Unvented Conditioned Attic

Code requirements vary across the country.

Unvented conditioned attic. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. Among the early promoters of conditioned attics was joe lstiburek a principal of the building science corporation. Unvented attic assemblies code notes 2009 irc 2012 irc. The irc also prohibits a vapor retarder on the attic floor of conditioned attics so that any moisture that may build up in the attic can dissipate into the house.

This air seal will help to make your home more energy efficient. The acceptance of unvented conditioned attics continues to grow among builders and building officials. The roof deck in an unvented attic must be exceptionally airtight. The unvented attic system or conditioned attic is the new way to make your attic energy efficient.

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. Systems where condensing surface temperatures are not controlled figure 4 and systems where condensing surface temperatures are. The irc has permitted unvented conditioned attics since 2006 with certain requirements. Adding unvented attic insulation like spray foam seals the building envelope and stops airflow.

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. If wood shingles or shakes are used a inch air gap must. Lstiburek s enthusiasm was rooted in his desire to bring attic ductwork inside a home s thermal envelope. Unvented conditioned attics were quite rare before the 1980s.

With vented attic assemblies moisture that diffuses into the attic space from the conditioned space is vented to the exterior by attic ventilation. 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 design unvented attic design falls into two categories. In warmer climates unvented attics can prevent the condensation that occurs on ductwork in some vented attic spaces.

The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling. 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. Making the attic a conditioned space means the space will be.