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Structural Testing of Screws Through Thick Exterior Insulation

Report prepared by RDH Building Science

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).

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