Unvented Roof Unvented Cathedral Ceiling Insulation

This document provides a brief description of different types of unvented roof assemblies and the benefits of unvented roof construction.

Unvented roof unvented cathedral ceiling 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. Four options for building an unvented roof assembly option 1. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. 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.

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. 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. It is also one of the most expensive and most building inspectors will not allow it to be left uncovered for fire code reasons.

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