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 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. 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 savings have ever been measured. No interior vapor retarders are installed on the ceiling side attic floor of the unvented attic assembly 2009 irc.

Traditionally building codes have required attic ventilation. 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. The difference in attic temperature between a vented an unvented attic with r 30 at the ceiling translates into minuscule savings. However if moisture is able to enter the unvented attic space it may lead to roofing panel issues.

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

Where wood shingles or shakes are used a minimum inch vented air space separates the. Unventilated attics can help to mitigate energy loss through leaky ducts or ceiling fittings. Finally in wildfire zones unvented roofs and attics have significant benefits in terms of fire safety over vented roof assemblies. The intended purpose was to allow warm air and moisture to escape.

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 energy savings touted by unvented attics can be as high as 20.