbs local ecosystems [45]. The intrusion into these sensitive areas causes habitat loss and reduces biodiversity as informal settlements replace natural environments.

A Rwanda Environment Management Authority (REMA) research report indicated that wetland degradation from human activities adversely affects the provision of ecosystem services essential for the livelihoods of residents [46]. The loss of biodiversity and disruption of natural habitats can have enduring effects on the resilience of the local ecosystem, making it more vulnerable to climate change and other environmental pressures [47,48]. The lack of access to clean water and adequate sanitation facilities is another significant environmental challenge noted in Akabahizi village [49]. The absence of a centralized water supply and sewage treatment infrastructure in informal settlements frequently contaminates groundwater and surface water sources [50]. Rwanda’s water quality management indicates that most untreated residential and industrial wastes is released into watercourses, leading to increased pollution levels in urban areas and their surroundings [51]. This contamination poses considerable health hazards by causing waterborne diseases among inhabitants. Moreover, improperly disposed of solid waste can interfere with drainage systems, resulting in flooding and environmental deterioration. Poor sanitation and water pollution threaten human health and compromise environmental sustainability [46,52]. The social challenges faced by residents of Akabahizi village are strongly linked to their economic conditions, especially within the framework of informal settlements [53]. These challenges significantly hinder the achievement of sustainable GB design.

The residents of Akabahizi, similar to those in other informal settlements, primarily comprise low-income individuals who face challenges in fulfilling their basic needs [54]. The increased cost of ecofriendly building materials and technologies presents a challenge to the implementation of a GB strategy [54]. Many families lack the financial means to invest in energy-efficient technology, sustainable materials, or advanced construction methods that might yield long-term savings and improve living conditions [55]. A study on GBs in Rwanda indicated that economic constraints lead to greater dependence on traditional construction methods, emphasizing immediate shelter needs over sustainability, thus perpetuating a cycle of poverty and environmental damage [54,56].

Another challenge is inadequate awareness and education regarding the potential benefits of sustainable and GB strategies [54]. Many people living in Akabahizi may lack a comprehensive understanding of the cost savings and improved health benefits that result from GB practices [57]. GBs typically offer enhanced indoor air quality along with better thermal comfort, which can significantly affect the well-being of occupants [14,58]. Nonetheless, in the absence of adequate education and outreach, individuals may remain doubtful or indifferent toward these advantages, preferring traditional construction techniques with which they are familiar [57]. Studies show that education is crucial for the adoption of green technologies, as informed communities are more inclined to adopt sustainable practices when they understand the related benefits [58].

The inhabitants of Akabahizi village have long faced challenges related to informal building practices, resulting in the emergence of informal settlements characterized by substandard dwellings lacking sufficient ventilation and lighting, overcrowding, insufficient basic infrastructure, use of substandard building materials, lack of green spaces between residences, inadequate waste disposal, and an insufficient water management system, all of which have detrimental effects on their well-being [31,59,60]. Only a few studies have been conducted on enhancing housing conditions and other basic amenities in Akabahizi village.

Addressing the challenges of informal settlements requires innovative and sustainable construction techniques that can improve the living conditions of residents [60]. To solve the problems faced by people in informal settlements, the government of Rwanda has initiated modern building projects aimed at complying with green building standards to improve living standards in informal settlements and protect the environment at the same time. The initiative to develop modern buildings aims to upgrade settlements in Akabahizi village and is the object of our case study. It is one of the government projects designed to provide sustainable residential buildings to people living in informal settlements, especially in the capital city of Kigali.

1.4. Overview of the Existing Design Initiated by the Government

The building initiative in Akabahizi village, located in Rwanda’s Nyarugenge district, aims to upgrade informal settlements and improve living standards through urban planning strategies. Developed over four years, this project targets approximately 34,817 residents across 137 hectares, focusing on the Gitega sector of Akabahizi and nearby Kimisagara districts along the Mpazi River, including a 20 m buffer zone between drainage systems and residential areas for safety [61]. As depicted in Figure 1c, the existing buildings significantly differ from traditional informal structures. It presents the architectural design and elevation of this new typology, showcasing a compact, rectangular footprint with a structured layout that maximizes density, a stark contrast to the organic sprawl of traditional housing. These buildings feature a net floor area of 750 sqm in a G + 2 configuration, with 26–30 units per block ranging from small studios to four-to-five-bedroom apartments. Ground-floor rental units and small-scale commercial activities are included to promote income generation. The initiative emphasizes green sustainability, utilizing locally sourced materials such as white stones and bricks to enhance durability and reduce environmental impact, as well as improving energy efficiency [12,62]. Designed to accommodate larger families, the buildings can house over 80 individuals, addressing overcrowding issues. For instance, on 4 July 2022, housing units were allocated to 56 families.

Figure 1d provides an exterior view of this newly constructed building, illustrating the realized design: a multi-story structure with a finished façade, defined balconies, and a formal architectural presence that marks a definitive shift from the informal settlement context. Although this approach offers a more organized distribution method [8], community feedback evinced several concerns. These issues included limited accessibility for people with disabilities, insufficient drying space, and inadequate waste collection. Participants further emphasized the need for greater privacy in cooking areas, the implementation of rainwater harvesting systems, and more effective management of common spaces. While the current government initiative incorporates essential infrastructure, including critical amenities such as health clinics and recreational facilities, it still exhibits gaps in energy efficiency, thermal comfort, and certain aspects of community well-being. The absence of a fully integrated, sustainable design restricts access to comfortable living environments and energy-saving benefits, negatively impacting residents’ overall quality of life. Therefore, this study proposes a modern architectural design for future projects to address these deficiencies and enhance community well-being and sustainability [62,63].

By examining existing government-initiated buildings, this research identifies effective design strategies to improve sustainability and resident satisfaction. Key focuses include enhancing natural ventilation, optimizing solar gain, and maximizing natural illumination to transform Akabahizi into a model for environmentally friendly residential complexes. The findings will provide valuable insights and replicable models for future upgrading projects in Rwanda and other regions facing similar challenges.

2. Research Methodology

2.1. Study Area Description

As detailed in Figure 2, Gitega is one of the 10 sectors that make up the Nyarugenge district in Kigali city. It is located at 1°57′16.9′′ S and 30°03′24.1′′ E, with an elevation of 1509 m. It has a population of 26,668 and a total surface area of 1.174 km². The district comprises six cells: Akabahizi, Kora, Akabeza, Kigarama, Kinyanye, and Gacyamo. Akabahizi is our study area and is located at −1.9459° (or 1°56′45′′ south) and 30.052° (or 30°3′7′′ east), with an elevation of 1426 m. It is situated near the locality of Cya-hafi and the suburb of Nyarugenge. Akabahizi has approximately 17,000 inhabitants crowded into 124.7 hectares, resulting in a population density of around 139.4 inhabitants per hectare. The population is primarily composed of young and elderly adults, which influences housing needs and community dynamics [64].

2.2. Data Collection

2.2.1. Questionnaire Survey

The questionnaire survey aimed to focus on understanding the preferences, experiences, and expectations of the community regarding green construction practices. The questionnaire survey is a fundamental tool before undertaking any green building project work, as it gives a general understanding of the site’s situation and gathers input from different stakeholders, developers, and the local government involved in the project. During the questionnaire survey step, information about available local materials, transportation, and much more can be obtained, all helping in decision-making on the successful implementation of the green building plan, design, and practice [65,66,67,68]. Our participants included engineers, architects, urban planners, environmentalists, local government officials, and educators. The structured questionnaire focused on several critical areas relevant to GB initiatives in informal settlements, including awareness and understanding of GB principles; current practices and implementation challenges; stakeholder engagement and collaboration; policy, regulatory frameworks, and support systems; and future opportunities and long-term impacts.

The questionnaire survey primarily targeted individuals working in construction-related fields to obtain accurate information and avoid potential issues, such as participants expecting monetary compensation or those not interested in building, as they may provide irrelevant responses. This approach was fundamental, since the sample size was relatively small. The required population size for sampling in each selected sector was determined using the following formula: $\mathrm{n}={\displaystyle \frac{N}{1+(N\times e^2)}}$ [69], where n is the sample size, N is the total population, and e (e = 0.05) is the margin of error.

2.2.2. Field Observations

Field observation is essential during the planning and design of a green building project. Data from this methodological step confers crucial information on site suitability, waste management, water management, and site accessibility to transport [65,70,71,72]. Systematic observations of the physical environment were conducted as part of a study on sustainable building practices in Akabahizi village. The assessment through observation focused on various aspects, including materials used in construction, building design, passive strategies, land use patterns, green infrastructure and microclimate, water management and drainage systems, socioeconomic conditions and affordability, and alignment with GB standards.

