Perspective Chapter: Promoting Circular Design Strategies in Housing Delivery in Nigeria

Abstract

Circular economy principles are gradually replacing the linear economy model, which has been found to promote waste and resource inefficiency. The circular model is of particular interest to the built environment due to its benefits in resource optimization and waste minimization. Given the huge housing deficit in Nigeria and the attendant resources needed to mitigate the deficit, circular strategies are apt for the massive housing delivery required to bridge the deficit. This chapter examines the concept of circular economy as it affects the built environment. Specifically, design strategies that tend to promote circular housing delivery are examined. The public housing delivery process in use in Lagos, Nigeria’s most urbanized city is evaluated to ascertain its alignment with circular principles. The study found that even though opportunities exist for the massive deployment of circular strategies, its adoption is still very low. The chapter recommends more deliberate actions at the design and implementation stages of housing projects to promote circular economy for the housing sector in urban Nigeria.

1. Introduction

Housing is a basic need of human beings and a significant part of the infrastructural requirements of any society. The housing sector constitutes about 38% of the construction industry globally [1]. Over the years, concerns about housing have been directed at availability, adequacy, affordability, and sustainability. Housing availability is a major challenge as housing deficit has been ascribed to some major global challenges, especially population growth and urbanization [1, 2]. Already, more than 50% of the world’s population currently lives in urban areas with a future projection of approximately 70% by the year 2050 [3]. This growing population will require functional facilities to sustain livelihood of which housing is one of the most prominent.

Responding to the housing deficit effectively will result in high resource extraction and utilization, which are often associated with negative environmental impacts. Hence, mitigating the impact of housing delivery is important in the efforts to provide adequate housing. Hence, emphasis is shifting toward sustainable options in housing delivery. In this respect, life cycle assessment (LCA) has become a widely accepted methodology for estimating the environmental impact of housing provision toward ensuring sustainability [4]. However, the LCA approach has some limitations, especially with respect to its close affinity with the linear materials and energy flow model as against the circular economy model, which has become a preferred option.

In order to promote sustainability through efficient resource utilization, the circular economy (CE) approach has gained ascendancy. CE refers to an economic growth model that prevents environmental degradation by promoting resource efficiency through waste minimization and adoption of regenerative and restorative practices as against end-of-life approach [5]. The concept is, therefore, closely linked to the sustainable development goals SDGs through Target 12.5, which seeks to substantially reduce waste generation through prevention, reduction, recycling, and reuse (3Rs). The circular economy approach when extended to the housing sector seeks to improve sustainability of housing through the use of circular materials, adoption of circular design strategies, reduction of waste in the housing delivery value chain, and adoption of regenerative strategies in housing design and delivery using innovative processes [2].

In the building and construction industry, the design stage has been recognized as the most efficient and effective stage for adopting sustainable practices in which CE strategies can be explored [6, 7]. According to Fatourou-Sipsi and Symeonidou [8], sustainable building design has become necessary with the enormous environmental impact of the building construction and demolition. It has been estimated that CE will result in 4% of economic growth by 2030 in the EU countries [9]. Hence, the EU through the European Green Deal is active in pushing for a more sustainable Europe [10, 11]. However, developing economies in Sub-Saharan Africa, especially Nigeria, are still grappling with the uptake of sustainable buildings. It is, therefore, necessary to fast-track the uptake, especially in the housing sector through the route of CE adoption.

In Nigeria, housing deficit has been estimated to be up to 20 million [12]. In addition, awareness of circular economy is growing in Nigeria [13]. However, solid waste management practices appear to dominate discourse on circular economy in the Nigerian context [14, 15, 16]. Meanwhile, the construction industry is growing with technology adoption remaining rather rudimentary in the housing sector. The construction waste implications associated with low technology adoption in the housing construction sector can be very profound. This presents an opportunity to evaluate the prospects of circular design strategies in the Nigerian housing sector. Hence, relevant literature were deployed to underscore circular strategies applied to the design of housing. Built examples of public housing in Lagos, Nigeria were also evaluated to determine the extent of alignment with circular design and construction principles. Given the push towards sustainable buildings in Nigeria and the gradual ascendance of life cycle assessment studies in the Nigerian built environment, the current paper also makes good effort to align circular design strategies with the LCA framework.

