Truss Terminology A-F

Connection between the roof or floor framing members (e.g., trusses, bracing, etc.) and the building structure, which is required to transfer the forces from these members into the building.

American National Standard, National Design Standard For Metal Plate Connected Wood Truss Construction.

American National Standard, Standard For Testing Performance For Metal Plate Connected Wood Trusses.

Any registered architect who designs all or a part of the Building Structural System and/or who produces all or part of the Building Structural System Design Documents.

Framed opening with removable cover providing access to the attic.

Push (compression) or pull (tension) force acting along the length of a member. Usually measured in pounds, kips (1000 lb), tons (2000 lb) or the metric equivalents.

Axial force acting at a point along the length of a member, divided by the cross sectional area of the member. Usually measured in pounds per square inch.

Guide to Good Practice for Handling, Installing, Restraining & Bracing of Metal Plate Connected Wood Trusses jointly produced by SBCA and the Truss Plate Institute.

Void or cut-out built into truss to allow beam support.

Structural support, usually a beam or wall, that is designed by the building designer to carry the truss reaction loads to the foundation.

Measure of the bending effect due to the live load and dead load on a given truss chord member. The bending moment at a given point along a member equals the sum of all perpendicular forces, either to the left or right of the point, times their corresponding distances from the point.

Force per square inch of area acting at a point along the length of a member resulting from the bending moment applied at that point. Usually measured in pounds per square inch (psi) or metric equivalent.

Formed by a plumb and seat cut at the eave end of a rafter that allows the rafter to sit on the top plate.

A solid member placed between structural members, usually at the bearings, to provide lateral support.

Lumber less than 2" in nominal thickness.

Unit of measurement represented by a board 1' long, 1' wide, and 1" thick. Abbreviation ft. b.m., bd. ft., or fmb. In finished or surfaced lumber, the board-foot measure is based on the nominal size. In practice, the working unit is 1000 board feet. Abbreviation M bd. ft., M B.M., or M B.F.

Inclined (e.g., scissors truss) or horizontal member that establishes the bottom of a truss, usually carrying combined tension and bending stresses.

Bearing condition of a parallel chord truss that bears on its bottom chord.

Structural members installed at right angles to the Bottom Chord of a Truss during construction to reduce the laterally unsupported length of the Bottom Chord.

The two-dimensional area formed by the top or bottom edge of adjacent similar Bottom Chords allowing for the connection of a roof Diaphragm, or Bracing members in a linear fashion.

Bottom horizontal framing member of a stud wall.

Distortion of a piece of lumber in which there is a deviation in a direction perpendicular to the flat face from a straight line from end to end of the piece.

See Permanent Bracing and Temporary Bracing.
Synonyms: Permanent Bracing, Temporary Bracing

Top chord joint of a hip truss where the sloping chord member and horizontal member meet.

Owner of the Building or the person that contracts with the Owner for the design of the Framing Structural System and/or who is responsible for the preparation of the Construction Documents. When mandated by the Legal Requirements, the Building Designer shall be a Registered Design Professional.

Officer or other designated authority charged with the administration and enforcement of the building code, or a duly authorized representative.

The completed combination of Structural Elements, Trusses, connections and systems, which serve to support the Building's self weight, the applicable live load, and environmental loads.

The architectural drawings, structural drawings, and any other drawings, specifications and addenda, which set forth the overall structural design of the Building Structural System.

Single member composed of two wood members having the same thickness but not necessarily the same depth, which provides greater load carrying capability as well as lower deflection (e.g., garage door, stairwell and fireplace headers).

Roofing composed of three to five layers of asphalt.

Vertical cut at outside edge of a truss bottom chord to ensure uniform nominal span and tight joints, typically 1/4".

Interface at which the ends of members meet in a square cut joint.

Upward curvature built into a truss bottom chord to compensate for deflection due to loading conditions.

Part of a truss that extends beyond its support, exclusive of overhang.

Truss with structural support at center of truss span as well as at heel joints.

Theoretical span sometimes used to design trusses.

Rectangular opening in a floor or sloping flat truss for the purpose of running utilities through it, such as heating and air conditioning ducts.

Separation of the wood along the fiber direction that usually extends across the rings of annual growth, commonly resulting from stresses set up in wood during seasoning.

See Top Chord and Bottom Chord.

Indicates the inside or interior frame-to-frame dimensions. Not to be confused with span.

Wooden member connecting opposite roof rafters.

Horizontal member placed between two rafters a specific vertical distance above the very top plate line for the purpose of limiting outward thrust of the rafters.

Summation of axial and bending stresses divided by their respective allowable stresses for a specific truss member. This ratio, or index, represents the structural "efficiency" of the member. The CSI shall not exceed 1.00.

Family of materials that contain wood in whole or fiber form bound together with an adhesive of natural or synthetic form.

Double cut made across the member width.

Chord members in a truss that resist compression (push) forces.

