Thermal performance of aluminium-timber composite frames in curtain wall systems

Space heating and cooling account for a significant portion of building operational energy use, with considerable heat exchange occurring through the building envelope. Aluminium-framed curtain walls are widely adopted for their structural performance, durability, and corrosion resistance, yet their high thermal conductivity contributes to significant building energy loss. This study introduces a novel aluminium-timber composite curtain wall frame where aluminium serves as a structural core encased by glulam timber, combining durability with superior thermal performance. A comprehensive parametric study was conducted using a hybrid assessment approach following ISO 10077-2:2017 standards. Thirty-six configurations were evaluated across three timber species, three thicknesses, various thermal break and structural design options. Results demonstrate that the composite frame achieves substantial U-value reductions compared to conventional aluminium frames. Thermal breaks provide an additional reduction, enabling U-values below 2.0 W/m 2 · K when combined with cedar timber. The structural glazing offered an additional 35-40% improvement over captive glazing. The analytical method showed excellent agreement with numerical simulations, enabling rapid design optimisation. The linear regression analysis also demonstrates a clear linear relationship between the thermal performance of the frame and the window panel. This hybrid evaluation methodology provides designers with a practical tool for early-stage thermal optimisation without requiring expensive physical testing, supporting the development of high-performance, energy-efficient curtain wall systems for sustainable building design.