A cathedral ceiling does wonders to make a room seem larger than it is. Soaring space and high walls also give you the opportunity for large windows, which bring in outdoor light and create the illusion of even more space.
But building a cathedral ceiling is not simply a matter of leaving out the ceiling joists and putting drywall on the rafters. For one thing, the lack of an attic creates a challenge when it comes to providing sufficient insulation in the roof. You need to make sure you allow enough room for both the insulation and an air space to allow for ventilation.
Beyond the insulation issues, you face structural challenges. The ceiling joists in a conventional house design do more than provide a frame on which to attach the ceiling drywall and the attic floor. They also hold the walls upright.
But isn’t it the other way around? Don’t the walls hold the joists up? It’s actually a little of each. The force of the rafters on the tops of the walls creates outward pressure. By connecting the walls with joists you counteract that outward thrust on the walls. But with a cathedral ceiling, you’ve removed that tie, and you need to eliminate or counteract the outward thrust in some other way.
There are essentially three techniques you can use when building a cathedral ceiling. One method involves installing a series of rafter ties to replace the joists. In the second method, you install a ridge beam, which will bear the load of the rafters (as opposed to the usual non-load-bearing ridge board.) In the third method you would use trusses specifically designed to give you a raised ceiling.
Each method has advantages and disadvantages, and we’ll talk a bit more about these in the next two issues.