During the field survey and observation, one building on the site was selected as a sample for the assessment of the design of the existing building. The goal was to collect data on the physical features of the building envelope and geometry, including the surface area and thickness of the floor, walls, and roof; shading and ventilation elements such as overhangs and louvers; the orientation of the building relative to the north; and the ratio of wall to window to determine the percentage of glazing on fades. All other necessary and relevant data required for building energy modeling were acquired during the field survey, including data on heating and ventilation systems, occupancy information, electrical equipment data, and the operational schedule [73,74]. Data on the utilization of renewable energy were also collected during this step of field observation. Field observation played a key role in gathering data on the existing energy supply, which contributed to essential decisions during the design of the modern building model that the study aimed to propose.

2.2.3. PRISMA Methodology

The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) methodology is a systematic review of existing literature. It was conducted here by identifying, selecting, and synthesizing relevant studies focusing on green building (GB) practices and urban planning within Rwanda and surrounding East African countries. Our review encompassed various sources, including peer-reviewed academic articles, reports from nongovernmental organizations (NGOs), and essential policy documents that shape the urban landscape [75]. Of particular importance were the Rwanda GB Compliance System (GBMCS), which establishes guidelines for sustainable building practices, and the National Informal Urban Settlement Upgrading Strategy, which aims to improve living conditions in informal settlements. The use of the PRISMA methodology enabled access to documents related to commonly used building materials in Rwanda, GB practices and regulations, information about the master plan of Kigali city, and more [35,76,77].

2.2.4. Building Energy Modeling Analysis and Design Considerations

In this methodology section, many details are not mentioned on the stages of field observation and PRISMA; however, these two stages were crucial, as the building simulation analysis (BEM: building energy modeling) was primarily based on the data acquired during these two steps. ASHRAE standards were considered, as Rwanda has yet to develop sufficient data for BEM [78,79].

In this context, various meteorological data sources for Rwanda and Kigali City were consulted during this stage of the PRISMA process. The Rwanda Meteorological Agency and other online weather data providers were included in this stage. Platforms such as Google Maps were used to obtain geographic data (latitude, longitude, azimuth, etc.). At the same time, EnergyPlus Weather, SunCalc.org, Climate.OneBuilding.org, and the National Solar Radiation Database were consulted to gather environmental data related to weather and atmospheric conditions (such as cloud cover and sunlight position). Moreover, existing building design documentation was acquired to facilitate the analysis of building material properties (including transmittance, reflectance, etc.).

The proposed building model for Akabahizi was designed to attain compliance with the Rwanda Building Code and Green Building Regulations, combined with ASHRAE 90.1 standards, which served as the main baseline model for code comparison [76,77,80,81]. The building features a linear rectangular shape and is oriented toward the north azimuth direction. Priority was given to the use of construction materials made in Rwanda for both the substructure and superstructure, in compliance with national building regulations for sustainability [60,82]. Various design considerations were implemented according to the Rwanda Building Code, supplemented by ASHRAE 90.1 standards, to achieve a sustainable design. Illumination within the residential spaces ranges between 100 and 300 lux, with openable wall openings accounting for at least 10% of the floor area of each room. These openings ensure natural light and ventilation, facilitating communication with the external environment. The design provides a ventilation rate of 0.5–1 air change per hour (ach) and includes mechanical ventilation at a rate of 1 L/s/m² of floor area. Indoor thermal comfort is maintained with a dry-bulb temperature between 24 and 26 °C, and air movement is limited to no more than 0.3 m/s at the occupant level, measured 1500 mm above the floor. Additionally, the roof pitch is designed not to exceed 45°, allowing for the integration of solar power (renewable energy) to support the sustainable operation of lighting systems, various appliances, and heating, ventilation, and air-conditioning systems [77].

2.3. Data Analysis

Various software tools were utilized to enhance our research’s design, analysis, and simulation processes. Archicad and Revit were used to model building massing geometry and building envelope, providing detailed and accurate representations of complex architectural forms [83,84]. Climate analysis, an essential component during this study, was conducted using cove.tool and Climate Consultant, which provided valuable insights into existing environmental conditions and their impact on building performance, helping us make informed design decisions. These two software tools are essential for experts in design and building, especially for any work requiring BEM, as in green building design work [85,86,87]. Revit, DesignBuilder, and EnergyPlus were intended for simulation purposes, facilitating comprehensive energy efficiency and sustainability metrics evaluations throughout the project’s development [88,89]. SPSS (Statistical Package for the Social Sciences) version 27 is a powerful software tool for studies requiring quantitative data analysis and other related research. SPSS was used to analyze survey data to determine trends, correlations, and overall compliance with GB standards [90,91].

All the software tools utilized were selected based on their high accuracy, whether in modeling, simulation analysis, or calculation, and compliance with the GB design concept. The utilization of both Archicad and Revit enabled the achievement of requirements for strong geometric control, parametric control, and computational design [83,84,92]. The use of both DesignBuilder and EnergyPlus contributed to high accuracy in simulation analysis (thermal comfort, natural cooling and ventilation, daylighting, etc.) and energy calculation (cooling and heating energy), as well as achieving GB standards certifications such as LEED, BREEAM, Passive House, and ASHRAE 90.1 [93,94,95,96]. The GB concept is being advocated as a new approach to overcoming challenges related to the rapid increase in informal settlements in urban areas.

3. Results and Discussion

3.1. Analysis of the Current Situation in the Existing Building

3.1.1. Analysis of Questionnaire Responses

A total of 103 respondents participated in the research survey, including construction and design experts, who provided valuable information through their feedback about Akabahizi village. The analysis of the feedback from respondents is summarized, considering factors such as demography, climatology, housing conditions, awareness and perception, energy efficiency and renewable energy, environmental concerns, and waste management. Further details on the questionnaire responses analysis can be found in a separate document as Supplementary Material.

Demographic Data

The demographic data of participants were collected, considering factors such as age, gender, country of origin, education, professional roles, and experience in environmental or construction fields (Figures S3 and S4). The majority of participants were male (61.2%) and female (37.9%) (Figure S1b). Most were from Rwanda (60.2%), with smaller contributions from other African countries (Figure S3c). The dominant age group (38.9%) was between 26 and 31 years, followed by the 32–39 age group at 30.1% (Figure S1a), reflecting a strong local focus in the findings. Most participants held a master’s degree (45.6%) or a bachelor’s degree (3.8.8%), with a few pursuing higher qualifications (Figure S4a). The majority were architects (39.8%) or engineers (26.2%) working in construction management or NGOs, indicating a diverse professional background (Figure S4b). In terms of experience, many participants had between four and six years of experience (37.9%), with a significant portion (33%) having between one and three years of experience, suggesting varying levels of expertise (Figure S4c). Participation and cooperation of local stakeholders, experienced developers, and local government are important for decision-making about green building project planning and design.

Climatology of Rwanda Data

The participants responded to the part of the survey on climatic conditions in Rwanda, revealing their understanding of local climate issues related to green residential building design (Figures S5 and S6). A strong majority (89.3%) reported being familiar with the local climate, indicating a well-informed participant group (Figure S5a). Most participants described the climate as hot and humid (71.8%), while others noted mild and moderate conditions (30.1%) or cold and dry conditions, reflecting a variety of perceptions about local weather (Figure S5b). The majority (89.3%) experienced extreme weather events in the past year, with a small number reporting no experience (6.8%) or uncertain experiences (3.9%), highlighting concerns about climate resilience in the region (Figure S3c). Most participants (96.1%) were aware of the impact of climate change on their locality (Figure S4a), and 88.3% noted the influence of the local climate on thermal comfort with regard to a moderate climate that balances heating and cooling needs (Figure S6b). The most critical climate-related factors for designing green buildings (GBs) include temperature (92.8%) and rainfall patterns (87.4%), emphasizing the need for climate-sensitive design approaches (Figure S6c). Most participants (73.8%) believed that the local climate positively affects building design performance, while another group (42.7%) believed it has negative effects (Figure S6d) From this part of survey, the perspective of local community on severity of local climate was revealed, and expectations and suggestions from respondents were recorded to consider during decision making for better and more sustainable solutions.

