This study presents an integrated digital methodology for evaluating sustainable insulation materials in the context of energy retrofitting of public buildings. Focusing on a representative case study in Catania (Climate Zone B), the research combines Building Information Modeling (BIM) with parametric scripting to assess thermal performance, regulatory compliance, and cost-efficiency of different external wall insulation systems. Four insulation materials—wood wool, pressed wood fiber, expanded cork, and expanded polystyrene—were analyzed based on data from the Sicilian Regional Price List. Material properties were embedded into Autodesk Revit, enabling the simulation of thermal transmittance (U-value) and surface mass. A custom Dynamo script automated the verification of performance thresholds defined by Italian regulations (DM 26/06/2015), and compliance with environmental criteria set by CAM (DM 23/06/2022) was ensured through material selection. Results show that only pressed wood fiber (80 mm) and expanded cork (100 mm) satisfy both regulatory thresholds. Among them, pressed wood fiber proved to be significantly more cost-effective, with a total retrofit cost 65% lower than cork. EPS, while offering low U-values, failed to meet the required thermal mass and is not CAM-compliant. The methodology demonstrates how BIM and visual programming can streamline early-stage design decisions, ensuring regulatory alignment and sustainability. The workflow supports the goals of the ecological and digital transition in public construction and is replicable across various building types and climatic contexts.