Unvented Roof Assembly

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.

Unvented roof assembly.

Recent building codes only allow unvented roof assemblies for pitches 3 12 and greater irc 2015 section r806 5 2 7. Insufficient fill below the impermeable insulation layer. Read all of r806 5 carefully. If you don t want to use sips or nailbase there are four basic approaches.

This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. Unvented roof assemblies should be insulated either with air impermeable insulation rigid foam or spray polyurethane foam or with a combination of foam and air permeable insulation. They are designed without ventilation openings and the attic is conditioned like the rest of the living space. In some climates it requires a vapor barrier.

Monolithic continuous exterior insulation ci above structural sheathing. Unvented roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs. It s not and so code doesn t require r value ratios. Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof.

Two potential unvented roof assemblies. Unvented roofs operate by the principle that venting is not necessary to control moisture accumulation. Figure 6 describes open cell spray foam as air permeable. If air gaps are present between insulation layers convection currents can significantly reduce the performance of the assembly and compromise durability.

These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck.