Unvented Attic Insulation Requirements

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

Unvented attic insulation requirements.

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. 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. An unvented attic air sealed with spray foam insulation limits outdoor air entry and as a result indoor combustion air should not be considered available for fuel fired combustion appliances located within the attic space. For unvented attics having the spray foam layer applied continuously from the roof wall intersection to the roof peak at the specified thickness encapsulating the entire interior surface area of the attic will hinder airborne moisture entry while providing an energy efficient environment.

The irc has permitted unvented conditioned attics since 2006 with certain requirements. Code requirements vary across the country. The acceptance of unvented conditioned attics continues to grow among builders and building officials. If you don t want to use sips or nailbase there are four basic approaches.

Section r806 4 of the 2009 international residential code irc and section r806 5 of the 2012 irc have requirements for unvented conditioned attic assemblies. 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 soffits etc which make it difficult to achieve an airtight ceiling plane. Further the relationship of unvented attic spaces to maintaining the interior environment through use of insulation is also discussed in chapter 12 a section seldom associated with roofing materials. Insulation requirements for roofs are therefore spread across ibc chapters 12 13 and 15.

Four options for building an unvented roof assembly. Unvented roof assemblies should be insulated either with air impermeable insulation rigid foam or spray polyurethane foam or with a combination of foam and air permeable insulation. 1 an approved vapor diffusion port shall be installed not more than 12 inches 305 mm from the highest point of the roof measured vertically from the highest point of the roof to the lower edge of the port. The roof deck in an unvented attic must be exceptionally airtight.

These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck.