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.
Rafter and Roof Truss Definitions
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.
In roofing, the ridge refers to the top of the roof or the peak.
A ridge board is a non-structural board between the peak of two rafters. In particular, it provides a nailing surface for the rafters.
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 roof gutters get attached to the eaves.
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.
Studs are the vertical members of a wall. They are typically made from 2×4 or 2×6 lumber. (Think stud finder)
Ceiling Joists/Rafter Ties
What is a Roof Rafter?
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. These wood beams are made 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.
Rafters are nailed to a 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. It consists of interconnected triangles made of wood, steel, or other materials that distribute weight evenly across the entire roof structure, allowing for a longer span than traditional rafters. Trusses are typically prefabricated off-site and then installed at the construction site.
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, and can be quickly and easily installed, which can save 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. This makes them a versatile option for multiple building types and architectural styles.
- Customization: Rafters can be easily customized 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. Trusses, on the other hand, can not be modified without engineering design and approval.
- Aesthetics: 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: 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: Rafters must be cut and installed individually on-site. This process is time-consuming, especially for larger or more complex roof designs. This time and labor typically means its
- 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: Roof trusses are engineered structural supports designed to be strong and durable. 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: Trusses get built in a controlled environment and delivered to the building site. This allows for better quality control and more structural integrity.
- Cost-effective: Roof trusses can be manufactured off-site and transported to the construction site. This means they can be installed 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: Trusses are designed to tackle longer spans without intermediate supports, allowing for more open interior spaces.
Cons of Roof Trusses
While roof trusses have many advantages, some potential disadvantages should be considered.
- Less flexibility for changes: Once installed, roof trusses are challenging to modify or change without significant structural alterations. These changes need to be designed and approved by a licensed 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.