Roof Trusses - Floor Trusses
Engineered Wood Products
22256 Fabco Road - Watertown, NY 13601
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American Softwood Lumber Standard: Voluntary product standard of the U.S. Department of Commerce that serves as a basis for the preparation and revision of industry-sponsored grading rules for lumber.

American Standard Lumber:
Lumber conforming to the basic provisions of the American Softwood Lumber Standard.

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: Publication of the Truss Plate Institute (TPI) developed under the American National Standards Institute (ANSI) consensus process. Provides the analysis, design and manufacturing criteria for the metal plate connected wood truss industry.

ANSI/TPI 2, American National Standard, Standard For Testing Performance For Metal Plate Connected Wood Trusses: Publication of the Truss Plate Institute (TPI) developed under the American National Standards Institute (ANSI) consensus process. Provides a state-of-the-art consensus standard for testing and evaluating wood trusses designed and manufactured in accordance with ANSI/TPI 1.

Architect: 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.

Attic Scuttle: Framed opening with removable cover providing access to the attic.

Axial Force: 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 Stress: 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.
BCSI: Guide to Good Practice for Handling, Installing, Restraining & Bracing of Metal Plate Connected Wood Trusses jointly produced by WTCA – Representing the Structural Building Components Industry and Truss Plate Institute.

BCSI-B1: Guide for Handling, Installing, Restraining & Bracing of Trusses of the Building Component Safety Information (BCSI) Guide to Good Practice for Handling, Installing, Restraining & Bracing of Metal Plate Connected Wood Trusses.

Truss Installation and Temporary Restraint/Bracing of the Building Component Safety Information (BCSI) Guide to Good Practice for Handling, Installing, Restraining & Bracing of Metal Plate Connected Wood Trusses.

BCSI-B3: Permanent Restraint/Bracing of Chords and Web Members of the Building Component Safety Information (BCSI) Guide to Good Practice for Handling, Installing, Restraining & Bracing of Metal Plate Connected Wood Trusses.

Beam Pocket: 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.

Bending Moment:
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.

Bending Stress: 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.

Bird’s Mouth Cut Notch: formed by a plumb and seat cut at the eave end of a rafter that allows the rafter to sit on the top plate.

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

Board: Lumber less than 2" in nominal thickness.

Board Foot: 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.

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

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

Bottom Chord Installation Lateral Restraint:
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.

Bottom Chord Plane:
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 Chord Upset: See Butt Cut.

Bottom Plate: Bottom horizontal framing member of a stud wall.

Bow: 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.

Bracing: See Permanent Bracing and Temporary Bracing.

Break Point Joint:
Top chord joint of a hip truss where the sloping chord member and horizontal member meet.

Building: A structure intended for supporting or sheltering a specific use or occupancy.

Building Designer: 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.

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

Building Structural System: 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.

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

Built-Up Beam:
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).

Built-Up Roof:
Roofing composed of three to five layers of asphalt.

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

Butt Joint: Interface at which the ends of members meet in a square cut joint.
CAD: Computer aided design and drafting software.

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

Layer of cells that lies between the inner bark and the wood of a tree, that repeatedly subdivides to form new wood and bark cells.

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

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

Center Line Span:
Theoretical span sometimes used to design trusses.

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

Check: 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.

Chord: See Top Chord and Bottom Chord.

Clear Span (Clear Opening):
Indicates the inside or interior frame-to-frame dimensions. Not to be confused with span.

Clinched Nail:
Nail selected to be longer than the member it is driven through and which is bent back the dimension of its excess length.

Clipped End:
See Stub Truss.

Cold-Formed Steel Trusses: Trusses constructed entirely of steel structural members cold-formed to shape from sheet or strip steel.

Collar Beam: Wooden member connecting opposite roof rafters.

Collar Tie: 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.

Combined Stress: Combination of axial and bending stresses acting on a member simultaneously, such as occurs in the top chord (compression + bending) or bottom chord (tension + bending) of a truss.

Combined Stress Index (CSI):
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.

Composite Lumber (Structural, Wood Composites):
Family of materials that contain wood in whole or fiber form bound together with an adhesive of natural or synthetic form.

Compound Cut:
Double cut made across the member width.

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

Compression Parallel-To-Grain: 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 Perpendicular-To-Grain: 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.

Compression Wood:
Abnormal wood formed typically on the lower side of branches and inclined trunks of softwood tress. Compression wood is identified by its relatively wide annual rings, usually eccentric, relatively large amount of late wood, sometimes more than 50% of the width of the annual rings in which it occurs, and its lack of demarcation between early wood and late wood in the same annual rings. Compression wood shrinks excessively lengthwise, as compared with normal wood.

Concentrated Load: 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.

Tree belonging to the order Coniferae, usually evergreen, with cones and needle-shaped or scale-like leaves, and producing wood known commercially as "Softwood."

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

Construction Documents: 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.

