Cathedral ceilings insulation and ventilation

Cathedral ceilings - with their high sloping ceilings closely attached to the roof trusses - offer an open and a more spacious feel, but they require more cares and proper insulation and ventilation.

Energy efficiency Problems

Cathedral ceilings (vaulted ceilings are a variant of cathedral ceilings) are high sloping ceilings closely attached to the roof trusses, without attic space.

Cathedral ceiling height raises practical and economical questions.

Since the ceiling is attached directly to the roof trusses, a proper insulation and ventilation demands wider trusses (at least 12 inches) and also higher costs...

Besides, higher ceilings involve larger volumes of air to heat or to cool, which also means higher energy costs.

Take into account these disadvantages, if you are considering cathedral ceilings for a new home.

Ventilation and insulation Issues

Cathedral ceiling insulation The cathedral ceiling design must provide enough space between the roof deck and the ceiling panels for adequate insulation and ventilation.

If the trusses are too thin, there will be problems of space for proper ventilation or for proper insulation… Wider trusses – or truss joists and scissor truss framing - are mandatory to good insulation and ventilation.

Insulation levels

Cathedral ceilings insulation levels vary with climate. Most codes recommend R-25 to R-38 insulation levels, but more is not to much. Bet on R-49 or more in colder climate zones.

2x12 rafters are sufficient for standard 10-inch-R-30 insulation batts for cathedral ceilings, and will allow space for ventilation. For higher insulation levels you should have larger rafters, or use truss joists or scissor truss framing.

Foil-faced batt insulation and rigid foam insulation

Fiberglass, rock wool and cellulose foil-faced batts are good insulation solutions for cathedral ceilings; they have also the advantage of a good Perm rating (ability to pass water vapor).

Rigid foam insulation is another advantageous alternative. It involves higher insulation value for the same space, but it also demands the use drywall or other fire-rated material covering (the thickness of the covering varies with local codes).

Insufficient Cathedral Roof space

If the trusses and the roof framing do not provide sufficient space for the application of the insulation, attach furring strips to the underside of the rafters; they will accommodate higher insulation levels.

You may also use rigid foam insulation or high-density batts (R-30) to get a higher insulation value for the same thickness. High-density R-30 batts have the same thickness as R-25 batts, and can be used in 2x10 framing.

Rafter baffles

Rafter baffles (pictured in yellow, in the image above) are a strategic element for cathedral ceiling insulation and ventilation. They ensure the ventilation channel, and are installed between the roof decking and the insulation.

For more details on baffles, see: Rafter Vents (Baffles).