Unvented Finished Attic Insulation

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.

Unvented finished attic insulation.

If you don t want to use sips or nailbase there are four basic approaches. Un vented hot roof designs indoors finished attic. 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. 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.

This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. This allows you to install your bulkheads above the ceiling plane without the need for spray foam insulation. The advantages of unvented attic construction using spray foam insulation are numerous.

The roof insulation and air barrier must follow the plane of roofing materials rather than diverge figure 2. 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. The unvented attic space is completely within the building thermal envelope. This reduces latent air conditioning loads and provides further reductions in energy consumption.

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. Proper attic insulation is the best way to prevent heat loss in the winter and retain cool air in the summer. So it s time to pay close attention to what s happening up there. Fibrous insulation fibrous insulation e g batt or blown in can be installed under the roof deck in the hot dry.

Insulation approaches for unvented attics vary by climate. 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. 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.