2. Circular economy and the built environment

The primary objective of circular economy is to change materials use from the linear model to the circular model. The linear model is a straight-line flow of materials from extraction of raw materials to product use and ultimate disposal to landfill or through incineration at the end of the product life cycle. The circular model promotes use and reuse of materials, through a process usually referred to as “closing the resource loop.” In addition to closing the resource loop, circular strategies can also lead to “narrowing” or “slowing” of resource loops thereby improving the efficiency of processes and extending the lifespans of products [17].

In a linear economy, goods are designed for a single lifetime and disposed of at the end of their useful life (cradle-to-death). In contrast, a circular economy aims to eliminate the concept of waste altogether through continuous use of materials. The idea is that the material from the end of one product’s life cycle acts as the input for another product’s life cycle (cradle-to-cradle). As a result, demand pressure for virgin material is greatly reduced, thus leading to resource optimization. CE slows down the depletion of natural resources and reduces environmental damage resulting from material extraction and processing of virgin materials [18].

Circular design is at the service of a circular economy. Design is the basis of all innovations in products, services, and systems. Circular design is the application of circular economy principles at the design stage of any product, service, or system. It has been estimated that about 80% of a product’s environmental impact is determined by the design process [19]. Hence, designing products for reuse can reduce materials and environmental costs. In addition, it has been estimated that over 70% of a product’s life cycle costs and environmental footprint are determined at the design stage [20].

Circular design is of particular interest to the built environment. This is so because the built environment is known to be a heavy consumer of resources and energy, as well as a heavy emitter of carbon dioxide and the attendant consequences to the environment. Specifically, the built environment consumes about 50 percent of global materials resources, 50 percent of energy resources, 40 percent of global water use, and 60 percent of prime land, as well as 70 percent of global timber products [21]. More recent estimates put resource use and waste generation by the built environment at about 40% [22]. In addition, the United Nations Environment Programme [23] estimated that the building and construction sector accounted for 35% of global energy use and 38% of all energy-related carbon dioxide emissions in the year 2019. Hence, the built environment needs strategies to reduce its environmental impact in terms of resource utilization, energy use, and carbon dioxide emissions.

Sustainability has been adopted as a preferred development paradigm to ensure efficient resource use while minimizing waste generation in the built environment. In addition, the metrics deployed in the assessment of sustainability have also evolved and can be grouped into three main categories as enunciated by Forsberg and Von-Malmborg [24]. As a result of these metrics, sustainable buildings have evolved, resulting in the reduction of the environmental impact of buildings and the built environment as a whole. However, sustainable buildings have limitations in the sense that they are based on the linear model, which follows the life cycle path of design, construction, use and disposal [25].

Similarly, uptake of circular buildings can be facilitated through adoption of appropriate metrics. In broad terms, Attia and Al-Obaidy [26] identified four primary criteria for assessing the circularity of buildings namely: carbon footprint of building materials used, reused content of the building materials, disassembly potential and longevity of the building, and building design flexibility and longtime use.

Circularity metrics can be applied at micro-, meso-, and macro-levels. At the micro- or product level, one of the popular metrics for measuring circularity is the material circularity indicator (MCI) as articulated by the Ellen MacArthur Foundation [27]. Other indicators include Material Efficiency Metric, Circular Economy Indicator Prototype, and Circularity Potential Indicator [28]. Meanwhile, Drager et al. [29] referred to six circularity metrics aimed at actualizing the major objectives of circular economy as enunciated by the European Environment Agency. These objectives of circularity metrics were further summarized into three categories namely: protection of materials stock, protection of the environment, and value retention [30].

One thing that is clear with respect to circularity metrics is the plethora of methods available. It has been observed that this multiplicity of metrics can be conflicting and even confusing, and may sometimes lack clarity [31]. In response to the foregoing, the World Business Council for Sustainable Development (WBCSD) developed a comprehensive indicator-based metric for measuring all aspects of circular economy [32, 33]. The WBCSD framework also referred to as circular transition indicators (CTI) comprises a suite of indicators grouped into three broad categories. The first category (close the loop) measures the effectiveness of closing the material loop, while the second category (optimize the loop) demonstrates how material recovery strategies are optimized. The third category (value the loop) demonstrates the business value derivable from applying circular strategies. The CTI framework aligns very well with the major principles of circular economy as enunciated by EMF as follows: design out waste and pollution, keep products and materials in use, and regenerate natural systems.

