Unvented Attic Assembly

However unvented attics can reduce residential energy needs and are allowed by the code under certain conditions.

Unvented attic assembly. Unvented attic assemblies and unvented enclosed rafter assemblies are permitted if all the following conditions are met. Unventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings. However designers of compact roof assemblies must consider vapor permeance and arrangement of the roofing materials to produce acceptable hygrothermal performance and low. The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling.

An unvented assembly can perform well but it s important to get the details right to avoid sheathing rot. No interior class i vapor retarders are installed on the ceiling side attic floor of the unvented attic assembly or on the ceiling side. Air permeable insulation such as fiberglass batts dense packed cellulose or blown in fiberglass can t be used alone for an unvented assembly since these types of insulation can allow moist indoor air to reach the cold roof sheathing leading to condensation or moisture accumulation. The energy savings touted by unvented attics can be as high as 20.

The unvented attic space is completely contained within the building thermal envelope. Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof. Unvented attic assemblies offer numerous performance advantages versus vented attic assemblies. When hvac equipment is in the attic insulation and an air barrier at the roof line brings that equipment within the conditioned enclosure envelope thereby allowing it to operate in more favorable temperature and humidity conditions without air.

Unvented attic assemblies code notes 2009 irc 2012 irc adequate attic ventilation is a long standing requirement in building codes for moisture control. Unvented roof assemblies are becoming an increasingly common construction alternative to traditional vented roofs. They are designed without ventilation openings and the attic is conditioned like the rest of the living space. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.

These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. However if moisture is able to enter the unvented attic space it may lead to roofing panel issues.