Trusses & Joists Glossary
Please use our glossary for any technical terms you are unsure of. You can always get in contact with us to discuss any details of the specification you may not understand.
Board fitted to conceal roof timbers at Gable End
Small timber members spanning over trusses to support tiles, slates, etc.
A member designed to distribute loads over a number of trusses.
The part of a truss receiving structural support. This is usually a Wallplate but can be an internal wall etc.
A longitudinal member nailed to trusses to maintain correct spacing.
A notch in the underside of a rafter to allow a horizontal seating at the point of support (usually used with raised tie trusses).
Short timbers fixed between chords to laterally brace them. They should be at least 70% of the depth of the chords.
A truss type formed by truncating a normal triangular truss.
This can be Temporary, Stability or Wind Bracing which are described under these headings.
The person responsible for the structural stability and integrity of the building as a whole.
An upward vertical displacement built into a truss in order to compensate for deflection which might be caused by the loadings.
The part of a structural member or truss which extends beyond its bearing.
The lowest member of a truss, usually horizontal which carries the ceiling construction, storage loads and water tank.
Diagonal bracing nailed to the truss in the plane of the specified webs to add stability.
A load applied at a point.
Connector Plate / Fastener
See Jack Rafter.
A vertical timber block fixed between the chords of an easi-joist.
Separating two dwellings and required to provide sound resistance and 1 hour fire resistance.
A vertical timber block fixed to the side of joists where substantial vertical loads are applied.
The deformation caused by the loads.
The load produced by the fabric of the building, always long term (see 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
Timber boarding providing the floor or roof surface.
A load bearing timber frame wall of similar depth to the floor joists.
The line where the rafter meets the wall.
See raised tie truss.
Eaves Joint / Heel
The part of the truss where the rafter and ceiling tie intersect. This is usually where the truss is supported.
An engineered joist made from stress graded timber chords fixed with galvanised steel webs.
Engineered Wood Product - a man-made composite timber product.
An Eaves joint where the rafter sits on the ceiling tie.
Horizontal board fitted along the length of the building to the edge of the truss overhangs.
The most common type of truss used for dwellings. It is duo-pitch, the rafters having the same pitch. The webs form a letter W.
A tapered timber member used to give a fall to flat roof areas.
The end wall which is parallel to the trusses and which extends upwards vertically to the rafters.
Components used to form an overhang at the gable end.
A truss made up of two or more fixed together and designed to take exceptional loads, such as those imposed by other trusses fixed to it.
See Eaves Joint.
A member sloping from ridge to corner in a Hip End construction.
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.
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 masonry as a bearing.
Horizontal length of timber fixed onto the top rail of a timber frame panel.
The load produced by occupancy and use including storage, inhabitants, moveable partitions and snow, but not wind. Can be long, medium or short term.
The area where roofs meet.
Structural support within the span of a joist.
An infill rafter completing the roof surface in areas such as corners of Hip Ends or around chimneys.
A truss in the form of a right-angled triangle with a single rafter.
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 Agrement Certificate and will be manufactured, usually, from galvanised steel. It is also available in stainless steel.
Point of a truss where the members intersect.
Timber pieces fitted at right angles between the rafters and ceiling ties to form fixing points.
The extension of a rafter or ceiling tie of a truss beyond its support or bearing.
Oriented Strand Board - a composite product made from strands of wood and glue.
Design Stresses for grades of timber published in BS 5268: Part 2: 1988.
The angle of the rafter to the horizontal, measured in degrees.
Plate Location / Position Tolerance
Acceptable deviation from specified location for the plate on a truss. This is usually 5mm but can be specified greater.
Timber used in cantilevered hips to support loose timbers.
Timber members spanning over trusses to support cladding or between trusses to support loose timbers.
Timber framed non-load bearing wall applying a load to the floor below.
A farce applied at a single position.
The point on a rafter where the strut intersects in a Fink Truss.
Internal member (web) which connects the Apex to a third point on a Fink Truss.
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.
See Valley Frames.
A modification produced by the Trussed Rafter Designer to overcome a problem with the truss after its manufacture.
The span of a truss being supported by a girder.
The line formed by the truss apexes.
Timber running along a ridge and sandwiched between loose rafters.
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.
See Attic Truss.
A product used on the perimeter of a building to enclose the floor structure.
A structural beam used to distribute floor loads evenly to the walls below.
Additional timber fitted to the side of a truss to effect a local reinforcement, particularly in Raised Tie Trusses.
The point of a truss where the undersides of the rafter and ceiling tie meet.
Board fixed underneath Eaves overhang along the length of the building to conceal timbers.
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.
A timber frame, triangular panel forming gable wall above ceiling line.
A joint between two members in line using a Nailplate or glued finger joint.
An arrangement of additional timbers fixed in the roof space to provide lateral support to the trusses.
Metal component designed to fix trusses and wallplates to walls.
Internal member connecting the third point and the quarter point on a Fink Truss.
Pipe work, ducting and cables laid within the floor zone.
OSB or plywood sheets nailed to timber frame panels to provide racking resistance.
A structural timber fixed perpendicular to a run of easi-joists to reduce deflection.
Soil Vent Pipe.
Point on the ceiling tie where the internal webs meet in a Fink Truss.
Timber Stress Grading
The classification of timber into different structural qualities based on strength (see BS 4978: 1988).
Trada Quality Assurance Scheme
Quality control method in truss manufacture administered by the Timber Research and Development Association.
A piece of timber used to frame around openings.
Truss / Trussed Rafter
A lightweight framework, generally but not always triangulated, placed at intervals of 600mm to support the roof. It is made from timber members of the same thickness, fastened together in one plane using nail plates or plywood gussets.
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.
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.
A metal component designed to provide a structural connection and support for a truss to a girder or beam.
Timber allowed for tolerance which can be removed without compromising the joist.
Uniformly Distributed Load
A load that is uniformly spread over the full length of the member.
Uniformly Distributed Load = either an area load (N/sq.m) or a line load (N/m)
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.
The line where the trussed rafters meet the gable wall.
A timber member laid along the length of the load-bearing walls to support the trusses. This must be at least 75mm wide.
Timber members that connect the rafters and the ceiling tie together forming triangular patterns which transmit the forces between them.
An arrangement of additional timbers, or other structural elements in the roof space, specially designed to transmit wind forces to suitable load-bearing walls.
Are composite beams consisting of two timbers, plated together to form a deeper section. They can be used as simple beams or incorporated into a trussed rafter to reinforce a highly stressed member. They re often used in raised tie trusses. They are sometimes referred to by others as 'superchords, stackchords or twinachords'.