Housing Conditions and Challenges

Analysis of responses on key aspects related to housing conditions in informal settlements in Kigali is presented in Figure S5. Most of the participants (78.8%) were familiar with these housing conditions (Figure S5a). The housing type relies on basic structures, as evidenced by the dominance of informal brick houses (94.2%), followed by shanty houses at 55.3% (Figure S5b). Lack of access to basic services (66%) and poor structural stability (83.5%) were significant challenges cited by participants, reflecting critical issues in living conditions (Figure S5c). However, the proposed solutions from green building (GB) concepts included improved structural stability (82.5%) and space optimization (72.8%), emphasizing the potential of sustainable strategies in addressing housing challenges (Figure S7d).

Awareness and Perception of GB Design Strategy

The assessment of perceptions regarding support and barriers to GB design strategies in Rwanda and participants’ perspectives on the benefits and challenges of implementing GB strategies in informal settlements is presented in Figures S6 and S7. The government supported GB design strategies at 49.5% and 34.0%, with a small percentage (1%) expressing uncertainty (Figure S8a). Surprisingly, the community’s support appeared to be strong (82.5%), affirming engagement in GB initiatives (Figure S8b). However, significant hindrances were pointed out, such as a lack of public awareness (75.7%), insufficient funding opportunities (87.4%), and inadequate policy incentives (50.5%) (Figure S8c). These findings highlight an overall positive perception of support, tempered by critical challenges that need to be addressed to enhance the implementation of GB strategies in informal settlements. The lack of financial resources (91.3%), followed by the lack of awareness and education (82.5%), were the key challenges identified in the area, highlighting the negative impacts on living conditions (Figure S9a). However, most participants (89.3%) agreed on the challenges or barriers encountered in implementing GB design strategies in informal settlements (Figure S9b). The importance of GB design for overall resident well-being was emphasized, with a consensus on its role in enhancing health and well-being conditions (87.4%), reinforcing the need for sustainable practices in informal settlements (Figure S9c).

Energy Efficiency and Renewable Energy

Figure S8 presents insights into energy efficiency and renewable energy initiatives in informal settlements. A significant majority (77.7%) reported the existence of initiatives targeting these areas (Figure S10a). Key factors influencing adoption included affordability (92.2%) and availability of resources (46.6%), indicating financial constraints as significant barriers (Figure S8b). Renewable energy technology (90.3%) and energy-efficient appliances (84.5%) were highlighted as practical solutions that can be implemented (Figure S10c). There was a unanimous belief (97.1%) in the benefits of integrating energy-efficient technologies for residents’ quality of life (Figure S8d). Major challenges included high costs (66%) and resistance to change (61.2%), underscoring hurdles to implementation (Figure S10e).

Environmental Concerns

The participants’ views on the environmental impacts of residential buildings in informal settlements are presented in Figure S11, where a strong consensus (93.2%) reflected significant concern regarding environmental impacts (Figure S11a). Water conservation and waste management practices (90.3%) and sustainable site selection (86.4%) were identified as priorities for key environmental considerations in GB strategies (Figure S11b). The majority (77.7%) acknowledged the existence of specific environmental regulations or guidelines (Figure S9c), and 87.4% of participants viewed the integration of nature-based solutions as very important, emphasizing a strong desire for environmentally sustainable development in informal settlements (Figure S9d).

Waste Management

The analytical insights on waste management practices in Akabahizi informal settlements (Figure S12) show that community collection points (75.1%) were dominant, followed by informal dumping sites (37.9%) and some on-site disposal (28.2%), indicating reliance on informal methods (Figure S12a). Participants suggested community-based recycling initiatives (77.4%) and waste-to-energy conversion (73.8%) as the most suitable strategies for improvement (Figure S12b). The majority expressed dissatisfaction, with 68.9% rating the existing systems as inadequate (Figure S12c), and there was unanimous agreement (97.1%) on the importance of prioritizing waste management in GB design, highlighting a strong desire for sustainable solutions in informal settlements (Figure S12d).

The overall implications of the results from the questionnaire survey indicate that the demographic data helped ensure more reliable responses from local and educationally qualified participants. Climatic data provided valuable information on people’s comfort levels in Akabahizi, which can aid decision making regarding comfort design. Housing conditions and awareness of green building data can assist in addressing challenges in the area and making recommendations on gaps in education. Energy efficiency, renewable energy, and environmental concerns can contribute to decision making for design, facilitating the integration of new sources of green energy and addressing environmental impacts present in the area. Waste management data can help in designing a proper and improved waste management infrastructure [67,68,70,71,97].

3.1.2. Climatic Conditions in Akabahizi

The local climate is a critical determinant of building design and material selection [98]. Understanding both the general climate and the microclimate of the location is essential to achieving the intended goal for Akabahizi village.

Temperature and Precipitation Variability

The analysis presented in Figure 3a for the monthly average temperature from 2018 to 2023 [44] indicates that the maximum temperature observed was above 28 °C, while the minimum temperature was 18 °C, with no significant difference among these five years despite variations in monthly temperatures over this period. However, climate change is causing elevated temperatures and prolonged dry seasons, which in turn is increasing the demand for energy-intensive cooling systems. Therefore, buildings must be designed to support both warm and cold climates, necessitating features that improve thermal comfort while reducing energy usage [99].

The annual rainfall (Figure 3b) in Rwanda exhibited significant fluctuations from 1961 to 2016. Over this period, the mean rain began to increase from January to April but then decreased in April, May, June, and July. From August onwards, it rose again, indicating a significant difference in rainfall patterns during these years, as depicted in Figure 2, which represents the monthly average temperatures from 2018 to 2023. Data analysis from the World Bank Group’s Climate Change Knowledge Portal (CCKP) provided historical information on the latest climatology from 1991 to 2020 (

Table 1. Historical information for the latest climatology, 1991–2020.

Climate Variables	1991–2020
Mean annual temperature (°C)	19.4
Mean annual precipitation (mm) Mean maximum annual temperature (°C)	1177.7
	25.5
Mean minimum annual temperature (°C)	13.3

).

Rwanda’s mean annual temperature is 19.1 °C, with average monthly temperatures ranging between 19.8 °C (September) and 18.8 °C (July). The mean annual precipitation is 1177.6 mm. Rainfall occurs throughout the year in Rwanda, with the most significant rain from September to May. However, the main data source for the World Bank Group’s CCKP was the CMIP5 (Coupled Model Intercomparison Project, Phase 5) data ensemble.

Table 2. CMIP5 ensemble projections.

CMIP5 Ensemble Projection	2020–2039	2040–2059	2060–2079	2080–2099
Annual mean temperature Anomaly (°C)	+0.7 to +1.5 (+1.1 °C)	+1.4 to +2.6 (+1.9 °C)	+2.3 to +4.0 (+2.9 °C)	+3.1 to +5.3 (+3.9 °C)
Annual precipitation Anomaly (mm)	−18.4 to +29.3 (3.3 mm)	−23.3 to +39.3 (5.1 mm)	−26.4 to +63.6 (9.5 mm)	−24.5 to +91.5 (18.2 mm)

presents the multimodel (CMIP5) ensemble of 32 global circulation models (GCMs), showing the projected changes in annual precipitation and temperature for the periods 2040–2059 and 2080–2099.

Relative Temperature and Humidity

A comprehensive analysis of outdoor comfort conditions in Kigali City, Rwanda, utilizing hourly temperature and humidity measurements throughout the year, is organized into two main graphs: dry bulb temperature (Figure 3c) and relative humidity (Figure 3d). High-temperature risk (too humid: above 71% or too hot: above 90 °F), represented by red and orange peaks on the graph, indicates discomfort periods when relative humidity and temperatures soar, often exceeding the threshold of 34 °C (93 °F). This requires passive and active cooling strategies, including dehumidification, the integration of water-absorbing materials, fans, and effective ventilation systems, to cope with such discomfort periods.

Medium temperatures and humidities (depending on climate), represented by light orange and white peaks, indicate the optimal comfort zones for outdoor activities, with humidity levels between 30% and 70% and temperatures ideally ranging from 10 °C (50 °F) to 32 °C (90 °F).

Low-temperature risk (too dry: below 29% or too cold: below 10 °C or 50 °F), represented by the blue valleys in the graph, indicates an uncomfortable chilly and dry environment affecting outdoor activities, with temperatures falling below 10 °C and relative humidity dropping to less than 30%. During this period, heating solutions are suggested, especially during occupied hours when individuals are more likely to be outdoors. These recommendations aim to ensure that outdoor spaces in Kigali remain comfortable and accessible across varying climatic conditions [100,101].

