Unvented Roof Assembly Detail

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.

Unvented roof assembly detail.

Unvented roofs operate by the principle that venting is not necessary to control moisture accumulation. This is how to detail an unvented roof assembly for flat and low slope roofs. This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. This is the recommendation of all three local insulation installers.

The point is that the inner face of that first layer the air barrier layer of insulation should always be warmer than the dew point or you ll get water in your roof. Yes unvented roof assemblies can be insulated with fiberglass a wufi post and not just in climate zones 2b amp. If not properly detailed partial penetrations into the unvented roof assembly for things like can lights or ceiling fans can undermine the insulation and or air tightness strategies alluded to above. Figure 6 describes open cell spray foam as air permeable.

This is a mis interpretation of the code. Unvented roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs. However as the future owner i m beginning maybe a bit too. The unvented attic space is completely contained within the building thermal envelope.

No insulation installed yet. If it all sounds simple there is certainly room for error. It s not and so code doesn t require r value ratios. Before constructing a flat roof assembly please refer to the unvented roof assembly comments under 6 2 vented and unvented roof assemblies and if applicable 6 3 parapet walls.

Read all of r806 5 carefully. 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. The key detail is that the air impermeable insulation must be suitably thick to stop condensation in the assembly. If you don t want to use sips or nailbase there are four basic approaches.

They are designed without ventilation openings and the attic is conditioned like the rest of the living space. Recent building codes only allow unvented roof assemblies for pitches 3 12 and greater irc 2015 section r806 5 2 7. There will be ducting and other hvac equipment in the attic. In some climates it requires a vapor barrier.

Unvented attic assemblies spaces between the ceiling joists of the top story of the roof rafters shall be permitted if all of the following conditions are met. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. In the process of construction. Martin s post focuses on the marketing of owens corning 039 s propink unvented attic insulation system.