Vented And Unvented Roof Assembly

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.

Vented and unvented roof assembly.

An unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. An unvented assembly can perform well but it s important to get the details right to avoid sheathing rot. Control construction moisture content with tenting or temporary roofing when necessary.

In other words vented roofs may well be the best design for one home while an unvented roof will be a better solution for another home. Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof. Moisture content in roof structure must be less than 18 prior to covering. Unvented roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs.

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.