Vented Attic Roof Assembly

Because the drying capacity of unvented roof assemblies is inherently lower than vented ones it is especially critical to control built in moisture during construction.

Vented attic roof assembly.

Vented roofs serve a number of different purposes and their roles vary from climate to climate. In colder climates the main purpose of a vented roof is to keep the roof cold and reduce the formation of ice dams. 2009 irc section r806 4. No interior attic assembly side vapor control is required or recommended in climate zones other than climate zones 6 or higher see map 1 for vented attic assemblies note the distinction this is not the case for unvented attic assemblies as will be discussed later.

Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof. Control construction moisture content with tenting or temporary roofing when necessary. 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. A vent space clearance of at least 1 must be maintained at the location of the vent and between insulation and roof sheathing.

Note that this would not apply where an unvented roof assembly is used as indicated in section r806 4. This section outlines the conditions for unvented attic roof assemblies. Unvented attic assemblies offer numerous performance advantages versus vented attic assemblies. Moisture content in roof structure must be less than 18 prior to covering.

They are designed without ventilation openings and the attic is conditioned like the rest of the living space. A secondary goal is to vent moisture that infiltrates the attic from the conditioned home. The unvented attic space is completely contained within the building thermal envelope. 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 are becoming an increasingly common construction alternative to traditional vented roofs. Un ven ted roof ˌənˈven t əd ro of an unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation. When hvac equipment is in the attic insulation and an air barrier at the roof line brings that equipment within the conditioned enclosure envelope thereby allowing it to operate in more favorable temperature and humidity conditions without air.