Unvented Roof Assembly Detail

Unvented roofs operate by the principle that venting is not necessary to control moisture accumulation.

Unvented roof assembly detail.

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 roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs. No insulation installed yet. Yes unvented roof assemblies can be insulated with fiberglass a wufi post and not just in climate zones 2b amp.

Recent building codes only allow unvented roof assemblies for pitches 3 12 and greater irc 2015 section r806 5 2 7. 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. There will be ducting and other hvac equipment in the attic. Read all of r806 5 carefully.

If you don t want to use sips or nailbase there are four basic approaches. However as the future owner i m beginning maybe a bit too. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. They are designed without ventilation openings and the attic is conditioned like the rest of the living space.

The unvented attic space is completely contained within the building thermal envelope. The key detail is that the air impermeable insulation must be suitably thick to stop condensation in the assembly. It s not and so code doesn t require r value ratios. In the process of construction.

The plan is to spray open cell foam under the roof deck. If it all sounds simple there is certainly room for error. This is how to detail an unvented roof assembly for flat and low slope roofs. Figure 6 describes open cell spray foam as air permeable.

This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. 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. Martin s post focuses on the marketing of owens corning 039 s propink unvented attic insulation system. This is the recommendation of all three local insulation installers.

In some climates it requires a vapor barrier. 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. Currently have a standing seam metal room installed over synthetic felt over osb.