Calculation of the roof truss system

Of all the nodes and elements of any building, the main part is the roof. And its foundation is a rafter structure that takes on all the loads, including the loads of the elements. Therefore, the calculation of the rafter frame must be carried out with all care, taking into account the quality of the materials. and the fortress of all compound catch. Usually, for the frame base of the rafter system, a tree is taken after a long exposure of several years, so that the material is well dried.

Types of rafters

Today there is almost no standard construction. All buildings of the private sector are different and differ in the design of the facade and the construction of the roof, on which the durability of the house depends. The roof system consists of several major structures. This is the base, the Mauerlat, to which the roof is attached, the rafter frame, which bears the whole burden of the roof and the loads of all the elements.

Of all the existing rafter systems in the construction of private houses, the most common are overhead and hanging rafters. To create a high-quality, but economical roof with the lowest financial costs, it is necessary to calculate the rafter system. Just with the choice of the type of house and roof, the design begins. Knowing all the advantages and disadvantages of a particular design, you can correctly make a choice.

Rafters

The hanging rafter system is characterized in that the rafters have two points of support, for example, two walls. Such a rafter system transfers all the roof loads to the rafter legs, while the bursting force is transmitted to the walls. Therefore, these structures require additional fastening of the rafters. And these are new materials and new expenses.

The layering system is arranged in a completely different way, when each rafter has already not two, but three points of support. Basically, such systems are suitable for houses with attic rooms. The rafter beam is supported by the Mauerlat and rests on the strapping beam of the ceiling of the attic. The third fulcrum is the skate. In the absence of a mansard room, the third fulcrum can be an inner wall, on which oblique or vertical posts abut, creating a fulcrum.

Factors Affecting Roof Calculation

Any calculations in the construction of the house begin, of course, with the determination of the factors of influence on the house and on the roof. In our case, we will only consider what has a direct effect on the roof and on the rafter system.

First of all, these are climatic conditions that are taken into account when calculating:

1. Wind pressure must be considered when calculating the roof height and shape. If, for example, the building is in strong wind currents, then it is certainly better to create a layered system that has great resistance against this element.
2. Rain affects the choice of not only the structure, but also the shape of the roof. It is necessary to protect the house in the best way both from above, and especially from the side of walls. To do this, you need the correct calculation of the overhangs.
3. Snow. This factor has a direct influence on the calculation and choice of material in order to create the greatest stability during heavy snowfalls, when a thick layer of snow can create pressure on the roof of hundreds of kilograms per square meter.

Area calculation

This unit of account is needed, like all other calculations. Knowing the area of ​​the roof plane, we can determine the amount of roofing material and not only. By the area, you can calculate the number of rafter legs, fasteners and beams to strengthen the rafter frame.

The area of ​​any plane is calculated by the well-known mathematical formula:

S = A x B.

S - Area.

A - The length of the plane.

B - Width.

In the event that the roof has a complex structure, the total roof area in the calculation of the rafter system is calculated by summing the areas of all slopes.

Rafter pitch and number of rafters

Knowing the area of ​​the roof, you can calculate how many rafters will be needed for one or another rafter structure. The calculation of the roof truss system directly depends on the quantity and quality of the material and also on the design. The weight of the structure depends on this, the main value responsible for the strength and resistance against loads.

The angle of inclination and the type of rafters also matter, but more on that later. First, let's decide how you can calculate the number of rafters, knowing the area and the pitch between the rafters.

Here is the approximate data of the rafter pitch, depending on the length of the rafter leg and the cross-section of the beam.

This is an approximate standard for SNiP of the rafter step, but this is not a standard.

Rafter pitch dependency

Here's what affects this setting:

1. The weight of the materials of the rafter system.
2. Weight of roofing material.
3. Waterproofing weight.
4. Weight of insulation.
5. Vapor barrier weight.
6. The weight of the lining of the attic.
7. Roof loads of natural factors - snow and wind.

For the correct calculation of the roof rafter system, the rafter pitch and the number of rafters, it is necessary to perform the following calculations:

1. Take the length of the roof.
2. We divide the length of the roof into the optimal rafter step.
3. One is added to the received amount and the result is rounded.
4. The length is divided by the rounded result.

The practical solution of the distance between the rafters

It must be borne in mind that the rafter step has a dependence on the size and quality of the roofing material, and on the size of the insulation. So, for example, when calculating the rafter pitch for a slate, you need to take into account that slate refers to heavy materials and requires a strong structure. Rafters need to be taken with a cross section of 150 x 30. And the rafter pitch is set within 700-800 mm. You also need to know that slate has certain restrictions for the angle of inclination. In many cases, for the selected roof configuration, calculation with the dimensions of the rafter system is performed using programs and calculators to calculate the rafter step, which is determined not only by the table, but in accordance with the materials used. Heavy roofing sheets require a reduction in the rafter pitch. In some cases, in order not to change the rafter pitch and not to increase the number of rafters, they fit the entire system under the roof with a stronger crate.

