In the field of Civil Engineering, the term "truss" refers to a triangular design. A joint framed structure that supports inclined, vertical or horizontal loads is called a truss. Eye bars, angles, plates, and channels make up a truss. Roof trusses are commonly used to support the roofs of auditoriums, stadiums, cinema halls, airports, railways, stations, etc.

Trusses are an extremely strong, well-known, and cost-effective option for constructing various structures. A suitable truss type should be chosen for the design to increase the productivity of the structure (which is frequently measured in the material used or labour). 

Roof trusses, types of roof trusses, roof truss components, functions of roof trusses, benefits and advantages of roof trusses are all discussed in this article. This article will surely boost your learning for your upcoming SSC JE CE examination, GATE CE examination and RRB JE CE examination.

Roof Trusses Definition

\Roof trusses offer a flexible solution for roofs that need to be strong yet spacious, and can be used in any type of building, regardless of size or purpose. Their flexibility in layout design allows for versatile use, and they are particularly useful in modern buildings that prioritize openness and adaptability. As a result, roof trusses have become increasingly popular in various building types.

A roof truss is a prefabricated structural framework used to support a building's roof. It is also called a trussed rafter. Roof trusses are typically triangular in shape and include triangular shapes in various configurations to suit the pitch, size, or design of the roof. Roof trusses are required when sloping roofs are required in a building. Sloped roofs are required in areas with heavy rainfall or snowfall, and they must be supported by roof trusses. Workshops, warehouses, and industrial buildings all require sloping roofs and, thus, roof trusses. Sloping roofs on trusses are common for many single-storey buildings. 

When a roof is required for a building that lacks interior supports and the exterior walls are more than 12 m apart, a roof truss is a practical way to support the roof. Roof trusses serve as large beams, supporting the roof and covering long distances. They must carry not only their own weight but also the weight of the roofing and roof beams, or purlins, wind loads, snow loads, suspended ceilings, and equipment, as well as a live load for construction, maintenance, and repair loading. These loads are applied at the intersections of the members or panel points so that the members are primarily subjected to axial stresses, tension, or compression.

Roof trusses have stood the test of time in construction because of their numerous structural benefits to homes and buildings. Roof trusses offer a versatile solution for building roofs that need to be strong yet spacious. Roof trusses offer a flexible solution for roofs that need to be strong yet spacious, and can be used in any type of building, regardless of size or purpose. Their flexibility in layout design allows for versatile use, and they are particularly useful in modern buildings that prioritize openness and adaptability. As a result, roof trusses have become increasingly popular in various building types.

What are Roof Trusses?

A truss is a joint-framed structure designed with a triangular pattern that can sustain vertical, horizontal or inclined loads. It consists of straight interconnected structural elements such as top chords, bottom chords, internal web members and steel connector plates, which are joined at the nodes by welding. The truss system supports the loadings on the roof throughout the structure, and the external forces and reactions at the supports are applied at the nodes. Steel roof trusses and timber roof trusses are commonly used to support roofs in various structures such as auditoriums, stadiums, cinema halls, airports, railways, and stations. A steel roof truss is a triangle-shaped structural member that adds strength and support to the roof.

Components of Roof Trusses

The various components of the roof trusses are explained below:-

• Apex- It is the highest point where the sloping top chords join together.
• Bearing- It is the structural support of trusses, which is usually accompanied by a timber wall plate.
• Bottom Chords- These are the shortest longitudinal member of the roof trusses
• Cantilever- Cantilevers are part of a structural member which are extended beyond their supports.
• Cantilever Strut- It is a web that connects the chords of the bottom part over the bearing point to the chords of the top part of the cantilevered truss.
• Chord- The main member that forms the outline of a truss and is subjected to enormous axial force and bending moment.
• Clear Span- The horizontal distance between the inside edge of the supports is called the clear span.
• Heel- It is a truss point where the top and bottom chords meet.
• Joint- A joint is the point at which at least one web intersects with a chord.
• Nail Plate- It is the galvanised steel plate that is punched to form a nail design that is needed with the plate and is used to connect the members.
• Node- The point of convergence of at least two members that make up the panels of a truss is referred to as a node.
• Nominal Span- It is the horizontal distance between the outside edges of the supports, which is commonly used as the tie beam length.
• Overhang- The extension of a truss's top chord past the bearing support is referred to as the overhang.
• Panel- It is a truss segment with two adjacent joints or nodes.
• Plumb Cut- The vertical slice to the end of the top chord to allow for vertical installation of the gutter or fascia.
• Splice Point- The splice between the top and bottom cords is the splice point.
• Square Cut- The Square cuts are perpendicular to the chord's edge.
• Stub End- A truss type formed by truncating a typical triangular truss.
• Top Chord or Rafter- A top chord, also known as a rafter, is a horizontal member that supports the upper edges of a truss.
• Web- The members that connect the bottom and top chords to form a triangular shape are the webs of roof trusses.

