Unvented Roof Assembly

If air gaps are present between insulation layers convection currents can significantly reduce the performance of the assembly and compromise durability.

Unvented roof assembly.

Four options for building an unvented roof assembly. This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. Recent building codes only allow unvented roof assemblies for pitches 3 12 and greater irc 2015 section r806 5 2 7.

In some climates it requires a vapor barrier. Monolithic continuous exterior insulation ci above structural sheathing. 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 roofs operate by the principle that venting is not necessary to control moisture accumulation.

Two potential unvented roof assemblies. Un ven ted roof ˌənˈven t əd ro of an unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation. Read all of r806 5 carefully. Unvented roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs.

They are designed without ventilation openings and the attic is conditioned like the rest of the living space. Figure 6 describes open cell spray foam as air permeable. It s not and so code doesn t require r value ratios. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck.

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.