Board for rafters: selection of building materials, calculations of parameters, mounting nuances

Selecting the appropriate roofing materials requires thought, particularly with regard to the rafter boards. These boards give the roof the necessary structure and support so that it can endure the weather over time. Making an informed choice requires having a thorough understanding of the various options and their characteristics.

Choosing boards for rafters involves taking a few things into consideration. The kind of material is one of the main factors to take into account. Plywood, oriented strand board (OSB), and timber boards are typical choices. Every material has advantages and disadvantages. Plywood is renowned for its strength and durability, OSB provides good dimensional stability, and timber boards have a classic and frequently beautiful appearance.

Evaluating the boards’ dimensions and weight-bearing capability is necessary to determine their parameters. The necessary board thickness and width are determined by the rafters’ size and spacing. These computations are also influenced by variables like the roof pitch, regional building codes, and anticipated snow loads. Long-term structural integrity depends on the boards’ ability to sustain the weight of the roofing materials and endure environmental stresses.

To guarantee a safe and sturdy roof structure, mounting boards for rafters need to be installed with precision. Appropriate installation methods, such as fastening strategies and spacing considerations, are essential to the roof’s performance. To avoid problems like mold growth or early deterioration, installation procedures should also take moisture protection and ventilation needs into account.

Selection of Building Materials Various materials such as wood, steel, or engineered products like LVL (Laminated Veneer Lumber) are considered based on strength, cost, and availability.
Calculations of Parameters Factors like span, load-bearing capacity, and environmental conditions influence the dimensions and spacing of rafters.
Mounting Nuances Proper fastening techniques and considerations for thermal expansion ensure stability and longevity of the roof structure.

Boards for the rafter system: make or order?

Let’s begin by discussing the specific location where you will purchase rafters. This will depend on how exactingly you need to determine the dimensions of each board used in the construction.

Therefore, it’s best if you can trust an expert, like t.To, with the purchase of boards and beams. He can even use his eyes to judge the material’s quality and determine if the quantity he has acquired will be sufficient. Nevertheless, if you follow our advice, you will be able to handle this task just fine.

This little video clock will clarify which boards work best with the rafter system:

There are three options available to you for purchasing rafter boards, and we will examine the benefits and drawbacks of each.

Method number 1. Cubeters of lumber

Thus, pay close attention to these crucial details. It is perfectly acceptable to accept wood that is offered to you in cubic meters; you just need to tell a specialized company how many cubic meters of boards and timber you would like. You will process all of this immediately with protective impregnations and construct a roof.

The only thing to note is that there will be a significant amount of waste and labor. According to your calculations, you will therefore need to buy 10% more boards than you had initially anticipated in order to account for trimming, waste, and unforeseen defects before they become illegal.

Method number 2. Clotted boards

Another option is to purchase ready -made rafters after cutting. Many companies to order cut wood for the right parameters and provide a ready -made option, it remains only to collect the structure on the roof. There will already be a minimum of waste, work will go faster, it is only important to pre -guess with the size of the rafters. But there is one minus: in the overall kit it may not get one or two boards. After all, especially attentive people do not always work at such enterprises and not the fact that the same workers will not hide the bar from each order. And you will have to roll up the sleeves and make additional templates for the absent elements.

How can I order pre-cut, ready-to-assemble rafter boards? Simply create a roof project on paper or in a unique program, present it to the designer, and then to the company representative. Quite easy!

Method number 3. Ready -made rafter farms

Acquiring prefabricated rafter farms represents the third alternative. The entire structure can be put together in one to three days, and it is simpler to install them directly on the roof than to gather them separately. And a carpenter is no longer needed for this! These rafter farms are gathered in the factory and are of a fairly good caliber. All you need to do is install and connect them to the skate.

There won’t be any waste produced here, but naturally, prefabricated rafter farms will cost more than just rafter boards. Furthermore, the measurer is typically sent by the manufacturer to the intended object so that the user can verify the measurement between the walls of the house and make any necessary adjustments to the design documentation. Furthermore, if you find the rafter system calculations challenging (believe me, even for experts), this already functions somewhat as insurance for you.

Self -manufacture of rafters from boards

Thus, prepare to visit the designer, architect, and carpenter simultaneously if you are dissatisfied with the concept and the cutting of the boards. Actually, the only information you’ll need to know about your rafters is their section, distance, angle of inclination, and fastening technique.

If you have ever observed the work of professionals, then you were probably delighted with how virtuoso and without much effort they measure the desired length of the rafters and make them in their complex cuts. Moreover, all that they need to know is the parameters of the roof. And at the same time they use the most elementary tools: a carpentry square, their own recorded calculations or a “smart” book. But, in a good way (and according to all the rules), you should initially calculate everything using special construction calculators. By the way, special application for smartphones are also popular today. Although you will make the most basic calculations without problems yourself.

