Unvented Roof Unvented Cathedral Ceiling Insulation

Four options for building an unvented roof assembly option 1.

Unvented roof unvented cathedral ceiling insulation.

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. 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. In general closed cell foam is the best choice for unvented cathedral ceilings.

The rigid foam will be fairly thick see sidebar how much insulation. Unvented attics and cathedral ceilings 2 air permeable insulation only irc r806 5 5 2 attic while the irc refers to this assembly as air permeable insulation only it also involves installation of rigid board insulation above the roof sheathing. Rigid foam above roof sheathing you can install all of the insulation above the roof sheathing but the foam has to be thick enough to meet minimum code requirements for ceiling r value. 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.

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