Elevations Comparison

This article is to explain the difference between a truss elevation and a profile rafter elevation.

The profile rafter is a theorical line (the French word is: "chevron d'emprunt", "emprunt" meaning: that has no existence.)

Do not confuse it with the Common Rafter. 

On the plan view a profile rafter is ALWAYS perpendicular to the overhang. 

Wisely used in “l’art du trait”, it is THE reference in French carpentry.

Bounded by three lines:

               - The run line (or base line), always horizontal, this line is located at the lowest top point of the roof. Its length corresponds to the width of the roof. (fr = ligne de trave).
Identified by this symbol:

                     - The axis line: (or rise line), always vertical, this line’s length correspond to the rise of the roof. (fr = ligne d’axe).
     Identified by this symbol:

                    - The battern: top of the roof. It’s the border line between the frame and the roofing.

      Unlike the profile rafter, a truss is not necessary perpendicular to the overhang (e.g. on a sloped ridge building). Its elevation is used to design it, that means that the dimensions of the pieces of wood composing it need to be know.
      On the opposite a profile rafter has no element. It has to be drawn only with simple lines (French : "par simple ligne".)

Download: ElevationsComparison.pdf