What is the correct definition of the soffit in a pipe?

• A. The crown of the pipe
• B. The pipe invert
• C. The outside diameter of the pipe
• D. The vertical alignment of the pipe

Answer: (B)

In piping, the soffit refers to the bottom interior surface of the pipe—the invert. It acts as the floor through which the fluid flows and serves as the reference level for calculating slope and depth. The crown is the top interior surface, the outside diameter is the pipe’s external size, and vertical alignment describes how the pipe is oriented. Since the bottom interior surface defines where flow actually occurs and is used to measure invert elevation for hydraulics, it’s described as the invert.