Structural Testing of Screws through Exterior Insulation for Steel-Frame Walls

As the construction industry moves toward more energy-efficient buildings, exterior insulation has been recognized as an effective solution for increasing thethermal performance of wall assemblies. Previous research and in-situ performance have shown that using only screws directly through exterior insulation toprovide cladding attachment is a thermally and structurally efficient solution for wood-frame walls (Baker and Lepage 2014). For steel-frame walls,however, there is still scepticism regarding this method of cladding support, and cladding attachment clips are currently the more common solution.This study focused on the impact of density and thickness of insulation materials on the structural performance of a cladding attachment system where theexterior insulation is installed and held in place using only screws and steel furring fastened in to a steel stud back-up wall. In particular, this studyinvestigated the use of exterior stone wool insulation, which may be perceived as insufficiently rigid in comparison to competing foam plastic insulations suchas extruded polystyrene insulation (XPS) for this type of insulation and cladding installation approach. In addition to the structural performance,airtightness, water penetration, and constructability considerations of this system are also discussed.Overall the study aims to provide important information for the industry as to the viability of the screws through exterior insulation cladding attachmentapproach in steel stud wall applications to facilitate the expanded use of exterior insulation as part of non-combustible wall assembly design. This studyfound that insulation thickness to be the most impactful on the measured load-deflection response of the system; however, the load-deflection response wastypically similar and sufficiently strong and stiff within the range of typical cladding weights such that this system would likely be able to provide sufficientcladding support for the insulation thicknesses tested.