We have compiled the following glossary to explain some of the terms used within our industry and associated with our products. We hope you will find it of use. If you require any further clarification or if a term is not listed here, please contact us and we will be delighted to help.
The uppermost point of a truss.
A truss with two rafters meeting at the APEX, having a different pitch on both sides.
A truss forming the top storey of a dwelling. Characterised by a central habitable area free of web members with large timber members elsewhere. May have to be assembled partly on site because of transport difficulties.
Uncommon build type in the UK for timber frame whereby the panels are built to roof/wallplate level and the floor is then hung internally from poleplates or hangers.
Small timber members spanning over trusses to support tiles, slates, etc.
A member designed to distribute loads onto 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 loose rafter to allow a horizontal seating at a point of support (not normally used on trussed rafters except with a raised tie feature).
Short timbers fixed between chords or joists to laterally brace them - at least 70% as deep as chords.
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.
See STABILITY BRACING.
A man made material, generally stapled to the outside face of an external timber frame panel. It allows water vapour to pass through from the inside to the outside of a timber frame wall, but does not allow the passage of vapour in the opposite direction.
Breathing Wall (Panelvent or Bitvent)
These boards manufactured from wood chips, selected wood waste and forest thinnings have been designed as a sheathing board for the timber frame industry and a sarking board in most forms of construction. In normal situations they do not require a breather paper or vapour barrier. This allows moisture migration from the inside to the outside of the structure as well as providing racking resistance to the structure.
GTE™ try to ensure wherever practicable to position openings in timber frame such as windows and doors and soffit lines to brickwork coursing. This is to enable complete bricks to line up with the openings to avoid the bricklayers having to cut more bricks than is necessary.
Galvanised steel lintels that are fixed to the external timber frame panel and support brickwork / blockwork over window / door openings in timber frame.
Solid pieces of timber generally at mid spans of floor joists to prevent distortion/twisting of timber.
The person responsible for the structural stability and integrity of a building as a whole.
An area of building control that states how a building should be constructed to ensure safe and healthy accommodation and the conservation of energy. This form of control is administered by the relevant local authorities, to whom an application must be made and permission received (generally a conditional approval) before work is started.
An upward vertical displacement built into a truss in order to compensate for anticipated deflection caused by applied loads.
The part of a structural member or TRUSS which extends beyond one or both of its bearings.
Either timber/wire reinforced mineral wool blanket or polythene sleeved mineral wool used to seal off the cavities into zones
See BOTTOM CHORD.
Diagonal bracing nailed to the truss in the plane of specified webs to add stability.
Refer to the Top and Bottom Chords which are respectively the RAFTER and CEILING TIE.
Canadian Lumber Stock/Sawn/Stud - generic term for timber used to construct timber frame panels.
Combined Stress Index (C.S.I.)
Measures how much of the strength of a member is being used by the design.
A load applied at a point.
An in situ flooring of cement mortar laid to an accurate flat surface by screeding. Screeds are laid on the structural floor and usually have no reinforcement - in a timber frame situation it would be laid after the structural shell has been erected (generally approx 65mm deep).
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. Supplied by system owners and the subject of an Agrement Certificate. Not usually for site application.
Cripple Rafter/Jack Rafter
An infill rafter completing the roof surface in areas such as the corners of hip ends.
A short stud that is connected to a full height stud to form a bearing for a horizontal lintel for a window or similar opening.
The permanent load produced by the fabric of the building.
The deformation caused by the loads.
Collectively 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.
Timber being a natural resource is prone to some shrinkage across the grain although it is stable in the longitudinal section. An allowance is made in the floor where joists do have to lye across the grain. The difference between the timber frame movement and that of the external brickwork is the differential movement.
Also sometimes known as a one and a half storey house or room in the roof bungalow. This is where the roof space is utilised by using Attic Trusses or similar. The rooms on the first storey will have sloping ceilings and either dormer windows or velux roof lights to allow light into the rooms
DPC - Damp Proof Course
A strip of impervious material that sits underneath the timber frame soleplates or brickwork / blockwork to keep out moisture. The DPC at ground level excludes rising damp but they are also used to divert rain out of the cavity, to drain through weepholes at the lintel above door or window openings. DPC comes in preformed rolls and made of flexible materials such as bitumen-polymer or pitch-polymer.
DPM - Damp Proof Membrane
A wide layer of impervious material such as mastic asphalt or a plastic sheet underlay beneath a ground slab to create a waterproof skin. A surface damp proof membrane can also be used such as what is supplied with a floating floor.
