Development of Workflows for OTTV and U-Value of Roof Calculation Using BIM-VPL to Assess Envelopes Thermal Performance

Abstract

Envelope thermal performance has been found to have a significant effect on a building's energy performance. In Malaysia, the Overall Thermal Transfer Value (OTTV) is a mandatory metric regulated by MS 1525:2019 to limit heat gain through façades. Conventional OTTV calculation is a manual, time-consuming process prone to human error, hindering rapid design iteration. This study offers a novel methodology to automate this process by developing integrated workflows that connect Building Information Modeling (BIM) with a Visual Programming Language (VPL). The proposed system will automatically extract essential thermal and physical properties from the BIM database and compute the OTTV and roof thermal transmittance (U_r) in accordance with the MS 1525:2019 formula. The workflows were rigorously validated through a comparative analysis with traditional manual calculations, utilizing both a controlled hypothetical model and real-world case studies of residential buildings. The results demonstrate that the proposed BIM-VPL system achieves a high degree of accuracy, with deviations of less than 0.6% for OTTV and under 1% for Ur, while concurrently reducing processing time by 70–80%. Equip designers with a robust, efficient tool to rapidly assess and optimize envelope designs, enhance material selection in early project stages, ensure compliance, and drive sustainable building development.