Terminology

While we’re passionate about trusses, we realise that not all of our clients are intimately familiar with all aspects of the industry. To make communicating with us simpler, we’ve compiled a glossary of terms that may come in handy:
  • Apex - The highest point of a truss
  • Barge – The trim along the edge of roofing at a gable end. It slopes at the roof pitch.
  • Batten – This can refer to roofing battens or ceiling battens. Battens are usually timber members fixed at right angles to the truss chords to support roof tiles or ceiling material. They also provide lateral restraint to the truss.
  • Bearing/Support Point – The point at which the truss is supported. A truss must have two or more supports located at truss panel points.
  • Bottom Chord – The truss member forming the bottom edge of a truss
  • Camber – The vertical displacement built into a truss to compensate for the downward movement expected when the truss is fully loaded.
  • Cantilever - The part of a truss that projects beyond an external main support, not including top chord extensions or overhangs.
  • Chord - The truss members forming the top and bottom edges of the truss.
  • Clear Span – The horizontal distance between inner edges of supports.
  • Concentrated Load - A load applied at a specific position, such as a load applied by an intersecting truss.
  • Connector (or Connector Plate) -  A light gauge steel plate with teeth projecting from one face. When pressed into intersecting timber members the plate connects the members in a rigid joint.
  • Creep - Movement resulting from the long term application of load to a timber member.
  • Cut-Off – A descriptor to refer to a truss that is cut short of its full span when compared to a standard shape. 
  • Dead Load - Permanent loads due to the weight of materials and truss self weight.
  • Deflection - Vertical and horizontal movement in a truss due to the applied load.
  • Design Loads - The various loads that a truss is designed to support.
  • Distributed Loads - Loads spread evenly along truss member.
  • Fascia – The trim along the edge of the eaves.
  • Gable Truss – A standard triangular shaped truss.
  • Girder Truss – A truss designed to support one or more trusses.
  • Heel Joint - The joint on a truss where the top and bottom chords meet.
  • Heel Point - The position on a truss where the bottom edge of the bottom chord meets the top chord.  Used for setting up production jigs. 
  • Hip – The intersection of two roof surfaces over an external corner of a building.
  • Hip Roof - A roof constructed with rafters or trusses pitched over all perimeter walls.
  • King Post – A vertical web at the centre of a gable truss, or the vertical web at the end of a half gable truss.
  • Lateral Brace – A bracing restraint applied at right angles to web or chord to prevent buckling.
  • Longitudinal Tie – A bracing restraint applied at right angles to web or chord to prevent buckling.
  • Live Load – A temporary load applied due to traffic, construction, maintenance, etc.
  • Overall Length – The length of truss excluding overhangs.
  • Overhang – The extension of a top chord beyond support.  Provision of eaves on gable trusses.
  • Nominal Span - The horizontal distance between supports of a truss.
  • Panel-point - The point where several truss members meet to form a joint.
  • Panel-point Splice – A splice joint in a chord coinciding with web intersection.
  • Pitch – The angular slope of truss chord measured in degrees.
  • Purlin - Roofing purlins are usually timber members fixed at right angles to the truss chords support roof sheeting. They also provide lateral restraint to a truss.  Purlins are similar to battens, except more widely spaced.
  • Rafter - A roof member supporting roofing battens or roofing purlins in conventional construction.  Rafters employ only the bending strength of the timber.  A roof truss may also be called a trussed rafter.
  • Ridge - The highest point on a gable roof.
  • Span - The horizontal distance between the outer edges of the truss supports.
  • Span Carried - The span of standard trusses that are supported by a girder truss.
  • Stress Grade – A strength classification of timber, based on species, seasoning and frequency of defects such as knots and sloping grain.  The stress grade can alternatively be based on actual mechanical testing of each piece.
  • Station - The position of a truss measured from the outside face of the end wall.  It’s usually used to describe the position of truncated girder and standard trusses in a hip end.
  • Top Chord – The truss member forming to edge of truss.
  • Truss – A trussed rafter is a triangulated, self-supporting framework of chords and webs that supports applied loads by a combination of the bending strength of the chords and the axial compressive and tensile strength of the chords and webs.
  • Valley – The intersection to two roof surfaces over an internal corner of a building.
  • Verge – The roof overhang at a gable end.
  • Verge Rafter – The rafter projecting from gable end to support the verge.
  • Waling Plate – A timber member bolted to the face of a truss to support intersecting rafters or trusses.  May also be used to support intersecting battens or purlins.
  • Web - The internal members of a truss.  Usually only subject to axial loads due to truss action.
  • Wind Load - Load applied to the roof by the wind.



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