Given the differences between linear and circular approaches, it would appear that the metrics are parallel. However, it has been shown that LCA, which is the most scientific metric for linear systems, has some usefulness in circularity metrics. Brandstrom and Saidani [28] indicated that material-based circularity metrics align very well with LCA measures in some specific instances. Also, Saade et al. [34] underscored the complementary roles of LCA and circularity indicators in measuring sustainability, especially in relation to early design of urban projects. Similarly, Weidemann et al. [35] demonstrated the complementary roles of LCA and circularity indicators in measuring sustainability, especially in an industrial production context. Realizing that the closed-loop concept of CE does not always ensure environmental benefits, Mannan and Al-Ghamdi [36] demonstrated that LCA can be beneficial for assessing CE options in product design. Very importantly, Van Stijn et al. [37] proposed and successfully tested an LCA-based CE model for the assessment of circular building products.

3. Circular design strategies in housing delivery

From the literature, circular design strategies for housing delivery can be considered under nine subheadings. Most of the strategies are interrelated and complementary. For example, even though treated separately, design for standardization, prefabrication, and modularization are all related but slightly different concepts in circular design. In fact, prefabrication and modularization should ideally go together [38].

3.1 Design for standardization

Standardization is the repeated production of standard sizes and/or layouts of components or complete structures [39]. Design for standardization is deployed to achieve maximum resource and component recovery at end-of-life to support recycling and reuse. The key considerations to achieve design for standardization are avoiding material off-cuts and limiting the use of varying component sizes and the use of standardized connections between elements [40].

3.2 Design for prefabrication

Prefabrication can be referred to as the off-site production of standardized or customized components or complete structures [39]. Design for prefabrication is also known as design for off-site construction or modern method of construction (MMC). It enhances resource optimization by producing building components or the entire building under strictly controlled conditions. Digital technology, in recent times, has been used to optimize the design for prefabrication in the areas of generative design through building information modeling (BIM), parametric designs, and additive and robotic manufacturing [41]. Some countries, such as Hong Kong, North America, Japan, some regions in Europe, and China, have adopted industrialized housing construction through the embrace of design for prefabrication. Prefabricated housing has been employed in Poland since the 1960s; currently, more than 20% of its population lives in prefabricated housing [42]. In Nigeria, rate of adoption of prefabrication in housing is low even though critical stakeholders are familiar with the advantages that can be derived therefrom [43]. According to Silva [3], prefabrication and modularity in housing construction are cost-effective means of achieving affordable housing and also result in a reduction in environmental footprint, flexibility, and the possibility for future selective demolition and recycling.

3.3 Design for modularity

Design for modularity is deployed to achieve easy assembly and disassembly of building components through lean production of building component modules that cut down on time and are less labor-intensive [40]. Modularization is cost-effective and facilitates timely completion of projects as well as construction waste reduction [44]. Modular construction components are also linked to prefabrication, standardization, and system building. Also, Silva [3] investigated ways to implement circularity in the architectural design process that adopts the design for standardization, prefabrication, and modularity through a research-by-design methodology. This resulted in lesser environmental impact and space efficiency and also tended to support disassembly and recycling. The circular design strategies are summarized subsequently.

3.4 Reversible building design

Design for adaptability and flexibility is also known as reversible building design or transformable building design. Design for reversibility supports multiple resource life cycles by integrating other strategies, which includes the design for adaptation, modularity, standardization, prefabrication, disassembly, up-cyclability and adjustment, and flexibility [45]. According to Durmisevic [46], reversible building design protocol on resource circulation covers three main dimensions: functional (spatial), technical (structure), and esthetic (physical) alongside their associated design indicators. Functional reversibility is a design dimension that involves the change of use of space into another without recourse to further material or component use. Technical reversibility is concerned with the design approach that transforms the whole or parts of a building through the rearrangement of the structural components [45]. Design error has been identified as the major barrier to reversibility.

Design for flexibility can facilitate easy refurbishment in the housing sector to avoid untimely demolition through adaptation and material recirculation potentials at building end-of-Life (EoL), and building lifetime extension [47]. Through reversible building design in the housing sector, it can lead to high-value retention in the environment. A study established that reversible design can lead to a 14% reduction in greenhouse gas emission, which corresponds to 1740 t CO2-eq for building components, such as structural elements, foundation, and ceiling components, as evidenced in the study carried out by Kröhnert [47]. Similarly, Kröhnert [47] investigated the adoption of reversible building design principles in multi-story residence building components, which resulted in a reduction in embodied GHG emission, improvement in re-cyclability and re-usability of components, and retention of environmental value.

