Thursday, July 2, 2009

Roofing Terminology

Much of the terminology used by architects, contractors and engineers to describe roofs and their components is unique to their trade. Since so much of it appears in the updates on this blog it seems like a good time to provide some definitions so that everyone can understand.

Bottom Chord - A horizontal or inclined member that establishes the bottom member of a truss. ( The Top Chord would therefore establish the top member of the truss.

Dead Loads - Any permanent load such as the weight of roofing, flooring, sheathing, insulation, or ceiling material, as well as the weight of the truss itself. (

Fascia - The flat surface located at the outer end of a roof overhang or cantilever end. (

Heel­ - Point on a truss at which the top and bottom chords intersect. (

Masonry Walls - Wall comprised of brick, stone, cement, etc. (

Purlin - A horizontal member attached to and placed perpendicular to the truss top chord to support the roofing. (

Sheathing - Plywood, gypsum, wood fiber, expanded plastic or composition boards encasing walls, ceilings, floors and roofs of framed buildings. May be structural or non-structural, thermal-insulating or non-insulating, fire-resistant or combustible. (

Sill Plates - Horizontal member laid directly on a foundation on which the framework of a building or the roof of a building is erected. (

Structural Tie Rods - a rod or bar in a truss or other frame that transmits tensile stress (

Trusses – An engineered structural component assembled from wood members, metal connector plates and other mechanical fasteners. Designed to carry its own weight and superimposed design loads. The truss members form a semi-rigid structural framework and are assembled such that the members form triangles.. (