Influence of cladding attachment structural elements on the thermal performance of lightweight steel-framed walls

Abstract

The thermal transmittance characteristics of the building envelope significantly influences the whole building energy performance. Lightweight steel framed (LSF) systems with cladding attached back to structures using thermal clips or bracket systems are widely used in heating dominated climates. Thermal bridging associated with the cladding structural elements that bypass the exterior insulation to attach the cladding cannot be avoided, but their impact can be significantly mitigated. This study investigates the thermal influence of a generic aluminum cladding attachment system that has varying levels of complexity associated with thermal breaks, and rail penetration into the insulation. A total of five configurations were assessed besides a reference configuration, which was devoid of any cladding attachment structure. Three-dimensional finite element software (HEAT3) and a small-scale calibrated hot box apparatus were employed to perform the analyses. The objectives were to show the influence of the cladding attachment elements and demonstrate the ability of hot-box measurements and numerical simulations to quantify the influence. Results show a small deviation between numerical simulations and experimental measurements, ranged between - 0.85% and 3.70%. The variations in thermal transmittances properties of the investigated wall assemblies are presented, which vary from 40% to 57% compared to the reference case. These findings highlight the significant influence of the structural elements that bypass exterior insulation and how small variations of the same system can impact the whole thermal performance. The heat loss through the cladding attachment structural elements, which bypass exterior insulation, can be reduced by using thermal breaks like neoprene spacers appropriately.