3.5 Design for reuse

Design for re-usability involves the direct reuse of elements, components, or the entire building with or no recourse to the introduction of additional resources in new construction. Design for re-usability is facilitated by integrating design for modularity, adaptability, flexibility, standardization, dimensional coordination, building reversibility, and specifying reclaimed materials. This can aid in climate change mitigation [47]. The adoption of expandable housing can facilitate the reuse of building components [48].

3.6 Design for disassembly

Across the literature, design for disassembly/deconstruction (DfD) is the most mentioned literature on circular building design [49]. It is a CDS that focuses on the activities that take place at the end-of-life of buildings to recover building elements and components for reuse thereby minimizing waste. The major impediment to design for disassembly is the use of irreversible connections between elements, and other major considerations for design for disassembly are reduced number of components, lightweight elements, avoiding binders, use of accessible connections, and the use of recyclable and reusable components [50]. Another CDS that works with DfD is the design in layers, and this assists in easy deconstruction. DfD supports adaptability, flexibility, and selective deconstruction. The adoption of design for the disassembly has been recognized to be effective in the management of building components for future reuse, which is to be incorporated in the design of new construction at the early stage [8].

3.7 Use of reclaimed or bio-based materials

This is a design strategy that involves the integration of recycled or reclaimed materials or components or the specification of bio-based or circular materials in a new building wholly or partly to enhance the closing and slowing of the resource cycles. Bio-based materials possess several advantages that dispose of them for use as circular materials [51]. In regions with a large stock of buildings for renovation, bio-based products can be deployed to contribute to circularity [52]. It has also been shown that agro-industrial wastes can be converted to building materials thereby contributing to sustainability and circular economy [53].

3.8 Regenerative and restorative design

The regenerative and restorative concepts refer to two aspects of design that align with nature and promote natural processes. Sometimes, the scope of restorative and regenerative designs can extend to socio-technical systems as a wider context within which buildings are situated [2]. Similarly, they refer to integration of building design with natural and natural support systems such as green and gray infrastructure to achieve a harmonious relationship between building and the natural ecosystem [54]. While restorative designs aim at restoring ecological systems to a healthy state, regenerative designs aim at enabling ecological systems to maintain a healthy state [55, 56]. It, therefore, implies that restoration is ameliorative while regeneration is preventive. In addition, Petrovski et al. [57] investigated the adoption of regenerative design principles in the design and construction of a residential building for refurbishment in Spain through a case study approach. The study revealed reduced costs and minimized environmental impact of the refurbishment process.

3.9 Design for energy efficiency

All energy in their most rudimentary and primary level is derivable from nature even though it exists in various forms. Energy efficiency can be examined both from the embodied and operational dimensions. At the operational level, energy efficiency entails use of low energy-consuming appliances, while at the embodied level, it entails use of low-impact materials for buildings. It can also be considered from the perspective of passive and active strategies. While passive strategies promote natural solutions, active strategies deploy technology to achieve efficiency. Integration of passive strategies and circular design principles has been shown to be complementary to promoting resource efficiency in buildings [58]. In addition, the use of renewable energy is a major component of circular economy as it ensures minimal use of fossil-based fuels and a cleaner energy regime [18, 59].

4. Housing challenge and delivery in Nigeria

Affordable housing has become a major concern in Nigerian urban areas. The urban poor constitutes approximately 50% of the Nigerian population living in urban centers [60, 61]. The urbanization rate is inversely proportional to the quality and quantity of housing in Nigeria with a total population currently estimated at 262 million [62]. According to Refs. [61, 62, 63], the Nigerian housing sector has been adjudged as unsustainable due to a myriad of challenges. These challenges have given rise to the formation of informal settlements at both the urban core and fringes [62].

Different approaches and various interventions have been employed by the Nigerian government in housing delivery over the years since the colonial era. They include housing for local workers and expatriates in the face of the bubonic plague of 1928 [64], the postindependence housing programs by the Federal Housing Authority, and subsequently followed by Public-Private Partnership [62, 65]. However, as indicated in Table 1 and further highlighted by Refs. [64, 67, 68], the housing deficit is spiraling and would require over 50 trillion in local currency terms to fix [69].

Year	Housing Deficit	Estimated Population
1991–1993	4–7 million	104 million
2007	8–10 million	145 million
2013–2015	16–17 million	178 million
2017–2019	18–22 million	184 million

Table 1.

Trend in housing deficit in Nigeria.

Source: [66].

As a way forward, Olubi and Aseyan [62] emphasized the need for locally inspired housing designs and construction methods using local materials and techniques in housing delivery to assist affordability. Alabi and Fapohunda [70] also advocated for the adoption of cost-reduction strategies, which can stem from the use of locally available materials, the specification of reclaimed materials, and material optimization through design. The material cost of a building project is the major determinant of the construction cost and poor workmanship during the construction phase result in high maintenance cost [70]. Using environmentally friendly construction materials such as timber, compressed earth bricks, lime, hemp, hydra form, stone, cob, and rammed earth will assist in achieving sustainability in the Nigerian housing sector [71]. Also, Okoye et al. [67] pointed out the roles of design strategies in affordable housing delivery in Nigeria and further identified that architectural design influences the affordability and simplicity of core houses.

The adoption and implementation of strategies that align with sustainability and affordability in housing delivery have been heralded to be beneficial to the housing sector globally [71]. Of added importance to the Nigerian housing sector is the adoption of circular strategies. The adoption of circular design for sustainable affordable housing aligns with SDGs 11, 12, and 15 [3, 72, 73]. This is a sustainability dimension that needs to be scaled up in the Nigerian context.

According to Refs. [45, 47], CE is a growing area of research in housing delivery that spans from material to city-scale dimensions. Limited investigations exist on CE in housing delivery [45, 47]. The adoption of circular design in the Nigerian housing delivery system will orchestrate the development of new cutting-edge technologies and economical construction methodologies, which have been found advantageous in the delivery of sustainable and affordable housing for low- and middle-income earners [74]. It was projected that the deployment of economically efficient technologies in housing delivery can lead to a 26.11% reduction in the cost of building [74].

5. The context of Lagos

As the most urbanized state in Nigeria, the housing challenge in Lagos is obvious. The housing deficit in Lagos has been estimated to be about 16% of the total estimated deficit in Nigeria [75]. It has been estimated that Lagos has a housing need of 4.69 million housing units with a housing stock of 1.49 million units, thus leaving a deficit of 3.2 million housing units [75]. Multiple stakeholders are involved in the Lagos housing market, which is dominated by private individuals and organizations. However, government plays the role of policy formulator and regulator.

As part of the social function of government, the Lagos State government has also been actively involved in public housing provision. It has been estimated that between 1999 and 2020, over 7,000 housing units of different typologies have been provided by the Lagos State Government [76]. The first phase of the program was targeted to deliver 3632 housing units in about 13 locations in the city of Lagos (see Table 2). Additional units are provided on a continuous basis through direct budgetary allocation and through public-private partnerships. Seven thousand units of housing were projected to be delivered at the end of 2022 under the Lagos HOMS program. Hence, more units are being added as new estates or as extensions to existing ones. However, the units have largely maintained the original design and procurement procedure in the last 10 years.

Location of Estate	Number of Blocks	Number of units
Igbogbo	22	264
Sogunro 1	12	144
Sogunro 2	8	96
Shitta	3	36
Igando	41	492
Omole	7	84
Magodo	4	48
Lekki 1 & 2	15	180
Mushin	5	60
Ilupeju	10	120
Sangotedo	45	540
Agbowa	70	560
Ijora-Badia	—	1008
		3632

Table 2.

Distribution of Lagos HOMS estates phase 1.

Source: [77].

The key delivery strategies include direct construction of housing, site-and-services schemes, and access to mortgage facilities, among others. Since 2012, the Lagos State Government under the coordination of the Ministry of Housing has been providing housing to residents through the Lagos Home Ownership and Mortgage Scheme (Lagos HOMS). The scheme provides access to both the housing units and the mortgage facilities needed to secure the housing units. The scheme is a multiagency scheme involving key players such as Ministry of Housing, Lagos State Development and Property Corporation (LSDPC), Ministry of Physical Planning and Urban Development, and the New Towns Development Authority (NTDA). The mortgage component is facilitated by the Lagos Building and Investment Company—Mortgage Bankers [78]. Another variant of the scheme is the rent-to-own system where occupants pay rent for a stipulated time after which ownership is transferred to them [79]. About 70% of the public housing provided from 1999 was done under the Lagos HOMS program. Hence, the Lagos HOMS project is used as an index to examine the extent of circularity in the provision of the housing schemes.

