Welcome to our learning centre, below you will find a list of useful terminology as well as examples of trusses.
Beam
A solid or composite timber lintel that usually supports trusses or rafters.
Beam Pocket
A void deliberately set into a wall to allow a beam or floor truss to bear on the wall.
Eaves
The part of a building that meets or overhangs the load bearing walls.
Gable Wall
The vertical wall at the end of a pitched roof extending to the underside of the roof covering.
Girder Truss
A truss that performs the special function of supporting other trusses.
Ridgeline
The line formed at the top of the roof by the intersection of the two sloping planes.
Roof Covering
The roofing material – sheeting, tiles, or slates – placed on top of the timber roof structures.
Roof Pitch or Slope
The angle of a roof plane with respect to the horizontal.
Truss Spacing or Truss Centres
Space between the centre-lines of adjacent trusses.
Valley
The part of a pitched roof forming the junction between two perpendicular roof sections.
Top Chord Pitch
The angle of the top chord (TC) or rafter with respect to the horizontal.
Overall Height
The vertical height from the bottom of the bottom chord to the top of the apex.
Nominal Span
The horizontal distance between the outside edges of the supports (wall plates) – usually the tie beam length.
Wall Tiles
Galvanised steel straps or wire ties that are securely embedded in load bearing walls at suitable positions, to anchor roof trusses or rafters to the wall.
Roof Plane
The two-dimensional, usually sloping surface of a roof, extending from the eaves to the ridge line between hip, valley, gable, or parapet lines.
Hip Line
The diagonal line formed by the intersection of two planes, sloping downwards from the intersection.
Wall Plates
Timber members, usually 38x76cm or 3x114cm. South African pine laid flat on top of the load bearing walls. The roof trusses are placed in their vertical positions on top of the wall plates, which assist in spreading the roof loading evenly over the brickwork.
Heel Line
A line connecting the heels of trusses, usually vertically above the outside edge of the wall plate.
Hip
The end of a roof section with a sloping end plane.
Longitudinal
Refers to the direction of the roof (usually at right angles to the trusses).
Parapet Wall
The vertical wall at the end of a building section, extending above the roof covering.
Batten Centres
The distance, measured along the slope of the top chord, between battens.
Bearing Width
The horizontal width of the structural support of trusses – usually the timber wall plate.
Bottom Chord Pitch
The angle of the bottom chord (BC) or tie beam with respect to the horizontal.
Pitch Or Slope
The angle of a chord with respect to the horizontal.
Purlin Centres
The distance, measured along the slope of the top chord, between purlins.
Overhang Length
The horizontal length of the extension of the top chord beyond the bearing support.
Clear Span
The horizontal distance between interior edges of supports.
Valley Line
The diagonal line formed by the intersection of two planes, sloping upwards from the intersection.
Stub Height
The vertical height from the bottom of the bottom chord to the top of the top chord at the outside edge of the support (wall plate).
Panel Length
The distance between the centres of adjacent joints or nodes, measured horizontally along the chords.
Load Bearing or Supporting Walls
The walls of a building that support the roof trusses, where all walls, except the Gable and Parapet walls, are Load Bearing.
Effective Lengths
The distance, measured along the slope of the top chord, between lateral bracing members – usually purlins – connected to the top chord.
Heel Height
The vertical height from the bottom of the bottom chord to the top of the top chord at the heel line (usually at the outside edge of the bearing).