Compression, endwise (parallel to the grain). The imposition of a compressive stress that acts in a direction parallel to the grain of the wood, as in a column.

Compression, sidewise (perpendicular to the grain). The imposition of a compressive stress that acts in a direction approximately perpendicular to the grain of the wood.

Loading applied at a specific point, such as a load-bearing wall running perpendicular to a truss, or a roof-mounted A/C unit hanging from a truss.

Fasteners that join two or more members together, including: screws, Truss and joist hangers, and bolts.

Written, graphic and pictorial documents prepared or assembled for describing the design (including the Framing Structural System), location and physical characteristics of the elements of a Building necessary to obtain a Building Permit and construct a Building.

The Loads from workers and building materials on an unfinished structure, for example, when builders stack bundles of panel sheathing or gypsum board on Trusses during the construction process.

A line of continuous structural members (typically metal) installed at right angles to a chord or web member of a Truss to reduce the laterally unsupported length of the Truss member. The CLR must be properly braced to prevent the simultaneous lateral deformation and/or buckling of the series of Truss members to which it is attached due to laterally imposed Loads on, and/or the accumulation of buckling forces within, the Truss members, respectively. See also Lateral Restraint.

A legally recognized document between two or more parties and includes the agreement between the Truss Manufacturer and its customer which sets forth the terms and conditions (and scope of work) applicable to the Truss Manufacturer.

Owner of a Building, or the person who contracts with the Owner, who constructs the Building in accordance with the Construction Documents and the Truss Submittal Package. The term "Contractor" shall include those subcontractors who have a direct contract with the Contractor to construct all or a portion of the construction.

Framing with conventional joists, rafters and wall studs.

Time-dependent deformation of a structural member under constant load.

Drainage-diverting roof framing. Generally found on the high sloped end of a chimney.

Distortion of a piece of lumber in which there is a deviation in a direction perpendicular to the edge from a straight line from end to end in a piece.

Bracing installed in the web member plane of trusses to transfer lateral loads out of the truss system and up into the roof and down into the ceiling diaphragms.

Wood or metal members that are placed between trusses or joists in an angled position intended to spread the load.

Distortion of a board on which there is a deviation flat-wise from a straight line across the width of the board.
Diagram of lumber lengths and angles of cut for truss web members and chords.

Any permanent load such as the weight of the truss itself, purlins, sheathing, roofing and ceiling, acting vertically on the truss or truss members.

Any irregularity or imperfection in a tree, log, piece, product, or lumber that reduces the volume of sound wood or lowers its durability, strength, or utility value.

Amount a member sags or displaces under the influence of forces.

Dead and live loads for which a truss is designed to support.

Structural member installed at an angle to a Truss chord or web member and intended to temporarily and/or permanently stabilize Truss member(s) and/or Truss(es) (See BCSI-B1, BCSI-B2, BCSI-B3, BCSI-B7, and BCSI-B10). Used in conjunction with lateral bracing to transfer brace forces into the supporting structure. Diagonal braces are installed in the same plane as lateral bracing but at 45° angle to the lateral brace.

The horizontal or sloped system defined by the ceiling floor or roof plane acting to transmit lateral forces to the vertical lateral force resisting elements (e.g., walls).

Type of lumber from nominal 2" through 4" thick and 2" or wider.

A truss or trusses designed to assist in resisting the effects of seismic events by acting as a drag strut. This drag strut, drag truss or collector is a single element or component designed to transmit lateral loads to lateral load resisting systems that are parallel to the applied force.

Truss that changes pitch at the top chord peak joint.

Duration of stress or the time during which a load acts on a member. In wood, a design consideration for modifying allowable stresses, based on the accumulated loadings anticipated in the life of a structure.

Relatively short and usually mono-pitched truss used to frame the hip end of a hip roof system.

Any registered engineer who designs all or a part of the Building Structural System and/or who produces all or a part of the Building Structural System Design Documents.

Registered professional engineer responsible for the structural design of the structure and who produces the structural drawings included in the construction design documents.

Moisture content at which wood neither gains nor loses moisture to the surrounding air.

A written plan prepared for the prevention of injuries associated with falls. A Fall Protection Plan must be developed and evaluated on a site-by-site basis.

Any means used to protect a worker from a fall or minimize the risk of falling. Options include: guards or railings; Personal Fall Arrest System; safety net; control zone; safety monitor with a control zone; and other procedures acceptable to OSHA. See Personal Fall Arrest System.

Any means used to protect a worker from a fall or minimize the risk of falling. Options include: guards or railings; Personal Fall Arrest System; safety net; control zone; safety monitor with a control zone; and other procedures acceptable to OSHA. See Personal Fall Arrest System.

Trim board applied to ends of overhangs.

Heel cut that has been made with a zero butt cut.

Having or providing comparatively low flammability or flame spread properties.

Graphical solution of axial forces as they interact within the members of a truss.

Completed combination of Structural Elements, Trusses, connections and other systems, which serve to support the Building's self-weight and the specified loads.