Housing growth: impacts on density, space consumption and urban morphology
Buildings and Cities
How and why do houses densify over time? What is the impact of that growth and what kind of constraints affect their potential to change? This research explores built form change and densification, providing historical evidence from the incremental transformation of a 19th-century housing scheme, Cité Ouvrière, in Mulhouse, eastern France. This granular longitudinal morphological study uses historical planning applications and images to map the external volumetric transformations of 1253
... family houses over a 165-year period. The research combines archival work with three-dimensional (3D) architectural modelling and an advanced density method to record, visualise, analyse and evaluate the densification process at the microlevel. Statistical computing traces the densification process and the Spacematrix tool analyses the impact on open space consumption for different building typologies and for the neighbourhood as a whole. The results highlight seven types of transformations, affected by seven drivers of physical change. Densification is manifested either through built intensification or plot union/subdivision, and its degree is determined by the extent to which non-built space is consumed. These depend on socioeconomic, legal and physical constraints imposed by the original design. PRACTICE RELEVANCE This work informs architects and planners how the design of houses together with non-formal constraints affect buildings' resilience and longevity and their capacity to accommodate growth over time. By tracing the successful transformation of a suburban settlement to a dense and morphologically diverse city quarter, the results support the slow and contained densification of existing housing through small changes-an approach which can benefit the sustainability and energy agendas of cities and settlements in Europe and abroad. This expands the current understanding of built density, advances our knowledge in the simulation and forecasting of dynamic change in the building stock, and contributes methodologically to the fields of urban morphology, geography and data computation.