Non Vented Attic System

In order for an un vented roof assembly to function properly the following conditions must be in place.

Non vented attic system.

Unventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings. Because the drying capacity of unvented roof assemblies is inherently lower than vented ones it is especially critical to control built in moisture during construction. 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. The attic space becomes indirectly conditioned as a result of the air leakage heat transfer and vapor diffusion through the ceiling.

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. 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. 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.

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