What Is a Roof Truss?

 In Roof trusses

Are you wondering, “What in the world is a roof truss?” Then you’ve come to the right place!

In this article, our prefabricated wood structure experts will answer this (common!) question and 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. The triangle structure makes the 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 rafters. Be careful though: these expressions do not always mean the same thing.

Different types of roof trusses

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 types of roof trusses 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. The horizontal beam distinguishes them from scissor trusses.

Double trusses

When trusses are too large to be built and/or delivered, they can be designed in two pieces. These double truss structure must be assembled on the job site but are just as sturdy as one-piece standard trusses.

Single-pitched roof truss

Single-pitch trusses look like right angled triangles. In reality, they are one half of a common truss. This type of roof truss is often used to construct sheds, garages or to add an extension to an existing roof.

Wood types 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:

Durability

Their triangular design makes roof trusses durable against high levels of different stresses.

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.

Lightweight

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.

Extremely precise measurements

Trusses are computer-designed and manufactured with high-tech equipment, ensuring a uniform product with measurements that are accurate to the millimetre.

Low environmental impact

The lumber used to make roof trusses is the only sustainable building material. What’s more, the wood also sequesters the carbon stored during its growth.

Rapid manufacture times

Roof trusses are manufactured in a weatherproof factory with automated tools. These conditions allow 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 installed via simple and 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.

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.

Roof truss pricing

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 roof truss cost:

Building size

The larger the building, the more expensive the roof trusses will be to cover the cost of the added materials and labour.

Building shape and architecture

Suppliers may need to fabricate 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 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.

UsiHome: your one-stop-shop for roof trusses

We hope this short guide has given you a better idea of what roof trusses are their many potential benefits!

Have any questions about the construction, availability or price of our wooden roof trusses? Contact our experts today!

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