Therefore, you already know the width of the building and the thickness of the skating board if you have decided to manufacture the rafters yourself from the boards. Here’s where it gets crucial to avoid making a mistake when estimating the future length of the rafters: make sure to deduct the skating board’s thickness from the building’s total width. Trust me, a lot of people just forget about it. At this point, divide the result by two to determine the mileage of each rafter leg.

Geometric formulas can be used to calculate the roof’s angle of inclination; the kind of formula you use will depend on the type of roof you’re building—a traditional gable roof or a more intricate four-sloping roof. Since their structural nodes differ, so do the specifications for their capacity to support particular loads.

Rafters for a gable roof: simple calculation

Since they are simply regular triangles that must only be arranged in a row strictly vertically with a specific step and fixed at the tops of the skating run, the rafters for the gable roof are the easiest to construct:

The rafters’ length from the skate to the wall can be easily calculated; this is the triangle’s hypotenuse:

Rafters for a four -skeet roof: triangles + rectangles

Your task of making rafters for a typical four-sloped roof (tent, valmova) will be slightly more challenging. Here, you must compute with greater accuracy:

The rafters are positioned here with their diagonal orientation toward the wall corners, which distinguishes the four-sloping roof’s rafter system. Furthermore, these boards form the foundation for additional rafters on slopes. This is the reason why the same rafters, also known as "diagonal" rafters, are longer than standard boards and can support a load 1.5 times higher than regular ones.

These rafters are typically made in pairs:

Rafters for unusual roof shapes: complex design

Standard guidelines for rafter construction, load calculations, and structural design apply to both pitched and flat roofs. However, a totally different strategy when building arbors, extensions, and other commercial facilities. In this instance, the roof should not always resemble a scaled-down replica of a real, large one. On the other hand, in order to invest in the budget and appropriately combine a small structure with a large one, it is crucial to carefully consider everything.

For instance, in order to arrange an extension roof to the house, special elongated rafters are made as an option:

Because the shown rafters do not produce spot loads on the roof’s edge—which is regrettably frequently the case in private construction practices—the roof will not roll over in one direction over time. Because of the rafters’ unusual length, the load is distributed evenly throughout the entire slope with less pressure. Additionally, this design exudes professionalism and competence.

But these rafters are used to build arbors for round roofs, outbuildings, and tiny houses:

Lastly, there are instances where a portion of the rafters is merely ornamental and serves no practical purpose within the overall structure. Although it takes a long time to make them, there is no need to calculate their strength. And observe how the entire species of the roof is altered by just one extra board in the rafter system:

Bent boards for rafters of lancet roof

And lastly, know that all of this is actually realized if you enjoy unique and stylish roofs with a lancet form. In a factory, steam up to 100 degrees is used to create these boards. The increased humidity provides elasticity, and the boards are then bent around a specially designed template. They aren’t glued or dried in special cameras until after that.

However, additional cuts are made along the bend of these bars, which presents its own set of challenges. Consequently, the cost of such a rafter system will be higher. It will also be difficult for you to turn up all this technological stage if we talk about private construction. However, such a chance does exist.

We have determined the design and parameters of the rafters. The next challenging step is to calculate the total amount of loads that impact these types of roofs. You can accurately determine the section of the rafters as well as their length by using the answers to these kinds of questions.

It is essential to comprehend which board is appropriate for rafters at "All about the roof." This article covers the necessary computations for dimensions and load-bearing capacity, as well as how to choose building materials that strike a balance between strength and affordability. We explore the subtleties of mounting and offer helpful advice for maintaining structural longevity. Knowing these fundamentals guarantees your roof is sturdy and secure, regardless of whether you’re a professional builder or a do-it-yourself enthusiast."

How to calculate the load on the rafter system?

You must therefore begin by identifying the type of area in which you reside. The rafters’ board ultimately depends on this: the dimensions are chosen to ensure that the roof maintains its maximum integrity while successfully resisting both static and dynamic loads.

The entire set of loads that you will need to take into account when creating the rafter system’s specifications is as follows:

What are the limiting states of the roof?

And now for something more. To ascertain the precise rafter section required for the roof device, you must first compute the total of all potential loads. This computation is done using the "maximum states" approach, which is applied when the roof structure can no longer withstand the effects of wind, heavy snowfall, or substantial deformation.

When does this occur? when the bearing capacity, stability, and endurance of the roof structure have already been depleted. T.e. This is the exact moment when there is so much snow on the roof that the rafter system breaks or when the roof is built in a way that eventually allows a strong wind to damage it. And in this case, it’s important to simultaneously consider static and dynamic loads:

  • when snow, insulation and roofing are pressed on the roof, this is a static load;
  • the wind and other influences that cause the disclosure of the roof nodes or the deflection of the rafters are dynamic loads.

Negative effects will result if the roof is unable to handle any of this individually or collectively. Furthermore, it is dangerous in and of itself when the rafters exhibit deflection, cracks, and other initially undetectable issues that are not significantly impacted by the structure’s ability to support itself. It is imperative that all of this be avoided.

How to find out typical loads of a certain area?

