Which of the following is not required in exterior nonbearing walls?

The requirement of load-bearing headers primarily pertains to structural walls, which are designed to support weight above them, such as the weight of beams, floors, or roofs. In this context, exterior nonbearing walls are not intended to bear any structural loads other than their own weight. Therefore, the inclusion of load-bearing headers is not necessary in the construction of nonbearing walls. These walls can still incorporate other elements like insulation, vapor barriers, and siding for thermal efficiency, moisture control, and aesthetic purposes, but they do not require the structural support that would be provided by load-bearing headers.

Insulation helps to improve energy efficiency, vapor barriers protect against moisture intrusion, and siding serves an important role in weather resistance and appearance, making them necessary components for such walls.