Roof trusses - types, construction and installation
A roof truss is the framework of a roof, responsible for its stability and durability. Choosing the right type of truss and its proper installation are crucial for the safety and comfort of your home. In this article, you'll learn what a roof truss is, its different types, its structure, and how to install it. We've also prepared practical tips on what to consider during installation.
Types of roof trusses
Rafter roof truss
This is the simplest and most economical form of roof truss. It consists of rafters resting on wall plates, or beams attached to the building’s walls. For simplicity, the maximum spacing between supports (walls) is assumed to be 6 meters. Ideal for small buildings, such as garages or summer houses.
Collar beam roof truss
Unlike the previous type, a horizontal element called a collar beam is introduced to improve rafter stability. The recommended support spacing for this type of truss is a maximum of 9 meters. These are so-called expansion trusses, which generate relatively large horizontal forces on the wall plate and, consequently, on the walls. Particular attention should be paid to properly designing the rafter-to-wall plate connection. Often, we encounter a lack of a connection design or an insufficiently strong connection. The choice of connector depends on the forces acting at the joint. Simpson Strong-Tie, among others, offers good connection solutions for rafter-collar beam trusses. The main advantage of this structural system is that it does not require any internal support.
Rafter-purlin roof truss
This is an advanced structure in which the rafters are supported by purlins (horizontal beams) and the entire structure is reinforced by clamps. This structural arrangement eliminates the problem of roof span. Often used in traditional construction due to its structural advantages, it also has its drawbacks, such as complicated assembly and supports (columns) in the attic, which can complicate interior design.
Installation of roof trusses
Installing a roof truss is a task that requires precision and proper preparation. Installing a truss is similar to buttoning a shirt: if the first button is buttoned incorrectly, the rest will be attached incorrectly. Therefore, it’s crucial to be precise and consistent throughout. Furthermore, the components should be connected as shown in the design, as this is crucial for the structure’s safety. Here’s how the process works and what to pay attention to.
Stages of installation of basic types of roof trusses
- Installing the wall battens: We begin by determining their location according to the design. Precision is essential. Next, drill holes for the existing studs in the tie beam (we use a CNC machine, after measuring with a laser total station).
- Installing the purlin frames: The purlins must be positioned very precisely. A level is helpful during purlin installation. Due to the large size of these elements, a crane is often helpful.
- Setting the rafters: Attaching the rafters to the wall battens at the appropriate spacing, according to the design. This seemingly simple step can pose many challenges.
- Adding additional load-bearing elements: Installing collar beams, purlins, and tie rods, depending on the truss type.
- Ensuring spatial stability: For example, by installing boards or wind strips.
What to pay attention to
- Material: It’s not worth skimping on wood quality. Make sure the material you’re buying is certified and meets the requirements of your project. It’s often necessary to protect wood from insects and fungi that can destroy it. Ask your contractor what wood protection methods they plan to use. Wondering which impregnation is best? Click to learn more about impregnation types and ensure the durability and aesthetics of your project.
- Execution: The role of CNC technology in modern construction is impossible to overlook. Of course, in Poland you can still find skilled craftsmen who can hand-make precise carpentry joints. However, such specialists are not easy to find, and their services are often expensive. What can you do when the project is complex, the shape and processing require extreme precision, and there’s no local specialist capable of constructing a roof truss using traditional methods?
- Prefabrication: This is where CNC machines come in handy. Thanks to computer control, they can produce roof truss elements with unparalleled precision and repeatability in a short time, with minimal effort. This solution allows us to construct even the most complex structures quickly, economically, and without compromising quality.
- Design: We often receive roof truss designs that are insufficiently detailed because they lack key information, especially the design of structural joints. For example, the design might recommend connections “in accordance with the art of carpentry,” which can lead to assembly errors, such as the use of inappropriate fasteners, which in turn results in deformation and damage to the structure. In such a situation, how would the carpenter know the force at the joint? Therefore, if your design is poor, look for a company that will take the time to determine the forces at the joints and design the appropriate connections. These connections will not expose you to failure, and at the same time, will not be unnecessarily expensive.
- Assembly: Precision matters. It can affect the load-bearing capacity of the joints and the geometry of the structure. It is worth choosing a team that is experienced and aware of the risks resulting from amateur installation.
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