It is possible to make your cathedral ceilings into an energy efficient part of your home. Cathedral ceilings are high and open, created by simply covering and finishing exposed rafters in the roof. The ceiling follows the angle, or pitch, of the roof, and it can be considerably more difficult to properly insulate or ventilate than traditional ceilings.
When considering a cathedral ceiling, you must bear in mind that there is very little room or space available for insulation. This means that insulation for this project can be very expensive. In fact, it can be up to 4 or 5 times more than the cost of standard insulation materials. Many contractors choose to use insulation with an R-factor as much as 30 or higher for these types of installations.
Just as in a regular attic, ventilation is very important. Also, minimum rafter sizes should be maintained to ensure adequate ventilation in cathedral ceilings. An average R-30 rating for the insulation installed in the ceiling will require about 9 inches of fiberglass insulation, so to ensure adequate ventilation, you will need to make sure that there is at least 2½ or 3 inches of additional space for the ventilation system. So, the minimum rafter size to consider would be at least 2x12 inches.
Cathedral ceilings provide a very open and roomy feel to an area, and they can increase the value of your home. However, you must decide on a design that is both efficient and maintainable. Choose a designer or contractor that has experience installing several successful cathedral ceilings in your climate.