Non Vented Attic System

The unvented attic space is completely contained within the building thermal envelope.

Non vented attic system.

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. In order for an un vented roof assembly to function properly the following conditions must be in place. Unventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings. However if moisture is able to enter the unvented attic space it may lead to roofing panel issues.

In reality if spray foam insulation is used on the roof deck it could raise the temperature of the shingles a few degrees but not enough to cause any damage. The energy savings touted by unvented attics can be as high as 20. Control construction moisture content with tenting or temporary roofing when necessary. The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling.

Unvented attic assemblies spaces between the ceiling joists of the top story of the roof rafters shall be permitted if all of the following conditions are met.