Truss Terms

Allowable Stress Increase
A percentage increase in the stress permitted in a member based on the duration of the load causing the stress acts on the member.
The uppermost point of a truss.
Axial Force
A push(compression) or pull(tension) acting along the length of a member.
Timber sections spanning trusses to support roof covering.
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.
Bottom Chord
A horizontal or inclined member that establishes the lower edge of a truss. In a conventional system, this is the ceiling joist.
Butt Cut (Heel Cut)
Slight vertical cut at outside edge of truss bottom chord made to insure uniform span and tight joints-usually ¼ inch.
an upward vertical displacement built into a truss bottom chord to compensate for deflection due to dead load
extension of the bottom chord beyond its support, exclusive of overhang
Clear Span
horizontal distance between interior edges of supports
Combined Stress
the combination of axial and bending stresses acting on a member simultaneously
Concentrated Load
superimposed load centered at a given point (i.e. roof-mounted air conditioner)
Connector Plate
pre-punched metal toothed connectors located at the joints and splices of a truss
Cripple Rafter
infill rafter installed to continue the roof line
Dead Load
any permanent load such as the roofing, flooring, sheathing, insulation, or ceiling material, including the weight of the truss itself
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
Engineered Certified Drawing
a drawing by a certified engineer in which loading requirements, lumber species, sizes, grades, and connector plate requirements are specified
Girder Truss
usually a multiple-ply truss designed to carry other trusses over an opening
point on a truss where top and bottom chords intersect
Live Load
any loading which is not permanent such as snow or wind
Overall Rise
vertical distance from lowest part of the bottom chord to uppermost point on peak
the extension of the top chord of a truss beyond the heel measured horizontally
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)
line formed by truss apexes
vertical distance from lowest part of the bottom chord to inside of the peak
horizontal distance between outside edges of the supports
Top Chord
an inclined or horizontal member that establishes the upper edge of a truss