Distance between rafters: Learning to choose the right

Knowing how far apart rafters are on a roof is essential to maintaining structural stability and longevity. The incline of the beams known as rafter supports the weight of the roof and transfers it to the walls of a building. The strength of the roof, the kinds of materials that can be utilized, and the total cost of construction are all impacted by the distance between these rafters.

The amount of weight that a roof can support is largely determined by the spacing, or distance, between the rafters. Usually, the distance between them is between 16 and 24 inches, but local building codes may have different requirements. For heavier roofing materials like slate or tile, closer rafter spacing offers increased support for the roofing materials and the weight they support.

On the other hand, lighter roofing materials like asphalt shingles can benefit from wider rafter spacing, which can also be more affordable. However, in order to guarantee the roof’s long-term durability and safety, wider spacing might necessitate the use of thicker rafters or additional structural support. Making an informed choice requires knowing the particular regulations in your area and the kind of roofing material you intend to use.

Selecting the proper spacing between rafters requires taking into account more than just structural support. Closer rafters offer less space for insulation but can lessen thermal bridging, which has an impact on insulation efficiency as well. Rafter spacing also affects the roof’s overall appearance and design, affecting elements like attic space and possible additions or renovations down the road.

Roof loads and calculation of the rafter system

The process of developing a single-sloping or gable roof project starts with selecting the kind of rafter system, the angle at which the slopes (roof heights) are inclined, and the building materials to be used. The loads that the roof will encounter during operation are taken into consideration when calculating the distance between the rafter legs.

Among the constant loads are the following:

  • the weight of the materials from which the rafter system is made;
  • weight of roofing;
  • the weight of the roofing pies (waterproofing, vapor barrier, insulation);
  • Weight of the elements of the decoration of the residential attic or attic.

Apart from continuous loads, the roof encounters transient loads such as:

  • wind load;
  • weight of snow cover;
  • Human weight when servicing and repairing a roof.

The presence of roof insulation, the cross section of the structural elements, the kind of roofing material, and the crate must all be considered in order to accurately calculate the installation step. The computation is performed using "Loads and Influences" (SNiP 2.01.85).

The step is the separation on a single slope between the rafters.

Calculations for a pinch, single-sided, or complex roof typically follow this pattern:

  • The length of the future slope of the roof is measured;
  • The resulting value is divided into the optimal numerical value of the step of the rafters;
  • A unit is added to the resulting value, the result is rounded;
  • The length of the slope of the roof is divided into a rounded result.

The final outcome will dictate the spacing between the rafter legs. Since many other factors must be considered, such as the width of the insulation and the specifics of installing the crate for different types of roofing material, it is impossible to define a step with absolute precision.

If a roof has a chimney, a step can be built in with consideration for its placement, saving you from having to remove additional rafters and replace them with a supporting structure—like a custom rafter system—instead of having to remove part of them.

Selecting the appropriate spacing between rafters is essential for maintaining the structural soundness and functionality of your roof. Everything about the roof is impacted by the spacing, including its ability to support weight, insulation, and general durability. Knowing how to choose the ideal distance requires taking into account things like the kind of roofing material, the climate where you live, and how the roof space will be used. Homeowners can guarantee that their roofs are not only long-lasting and safe, but also energy-efficient and perfectly matched to their individual requirements by choosing their rafter spacing carefully.

The distance between the rafters under the slate

Traditional roofing material: slate. Its low cost and resistance to external influences (apart from mechanical ones) are among its advantages.

With slate, you can build a roofing that only requires the replacement of individual parts for maintenance. Because slate weighs a lot, a rafter system that is strong enough must be installed. The cross section for the purpose of manufacturing rafter legs is taken into consideration when calculating the distance on which rafters should be placed beneath the slate.

Installing a slate system, which requires a minimum of 800 mm between rafters, is the best course of action.

The crate is constructed from a beam or board with a cross section of at least 30 mm in order for the design beneath the slate to withstand increased external loads in addition to the weight of the material. Slate has significant limitations when it comes to the angle at which the slopes can be chosen, so keep that in mind when calculating the rafter system.

Rafters under a metal tile

When designing a single-slot, forceps, hip, or complex roof, metal tape is actively used as a functional and beautiful roofing material. The metal tile’s frame is constructed using accepted building practices. Both the load and the roof’s angle of inclination must be considered when determining the optimal spacing between rafters.

Because of its comparatively light weight, metal tiles can be used in place of the outdated slate or ceramic roofing tiles. In this instance, strengthening or altering the installation step of the rafters is not necessary.

