What are Timber Frame Rafters?

 In Roof trusses

Are you looking for information about building a timber frame? Have you come across the term “rafter” while reading or in conversation and wondered what exactly it means?

In this article, our prefabricated wood structure specialists provide a comprehensive overview of different types of rafters and their uses.

Let’s get started!

A brief definition of roof rafters

A rafter is a structural component of a roof that extends from the roof ridge to the top plate of the exterior wall. When the rafter extends past the top plate, it creates an overhang.

Generally placed side by side, rafters support much of the weight of the roof and serve as a base for attaching the roof covering. Their spacing must be precise and is calculated based on factors such as:

  • The load the roof will need to support (covering materials, snow, etc.)
  • Purlin spacing (ridging and top plates)
  • The length of the overhang

The uses of rafters

A few decades ago, stick framing was the preferred method of roof construction. In this method, rafters were custom-made on the construction site using softwood lumber. Measuring, cutting and assembling every rafter on-site was enormously time-consuming.

Today, the stick framing method has largely been replaced by prefabricated roof trusses, but rafters are still used. In fact, they are a component of most truss designs.  In this context, the term « top chord » is sometimes used.

Materials used to make rafters

Rafters can be made from a variety of materials, the most common being steel alloys and wood.

Softwood (pine, cedar, spruce, etc.) is the type of wood most frequently used to manufacture rafters. However, for longer rafters, it can be advantageous to use structural composite lumber like LVL (laminated veneer lumber). This type of engineered wood can be used to create rafters 2 to 5 times longer than those made of regular lumber.

Types of rafters

Here are a few of the different types of rafters:

Principal rafters

The principal rafter is always one of the longest rafters in a roof structure. It is supported by a connecting beam.

Common rafters

Common rafters can be used by themselves or in combination with a principal rafter, which they help support. They can also be called minor rafters.

Intermediate rafters

These rafters are placed between the principal or common rafters to reinforce a specific part of the roof. They are rarely used.

Jack rafter

This type of rafter doesn’t reach the ridge or top plate because it hits another component of the frame.

Barge rafter

A barge rafter is sometimes used to form a roof overhang. In such cases, it is the outermost rafter at the gable end.

How much do roof rafters cost?

It’s difficult to define a price range for rafters, because the cost varies depending on the materials, size and supplier.

For wooden rafters, the price will also depend on the type of wood and the treatments that can be used on it.

UsiHome: timber frame specialists in Quebec

Rafters are an important part of a roof structure. They are essential for the stick framing method of building a roof, but can also be used in roof trusses. They come in many different materials and dimensions.

For more information about wooden constructions, check out our blog or contact our structural wood product experts.

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