A truss with two top chords meeting at an apex and not necessarily being at the same pitch on both sides.
The line where the rafter meets the wall - The eaves are the roof overhang (usually clad in fascia and soffit) which protects the brickwork, or other external cladding from rain. It generally allows air ventilation to the roof void while keeping out insects and other animals.
The part of the truss where the rafter and the ceiling tie intersect. This is usually where the truss is supported.
The on site construction of the timber frame structural shell by a specialised team that usually include for there own mechanical handling and accommodation whilst working. A structural shell for an average 3/4 bed house will generally take approximately 7 - 10 working days.
Extended Rafter/Raised Tie Truss
A truss which is supported at a point on the extension of the rafter, beyond the point where the bottom chord meets the top chord.
N.B. Such trusses must be the subject of a special design.
The windows and doors etc. produced from high quality planed timber or UPVC.
A company engaged in the design & manufacture of Engineered Timber Products i.e.roof trusses, timber frame homes, metalweb joists & glulam trusses etc...
Horizonital board fitted along the length of the building to the edge of the truss overhangs.
Fascia/Barge & Soffit
A board which is generally timber or upvc set on edge along the eaves. This covers the rafter ends and will usually carry the gutter. Bargeboard - As above but used on the sloping areas of the roof. They are fixed in pairs along the edge of the gable to cover the roof timbers and protect them from rain. They can be ornately carved or moulded if required to create a feature. Soffit board - A horizontal sheet fixed under the eaves, concealing the rafters and the underside of the roofing. It runs between the back of the fascia and the face of the outer wall. The soffit can be either flat or sloping.
See CONNECTOR PLATE/NAIL PLATE.
GTE™'s premium Nationwide 5 Day delivery service for roof trusses.
Named after the original designer. A duopitch truss, the two top chords having the same pitch and the webs forming a letter W. The most common truss type used for dwellings.
Cavity barriers such as flexible mineral fibre strips in polythene sleeves required at junction of separating and compartment wall and external wall with roof.
A tapered timber member used to give a fall to flat roof areas or adjust the pitch on a roof truss.
A timber (or steel) beam which directly supports flooring in common with other joists (or a ceiling lining as a roof joist) Types of floor joists generally used by GTE™ are - Engineered Timber or Metalweb Joists at 600mm centres, or traditional solid timber softwood floor joists at 400 centre spacings. The cross sectional sizes usually used are 195 x 44mm/ 195 x 70mm and 195 x 90mm.
A heel joint where the top chord sits on the top of the bottom chord.
The end wall (parallel to the individual trusses) extended up vertically to the plane of the top chords of the trusses.
The structural link between trusses and gable panels that will overhang to form the eaves. They will often be used as a fixing for barge board and soffit
Gable Panels/Spandrel Panels
Triangular external infill wall panels that form the gable ends of a House and follow the roof profile or pitch.
Registered tradename of Gang-Nail Systems Limited.
A truss comprising two or more individual trusses fixed together and designed to carry exceptional loads such as those imparted by other trusses.
Large section timber material for structural applications. It is an engineered product built up by gluing together layers of timber boards with staggered joints in lengths up to 13.5 metres.
Ground Floor Finishes/Floating Floor
Ground floor finish layed when the structure is watertight which generally consists of Vapour barrier / 60mm Polystyrene and 18mm V313 Moisture resistant floor decking POWER FLOAT FLOOR - A finished concrete floor that is layed using a power float machine before the timber frame arrives. The concrete is screeded off flat and allowed to reach initial set before work starts. This method avoids having to lay a screed or a floating floor at a later date.
A metal component designed to provide a connection between a truss or other component and its support.
Horizontal timber member that ties together individual wall panels.
The part of a truss where the top and bottom chords intersect, normally where a truss is supported.
A raking member extending from ridge to corner in hip end construction.
A corner turn in a building incorporating a 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. See HIP SET.
The trusses and possibly loose timber forming a hip end.
The projection of the bottom chord of a trussed rafter built into masonry as a bearing. Used on monopitch and stub end trusses.
I Beams/Engineered Timber Joists
These generally use laminated veneer lumber flanges, routed to accommodate an OSB centre web. They can accommodate larger spans than standard joists and are a lightweight, uniform product. Advantages include reduced shrinkage, cupping, bowing, twisting and splitting that can be associated with standard joists.
