APB » Roof Trusses » Truss Terminology

Roof Truss Terminology

Bottom Chord: A horizontal member that establishes the lower edge of
 a truss, usually carrying combined tension and bending stresses.

Butt Cut: Slight vertical cut on the outside edge of truss bottom chord to make sure uniform nominal span.
 (Typically 1/4 inch)

Cantilever: A condition where both the top and bottom chords extend beyond a support structure with
 no bearing  at the extended end.

Chase Opening: An open panel in a floor truss for used for running utilities through it such as
 air conditioning  or heating ducts.

Clear Span: The horizontal distance between interior edges of support.

Concentrated Load: Superimposed load centered at a given point; (like roof mounted air conditioners).

Dead Load: Any permanent load such as the weight of the truss, sheathing, or purlins, roof material,
 ceiling, etc.

Deflection: Movement of an in place truss caused by dead and live loads.

Design Loads: The live and dead loads which a truss is designed to support.

Fascia: Dimensional lumber used as trim board applied to ends of overhang.

Heel: The point on a truss where the top and bottom chords intersect.

Heel Height: Height of truss at end of span (excluding overhangs) or plumb cut & butt cut.

Interior Bearing Truss: Truss with structural support in the center of a truss span as well as at end points.

Lateral Brace: A dimensional lumber member connected at right angles to a chord or web member of a truss,
 (typically three trusses continuous required).

Live Load: Loading which is not permanent, such as snow, wind, temporary
 construction loads, etc.

Overhang: The extension of the top chord of a truss beyond the bearing support.

Peak: Point on a truss where the sloped top chords meet.

Plumb Cut: Top chord cut to provide for vertical (plumb) installation of fascia.

Reaction: The total load transmitted to its support by a truss.

Sealed Drawings: Structural Drawings or truss drawings having the seal of a
 registered professional architect or engineer.

Slope: (Pitch) The inches of vertical rise in 12 inches of horizontal run for inclined members

Square Cut: End of top chord cut perpendicular to the slope of member.

Top Chord: The inclined horizontal member that makes up the upper edge of a truss, usually
 carrying bearing and compression stresses.

Uniform Load: A total load that is equally distributed over a given length, usually expressed in
 pounds per linear foot (PLF).

Valley: A depression in a roof where two roof slopes meet.

Webs: Members that join the bottom and top chords forming the triangular patterns that give truss
 action, usually carrying tension or compression stresses.