Abstract
Vegetated façade systems (VFS) are increasingly investigated as passive envelope strategies capable of improving building energy performance in hot–arid climates. However, most previous studies evaluate VFS performance using isolated environmental indicators such as energy reduction or thermal improvement. Such approaches provide limited support for early design decisions where environmental performance, cost, and user-related aspects must be evaluated simultaneously.This study develops and validates a multi-criteria assessment methodology for evaluating VFS performance in residential buildings located in hot–arid climates. The proposed framework integrates environmental, user-related, and cost indicators within a hierarchical decision structure to calculate a composite Vegetated Façade System Performance Index (VFS-PI). The methodology was first applied to simulation-based residential case studies representing typical housing units in Egyptian new urban communities. Different configurations were evaluated, including direct and indirect vegetated façades with varying air-gap depths. To examine the reliability of the proposed framework, selected façade configurations were experimentally evaluated under real operating conditions at the Renewable Energy Laboratory, Cairo University.The results indicate that indirect VFS generally outperforms direct façades when evaluated using integrated performance criteria. Façade orientation, internal space geometry, and air-gap depth were found to significantly influence the resulting performance index. Sensitivity analysis further confirmed the robustness of the proposed framework under different stakeholder weighting scenarios. The developed methodology provides a practical decision-support tool for evaluating VFS alternatives during early design stages. It contributes to improving façade design strategies for energy-efficient residential buildings in hot–arid climates.