Unvented Roof Assembly Detail

This is how to detail an unvented roof assembly for flat and low slope roofs.

Unvented roof assembly detail.

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. Insufficient fill below the impermeable insulation layer. It s not and so code doesn t require r value ratios. 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. Unvented roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs. The plan is to spray open cell foam under the roof deck. 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.

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. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. However as the future owner i m beginning maybe a bit too. This is a mis interpretation of the code.

The unvented attic space is completely contained within the building thermal envelope. In some climates it requires a vapor barrier. 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.

Read all of r806 5 carefully. Recent building codes only allow unvented roof assemblies for pitches 3 12 and greater irc 2015 section r806 5 2 7. Martin s post focuses on the marketing of owens corning 039 s propink unvented attic insulation system. Figure 6 describes open cell spray foam as air permeable.

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. In the process of construction. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. No insulation installed yet.

The key detail is that the air impermeable insulation must be suitably thick to stop condensation in the assembly. There will be ducting and other hvac equipment in the attic. Currently have a standing seam metal room installed over synthetic felt over osb. If it all sounds simple there is certainly room for error.