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.

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 energy savings touted by unvented attics can be as high as 20. No savings have ever been measured. In coastal areas salt spray and corrosion are a major concern with steel frames metal roof trusses and truss plate connectors in vented attics.

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. 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 unvented attic space is completely contained within the building thermal envelope 2. Unvented attics research has shown conditioned unvented attics can be an effective alternative to ventilating attics for steep slope roof assemblies.

Unvented attics have entered fray as an alternative. 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. 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.

No interior class i vapor retarders are installed on the ceiling side attic floor of the unvented attic assembly 2012 irc 3. No interior vapor retarders are installed on the ceiling side attic floor of the unvented attic assembly 2009 irc. 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. Traditionally building codes have required attic ventilation.

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