Unvented Roof Assembly

This is a mis interpretation of the code.

Unvented roof assembly.

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. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. It s not and so code doesn t require r value ratios.

If you don t want to use sips or nailbase there are four basic approaches. Unvented roofs operate by the principle that venting is not necessary to control moisture accumulation. 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.

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. Four options for building an unvented roof assembly. 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. Recent building codes only allow unvented roof assemblies for pitches 3 12 and greater irc 2015 section r806 5 2 7.

If air gaps are present between insulation layers convection currents can significantly reduce the performance of the assembly and compromise durability. Read all of r806 5 carefully. Unvented roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs. Figure 6 describes open cell spray foam as air permeable.

They are designed without ventilation openings and the attic is conditioned like the rest of the living space.