Unvented Roof Assembly

Four options for building an unvented roof assembly.

Unvented roof assembly.

It s not and so code doesn t require r value ratios. This is a mis interpretation of the code. They are designed without ventilation openings and the attic is conditioned like the rest of the living space. Two potential unvented roof assemblies.

Unvented roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs. Recent building codes only allow unvented roof assemblies for pitches 3 12 and greater irc 2015 section r806 5 2 7. This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. If air gaps are present between insulation layers convection currents can significantly reduce the performance of the assembly and compromise durability.

Monolithic continuous exterior insulation ci above structural sheathing. Read all of r806 5 carefully. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof.

Insufficient fill below the impermeable insulation layer. Figure 6 describes open cell spray foam as air permeable. 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. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.

In some climates it requires a vapor barrier.