Construction Loading: 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.

Continuous Lateral Restraint (CLR):
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.

Contract: 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.

Conventional Framing:
Framing with conventional joists, rafters and wall studs.

Cover/Truss Index Sheet: Sheet that is signed and sealed, where required by the Legal Requirements, by the Truss Design Engineer, and depending on the Legal Requirements shall be permitted to contain the following information: (1) identification of the Building, including Building name and address, lot, block, subdivision, and  city or county; (2) identification of Construction Documents by drawing number(s) with revision date; (3)  specified Building Code; (4) computer program used; (5) roof dead and live loads; (6) floor dead and live loads; (7) wind load criteria from a specifically defined code (e.g., ASCE 7) and any other design loads (such as ponding, mechanical loads, etc.); (8) name, address and license number of Registered Design Professional for the Building, if known; (9) a listing of the individual identification numbers and dates of each Truss Design Drawing referenced by the Cover/Truss Index Sheet; and (10) name, address, date of drawing and license number of Truss Design Engineer.

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

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

Crook: 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.

Cross Bracing: 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.

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

Cup: Distortion of a board on which there is a deviation flat-wise from a straight line across the width of the board.

Cutting Sheets:
(Cut Sheets) Diagram of lumber lengths and angles of cut for truss web members and chords.
Dead Load: Any permanent load such as the weight of the truss itself, purlins, sheathing, roofing and ceiling, acting vertically on the truss or truss members.

Decay: Decomposition of wood substance caused by action of wood-destroying fungi, resulting in softening, loss of strength and weight, and often in change of texture and color.

Defect: 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.

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

Dense: (1) Term used in stress grading of certain softwood species to signify a high specific gravity. (2) A visual estimate of high specific gravity. To be classified as dense, the softwood species shall average on one end or the other of each piece, not less than six annual rings per inch and one-third or more late wood. Pieces not less than four rings per inch shall be accepted as dense if they average one-half or more late wood.

Depth Effect Factor: See Size Factor.

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

Diagonal Bracing: 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).

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

Drag Truss: 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.

Dressed Lumber: Type of lumber that is surfaced by a planing machine on one side (S1S), two sides (S2S), one edge (S1E), two edges (S2E), or any combination of sides and edges (S1S1E, S2S1E, S1S2E, or S4S). Dressed lumber may also be referred to as planed or surfaced.

Dressed Size: Dimensions of lumber after surfacing with a planing machine. Usually 1/4" or 3/4" less than nominal size. The American Softwood Lumber Standard lists standard dress sizes.

Drywall: See Gypsum Board.

DSB-89, Recommended Design Specification for Temporary Bracing of Metal Plate Connected Wood Trusses: Publication of the Truss Plate Institute (TPI) developed for use by architects and engineers to provide guidance for design specification for temporary bracing.

Dual Pitch Truss: Truss that changes pitch at the top chord peak joint.

Duration of Load: 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.
E: See Modulus of Elasticity.

Early Wood:
Less dense, large-celled, part of the growth layer formed first during the annual growth cycle. Also called spring wood.

Earthquake Load: See Seismic Load.

End Jack: 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.

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

Equilibrium Moisture Content:
Moisture content at which wood neither gains nor loses moisture to the surrounding air.
Fall Protection Plan: 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.

Fall Protection 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.

Fascia: Trim board applied to ends of overhangs.

Feather Cut: Heel cut that has been made with a zero butt cut.

Fiber Saturation Point:
Moisture content at which the cell walls are saturated with water (bound water) and no water is held in the cell cavities by capillary forces. It usually is taken as 25 to 30% moisture content, based on weight when ovendry.

Fire Retardant: Having or providing comparatively low flammability or flame spread properties.

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

Framing Structural System: Completed combination of Structural Elements, Trusses, connections and other systems, which serve to support the Building's self-weight and the specified loads.
Gable: Portion of the end wall above the eave line of a double sloped roof.

Gable End Frame: A component manufactured to complete the end wall of a building. The bottom chord of the gable end frame is continuously supported by the end bearing wall. Verticals between the top and bottom chords are typically spaced at 24” on center. The verticals function as load carrying members and as attachment members for sheathing or other end wall coverings. The gable end frame must be incorporated into the end shear wall by the building designer.

Gambrel: Roof having two slopes on each side of the peak, the lower slope usually steeper than the upper one.

Girder Truss: Truss designed to carry heavy loads from other structural members framing into it. Usually a multiple-ply truss.

Grade: Designation of the quality of a manufactured piece of wood.

Green: (1) Freshly sawed wood, or wood that has received no drying; unseasoned. Lumber that may have become wet to above the fiber saturation point may be referred to as being in the "green condition." (2) Wood above a stipulated moisture content, as lumber above 19% moisture content in accordance with the American Softwood Lumber Standard.

