Allowable Stress Increase
A percentage increase in the stress permitted in a member based on the length of time that the load causing the stress acts on the member. The shorter the duration of the load, the higher the percent increases in allowable stress.

Apex/Peak
The uppermost point of a truss.

Axial Force
A push (compression) or pull (tension) acting along the length of a member. Usually measured in pounds, kips (1,000 lbs.) or tons (2,000 lbs.), or metric equivalent.

Axial Stress
The 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.

Battens/Purlins
Timber sections spanning trusses to support roof covering.

Bearing
A structural support, usually a wall, that occurs at the top or bottom chord or between the end points of a roof or floor truss.

Bending Moment
A measure of the bending effect on a member due to forces acting perpendicular to the length of the 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
The force per square inch of area acting at a point along the length of the member, resulting from the bending moment applied at that point. Usually measured in pounds per square inch or metric equivalent.

Bottom Chord
A horizontal or inclined (e.g., Scissors Truss) member that establishes the lower edge of a truss. In a conventional system, this is the ceiling joist.

Butt Cut
Slight vertical cut at the outside edge of truss bottom chord made to ensure uniform span and tight joints- usually 1/4 inch.

Camber
An upward vertical displacement built into a truss bottom chord to compensate for deflection due to dead load.

Cantilever
Extension of the bottom chord beyond its support, exclusive of overhang.

Check
A lengthwise separation of wood fibers, usually extending across the rings of annual growth, caused chiefly by strains produced in seasoning.

Clear Span
Horizontal distance between interior edges of supports.

Combined Stress
The 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.

Concentrated Load
Superimposed load centered at a given point (e.g., roof-mounted air conditioner, furnace.)

Connector Plate
Pre-punched metal toothed connectors located at the joints and splices of a truss and designed to hold the forces, which occur, at those locations.

Cripple Rafter
Infill rafter installed to continue the roof line- fixed to valley board in valley construction.

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
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.

Engineer Certified Drawing
A truss design where loading requirements, lumber species, sizes, grades and connector plate requirements are detailed and a certified engineer's seal is affixed.

Girder Truss
Usually a multiple-ply truss designed to carry other trusses over an opening.

Heel
Point on a truss at which the top and bottom chords intersect.

Heel Cut
See butt cut.

Jack Rafter
Infill rafter installed to continue the roof line- fixed from wall plate to hip board in hip end construction.

Joint
See Panel Point

Lateral Brace
A member placed and connected at right angles to a chord or web member of a truss.

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

Live Load
Any loading which is not of a permanent nature (e.g., snow, wind).

Moisture Content of Wood
The weight of the moisture in wood expressed as a percentage of its oven-dry weight.

Overall Rise
Vertical distance from bottommost part of the bottom chord to uppermost point on peak.

Overhang
The extension of the top chord of a truss beyond the heel measured horizontally.

Panel
The chord segment defined by two adjacent joints.

Panel Length
The centerline distance between joints measured horizontally.

Panel Point
The point where a web or webs intersect a chord.

Peak
Point on truss where the sloped top chords meet.

Pitch
Inches of vertical rise for each 12 inches of horizontal run.

Plumb Cut
Top chord end cut to provide for vertical (plumb) installation to fascia (face trim board).

Plumb Rise
Vertical overall measurements at the end of a truss where the top and bottom chords meet.

1/4 Point
Point on triangular Fink or Howe truss where the webs connect to the top chord.

1/3 Point
Point on triangular Fink truss where the webs connect to the bottom chord.

Purlin
A horizontal member attached to and placed perpendicular to the truss top chord to support the roofing.

Reaction
Forces acting on a truss, through its support, that are equal but opposite to the sum of the dead and live loads.

Ridge
Line formed by truss apexes.

Rise
Vertical distance from bottommost part of the bottom chord to inside of the peak.

Scab
Additional timber connected to a truss to effect a splice, extension or general reinforcement.

Shop Drawing
Detailed drawings of roof truss or roof framing showing critical dimensions such as span, overhang, cantilever, slope, etc.

Slope
See Pitch

Spacing
Centerline distance between trusses, usually 24" O.C. (on center)

Span
Horizontal distance between outside edges of the support.

Splice Point
(Top and bottom chord splice) 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 cut perpendicular to slope of the member.

Symmetrical Truss
Truss with the same configuration of members and design loading occurring on each side of truss centerline.

Top Coard
An inclined or horizontal member that establishes the upper edge of a truss- rafter in conventional frame.

Truss
A pre-built component that functions as a structural support member. A truss employs one or more triangles in its construction.

Truss-clip
Metal component designed to provide structural connection of trusses to wall plates to resist wind uplift forces.

Webs
Members that join the top and bottom chords to form the triangular patterns that give the truss strength.