Unvented Attic Design

Both vented and unvented attic roof designs can be used in all hygro thermal regions.

Unvented attic design. The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling. However if moisture is able to enter the unvented attic space it may lead to roofing panel issues. The roof deck in an unvented attic must be exceptionally airtight. Unventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings.

Vented roofs serve a number of different purposes and their roles vary from climate to climate. To provide an unvented conditioned space for locating hvac equipment in the attic and or to provide a continuous thermal barrier for designs that have complex coffered ceiling planes and or numerous penetrations for lights speakers vents. In unvented roof assemblies the thermal moisture and air control boundaries are moved to the roof deck so that the attic space is at the same condition as the living space and air movement between the two does not contribute to energy waste occupant discomfort or contaminant problems. Also unvented roof assembles make complicated roof geometries more viable as they are difficult to ventilate effectively.

Because the temperature in unvented attics is more easily controlled they can be furnished and incorporated into the living space or used as a conditioned storage space. The acceptance of unvented conditioned attics continues to grow among builders and building officials. The choice of the venting approach is up to the designer. In colder climates the main purpose of a vented roof is to keep the roof cold and reduce the.

A fundamental requirement of an unvented attic assembly is the use of air impermeable insulation on the underside of the unvented roof to prevent air infiltration and exclude airborne moisture from the attic. An unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation. Install insulation along the underside of the roof deck of an unvented attic rather than on the ceiling deck of a vented attic for either of two reasons. 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.

The irc has permitted unvented conditioned attics since 2006 with certain requirements. Code requirements vary across the country. Control of ice dams moisture accumulation and heat gain can be successfully addressed by both vented and unvented attic or roof design. However the designs need to be climate sensitive.

Expanded use and design options. Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof. Performance attic options any attic insulation not listed under prescriptive must use performance options e g unvented attics or attics with foam board above the roof deck.