What Are Roof Trusses?

By Amanda Lutz Updated March 28, 2024

Your roof’s design plays a major role in the layout of your home, its structural integrity, and the materials you can use to build your roof. A roof truss is one essential component used in building and supporting roofs throughout the United States. This structural framework connects the space above a room and provides support and strength for your roof.

Whether you’re preparing to build your own home or want to learn more about the structural integrity of your current home, this guide will help you navigate the advantages of roof trusses, common alternatives to roof trusses, how much this framework costs, and different truss styles for a safe and sound roof.

Understanding Roof Trusses

A roof truss is a prefabricated structural framework that builders can install on top of an in-progress home to support the roofing materials and give the roof its final shape. It looks like a hollow triangle with an array of lines and triangles within a larger frame. 

The wood pieces descending from the top peak are called the top chords, and the wooden pieces running along the bottom are the bottom chords. The pieces are connected by nail plates or web ties, and there are wooden webs or webbing running through the triangle—all of these smaller internal supports strengthen the entire triangle so it can support sheathing, shingles, tiles, and even solar panels.

Different trusses will have distinct webbing structures designed to provide varying levels of strength or give the roof a particular shape.

Roof trusses are installed on the home’s framing down the length of the home. Builders will lay out a series of roof trusses, standing them upright and securing them to the exterior walls at regular intervals. As the home build continues, builders will attach sheathing, underlayment, and the roof on top.

Here are the main benefits of roof trusses:

Trusses offer superior structural integrity. Each triangular web is structurally sound and unlikely to break or come apart over time. They also reinforce the home’s overall structure because they tie the exterior walls into a fixed position rather than simply resting on them.

Types of Roof Trusses

There are a variety of roof trusses that give roofs their form. The shape of the exterior triangle and the composition of the wooden webbing inside the truss are two factors that can affect a roof’s form and support. Some of the most common types of roof trusses include fink trusses, gambrel trusses, and scissor trusses.

Fink Truss

A fink truss has a diagonal web arranged in a “V” shape and a structural system that spans long distances. Its design can support steep inclines and heavy materials, but it can also limit the use of attic space. This type of truss is commonly found in residential homes and bridge architecture, but it also can be seen in barns and garages.

Gambrel Truss

Most commonly used in barns, a gambrel truss is a tall truss that supports a wide span and can add to the vertical space in a building. It has two slopes that descend on both sides of a peak, providing additional storage in your roof without taking up additional space. A few disadvantages to a gambrel truss is that it’s more susceptible to collapse and isn’t great for areas that experience heavy rain or snowfall.

King Post Truss

A king post truss has a simple design of two triangles that form the base and a diamond configuration with a vertical frame that forms the top and middle. The central vertical post is called the “king post,” giving the truss its name. These trusses extend up to 26 feet across and can help disperse the load of a roof. Their simple design also makes them one of the most cost-effective roof trusses available.

However, its limited span doesn’t make the king post truss suitable for larger buildings or homes. In fact, king post trusses are typically found in older homes and are used for building small homes.

Queen Post Truss

A queen post truss differs from a king post truss in that it has two vertical posts instead of one central vertical post. This type of truss can be much larger than king post trusses, with a length of up to 40 feet, making it better for longer spans. This type of truss provides a lot of support for mid-sized homes and sheds.

Scissor Truss

A scissor truss, also called a vaulted truss or cathedral truss, is an A-frame structure that connects two triangular legs with a top beam. This type of truss supports pitched roofs, where a raised or vaulted ceiling is desired. While scissor trusses are easy to install and have a low installation cost, they’re difficult to insulate and provide narrow access at the eaves, making it hard to perform roof repairs.

Other types of trusses with varying levels of complexity include the double fink truss for large homes, flat trusses for commercial buildings, and mono trusses for roof extensions.

Roof Truss vs. Roof Rafter

Roof rafters are a popular alternative to trusses. These wooden beams slope downward from the central ridge or hip of the roof down to the top of the wall, where a series of ridge boards (or ridge beams) and ceiling joists hold the rafters in place. Rafters are measured, cut, and arranged on-site rather than being prefabricated at an off-site factory and transported to the build site.

Here are some of the advantages of choosing this stick-frame roof construction method:

While rafters have some advantages over trusses, some of these conveniences come at a cost. Rafters cost more to build and install than trusses, and they take more time to install because all the work happens at the building site. They don’t offer the same durability as trusses, and because trusses are becoming more popular, it’s also harder to find contractors who specialize in high-quality rafter design.

Roof Truss vs. Joist

A joist is a horizontal beam that provides structural support and prevents the “A” shape in a roof rafter from twisting and falling. Builders add joists to rafters through collars and metal fasteners. Joists are placed along the ceiling, run horizontally to connect a series of parallel rafters, or bear weight as part of a ceiling or floor (or both, in an attic).

Joists are a good option if you have a stick-frame roof and want the option to modify the structure later. Compared to trusses, attic spaces defined by joists are simpler to renovate and restructure.

Joists do have some limitations. They handle a lot of structural load, so they can’t have defects or be joined from multiple pieces of wood; they can be only as tall or strong as the tree they came from. Builders also can’t drill holes or notches into joists because that compromises their structural integrity. As a result, roof trusses are often a better option for larger structures or very heavy roof materials.

Roof Truss Cost Factors

Roof trusses are a cost-effective alternative to traditional rafter and joist-based roofing. However, there are a variety of factors—from your building time line to the truss materials used—that can affect the overall cost of your project. Consider the following cost factors to plan your project accordingly:

How to Save on Roof Truss Costs

The average cost of a new roof truss is $21,000,* with prices ranging from $7,500–$35,000 for most home construction projects. However, there are some steps you can take to reduce the cost of a truss system. Consider these factors to help you save on your roof truss installation:

*All cost data in this section via Angi.

Our Recommendation

Roof trusses are an essential part of building a new home or modifying a roof on an existing property. They can support roofs on various homes and are a cost-effective way to offer structural integrity. Before you begin your roofing project, we recommend contacting an experienced roofing contractor who can help you assess your roof truss needs and make the right choice for your home.

Roof Trusses FAQ

What is the purpose of a roof truss?

The purpose of a roof truss is to support your roof and add more structural stability to the home. Roof trusses are the foundation for the roof materials, and they keep the exterior walls locked in alignment.

What is the difference between a roof rafter and a roof truss?

The difference between a roof rafter and a roof truss is their construction method. Roof rafters are installed on-site and don’t require a prefabricated support web. A roof trust is built off-site and shipped to the construction site.

What is the difference between a roof truss and a joist?

The difference between a roof truss and a roof joist is similar to the difference between a roof truss and a rafter. Roof trusses are complete structural frameworks for a roof, while joists are horizontal members that run across an open space and join opposing walls to support the ceiling below.

How do I know if my roof has trusses?

You can tell if your roof has trusses by going to your attic. You have trusses if you see a web of diagonal and perpendicular beams supporting the roof frame. You have rafters if your attic is easy to walk through and you see only diagonal beams along the sloping exterior walls.