Vaulted ceilings, sometimes referred to as "cathedral ceilings," occur in steep-slope
roof assemblies in which there is no attic space between a ceiling and roof deck.
These assemblies pose unique ventilation problems.
Properly insulated cathedral ceiling assemblies incorporating air and vapor retarders
can function without ventilation. Vented cathedral ceiling assemblies incorporate
soffit or eave vents, adequate open air space between insulation, and roof deck
sheathing and ridge vents.
For buildings located in a heating climate zone, a problem often associated with
inadequately ventilated improperly insulated cathedral ceiling roof assemblies is
the formation of ice dams and icicles at the eaves of
these roof assemblies. Ice dams form when heat from a building's interior escapes
through nail-base insulation panel joints in a cathedral ceiling and warms the roof
deck from below.
For this reason, NRCA recommends provisions for ventilation are included in asphalt
shingle roof assemblies with vaulted ceilings.