Solar Radiation

A comprehensive view of solar radiation patterns in Kigali City, Rwanda, using a sky dome format to illustrate the intensity of solar energy throughout the year, is presented in Figure 4a. It displays the cumulative solar radiation measured in kilowatt-hours per square meter (kWh/m²) across the cardinal directions: north, south, east, and west. The high radiation levels could reach above 53.17 kWh/m² in the case of high solar exposure, and the low radiation levels reached below 5.32 kWh/m² in the case of low solar exposure. Areas pointing towards the east exhibited higher values, often exceeding 42.54 kWh/m², while regions facing north and west reflected lower levels (21.27 kWh/m²). The three categories of solar radiation levels, high, medium, and low, shown in Figure S13 provide guidance for optimal glazing placement and traditional shading strategies for enhancing thermal comfort in buildings. In order to maintain comfort, overhangs and skylights are recommended for high radiation levels; medium-radiation zones require additional heat, while low-radiation regions are suitable for glazing.

Overall, understanding the situation of sunlight provides data for the optimal orientation of buildings to maximize passive solar heating and assist in the effective placement of solar panels.

Internal Air Temperature

A predictive model for internal air temperature and comfort levels throughout the year at the cardinal points for Kigali City, Rwanda, is provided in Figure 4b, highlighting three different periods: high-temperature risk (red and orange peaks), requiring passive or active cooling strategies to maintain comfort; medium temperature (yellow), comfortable during midrange hours without requiring active cooling or heating systems; and low-temperature risk (blue), requiring supplemental heating solutions to ensure thermal comfort during occupied hours. Understanding these dynamics allows for informed decisions regarding building design and operational strategies in Kigali’s unique climatic context. According to the color gradients in a radiation map (projected onto a dome) for designing energy-efficient and comfortable buildings (Figure 4c), there is beneficial radiation (deeper reds and oranges) during colder months, semibeneficial radiation zones, and nonbeneficial radiation (blues) during warmer periods. Understanding solar radiation helps inform decisions about facade orientation, window placement, and material selection, ultimately enhancing occupant comfort and reducing energy consumption.

Relationship Among Temperature, Humidity, and Comfort Strategies

The relationship among temperature, humidity, and comfort strategies was analyzed based on ASHRAE 55-2013 under standard conditions, which is represented in the chart providing effects of different environmental parameters on occupant comfort throughout the year (Figure S14). In this chart, the operative temperature is plotted against humidity levels, demonstrating the optimal comfort zone where temperatures and humidity align to enhance overall well-being, providing insights into specific comfort enhancement strategies and their effectiveness. In this analysis of the dynamic interaction among temperature, humidity, and comfort strategies, tailored to Kigali, Rwanda in alignment with ASHRAE 55-2013 standards for thermal comfort, the comfort zone (denoted as black dotted lines) represents a specific range of temperatures and humidity levels where most individuals feel comfortable (Figure S15). This zone is not static; it fluctuates based on personal factors, such as clothing choices and physical activity levels. Typically, it encompasses a moderate range of temperature and humidity, which is crucial for informing building design and operational strategies aimed at maximizing occupant comfort. Additionally, the chart features air properties, where multicolored polygons visually delineate various climate conditions based on air temperature and humidity. These classifications are vital for identifying the most effective HVAC (heating, ventilation, and air conditioning) strategies necessary to ensure comfort in Kigali’s unique climate.

Wind Direction, Intensity and Speed

Figure 5a indicates the monthly variation of wind direction and speed for Kigali, Rwanda. These show that winds approach the site from various compass points, with the length of each segment indicating how persistent and dominant the wind is from that direction. The color gradient on these plots reveals wind intensity: deep reds indicate lower wind speeds, while cooler blues correspond to higher wind speeds. Typically, the strongest and most consistent winds come from the northwest, with moderate to high intensities during several months.

Figure 5b highlights the prevailing wind direction (northwest) and displays how wind speed varies, with longer and wider segments showing directions with more hours of wind activity and blue shades marking higher speeds. Overall, Kigali experiences seasonal variability in wind patterns, with significant northwest winds that are most effective for ventilation and passive cooling strategies, helping architects optimize building designs for comfort and energy efficiency.

3.1.3. Analysis of Current Buildings in Akabahizi

Simulation Analysis of an Existing Building

(a)

Solar path analysis

Figure 6a presents a three-dimensional view of the existing building, overlaid with the solar path diagram. The diagram shows the sun’s trajectory throughout the year and highlights how the building casts significant shadows on its surroundings. The extent and orientation of these shadows indicate that large portions of the building and adjacent areas receive limited direct sunlight, especially during certain times of the day. Figure 6b further clarifies the shadowing effect, showing the building’s footprint relative to the sun’s path. The shadow cast is prominent, suggesting that the current design does not optimize solar exposure. This lack of adequate sunlight can lead to poor natural lighting and reduced passive solar heating. Given these observations, it is clear that the building needs to be upgraded. Improvements such as adjusting orientation, increasing window areas, or adding shading devices could enhance solar access, improve energy efficiency, and create a more comfortable indoor environment.

(b)

Building daylighting analysis

Figure 6c presents a top-down (plan) view of the daylight distribution on a single floor of the existing building. The color scale at the bottom indicates light intensity, ranging from blue (lowest) to red (highest). Most of the floor area is shown in dark blue, especially in the central zones, signifying very low daylight levels. Only the areas near the building’s perimeter and windows show slightly lighter shades, indicating somewhat higher daylight availability. Figure 6d provides a three-dimensional perspective of daylight distribution across multiple floors. The visualization reveals that the majority of the building, particularly the inner spaces and lower floors, remain in the blue to dark blue range, confirming low daylight levels throughout the structure. The 3D view helps illustrate how daylight diminishes further inside and on lower levels, with only the outermost areas near windows receiving marginally lighter. This suggests that daylight penetration is poor, with the interior spaces receiving minimal natural light. Therefore, optimization of daylight quality [65,102,103] in both private and living spaces, as well as in corridors, staircases, and particular interior areas, is an imperative consideration for the better health of dwellers.

(c)

Heating design analysis

• Temperature and heat loss analysis

A simulation for temperature and heating design analysis for the existing massing topology “MODEL 1” is presented in Figure 7a,b. Figure 7a shows that “MODEL 1” maintained an internal air temperature of 28.09 °C, despite an external dry-bulb temperature of 30.00 °C, showing a reduction of 1.91 °C. The operative temperature, a key indicator of thermal comfort, was 27.95 °C, influenced by the air temperature (28.31 °C) and radiant temperature (27.81 °C). These values confirmed a warm indoor environment despite external conditions, highlighting the need for effective thermal management.

The heat loss analysis (Figure 7b) indicates that the building gained significant heat from external air (1.20 kW/m²), likely contributing to the relatively high internal air temperature. While glazing contributed minimally to heat gain (0.08 kW/m²), and ceilings contributed 0.25 kW/m², walls added 0.45 kW/m², suggesting that the building envelope absorbs heat from the surroundings. The roof lost a small amount of heat (−0.07 W/m²), but the building also experienced heat losses, particularly through the ground floor (−0.90 W/m²) and internal floors (−0.56 W/m²). The partitions further contributed to heat loss (−0.43 kW/m²), possibly because of their material properties or contact with cooler areas.

Taken together, “MODEL 1” in Akabahizi exhibited a complex interplay of heat gains and losses, with the overall heat gains remaining at 0.02 kW/m². There is a need for sustainable design to address issues related to heat balance in the current building, especially by taking into consideration the excessive heat gain from external air, improving natural ventilation, optimizing insulation in the walls and roof, and managing heat losses through the ground floor, to enhance thermal comfort and reduce the need for active cooling, aligning with GB design principles for buildings [104,105,106].

• Analysis of indoor comfort conditions

As indicated in Figure 7c, air, radiant, operative and outside dry-bulb temperatures were at their highest levels in January and February, hovering around 25–26 °C, and gradually decreased to reach their lowest point near 16 °C or below around June and July. Subsequently, they rose again as the year progressed. The outside dry-bulb temperature followed a similar trend, albeit consistently lower, bottoming out at approximately 9.76 °C in July, indicating a considerable difference between indoor and outdoor temperatures during the cooler months.

As shown in Figure 7d, the relative humidity started at 53.72% in January and increased to a peak of 61.16% in April, indicating greater moisture during this period, likely due to rainfall patterns. It then declined to approximately 51.03% in September before rising to 56.06% by December. This fluctuation demonstrates a variable humidity pattern throughout the year, influenced by seasonal changes. The moderate humidity levels, ranging from 51% to 61%, generally suggest a comfortable indoor environment, although the peak in April may warrant attention for potential moisture-related concerns.