Ground Bracing: Used to provide stability for the first Truss or group of Trusses installed. It is composed of vertical and diagonal members providing support for the installed Trusses from the earth, floor, foundation or slab. Ground Bracing should be located in line with the Top Chord Lateral Restraint. Proper Ground Bracing also requires lateral and strut Bracing to ensure stability and support.

Gypsum Board: Interior finish sheet material manufactured with gypsum.
Header: Structural member located between stud, joist, rafter, or truss openings.

Heart Shake: Shake that starts out at or near the pith and extends radially. Also know as heart crack and rift crack.

Heartwood: Inner layer of a woody stem wholly composed of nonliving cells and usually differentiated from the outer enveloping layer (sapwood) by its darker color. It is usually more resistant to decay than sapwood.

Heel Cut: See Butt Cut.

Heel Joint: Point on the truss where the top and bottom chords intersect.

HIB-91, Commentary and Recommendations for Handling, Installing and Bracing Metal Plate Connected Wood Trusses: Publication of the Truss Plate Institute (TPI) providing recommendations and guidelines to contractors for handling, installing and bracing metal plate connected wood trusses for applications up to 2' on center. This publication has been replaced by the Building Component Safety Information (BCSI) booklet.

Hip Corner: Either truss or conventional framing, that along with the end jacks, forms the hip ridge and roof areas between the end wall and hip girder.

Hip Girder: Truss designed to carry end jacks and hip corners or common framing.

Hip Roof: Roof system in which the slope of the roof at the end walls of the building is perpendicular to the slope of the roof along the sides of the building.

Hip Set: Series of step down trusses of the same span and overhang, that decrease in height to form the end slope of a hip roof system.

Hip Truss: Trusses used in a hip set roof system. Each Hip Truss has the same span and Overhang as the adjacent standard Trusses but decreases in height with the top and bottom chords of its center portion parallel to each other and horizontal. Also referred to as a step-down Truss.

Horizontal Shear: Shear that occurs in planes parallel to the longitudinal axis of the member; sometimes referred to as longitudinal shear.

Hydraulic Press: Press consisting of a "C" clamp hydraulic cylinder; or an I-beam platen, or flat upper pressing platen, powered by hydraulic cylinders that are used to embed metal connector plates into a truss.
I-Joist: Structural member manufactured using sawn or structural composite lumber flanges and structural panel webs, banded together with exterior exposure adhesives, forming the cross-section shape of the capital letter "I". These members are primarily used as joists in floor and roof construction.

Impact Load: Load resulting from moving machinery, elevators, craneways, vehicles or other similar forces and kinetic loads.

Incise: To make slit-like lacerations generally parallel to the grain in the lateral surface of timbers that are resistant to treatment so that deeper and more uniform penetration of preservative may be obtained.

Installation Lateral Restraint:
Lateral Restraint that is attached to Truss members during installation of the Trusses and is intended to be temporary. See Lateral Restraint.

Installation Restraint/Bracing:
Lateral Restraint and Diagonal Bracing installed during construction for the purpose of holding Trusses in their proper location, plumb and in plane, until Permanent Individual Truss Member Restraint, Diagonal Bracing and Permanent Building Stability Bracing are completed.

Interior Bearing: Supports that are interior to two exterior supports.

International Code Council (ICC):
Group that oversees the International Building Code (IBC) and the International Residential Code (IRC).
Jig: Fixture that holds the truss in position until rigidly fastened with connectors.

Joint: See Panel Point.

Joist: Horizontal roof or floor framing member.

Jurisdiction: Governmental unit that is responsible for adopting and enforcing the Building Code.

Juvenile Wood: Wood formed adjacent to the pith, characterized by progressive change in cell dimension, different microstructure than mature wood, and greater shrinkage parallel to grain.
Kicker: Web at panel point above a cantilever bearing.

Knee Brace: Brace positioned between a column and truss panel points when trusses are supported by columns lacking transverse bracing.

Knot: Portion of a branch or limb that has been surrounded by subsequent growth of the wood of the tree. As a knot appears on the cut surface it is merely a section of the entire knot, its shape depending upon the direction of the cut.
Ladder Panel: (Ladder Framing) Prefabricated panel fastened to the roof eave to create a sloped overhang.

Laminated Veneer Lumber (LVL): Composite of wood veneer sheet elements joined with an adhesive with wood fibers primarily oriented along the length of the member. Veneer thickness does not exceed 0.25".

Late Wood: Denser, smaller-celled, later-formed part of a growth layer. Also called Summer Wood.

Lateral Bending: Bending out of the plane of the Truss.

Lateral Restraint: Also known as continuous lateral brace or CLB. A structural member installed at right angles to a chord or web member of a Truss to reduce the laterally unsupported length of the Truss member (See BCSI-B1, BCSI-B2, BCSI-B3, BCSI-B7, and BCSI-B10).

Legal Requirements: Applicable provisions of all statutes, laws, rules, regulations, ordinances, codes, or orders of any governmental authority of the United States of America, any state, and any political subdivision or quasi-governmental authority of any of the same, including, but not limited to, departments, commissions, boards, bureaus, agencies, counties, municipalities, provinces, and other instrumentalities.

Let Tails Run: When a piece of lumber making up the top chord is not cut off to a specified overhang length, but retains the length of the lumber used for the purpose of meeting specific overhang requirements in the field.

Level Return: Lumber filler placed horizontally from the end of an overhang to the outside wall to form a soffit.

Live Load: Loads produced by the occupancy of the building or structure, not including construction loads or environmental loads such as wind loads, snow loads, rain loads, earthquake loads, flood loads or dead loads. Live loads on a roof are those produced during maintenance by workers, equipment and materials, and during the life of a structure by people and moveable objects.

Forces or other actions that arise on structural systems from the weight of all permanent construction, occupants and their possessions, environmental effects, differential settlement and restrained dimensional changes.

Load-Bearing Wall: Wall specifically designed to transfer loads from above to the framing or foundation below.

Local Building Official:
The individual or organization who in accordance with the Legal Requirements may impose requirements on Truss Manufacturers and Truss Designers relating to the Trusses and the Truss Submittals.

Long Span Trusses: Trusses over 60' in length.

Longitudinal: Direction parallel to the grain of wood.

Lumber: Product of the sawmill and planing mill usually not further manufactured other than by sawing, resawing, passing lengthwise through a standard planing machine, crosscutting to length, and matching.
Machine Evaluated Lumber (MEL): Type of machine-graded lumber designated by the letter "M" followed by a number (e.g., M-10, M-19, etc.) which increases with increasing values for design properties. MEL grade design properties are listed in the NDS.

Machine-Graded Lumber: Type of lumber that has been evaluated by mechanical grading equipment approved American Lumber Standards Committee (ALSC) Board of Review. Machine-graded lumber is distinguished from visually graded lumber in that each piece is nondestructively evaluated and marked to indicate a grade classification. Machine-graded lumber is also required to meet certain visual requirements as set forth by the grading agency. Examples of machine-graded lumber include: Machine-Stress Rated Lumber (MSR) and Machine Evaluated Lumber (MEL).

Machine-Stress Rated Lumber (MSR): Type of machine-graded lumber designated by the design bending stress, Fb, and modulus of elasticity, MOE or E, values. For example, an MSR grade of 1650f-1.5E designates the bending stress of 1650 psi and an MOE of 1.5 million psi. Other design properties are listed in the NDS.

Mean Roof Height: The elevation of the roof mid-way between the eave and the ridge.

Mechanical Property:
Property of wood that relates to its ability to support load or resist deflection.

Metal Connector Plate: Connector plate manufactured from ASTM A653/A653M, A591, A792, or A167 structural quality steel protected with zinc or zinc-aluminum alloy coatings or their stainless steel equivalent. The metal connector plate has integral teeth and shall be manufactured to various sizes (i.e., length and width) and thickness or gauges and shall be designed to laterally transmit loads in wood. Also known as truss plate, plate, metal plate, etc.

Miter Cut: Single cut made at an angle to the member length.

Model Building Code: Building codes developed by national organizations for adoption by state and local building officials. Also called model code.

Modulus of Elasticity (MOE or E): Measure of the inherent rigidity or stiffness of a material. For a given geometric configuration, a material with a larger MOE deforms less under the same stress.

Moisture Content:
Amount of water contained in the wood, usually expressed as a percentage of the mass of the ovendry wood.

Moment: Force that produces rotation of a member and resulting bending stresses.

Monopitch Truss: Truss that has a single top chord, and a slope greater than 1.5/12.

Multi-Ply Truss: A Truss designed to be installed as an assembly of two or more individual Trusses fastened together to act as one. Ply-to-ply Connections of Multi-Ply Trusses are specified on the Truss Design Drawing.
Nail-On Plate: Light-gauge cold-formed steel metal connector plates with pre-punched holes or, if cut to size, without holes having identifying marks through which nails are driven by hand or pneumatic means into the lumber. They are typically used in repairs.

Nailer: See Scab.

National Design Specification® (NDS ®) For Wood Construction:
Publication of the American Forest & Paper Association (AF&PA) providing an appendix of lumber sizes, grades, species and allowable stresses.

National Evaluation Report (NER): Product acceptance research report prepared for construction products in compliance with requirements of the three model codes and the International Code Series of the International Code Council. National Evaluation Service, Inc. (NES) prepares this evaluation report.

Net Free Ventilated Area: Area required by building codes to allow for proper ventilation in enclosed building spaces.

Nominal Size: As applied to products such as lumber, traditionally the approximate rough-sawn commercial size by which it is known and sold in the market. Actual rough-sawn sizes may vary from the nominal. Reference to standards or grade rules is required to determine nominal/actual finished size relationships.

