Roof sheathing

Boards or OSB fastened to the roof trusses onto which roof covering is laid. It can also partly work as bracing and prevent out of plane buckling of upper chords.


Truss web member in tension or compression. Lateral braces are usually designed to prevent out of plane buckling of diagonal members in compression.


Straight load carrying element connecting two end joints and containing arbitrary number of other joints or connections. It may consist of few timber cut-pieces or other profiles and materials.

Lower chord

Straight or cornered Truss member connecting support details. It is usually in tension or combined tension and bending when ceiling is installed. In case of low permanent load together wind suction it may be in compression and proper bracing to prevent buckling is required.

Timber structure

Building with load bearing structure made mostly from timber or wood based materials.

Spanner roof

Roof with room in attic mainly used for housing. Gypsum board ceiling is fastened to a spanner – horizontal timber member connecting upper chords. Considering size of these structures, they are usually designed and assembled in two pieces and connected on site.

Main hip truss

Truss with the lowest height in hip set placed perpendicularly to roof ridge. Skew fillets and corner trusses are connected to this truss. Considering heavy loading it is often designed as multiple truss (double or triple)

Main valley truss

The first (largest) truss in valley set.


Sometimes also called Bulldog. Steel fastener intended for timber structures. Any connector needs a bolt to work properly.

Upper chord

Outer truss member located in the roof plane. Upper edge of the chord supports roof sheathing, purlins or roof lathing. It is usually under combined bending and compression stress and proper bracing to prevent out of plane buckling is required.


Top intersection of roof planes

Non-structural nail plate

Nail plate connecting non-structural members to each other or to structural members. No verifications and checks are performed for this type of nail plate.


Member of traditional roofs located in the roof plane. It is usually under combined bending and compression stress and proper bracing to prevent out of plane buckling is required.

Laths, lathing

Roof laths are lateral timber elements onto which roof covering is installed. In some case (if they are designed for such load) laths can prevent out of plane buckling of rafters or upper chords, however they must be additionally diagonally braced.

Linear stability

Determination of critical load intensity as a multiple of load currently applied to the structure. Critical load causes loss of stability of some members and collapse of the structure. Besides the critical multiple of load, eigen buckling shapes are also results of this analysis.

Linear analysis

Linear relationship between load and deformation is applied in linear analysis.


Slightly arched bottom chord to act against its deformation due to structure deflection. It is usually accomplished by raised mid point or third points of the lower chord.

Skew fillets

Hip set trusses parallel to roof ridge. They rest on the hip wall and are supported by the main hip truss.


Intersection of two roof planes with their bottom edges at angle less than 180°

Corner truss (rafter)

Truss centred onto projection of roof corner.

Long members splice

If there are members longer than the maximum plank length, it is necessary to design a splice joint for them. In general, it is a butt joint of the adjacent members connected by a nail plate. Two types of splices are recognized in Truss 4 according to their bending capacity: hinge and fixed splice.

Designing standard

Set of regulations for truss structural analysis.

Non-linear analysis

Non-linear relationship between load and deformation is applied in non-linear analysis.

Arc cut-pieces

Cut-pieces with arched edges. They provide arched upper edge of arches used for arc structures.


Bottom edge of roof planes

Mounting layout

Simple layout of structure displaying mostly joints and members. Used for modelling of details.

Lateral braces

Bracing elements located perpendicularly to truss plane, reaching from one end of the structure to the other one. They are designed to connect trusses and to prevent out of plane buckling. To perform their function properly, they shall be additionally braced by diagonal members or bracing trusses.


Place where truss rests on load bearing substructure. Internal forces due to loads applied to the truss are transferred into the substructure.

Half hip

Type of hip with trapezoidal gable wall. The roof ends above the gable.

Auxiliary nail plate

Extra nail plate added to a joint with a regular structural nail plate. Even if it connects structural elements, it does not have any load bearing function.