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 materials used in walls / floors and roof space to create a warm structure to satisfy the clients requirements and comply with part L of the building regulations . Types of insulation are- TIMBER BATTS - A semi-rigid unfaced slab designed to give thermal and acoustic insulation and fire resistance. It is push fitted between studs at 600mm centres and is made from natural materials and recycled glass. (generally used for external and internal panels) ROLLS - A product that is produced from fine, non-combustible glass mineral wool and generally used in horizontal applications such as roof and floor areas. POLYURATHANE - Expanded plastics that have excellent insulation properties. It is generally used as a rigid board for installation in sloping roofs or even between the studs in external wall panels. It can also be sprayed in situ as an expanding foam to follow complex shapes. WARMCELL - This is an insulation material made from recycled material such as paper. It is blown into the required area pneumatically by specialist contractors on site from a van mounted machine. It is used in wall panels / horizontal and sloping roof areas and floors and can result in high U values.
A timber member used to transmit forces between chords.
Timber wall panels that are prefabricated and generally without sheathing unless required for engineering purposes.
The area where one roof meets another.
Equipment used in the laying out and clamping in position of the components of a truss prior to pressing.
Galvanised steel hangers that can be nailed to timber or other materials that floor joists or roof trusses sit into for support.
Internal member (web) which connects the APEX to the bottom chord/ceiling tie on a truss.
A term often used instead of IMPOSED LOAD.
Component of STABILITY BRACING.
Members not forming part of a truss but necessary for the formation of the roof. See JACK/CRIPPLE RAFTER.
A truss in the form of a right-angled triangle, having a single top chord.
See CONNECTOR PLATE.
National House Building Council - NHBC
(NHBC / NHBC Builder) An organisation that encourages better house building. It has a register of reputable house builders and includes services such as conciliation between builders and purchasers, the NHBC Warranty, ten year insurance on new houses and advice on proper site practices. GTE™™ will provide a suitably signed engineers certificate for the timber frame structure if the NHBC route is chosen by the client for insurance and warranties.
Point on a truss where members intersect.
Timber pieces fitted at right angles between the chords of trusses to form fixing points for ceiling materials.
A horizontal member fitted between 2 studs, Joists or Trusses generally to supply a fixing for plasterboard.
Notching & Drilling (For services)
It is important the joists and studs are notched and drilled for services (to run cables and pipes through) in areas indicated by the supplier only. Notching and drilling zones will be indicated by the manufacturer in their standard details so as not to impair the structural integrity of the structure.
Oriented Strand Board (OSB)
Timber board generally used to sheath external panels of timber frame. It is manufactured by flakes of timber 'snowed' into a mat using a small electrical charge so the resulting board has a specific strength.
Measurement on plan from the intersection point of the underside of top and bottom chords to the end cut of the rafter.
A reinforced member/area built in a wall to distribute the pressure from a concentrated load onto a larger area of wall.
In a panel system the structural studs are spaced at 400 / 600mm centres and carry the loads down to the foundations via the soleplate. Timber frame external walls (and internal loadbearing) are required to carry the dead and imposed loads acting on the structure and transmit them to the foundations. On average the panels can vary from around 2 metres in length upwards if a crane is being used on site.
See STUB END.
A separating floor between flats that has to perform similar duties to the party wall above. A party floor has to give more consideration to impact sound insulation as well as airborne sound.
A separating wall between two dwellings that must fulfil two main requirements 1, To reduce the passage of sound between the dwellings to levels set out in part e of the building regulations. 2, To comply with regulations as to give adequate fire protection between the buildings right up to the roof and through the cavities. Timber frame party walls perform well above building regulation requirements and the main components that improve sound and fire insulation is the type and mass of plasterboard used, the addition of insulation and adequate cavities between structures.
Design stresses for grades of timber published in BS5268:Part 2 .
The angle of the chord (usually rafter) to the horizontal measured in degrees.
See CONNECTOR/NAIL PLATE.
Plate Location/Position Tolerance
Acceptable deviation from specified location. Design allowance is 5mm in both orthogonal directions. May be specified greater.
Most timber frame construction in the UK is generally platform frame. It is where a structure is built sequentially upwards in platforms (floor by floor).
These consist of an odd number of thin layers of timber with their grains alternating across and along the panel or sheet. They are then glued together to form a strong board which will retain its shape and not have a tendency to shrink, expand or distort. Generally used for floor decking or as sheathing boards.
Post & Beam Construction
Differing Timber frame construction method to the panel construction that GTE™ generally use. It is where heavy structural Glulam or timber posts and beams are used (generally 150 x 150mm or larger) to transfer all the loads of the structure down to the foundations.
