Unvented Attic Air Exchanger

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.

Unvented attic air exchanger. 1 air shall be supplied to the attic by a fan blowing air from the occupiable space into the attic. Codes for unvented attics. 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. The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling.

These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. Code requirements vary across the country. The acceptance of unvented conditioned attics continues to grow among builders and building officials. 2 transfer air from the occupiable space shall be provided by a fan exhausting attic air to the outside or 3 mechanical dehumidification shall be provided to the unvented attic air space.

However if moisture is able to enter the unvented attic space it may lead to roofing panel issues. Requirements for unvented attic assemblies are provided in section 0806 4 of the international residential code 2009 irc. The energy savings touted by unvented attics can be as high as 20. This section addresses ways to prevent condensation on the inner surface of the roof deck if temperatures are significantly lower on the inside than on the outside of the roof.

The irc has permitted unvented conditioned attics since 2006 with certain requirements. 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. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. The problem that can occur in a closed attic assembly is the management of the moisture that rises and accumulates in the attic space.

Unventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings. Unvented attic assemblies code notes 2009 irc 2012 irc adequate attic ventilation is a long standing requirement in building codes for moisture control. We are going to address the idea of air exchange in closed attics that use open cell foam.