Psychiatric emergencies are increasing, placing strain on emergency departments (EDs) that lack specialized care environments. EmPATH (Emergency Psychiatric Assessment, Treatment, and Healing) units have emerged as an alternative, offering rapid assessment, short-term stabilization, and a therapeutic, open-milieu environment. While these units improve patient outcomes and reduce ED overcrowding, there is no standardized tool to evaluate their spatial effectiveness. Existing mental health facility assessment frameworks do not fully address the unique design features of EmPATH units, such as their open layout, emphasis on social interaction, and balance between autonomy and safety. This study develops an evaluation tool and a set of design guidelines tailored to EmPATH units. Using a multi-method approach, it integrates semi-structured interviews with staff and designers (n=15) and spatial analysis of eight case studies through floor plans and space syntax tools. The research identifies eight key design goals—homelike environments, social interaction, maintenance, autonomy, inclusivity, safety and security, positive distractions, and staff respite—and examines the environmental characteristics that support these goals. Among them, social interaction, homelike settings, autonomy, and safety/security emerged as the most critical factors in effective EmPATH unit design. The research contributes the first systematic framework for evaluating EmPATH units, equipping designers, healthcare administrators, and policymakers with evidence-based strategies for optimizing psychiatric crisis care environments.