Unvented Attic Insulation Requirements

In climate zones 1 2 and 3 when air permeable insulation is installed in unvented attics it shall meet the following requirements.

Unvented attic insulation requirements.

The irc has permitted unvented conditioned attics since 2006 with certain requirements. 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. 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. 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.

Insulation requirements for roofs are therefore spread across ibc chapters 12 13 and 15. 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 should be insulated either with air impermeable insulation rigid foam or spray polyurethane foam or with a combination of foam and air permeable insulation. Code requirements vary across the country.

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. 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. The roof deck in an unvented attic must be exceptionally airtight. The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling.

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 acceptance of unvented conditioned attics continues to grow among builders and building officials. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. The overall insulation level in the roof assembly must meet the baseline requirements for energy efficiency as given in the irc section n1102 or iecc section 402.

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