From previous empirical studies on the reduction of waste associated with buildings in the study area, the approaches considered most valuable by built environment experts include design for standardization, disassembly, reuse, prefabrication, and modularity [80, 81, 82]. These approaches have been referred to as modern methods of construction (MMC). However, there is a well-defined planning and design component that precedes the construction phase. The underlying principle in this respect is resource optimization in terms of time, money, and materials. Most of the materials deployed in modern methods of construction are conventional materials but deployed innovatively. Also, an important aspect of resource optimization literature in the study area is the use of alternative materials such as renewable materials and materials made from byproducts of industrial and agro-based processing [83, 84, 85]. In addition, the use of renewable energy and the adoption of passive strategies are considered other avenues for optimizing energy-based resources in the study area [86, 87, 88, 89, 90]. From the foregoing, four planks can be isolated upon which the assessment of the selected public housing program can be based namely:

1. adoption of MMC and associated strategies,

2. use of renewable, bio-based, and waste-based materials,

3. adoption of renewable energy, and

4. deployment of passive and regenerative strategies

As a prelude, full description of the building and the procurement process is based on the understanding that the design process is critical in the adoption of circular strategies.

6. The Lagos HOMS project

The predominant typology is a rectangular plan with four floors accommodating twelve (12) residential units of various sizes.

Each floor of the prototype is made up of three apartments (one bedroom, two bedrooms, and three bedrooms). There are three staircases for the combined use of the occupants. Each block, therefore, accommodates mixed-income dwelling units rather than previous government estates that have separate sections for low-income and medium-income dwellers. This prototype has been retained over the past 10 years for subsequent housing units with only minimal modifications (Figure 1).

Figure 1.

Schematic layout of a block. Source: Adapted from [91].

The design intended to incorporate sustainable strategies such as natural ventilation, natural lighting, and use of low-impact appliances such as energy-saving electricity bulbs. However, the prototype design is a very compact design and devoid of the openness required in a warm-humid tropical environment. The compact design (as indicated in Figure 2) is effective in optimizing building materials used in the buildings. The highly optimized floor plan has minimal circulation area. In terms of emergencies, only the staircases are the escape route as balconies are nonexistent in the buildings. Rainwater harvesting and storage for use in washing and watering plants was also intended but this was not carried through to the implementation stage. The use of ducts for plumbing pipe installation facilitates easy maintenance.

Figure 2.

Compact arrangement of the blocks under construction. Source: [91].

Natural ventilation and lighting were fairly achieved in the building design. However, cross-ventilation as recommended for a warm-humid tropical environment was not fully achieved. In practical terms, cross-ventilation is deemed to have been achieved when a space has window openings on at least two sides. Specifically, the living rooms of the one-bedroom apartment and the two-bedroom apartment have limited opportunity for cross-ventilation. The atrium introduced in the building is not large enough to encourage substantial air flow. No shading devices were observed in the buildings as built. The lean-to-roof deployed for the project did not have deep overhangs to help shade the walls and openings. Meanwhile, the vegetative cover is low when compared with built-up areas of buildings and paved areas. Hence, passive design principles were not substantially applied (see Figure 3). The spacing between buildings is rather narrow relative to building height, which may impair effective air movement around the buildings. Hence, many of the occupants can afford to have opted for air-conditioning for thermal comfort in the buildings.

Figure 3.

A Section of the Lagos HOMS layout showing the closeness of the blocks. Source: [92].

The construction materials used were conventional materials and the technology adopted was mostly in situ construction technology. Table 3 depicts the materials deployed in the construction of the buildings. The buildings are made of reinforced concrete structural frames (columns, beams, and slabs) with sand-cement blocks as external envelopes and internal partition walls. All wall and concrete surfaces are rendered with sand-cement mortar. The roof structure is made of treated timber, while the roof covering is long-span aluminum roofing sheets. The lean-to-roof design optimized the materials used in the roofing when compared to prevailing roof designs in the study context.