• Energy consumption analysis: comparison of baseline with proposed design

A comparison between the annual energy consumption of the baseline design and the proposed design for a settlement in Kigali, Rwanda, according to ASHRAE 90.1 standards (Figure 7e), revealed that the baseline design registered 0.0 kWh consumption across all categories, implying that it was a theoretical or reference model with no active energy use. In contrast, the proposed design exhibited a total annual energy consumption of 603,131.5 kWh, with significant energy needs for heating (149,177.08 kWh) and cooling (175,353.70 kWh), representing the highest energy demand at 54.5% of all energy used. At the same time, water systems consumed 192,702.19 kWh, approximately 32% of all energy consumption, further emphasizing the water infrastructure energy requirements of the proposed design.

The proposed design highlights significant energy needs primarily driven by heating, cooling, and water systems. There is a need for a sustainable building design incorporating an energy efficiency system, optimization of natural ventilation and building insulation, green roofs (provided with plants), adequate suitable openings (doors, windows, louvers…), water conservation, etc., to reduce the cost of energy [55,104,107,108]. Green building design practice is needed to attain high-level energy efficiency in current ongoing projects of residential buildings to improve informal settlements in Kigali.

(d)

Thermal performance and energy consumption analysis

• Temperature

As depicted in Figure 8a, the air, radiant, and operative temperatures all followed a similar diurnal pattern. Starting around 26 °C at 2:00 AM, they slightly decreased before rising to peaks between 27 and 29 °C around 12:00 PM to 2:00 PM. They then gradually decreased throughout the afternoon and evening. The outside dry-bulb temperature started at 18.92 °C, rose to a peak of 29.0 °C around 2:00 PM, and then decreased to 21.68 °C by 10:00 PM, showcasing the typical daily temperature swing.

• Heat balance

As represented in Figure 8b, solar gains through exterior windows significantly impacted the heat load of the building. These gains were highest between 8:00 AM and 6:00 PM, peaking at 160.79 kWh, dropping to 0.00 kWh, and then increasing to 173.37 kWh before decreasing to 4.81 kWh later in the evening. Walls also contributed to substantial heat gains, peaking at 113.07 kWh at 8:00 AM. Internal heat gains from computers and equipment were relatively constant at 9.00 kWh from 6:00 AM to 6:00 PM and 16.93 kWh from 8:00 PM to 10:00 PM.

• Cooling

The zones of sensible and total cooling demands were highest during the nighttime and early morning hours, reflecting the need to remove accumulated heat. Sensible cooling reached a minimum of −303.68 kWh at 6:00 AM, rising to 0.00 kWh from 12:00 PM to 4:00 PM. Total cooling demand followed a similar pattern, with a minimum of −416.41 kWh at 6:00 AM (Figure 8c).

• Relative humidity

The relative humidity fluctuated inversely with the temperature. It started at 55.50% at 2:00 AM, decreased to a low of 53.56% at 6:00 AM, and then gradually rose to a peak of 74.06% around 4:00 PM before reducing to 55.74% by 10:00 PM. This suggests drier conditions during the warmer parts of the day and more humid conditions as temperatures cool down in the afternoon and evening (Figure 8d).

• Mechanical and natural ventilation, as well as infiltration rate

The combined mechanical ventilation, natural ventilation, and infiltration rate varied throughout the day. It started at 0.79 ac/h, increased to a peak of 0.87 ac/h at 6:00 AM, then fell to 0.75 ac/h from 12:00 PM to 4:00 PM before rising to 0.83 ac/h by 10:00 PM, indicating changes in ventilation strategy or occupant behavior throughout the day (Figure 8e).

3.2. Comprehensive Analysis of the Proposed Sustainable Design in Akabahizi

3.2.1. Overview of the Proposed Building

A sustainable design framework for Akabahizi was proposed after considering different results from extensive research and field observations, as well as evaluation of existing buildings initiated by the government and comparison with other sustainable design baselines using building information modeling (BIM) and other related simulation software tools [65,71,94,109,110]. The courtyard design approach was proposed as an effective strategy to promote resilient communities and sustainable living environments and to overcome critical issues underscored in existing government-mandated massing strategy, such as inadequate housing, environmental degradation, and socioeconomic vulnerabilities associated with unplanned urban developments [111,112]. The courtyard is an open space surrounded by rooms, allowing for air exchange, daylight entry, and views [21]. This passive design device not only modifies the microclimate but acts as a heat sink and cold air storage, making it particularly effective in hot climates [113,114].

Buildings with internal courtyards demonstrate significant cooling potential, providing indoor spaces with cooler air and ample daylight. The courtyard’s functioning (working mechanism) relies on the daily cycle of temperature changes, affecting air exchange between indoor spaces, the courtyard, and the external environment (Figure 9a,b). It operates in three phases. First, cool night air enters the courtyard, cooling the surrounding rooms. Second, hot air rises as the sun heats the courtyard, drawing cooler air from adjacent rooms. Finally, cool air escapes as temperatures rise, resetting the system for the next cycle. This mechanism enhances thermal comfort and ventilation in courtyard houses. Research has indicated that courtyard configurations can improve building performance compared with conventional single-block designs.

Different studies have demonstrated that courtyard layouts provide superior thermal comfort and energy efficiency by enhancing natural ventilation and daylighting, which leads to significant reductions in mechanical cooling and lighting needs [111,113,114]. The courtyard strategy promotes multiple benefits sought in sustainable design, including increased natural ventilation, improved daylight penetration, and outdoor communal spaces that foster social interaction. Moreover, a study by Azimi et al. [100] showed that proper ratios in courtyard design significantly enhance thermal comfort and lighting, thus reducing cooling energy consumption.

3.2.2. Design Philosophy and Conceptual Framework

The proposed design for residential buildings in Akabahizi was informed by extensive site visits and in-depth community research. It highlights the unique characteristics of informal settlements, as many residents migrate to Kigali for better living conditions. Proximity to the central business district attracts low-income workers, though unplanned developments and substandard materials pose challenges. Affordability remains crucial despite health issues linked to housing quality. The design proposed herein integrates traditional elements with modern sustainable practices, adopting a courtyard style (Figure 9c–f) that fosters community ties. Integration of a courtyard style is the best match to the model village (umudugudu w’icyitegererezo) initiated by the government of Rwanda in its Integrated Development Plan [59] to maintain and improve the long-existing Rwandan cultural building style of agglomeration (umudugudu), which brings many families closer, reflecting the unity of Rwandans and enhancing security and social interaction between inhabitants. The courtyard design approach prioritizes sustainability, enhancing energy efficiency, air quality, and biodiversity, while also acting as a collaborative hub for NGO and government community engagement.

Space Arrangement Strategies and Functionality

After conceptualizing the design, analyzing research findings related to the challenges faced by the settlements, and examining case studies on the adoption of GB strategies, the selected research site was designed with various elements in mind. Central to our site arrangement is a focus point transformed into a public garden for community gathering and recreation space. The open space in the center is surrounded by a community square and rectangular form. Each massing features a central courtyard, designed as a green space dedicated to the residents of that specific block (Figure 9g,f). Sustainable GB intends to improve living conditions while reducing negative environmental effects [12]. This strategy is crucial, since an increasing number of people are moving to cities, a phenomenon that frequently increases informal settlements that face numerous challenges [36]. For example, in Akabahizi Village, constructed buildings lack green infrastructure and other features of GBs, such as water management, particularly rainwater harvesting [60]. Nonetheless, energy efficiency and renewable energy should be given top priority in sustainable building designs in informal settlements by utilizing design techniques that maximize natural light and ventilation [116]. Reorienting roofs to follow the path of the sun can greatly increase solar gain and decrease the need for artificial lighting and heating [117].

Comprehensive Design Variables for the Proposed Building

(a)

Strategy overview

This strategy will open up space for the production of solar energy, which is especially advantageous in areas such as Kigali that receive a lot of sunlight [118]. For instance, adding solar panels and energy-efficient windows to already-existing buildings in Akabahizi can significantly reduce energy costs and enhance the quality of the internal environment [116,119]. As depicted in Figure 10a, GB features trees surrounding and within the building corridors, creating a pleasant environmental atmosphere and facilitating easy movement for people with disabilities and elderly individuals. Figure 10b shows an overview of the proposed project within the Akabahizi site, the buildings’ alignment, vegetation covers around the roads, and houses leading to the sustainability of the building. Using long-lasting and ecologically friendly building materials is another aspect of sustainable GB that should be included in the design [12,25]. Using locally obtained materials reduces transportation-related carbon emissions and boosts the local economy, such materials are stabilized earth blocks and recycled materials (Figure 10c,d). These materials are frequently more economically and culturally feasible for locals, for instance, in Akabahizi village, shifting from corrugated metal roofing or stabilized earth blocks can improve durability, lessen its negative effects on the environment, and offer thermal insulation [120]. The sustainability of residential structures in Akabahizi village is affected by multiple design variables, and climate factors. Design variables like building envelopes, orientation, and layout are essential for increasing energy efficiency and ensuring comfort in residential settings. The proposed community design for residential buildings in Akabahizi focuses on integrating open-air courtyards to enhance health, well-being, and passive cooling.

