Unvented Roof Assembly

Four options for building an unvented roof assembly.

Unvented roof assembly.

Two potential unvented roof assemblies. 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. In some climates it requires a vapor barrier.

Recent building codes only allow unvented roof assemblies for pitches 3 12 and greater irc 2015 section r806 5 2 7. 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. Insufficient fill below the impermeable insulation layer.

It s not and so code doesn t require r value ratios. Unvented roofs operate by the principle that venting is not necessary to control moisture accumulation. This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. Unvented roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs.

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. 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. If you don t want to use sips or nailbase there are four basic approaches.

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