Gantry frame press

Press suspended from movable gantry frame operating over the whole assembly desk. The press embeds nail plates of truss structures.

Wall plate

Timber member laid on outer walls supporting the roof structure.

Elastic (spring) support

Support allowing partial deformation (displacement or rotation) in chosen direction.


Special structure or arrangement to provide global stiffness of roofs built from trusses with punched metal plate fasteners. It holds trusses in vertical position and prevents buckling of members in compression. Bracing system consists of long lateral braces and diagonal members or bracing trusses.


Part of structure exceeding structure span. It may be either load bearing or non-structural, according to its static behaviour.


Timber member. It is a fundamental element of trusses with punched metal plate fasteners. It is cut to be mounted in structure and connected by nail plates with other cut-pieces. There are two to four cuts on one cut-piece.


Planar bar structure carrying load in its plane to supports (wall plates, walls). Trusses are mostly exposed to bending moments.


Cornered truss structure (structure with so called rigid frame corner).

Connecting plates

Steel plates with openings for nails to connect members of timber structures.

Static layout

Simplified structure layout for performing structural analysis and determination of internal forces.


Point of connection of truss members. The connection is provided by embedded punched metal plate fastener.

Punched metal plate fastener

Mechanical fastener for connecting timber elements. It merges advantages of nailed connections by high anchorage capacity and steel connecting plates by high fasteners capacity. Nail plates are embedded from both sides of the joint by appropriate pressing equipment. Punched metal plate fasteners have the highest stiffness from all mechanical fasteners.

Gable wall

Wall perpendicular to ridge and ending the roof.

Symmetric structure

Geometric property of structure determined by symmetric display of all topological elements of the structure with respect to calculated or manually defined axis of symmetry. Symmetry provides easy editing of two symmetric elements at once and also simplifies entering of non-symmetric load and combinations. The program automatically designs the structure to the most unfavourable actions.

Mechanically jointed beam (Members with stiffeners)

Two wooden members laid on each other and connected by nail plates in given spacing. The final member has greater stiffness then individual unconnected members.

Grade of timber

Timber is sorted into grades by its strength properties. Characteristics of individual timber grades are listed in designing standards.


Steel fasteners providing perpendicular butt connection of timber beam to another member. Hangers are fastened to members by convex nail plates.

Effective width of nail plate

Nail dimension decisive for nail plate capacity analysis. In general it is a projection of connection line on a nail plate.

Effective nail plate area

Nail plate area in contact with the connected member after subtracting ineffective edge strips. It is taken into account in analysis of nail plate anchorage capacity.

Angle saw

Sawing machine cutting under various angles. It may be controlled manually or automatically from a computer and special software.


Intersection of two roof planes with bottom edges at angle greater than 180°.


Roof end detail with roof plane perpendicular to roof ridge and without a gable.

Hip wall

Gable wall of a building with roof ended by a hip (not with gable). It supports skew fillets of the hip set.


Horizontal elements resting on upper chords of roof trusses. They carry load from roof covering to trusses.


Load state including self-weight of the structure.

Internal forces

Forces in members due to load acting on the structure. Internal forces include axial (normal) and shear forces and bending moments.

Analysis layout

See static layout

Analysis nail plate

Nail plate connecting individual load-bearing members of the structure. It is verified (checked) according to selected standard.


Timber wedge inserted to support joint of truss (only if the support is shifted inwards the truss). It provides transfer of internal forces from upper chord directly into support without additional stresses in lower chord. It is hold in its position by auxiliary nail plates.


Outer actions acting on structures and causing response (deformations, internal forces).

Load state

Set of load states applied to structure.

Load states combination

Set of selected load states possibly acting at the same time. Rules for generating load states combination are included in selected standard.

Bracing strap

Perforated steel strap used for bracing of timber roof structures. It is nailed to the structure through the openings.

Bracing truss

Rectangular truss inserted horizontally between regular trusses. It provides bracing of the structure and also transfers horizontal loads to supports (walls).

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