Rafters And Roof Trusses: Complete Structural Guide

When it comes to your roof/attic structure, there are two primary construction types: rafters and roof trusses. Knowing the difference between rafters and trusses helps you choose between the two when building a new home, communicate better with contractors, and know whether or not you need an engineer for modifications.

Basically, it’s just one of those things you need to know as a homeowner.

Juan Jimenez
March 20th, 2023
Home Guideshouse structure

Rafter and Roof Truss Definitions

Stick-built

In construction, “stick-built” or stick framing refers to the traditional method of building a house by assembling it’s framing on-site using individual pieces of lumber. To clarify, rafters refer to stick-built construction, while trusses do not.

Ridge

In roofing, the ridge refers to the top of the roof or the peak.

Ridge Board

A ridge board is a non-structural board between the peak of two rafters. In particular, it provides a nailing surface for the rafters.

Eaves

An eave is the part of a roof that overhangs the outside walls of a building. Functionally, an eave is an important component of the roof system as it helps to protect the walls from rainwater by directing it away from the building. Plus, the eaves support the gutter attachment.

Dimensional Lumber

Dimensional lumber is a generic term that refers to industry-standard lumber used in construction. For example, 2×4, 2×8, and 4×4 are all typical dimensional lumber sizes used in a wooden structure.

Stud

Studs are the vertical members of a wall. They are typically made from 2×4 or 2×6 lumber. (Think stud finder)

Collar Ties

Framers install collar ties in the upper third of opposing rafters to resist rafter separation from the ridge beam during periods of unbalanced loads. For example, loads caused by wind uplift or unbalanced roof loads from snow.

Ceiling Joists/Rafter Ties

On the other hand, framers install rafter ties in the lower third of opposing rafters to resist the outward movement of rafters. In many situations, you’ll find that ceiling joists installed parallel to the rafters function as the rafter ties.

What is a Roof Rafter?

Primarily, roof rafters are structural components that support the roof deck and the weight of the roof itself. In addition, rafters support additional loads such as snow and people. Rafters are typically long, angled wood beams that run from the peak of the roof (the ridge) down to the eaves. Framers make these beams from regular dimensional lumber cut to size at the job site.

They are usually spaced evenly across the roof (every 16 inches like studs), and the size and spacing of the rafters will depend on the design of the roof, the weight of the materials, and the local building codes and regulations.

Finally, framers the rafters to the ridge board at the top and to the exterior walls at the bottom.

What is a Roof Truss?

A roof truss is a structural support engineered to support a roof. Simply put, it consists of interconnected triangles made of wood, steel, or other materials that distribute weight evenly across the entire roof structure. As a result, builders have the freedom to make longer spans than traditional rafters. Also, trusses are typically prefabricated off-site and then installed at the construction site.

Summing it up, trusses incorporate rafter boards, ceiling joists, and collar ties into one structural unit and eliminate the need for a ridge board.

Roof truss systems are a popular choice for building construction because they are strong, lightweight. Plus, framers can quickly and easily install them saving time and money during the construction process. They also provide a more open space in the attic or roof area than traditional rafters, which can be helpful for storage space or for creating living space.

Pros and Cons of Rafters and Trusses

Pros of Rafters

Roof rafters have several advantages over roof trusses

Versatility: Rafters can create various roof designs, from simple gable roofs to complex hip and valley roofs. As a result, they are versatile option for multiple building types and architectural styles.
Customization: Next, framers can easily customize rafters to fit the unique needs of a project, including the size and shape of the roof, the weight of the roofing materials, and the local building codes and regulations. For example, adding a skylight to a rafter system is simple for a contractor. On the other hand, framers and contractors cannot modify a truss without engineering design and approval.
Aesthetics: Lastly, rafters can provide a traditional and rustic look to a building, which is popular in some architectural styles. They can also be left exposed for an attractive and decorative effect.

Overall, roof rafters provide a practical, alterable, and aesthetically pleasing option for roof support in various building types and architectural styles.

Cons of Rafters

While roof rafter construction has many advantages, there are some potential disadvantages to consider as well.

Limited span: First, rafters are typically limited in the span they can cover without additional support. This may require supplemental materials, such as posts or columns, that can increase the project’s cost.
Time-consuming installation: Framers must cut and install rafters individually on-site. Unfortunately, this process is time-consuming, especially for larger or more complex roof designs. This time and labor typically means its more expensive to use rafters.
Design limitations: Rafters may not be suitable for certain types of roof designs, such as those that require a flat roof or a large span.

Overall, roof trusses shine where rafters fall short.

Pros of Roof Trusses

Roof trusses have several advantages over traditional roof framing methods like rafter construction.

Strength and Durability: First, engineers specifically design trusses with more strength and durability than a standard rafter. Specifically, they can withstand heavy loads and high winds, making them a good choice for areas with extreme weather conditions. Plus, they’re better suited for multiple layers of shingles.
Superior Quality: Plus, trained factory workers build trusses in a controlled environment and delivered to the building site. This allows for better quality control and more structural integrity.
Cost-effective: Roof trusses are manufactured off-site and transported to the construction site. This means framers can install them quickly and efficiently, saving time and money. Although the trusses are more expensive than rafters, the savings are realized with the ease of installation.
Space-saving: Engineers design trusses to tackle longer spans without intermediate supports, allowing for more open interior spaces.

Cons of Roof Trusses

While roof trusses have many advantages you should also consider their disadvantages.

Less flexibility for changes: Once installed, roof trusses are challenging to modify or change without significant structural alterations. Building codes require that all changes receive approval from a licensed architect or engineer.
Limited attic space: Trusses are designed to span long distances without intermediate supports, so they may not provide as much usable attic space as traditional roof framing methods.
Potential for fire damage: Trusses can be more vulnerable to fire damage than traditional roof framing methods, which may increase the risk of a fire spreading.

It’s essential to consider both the pros and cons of using roof trusses when deciding on the best roofing system for a particular building project.

Rafters VS Roof Trusses: Main Differences

Both roof trusses and rafters support the roof and roof loads. However, there are some important differences between the two.

Rafters are easily cut on-site, are great for custom jobs, and offer more attic space. Plus, they’re easy to modify.

On the other hand, roof trusses are built off-site, requiring a lot of design and lead time for delivery. As a result, your construction project could get delayed while waiting for trusses. However, trusses span longer distances, reduce labor costs, and allow fewer internal load-bearing walls. In addition, unlike rafters, trusses require a structural engineer for modifications.

When to use Rafters

For the most part, trusses are the right option for most new home construction. However, sometimes rafters are the best option. Use rafters when you want to turn the attic into living space, on a small addition, or a specialty roof design.