Figure 10a employs a color-coded key to represent various features in the proposed community. The red areas indicate the locations for proposed residential buildings, designed to enhance community living. Green zones highlight areas where bamboo trees will be planted along the riverside, serving as a buffer for conservation. Blue marks outdoor low-emission traffic parking areas, promoting sustainable transportation options. Meanwhile, light green sections represent the existing site river, which is crucial for conserving the Mpazi river ecosystem. Yellow areas are designated as buffer zones for recreational purposes, enhancing community space for leisure and activities. The purple areas illustrate proposed public gathering spots, fostering community interaction. Light blue routes denote “middle zero-emission” paths aimed at optimizing circulation and minimizing noise, while the darker blue routes indicate “side zero-emission” paths, which are also focused on improving circulation and reducing noise levels throughout the community. Collectively, these color codes provide a clear visual representation of the community’s planned layout, which prioritizes sustainability and social interaction.

(b)

Orientation and layout

The layout consists of seven community blocks with entrances aligned to the site’s orientation, featuring stepped massing models that improve the central public gardens, which are equipped with pavilions and playgrounds. A comprehensive transportation system featuring bicycle paths, pedestrian walkways, and a main road with bus stops supports community mobility. Each block includes mixed spaces: residential, commercial, and healthcare, centering a courtyard with native greenery. The buildings are strategically oriented to maximize energy efficiency and ecological performance, improving natural light and ventilation. The careful orientation and layout of the buildings are critical for enhancing energy efficiency and environmental performance, improving the availability of natural light, ventilation, and cooling through strategic alignment with prevailing winds [121]. Furthermore, adopting more compact geometries such as squares or rectangles reduces heat transfer, making these configurations particularly advantageous in colder climates, ensuring increased thermal efficiency during warm and cool seasons [122].

(c)

Building envelope

The building envelope is crucial for influencing internal comfort and external environmental conditions. It encompasses all components that separate a structure’s interior from its exterior, including walls, roofs, and floors. A well-designed envelope regulates thermal gain and loss throughout the year [103,123]. The proposed design can efficiently control indoor temperatures by utilizing high-quality insulation materials with significant thermal mass, such as masonry, concrete, and bricks. These materials capture thermal energy during the day and release it at night, maintaining comfort while reducing energy loss [30]. The insulating qualities of these materials ensure that structures consistently maintain pleasant temperatures, ultimately minimizing dependence on mechanical heating and cooling systems [106]. This approach enhances occupant comfort and contributes to the overall sustainability and efficiency of buildings in the Akabahizi community.

Table 3. Key to understanding the spatial organization and land use designations within the master plan.

Two-Dimensional Masterplan Key Words (Figure 10b)
1	Existing study area river (the conservation of the Mpazi river ecosystem)	B1	Building block volumetric mass (the community proposed a building massing block with a central courtyard)
2	Bamboo trees to be planted on the riverside reserved for the buffer zone according to the master plan of Kigali	B2	Building block volumetric mass (proposed strategy massing model block with courtyard)
3	Existing bridge	B3	Building block volumetric mass (proposed strategy massing model block with courtyard)
4	Buffer zone reserved for the recreation area	B4	Building block volumetric mass (proposed strategy massing model block with courtyard)
5	Low-carbon circulation paths—a perspective view of a community garden featuring outdoor elements, including a public bench set within the community and surrounded by low-carbon	B5	Building block volumetric mass (proposed strategy massing model block with courtyard)
6	Outdoor low-emission traffic parking	B6	Building block volumetric mass (proposed strategy massing model block with courtyard)
7	Smart bus shelter	B7	Building block volumetric mass (proposed strategy massing model block with courtyard)
8	Middle zero-emission route optimizing circulation and minimizing noise	G	Proposed community gathering area: public garden
9	Existing site access to the main road	G1	Kids’ gathering space—an ecocave designed for daycare and play activities
10	Rainwater channeling	G2	Wooden open pavilion structure—a perspective view of the proposed design strategy, featuring a community wooden pavilion and an indoor ecocave designed to host adult gatherings
11	Side zero-emission route	G3	Adult gathering space
12	Community school bus stop

outlines key land use designations and their functions within the master plan. It includes descriptions of various community features, such as proposed residential blocks, public gathering areas, and recreational spaces along the Mpazi River. Additional elements include low-emission parking, community transit hubs, sustainable transport routes, and primary access roads, promoting environmentally friendly transportation and community connectivity.

Sustainable Materials of Choice for Proposed Building Design

Sustainable building practices are increasingly recognized as essential for addressing environmental challenges and enhancing the resilience of communities. The act of choosing sustainable materials for construction is crucial, and careful consideration must be taken, especially for locally available materials and recyclable materials to reduce economic burden and minimize waste production; however, most importantly, environmental protection should be given top priority [36,65,71,72,124]. In Rwanda, the construction sector has traditionally relied on concrete, clay bricks, stones, earthen blocks, and timber. However, these materials often carry significant environmental costs, including high carbon emissions during production and transportation. Accordingly, the government of Rwanda has acknowledged these challenges and is actively promoting a shift towards more sustainable building practices. The GB Materials Code of Standards (GBMCS) was established to encourage the use of locally sourced and ecofriendly materials to balance economic development with environmental sustainability. This research study focuses on sustainable materials in the proposed master plan for community blocks, such as masonry bricks, rammed earth, wood, bamboo, and stone.

(a)

Foundation

The foundation design used in this proposed project conforms to the steeply sloped landscape by following its natural contour. It integrates two locally sourced materials, stones and concrete (aggregate, cement, and water). The cut-and-fill technique optimizes the terrain’s utilization, minimizing excavation waste while providing a stable building foundation. This method improves structural stability and decreases the overall carbon footprint by reducing the need for extensive material transport and consumption.

(b)

Structural frame supporting system

The structural frame comprises concrete footings and columns, showcasing an innovative composite approach. The footings are constructed using a hybrid method: half are filled with concrete, while the other half are compacted with stones. This technique effectively reduces the required concrete while enhancing distribution and stability. By optimizing material usage in this manner, the project aligns seamlessly with sustainable construction practices, ensuring a robust and environmentally friendly structural framework.

(c)

Slab construction method

The design prioritizes structural efficiency by utilizing ribbed, waffle, and hollow concrete block slabs for two-way spans (Figure S16). These methods are highly efficient in accommodating typical living loads while minimizing structural demands. For example, ribbed slabs enhance performance by reducing the volume of concrete in the tension zone, substituting it with hollow blocks or voids. This method is based on the characteristics of concrete, which exhibits minimal tensile strength, thus ensuring that tensile stress is transferred solely to the reinforcements. The adopted slab types significantly reduce self-weight, which is especially beneficial for long-span constructions exceeding 5 m. Using ribbed and waffle slabs alleviates the need for extensive foundations and mitigates vibration issues, fulfilling contemporary architectural goals of sustainability and efficiency.

(d)

Load-bearing walls made of brick masonry

Approximately 80% of the load-bearing walls are crafted from locally sourced masonry bricks (Figure S17), supporting GB practices and contributing to indoor thermal comfort via the material’s excellent insulating properties. Durable and aesthetically appealing, masonry bricks enhance the overall stability of the structure while minimizing maintenance needs. This traditional material also fosters local craftsmanship, supporting community development and resilience. Based on climate analysis, perforated brick walls are incorporated into the design to create shading while allowing for cross-ventilation.

(e)

Rammed earth materials

The construction of interior partitions and exterior walls incorporates stabilized rammed earth mixed with 6% cement (Figure S18). This approach not only ensures stability and durability but relies on locally sourced materials, which contribute to the thermal mass of the building and aid in regulating indoor temperatures. Using rammed earth is aligned with GB practices and promotes environmental sustainability, particularly in unplanned urban areas in Rwanda. The process encourages the use of aggregate soils that are excavated from local communities, thus fostering a circular economy while minimizing transportation emissions [125].

