Roof Truss Glossary

Apex/Peak
The upper most point of a truss.

Attic Truss/Room-in-the-Roof
A Truss forming the storey of a dwelling. Characterised by a central, habitable area free from web members. Timber sections are generally larger than a standard Truss.

Birdsmouth
A notch in the underside of a loose rafter to allow a Horizontal setting at a point of support (not usually used On Truss Rafters except with a Raised Tie Truss).

Bobtail
See STUB END.

Bottom Chord/Ceiling Joist/Tie
The lower member of a Truss, normally horizontal, which carries the ceiling construction, storage loads and water tank.

Bracing
See STABILITY BRACING.

Building Designer
The person responsible for the structural stability and integrity of a building as a whole.

Cantilever
The part of a structural member or truss that extends beyond it's bearing.

Connector Plate/Fastener/Nail Plate
Metal plate having integral teeth punched from the plate material. Used for joining timbers in one plane with no overlap within Truss over Joints/node points. Usually in Galvanised steel. Not usually for site application.

Jack Rafter
An infill rafter completing the roof surface in areas such as the corners of hip ends.

Dead Load
The permanent load produced by the fabric of the building

Deflection
The deformation caused by the loads.

Extended Rafter/Raised Tie Truss
A Truss which is supporting at a point on the extension of the rafter, beyond the point where the bottom chord meets, creating a part sloping ceiling within the rooms below. Not only used as a decorative feature but to achieve greater overall ceiling height where wall height is restricted.

Fink Truss
Named after the original designer. A duopitch truss with a wed configuration within forming a letter W. The most common truss type used for dwellings.

Gable End
The end wall (parallel to the individual trusses) extended up vertically to the plane of the top chords of the trusses.

Gable Ladder
Components used to bridge across a gable end to form the roof overhang

Girder Truss
A truss comprising of two or more individual trusses fixed together and designed to carry exceptional loads, such as those imparted by other trusses.

Hip End
An alternative to a gable end. The end wall is finished to the same height as the adjacent walls. The roof inclines from the end wall usually at the same pitch as the main Trusses.

Pitch
The angle of the chord (usually rafter) to the horizontal measured in degrees.

Span
Span over all wall plates. The distance between the outside edge of the two supporting wall plates situation on the cavity walls.

Stability Bracing
An arrangement of loose timbers installed in the roof space to provide lateral support to truss members and to the trusses.

Stub End
A truss type formed by the truncation of a normal triangular truss.

Top Chord/Rafter
The uppermost member of a truss normally carrying the roof covering and snow

Truss/Trussed Rafter
A lightweight framework, normally triangulated, spaced at intervals generally not exceeding 0.6m and made from timber members of the same thickness fastened together in one plane by metal fasteners.