Unvented Roof Assembly

Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof.

Unvented roof assembly.

Unvented roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs. This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. If you don t want to use sips or nailbase there are four basic approaches. Insufficient fill below the impermeable insulation layer.

Figure 6 describes open cell spray foam as air permeable. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. This is a mis interpretation of the code. If air gaps are present between insulation layers convection currents can significantly reduce the performance of the assembly and compromise durability.

Recent building codes only allow unvented roof assemblies for pitches 3 12 and greater irc 2015 section r806 5 2 7. It s not and so code doesn t require r value ratios. They are designed without ventilation openings and the attic is conditioned like the rest of the living space. 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.

These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. Read all of r806 5 carefully. Four options for building an unvented roof assembly. Monolithic continuous exterior insulation ci above structural sheathing.

Unvented roofs operate by the principle that venting is not necessary to control moisture accumulation.