Unvented Cathedral Ceiling

All unvented attic and cathedral ceiling designs must provide for either a very high degree of airtightness or avoidance of condensation due to warming of cold surfaces.

Unvented cathedral ceiling. Many contactors use closed cell foam for unvented ceilings because the foam if properly installed blocks moist air from entering the roof structure. The primary purpose for the ventilation requirements are to remove moisture that can accumulate in the attic and potentially result in condensation. Insulating unvented cathedral ceilings if there are no codes to comply with then there are no codes to comply with.

With an unvented cathedral ceiling it is critical to keep moist air and water vapor away from the roof sheathing where it can build up and lead to wood decay. Moisture problems in unvented or poorly vented cathedral ceilings are not uncommon especially in cold climates where water vapor can enter the joist space and condense on the underside of the sheathing in cold weather. If you don t want to use sips or nailbase there are four basic approaches.

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. I might suggest using about two inches of foam board directly attached to the underside of the deck in the bays then fill the rest with fg batts. In particular using fiberglass insulation in an un vented cathedral ceiling is most likely to give way to discovery of advanced hidden damage and or mold over the life of the building and may give shorter roof shingle life as well as causing higher indoor temperatures than with a vented roof cavity design.

The primary source of water vapor that enters an. Unvented attics or unvented cathedral ceilings. The building codes have included requirements for ventilating attics for some time.

To meet durability goals in most applications the airtightness must be provided by a continuous membrane preferably adhered to the top surface of the structural roof deck and under rigid insulation that provides condensation control. The building codes have included requirements for venting attics for some time. The primary purpose for the ventilation requirements are to remove moisture that can accumulate in the attic and potentially result in condensation.

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction.