Roof Frames & Trusses

About Roof Frames and Trusses

Roof frames and trusses are essential for completing structural and framing tasks. They are a practical substitute for traditional hand-framed rafters, which are made from solid wood.

These components play a critical role in distributing the weight and forces exerted on the roof down to the walls, beams and columns, or other foundational supports of a building. Roof structures are periodically subjected to dynamic forces such as wind, rain, or snow, and must also withstand the constant weight of materials like roofing sheathing.

Elements of Roof Frames

Roof frames are essential for structural integrity, and among their components, three stand out as crucial:

• Top chord - serving as the upper boundary of a truss, the top chord can be horizontal or angled. It plays a critical role in stabilising the frame, supporting the roof's weight, and resisting compressive forces.
• Bottom chord -  positioned at the truss's lower edge, the bottom chord may be angled or horizontal. It secures the frame's base and endures both tension and bending stresses.
• Web - this network of interlinked struts forms a triangle within the truss, connecting the top and bottom chords. The web is key to preventing the truss from bending by resisting intense tension or compression forces.

Benefits of Roof Trusses

There are numerous advantages to building roof trusses. Each element of the roof frame is designed to manage specific loading and spacing requirements. Trusses pre-made from engineered wood feature extremely precision cuts, enabling rigid uniformity. Excellent balance to the roofing structure can be established as a result. Their lightweight nature allows for a fast and easy installation, more accessible than other framing systems. In addition, the open web design makes the installation of electrical, plumbing, and heating and cooling systems a breeze.

Trusses are available in a range of styles, providing great design flexibility for the interior layout of a building. Apart from the formation of functional attic spaces, it also supports different partitioning and arrangements. Building with trusses allows interior layout changes after construction as well as before it.

Types

Standard

Standard or common trusses feature four-inch heels and a pitch on both sides, with a peak at the centre. 

Girders

Girder trusses are intended for carrying both standard and additional roof loads. That includes other trusses attached on the top of the girder or its sides, using truss hangers. Girder trusses can be customised and suited to particular applications or designs.

End Trusses 

This type closes at the end of a building, providing a nailing surface for the rigid sheathing or upper-end walls. It’s typically placed in a way that allows the entire bottom chord to be supported by the wall. All the load applied to the end truss is therefore directly shifted to the end wall and further down towards the foundation.

Energy Trusses

As the name indicates, energy trusses are designed to provide greater insulation depths at the heel. While most standard models can achieve certain R-values, the raised heels of energy design allow it to reach the values of 30 or higher.

Post Frame

Post-frame trusses are typically found at spans greater than 50cm on the centre. They are suitable for a variety of applications, including residential, commercial, and agricultural.

Spread Web

Also known as storage trusses, this type is engineered to form a small area that can serve as functional storage. It’s achieved through the centre webs spreading wider than average, to release the space at the centre of the truss. This storage area is not sufficient to allow human occupancy.

Speciality Trusses

Some truss designs allow the formation of unique shapes and configurations, intricate rooflines, cathedral or vaulted ceilings.

• Scissor trusses feature a slope on the outside and inside with angled bottom chords, ideal for creating vaulted ceilings. 
• Parallel chord design improves interior clearance in buildings. 
• The offset scissor scheme features a flat bottom chord, vaulted up and back down. 
• Partial scissor design is similar to offset, with the bottom chord sloped and straight down while the rest is flat.
• Mono and vaulted mono pattern descends only in one direction, ideal for creating additions to an existing building.
• The cantilever extends beyond the exterior wall framing to cover porches, entryways, patios, and similar offsets in the building elevation.
• Bobtail trusses are characterised by the same pitch on each side, with a peak displaced from the centre of the span and a heel taller at one side.

Room-in-Attic Styles

Trusses are designed explicitly to create living space in the attic. They allow for the addition of a second-floor without having to build an actual floor system. 

• Gable room-in-attic is a cost-effective method for adding living space to a home or garage.
• A gambrel room-in-attic forms a roof with a distinctive barn-like appearance.
• Hip sets, as the name says, are used in the creation of hip roofs sloping from all sides. 
• Valley sets are defined by the intricate ridge line and framing. They can be common, mono-shaped, or dual pitch, used for decorative gables, porches, and more.

Things to Consider Before Buying

Location is a vital factor in choosing the right type of roof frames and trusses. Different conditions, such as climate, average snow and wind expectations, and similar, can determine the best roof style and elements that should be used. Building layout and size, as well as the truss spacing, are also important.

The function of the building is directly related to the building code and design perimeters that will be applied in truss design.