Unvented Attics In Metal Buildings

The intended purpose was to allow warm air and moisture to escape.

Unvented attics in metal buildings.

However if moisture is able to enter the unvented attic space it may lead to roofing panel issues. 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. Usually there is a penalty with venting because venting causes greater air pulsing across the ceiling. 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.

No interior class i vapor retarders are installed on the ceiling side attic floor of the unvented attic assembly 2012 irc 3. The unvented attic space is completely contained within the building thermal envelope 2. 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. The difference in attic temperature between a vented an unvented attic with r 30 at the ceiling translates into minuscule savings.

In coastal areas salt spray and corrosion are a major concern with steel frames metal roof trusses and truss plate connectors in vented attics. Where wood shingles or shakes are used a minimum inch vented air space separates the. Traditionally building codes have required attic ventilation. Unventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings.

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. Venting will reduce the temperature in an open attic. Unvented attics have entered fray as an alternative.

The energy savings touted by unvented attics can be as high as 20. Unvented attics research has shown conditioned unvented attics can be an effective alternative to ventilating attics for steep slope roof assemblies.