Roof Geometry – Internal intersection line of two sloping roof surfaces What is the name of the line formed by the intersection of two sloping roof surfaces that meet to create an internal angle (less than 180°)?

Introduction / Context:
Complex roofs contain several intersection lines, each with distinct detailing for weatherproofing. Correctly naming these lines is essential for specifying flashings, gutters, and tile or sheet layouts.

Given Data / Assumptions:

• Two sloping roof planes intersect to form an internal angle (re-entrant).
• Conventional pitched roof construction.
• Terminology as used in roofing practice.

Concept / Approach:
A valley is the internal intersection where rainwater naturally concentrates and runs downward. A hip is the external, convex intersection. The ridge is the top horizontal intersection, and the eave is the lower edge of a roof.

Step-by-Step Solution:
Identify the internal angle intersection → valley.Differentiate from hip (external angle) and ridge (top horizontal line).Confirm correct term among options.

Verification / Alternative check:
Detailing manuals show valley gutters or valley flashings due to concentrated runoff, underscoring the importance of this junction.

Why Other Options Are Wrong:

• Hip: external convex junction, not internal.
• Ridge: horizontal apex line.
• Eave: lower edge of roof; not an intersection line.
• “None of these”: incorrect because “valley” is the standard term.

Common Pitfalls:
Under-sizing valley gutters or incorrect underlay laps can cause leaks at this highly stressed junction.

Final Answer:
Valley