Unvented Attic Space

Adding unvented attic insulation like spray foam seals the building envelope and stops airflow.

Unvented attic space. Unvented design unvented attic design falls into two categories. The typical construction scenario involved the use of low density open cell spray foam insulation for the thermal barrier at roof deck and duct work installed in the unvented attic space. When all of the insulation is tight to the roof deck the unvented enclosed rafter truss assembly or unvented attic is within the. The unvented attic space is completely contained within the building thermal envelope.

In the early 1990s construction of unvented attics became popular especially for structures in warmer climates. 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. The roof insulation and air barrier must follow the plane of roofing materials rather than diverge figure 2.

Code requirements vary across the country. Systems where condensing surface temperatures are not controlled figure 4 and systems where condensing surface temperatures are. The roof deck in an unvented attic must be exceptionally airtight. The energy savings touted by unvented attics can be as high as 20.

The unvented attic space is completely 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. This air seal will help to make your home more energy efficient. 2009 irc section r806 4.

The acceptance of unvented conditioned attics continues to grow among builders and building officials. With vented attic assemblies moisture that diffuses into the attic space from the conditioned space is vented to the exterior by attic ventilation. The unvented attic system or conditioned attic is the new way to make your attic energy efficient. 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.

Unventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings. The irc has permitted unvented conditioned attics since 2006 with certain requirements. However if moisture is able to enter the unvented attic space it may lead to roofing panel issues.