Unvented Roof Assembly

Read all of r806 5 carefully.

Unvented roof assembly.

Figure 6 describes open cell spray foam as air permeable. 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 assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. If you don t want to use sips or nailbase there are four basic approaches.

Insufficient fill below the impermeable insulation layer. 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. 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. Unvented roofs operate by the principle that venting is not necessary to control moisture accumulation. Four options for building an unvented roof assembly. This is a mis interpretation of the code.

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. Monolithic continuous exterior insulation ci above structural sheathing. In some climates it requires a vapor barrier. Two potential unvented roof assemblies.

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