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Report prepared by RDH Building Science

Structural Testing of Screws Through Thick Exterior Insulation

Background Info:
As the construction industry moves toward more energy-efficient buildings, installing
exterior insulation is an effective solution to increasing thermal performance of wall
assemblies. Previous research and in-situ performance has shown that using long screws
to attach cladding directly through an exterior insulation layer without the use of clips or
girts is a thermally and structurally efficient solution for lightweight cladding (~2.5psf or
~12.2kg/m², e.g., vinyl, metal, wood siding) with relatively small thicknesses of exterior
insulation (~1-1/2" or ~38mm). However, there is still significant skepticism regarding
supporting cladding with screws only when using thicker exterior insulation or supporting
heavy claddings. These concerns—though largely unsupported by existing research—are
creating a barrier to the widespread adoption of this cladding attachment method, in
particular with exterior mineral wool insulation, which is perceived as insufficiently rigid
in comparison to competing foam plastic insulations such as extruded polystyrene
insulation (XPS).

Energy Performance Ratings of Buildings
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