Cathedral ceiling construction is inherently more prone to moisture damage than open attic construction, because cathedral ceiling construction creates isolated air spaces in rafter cavities. Although providing effective ventilation to attics with simple geometric roofs (straight pitch) is relatively easy and inexpensive, providing soffit and ridge ventilation to each individual cavity in cathedral ceilings may be impractical, and in many cases, impossible.
Properly packing high density Nu-Wool Premium Cellulose Insulation into cathedral ceilings significantly reduces both the air pockets that cause moisture problems and the need for getting rid of condensation. The bulk of moisture moving into any insulated cavity is driven primarily by air. Stopping air movement should be the primary focus in insulating cathedral ceiling assemblies. High-density Nu-Wool Premium Cellulose Insulation, installed at greater than 3.0 lbs. per cubic foot, greatly reduces the voids and restricts the movement of air through the insulation.
There are two acceptable methods to dense pack Nu-Wool Premium Cellulose Insulation into cathedral ceilings. The first method requires a vapor retarder be installed between the interior ceiling and the insulation, and a continuous ridge vent be installed at the roof peak to provide a point of moisture vapor relief. The second method is based on the code-accepted practice of conditioned attic assemblies. This method requires air impermeable insulation, such as closed cell spray foam or extruded polystyrene rigid foam, to be installed against the roof deck to an R-Value determined by the climate zone. The remainder of the cavity must be dense packed with Nu-Wool Premium Cellulose Insulation. When using this second method neither the vapor retarder nor ridge vent is required.