Affordability is a dominant factor in the design of subsidized housing. However, the pressure to minimize initial construction costs often results in rigid spatial configurations that are not designed for future expansion. This condition frequently leads to informal renovations that compromise structural safety and overall housing quality. While the concept of incremental housing has long been recognized as an adaptive strategy for low-income communities, its implementation within subsidized housing schemes remains constrained by conventional structural systems that do not support planned spatial growth. This study examines how affordability can function as a design logic when integrated with the RISHA prefabricated modular structural system. Using a design-based research (DBR) approach, the study integrates occupants' spatial requirements, staged vertical growth (from 36 m2 to 72 m2), compatibility with two RISHA modular grids (1.8 × 3 m and 3 × 3 m), and structural cost threshold evaluation based on government-regulated subsidized housing price limits. The findings indicate that the 3 × 3-meter module accommodates all stages of vertical growth without requiring demolition or modification of the initial structural system, whereas the 1.8 × 3-meter module is only compatible at the initial stage and does not support second-floor expansion. Cost evaluation further demonstrates that all design alternatives based on the 3 × 3-meter module remain below the maximum allowable structural cost threshold within the subsidized housing scheme. These findings suggest that prefabricated modular systems function not merely as construction efficiency solutions but as spatial governance frameworks that direct housing growth in a structured and economically controlled manner. Affordability, therefore, can be repositioned not as a design constraint but as a generative parameter in the development of modular incremental housing.
Carissa et al. (Mon,) studied this question.