Comparative Analysis of Urban Green Roofs on Thermal Comfort Variations

Thesis Abstract

Urban heat stress and thermal discomfort in cities are intensified by limited vegetation and built-environment heat sinks, undermining occupant well-being and energy efficiency. This study addresses the gap in comparative evidence on how different configurations of urban green roofs influence indoor and microclimate thermal comfort across varied building typologies. The aim is to quantify and compare thermal comfort variations attributable to green roof interventions in temperate-climate urban settings, with objectives to (1) evaluate surface and ambient temperatures on buildings with extensive, intensive, and systemized green roofs; (2) assess occupant thermal sensation and comfort using standardized scales; (3) examine the mediating role of roof substrate depth, plant diversity, and irrigation regime on microclimate indicators; (4) test the applicability of established theories of biophilic design and urban microclimate regulation to roof-level interventions; and (5) develop a transferable framework for evaluating green roof performance on thermal comfort in dense urban areas. The methodological approach adopts a comparative cross-sectional design across three districts within a metropolitan region featuring diverse building stocks and green roof implementations. The population comprises commercial and residential buildings equipped with one of three green roof typologies (extensive, intensive, and modular-system roofs). A stratified random sampling method selects 60 buildings (20 per roof type), with an additional control group of 20 comparable buildings without green roofs. Data collection combines quantitative sensors and qualitative assessments (i) microclimate measurements using in-situ sensors for air temperature, radiant temperature, humidity, and surface temperature at 1.5 m height and on roof terraces; (ii) thermal comfort surveys administered to building occupants (n ? 360) using PMV/PPD, CET, and local adaptation questions; (iii) roof-specific attributes recorded through site observations and architectural plans (substrate depth, plant species richness, irrigation frequency, and roof area-to-building footprint). Instrument validity and reliability are established through pilot testing and Cronbach’s alpha assessments for the survey instruments. Data collection occurs over a full seasonal cycle to capture temporal variation. Analytical procedures include descriptive statistics to profile thermal indicators by roof type, followed by inferential analyses using multivariate regression and mixed-effects models to isolate the effect of roof typology on thermal comfort metrics while controlling for building height, occupancy, and urban canyon effects. ANOVA tests compare mean differences in thermal sensations and microclimate indicators across roof types. Structural equation modeling (SEM) investigates the pathways linking roof characteristics (depth, vegetation density, irrigation) to microclimate outcomes and occupant comfort, testing mediation effects proposed by biophilic design theory and urban microclimate regulation frameworks. A subset of qualitative data from occupant feedback is analyzed thematically to contextualize quantitative findings and identify adaptation strategies. The study draws on theories of biophilic design, urban microclimate regulation (surface albedo, evapotranspiration), and human-environment interaction to interpret results and guide model specification. Expected findings anticipate that intensive and well-maintained extensive green roofs will yield lower surface and ambient temperatures, higher relative humidity buffering, and improved thermal comfort indices (lower PMV/PPD scores) compared with modular and non-green-roof counterparts, with stronger effects during peak heat periods. Substrate depth, plant diversity, and consistent irrigation are hypothesized to amplify cooling benefits and comfort improvements, with mediation effects observable in SEM pathways. The research contributes to knowledge by providing robust, cross-sectional evidence on how roof typologies differentially affect thermal comfort in urban settings, advancing a transferable framework for evaluating green roof performance that integrates microclimate physics with occupant-perceived comfort. The study will inform urban design and policy by identifying roof configurations that most effectively mitigate thermal stress and enhance occupant well-being, energy efficiency, and resilience. Recommendations emphasize standardized monitoring protocols for green roofs, optimization of substrate and vegetation strategies, and the deployment of adaptive management practices to sustain thermal comfort across seasonal variations.