From Courtyard to Corridor: Quantifying Five Decades of Residential Architectural Transformation and Passive Design Loss in Indian Cities (1975–2025)

This study quantifies five decades (1975–2025) of residential architectural transformation in Delhi (Tier-I) and Patna (Tier-II), India, among middle-income-group households, and evaluates its implications for passive design loss and mechanical cooling dependence. A stratified survey of 1080 middle-income-group (MIG-I and MIG-II) households across six construction decades documents the systematic elimination of passive features: courtyard presence collapsed from 54.44% (Cohort A, 1975–1985) to 1.39% (Cohort C, 2015–2025); load-bearing masonry declined from 47.78% to 7.78%; and houses lacking passive cooling features quadrupled from 10.83% to 40.83%. Correspondingly, households with three or more air conditioning (AC) units rose from 12.78% (Cohort A) to 33.06% (Cohort C). However, 30–35% of households across all cohorts stated that the ‘indoor temperature remains comfortable without AC’, challenging deterministic AC-dependence assumptions. Regional divergence in drivers is evident: globalization dominates in Delhi (59.24%), while lack of traditional awareness dominates in Patna (39.29%), suggesting hierarchical diffusion and indicating a need for differentiated policy responses. Architectural homogenization shows a consistent association with higher AC ownership and electricity consumption, raising concerns about energy insecurity and climate vulnerability. Hybrid design, integrating traditional passive strategies with contemporary spatial needs, offers a pathway toward climate-resilient urban futures.