Unvented Conditioned Attic

The advantages of the unvented conditioned attic construction are increasingly being recognized within the industry to help with the following.

Unvented conditioned attic.

This sheathing is less than a year old. Energy conservation moisture management. Among the early promoters of conditioned attics was joe lstiburek a principal of the building science corporation. 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.

This system can help you avoid. The builder or homebuyer if the buyer has purchased prior to construction may want the attic space to be conditioned for additional living or storage space. Poorly insulated ducting can cause heat loss in colder months and the loss of conditioned air in the summer in vented attics. Unventilated attics are common where roof assemblies are complex and it s difficult to create a sealed ceiling plane.

Traditionally building codes have required attic ventilation. Lstiburek s enthusiasm was rooted in his desire to bring attic ductwork inside a home s thermal envelope. Other reasons for constructing an unvented attic include the following. Adding unvented attic insulation like spray foam seals the building envelope and stops airflow.

Mixing vented and unvented portions will lead to heavy condensation on the exposed roof sheathing. In most cases the existing insulation on an attic floor should be removed when an unconditioned attic is converted to a conditioned attic. The intended purpose was to allow warm air and moisture to escape. A conditioned attic requires a full commitment.

Depending on the climate and the thickness of the existing insulation it may make sense to leave the old insulation in place. This air seal will. Making the attic a conditioned space means the space will be the same temperature as the rest of your home. When all of the insulation is tight to the roof deck the unvented enclosed rafter truss assembly or unvented attic is within the building envelope and the attic will be conditioned to have a similar temperature as the interior space.

Unvented conditioned attics were quite rare before the 1980s.