We have a different article that will carefully calculate the pressure on the roof. To find the minimum thickness of the rafters’ cross-section and their minimum step along the slope, all you need to do is look at the average wind and snow loads on your area’s map:

There are two methods for utilizing all of these data:

  • Method number 1. Calculate everything up to a millimeter using special formulas, an online calculator or mind of a hired roof specialist.
  • Method number 2. Focus on the traditions of construction in a particular region and make the simplest calculations with a margin.

The truth is that not all nations are able to do so among themselves. For instance, high, pointed roofs have long been constructed in Russia’s snowiest regions; in particularly windy conditions, they are more gentle. If the typical height of the snow cover in your region is higher than the national average, you should either construct a roof with steep inclines or double the thickness and strength of the rafters to ensure they can support the entire weight required. Thus, the whole trick is to arrange the roof’s tilt at the same angle as your neighbors if you want to buy rafter boards with standard values.

Thus, you will be able to determine which load will impact each individual rafter if you are aware of how the roof’s load will behave roughly during its servicing. How? Simply divide the load among them; at this point, it’s critical to determine whether the rafters can handle the responsibility that has been placed on them. And it is also possible to find out this in turn.

How to calculate the strength for bending and stretching?

A multitude of physical forces impact every single rafter. Additionally, it is easier to handle each rafter individually the more there are on each interval, and vice versa. However, putting continuous rows is illogical; instead, it is more sensible to compute and ensure everything is safe.

Tense states of rafters from different wood

The material of the rafters as well as their thickness determine how precisely they will bend and stretch during the operation. especially the type, breed, and moisture content of the wood. These data tables will assist you in determining it:

The following characteristics of tree species that are good for rafters:

  • Little trees deciduous breeds have less flexibility, compared to pine, and their properties in all directions are different. Therefore, boards from this wood are less often used specifically for rafters. On the other hand, the larch has so good characteristics that it can be compared with an oak in durability.
  • Pine is relatively inexpensive, but has a large number of knots. On the other hand, the tarry tree will always provide high resistance to rotting, and a pine beam is great for arranging a rafter system due to its lightness and strength.
  • Spruce is ideal for beams of ceilings and rafters. Moreover, dry spruce is as strong as pine. Such wood is perfect for those areas that the whole load is on.
  • Oak wood is more durable and durable, and therefore more expensive, because in order to be used in construction, its age should be about 120 years old! While the pine has only 30.
  • All other wood species should be used for the manufacture of rafters carefully, carefully studying their properties.

In summary, the strength of the deflection is the primary characteristic of wood as a material. If, however, this proves insufficient, the boards are merely made longer. Furthermore, based on the SNiPs of "load and influence," you should always take such values with a margin because the load on all rafters is uneven and the rafters on the left can be loaded much more than the rafters on the right.

The choice of the length and cross -section of the rafter elements

Depending on the rafters’ step and the weight that will be applied to them, each rafter leg has the same thickness and length:

Rakes are fastened to roof structures in a variety of ways, but the two most common types nowadays are those with hanging and inclined rafters.

  • Nammed rafters Strongly interconnected, lie in one plane and have only two points of the support – these are external walls. And the rafters at the same time rely on the Mauerlat or the upper crown of the log house.
  • Hanging farms, On the contrary, they consist of rafter legs, which work for compression and bend, and under the weight of the structure, they are bursting, which is transmitted to the wall. To compensate for these forces, rafter legs must be pulled off with puffs – these are horizontal beams that will need to be fixed at the base of the rafters or above. They are also important to calculate correctly.

Furthermore, the angle of inclination of the roof directly affects the length of the rafters in both rafter system variants:

Furthermore, by using the most common formulas from geometry class, you can quickly calculate the length of the rafters if you know the width of the house’s end and the height of the future roof.

Selecting the appropriate board for your rafters is essential to the long-term stability and longevity of your roof. There are benefits to using both more modern composite materials and conventional wood planks. Spruce or pine wood boards are lightweight and simple to work with, which makes them perfect for do-it-yourself projects. They are reasonably priced and offer good insulation, but they might need to be treated to keep out pests and moisture.

Conversely, composite boards are more resilient and frequently come pre-treated to be fire and weather resistant. Although they cost more, they may eventually result in lower maintenance costs. Think about things like your budget, local building codes, and climate when choosing the material for your boards.

By calculating the rafters’ dimensions and spacing, you can make sure your roof is weather-resistant. The width and thickness of the board are determined by various factors, including the span between rafters, roof pitch, and snow load. Accurately calculating these parameters can be aided by using online calculators or speaking with a structural engineer.

To guarantee a stable roof structure, mounting boards for rafters need to be installed precisely. It is crucial to align and fasten the boards correctly in accordance with local building codes and manufacturer guidelines. By doing this, you can avoid future problems like sagging or structural damage in addition to improving safety.

Video on the topic

Calculation of the rafter system with optimal parameters

Calculator on rafters. Sopromat for the roofer. Part 2

The rafters of the Endovs. Installation of a support board. Calculation of the lifting of the roof of the adjacent pediment.

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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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