Fig.1: Components of Roof Truss

Types of Roof Trusses

Different types of roof trusses are used depending on the span, load requirements, and architectural needs of a building. Each truss type has a unique geometry and application, making it suitable for specific structural conditions. Below are the commonly used types of roof trusses:

King Post Roof Truss - This is the simplest form of truss, consisting of two angled supports joined at the top and a central vertical post (king post). It is designed to span short distances—typically up to 8 metres. King post trusses are ideal for small residential structures due to their economical design and ease of construction.

Queen Post Roof Truss - A queen post truss uses two vertical posts instead of one, providing a slightly longer span of around 10 metres. These trusses are stable and efficient, suitable for medium-sized residential and public buildings. Their simplicity allows for easy construction and maintenance.

Howe Roof Truss - The Howe truss features vertical members in tension and diagonal members in compression. It can be made using timber, steel, or a combination of both. Suitable for spans ranging from 6 to 30 metres, it is widely used in industrial sheds, bridges, and warehouses.

Pratt Roof Truss - The Pratt truss uses vertical members in compression and diagonals sloping down toward the center in tension. Known for its efficiency, it is one of the most popular steel trusses. It typically spans between 6 and 10 metres and is ideal for bridges and roof systems where tension handling is critical.

Fan Roof Truss - This truss features a fan-like arrangement of members extending from a single point, offering uniform load distribution. Fan trusses are simple in design and are commonly used for spans of 10 to 15 metres in industrial buildings.

Quadrangular Roof Truss - Also known as a lattice truss, it has parallel top and bottom chords connected with a network of vertical and diagonal members. These trusses are strong and ideal for wide-span buildings like railway sheds, halls, or auditoriums.

North Light Roof Truss - These are used in buildings where natural light is needed, such as factories and drawing halls. North light trusses have a steep pitch on one side to accommodate glazing, allowing diffused light to enter. They are economical and used for spans between 20 and 30 metres.

Raised Heel Roof Truss - A raised heel truss lifts the top chord above the wall plate, allowing for more attic insulation and better energy efficiency. It improves ventilation and is suitable for both residential and energy-efficient buildings.

Parallel Chord Roof Truss - This truss has top and bottom chords running parallel, joined by a web of diagonal and vertical members. It is ideal for floor systems and flat roofs and also helps control internal moisture and condensation.

Functions of Roof Trusses

A roof over one's head is a basic human need that we've evolved through hundreds of years of architectural ingenuity. Since the beginning of thatched roofs with straw and reeds, the roofing system has gone through an emotional transformation. When a roof truss is installed, it helps to protect the exposed roof from damage. Because the roof is the first line of defence against environmental elements, it must be protected. 

Its function is to shade and protect the home from the sun, rain and other environmental attributes. The roof trusses are complex architectural components that serve as the basic support for a roofing system. The major function of the roof trusses is to act as the major load-bearing element of the roof structure and to transfer the loads to the main supports.

Loads Acting on Roof Trusses

Roof trusses are designed to resist and transfer a variety of loads to the building’s supports. These loads may be temporary or permanent and are considered during structural analysis and design. The main loads acting on roof trusses include:

• Dead Load: This includes the self-weight of the truss, roofing materials, purlins, and any permanent installations on the roof.
• Live Load: Temporary loads like people working on the roof during maintenance, or construction-related activities.
• Wind Load: Acts laterally or upward on the roof surface, depending on building geometry and wind speed.
• Snow Load: In areas with snowfall, this load becomes critical and must be considered in truss sizing.
• Seismic Load: Roof trusses must be evaluated for lateral forces during earthquakes, especially in seismic zones.
• Equipment Load: HVAC units, solar panels, or suspended ceiling systems can exert additional point loads on trusses.

