Unvented Finished Attic Insulation

These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck.

Unvented finished attic insulation.

This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. Un vented hot roof designs indoors finished attic. Where the attic space is finished with drywall or other ceiling materials installed against the underside of the roof rafters while we prefer in floor insulation here we ll have to insulate the roof cavity between the rafters. Fibrous insulation fibrous insulation e g batt or blown in can be installed under the roof deck in the hot dry.

The roof insulation and air barrier must follow the plane of roofing materials rather than diverge figure 2. So it s time to pay close attention to what s happening up there. A fundamental requirement of an unvented attic assembly is the use of air impermeable insulation on the underside of the unvented roof to prevent air infiltration and exclude airborne moisture from the attic. It is a proven cost effective approach to creating a more energy efficient building particularly when the hvac system is located in the attic space.

This reduces latent air conditioning loads and provides further reductions in energy consumption. An alternate to spray foam insulation in an unvented attic is plenum trusses which allow you create a reverse bulkhead above the ceiling plane that is insulated. Four options for building an unvented roof assembly. If you don t want to use sips or nailbase there are four basic approaches.

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. 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. Insulation approaches for unvented attics vary by climate. 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 roof assemblies should be insulated either with air impermeable insulation rigid foam or spray polyurethane foam or with a combination of foam and air permeable insulation. Proper attic insulation is the best way to prevent heat loss in the winter and retain cool air in the summer. The unvented attic space is completely within the building thermal envelope.