What is a roof truss? Definition, types and advantages

 In Roof trusses

Are you wondering what a roof truss is? If so, you’ve come to the right place!

In this article, our prefabricated wood structure experts will tell you everything you need to know about roof trusses.

We’ll pay particular attention to timber (wood) roof trusses, as they’re one of our company’s specialities.

Roof truss definition

Prefabricated roof trusses are triangular frames composed of softwood lumber in various lengths and sizes. Their triangle structure makes their frame more rigid and provides support to the roof without requiring large planks of wood.

The pieces of wood are usually assembled with metal connectors made of galvanized steel sheets but can also be reinforced with nails and braces.

Manufacturers use advanced architectural and engineering software to custom design the timber trusses according to the construction plans. That’s why it’s so important to use accurate measurements.

Prefabricated structures have now replaced traditional wood frames that are built directly on site. They are widely used in residential, commercial and agricultural construction.

Depending on the region, roof trusses are also called: frames, industrialized frames and even timber frame rafters. Be careful though: these expressions do not always mean the same thing.

Types of roof truss

As we previously mentioned, manufacturers use computer tools to design a wide variety of timber truss models, adapting their size to each project.

By producing timber trusses in factories, manufacturers can create complex geometric structures quickly.

The most popular roof truss models are:

Common roof truss

Common (or ‘standard’) roof trusses are reliable and versatile. They span up to 72 feet (22 metres) and their simple triangular design makes them easy to integrate into many types of construction projects.

Barn trusses

Barn trusses are ideal for erecting agricultural buildings or residential buildings with a barn-like architecture.

Attic truss

As the name suggests, attic trusses are used to create more living space in the attic. The bottom beam is used as a floor joist and the supporting beams become the walls of the converted room.

Scissor truss

Scissor trusses are often used to create vaulted ceilings. They do not have to be installed on load-bearing beams or walls.

Flat truss

Flat roof trusses are frequently used to construct flat roofs but are also sometimes used in floor construction. They have a shallow slope to compensate for deflection and allow proper drainage.

Cathedral truss

Cathedral roof trusses are ideal for vaulting ceilings in residential or commercial buildings. Their horizontal beam distinguishes them from scissor trusses.

Double trusses

When roof trusses are too large to be built and/or delivered, they can be designed in two pieces, or two half roofs. These wood roof frames are known as double trusses and must be assembled on the job site. They are just as sturdy as one-piece standard trusses!

Mono-pitch roof truss

Mono-pitch trusses look like right angled triangles. In reality, they are one half of a common truss. Mono-pitch roof trusses are often used to construct sheds, garages or to build a house extension.


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Types of wood used and dimensions

In Quebec, timber trusses are most commonly made from SPF lumber a.k.a. spruce, pine and fir.

The dimensions of the roof truss wood beams will vary according to their function. For example, the top and bottom chords are generally between 38 x 89 mm to 184 mm (2 x 4 to 2 x 8) and the web members vary from 38 x 64 mm to 184 mm (2 x 3 to 2 x 8).

For special projects like attic trusses and agricultural arches, you can use larger-sized lumber, e.g. 38 x 235 mm and 38 x 286 mm (2 x 10 and 2 x 12) boards.

Roof truss advantages

There are many advantages to using prefabricated wood trusses. Here are the main reasons they’ve become so popular in construction and renovation:


Their triangular design gives roof trusses a very high level of resistance to different types of stresses. They are therefore ideal for a Quebec home since they can withstand harsh winters and heavy snowfall.

An impressive span

Roof trusses span over 80 ft (24 m) which leaves plenty of room for large interior spaces without columns or load-bearing walls. If you would like to add a touch of grandeur to your home, consider roof trusses!


In general, roof trusses weigh between 0.04 and 0.07 kN/m (3 to 5 lb/ft), depending on the size of the members. Their lightness not only makes them easier to handle, but also helps to reduce seismic loads in buildings with roof trusses.

Precise measurements

Trusses are computer-designed and manufactured with high-tech equipment, ensuring a uniform product with measurements that are accurate to the millimetre. To access all these advantages, contact a professional!

Low environmental impact

The lumber used to make roof trusses is the only sustainable building material. In addition to having excellent acoustic properties, the wood also sequesters the carbon stored during its growth.

Rapid manufacture times

The manufacturing process for roof trusses is meticulously engineered for top-notch results. Weatherproof factory manufacturing with automated tools allows roof truss suppliers to offer extremely short production times, even for large orders.

Easy installation

Roof trusses are easily transported by crane and can be quickly installed via a few simple, repetitive steps. Roof trusses typically require only two people to install.

Low cost

Using roof trusses in a construction project saves on both the cost of materials and labour. If you’re looking for a quality product at a low cost, a roof truss is ideal.

Roof truss regulations

The National Building Code of Canada (NBC) requires all prefabricated structures used in building construction to meet the same basic functional specifications.

Specifically, manufacturers must guarantee that the roof won’t collapse during and after construction, and the trusses must remain reliable and secure throughout their lifespan.

How much does a roof truss cost?

In most construction or renovation projects, you’ll save a lot of money by choosing roof trusses over conventional framing.

That said, that there are several factors that affect the cost of a roof truss:

Building size

The larger building, the more expensive the roof truss will be. This is because more materials and time will be required to make it.

Building shape and architecture

Suppliers may need to build different trusses if a building’s roof has a very complex design, e.g. more faces, different slopes, gables, etc. These jobs are more intensive and therefore may affect the cost.

Converting attic space

It is standard in the industry to charge between 20% and 30% more for attic trusses than standard trusses.

Type of construction project

Roof trusses are not only used in the residential sector. Multi-residential, commercial and institutional buildings can also be constructed using roof trusses. Construction standards will differ depending on the type of building. Since the space between trusses can vary, more or fewer trusses will be required for each project, which will influence building costs.

Project location

Location plays a crucial role in determining the potential load the roof will support, which is influenced by factors such as snow and wind. It’s vital to know the precise location of the construction project before you start designing the trusses.

Type of roof and trusses

The choice of roofing materials is also an important factor. The weight of the roofing materials will dictate the amount of support each truss will need to provide. The more roof trusses your project requires, the higher the cost will be, even if higher production means lower unit costs. Whether you produce one or ten trusses, the design, manufacturing and delivery process is the same.

In summary, roof trusses are available in a variety of forms, and prices will vary. When you draw up an estimate for your roofing project, remember that the type of truss and roofing you choose will both impact the total cost.

Hire UsiHome to make your roof truss

That concludes this guide to roof trusses. With this information in hand, you’ll surely have a better idea of what roof trusses are, and what their advantages are.

As specialists in the construction of prefabricated wooden structures since 1967, we’d be delighted to help you with your building project. To make it easier for you to work with a single supplier, we offer a complete solution, including the manufacture of prefabricated walls and wooden floor trusses. If you need any further information, please don’t hesitate to contact our representative!

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