A timber roof truss is a structural framework made of wood used to support its weight. It consists of a series of interconnected triangles that distribute the weight of the roof evenly across the walls of the structure. The truss can span large distances without the need for internal load-bearing walls, allowing for open floor plans and more flexibility in design.
Roof trusses are commonly used in South Africa (as well as in many other parts of the world) because they offer several advantages over traditional methods of roof construction.
They are made from high-grade timber and are designed to withstand the weight of the roof and any additional loads, such as snow or wind. They are manufactured offsite, typically in a factory or workshop, and then transported to the building site for installation.
Timber roof trusses in comparison to other materials.
When it comes to roofing materials, timber roof trusses offer several advantages over other materials like steel, concrete, and masonry.
Strength and Durability
Timber roof trusses are strong and durable, able to withstand heavy loads and extreme weather conditions. They also have a natural resistance to fire, making them a safer option in the event of a fire.
Timber is a renewable resource that can be sustainably sourced, making it a more environmentally friendly option compared to non-renewable materials like steel and concrete. Timber also has a lower carbon footprint and can store carbon throughout its life, helping to mitigate climate change.
Flexibility in Design
Timber roof trusses can be designed to span long distances without the need for internal load-bearing walls, creating more flexible and open floor plans. They can also be prefabricated offsite, allowing for faster and more efficient construction.
Timber roof trusses are often more cost-effective than other materials, especially when factoring in the cost of labor and transportation. They are also lightweight, making them easier to handle and transport.
The most common type of roof truss built in South Africa
The most common type of roof truss used in South Africa is the “Common Truss” or “Fink Truss.” This type of truss consists of a series of interconnected triangles, which provide stability and support for the roof structure. It’s main function is to carry snow, wind, live and dead load and distribute it to its supports (walls or columns).
The web members form a ‘W’ to provide a high-strength structure with good load-carrying capacity. The roof load is transmitted entirely to support the wall plates. They are popular because they are simple and relatively inexpensive to construct, while still providing a strong and reliable roofing solution.
The fink truss can also be used as a support for other trusses by doubling or trebling the number of plies. They are mainly used as roof structures for, residential buildings, farms, garages, etc.
Building a fink/common roof truss.
Building a timber fink truss involves several steps, including:
Design the truss.
The initial step to design a truss is to determine the appropriate span, pitch, and spacing of the trusses. You can accomplish this by utilizing specialized software designed for this purpose or by consulting with a structural engineer or truss manufacturer who can provide guidance on the optimal design.
Determining these key factors enables the design of a truss that can provide the necessary support for the intended application while also meeting any relevant safety or building codes.
Purchasing and cutting the timber.
Once the design is complete, the timber can be cut to the appropriate lengths and angles using a saw or other cutting tools. You can purchase your timber from Sabie Poles.
We supply top-quality CCA-treated and untreated Poles (Building and fencing) and timber (S5 Grade Construction) in various sizes and lengths. Most customers prefer to buy 6.6m meter timber which they will cut to other required lengths.
The most common timber sizes purchased for roof trusses are:
- 38mm x 114mm
- 38mm x 76mm
- 38mm x 152mm
- 38mm x 228mm
Additionally, for roof covering:
- Tiles and slates: 38mm × 50mm battens
- Metal or fiber-cement sheets: 50mm × 76mm purlins
- Metal tiles: 38mm × 38mm battens
Assemble the truss.
Once you have determined the design for the truss, the next step is to assemble it. This involves connecting the individual pieces of timber together using metal connector plates. The specially designed plates securely attach the timbers together and ensure that the truss is structurally sound.
You can install the plates using specialized nail guns or screws. Then place the connectors in specific locations on the timbers to ensure that the truss maintains its shape and strength.
Brace the truss.
Bracing the truss is important for ensuring its stability during installation after assembling it. Bracing helps to prevent the truss from buckling or collapsing under load during the construction process.
Several methods can brace a truss, including using temporary wooden braces or steel cables. People often use temporary wooden braces for smaller trusses by installing them diagonally between the bottom chord and top chord of the truss. These braces transfer the load between the chords and keep the truss in place.
To brace larger trusses, one can use steel cables. People install these cables diagonally between the chords and anchor them to the ground or adjacent structures. The tension in the cables helps keep the truss stable and prevents it from moving or buckling during installation.
Install the truss.
The final step in the process of installing a truss is to lift it into place and secure it to the building’s walls using specialized brackets. This is typically done with the help of a crane or other equipment designed for lifting heavy objects.
The installer lifts and maneuvers the truss into position over the building’s walls and carefully secures it using brackets designed for this purpose. Once the truss is securely attached to the building, any temporary braces or cables used during installation can be removed.
You should note that it is important to ensure that the installation process is done correctly to prevent any potential structural issues or safety concerns. Proper installation is crucial for ensuring that the truss can provide the necessary support and stability for the intended application. It’s also important to follow any relevant safety guidelines or building codes during the installation process to ensure that the final structure is safe and meets all applicable regulations.