Notch: Vertical and horizontal cut at the end of a chord, joist or rafter.
Old Growth Timber: Timber in or from a mature, naturally established forest. If the trees have grown during the most of their lives in active competition for sunlight, the bole is usually straight and relatively free of limbs.

On Edge: Vertical placement of a member's wide edge.

On The Flat: Horizontal placement of a member's wide edge.

Out-To-Out Span:
See Overall Span.

Wood member nailed to a truss to form a rake overhang beyond the wall line.

Overall Span: Outside-of-frame dimensions, not outside-of-sheathing dimensions.

Overall Truss Depth: Vertical distance between bearing and the uppermost point of the peak.

Overhang: Extension of the top chord of a truss beyond the outside of the bearing support.

Owner: Person having a legal or equitable interest in the property upon which a Building is to be constructed, and: (1) either prepares, or retains the Building Designer or Registered Design Professional to prepare the Construction Documents; and (2) either constructs, or retains the Contractor to construct the Building.
Panel: Chord segment defined by two adjacent panel points.

Panel Length:
Horizontal distance between the centerlines of two consecutive panel points along the top or bottom chord.

Panel Point: Location on a truss where the web members and top or bottom chords intersect and are connected by metal connector plates.

Parallel Chord Truss (PCT): Truss with top and bottom chord slope less than 1.5/12.

Parallel Strand Lumber (PSL):
Composite of wood strand elements joined using an adhesive with wood fibers primarily that are oriented along the length of the member. The least dimension of the strands shall not exceed 0.25", and the average length shall be a minimum of 150 times the least dimension.

Particleboard Underlayment:
Underlayment grade particleboard made or machined to close thickness tolerances for use as a leveling course and to provide a smooth surface under floor covering materials.

Peak: Point on the truss where the sloped chords meet.

Penny: Common nail length. Originally, nails were sold by "penny weight", or price per hundred.

Permanent Bracing:
Bracing installed to provide support at right angles to the plane of the truss to hold it in its assumed design position. Permanent bracing stays in place for the life of the structure. The Building Designer may design the permanent bracing to resist lateral forces imposed on the completed building by wind load or seismic load.

Permanent Building Stability Bracing (PBSB): Lateral force resisting system for the Building that resists forces from gravity, wind, seismic and/or other loads.

Permanent Individual Truss Member Restraint (PITMR): Restraint that is used  to prevent local buckling of an individual Truss chord or web member due to the axial forces in the individual Truss member. (See BCSI-B2 and BCSI-B3)

Personal Fall Arrest System:
An individual worker’s Fall Protection System, composed of a safety belt or full body harness, and lanyard, lifeline, and any other connecting equipment that is used to secure the worker to an individual anchor or to a horizontal lifeline system; designed to stop a worker’s fall before the worker hits the surface below.

Piggyback Truss: Truss made in two pieces usually consisting of a hip type truss with a triangular cap fastened to it. Designed when shipping or manufacturing limitations are affected by overall truss height.

Pitch: (1) Incline of the roof described as inches of rise over inches of run. For example, 5/12 is 5" of rise over 12" of run. (2) Resin occurring in the wood of certain conifers.

Pith: Small, soft tissue occurring in the structural center of a tree trunk, branch, twig, or log.

Plate: See Metal Connector Plate.

Plenum: The cavity formed by the floor above and the ceiling below a floor truss as a supply or return air duct.

Plumb Cut: Top chord end cut to provide for vertical (plumb) installation of fascia.

Ply: One truss of a multiple-truss girder.

Plywood: Usually, a cross-banded assembly made of layers of veneer or veneer in combination with a lumber core or other wood-based panel material joined with an adhesive. Plywood generally is constructed of an odd number of layers with grain of adjacent layers perpendicular to one another. Outer layers and all odd-numbered layers generally have the grain direction oriented parallel to the long dimension of the panel.

Press: See Hydraulic Press.

Press-On Plate: See Metal Connector Plate.

Pressure-Treated Wood: Wood treated by applying pressure to force the preservative into it.

Professional Engineer (PE): Registered Professional Engineer holding a current license in each state in which s/he conducts business.

Profile Drawing: Sketches of truss profiles used by a mechanical engineer to determine where mechanical ducts, piping, etc., are located.

Proprietary Metal Restraint/Bracing Products: Metal products used as Diagonal Bracing, Lateral Restraint, bridging and Web Reinforcement, which are available from a number of manufacturers.

Purdue Plane Structures Analyzer (PPSA): Wood structures computer program developed at Purdue University. This program is currently used primarily as a research tool.

Purlin: Horizontal member attached perpendicular to the truss top chord for support of the roofing (e.g., corrugated roofing or plywood and shingles).
Radial: Coincident with the radius from the pith to the circumference of the tree or log. A radial section is a longitudinal section in a plane that passes through the pith of the tree.

Rafter: Sloping roof framing member.

