What Is a Truss? Common Types Explained

A truss is a structural frame built from straight members arranged in triangles and connected at joints called nodes. The triangular geometry converts bending forces into simple tension and compression, which lets a truss span long distances with far less material than a solid beam. Roofs, bridges, and stadium canopies all rely on this principle.

Once you know what to look for, you start seeing trusses everywhere: above the ceiling of almost every suburban house, under railway bridges, and across the roofs of airport terminals. This breakdown covers how a truss actually works, the most common truss types in timber and steel, and how designers decide which one fits a project.

How Does a Truss Work?

A truss works by breaking a load into axial forces. Instead of one deep beam resisting bending along its whole length, a truss uses a network of slender members that are either pulled (tension) or squeezed (compression). Because each member carries force along its axis only, the material works at close to full efficiency, and the frame stays light.

Every truss has the same basic anatomy. The chords are the outer members: the top chord follows the roof slope or the upper edge, and the bottom chord ties the frame together along its lower edge. The webs are the internal members that connect the two chords and form the triangular pattern. The Structural Building Components Association keeps a useful glossary of truss terminology that defines these parts precisely, which helps when you read fabrication drawings.

The triangle matters because it is the only polygon that cannot change shape without changing the length of a side. A rectangle can rack into a parallelogram under load. A triangle cannot. String enough triangles together and you get a frame that behaves almost like a single deep beam, at a fraction of the weight.

One more distinction helps before we get to specific truss types. In an ideal truss, loads are applied only at the joints, called panel points. In real buildings, purlins, decking, and ceilings load the chords between joints too, so chords are designed for some bending as well. Fabricators handle this in software, but it explains why chord members are usually heavier than webs.

Common Timber Truss Types

Timber trusses dominate housing and light commercial work. Most are metal plate connected wood trusses, prefabricated frames of dimensional lumber joined with toothed steel plates pressed into the wood. The shape you choose interacts directly with the roofing style of the building, since the top chord profile defines the roofline.

King Post and Queen Post

The king post truss is the simplest form: two sloped top chords, a horizontal bottom chord, and a single vertical member (the king post) down the middle. It suits short spans, roughly up to 8 meters, and shows up in porches, garages, and exposed feature roofs. Add two verticals instead of one, plus a straining beam between them, and you have a queen post truss, which stretches the same idea to slightly longer spans.

Fink Truss

The Fink truss is the workhorse of residential construction. Its webs form a W shape between the chords, which distributes forces evenly and uses short, economical web members. If you crawl into the attic of a typical gable-roofed house built after the 1960s, a row of Fink trusses at 600 mm centers is most likely what you will find.

Howe Truss

The Howe truss, patented by William Howe in 1840, arranges its diagonals so they slope toward the center of the span, putting the diagonals in compression and the verticals in tension. In its original bridge form the verticals were iron rods threaded through timber members, an early hybrid of wood and metal. Today the Howe pattern appears in both timber roof trusses and steel frames.

Scissors Truss

A scissors truss has bottom chords that slope upward toward the center, so the ceiling plane follows the roof pitch. It creates a vaulted interior without the cost of exposed rafters and structural ridge beams. The tradeoff is reduced stiffness, so spans are shorter and heel details need care.

Mono Truss

A mono truss has a single sloped top chord, producing a lean-to or shed profile. Designers use them for single-pitch roofs, split-level rooflines, and clerestory arrangements where two mono trusses face each other with a band of glazing between them.

Truss Types at a Glance

The table below summarizes the common truss types and where each fits best:

Truss Type	Usual Material	Typical Span	Common Use
King post	Timber	Up to 8 m	Porches, garages, feature roofs
Queen post	Timber	8 to 12 m	Small homes, outbuildings
Fink	Timber	Up to 14 m	Standard residential gable roofs
Scissors	Timber	Up to 12 m	Vaulted ceilings, churches, great rooms
Mono	Timber	Up to 9 m	Shed roofs, clerestories, additions
Howe	Timber or steel	6 to 30 m	Roofs, historic covered bridges
Pratt	Steel	20 to 100 m	Industrial roofs, bridges
Warren	Steel	20 to 100 m	Airports, stadiums, long-span floors

Steel Truss Types for Longer Spans

Steel takes over where timber runs out of span. According to SteelConstruction.info, the industry resource maintained by the British Constructional Steelwork Association and the Steel Construction Institute, trusses generally become the economic choice for steel roofs spanning beyond 20 meters, with Pratt and Warren configurations covering spans from 20 to 100 meters.

The Pratt truss slopes its diagonals down toward midspan, so under gravity loads the long diagonals work in tension while the short verticals take compression. That is an efficient arrangement for steel, since slender tension members do not buckle. The Warren truss drops the verticals entirely and uses alternating diagonals that form a chain of equilateral triangles, which reduces the member count and gives a clean, repetitive look often left exposed in terminals and sports halls.

Two variants worth knowing: the North light truss, with its asymmetric profile that admits south-shaded daylight into factory floors, and the saw-tooth truss that repeats this shape across multi-bay industrial buildings. For exposed exterior trusses, some projects specify weathering steel so the structure protects itself without a coating system.

How Do You Choose the Right Truss Type?

Pick a truss type by matching four factors: span, roof profile, interior space needs, and budget. For spans under 14 meters with a flat ceiling, a Fink truss is almost always the cheapest answer. If the design calls for a cathedral ceiling, move to a scissors truss. Once spans pass roughly 20 meters, or loads get heavy, steel Pratt and Warren trusses take over.

Material availability matters too. Timber trusses arrive as light, craneable units built from the same construction materials architects already specify for framing, while steel trusses need shop fabrication, welding inspection, and corrosion protection. Hybrid approaches also exist: some projects combine trusses with panelized systems such as structural insulated panels, using the panels as the roof deck over widely spaced trusses.

In North America, metal plate connected wood trusses are designed to the ANSI/TPI 1 national standard published by the Truss Plate Institute, which has maintained the engineering basis for the industry since 1961. Specifying a truss package to this standard means each unit ships with sealed design drawings covering loads, reactions, and bracing requirements.

One practical warning applies to every truss type: the frame is only stable once braced. Individual trusses are thin and floppy on their own, and most erection accidents happen before permanent bracing goes in. Temporary bracing plans deserve the same attention as the truss design itself.

Technical specifications and span figures given here are indicative. Truss designs should always be verified by a licensed professional for your specific project and local code requirements.

Putting It All Together

Bottom Line: A truss turns bending into tension and compression through triangulated geometry, which is why it beats a solid beam on weight and cost at almost any span. Learn to recognize the handful of common truss types, king post through Warren, and you can read the structural logic of most roofs and bridges at a glance.