Building Component	Main Material Used
Substructure	Concrete, reinforced concrete, sand-cement blocks
Frames and Upper Floors	Reinforced concrete
Walls	Sand-cement blocks (rendered)
Roof Structure	Treated Timber
Roof Covering	Aluminum long-span roofing sheets
Ceiling	Treated Timber noggins, PVC ceiling
Wall Finishes	Sand-cement rendering, emulsion paint, ceramic wall tiles for wet areas
Floor Finishes	Sand-cement backing, Vitrified ceramic tiles
Doors	Steel doors, timber doors
Windows	Aluminum-framed glass

Table 3.

List of components and materials used for the work.

Source: Adapted from [91].

Other materials include vitrified ceramic tiles for the floors and glazed wall tiles for the walls of wet areas. The ceiling is made of PVC ceiling tiles supported on timber noggins. External doors are steel doors fabricated and fixed with mortar-to-door openings. Similarly, windows are made of aluminum framed glass fabricated and fixed with mortar to the window openings. Internal doors are made of timber.

The estate road networks are paved with concrete interlocking stones. This helps to manage stormwater drainage within the estates. It also facilitates ease of maintenance without destroying the pavements as paving stones removed for routine maintenance can be reused in the making good process. Vegetative cover for the buildings is limited, which facilitates heat gain in the buildings emanating from the paved surroundings. As a result, residents are resorting to installation of air conditioners for indoor thermal comfort. Electricity supply is from the national grid, while water supply is from dedicated boreholes and associated storage facilities.

6.1 Adoption of MMC and associated strategies

The associated strategies refer to design for standardization, modularization, and prefabrication. They also include design for disassembly and incorporation of modern construction methods. The adoption of prototype design options disposes the housing scheme to standardization, modularization, and prefabrication. However, prefabrication was not deployed on a significant scale. Some floor components were prefabricated and installed at some of the Igando Lagos HOMS buildings (See Figure 4).

Figure 4.

Hoisting of Prefabricated Slabs. Source: [91].

With respect to design for reuse and disassembly, the in situ construction adopted for the projects hinders the possibility of disassembly of the building components and their subsequent reuse. The in situ reinforced concrete components cannot be reused or disassembled without full demolition. Similarly, in situ masonry walls cannot be disassembled and reused. The installations of doors, windows, and anti-burglary metal components are installed in such a way that some demolition of parts of the building must be carried out before the components can be removed. Such partial demolitions can impair the components and render them unusable subsequently. This also applies to building services installations water, drainage, and air-conditioning services. This is particularly challenging during routine maintenance work especially for building services.

In terms of construction methods adopted, the in situ construction methods characterized most of the building construction activities executed under the program. Hence, labor-intensive methods rather than technology-intensive methods were deployed in the construction of the buildings. Even though labor-intensive methods tend to be advantageous in terms of creating employment opportunities for the population, it often leads to so much waste that runs against the tenets of circular economy.

6.2 Use of renewable, bio-based, and waste-based materials

Specification of materials for the project favored conventional building materials as indicated in Table 3. Even though lightweight composite materials are lighter and faster to erect as partition walls, none were used for the buildings. High reliance on cement as a major building material makes the buildings less energy-efficient in terms of the embodied energy content of cement and cement-based materials. This can be mitigated by reducing the quantity of cement used in housing development by using cement substitutes usually referred to as supplementary cementitious materials (SCMs). There is also the need to adopt construction methods that would minimize the use of Portland cement and other energy-intensive materials. A number of alternative building materials that combine low embodied energy with speed of erection have been identified in Nigeria and they include interlocking bricks for mortar-less wall construction, expanded polystyrene panels for internal walls, and composite building panels for walls and ceilings. Similarly, bio-based materials most of which are by-products of agricultural processing have been found to be very useful, though poorly deployed in the Nigerian context. Apart from timber, no bio-based material was specified in the buildings.

6.3 Adoption of renewable energy

There is no planned integration of renewable energy whether at micro- or mini-grid levels. However, energy-efficient appliances were installed in the apartments. Given the household energy situation characterized by low access and increasing cost of available ones, the residents have on their own started the introduction of renewable retrofits in the buildings. However, this has not proceeded on an organized basis to accommodate all occupants. Going forward, renewable energy integration into the planning and implementation of the housing projects should be considered a priority so the buildings do not go into early obsolescence. The deployment of passive design principles is not profound as observed previously.

