by Jamie Fisher In the never-ending quest to make houses feel more spacious, the vaulted or cathedral ceiling is a natural temptation. After all, the space is already there, so you might as well put it in a room instead of in the attic, right? There are certainly times when a vaulted ceiling enhances a space. But even when the considerable technical difficulties can be overcome (see "Venting Details for Cathedral Ceilings," 12/96), the vaulted ceiling, though a natural first impulse, is not always the best solution. Sometimes the floor plan is better served by a flat ceiling. At other times, the space is best enhanced by a sculpted ceiling plane that is not a direct reflection of