Timber members spanning over trusses and supporting cladding such as galvanised corrugated steel sheet. Also, spanning between trusses and supporting loose rafters.
The point on the rafter where an internal member/web connects in a 'FINK' type trussed rafter.
Internal member (web) which connects the APEX & CEILING JOIST/TIE to a third point on a TRUSS.
The wall panel studs (generally set at 600mm centres) carry the vertical loads from the floor/roof down to the foundations. The studs must be restrained using a sheet material such as plywood or oriented strand board to provide resistance to racking and stiffen the structure.
Rafter Diagonal Bracing
Component of STABILITY BRACING.
A sloping roof beam that generally runs from eave to ridge. Most roof elements are generally pre-fabricated trusses but rafters are used for infilling and for other areas where prefabrication is not practical. This term can also be applied to the principal rafter of a truss.
Raised Tie Truss
See EXTENDED RAFTER TRUSS.
See VALLEY FRAMES.
A modification produced by the Trussed Rafter Designer to overcome a problem with the trussed rafter after its manufacture.
The span of a truss being supported by a girder truss.
The line formed by truss apexes.
Timber running along a ridge and sandwiched between oncoming loose rafters.
The person responsible for the design of the roof as a whole so that it is stable in itself and is capable of transmitting wind forces on walls and roof to suitable buttressing walls. The Roof Designer is appointed by the Building Designer or can be the Building Designer himself.
These are triangulated plane roof frames designed to give clear spans between the external supporting walls. They are delivered to site as prefabricated components and fixed to wall plates generally at 600mm centres. They receive lateral stability through wind bracing timbers that are fixed through them to bind them together.
See ATTIC TRUSS.
The standard application procedure that defines the energy efficiency of a structure by taking into account items such as heating systems, the position of the site and the makeup and materials of the structure.
A material such as plywood or OSB applied to the upper surface of rafters on a roof to give a continuous panel support. A system that is used as standard in Scotland, but uncommon in England and Wales.
Additional timber connected to a truss to effect a splice, extension or local reinforcement.
These are temporary working platforms erected around the perimeter of a building to provide a safe working place at a convenient height. With timber frame the scaffolding is generally erected around three sides of the building before the kit is delivered. It is then enclosed at a suitable time. The scaffolding is erected far enough away from the external wall panels so it can stay up throughout the build for use by bricklayers and roofers etc.
The point on a truss where the undersides of the top and bottom chords intersect.
Boards laid side by side - tongued and grooved boarding is used for flooring (generally 18 or 22mm moisture resistant chipboard/OSB or plywood) and close boarding for timber frame panels and roofs (9mm OSB or plywood generally used for panels)
Driving nails at angles into the surfaces to be joined. A method of fixing trussed rafters to wall plate by use of nails applied through chords.
Board fixed underneath EAVES overhang along the length of the building to conceal timbers.
A horizontal timber member fixed to the ground floor slab to which the wall panels are then nailed to. It is generally treated with a powerful preservative.
One of the first jobs to be done by GTE™ after receiving an order is to issue a soleplate layout. This is an accurately dimensioned drawing for the ground workers to set out the foundations precisely. It indicates the load bearing and non-loadbearing panels. It is important that the foundations are constructed accurately to the timber frame soleplate to ensure a successful and smooth running project.
The soleplate fixings serve two purposes, to locate the plates accurately during construction setting out the superstructure. They also transfer wind loads down to the foundations once the building is completed. The soleplates may be fixed by shot-firing through the timber into the concrete slab or using stainless steel soleplate fixing anchors/shoes. Soleplates may also be fixed to brickwork substructures using stainless steel straps.
The reduction of the sound transmission from one space to another especially significant through walls and floors between separate dwellings (see party wall / party floor)
Span over all wall plates. The distance between the outside edge of the two supporting wall plates and sometimes equal to overall length of bottom chord.
Timber frame triangular panel forming gable wall above ceiling line.
A joint between two in-line members employing a metal connector plate or glued finger joint. Spreader Beam
An arrangement of loose timbers installed in the roof space to provide lateral support to truss members and to the trusses.
A method of timber frame where a structure is built on site from loose materials as opposed to in the factory. This type of construction is more common in the United States and Canada than in Britain.
Metal component designed to fix trusses and wall plates to walls. Heavy duty type for lateral fixing and standard used for holding down.
Internal member connecting the third point and the quarter point on a FINK TRUSS.
A truss type formed by the truncation of a normal triangular truss.
