Unvented Roof Assembly Detail

Unvented roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs.

Unvented roof assembly detail.

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. There will be ducting and other hvac equipment in the attic. This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. This is how to detail an unvented roof assembly for flat and low slope roofs.

This is a mis interpretation of the code. Recent building codes only allow unvented roof assemblies for pitches 3 12 and greater irc 2015 section r806 5 2 7. Unvented roofs operate by the principle that venting is not necessary to control moisture accumulation. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck.

Insufficient fill below the impermeable insulation layer. 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. In the process of construction. 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.

Currently have a standing seam metal room installed over synthetic felt over osb. Read all of r806 5 carefully. The plan is to spray open cell foam under the roof deck. Yes unvented roof assemblies can be insulated with fiberglass a wufi post and not just in climate zones 2b amp.

This is the recommendation of all three local insulation installers. The unvented attic space is completely contained within the building thermal envelope. They are designed without ventilation openings and the attic is conditioned like the rest of the living space. The key detail is that the air impermeable insulation must be suitably thick to stop condensation in the assembly.

Martin s post focuses on the marketing of owens corning 039 s propink unvented attic insulation system. 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. If it all sounds simple there is certainly room for error.

No insulation installed yet. However as the future owner i m beginning maybe a bit too. Figure 6 describes open cell spray foam as air permeable. In some climates it requires a vapor barrier.