Supra Trusses Learning Centre
Welcome to our learning centre, below you will find useful terminology as well as examples of trusses.
Roof Trusses Terminology:
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
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
Hip Line The diagonal line formed by the intersection of two planes, sloping
downwards from the intersection
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).
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.
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.
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.
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.
Valley Line: The diagonal line formed by the intersection of two planes, sloping upwards
from the intersection.
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.
Wall Plates: Timber members, usually 38 x 76 or 38 x 114 S.A. 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.
Batten Centres: The distance, measured along the slope of the top chord, between battens.
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).
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.
Effective Lengths: The distance, measured along the slope of the top chord, between lateral bracing members - usually purlins - connected to the top chord.
Panel Length: The distance between the centres of adjacent joints or nodes, measured horizontally along the chords.
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.
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).
Top Chord Pitch: The angle of the top chord (TC) or rafter with respect to the horizontal.
Nominal Span: The horizontal distance between the outside edges of the supports (wall plates) -
usually the tie beam length..
Overall Height: The vertical height from the bottom of the bottom chord to the top of the apex.
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.
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
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
Hip Line The diagonal line formed by the intersection of two planes, sloping
downwards from the intersection
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).
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.
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.
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.
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.
Valley Line: The diagonal line formed by the intersection of two planes, sloping upwards
from the intersection.
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.
Wall Plates: Timber members, usually 38 x 76 or 38 x 114 S.A. 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.
Batten Centres: The distance, measured along the slope of the top chord, between battens.
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).
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.
Effective Lengths: The distance, measured along the slope of the top chord, between lateral bracing members - usually purlins - connected to the top chord.
Panel Length: The distance between the centres of adjacent joints or nodes, measured horizontally along the chords.
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.
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).
Top Chord Pitch: The angle of the top chord (TC) or rafter with respect to the horizontal.
Nominal Span: The horizontal distance between the outside edges of the supports (wall plates) -
usually the tie beam length..
Overall Height: The vertical height from the bottom of the bottom chord to the top of the apex.
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.