Unvented Roof Unvented Cathedral Ceiling Insulation

The rigid foam will be fairly thick see sidebar how much insulation.

Unvented roof unvented cathedral ceiling insulation.

In general closed cell foam is the best choice for unvented cathedral ceilings. Foil faced iso board can be cost effective insulation for finished attics and cathedral ceilings. 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. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.

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

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.