Non Vented Attic System

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

Non vented attic system.

The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling. 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. It is a common misconception that one of the unvented attic problems is that the roof needs to breathe or that the insulation will make the roof hot. Unventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings.

The energy savings touted by unvented attics can be as high as 20. 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. In order for an un vented roof assembly to function properly the following conditions must be in place. Control construction moisture content with tenting or temporary roofing when necessary.

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.