Thermal Bridge Analysis for Offsite Manufactured Closed Panel Timber Frame Walls

Student Paper. This paper reports on the need for calculating thermal bridges (TBs) for timber frame (TF) closed panels, used in exterior walls of dwellings in Wales, UK, rather than using default TB values. The use of tabular TB values for exterior walls construction systems can lead to a performance gap at the design stage, whereby heat losses are different than as-design and predicted. Indeed, a housing developer in Wales constructing 1500 houses for Cardiff Council has calculated actual TB values for its brick-concrete block exterior wall systems used in dwellings and achieved a 17% improvement in thermal performance against Welsh Building Regulations in 2018. This paper documents collaboration with a Welsh-based offsite (referred to as the company hereafter) manufacturer (OSM) of modern methods of construction (MMC) systems using timber, and the TB calculation process for two elements used in the manufacture of their exterior wall system. The methodology uses manufacturing drawings to evaluate the thermal performance of the frame fraction and both two-dimensional (2D) and three-dimensional (3D) finite element analysis, to model heat flow in the company’s TF closed panel exterior wall systems, thereby assessing the impact of fixings and Psi (ψ) values. The paper will be useful for academics, architectural designers, building contractors, engineers, housing developers, OSMs of MMC and government stakeholders evaluating the thermal performance of TF construction systems to be used in nearly zero operational energy dwellings.