Unvented Roof Assembly Detail

Read all of r806 5 carefully.

Unvented roof assembly detail.

The unvented attic space is completely contained within the building thermal envelope. 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. This is how to detail an unvented roof assembly for flat and low slope roofs. In the process of construction.

This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. They are designed without ventilation openings and the attic is conditioned like the rest of the living space. 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. This is the recommendation of all three local insulation installers.

These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. The key detail is that the air impermeable insulation must be suitably thick to stop condensation in the assembly. 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.

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. It s not and so code doesn t require r value ratios. In some climates it requires a vapor barrier. If it all sounds simple there is certainly room for error.

There will be ducting and other hvac equipment in the attic. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. 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. 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.

Martin s post focuses on the marketing of owens corning 039 s propink unvented attic insulation system. No insulation installed yet. Figure 6 describes open cell spray foam as air permeable. Currently have a standing seam metal room installed over synthetic felt over osb.

Insufficient fill below the impermeable insulation layer. If you don t want to use sips or nailbase there are four basic approaches. 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.