There are many terms, words and phrases used when referring to trusses and joists. Therefore, to make things a little less complicated we have put together the below glossary to explain the most important and widely used industry and technical terms.

Apex/Peak

The uppermost point of a truss.

Asymmetric Truss

A truss with two pitch on both sides.

Attic truss/room-in-the-roof.

An attic truss is 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.

Chords

Refer to the top and bottom chords which are respectively the rafter and ceiling tie.

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

Fink Trusses are 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 mono truss is a truss in the form of a right-angled triangle with a single rafter.

Node

Point on a truss where the members intersect.

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.

Noggins

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.

Truss/Trusses Rafter

A lightweight framework, generally but not always triangulated, placed at intervals of 600mm (centres) to support the roof. It is made from timber members of the same thickness, fastened together in one plane using steel nailplates.

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, specially designed to transmit wind forces to suitable load-bearing walls.

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