Wood Truss Glossary: Terms Every Builder Should Know
If you've ever reviewed a set of truss drawings and hit a term you didn't recognize, you're not alone. Pre-engineered wood trusses come with their own vocabulary, and a lot of it gets thrown around without explanation. Knowing what these terms mean isn't just useful trivia. It helps you catch errors in shop drawings, ask the right questions before delivery, and understand exactly what you're installing.
This glossary covers the terms you're most likely to encounter when ordering, receiving, and framing with wood trusses. We've written it for contractors and builders, not engineers.
The Basic Structure
Before getting into the list, it helps to understand what a truss actually is. A truss is a pre-built component that functions as a structural support member, employing one or more triangles in its construction. That triangular geometry is what gives a truss its strength and allows it to span long distances without interior support walls.
Every term below relates to some part of that structure or the process surrounding it.
A
Apex
The highest point on a pitched truss where the two top chords meet. Also called the peak.
B
Bearing
The structural support of a truss, usually walls, hangers, or posts. Bearing points are where the truss transfers its load to the structure below. Your truss design is engineered around specific bearing locations, so any change to wall placement needs to be communicated before fabrication.
Bottom Chord
The horizontal member defining the lower edge of a truss, carrying ceiling loads where applicable. The bottom chord is typically what your ceiling attaches to in a finished build.
Bracing
Temporary or permanent members used to stabilize trusses during and after installation. Bracing is not optional. Trusses are designed as part of a complete roof system, and individual trusses can fail during installation if proper bracing isn't in place before the next truss goes up.
Built-Up Beam
A single unit composed of multiple wood members having the same thickness but not necessarily the same depth, which provides greater load-carrying capability as well as greater resistance to deflection. You'll often see built-up beams used as girder trusses in hip roof systems.
C
Camber
An upward vertical displacement built into a truss bottom chord to compensate for deflection due to dead load. In simple terms, the truss is built with a slight upward bow so that when the roof load is applied, it flattens out to level. If you lay a truss flat on the ground and notice it doesn't sit perfectly flush, camber is usually why.
Cantilever
The part of a truss that extends beyond its support, exclusive of overhang. A cantilever carries load beyond the bearing wall without additional support underneath.
Check
A lengthwise separation of wood fibers, usually extending across the rings of annual growth, caused chiefly by strains produced in seasoning. Surface checks are common in kiln-dried lumber and are generally cosmetic. Deep checks that affect structural members should be flagged.
Chord
The horizontal members of a truss that form the top and bottom edges of the truss triangle. See also: top chord and bottom chord.
Clear Span
The horizontal distance between inside faces or supports. Clear span is what determines how much open floor or ceiling space you get without interior bearing walls.
Connector Plate
A galvanized steel plate with teeth punched out on one side, which is hydraulically pressed into the wood members at each joint. Connector plates are what hold a pre-engineered truss together. They're structural components, not hardware, and should never be modified or removed on site.
D
Dead Load
Permanent loads that are constant on the truss, including the weight of the truss itself, purlins, sheathing, roofing, and ceiling. Dead load is calculated into the truss design. If you're adding a heavier roofing material than what was specified, that needs to go back to your truss manufacturer before installation.
Deflection
Downward vertical displacement of a truss due to loads. Some deflection is expected and engineered for. Excessive deflection is a sign something is wrong, whether in the design, the materials, or the installation.
F
Flat Truss
A truss which has the top chord parallel to the bottom chord over the entire length of the truss. Flat trusses are used primarily in floor systems and low-slope roof applications.
G
Girder Truss
A main truss supporting secondary trusses. In hip roof systems, girder trusses carry a significant portion of the roof load. They're often multi-ply, meaning several trusses are fastened together to form a single unit. Girder trusses are heavier than standard trusses and typically require crane or boom truck placement.
H
Heel
The joint in a pitched truss where the top and bottom chords intersect. Heel height matters when you're planning for insulation and ventilation at the eave. It's specified in your truss drawings and should be confirmed before framing begins.
Hip Truss
A truss designed for hip roof systems, where the roof slopes on all four sides. Hip systems require a combination of girder trusses, hip trusses, and jack trusses and are more complex to sequence and install than a standard gable roof.
K
King Post
The vertical web at the center of a common or gable truss, or the vertical web at the end of a mono truss. The king post is one of the simplest truss configurations and is common in smaller residential spans.
