RDH Building Science
    RDH Building Science

Using long screws directly through an exterior insulation layer to provide cladding attachment without the use of clips or girts has been shown to be a thermally and structurally efficient solution for more energy efficient wood-frame buildings. However, there is still significant scepticism regarding supporting cladding with only screws when using thicker exterior insulation (>38 mm or >1-1/2″), supporting heavy claddings (>48.8 kg/m² or >10 psf, e.g., stucco, stone veneer), or in particular, using exterior mineral wool insulation, which is perceived as insufficiently rigid in comparison to competing foam plastic insulations such as extruded polystyrene insulation (XPS).

Various studies have been conducted to address this gap in industry knowledge and familiarity to help promote adoption of this cladding attachment method. To build on this existing research, which focused on evaluation of screw bending and potential formation of a truss (created by the screw and compression of the insulation), this study focuses on the impact of the compressive strength of the insulation, large thicknesses of insulation (~305 mm or ~12″), and fastener embedment depth (framing member vs. sheathing only) on the structural performance of these systems. The impact of these parameters was evaluated in a laboratory condition using a custom-built apparatus to mechanically imitate cladding (gravity) load in an isolation from other factors such as various other forces building is subject to. The test specimens were selected so that the impact of these parameter can be evaluated by cross comparison. This study found that when 8.0 mm (5/16″) fasteners, fully embedded into the structural framing, were subjected to a common cladding load (9.1 kg or 25 lb per fastener) the deflection observed was typically less than 0.64 mm (0.025″), which is likely insignificant considering potential moisture shrinkage that could be anticipated in a typical one-storey wood-frame construction (10 mm or 3/8″).

Presented at the 15th Canadian Conference on Building Science and Technology.

View presentation slides here.