These loads are primarily applied at joints or panel points so that the truss members experience only axial forces—either tension or compression.

Design Considerations for Roof Trusses

While designing roof trusses, several engineering and architectural factors are considered to ensure strength, efficiency, and durability. Some key design considerations include:

• Span Length: Longer spans require deeper trusses or stronger materials to maintain stability and reduce deflection.
• Pitch or Slope: The angle of the roof affects drainage, load distribution, and architectural aesthetics.
• Spacing Between Trusses: Depends on roof load, purlin spacing, and construction material. Closer spacing enhances support but increases material use.
• Material Selection: Choice between timber or steel depends on span requirements, environmental exposure, and budget.
• Load Path: The truss must transfer all loads directly to supporting walls or columns without excessive bending or shear.
• Connection Details: Proper design of welded or bolted joints ensures safety and durability under loading conditions.

Efficient truss design balances material economy, load resistance, and structural simplicity.

Advantages of Roof Trusses

Some of its main advantages are as follows. 

• Steel roof trusses are more durable than wood roof trusses.
• They are lightweight and can be manufactured in any ideal instance to meet architectural requirements.
• There is no danger of white ants or other insects consuming the materials.
• They are more resistant to fire than timber trusses.
• They have no span limitations, so they can be used for industrial buildings and other structures where large areas must be covered without obstructions because of columns or other components.
• The transportation of the areas that shape a steel roof truss is simple.
• The areas can be obtained in any ideal structure or length to suit the requirements, and there is minimal material waste in cutting or other processes.
• Because of their simple erection strategies, roofing work with steel roof trusses advances quickly.

Timber vs Steel Roof Trusses – Key Differences

Timber and steel are the two most commonly used materials in roof truss construction. Each has distinct structural, economic, and practical advantages. The choice depends on the project scale, location, and functional requirements. Below is a comparison of their key differences:

Disadvantages of Roof Trusses

Despite their many advantages, roof trusses also have a few limitations that must be considered:

• Complex Fabrication: Trusses, especially custom ones, require precision fabrication and design.
• Transportation Issues: Large pre-fabricated trusses may be difficult to transport to the site.
• Installation Challenges: Heavy steel trusses often require cranes and skilled labor for erection.
• Restricted Ceiling Space: In some truss types, internal members reduce the possibility of having open or vaulted ceilings.
• Maintenance of Timber Trusses: Wood trusses may suffer from termites, moisture, or decay if not treated properly.
• Initial Cost for Steel Trusses: While durable, steel trusses may involve higher initial investment for small-scale projects.

Common Mistakes in Roof Truss Construction

Improper roof truss construction can lead to serious structural failures or long-term maintenance problems. Some common on-site mistakes include:

• Improper Joint Connections: Weak welds or loose bolts can compromise the load path and stability of the truss.
• Incorrect Truss Placement: Misalignment during installation leads to stress concentration and deformation.
• Unsupported Overhangs: Ignoring proper bracing or support for extended overhangs may lead to sagging or collapse.
• Using Damaged Materials: Bent steel or cracked timber members reduce strength and longevity.
• Lack of Bracing: Skipping lateral or diagonal bracing compromises overall rigidity during wind or seismic loads.
• Ignoring Load Combinations: Failure to account for all acting loads during design can result in underperformance.

Awareness of these errors helps civil engineers ensure safe and efficient truss systems.

This was all about the types, components, functions, benefits and advantages of Roof Trusses. It will amplify your preparation for various Civil Engineering competitive exams. You can avail AE/JE Civil Coaching and GATE CE Coaching to be on the merit list of various technical recruitments for Civil Engineers. 

You can also check out the Testbook app for accessing comprehensive study material, affordable online courses, SSC JE Civil previous years papers, AE/JE Civil Mock Tests and free SSC JE Civil Mock Tests to amplify your preparation.