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.
Unvented attic insulation requirements.
The roof deck in an unvented attic must be exceptionally airtight.
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.
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.
Code requirements vary across the country.
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.
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 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.
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.
In climate zones 1 2 and 3 when air permeable insulation is installed in unvented attics it shall meet the following requirements.
The irc has permitted unvented conditioned attics since 2006 with certain requirements.
Four options for building an unvented roof assembly.
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.
If you don t want to use sips or nailbase there are four basic approaches.
The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling.
Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.
