Unvented Attics In Metal Buildings

No interior class i vapor retarders are installed on the ceiling side attic floor of the unvented attic assembly 2012 irc 3.

Unvented attics in metal buildings.

The concept of conditioned unvented attics provides for moving ceiling air and thermal barriers to the roof plane as shown below where better building airtightness can be achieved. Where wood shingles or shakes are used a minimum inch vented air space separates the. The unvented attic space is completely contained within the building thermal envelope 2. Building america research has demonstrated unvented conditioned attics can substantially improve energy performance while allowing home builders to continue locating hvac systems in the attic space.

No interior vapor retarders are installed on the ceiling side attic floor of the unvented attic assembly 2009 irc. The difference in attic temperature between a vented an unvented attic with r 30 at the ceiling translates into minuscule savings. No savings have ever been measured. To construct an unvented attic air impermeable insulation think closed cell spray foam will be applied in direct contact with steel roofing or sheathing underside and gable end walls so as to tie roof insulation into wall insulation below.

Unvented attics research has shown conditioned unvented attics can be an effective alternative to ventilating attics for steep slope roof assemblies. To provide an unvented conditioned space for locating hvac equipment in the attic and or to provide a continuous thermal barrier for designs that have complex coffered ceiling planes and or numerous penetrations for lights speakers vents soffits etc which make it difficult to achieve an airtight ceiling plane. Venting will reduce the temperature in an open attic. Traditionally building codes have required attic ventilation.

Unventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings. The intended purpose was to allow warm air and moisture to escape. The energy savings touted by unvented attics can be as high as 20. Install insulation along the underside of the roof deck of an unvented attic rather than on the ceiling deck of a vented attic for either of two reasons.

Usually there is a penalty with venting because venting causes greater air pulsing across the ceiling. Finally in wildfire zones unvented roofs and attics have significant benefits in terms of fire safety over vented roof assemblies.