A vertical timber (generally 90 x 38mm, 115 x 38mm or 140 x 38mm) that forms the wall panels and is the height of the required wall.
A means of provinding deep chord memebers by connecting together two memebers at there edge using Gang-Nail connector plates, us
Owner of an integrated system of truss design and manufacture. Provides fabricators with application software,design expertise and fabrication machinery, In addition to the manufacture of nail plates (e.g. Gang-Nail Systems Ltd)
Tank Platform & Walkway
Timber bearers and floor decking such as chipboard or plywood that are installed in the roof space to form a walkway and take the load of the storage water tank.
TCB - Thermal Cavity Barrier
A non combustible material (generally flexible mineral fibre strips in polythene sleeves) which cuts off the path of smoke and fire. It is mainly used vertically either side of party walls and up the lengths of the eaves on gable ends. Fire Barrier consisting of 300 x 50mm x 4m wire backed insulation, single folded at floor & ceiling zones, rafter zone and vertically at external junctions and is also used in party wall /floor situations.
An arrangement of diagonal loose timbers installed for safety during erection. Often incorporated with permanent STABILITY BRACING.
Timber Frame Association. Organisation which represents the timber frame industry.
Point on a ceiling joist where an internal member/web connects in a truss.
See BOTTOM CHORD
Timber Stresss Grading
The classification of timber into different structural qualities based on strength.
The majority of timber used in the Timber Frame Industry is Canadian & Scandinavian softwoods. GTE™ ensure that all of our timber suppliers source their materials from renewable resources and properly managed forests.
Top Chord/ Rafter
Horizontal timber rail that ties together studs in a wall panel.
See SKEW NAILING.
Trussed Rafter Association. Organisation which represents the truss industry.
TRADA Quality Assurance Scheme
Formalised method of quality control in the manufacture of trusses administered by the Timber Research and Development Association.
Treatment of Timber
It is important that all timber used in the structural shell is sufficiently treated against insect attack and general decay and comply with the requirements of the N.H.B.C. and the Building Regulations 1995. The various types of timber used in different areas will be treated with a different material such as Tanalith or Vacsol.
A timber member used to frame openings.
A metal component designed to provide a structural connection of trusses to wall plates, to resist wind uplift forces and to eliminate the disadvantages of skew nailing.l
A metal component designed to support and provide a structural connection/support of a truss to a girder or beam.
A lightweight framework, normally triangulated, spaced at intervals generally not exceeding 600mm and made from timber members of the same thickness fastened together in one plane by metal fasteners 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.
The measure of the thermal insulation of a material or group of materials.
Uniformly Distributed Load(UDL)
A Load that is uniformly spread over the full length of a member.
A raking member from ridge to corner in valley construction.
A set of diminishing trusses that will infill an area of roof between two different roof directions.
Valley Jack Trusses
A set of diminishing trusses that will infill an area of roof between two different roof directions.
A set of diminishing trusses that will infill an area of roof between two different roof directions.
Usually a layer of polythene, GTE™ generally use125mu, supplied in rolls which is installed to restrict the passage of water vapour, e.g. on the inside of external wall panels on the warm side of insulation.
The line where the trussed rafters meet a gable wall.
See TANK PLATFORM.
The void between the timber frame wall panel and the external skin such as brickwork or blockwork. The standard timber frame cavity is 60mm below dpc and 50mm above as 10mm is used up by the external sheathing board of the timber frame.
Wall Panel Widths/Thicknesses
External wall panels generally consist of 90 x 38mm/115 x 38mm or 140x38mm timber studs, a 10mm sheathing board, breather paper and tape that is factory fixed. The internal panels are usually studwork (some internal panels are sheathed with a 10mm board for engineering purposes) Generally now 140mm external panels are used instead of the 90mm so that higher insulation values can be achieved.
A timber member laid along and fixed to the supporting walls on which the roof trusses bear. Not less than 75mm wide.
Stainless steel brackets and nails installed to tie back and brace the external brick or block cladding to the timber frame. Polypropylene tape fixed to the outer face of external wall panels indicate where the studs are so that the ties can be fixed back at approximately 5 per m2. Wall ties provide lateral restraint but do not carry the weight of the wall which is self supporting.
See INTERNAL MEMBER.
Web Longitudinal Bracing
A component of STABILITY BRACING.
Timber members that connect the rafters and the ceiling tie together forming triangular patterns which transmit the forces between them.
An arrangement of loose timbers or other structural system installled in the roof space to form diaphragms in the planes of the rafters and ceiling ties to transmit wind forces to suitable shear walls.