(f)

Finishing and outdoor paving

Clay tiles are employed for flooring, while bamboo is used for ceilings, creating a natural and sustainable aesthetic. Windows and doors are crafted from wood, ensuring durability and a strong connection to local materials. Most pathways utilize stones leftover from other construction activities, promoting recycling and minimizing waste. Masonry bricks are proposed for paving in public garden areas, enriching durability while maintaining aesthetic coherence with the overall design. (Figure S19) This combination not only enhances the visual appeal of the interiors but promotes sustainability by using renewable resources that support local craftsmanship and reduce environmental impact.

Passive Cooling Techniques

A cornerstone of the proposed design is the implementation of passive cooling techniques, which are essential for maintaining indoor comfort while minimizing energy consumption. The proposed design employs an array of passive strategies, including natural ventilation, shading, lighting, and efficient water management, to enhance overall energy efficiency and indoor comfort [115].

(a)

Natural ventilation

Natural ventilation allows the buildings to capitalize on wind and thermal buoyancy to promote airflow (Figure S20). Operable windows, vents, and strategically positioned openings facilitate cross-ventilation, maximizing indoor air circulation. Double-hung windows allow cool air to enter from the bottom while expelling warm air from the top, ensuring a continuous fresh air flow. Furthermore, tall windows and high ceilings enhance natural ventilation, providing comfort even during still outdoor conditions.

(b)

Shading strategies

The design optimizes energy use through the effective solar orientation of the building (Figure S21). In colder seasons, it harnesses solar heat gain from the southern sun while minimizing west-facing windows to reduce cooling loads during hotter months. Deciduous trees planted to the south and west provide essential shade and serve as passive barriers against high wind pressure and solar radiation, allowing sunlight to filter through in colder months, thus promoting warmth and light. Shades can keep the heat and glare of direct sunlight from coming through windows. They can also keep direct sunlight off walls or roofs, reducing cooling loads. The most common form of shade is an exterior fixed horizontal overhang. These are used on the side of the building facing the sun’s path, sometimes including east and west faces. However, east and west faces often need vertical fins to avoid low-angled sun. Shading can be designed to allow the sun’s light and heat into the building at some times of day or year while rejecting it at other times. The simplest method for this is to use a fixed horizontal overhang of which the width is calculated to shade during summer, when the sun is high, and allow sunlight in winter, when the sun is at a lower angle.

(c)

Natural lighting

Natural lighting is a key design aspect achieved through strategically placed openings engineered to maximize daylight penetration into indoor spaces (Figure S22). Each building area is oriented to optimize exposure to natural light, significantly reducing reliance on artificial lighting and enhancing the overall ambiance of the environment. For these openings, the use of low-e (low-emissivity) glass is highly recommended. This specialized glass features a heat-resistant coating that reflects heat while allowing abundant natural light to enter [123]. The integration of low-e glass not only improves the thermal performance of the building but contributes to its sustainability by decreasing energy consumption associated with cooling and artificial lighting. By prioritizing natural lighting and incorporating energy-efficient materials, the design fosters an environment that is both comfortable and environmentally responsible. This approach aligns with broader sustainability goals, ultimately leading to reduced energy costs for residents and a diminished ecological footprint for the building [123].

(d)

Noise-mitigation strategies

The building design incorporates materials selected for their sound-resistant properties (Figure S23). Community blocks and strategically planted landscaping, such as trees along community boundaries, act as natural sound barriers, improving the acoustic environment. Additionally, careful traffic management within the community, including designated traffic flow measures and promoting hybrid vehicles, will significantly minimize noise and emissions. In green building design and implementation, trees play a crucial role in controlling environmental noise, reducing wind intensity, providing shade, and cleaning the air by accumulating carbon dioxide. Apart from planting trees, mainly bamboo, the study suggests the introduction of electric vehicles for sustainable management of noise and a long-term solution to climate change by reducing greenhouse gas emissions [126,127].

(e)

Energy-efficiency measures

In this design, buildings oriented towards the east and south attract morning and midday sunlight, while west-facing structures benefit from late afternoon sun (Figure 10a,b). This strategic placement optimizes natural lighting and enhances passive solar heating, especially during colder months. Roofs are designed to accommodate solar panels (Figure 11a,b) strategically aligned for effective sunlight capture. This integration of solar energy not only contributes to lower electricity consumption but promotes environmental sustainability by reducing reliance on nonrenewable energy sources [119,128]. A study on sustainable building in Nairobi, Kenya [129] showed that this method of integrating PV cells for solar energy can produce enough energy for buildings to the extent of zero reliance on another source of energy, converting the building into a net-zero-energy building, particularly enhancing environmental sustainability.

(f)

Sustainable drainage system

The design incorporates a sustainable sponge city drainage concept using short channels lined with stones to manage rainwater efficiently (Figure S24). This method enhances natural filtration, promotes rainwater retention, and allows for recycling in underground tanks, helping to mitigate soil erosion and flooding risks while supporting the conservation of the Mpazi River. The upgraded drainage system directs rainwater toward the river and increases its capacity to manage heavy rainfall, reinforcing the community’s resilience against natural hazards. By emphasizing nature-based solutions, the design promotes improved resident comfort, environmental sustainability, and the conservation of the Mpazi River ecosystem, advocating for greener living environments in Kigali’s informal settlements.

(g)

High Point’s natural drainage system

This system, which informed the drainage system used in the master plan herein, beautifies streetscapes and parks while naturally managing storm water, improving water quality for residents, and protecting valuable environmental assets (Figure S25). This system treats stormwater runoff in an ecologically sensitive way and enhances the quality of water draining to Longfellow Creek. Since 8% of the storm water in Longfellow Creek falls on the ground at High Point, the neighborhood is a crucial part of the comprehensive community effort to restore this creek as a vital fish habitat. Improving the water quality of Longfellow Creek is a deep point of connection between the new community and the rest of West Seattle.

Greenery and Landscaping Strategy

The integration of greenery and landscaping plays a crucial role in enhancing the thermal comfort environment and reducing interior temperatures within buildings [65,70,71,97]. In this design, the planting strategy focuses on trees and landscapes that support environmental goals and enhance the conservation of the Mpazi River ecosystem. The Mpazi River surrounds the site and is vulnerable to soil erosion, particularly during the rainy season. This erosion is exacerbated by informal residential developments that fail to manage rainwater effectively, leading to uncontrolled drainage directly into the river. To address these challenges, the new urbanization master plan for Kigali establishes a 50 m boundary around the Mpazi River as a recreational zone (Figure 12a,b). This zoning encourages the community to connect with nature while promoting sustainable practices.

As part of this strategy, bamboo trees (Figure 12c,d) can be planted along the riverside to stabilize the soil and prevent erosion, aiding in preserving the river and its surrounding ecosystem. Furthermore, pedestrian pathways are designed to facilitate movement throughout the community, transforming open spaces into recreational areas without building structures. This approach encourages community interaction with nature, improving residents’ quality of life while supporting the health of the Mpazi River ecosystem. The design tackles environmental issues and fosters a harmonious relationship between the community and its natural environment through these integrated measures.

Transportation and Workability

The proposed design emphasizes sustainable circulation within the community, aiming to achieve a GB strategy [65,70,97]. This study identified challenges related to inadequate traffic management and road networks, which are being addressed through ongoing government upgrading projects. The new master plan incorporates a spatial organization that allows each community block access to improved road networks (Figure 13a). Given the low-income status of many residents, who typically do not own cars, the plan prioritizes walkability, enabling residents to reach their workplaces on foot. Additionally, bus stops are strategically placed throughout the community, with public buses directed to access from the eastern main road rather than the junction roads, which are primarily surrounded by residential buildings (Figure 13b–e). To enhance traffic flow and minimize noise, the design includes one-way junction roads and dedicated pathways for bicycles and pedestrians, promoting a culture of mobility that is friendly to both nature and users. The plan fosters a community environment that supports healthy lifestyles and greater connectivity by structuring sustainable circulation and implementing effective traffic flow measures.

3.2.3. Simulation Analysis of Proposed Design

Solar Path Analysis

Using a solar path diagram, the 3D solar access analysis (Figure 14a) shows a proposed building’s interaction with sunlight throughout the year. The diagram illustrates the sun’s trajectory, allowing assessment of solar exposure at different times and angles. This analysis informed design choices related to window placement, shading, and materials to optimize natural light while minimizing heat gain. Green and red lines highlight optimal solar access periods. The results supported the design’s sustainability goals by improving thermal comfort and reducing reliance on mechanical systems for heating and cooling.

