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.
Unvented attic insulation requirements.
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.
These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck.
The irc has permitted unvented conditioned attics since 2006 with certain requirements.
Four options for building an unvented roof assembly.
Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.
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.
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.
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.
Code requirements vary across the country.
The roof deck in an unvented attic must be exceptionally airtight.
In climate zones 1 2 and 3 when air permeable insulation is installed in unvented attics it shall meet the following requirements.
Insulation requirements for roofs are therefore spread across ibc chapters 12 13 and 15.
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.
The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling.
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.
If you don t want to use sips or nailbase there are four basic approaches.
The acceptance of unvented conditioned attics continues to grow among builders and building officials.