roof truss glossary

Apex/Peak – The uppermost point of a truss.
Attic truss/room-in-the-roof – A truss which forms the top storey of a dwelling but allows the area to be
habitable by leaving it free of internal WEB members. This will be compensated by larger timber sizes elsewhere.
Bargeboard – Board fitted to conceal roof timbers at GABLE END.
Battens – Small timber members spanning over trusses to support tiles, slates etc.
Bearer – A member designed to distribute loads over a number of trusses.
Bearing – The part of a truss receiving structural support. This is usually a WALLPLATE but can be an internal wall etc.
Binder – A longitudinal member nailed to trusses to restrain and maintain correct spacing.
Birdsmouth – A notch in the underside of a RAFTER to allow a horizontal seating at the point of support (usually used with RAISED TIE TRUSSES).
Blocking – Short timbers fixed between chords to laterally restrain them. They should be at least 70% of the depth of the CHORDS.
Bottom chord/Ceiling Tie – The lowest member of a truss, usually horizontal which carries the ceiling construction, storage loads and water tank.
Bracing – This can be Temporary, Stability or Wind Bracing which are described under these headings.
Building Designer – The person responsible for the structural stability and integrity of the building as a whole.
Cantilever – The part of a structural member of TRUSS which extends beyond its bearing.
Chevron Bracing – Diagonal bracing nailed to the truss in the plane of the specified webs to add stability.
Dead Load – The load produced by the fabric of the building, always long term (see DESIGN LOADS).
Deflection – The deformation caused by the loads
Design Loads – The loads for which the unit is designed. These consider the duration of the loads long term, medium term, short term and very short term.

Duo/dual pitch truss – A truss with two rafters meeting at the APEX but not necessarily having the same PITCH on both sides.
Eaves – The line where the rafter meets the wall.
Extended Rafter – See RAISED TIE TRUSS.
Fascia – Horizontal board fitted along the length of the building to the edge of the truss overhangs.
Fink Truss – The most common type of truss used for dwellings. It is duo-pitch, the rafter having the same pitch. The webs form a letter W.
Gable End – The end wall which is parallel to the trusses and which extends upwards vertically to the rafters.
Hip End – An alternative to a GABLE END where the end wall finishes at the same height as the adjacent walls. The roof inclines from the end wall, usually (but not always) at the same PITCH as the main trusses.
Hip Set – The trusses, girders and loose timbers required to form a hip end.
Horn/nib – An extension of the ceiling tie of a truss (usually monos or bobtailed trusses) which is built into
Imposed Load – The load produced by occupancy and use including storage, inhabitants, moveable partitions and snow but not wind. Can be long, medium or short term.
Internal Member – See WEB.
Intersection – The area where roofs meet.
Jack Rafter – An infill rafter completing the roof surface in areas such as corners of HIP ENDS or around chimneys.
Live Load – Term sometimes used for IMPOSED LOADS.
Longitudinal Bracing – Component of STABILITY BRACING.
Loose Timber – Timbers not part of a truss but added to form the roof in areas where trusses cannot be used.
Mono-pitch truss – A truss in the form of a right-angled triangle with a single rafter.
Nailplate – Metal PLATE having integral teeth punched from the plate material. It is used for joining timber in one plane with no overlap. It will have an accreditation certificate and will be manufactured, usually, from
galvanised steel. It is also available in stainless steel.

Node – Point on a truss where the members intersect.
Noggings – Timber pieces fitted at right angles between the rafters and ceiling ties to form fixing points.
Overhang – The extension of a rafter or ceiling tie of a truss beyond its support or bearing
Part Profile – A truss type formed by truncating a normal triangular truss.
Pitch – The angle of the rafter to the horizontal, measured in degrees.
Purlins – Timber members spanning over trusses to support cladding or between trusses to support loose timbers.
Queen – Internal member (WEB) which connects the APEX to a third point on a FINK TRUSS.
Rafter/Top chord – The uppermost member of a truss which normally carries the roof covering.
Rafter Diagonal Bracing – Component of STABILITY BRACING.
Raised Tie Truss – A truss which is supported at a point on the rafter which is beyond the point where the rafter meets the ceiling tie.
Return Span – The span of a truss being supported by a girder.
Ridge – The line formed by the truss apexes.
Roof Designer – The person responsible for the roof structure as a whole and who takes into account its stability and capability of transmitting wind forces on the roof to suitable load-bearing walls.
Scab – Additional timber fitted to the side of a truss to effect a local reinforcement, particularly in RAISED TIE TRUSSES.
Setting out Point The point on a truss where the undersides of the rafter and ceiling tie meet.
Soffit – Board fixed underneath EAVES overhang along the length of the building to conceal timbers.
Span – Span over wallplates is the distance between the outside edges of the two supporting wallplates. This is usually the overall length of the ceiling tie.
Spandrel Panel – A timber frame, triangular panel forming gable wall above ceiling line.

Splice – A joint between two members in line using a NAILPLATE or glued finger joint.
Strap – Metal component designed to fix trusses and wallplates to walls.
Strut – Internal member connecting the third point and the quarter point on a FINK TRUSSS.
Stub End – See PART PROFILE.
Temporary Bracing – An arrangement of diagonal loose timbers installed for safety during erection. Often incorporated with permanent STABILITY and WIND BRACING structures.
Timber Stress Grading – The classification of timber into different structural qualities based on strength (see BS4978: 1996).
Trimmer – A piece of timber used to frame around openings.
Trussed Rafter Designer – The person responsible for the design of the TRUSSED RAFTER as a component and for specifying the points where Bracing is required.
Truss clip – A metal component designed to provide a safe structural connection of trusses to wallplates. Also to resist wind uplift and to remove the damage caused by SKEW NAILING.
Truss Shoe – A metal component designed to provide a structural connection and support for a truss to a girder or beam.
Uniformly distributed load (UDL) – A load that is uniformly spread over the full length of the member.
Valley Board – A member raking from incoming RIDGE to corner in a valley construction.
Valley Frames/Set – Infill frames used to continue the roofline when roofs intersect.
Verge – The line where the trussed rafters meet the gable wall.
Wallplate – A timber member laid along the length of the load bearing walls to support the trusses.
Webs – Timber members that connect the rafters and the ceiling tie together forming triangular patterns which transmit the forces between them.
Wind bracing – An arrangement of additional timbers or other structural elements in the roof space, especially designed to transmit wind forces to suitable load-bearing walls.