In order to make renewable energy integration effective, passive strategies must be deployed fully. Building orientation, cross-ventilation, and use of shading devices and elements among others should be brought to the front burner.

6.4 Deployment of passive and regenerative strategies

Passive design strategies such as building orientation, cross-ventilation, vegetative cover, shading devices, and roof overhangs can be better deployed in the buildings. The atrium can be made to play a bigger environmental role. The design objective was aimed at maximizing the use of the site due to the development pressure on land. Green spaces were few and far between, while the buildings are closely spaced together to increase density. Lagos has a small build-able land area relative to the population and housing needs. As a result, densification is a deliberate development policy of the government. Such dense developments would have benefited from the installation of green roofs and other similar green infrastructure installations. However, no green roofs or green facades are incorporated. Hence, the ecosystem regeneration strategies were not substantially deployed. The roof adopted a lean-to design, which helped to reduce the roof footprint, thereby conserving usage of roofing materials.

7. Conclusions and recommendation

This chapter underscored the importance of circular economy as the preferred direction for all human activities. The advantage of circular economy with particular reference to the built environment was highlighted. Specifically, given the impact of the built environment in terms of resource use and waste generation, circular economy principles were adjudged to be the panacea. Given the importance of housing in the overall built environment, circular economy offers positive prospects. The relevance of circular strategies in housing delivery within a developing country context such as Nigeria becomes more apparent. With housing deficit running into millions, the resource implication of bridging the deficit is huge. Adoption of circular design strategies can effectively mitigate the negative resource implication of bridging the housing deficit.

The study also evaluated an urban public housing program in Lagos, Nigeria’s most populous and urbanized city. It was found that opportunities exist for the adoption of circularity in housing delivery given the huge housing need. Adoption of modern methods of construction, which will incorporate the circular design principles of standardization, prefabrication, modularity, reuse, and design for disassembly, was identified as good approach to reducing the housing deficit. However, the prevailing building procurement process followed a rudimentary process of wet or in situ construction. Similarly, the design of the buildings did not incorporate innovative processes that would facilitate modern methods of construction. In order to move the housing delivery process toward circularity in the study area, modern construction technology should be adopted. As an active player in the housing delivery process, the public sector can play an important role in the uptake of modern technology in building design and construction process. In this respect, the building procurement process should benefit from digital technology.

The importance of renewable materials was also highlighted in the chapter. Renewable materials can be brought into the material mix due to the high cost of housing procurement using conventional materials. A number of renewable materials are found in the study area that can be used for housing development. There are materials such as SCMs that can reduce the quantity of Portland cement deployed in the construction of the buildings. Incidentally, these SCMs can be obtained from byproducts of both industrial processes and as wastes from agricultural processing. In this respect, wastes from other processes are utilized as inputs into building materials for housing development, thereby promoting circularity. Also, the use of mortar-less interlocking blocks can reduce the use of high-impact Portland cement. Interlocking clay bricks stabilized with cement have also been found to be very useful in the study context.

Energy use accounts for a large proportion of resources used in housing, especially at the use/operational level. Renewable energy use is on the increase, driven by the need for cleaner and low-impact energy. As a result, public housing projects are increasingly adopted renewable energy to mitigate the waste associated with conventional energy supply. Even though renewable energy was not factored into the housing projects, residents and building occupiers have commenced energy retrofits using solar photovoltaic installations.

Hence, going forward, energy efficiency strategies that incorporate solar photovoltaic installations with other building components are desirable. Mini-grid PV networks can be considered for estates.

Finally, the adoption of passive and regenerative principles in housing design should be emphasized. Housing design should conform to context in order to maximize natural attributes through passive design principles. This can help to reduce overall environmental impact of the buildings and reduce the need for the use of high-impact equipment and accessories. In a similar vein, green infrastructure is a way of promoting regenerative principles in housing design. The preponderance of hard landscaping in the housing programs informs the need for green infrastructure incorporation. However, given the limited land area available in the study area for housing development, conventional green infrastructure may not be feasible. Hence, while increasing occupancy per unit area in response to estimated deficit, it is desirable to explore the adoption of green roofs as a way of recapturing the natural green areas displaced by the construction of buildings and other infrastructure.

Acknowledgments

The authors acknowledge the support provided by Covenant University Centre for Research, Innovation and Discovery CUCRID toward the research leading to this publication.

Conflict of interest

The authors declare no conflict of interest.