Unvented Attics In Metal Buildings

Where wood shingles or shakes are used a minimum inch vented air space separates the.

Unvented attics in metal buildings.

In coastal areas salt spray and corrosion are a major concern with steel frames metal roof trusses and truss plate connectors in vented attics. Unvented attics research has shown conditioned unvented attics can be an effective alternative to ventilating attics for steep slope roof assemblies. No interior vapor retarders are installed on the ceiling side attic floor of the unvented attic assembly 2009 irc. However if moisture is able to enter the unvented attic space it may lead to roofing panel issues.

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. 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. The difference in attic temperature between a vented an unvented attic with r 30 at the ceiling translates into minuscule savings. 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. The intended purpose was to allow warm air and moisture to escape. No interior class i vapor retarders are installed on the ceiling side attic floor of the unvented attic assembly 2012 irc 3. Unventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings.

Traditionally building codes have required attic ventilation. Unvented attics have entered fray as an alternative. Venting will reduce the temperature in an open attic. No savings have ever been measured.

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. Finally in wildfire zones unvented roofs and attics have significant benefits in terms of fire safety over vented roof assemblies.