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.
Unvented conditioned attic.
The intended purpose was to allow warm air and moisture to escape.
Adding unvented attic insulation like spray foam seals the building envelope and stops airflow.
Among the early promoters of conditioned attics was joe lstiburek a principal of the building science corporation.
Energy conservation moisture management.
Other reasons for constructing an unvented attic include the following.
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.
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.
This sheathing is less than a year old.
The advantages of the unvented conditioned attic construction are increasingly being recognized within the industry to help with the following.
This air seal will.
Mixing vented and unvented portions will lead to heavy condensation on the exposed roof sheathing.
Depending on the climate and the thickness of the existing insulation it may make sense to leave the old insulation in place.
Lstiburek s enthusiasm was rooted in his desire to bring attic ductwork inside a home s thermal envelope.
Unvented conditioned attics were quite rare before the 1980s.
Traditionally building codes have required attic ventilation.
However this recommendation should be addressed on a case by case basis.
Poorly insulated ducting can cause heat loss in colder months and the loss of conditioned air in the summer in vented attics.
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.
In most cases the existing insulation on an attic floor should be removed when an unconditioned attic is converted to a conditioned attic.
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.
Making the attic a conditioned space means the space will be the same temperature as the rest of your home.
