Unvented Flat Roof Assembly

An unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation.

Unvented flat roof assembly.

Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof. Foam free don t stay stuck in the sci finightmare of foam foam foam. We re big fans of fine homebuilding. An unvented assembly can perform well but it s important to get the details right to avoid sheathing rot.

All of the unvented roof assemblies are intolerant of incidental water leakage and the moisture sensitive layers i e sheathing and gypsum wallboard for open cell polyurethane insulation exceed the threshold for decay. In hot humid climates the most durable roof assemblies are the vented open cell polyurethane systems with shorter. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. Insulating unvented roof assemblies.

2012 irc section r806 5 unvented attic assemblies 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. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. We agree that avoiding sheathing rot is critical and that air permeable insulation such as fiberglass or cellulose cannot be used alone. Condensing surface temperature controlled the thickness of the rigid insulation at both the roof deck and perimeter is determined by a calculation procedure similar to figure 5.

The colder the climate the thicker the rigid insulation required. Yes unvented roof assemblies can be insulated with fiberglass a wufi post and not just in climate zones 2b amp. The higher the interior moisture level the thicker the. Unvented flat roof assembly.

By installing spf insulation spray in place insulation in lieu of mineral fiber insulation in the joist cavity of a flat roof or between rafters of a cathedral ceiling the assembly may perform the same as or better than that of a typical. Unvented roof systems where the insulation and air barrier are applied directly to the underside of the roof deck are common in applications where designers are seeking cost effective and energy efficient roof assemblies. Martin s post focuses on the marketing of owens corning 039 s propink unvented attic insulation system. In the most recent issue of fine homebuilding martin holladay wrote a piece on insulating unvented roof assemblies.

Air permeable insulation such as fiberglass batts dense packed cellulose or blown in fiberglass can t be used alone for an unvented assembly since these types of insulation can allow moist indoor air to reach the cold roof sheathing leading to condensation or moisture accumulation. The most common way to eliminate venting from a roof assembly is to use a spray foam spf insulation.