A reliable frame for a metal tile needs to be created from beams with a cross section of 50 x 150 mm. The standard rafter step for this material is calculated within 600 x 900 m, but sometimes, in the case of high-quality insulation, reinforcement of the frame is required by increasing the cross-section of the beam to 200 x 50. In some cases the rafter pitch is set relative to the size of the insulation bags.

Under other roofing sheets, the cross section of the rafters and the rafter pitch also change:

• Decking - 600-900 mm.
• Soft roof 600-1500 mm.
• Ondulin 600-1000.
• Polycarbonate sheets 600-800 mm.

Program for calculating the rafter system

It is very difficult to carry out calculations for complex roofs, which have many slopes and other porticoes. For such a case, various programs for calculating the rafter system are provided today. One of these programs is an online calculator for calculating the rafter system, the angle of inclination and the crate. To calculate these parameters, you need to enter the dimensional data of the roof.

• It is a roofing material used for coating.
• The laying width - And 1 - the distance from the base to the rack.
• Laying width - 2 - the width of the attic floor.
• Lifting height - B 1 - Attic floor height.
• Lifting Height - B 2 - The distance from the base to the ridge.
• Base length - D - The length of the base of the roof without overhangs.
• Overhang length - C - recommended length 50 cm.

Additional program parameters

For the roof system of the attic roof, the calculation is made according to these parameters, the program will give out all the main dimensions of the roof. In addition to the calculations already indicated, the calculator program for the attic roof will give additional roof parameters:

• The angle of the side rafters.
• The slope of the ridge rafters.
• The area of ​​the roof.
• The number of roofing sheets.
• The attic area.
• The length of the side rafters.
• The length of the ridge rafters.
• Estimated section of rafter legs.
• The number of battens.
• The distance between the battens.
• The number and volume of boards for the lathing.

Sloping roof system

In all calculations of a sloping roof, it is necessary to take into account that such a design is assumed for houses with attics, when the roof partially or fully performs the role of the walls of the attic space. Based on this, you need to use high quality materials. Calculation of the rafter system of a sloping roof has some general principles that can be applied to all types of sloping roofs for attic rooms.

The design and size of the rafter system is calculated relative to the size of the house and the attic. This is the height of the ridge, and the width of the pediment walls without overhangs, and the size of the overhangs. Everything needs to be considered here.

The design of the rafters of a house with an attic is calculated relative to the size of the attic, its width and height. The slope of the slopes of a sloping roof and the length of the rafters depend on these values.

Understanding that the loads on different parts of the rafter system differ from each other depending on the season, you need to create a structure with a safety margin of 10-15% of the design. It is possible to calculate the parameters of the rafter system both manually and according to the program. In each calculation of the rafter system, two load parameters must be taken into account, these are strength and deformation.

Rafter length

If you make the calculation of the rafter system of a gable or other design, then you need to know all the sizes of the attic room, its width, height, length. For example, to calculate the length of the rafters for the lower slope, the triangle formula is taken. For measurements, a triangle is taken, which is formed by the vertical rack of the attic space of one slope and the horizontal beam from the riser of the wall to the end of the overhang. In this triangle, the rafter acts as a hypotenuse. In accordance with the formula of the Pythagorean theorem, in a right triangle the hypotenuse is equal to the square root of the sum of squares of legs.

Tilt angle

Today on the Internet there are many programs for calculating the parameters of the rafter frame. It is enough to enter the required dimensions, and in a matter of seconds the program will display the required parameters. And if someone wants to try to calculate the parameters of the rafter system manually, then there is also a formula for this. Here, for example, it is possible to calculate the rafter system of a gable roof or another design of the angle of inclination of each plane of a complex system. The angle of inclination is calculated according to the formula for calculating the tangent of the angle:

tg A = H / L.

The tangent of the angle is calculated by dividing the height by half the width of the base. From the table of tangents we find out the angle. If, for example, the height is 4 m, the width of the half base is 4.75 m. Then, when dividing, we get 0.84. This will be the tangent of the angle. In the tangent table, we find that the tangent of the angle of 0.84 is 40. The number 40 makes the angle in degrees.

Hip construction

The hip system is a four-slope structure in which there are two pairs of ramps. Two pediment pairs in the form of trapezoids and two angular pairs are triangular. The calculation of the hip roof truss system is to choose the right angle. There are several types of such structures in which the inclination of all planes is the same. In some cases, a half-hip roof is created in which the corner slopes are much higher from the eaves of the pediment roofs.

There are also separate hip roof options. For each type of such a design has its own calculation rules. The main thing in the calculation of the rafter system is the determination of the slope of the slopes and the height of the ridge. In the previous section of this article, it was already said how to calculate the slope, surface area and rafter length. There are mathematical formulas for this. Well, if you don’t want to pore over these calculations, you can find programs on the Internet that calculate these parameters.