Rethinking Infill Development: A Regulatory Ecosystem Perspective from Riyadh, Saudi Arabia

Infill development is an important strategy for promoting compact and sustainable urban growth, yet its implementation can be constrained by interconnected regulatory, institutional, infrastructure, land, and market conditions. This study examines barriers to infill development in Riyadh, Saudi Arabia, their interrelationships, and priorities for regulatory reform. An exploratory sequential mixed-methods design combined interviews with seven experienced developers and a survey of 72 experts from government, the private sector, and academia. Qualitative data were analyzed thematically, while survey responses were examined using descriptive statistics, Spearman’s correlation analysis, and Kruskal–Wallis tests. Institutional coordination emerged as the highest-ranked barrier category, with multiple agency approvals, fragmented responsibilities, and poor interagency coordination among the most severe constraints. Significant associations across regulatory, infrastructure, land, mobility, and market dimensions indicate that these barriers are perceived as interconnected rather than independent. Synthesizing these findings, the study proposes a regulatory ecosystem framework distinguishing fragmented and coordinated ecosystem conditions and their associated infill development outcomes. The findings support integrated reforms centered on coordinated approvals, pre-acquisition infrastructure information, clearer by-right zoning, and greater alignment across regulatory domains to support more effective and sustainable infill development.