Original Theory of Incremental Urbanism: Self-Help Construction and the Production of Urban Space in Nigerian Cities

Incremental urbanism, the production of city fabric through the gradual, self-financed, owner-built construction processes that generate the majority of residential building stock in Nigerian cities, has been theorised primarily through the lens of informality, deficit, and irregularity, obscuring its character as a rational, strategic, and socially sophisticated mode of urban space production that deserves original theoretical treatment on its own terms. This dissertation develops an original theory of incremental urbanism, reconceptualising gradual self-help construction as a distinctive spatial production system with internal logics, design intelligence, and urban form-generating capacities that are neither reducible to formal planning theory nor adequately described by existing informality frameworks. The theory is developed through a comparative empirical programme in four Nigerian cities representing different urban scales and regional contexts: Onitsha, Sokoto, Benin City, and Jos. The empirical programme combines longitudinal building biography analysis tracing individual building development through multiple stages over periods of five to thirty years, construction process ethnography embedded within households during active building phases, spatial morphology analysis quantifying the urban form outcomes of incremental construction at the neighbourhood scale, and economic analysis of incremental construction as a household savings and investment strategy. Three original theoretical propositions constitute the theory: a staged spatial agency model that identifies the design decision points of incremental construction as a non-simultaneous design process; a household construction capital theory that explains the resource accumulation and investment logic driving incremental building timelines; and a neighbourhood form emergence model explaining how collective incremental decisions produce neighbourhood morphological outcomes without masterplan coordination. Keywords: incremental urbanism, self-help construction, Nigerian cities, informal housing theory, urban space production.