Vented Roof Cladding Substrate with Rigid Insulation
A vented roof cladding substrate can be installed over layers of exterior rigid insulation. Creates a vented space between the insulation and cladding layers.
It creates a vented space between the insulation and cladding layers and provides a nailbase for roof cladding material. A vented substrate is required in regions with high snow loads. It consists of purloins that are attached to the roof framing and plywood or OSB that is attached to the purlins.
A retrofit that involves re-roofing provides a great opportunity to install rigid foam insulation above the roof deck. However, in regions with high snow loads, purlins or furring strips must be installed above the rigid foam to provide an air gap for venting between the rigid foam and the new sheathing and roof cladding. The venting helps keep the surface of the roof cooler, minimizing the freeze-thaw cycles which lead to the formation of ice dams.
To create a vented substrate, purlins are fastened to the framing through the insulating sheathing. The substrate for the roof cladding is then fastened to the purlins much as it would be fastened to a new roof. Gaps along the length of the purlins provide cross ventilation. Large gaps in the purlins must be coordinated with the nailing pattern for the cladding substrate. Install roof underlayment, flashing, and cladding on top of the substrate as per best practices.