Rafting: The procedure of building the entire roof system, or portions thereof, on the ground and lifting it into place.

Rake: Edge of a roof with the intersection of the gable.

Reaction: Total load transmitted by a framing member to its bearing.

Registered Design Professional: Architect or engineer, who is licensed to practice their respective design profession as defined by the Legal Requirements of the Jurisdiction in which the Building is to be constructed.

Reinforcement: A piece of steel section attached along the length of a Truss member as reinforcement against buckling instability.

Repair Detail: A written, graphic or pictorial depiction of the required fix to an altered or damaged component or part.

Ridge: Line made by the intersection of two roof planes.

Ridge Vent: Prefabricated and formed metal strip placed along the peak of the roof to aid in ventilation.

Rim Joist: Framing member installed on edge of the exterior parameter, usually tying the ends of floor trusses together. Also called ribbon or band board.

Rise: Vertical distance from low end to the high end of a sloping member.

Roller Press: Press that embeds metal connector plates by forcing them through two opposing rollers.

Roof Jack: See End Jack.

Roof Scuttle: Framed opening in commercial roofs surrounded by a hinged door used for access to a commercial roof.

Horizontal distance from the low end to the high end of a sloping member.
Saddle: Covering on the ridge of the roof so that water will drain. Also called cricket.

Scab: Member fastened by nails to another member for reinforcement.

Scissors Truss: Dual pitch, triangular truss with dual pitched bottom chords.

Scupper: Opening in a roof or parapet usually faced with metal flashing to drain water from the roof at a given point.

Sealed Drawings: Drawings prepared, checked and/or approved by and having the seal of a registered professional engineer or architect.

Seasoning: Drying; often applied to the process of removing moisture from wood to achieve a moisture content appropriate for the performance expected of the final product.

Second Growth: Timber that has grown after the removal, whether by cutting, fire, wind, or other agency, of all or a large part of the previous stand. Often limited to that growth following removal of old growth timber.

Seismic Load: Assumed lateral load acting in any horizontal direction on the structural frame due to the dynamic action of earthquakes.

Self-Drilling Tapping Screw: A screw meeting the mechanical and performance requirements of SAE International Standard J78 that can drill a hole and form or cut mating threads in materials into which it is driven.

Set Back:
Distance from the outside edge of the wall exclusive of veneer to the face of a girder truss.

Set-Up: Manufacturing term for a run of trusses of the same design currently being manufactured.

Shake: (1) Longitudinal separation of the wood. Generally two forms of shake are recognized, although variations and combinations may be used in industrial definitions. (2) Rectangular, board-like element for roof cover construction, similar to shingles.

Shear: Relative displacement of adjacent planes in a member.

Shear Stress: State of stress where internal adjacent planes in a member tend to slip on one another.

Short Member Installation Lateral Restraint: Short, structural members fastened at right angles to the Truss chords during installation of the Trusses for the purpose of reducing the laterally unsupported length of the Truss member.

Shoulder Joint: See Break Point Joint.

Shrinkage: Reduction in dimensions due to lowering the moisture content below the fiber saturation point.

Sill: Horizontal wood member forming the lowest part of the framework of a construction.

Size Factor: Factor included in deriving the allowable bending stress for rectangular members that takes into account the somewhat lower unit strength developed in larger members as compared to smaller members.

Slider: Two inch dimension lumber inserted between the top and bottom chords at the heel joint in the plane of the truss to reinforce the top or bottom chord.

Slope: See Pitch.

Sloped Soffit: Sloped overhang with no level return.

Soffit: Level return or underside of an overhang or truss cantilever end.

Soffit Vents:
Prefabricated soffit material with perforated openings created for the purpose of providing intake ventilation.

Softwoods: One of the botanical groups of trees that in most cases have needle-like or scale-like leaves; the conifers; also the wood produced by such trees. The term has no reference to the actual hardness of the wood.

Sound-Deadening Board: Specially manufactured cellulosic fiberboard product for use in building construction in wall and floor assemblies to reduce sound transmission.

Span: Horizontal distance between outside edges of exterior bearings.

Specific Gravity: The ratio of the ovendry weight of a sample of wood to the weight of a volume of water equal to the volume of the wood sample at some specific moisture content, as green, air-dry, or ovendry.

Splice: Location at which two chord members are joined together to form a single member. It may occur at a panel point or between panel points.

Spreader Bar:
A specifically designed lifting device that enables the lifting cables to hang straight or toe-in to their points of connection so as not to induce buckling forces in the Truss being lifted.

Spring Wood: See Early Wood.

Square Cut: End of top chord perpendicular to the slope of the member. Cut made at 90º to the length of the member.

Stacked Chords: In agricultural trusses when two members are positioned on top of each other to create a bottom chord.

Stacked Web Reinforcement: Reinforcement member attached to the Web at the Truss plant to avoid the need for field-installed reinforcement or Lateral Restraint and Bracing.

