Glossary & Terminology
Apex: Same as Peak
Bearing: A structural support, usually a beam or wall that is designed by the building designer to carry the truss reaction loads to the foundation.
Birdsmouth Cut: A long notch at the ends of a member to allow for an overhang with an “over the wall height” less than the width of the member.
Blocking: Wood or metal members that are placed between trusses and joists in an angled position intended to spread the loads.
Bobtail: Same as Stub Truss
Bottom Chord: An inclined or horizontal member that establishes the bottom member of a truss. An example of an inclined bottom chord member is the bottom chord of a scissor truss or a truss positioned between supports at different elevations.
Bottom Chord Bearing: Term usually used to describe the bearing condition of a parallel chord truss that bears on its bottom chord.
Bottom Plate: The bottom framing member of a stud wall.
Bridging: Same as Blocking
Butt Cut: Slight vertical cut at outside edge of truss bottom chord to ensure uniform nominal span and tight joints – usually ¼ inch.
Butt Joint: The interface at which the ends of two members meet in a square cut joint.
CAD: Computer aided design and drafting software
Camber: An upward curvature built into a truss bottom chord to compensate for anticipated deflection due to loading conditions.
Cantilever: The part of a truss that extends beyond its support, exclusive of overhang.
Check: A lengthwise separation of wood fibres, usually extending across the rings of annual growth, caused chiefly by strains produced in seasoning.
Chord: The truss members forming the top and bottom edges of the truss.
Clear Span: Generally indicates the inside or interior frame to frame dimensions. Not to be confused with Span
Clinched Nail: A nail selected to be longer than the member it is driven through and which is bent back the dimension of its excess length.
Clipped Truss: Same as Stub Truss
Collar Beam: Wooden member connecting opposite roof rafters.
Collar Tie: A horizontal member placed between two rafters a specific vertical distance above the top plate for the purpose of limiting outward thrust of the rafters.
Composite Lumber: A family of materials that contain wood in whole or fiber form and are bound together with an adhesive of natural or synthetic form.
Compound Cut: A double cut made across the member width.
Concentrated Load: Superimposed load centered at a given point( ie roof mounted AC unit.)
Connector Plate: Pre-punched metal toothed connectors located at the joints and splices of a truss and designed to hold the forces that occur at those locations.
Conventional Framing: Framing with conventional joists rafters and wall studs.
Cottage Roof: Same as Hip Roof
Creep: Deformation of a structural member under constant load over time.
Cricket: A ridge or drainage diverting roof framing. Generally found on the high sloped end of a chimney.
Dead Load: Any permanent load such as the weight of roofing, flooring, sheathing, insulation or ceiling material, as well as the weight of the truss itself.
Deflection: Downward vertical movement of a truss (when in place) due to dead and live loads.
Design Loads: The dead and live loads which a truss is engineered to support.
Distributed Load: Loads spread evenly along truss members.
Fascia: The flat surface located at the outer end of a roof overhang or cantilever end.
Feather Cut: A heel cut which has been made with a zero butt cut.
Gable: The portion of the roof above the eave line of a double sloped roof.
Gable Truss: A component manufactured to the profile of the mating standard truss. It has vertical “in-plane” members fastened to the chords instead of diagonal web members. It is not a structural truss and requires continuous support by a bearing wall or other load bearing element such as a beam along the bottom chord.
Gambrel: A roof having two slopes on each side, the lower slope usually steeper that the upper one. Generally seen on farm structures.
Girder Truss: A truss designed to carry heavy loads from the structural members framing into it. Usually a multiple ply truss.
GSL Ground Snow Load: Historical snow load data based on geographical area. Used to design carrying capacities or roof systems.
Header: A girder (wood, composite or steel) located between stud, joist, rafter, or truss openings.
Heel: The point on the truss where the top and bottom chords intersect.
Heel Height: Height of the truss measured from the underside of the bottom chord of the top of the top chord at the end of the truss.
Hip: Intersection of two roof surfaces over an external corner of a building.
Hip Roof: Roof constructed with rafters or trusses pitched over all perimeter walls
Interior Bearing: Term used to describe supports which are interior to two exterior supports.
Joist: A horizontal roof or floor framing member.
King Post: Vertical web at the center of a common or gable truss, or the vertical web at the end of a mono truss.
Lateral Bracing: Members placed and connected at right angles to a chord or web members of a truss.
Live Load: Any loading which is not of a permanent nature (snow, wind, people).
LVL: Laminated Veneer Lumber
MSR: Machine stress rated lumber
Nailer: A member fastened to another member by nails for reinforcement
Nail On Plate: Light gauge cold formed steel truss connector plates with pre-punched holes for manually connecting framing members.
