Focus on Energy: A Nearly Perfect Cathedral Ceiling

Cathedral ceilings are an increasingly popular design option, because they provide a feeling of spaciousness that flat ceilings cannot. But to the designer and builder, cathedral ceilings pose several problems, including moisture control, providing adequate ventilation, and meeting minimum insulation requirements. The design offered here — I call it a "no-fault" cathedral ceiling — meets those challenges while also providing a space for mechanicals, an inside and outside radiant barrier, and the long-spanning advantage of wood I-joists (see Figure 1). Construction Details I tried out the design on an addition for my own home. I used 91/2-inch I-joists, as required for the span, and an LVL ridge beam. I cut the rigid insulation — foil-faced polyisocyanurate — on the table saw, ripping