Step Down Truss: Truss used in a hip set roof system. Each step down truss has the same span and overhang as the adjacent standard trusses, but decreases in height with the top and bottom chords of its centered portion parallel to each other and horizontal. See also Hip Set.

Stick Framing: See conventional framing.

Stiffback: The Spreader Bar when it is brought down alongside, and attached directly to the Truss being lifted to provide sufficient rigidity to adequately resist out-of-plane bending of the Truss. See Spreader Bar.

Stress: Force per unit of area.

Stress-Graded Lumber: Lumber of any thickness and width that is graded for its mechanical properties.

Strongback Bridging: Two-inch dimensional framing member attached perpendicular to floor trusses - often through the chase opening - and placed vertically against the vertical web.

Stub Truss:
Truss that is shortened in length but maintains the original profile.

Structural Board: Board graded for structural applications requiring stress grading for assignment of allowable properties. Also referred to as a Stress Rated Board.

Structural Building Components:
Specialized structural building products designed, engineered and manufactured under controlled conditions for a specific application. They are incorporated into the overall building structural system by the Building Designer. Examples are wood or steel roof trusses, floor trusses, floor panels, wall panels, I-joists, or engineered beams and headers.

Structural Composite Lumber (SCL):
Composite of wood veneer sheets, elements, or wood strand elements, joined with an adhesive with wood fibers primarily oriented along the length of the member. These materials are intended for structural use. Examples included LVL and PSL.

Structural Element: A single joist, rafter, beam, or other structural member (not including the Trusses) designed by others and supplied for the Building Structural System by either the Truss Manufacturer or others.

Structural Element Submittals: Documentation relating to the Structural Elements that are supplied by the Truss Manufacturer, if required by the Contract, submitted by the Truss Manufacturer to the Local Building Official, Owner, Building Designer and/or Contractor for their review and/or approval.

Structural Sheathing: The structural covering used directly over the roof, floor or wall framing members that transfers perpendicular Loads to the framing members. Structural Sheathing commonly used with Trusses includes plywood, oriented strand board (OSB), and certain types of metal decking. Properly sized and installed Structural Sheathing provides both Lateral Restraint and stability to the Truss members.

Stud: One of a series of slender wood structural members used as supporting elements in walls and partitions. In softwood grading, a stress grade to describe lumber suitable for stud use.

Studded Gable: Gable end frame built as a wall and resembling a stud wall built in the shape of a triangle. Chords are usually on the flat.

Submittal Documents: Construction Documents, special inspection and structural observation programs, data, guides, reports, and manufacturer’s installation instructions submitted for approval with each permit application or available at the jobsite at the time of inspection.

Substrate: Surface upon which the roofing membrane is placed.

Summer Wood: See Late Wood.
T-Brace: A piece of lumber attached to a web as reinforcement against buckling instability. The T-brace is installed so that in cross-section it forms a letter "T" with the web. See also Web Reinforcement.

Tangential: Strictly, coincident with a tangent at the circumference of a tree or log, or parallel to such a tangent. In practice, however, it often means roughly coincident with a growth ring. A tangential section is a longitudinal section through a tree or limb perpendicular to a radius. Flat-grained lumber is sawed tangentially.

Temporary Bracing: Bracing installed for the purpose of holding trusses true to line, dimension and plumb. In addition, temporary bracing holds trusses in a stable condition until permanent truss bracing and other permanent components that contribute to the overall rigidity of the roof or floor are in place. Temporary bracing may consist of ground bracing, continuous lateral sheets or ties, diagonals, cross-bracing or similar items. See WTCA Job Site Warning Poster and the Always Diagonally Brace for Safety TTB for more information.

Tension Parallel-To-Grain: Imposition of a tensile stress that acts in a direction parallel to the fiber direction of the wood.

Tension Perpendicular-To-Grain: Imposition of a tensile stress that sets in a direction perpendicular to the fiber direction of the wood.

Outward horizontal force.

Nail driven at an angle to the member.

Top Chord: Inclined or horizontal member that establishes the top member of a truss.

Top Chord Bearing: Bearing condition of a parallel chord truss that bears on its top chord extension. Can also apply to a sloping chord truss bearing on a top chord extension.

Top Chord Installation Lateral Restraint (TCILR): Structural members installed at right angles to the Top Chord of a Truss during construction to reduce the laterally unsupported length of the Top Chord.

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

Top Plate: Framing consisting of two members on the flat that form the top of exterior stud bearing walls of platform frame construction. A single member on the flat in non-bearing wall construction.

Directions in wood at right angles to the wood fibers. Includes radial and tangential directions. A transverse section is a section through a tree or timber at right angles to the pitch.

Triangulation: The act of forming rigid triangles with objects adequately fastened together.

Trimmer: Conventionally framed wall usually consisting of fastened multiple studs in a framed wall opening, used to carry the header reactions.