The typical rafter step for a metal tile is between 600 and 900 mm. The elements’ cross sections, which range from 50 to 150 mm, are sufficient to build a sturdy frame for a metal tile. However, if a heater is going to be used, which in places with cold winters should have a 200 mm layer, it is advised to use a 200 x 50 beam for rafters for metal tiles in order to avoid installing a separate system that keeps insulation in place.

It is preferable to fit the metal tile’s gap beneath the rafters beneath the sheet or roll heat insulator’s width.

Corrugated board: rafters and crate

The term "corrugated board" describes lightweight, practical roofing materials. A utility room or garage’s single-sloping roof or a residential building’s gable roof can be installed using galvanized or covered with a decorative-protective layer of corrugated board. How do I figure out how far I need to install rafters underneath corrugated board?

It is sufficient to place rafters 600–900 mm below the corrugated board to provide the structure with the necessary rigidity. In this instance, the roof’s angle of inclination must be taken into consideration.

According to the calculation, it is preferable to apply a minimum step to the system when dealing with high external loads.

However, the use of a more frequent crate improves the design if the angle of the roof slope is small and the distance between the rafters beneath the corrugated board is almost at its maximum. In this instance, the elements’ width should be at least 100 mm, and the corrugated board crate’s step should be roughly 50 mm.

Rafter system for a soft roof

Roof membranes, bitumen and bitumen-polymer roller materials, and soft tiles are all components of the soft roof. Soft roofs are characterized by their relatively light weight and lack of requirement for installing a substantial rafter structure.

The rafter legs can be separated by as little as 600 mm or as much as 1500 mm. The angle of inclination of the slopes must be considered when installing the support for a soft roof; the smaller the angle, the closer the supports should be to each other for a continuous crate.

The choice of step is also influenced by the thickness of the crate’s material; the thicker the plywood or OSP sheet, the larger the step required to install the rafter legs.

Ondulin: Calculation of rafters

Bitumen slate, or ondulin, is laid out on a continuous, level sheet of material. This makes it possible for the roofing to withstand snow loads and wind. The Ondulin crate is supported by the rafters, which, depending on the inclination of a gable or single-sloping roof, should be spaced 600 to 1000 mm apart.

Under Ondulin, the rafters are constructed from a beam measuring 200 × 50 mm in cross section. To make the installation of the insulation material easier, it is advised to consider the width of the material when determining the distance between the rafter legs and the ondulin in the design. By using this calculation, you can lower the price of setting up a roof.

Roof from sandwich panels

The sandwich roof is typically constructed from SIP panels or prefabricated buildings. One advantage of the sandwich is that it can be bent rigidly, eliminating the need for traditional rafters to be installed.

Installing a sandwich without the need for extra supports is made possible by narrow spans between the supporting structures of a single-sloping roof or the ridge of a gable roof and the upper portion of the wall.

Installing extra runs is required if the span length is greater than 4 meters. A typical rafter system is typically installed to install a sandwich roof on a residential building; however, in this instance, the rafters can be positioned in a large step, serving as support for the runs. The length of the load-bearing walls and the existing material for the runs are used to determine the spacing between the rafter legs.

The roof of Sandwich can sustain heavy operational loads due to its technical specifications.

Of course! Your article "Distance between rafters: Learning to choose the right" comes to an end here:

Selecting the appropriate spacing between rafters is essential for the durability and steadiness of your roof. It has an immediate impact on the roof’s capacity to endure different weather conditions over time, so it’s not just about appearance. Homeowners and builders can make educated decisions by being aware of the variables that affect rafter spacing, such as regional building codes, roof load requirements, and the kind of roofing materials utilized.

The length of the rafters is one important factor. The span is the maximum distance that a rafter can travel without the need for extra support. In order to avoid sagging or other structural problems, a longer span necessitates closer rafter spacing. The kind of roofing material also matters; lighter options like asphalt shingles may require longer rafter spans than heavier ones like slate or clay tiles.

Local construction codes and regulations are another important consideration. These recommendations establish minimum rafter spacing requirements based on regionally specific variables such as wind and snow loads. Following these guidelines lowers the chance of damage or collapse during severe weather events and guarantees that your roof satisfies safety requirements.

Finally, it is strongly advised to seek advice from a licensed architect, engineer, or roofing specialist. They can evaluate the unique features of your roof, take the surrounding conditions into account, and suggest the ideal rafter spacing for your project. In addition to guaranteeing structural integrity, this expert advice improves your roof’s overall longevity and performance.

What do you think, which element is the most important for a reliable and durable roof?
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Alexander Sorokin

The owner of the roofing company, an expert in the roofing markets. I'll tell you about the novelties of the roofing industry and help you choose the best option for your home.

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