**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. [61–63], 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].

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


## **Table 1.**

*Trend in housing deficit in Nigeria.*

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].