Truss: Individual metal plate connected wood component manufactured for the construction of a Building.

Truss Design Drawing: Written, graphic and pictorial depiction of an individual


Truss Design Standard: The latest approved edition of ANSI/TPI 1 National Design Standard for Metal Plate Connected Wood Truss Construction.

Truss Design Engineer:
Person who is licensed to practice engineering as defined by the Legal Requirements of the Jurisdiction in which the Building is to be constructed and who supervises the preparation of the Truss Design Drawings.

Truss Designer:
Person responsible for the preparation of the Truss Design Drawings. The individual or organization responsible for the design of Trusses in accordance with this Standard, the Truss Design Standard and all Legal Requirements. The Truss Designer is also referred to as a Truss Design Engineer when the Truss design calculations and/or Truss Design Drawings resulting from the design of the Trusses shall be sealed by an Engineer.

Truss Heel Height: The vertical depth of the Truss at the outside face of bearing.

Truss Manufacturer: An individual or organization regularly engaged in the manufacturing of Trusses and who manufactures Trusses and who may supply Structural Elements for the Building Structural System.

Truss Orientation:
The Truss position or alignment within a structure relative to bearing walls.

Truss Placement Diagram (TPD): Illustration identifying the assumed location of each Truss.

Truss Plate: See Metal Connector Plate.

Truss Profile: A side view representation or outline of a Truss.

Truss Spacing: On-center distance between trusses.

Truss Span: The horizontal distance between outside edges of exterior bearings.

Truss Submittals:
The Truss Design Drawings, and the Truss Placement Plan if required by the Contract, submitted to the Local Building Official, Owner, Building Designer and/or Contractor for their review and/or approval.

Truss Submittal Package: Package consisting of each individual Truss Design Drawing, and, as applicable, the Truss Placement Diagram, the Cover/Truss Index Sheet, Lateral Restraint and Diagonal Bracing details designed in accordance with generally accepted engineering practice, applicable BCSI defined Lateral Restraint and Diagonal Bracing details, and any other structural details germane to the trusses.

Truss System: An assemblage of Trusses and Girder Trusses, together with all Bracing, Connections, and other Structural Elements and all spacing and location criteria, that, in combination, function to support the dead, live and Wind Loads applicable to the roof of a structure with respect to a Truss System for the roof, and the floor of a structure with respect to a Truss System for the floor. A Truss System does not include walls, foundations or any other structural support systems.

Truss System Engineer: A Licensed Engineer who designs a Truss System.

Twist: Distortion caused by the turning or winding of the edges of a board so that the four corners or any face are no longer in the same plane.
Uniform Load: Total load that is equally distributed over a given length, usually expressed in pounds per lineal foot (plf).
Valley: Depression in a roof where two roof slopes meet.

Valley Set: Set of triangular components used to frame the shape of dormers and to complete the roof framing where Trusses intersect at perpendicular corners.

Valley Truss: Not a truss, but traditionally called so. Set of triangular components used to frame the shape of dormers and to complete the roof framing where trusses intersect at perpendicular corners. Valley members usually require support at a maximum distance of 24".

Visual Grade Lumber: Type of lumber that has been visually rated at the lumber mill for structural properties through rules established by the national lumber associations.
Wane: Bark or lack of wood from any cause on edge or corner of a piece.

Warp: Any variation from a true or plan surface. Warp includes bow, crook, cup, and twist, or any combination thereof.

Web Member: Members that join the top and bottom chords to form the triangular patterns typical of trusses. These members typically carry axial forces.

Web Member Plane: The two-dimensional area formed by the top or bottom edge of adjacent similar web members allowing for the connection of Lateral Restraint and Bracing members.

Web Reinforcement: A piece of stress-rated lumber attached to a web as reinforcement against buckling instability. Types of web reinforcement include T-bracing, L-bracing, scab bracing and metal reinforcement. The length of the reinforcement is up to 90% the length of the web.

Webs: Members that join the Top and Bottom Chords to form the triangular patterns typical of Trusses. These members typically carry axial forces.

Wedge: Triangular piece of lumber that has one side equal to the standard 2" dimension lumber widths, and is inserted between the top and bottom chords, usually to allow the truss to cantilever. Its use is determined through engineering analysis.

Wind Load: Lateral pressure on the building or structure in pounds per square foot (psf), or the metric pascals (Pa), due to wind blowing in any direction.

Wind Speed:
The design Wind Speed for the structure. The value is determined by the Building Designer, with the minimum determined by the building code in effect in the Jurisdiction where the structure is built.

Wood: Tissues of the stem, branches, and roots of a woody plant lying between the pith and cambium, serving for water conduction, mechanical strength, and food storage, and characterized by the presence of tracheids or vessels.

Wood-Destroying Organisms: Decay-producing fungi, beetle, termites, carpenter ants, marine borers, etc.

Worker Lift:
A machine intended to mechanically hoist a worker.

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