The dimensions of the roof boards: what should be the cross -section of the main elements of the roof

Knowing the size of roof boards is essential for roofing because it guarantees longevity and structural integrity. An essential part of supporting the entire roofing system is the cross-section of the main components of a roof, like rafters and joists. These components support the weight of the roofing materials as well as any additional loads, like snow or wind, in addition to serving as the roof’s framework. For safety, stability, and to avoid sagging, the right measurements are crucial.

The main structural elements that make up a roof’s framework are rafters. Rafferts, which are usually composed of metal or wood, provide the pitch or angle of the roof by sloping from the ridge or peak to the eaves. The weight of the roofing materials, the span of the roof, and local building codes are some of the factors that affect the cross-sectional dimensions of rafters, including their width and depth. The roof’s ability to sustain the applied loads and distribute them evenly to the supporting walls is ensured by rafters that are the right size.

Contrarily, joists are horizontal members that span between beams, girders, or walls to support the floor above and the ceiling below. Joists are frequently used in flat or low-slope roofing to support the membrane systems and any additional layers, such as insulation, on top of the roof decking. In order to keep the roof structurally sound and able to support the weight of all materials without bowing over time, the joist dimensions are essential.

There are factors to consider when interpreting roof board dimensions in addition to size. The choice of dimensions is influenced by various factors, including the kind of material, the distance between elements, and the surrounding environment. For example, in areas where there is a lot of snowfall, larger cross-sections might be needed to support the extra weight. In a similar vein, the load-bearing capacity required of the roof boards will depend on the type of roofing material—heavy or light.

Main Roof Element Recommended Cross-section
Rafters The cross-section of rafters typically depends on the span of the roof and the load it needs to support. For standard residential construction, rafters often range from 2 inches by 6 inches to 2 inches by 10 inches in size.
Ridge Board The ridge board, which runs along the peak of the roof, generally has a similar cross-section to the rafters. It"s crucial for providing structural support and ensuring the roof"s stability.

The dimensions of roof boards are important considerations when designing a roof’s structure because they guarantee stability and durability in a variety of weather scenarios. The strength of the roof and its capacity to support the weight of roofing materials and environmental stresses like wind and snow are directly impacted by the width and thickness of these boards in their cross-section. Determining the ideal dimensions requires striking a balance between practical factors like cost and local building codes and structural requirements. This article examines important variables to take into account when calculating the cross-section of roof boards and provides insights into how these choices may affect the resilience and lifespan of a roof structure.

Standard sizes of roof boards

In the event that you choose to utilize the standard section pillar instead of counting the rafter system, the roof’s board sizes will solely depend on the component for which they are designed. Choose lumber with a cross section that is close to the maximum if you need a dependable roof in addition to the desired margin of strength. If we are discussing a tiny, temporary building, you can use cheap, small-sized boards for the roof.


Mauerlat is typically formed of beams; given the forces acting on it, a rectangular shape is ideal for this element. However, the Mauerlat boards can also be used to make Mauerlat. Their typical measurements are 50 x 150 and 50 x 200 mm.

Mauerlat is also typically constructed from two boards that are nailed together. On the walls of homes with a small roof area, one board can be laid. In cases where there is a significant snow load and a heavy roof, three or even four boards are joined to form a square section.

It is acceptable to construct the Mauerlat roof on temporary or small buildings using boards measuring 25 by 100 mm.

The length of the boards is chosen based on two principles regardless of the section:

  1. Mauerlat is best made from whole boards if the wall length allows .
  2. If the wall of the house is longer than 6-9 m, then the Mauerlat must be made composite. In this case, the length of the boards must be selected so that they are connected approximately in the center of the wall. In this case, the end joints between the boards in different rows should be spaced by at least 500 mm.

You cannot connect the standard for Mauerlat with a node of the same due to the thin boards in Mauerlat.

Ridge run

The roof’s gear sizes correspond to those of Mauerlat. It receives boards measuring 50 × 150 mm and 50 × 200 mm. However, there’s one very important difference: if the rafter legs are laid without being washed down, they are based on the skate run; if they are laid with a nozzle, they are based on the skate run from above and on the side. This indicates that the horse’s primary focus is on deflection. For this reason, the skating run’s boards are mounted on the side line, in contrast to Mauerlat.

This effectively indicates that the boards are better suited for skating than for the beam. The maximum section of the ridge run will not be larger than 200 × 200 mm if it is made from the beam. Raising thicker lumber to the roof will be a daunting task, owing to the significant weight it will place on the rafter system and the house’s supporting structures.

