Board for rafters: selection of section and thickness

Selecting the appropriate board for your rafters is essential to the long-term stability and longevity of your roof. The board that holds up the rafters, also referred to as the collar tie or rafter board, is essential for stabilizing the roof in different weather scenarios and distributing the weight of the roof evenly.

Many considerations must be made when choosing the rafter board’s section or dimension. The rafters’ span—the distance they must span across the building’s width—is the most important factor to take into account. In order to guarantee that longer spans can sustain the weight without sagging over time, thicker boards are needed. The section also assesses the rafters’ resistance to twisting and bending loads, which aids in preserving the structural integrity and form of the roof.

Another important consideration when selecting rafter boards is thickness. Greater strength and durability are provided by thicker boards, which are especially beneficial in regions where there is a lot of snow or where the roof may be exposed to strong winds. Additionally, thicker boards add to the roof structure’s overall stiffness, which lowers the possibility of excessive deflection or movement during severe weather.

When choosing the section and thickness of rafter boards, it is imperative to refer to the building codes and regulations in your area. These codes frequently outline minimum specifications depending on variables like wind exposure, snow load, and roof pitch. Following these rules guarantees that your roof satisfies safety requirements and is resilient enough to endure the typical environmental conditions in your region.

The final decision regarding the thickness and section of rafter boards should be made after carefully evaluating the local building codes as well as your unique roofing requirements. You can guarantee a sturdy, stable roof that will dependablely protect your house or building for many years to come by choosing the right boards.


When calculating the rafter structure, which allows for the production of rafter legs from the board, it’s critical to consider both the quality of the lumber that will be used and the cross-section of these components.

Prior to anything else, the best type of wood must be chosen for rafter construction. The coniferous and deciduous lumber fully satisfies GOST 8486-86 and GOST 2695-83 requirements.

In accordance with these specifications, the board responsible for producing rafter legs could possess:

  • no more than three knots for each linear meter of lumber, the maximum permissible diameter of the bitch is 30 mm;
  • non -bloody cracks, the length of which does not exceed 1/2 of the length of the board;
  • humidity is not more than 18% (measured by a moisture).

When buying lumber to make rafters and other roof frame components, it is required by SNiP guidelines to review the document that provides information regarding the products’ quality.

It ought to be stated:

  • The name of the manufacturer and the basic data about it;
  • product name and its standard number;
  • the size of lumber, wood rock, degree of humidity;
  • the number of units in the package;
  • Party Party release date.

Wood is a natural material that can burn and be destroyed by biological processes. Pre-installation preparation of the board rafters is required in order to lessen the possibility of damage and destruction of the completed structure due to lumber. As part of preparation, protective and constructive measures must be put in place in compliance with SNiP regulations.

Among the safeguards are:

  • processing of wood with antiseptic compounds in order to prevent premature decay;
  • impregnation of wood with antipyrene products that prevent fire;
  • processing of rafters and other wooden elements with means protecting from insect pests.

Among the constructive actions are:

  • Installation of waterproofing gaskets in the places of adjoining wooden structures to brick;
  • the formation of a waterproofing carpet under roofing material and vapor barrier from the room;
  • Equipment of special openings for ventilation of a roof pie.

If roof arrangement technologies are followed, board rafter construction should result in a long lifespan with few need for repairs.

Wood processing with protective equipment

Following manufacture, the rafters should be fitted with specific fire and biosafety equipment. The joints between the rafter structure may become foci of roof frame decay if the already-collected rafter structure is processed without being protected from the elements. This will cause the roof to deteriorate earlier than necessary and necessitate spending a significant amount of money on roof replacement or repair.

It is advised that the rafters use coniferous wood with a high concentration of resin, as this acts as a natural defense against decay. However, even wood from pine and larch trees needs to be treated with specific substances.

If the rafters’ moisture content is higher than 18%, the components of the rafter structure may "story" during operation, leading to roof deformation and a reduction in the system’s overall strength.

A soft brush, roller, garden spray, or spray gun can be used to apply protective gear, and the dipping method is also practiced. The rafters’ surface should be clear, dry, and free of paint that would hinder the protective material from penetrating the wood fibers.