Building Daylight Factor Simulation Analysis

Figure 14b–d display the daylighting analysis of the building, visualized in a three-dimensional format. The color-coded scale represents the daylight factor, which ranges from 0.00 to 14.77. Areas depicted in blue daylight factors suggest insufficient natural light, while regions in yellow and red signify optimal lighting conditions. This analysis is essential for evaluating the effectiveness of natural light penetration into space, enhancing occupant comfort, and reducing reliance on artificial lighting, contributing to energy savings. The findings suggest that strategic adjustments such as optimizing window placement, increasing glazing areas, and improving light distribution can significantly enhance daylight access in dimly lit areas. In conclusion, the results indicate that the proposed design achieves a balanced daylighting solution. Simulation tests revealed that this design optimizes natural light access and improves overall energy efficiency, making it a highly effective option for residential spaces. This underscores the potential of buildings being designed to create comfortable, well-lit environments [100].

Thermal Performance and Energy Consumption Analysis

A simulation for annual temperature (air, radiant, operative) trends, heat gains/losses, and ventilation rates for the Akabahizi Sustainable Community Project, Kigali, Rwanda (1 January to 31 December) was performed using Energyplus (Figures S26 and S27), while ASHRAE 90.1 simulation was used for comparison of the annual energy consumption between the proposed building design and the ASHRAE 90.1 baseline (Figure S28). The monthly temperature variations (e.g., January: 25.77 °C, December: 28.02 °C) peaked in warmer months (e.g., February: 26.67 °C) and dipped in cooler months (e.g., July: 20.25 °C). However, the listed annual values in the figure (e.g., 4894 °C) were likely data errors or mislabeled cumulative metrics. Realistic monthly averages aligned with Kigali’s tropical climate, emphasizing the need for passive cooling strategies in densely built informal settlements. Glazing, walls, and ceilings showed uniform annual totals (4919 kWh each) suggesting aggregated yearly energy transfer. Monthly values, however, revealed seasonal dynamics. Positive values (e.g., +350.03 kWh in October) indicate heat gains from solar radiation or occupancy. Negative values (e.g., −748.93 kWh in July) signify heat loss, likely due to poor insulation or ventilation. Ground floors and partitions showed consistent losses, highlighting thermal inefficiencies in building materials.

The results for ventilation and infiltration rates (Mech Vent + Nat Vent + Infiltration) showed an annual average infiltration rate of 4902 ac/h, with monthly fluctuations (e.g., 0.63 ac/h in January vs. 0.66 ac/h in March) reflecting seasonal adjustments. Higher rates in warmer months may correlate with natural ventilation efforts to mitigate heat, while lower rates in cooler months suggest reduced airflow to retain warmth. Negative values (e.g.,−391.15 ac/h) could indicate pressure imbalances or simulation artifacts. The analysis provides valuable insights into the building’s energy behavior, providing valuable potential data for optimization of design strategies. The results of the ASHRAE 90.1 simulation indicate that the proposed design demonstrated a significant improvement, particularly in reducing the energy used for heating, cooling, and equipment operations, highlighting the potential energy savings achievable through the proposed design. The comparison serves as a valuable tool for validating design choices and guiding future modifications to align with energy efficiency.

Heating Design Analysis

The operative temperature (accounting for both air and radiant temperatures) was around 28.27 °C, with significant heat loss of 0.32 kW/m² for glazing (windows), followed by walls (0.22 kW/m²), and a considerable loss of 0.41 kW/m² for the ceilings (Figure 15a,b). The relative humidity level remained 100% (Figure 15c,d), and the ventilation rate was 0.30 air changes per hour (ach). There was a comfortable indoor environment with regard to temperature; however, some improvements in insulation and sealing of windows and roofs to reduce heat loss are necessary, as well as practical design strategies that incorporate both natural ventilation and moisture control. Reducing energy expenditure through better thermal performance is crucial in enhancing comfort and sustainability, particularly in densely populated areas such as Akabahizi. Ensuring effective energy management strategies will significantly improve living conditions and potentially lower energy costs for residents [111].

The annual hours of sunlight for all building floors (a) and for a single floor (b) in the proposed GB design for Akabahizi village, Kigali, Rwanda, are illustrated with a color gradient indicating sunlight exposure (Figure 15e,f), where blue represents zero hours and transitions through green to red, signifying maximum sunlight exposure of 3641 h annually. The sunlight distribution across multiple floors revealed areas that benefited from extensive sunlight, with some sections recording over 3041 h of sunlight, while others received minimal exposure, as low as 0 h. Some areas received up to 2637 h of sunlight for a single floor. This assessment is crucial for optimizing natural light and ventilation, essential components of sustainable building strategies, particularly in informal settlements where optimizing resources can significantly improve residents’ quality of life and energy efficiency.

3.3. Discussion: Comparative Analysis of Two Massing Strategies—Existing and Proposed Design

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In terms of sustainability, the existing government-mandated typology model (Figure 16a) depicts traditional building strategies with conventional layouts that meet basic functional needs but do not optimize natural resources or enhance community well-being. The analysis highlights how building geometry affects energy consumption, daylight access, and thermal comfort, revealing that existing designs limit resource efficiency and community sense.

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In contrast, the proposed courtyard design (Figure 16b) features a model utilizing advanced simulation software (DesignBuilder and EnergyPlus, version 7.0.2.006) to assess sustainability performance. This design integrates variables such as building orientation and footprint to establish benchmarks for energy efficiency and environmental impact. The simulations identified enhancements that can significantly improve resource efficiency and occupant comfort. In promoting courtyard designs, the analysis addressed the limitations of traditional layouts, showcasing the potential of environmentally conscious massing techniques. This study underscores the importance of innovative design in enhancing urban sustainability and contributes to strategies aligned with contemporary living needs. Ultimately, adopting courtyard designs can improve livability and sustainability in Akabahizi, fostering a more resilient urban environment [113].

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In terms of daylight factor analysis, Figure 16c represents the current design situation, characterized by simplistic cubic geometry with substantial deficiencies in natural light penetration, predominated by dark areas (blue and black) across the structure, leading to increased reliance on artificial lighting, higher energy costs, and adversely affecting occupant comfort as well as indoor environmental quality. In contrast, Figure 16d showcases a proposed design typology with more even distribution of natural light throughout space and improved illumination in central areas. Modifications such as altered configurations and potentially larger windows contribute to these enhancements, allowing daylight factors to reach up to 14.87 in some locations. This innovative design improves aesthetic appeal and fosters better living conditions by reducing reliance on artificial lighting [100,102,103]. The comparison between the two models underscores the critical role of thoughtful architectural design in informal settlements, highlighting how optimized natural light can significantly enhance the well-being of residents in Akabahizi.

The proposed design represents a progressive step forward in aesthetics, functionality, sustainability, community involvement, infrastructure integration, adaptability, and regulatory compliance, ultimately contributing to a more vibrant and livable urban environment in Akabahizi.

4. Conclusions and Recommendations

4.1. Conclusions

The transition from traditional building practices to sustainable design in Akabahizi village marks a crucial step in addressing the challenges related to an increase in urban informal settlements in Rwanda. The design of existing building initiatives mandated by the government incorporates essential infrastructure; however, some issues encountered, particularly the lack of health clinics and recreational facilities, need to be addressed to improve the accessibility of the community to medical care and recreational opportunities. The introduction of the courtyard concept in the design of the Akabahizi residential building will particularly overcome those issues encountered in the existing government-mandated topology model and significantly enhance both environmental sustainability and community well-being in informal settlements. This study emphasizes the need to reimagine courtyard spaces as integral components in the pursuit of sustainable urban living, contributing to the overall transformation of Akabahizi into a model for ecofriendly residential communities.

4.2. Recommendations and Future Research Developments

The survey’s predominance of male professionals and low number of middle-aged participants may skew perceptions of community needs; future studies should consider more residents and marginalized voices.

Overcoming the problem of growing informal settlements will need both education and collective effort between all professionals involved in design and construction:

• Educational institutions and professional organizations should focus on training on sustainable technologies such as LEED and BREEAM to make the knowledge of sustainable design practices more accessible for design and construction professionals.
• All professionals involved in design and construction should stay updated on the latest sustainable technologies and collaborate closely with community organizations to foster holistic approaches to sustainability, emphasizing integrated design that aligns with local needs and regulations.
• Building codes that prioritize energy efficiency, water conservation, and the use of sustainable materials should be established and enforced to ensure sustainability in all new constructions.

This study was carried out in Rwanda, a developing country facing the issue of informal settlements. It can be used as a model to address challenges associated with informal settlements in any developing country. The methodology and recommendations provided in this study can be a good foundation for any researcher who seeks to work on a similar project to improve life conditions in areas with informal settlements.