Glossary of  Common Terms Used in Timber Roof Structures

  1. Apex- Point on a truss where the sloped top chords meet

  2. Batten-small section timber member, used to support a roof covering of tiles or slates

  3. Bearing-structural support, usually a wall, positioned under the top chord or bottom chord

  4. Bottom chord-(tie beam)- horizontal or inclined (eg scissors truss) member that establishes the lower edge of the truss

  5. Brandering-small section timber member used to support a fixed ceiling; brandering is usually fixed to the underside of the truss bottom chord

  6. Cantilever-part of the truss (or beam) that extends beyond its support, (exclusive of the overhang)

  7. Centre Bearing truss-truss with a structural support at, or close to, the centre of the truss span as well as at the heel points

  8. Chord-one of the main members that form the top and bottom outline of the truss

  9. Clear span-horizontal distance between interior edges of supports

  10. Competent person-person who is qualified by virtue of his training and experience to design, erect, manufacture or inspect a roof structure

  11. Dual Pitch truss-truss that has two different pitches on its top chord

  12. Engineered truss design-truss design produced by a rational design process in accordance with an appropriate code of practice

  13. Fascia-trim Board applied to the ends of truss overhangs

  14. Girder Truss-truss that performs a special  function of carrying loads from other trusses that it supports

  15. Heel-point on a truss at which the top chord and bottom chord intersect, or where the first vertical web intersects with the bottom chord in a stub-ended truss

  16. Hip truss-used to form a hip-end configuration in conjunction with hip girders thus eliminating the gable wall

  17. Imposed load- (live load)- non-permanent loads such as snow, ice, rain, construction/maintenance activities etc

  18. Jack rafter-special rafter used in hip construction

  19. Lateral brace-member connected to certain truss members to prevent horizontal movement

  20. Monoplanar truss-truss with all chords and webs assembled in a single plane (usually associated with factory-made, nail-plated trusses)

  21. Nail plate-galvanised steel plate punched to form a nail pattern integral with the plate and used as a structural connector

  22. Node- point of intersection of various members that make up the panels of the truss

  23. Overhang-extension of the top chord of a truss, measured horizontally from the end of the bottom chord

  24. Panel- segment of a chord defined by two adjacent joints or node points

  25. Panel point- point of intersection between webs and a top or bottom chord

  26. Pitch-(slope)-angle of the top chord with respect to the horizontal or, in a scissors truss, the angle with respect to the bottom chord and the horizontal

  27. Purlin-horizontal member attached to and placed perpendicular to the truss top chord in order to support sheet roofing materials of steel or fibre-cement

  28. Registered person-person who is registered with the Engineering Council of South Africa (ECSA)

  29. Responsible person-competent person who takes responsibility for designing, erecting, manufacturing or inspecting a timber roof structure

  30. Runner-(binder)-continuous bracing member that runs the length of the roof to provide lateral stability for web members or the chords of trusses in conjunction with triangulated cross-bracing

  31. Scissor Truss-double pitched truss with sloping bottom chords

  32. Self-weight load -(dead load.)-a load that consists of the weight of all the members of the structure itself, plus the weight of all permanent finishes such as roof coverings and ceilings

  33. Splice-point at which two chord members are joined together to form a single member

  34. Stub end- when the top chords of the truss in a pitched roof do not coincide with the bottom members at the wall-plate but are supported by vertical members that form the end of the truss; these trusses are said to have stub ends or to be “bobtailed”

  35. Symmetrical truss-truss with the same configuration of members occurring on each side of the truss centre line

  36. Timber truss-with all structural members of timber but using metal connecting devices

  37. Top chord-(rafter)-horizontal or inclined member, establishes the upper edge of the truss

  38. Traditional truss-truss that is built with lapped members at joints and with bolted/nailed connections

  39. Truss-triangulated combination of members and joints which, when fitted together, form a rigid structural component intended to support both the permanent and imposed loads for which it was designed

  40. Valley truss-truss used to form a valley in association with standard or special trusses (usually the only type of truss which does not have structural triangulation)

  41. Web-member that joins the top and bottom chords to create triangular patterns that give truss action

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