Truss Terms
Here are some helpful terms that you will frequently hear when working with or ordering trusses.

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 increase 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 poitn 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 coverings.

Bearings
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 the 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 a member, resulting from the bending moment applied at the 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 Cutt
Slight vertical cut at the outside edge of truss bottom chord made to ensure uniform span and tight jointsusually 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 support.

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 linefixed 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 fo 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.

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 desinged 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 linefixed from wall plate to hip board in hip end construction.

Joint
See Panel Point

Lateral Brace
A emmber 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 uppoermost point on peak.

Overhang
The extension of the top chord of a truss beyond the heel measurement 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
Chord end cut to provide for vertical (plumb) installation to fascia (face trim board).

Plumb RiseVertical
Overall measurement at the end of a truss where the top and bottom chords meet.

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

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

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

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

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

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

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

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

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

RidgeLine
Formed by truss apexes.

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

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

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

Slope
See Pitch.

Spacing
Centerline distance between trussesusually 24" on center.

Span
Horizontal distance between outside edges of the supports.

Splice Point
(Top & Bottom chord splice). The poitn 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 occuring on each side of truss centerline.

Chord
An inclined or horizontal member that establishes the upper edge of a trussrafter 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 joing the top and bottom chords to form the triangular patterns that give the truss strength.