Nominal Span: Horizontal distance between outside edges of supports.
On Edge: Vertical placement of a member’s wide edge
On The Flat: Lumber used in a truss with the wide surface facing up and down.
Outrigger: A wood member nailed to a truss to form overhang beyond the wall line.
Out to Out Span: Same as Overall Span
Over The Wall Height: Height of the truss measured from the underside of the bottom chord to the top of the top chord at the outside edge of an exterior wall.
Overall Height: Vertical distance from the bottom most part of the bottom chord to uppermost point on the top chord.
Overall Length: Same as Overall Span
Overall Span: Outside of frame dimensions (not outside of veneer dimensions).
Overhang: The extension of the top (or occasionally bottom) chord of a truss beyond the heel measured horizontally.
P. Eng: Licensed Professional Engineer
Panel: The chord segment defined by two adjacent joints.
Panel Length: The distance between joints measured along the chord centerline.
Panel Point: The point where a web or webs intersect a chord.
Peak: Point on the truss where the sloped top chords meet.
Piggy Back Truss: A 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: Inches of vertical rise for each 12 inches of horizontal run.
Plumb Cut: Top chord end cut to provide for vertical (plumb) installation of fascia
Ply: One truss of a multi truss girder.
Press On Plate: Same as Connector Plate
PSL: Parallel Strand Lumber
Purlin: A horizontal member attached perpendicular to the truss top chord for support of the roofing (ie agricultural steel roofing).
Rafter: A sloping roof framing member.
Rake: Edge of a roof with the intersection of the gable.
Reaction: Forces acting on a truss, through its support, that are equal but opposite to the sum of the dead and live loads.
Ridge: The horizontal line made by the top surfaces of the two sloping roof surfaces.
Rise: Vertical distance from the bottom of the top chord at the butt cut to the bottom (inside) of the top chord or from the top of the top chord at the heel to the top of the top chord at the peak.
Scab: Additional timber connected to a truss to effect a splice, extension or general reinforcement.
Scupper: Roof drain.
Seat Cut: Horizontal cut made on the bottom of a sloping bottom chord to provide a level bearing surface.
Set Back: The distance from the outside edge of the wall exclusive of veneer, to the face of a hip master (girder) truss.
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: Same as Pitch.
Sloped Soffit: Sloped overhang with no level return.
Snow Load: Same as GSL Ground Snow Load.
Soffit: The under side of a roof overhang or truss cantilever end.
Span: Term generally used to communicate out-to-out span, or overall span of a truss design. Sometimes also indicates centerline to centerline of bearing.
Splice Point: The point at which two chord members are joined together to form a single member. It may occur at a panel point or between panel points.
Square Cut: End of top chord perpendicular to the slope of the member. Cut made at 90 degrees to the length of the member.
Strongback: Two inch dimensional framing member attached perpendicular to floor trusses – often through the chase opening – and placed vertically against the vertical web.
Stub Truss: A term used to describe a truss that is clipped at one end.
T-Brace: A brace consisting of two-inch dimension lumber nailed directly to the member requiring a brace, and with the width of the member perpendicular to the width of the brace.
Toenail: A nail driven at an angle to the member.
Top Chord: An inclined or horizontal member that establishes the top member of a truss.
Top Chord Bearing: The 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 Plate: Framing consisting of two members On The Flat that forms the top of exterior stud bearing walls of platform frame construction.
Truss: An engineered structural component, assembled from wood members, metal connector plates and other mechanical fasteners, designed to carry its own weight and superimposed design loads. The truss members form a semi-rigid structural framework and are assembled such that the members form triangles.
Truss Clip: Metal component designed to provide structural connection of trusses to wall plates to resist wind uplift forces.
Truss Engineering Drawing: Drawing prepared by a Professional Engineer which prescribes truss geometry (span, slope, panel point locations, lumber, plate type, size and location, design loads, spacing, forces, etc.) usually required for manufacturing and building inspection.
Truss Layout: Plan view of entire project created by the truss manufacture to indicate proper truss placement and location.
Truss Spacing: The on center distance between trusses.
Valley: The angle formed by two sloping sides of the roof.
Web Member: Internal members that join the top and bottom chord, to form the triangular patterns typical of trusses. These members typically carry axial forces.
Wedge: A triangular piece of lumber that has one side equal to the standard two-inch dimension lumber widths, and is inserted between the top and bottom chords, usually to allow the truss to cantilever. Its used is determined through engineering analysis.
Wind Load: Load applied to the roof by wind.