Vented Conditioned Attic
This facilitates the design of unvented attics in warm and mixed climates without an additional vapor retarder but requires an additional vapor retarder element in colder regions.
Vented conditioned attic. By using an air impermeable insulation like spray foam on the roof deck will stop any air movement. 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. The irc has permitted unvented conditioned attics since 2006 with certain requirements. The roof deck in an unvented attic must be exceptionally airtight.
The thermal boundary can be at the ceiling plane leaving the attic space above uninsulated and vented or the thermal boundary can be located at the roof line creating a sealed insulated conditioned or semi conditioned attic space. Lstiburek s enthusiasm was rooted in his desire to bring attic ductwork inside a home s thermal envelope. One static vent style is the turbine vent which uses wind to power its enclosed fan all it takes is a light breeze to rotate the blades and suck heat out of the attic view example on the home. The loss of energy efficiency means some designers choose to move the ductwork into the conditioned areas of the home and leave the attics unvented.
The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling. Unvented design unvented attic design falls into two categories. Systems where condensing surface temperatures are not controlled figure 4 and systems where condensing surface temperatures are. With vented attic assemblies moisture that diffuses into the attic space from the conditioned space is vented to the exterior by attic ventilation.
Either of these systems comes with a premium cost typically two to three times the price of a blown fiberglass or cellulose vented attic assembly. The acceptance of unvented conditioned attics continues to grow among builders and building officials. In warmer climates unvented attics can prevent the condensation that occurs on ductwork in some vented attic spaces. Unvented conditioned attics were quite rare before the 1980s.
Among the early promoters of conditioned attics was joe lstiburek a principal of the building science corporation. Code requirements vary across the country.