The locations of the rafter legs’ future joints are particularly meticulously impregnated. It is best to process during dry, warm weather. Two applications are made of antiseptics and fireproof compositions, also known as universal fireproof vehicles. The rafter boards should be allowed to dry in between the first and second processing steps.

Rafts that have been twice processed cannot be installed until they have dried.

Cross -section of the rafters from the board

Boards, timber, or logs can be used to make the rafters. The heavy weight of the log and the requirement for intricate cuts where fasteners are located are drawbacks that severely impair the element from the round’s supporting capabilities. While the beam is more expensive than the board, it performs much better in use.

Rafting legs from the board: this material is actively used to manufacture lateral rafter legs and is the best option. With the board, you can also construct sturdy clock (diagonal) rafter legs and extended lateral rafters.

A parameter like the board’s thickness has a big impact on its strength qualities. For the purpose of manufacturing rafters, boards with a thickness of 40–60 mm are ideal, though using a 40 mm board will save money towards roof construction. Simultaneously, this parameter should not be less than 50 mm when building a residential building’s roof.

The length of the opening, which must be blocked, is taken into consideration when choosing the width of the rafters boards. The longer the rafter leg, the wider the board that is manufactured. The minimum size of a rafter for a residential building’s roof is 50 × 150 mm, but rafters up to 6 meters long can be constructed from boards that are 150 mm wide.

The board’s width must be at least 180 mm if the rafter leg is longer than six meters. The 150 mm-wide coated boards that make up the extended leg should be placed as close to the ridge portion as possible. The overlap of the boards should measure at least 500 mm.

The weight of the rafter structure, the angle of the ramp’s slope, the width of the house, the overlapped opening’s length, and the snow and wind loads on the roof all affect the section of rafters. You can use the relevant computer program to calculate the section, which uses specific tables and formulas. It is advisable to leave the execution of computations to experts in complex situations.

After determining the ideal cross section of the rafter legs, you must be mindful of the rafter installation process. These are interrelated variables that can be slightly changed without affecting the roof’s dependability. You can slightly reduce the section of rafters by using struts.

Factors to Consider Guidelines
Load-bearing Capacity Ensure the board can support expected weight.
Wood Type Choose durable wood suitable for climate.
Section Size Typically ranges from 2×6 to 2×10 inches.
Spacing 16 inches on center for 2×6, 24 inches for 2×10.
Thickness Depends on span and load; commonly 1.5 inches.

Selecting the proper board for rafters requires careful consideration of both thickness and section. The board’s section refers to its measurements, which are usually indicated by width and depth. More strength and stability are provided by a wider, deeper board, which is essential for bearing the weight of the roof. It is crucial to choose a section size that corresponds with the rafters’ span and the weight they are intended to support. This guarantees that the roof structure will always be strong and resilient.

The board’s resilience and capacity to tolerate a range of weather conditions are largely determined by its thickness. In general, thicker boards are more resilient to bending and warping, which is crucial for long-span roofs and locations that frequently receive large snowfall. While thinner boards might be appropriate for lighter roof loads or shorter spans, they still need to adhere to structural specifications to ensure longevity and safety.

Following building codes and regulations that specify minimum requirements for structural components is crucial when selecting the board for rafters. These specifications guarantee that roofs will not fail even under anticipated stress conditions and environmental variables. Selecting the right board dimensions based on the needs of a particular project and local building codes can be greatly aided by consulting with a structural engineer or skilled contractor.

Choosing the ideal section size and thickness is crucial when choosing the correct board for rafters in roof construction. These choices have an immediate effect on the roof structure’s sturdiness, affordability, and strength. The thickness influences the board’s resistance to bending and ability to sustain the weight of the roof over time, while the section size determines the maximum load the board can support. Builders can guarantee a robust and dependable roof that satisfies safety regulations and longevity expectations by being aware of these factors and choosing boards that correspond with the particular requirements of the roof design.

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Gleb Zuev

Exterior designer, author of books about roofing materials. I will help you make your roof not only reliable, but also beautiful.

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