Final answer:
The base of the triangle in roof framing is known as the span, which is the total horizontal distance between the supporting ends of the roof.
Step-by-step explanation:
In roof framing, the base of the triangle is called the span. The span is the total distance the roof extends from one supporting end to the other, essentially representing the width of the building where the roof is being constructed. This is different from the pitch, rise, run, or slope, which are other measurements used to describe different aspects of a roof's geometry and design.