Unvented Roof Unvented Cathedral Ceiling Insulation

Foil faced iso board can be cost effective insulation for finished attics and cathedral ceilings.

Unvented roof unvented cathedral ceiling insulation.

Four options for building an unvented roof assembly option 1. The rigid foam will be fairly thick see sidebar how much insulation. It is also one of the most expensive and most building inspectors will not allow it to be left uncovered for fire code reasons. 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.

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

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