However, because of their weight and size, the roof boards can be installed above one another, creating a very sturdy horse with a cross section of 50 x 400 mm. Even in the most challenging weather conditions, this is typically more than sufficient.

Dimensions of the boards for the rafters of the roof

Since this part of the roof works on the bend, the rafters are almost always made from the boards. In this case, the rafter beam’s cross-section should be greater than two or three times in order to give strength equivalent to the boards for the deflection.

The most common materials used to make roof rafters are boards with the following measurements:

  • for temporary and small buildings – 50 × 150 mm;
  • for private houses – 50 × 180 mm and 50 × 200 mm;
  • For large cottages and houses in regions with a large snow load – 50 × 220 mm.

The distance between the rafting boards determines their cross section; the greater the distance, the higher the rafter legs should be. If the rafters are measured from the skate, they are spent in the middle or last third if their length exceeds 6 meters. Adding support or strut to the spinning area is a good idea.

Dimensions of the label boards

The only difference between the rafters’ and the crate’s board sizes is their thickness. Timber that is 40 mm thick is the best kind to use for crates. Even thinner boards—32 mm—may be used if the crate has a small step. Boards measuring 25 × 100 mm and 25 × 150 mm may be used for homes in the southern areas. But only provided that there is a maximum of 300 mm between the boards themselves and a maximum of 1 m between the rafter legs.

Standard or calculated section?

Any rafter system should compute a professional designer in accordance with the rules. Even after a careful examination of standards and profile literature, there are many subtleties that are difficult for a non-specialist to consider.

However, in reality, the owners of private homes typically count the roof using online calculators or, at most, specialized software. And that’s assuming it’s usually calculated; most people like standard projects, "by eye" solutions, and roof board cross-sections.

Strangely enough, it usually works, and there isn’t a noticeable epidemic of private home roof collapses. There are three reasons why this occurs:

  1. Variable loads on the roof (mainly snow and wind) in a particular area are the maximum loads recorded for 25-50 years of observation depending on the version of the standard. That is, even if the rafter system is not strong enough, while there are no record rainfall or winds, the roof will withstand.
  2. Standard sections, especially close to maximum, usually give a large margin of strength of the rafter system. Sometimes this margin of safety can be multiple. At the same time, saving on the services of a designer often pours into overpayment when buying lumber.
  3. Almost everywhere, the standards limit the maximum deflection, and do not give a calculation for a breakdown. Therefore, the incorrectly made rafter system usually leads not to the collapse of the roof, but to the rafters artistically curved under load. Of course, they can go cracks and break, but usually this does not happen immediately. Owners almost always have time to install a prosthesis and support.

This implies that you can typically depend on standard board and timber sizes when building a rafter roof system. However, never forget that there is a risk involved and that there could be dire consequences.

But occasionally, a thorough computation is necessary.

First and foremost, these are northern homes that have a lot of snow on them. The majority of conventional schemes are meaningless to them.

Any type of flat roof and a roof with a slope of less than 15 ° also require it. Snow almost never falls off such roofs naturally, so standard calculations are not appropriate.

In conclusion, the computation is necessary for all varieties of intricate roofs, in addition to basic roofs featuring anti-aircraft lights and other unusual components.

Assuring the stability and longevity of your roof structure depends on selecting the proper roof board dimensions. The main components’ cross-section, including the rafters and purlins, is dependent upon a number of variables that affect the roof’s overall functionality.

First off, the size of the roof boards is largely dependent on the span of your roof. In order to sustain the weight of the roof covering and endure wind and snow loads, longer spans necessitate larger dimensions. Smaller cross-sections might be adequate for shorter spans, but this relies on the structural requirements and local building codes.

Second, the size of the roof boards is determined by the kind of roof covering you select. Stronger support is required for heavier materials like slate or tile, which frequently calls for rafters and purlins that are wider or thicker. Smaller dimensions might be possible with lighter materials like metal or asphalt roofing, but this would again depend on the details of the design and load estimates.

The local climate should also be taken into account. Stronger roof structures may be necessary in areas that frequently experience strong winds or large snowfall in order to guarantee long-term safety. In order to achieve a balance between structural integrity and cost-effectiveness, engineers and architects frequently take these factors into consideration when designing roofs.

In conclusion, even though roof board dimensions might appear like a technical detail, they are vital to the overall functionality and durability of your roof. Through expert advice and compliance with regional construction regulations, you can guarantee that your roof structure is suitably sized to endure weather and offer dependable safeguarding for an extended period.

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Alexandra Fedorova

Journalist, author of articles on construction and repair. I will help you understand the complex issues related to the choice and installation of the roof.

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