L
Live Load
The variable loads on a truss that change over time, such as snow, wind, and occupancy. Live load is distinct from dead load and is calculated based on local building codes and geographic conditions. In Kentucky, design snow load varies by county, so your truss engineer accounts for your specific location.
M
Metal Plate Connected Wood Truss (MPCWT)
An engineered, pre-fabricated structural component assembled from wood members and metal connector plates, designed to carry superimposed dead and live loads. This is the formal definition of what SBCKY manufactures. When someone says "pre-engineered truss," this is what they mean.
Mono Truss
A truss that has a single top chord and a slope greater than 1.5/12. Mono trusses are used at the end of hip roofs and in shed-style additions.
O
On-Center Spacing (OC)
The measurement from the center of one truss to the center of the next. Standard residential roof truss spacing is 24 inches on center, though this varies by design. On-center spacing is specified in your truss placement diagram and affects sheathing, insulation, and ceiling attachment.
Outrigger
A wood member nailed to a truss to form overhang beyond the wall line. Outriggers extend the roof overhang on gable ends.
Overhang
The extension of the top chord of a truss beyond the bearing support. Overhang length affects the roof's appearance and is specified during the design phase.
P
Peak
The point on a truss where the sloped top chords meet. Same as apex.
Piggyback 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. If your build has a steep pitch and a long span, you may receive piggyback trusses. The two pieces are fastened together on site according to the manufacturer's instructions.
Pitched Truss
Any truss in which the top chord is sloped. Most residential roof trusses are pitched trusses. The pitch is specified as a ratio of rise to run, such as 4/12 or 6/12.
Purlin
A horizontal member in a roof perpendicular to the truss top chord, used to support the decking. Purlins are common in agricultural and commercial builds with wider truss spacing.
S
Scab
Additional timber connected to a truss to effect a splice, extension, or general reinforcement. Scabs are sometimes specified by the truss engineer for field connections. They should not be added on site without engineering approval.
Span
The horizontal distance between the supports or the length of the truss from one end to the other. Span is one of the first things your truss manufacturer needs to know. It determines the size, configuration, and cost of the truss.
Stub Truss
A truss that is cut or clipped at one end. Used in hip roof systems to fill in the end section of the roof.
T
Top Chord
An inclined or horizontal member that establishes the upper edge of a truss. The top chord is what your roof sheathing attaches to. Its slope determines your roof pitch.
Truss Design Drawing
The engineering document for an individual truss. It includes the truss geometry, lumber specifications, connector plate sizes and locations, load conditions, and bearing requirements. Truss design drawings shall be provided with the shipment of trusses delivered to the job site. Review them before installation begins.
Truss Placement Diagram (TPD)
A layout drawing identifying the assumed location for each truss based on the truss manufacturer's interpretation of the construction design documents. The TPD shows where each labeled truss goes in the building. It also indicates on-center spacing, special truss locations, and hanger schedules. The truss manufacturer is required to provide a truss placement diagram that identifies the proposed location for each individually designated truss and references the corresponding truss design drawing.
Truss Submittal Package
The package consisting of each individual truss design drawing, the truss placement diagram, the cover/truss index sheet, lateral restraint and diagonal bracing details, and any other structural details germane to the trusses. The contractor is required to review the truss submittal package and forward it to the building designer for review before installation begins. This step protects everyone on the project.
W
Web Members
The non-horizontal members that connect the top and bottom chords of a truss. Webs carry the internal forces of the truss in tension or compression. They should never be cut, notched, or drilled on site. Any modification to a web member changes the structural behavior of the entire truss and voids the engineering.
A Quick Note on Field Modifications
Several terms in this glossary relate to parts of a truss that contractors occasionally modify on site to accommodate HVAC, electrical, or plumbing. Cutting a web, notching a chord, or removing a connector plate creates a structural problem that cannot be seen until it fails. If your site conditions require a change to a truss, call your manufacturer before making any cuts. A revised engineering drawing costs far less than a failed roof system.
Questions About Your Truss Order?
If you're working through a set of truss drawings and something doesn't add up, we're easy to reach. Superior Building Concepts has been manufacturing pre-engineered wood trusses for Kentucky builders for years, and we'd rather answer a question before delivery than troubleshoot a problem on site. Give us a call or contact us through the website.
