The roof is one of the main elements of the house, so it is worth paying Special attention correct calculation roof frame. Which will serve as a skeleton in your home. Incorrect calculation of all loads can lead to disastrous results in the form of deformation of the roof, followed by its collapse.

Before proceeding with the installation of the roofing, it is necessary to make a calculation rafter system, which will depend on the material used, construction, climatic conditions.

What you should pay attention to before making a calculation

Before starting the construction of the roof, it is necessary to choose the type of rafter system. Then calculate all the loads that will fall on the roof. The main loads include the weight of the frame, roofing material, insulation, ceiling, and temporary loads are also taken into account, among which are the weight of the snow cover, possible gusts of wind, the weight of a person during the installation and operation of the roof.

The distance between the rafters is calculated based on the selected type of rafters and the material with which the roof will be covered.

Types of rafters

When building roofs of various designs use hanging or layered rafters. Recessed - used when installing single or gable roofs. They have two points of support - load-bearing walls or load-bearing wall and ridge beam. Hanging rafters are used when it is necessary to overlap large spans or a broken roof is created. In this case, the rafters are supported by one end on the wall, and the other on the opposite rafter. The quality of the material from which the frame is made will directly affect the reliability of the entire roof.

Rafter material

Currently, wood and metal are used. Wooden beams or a log is used in the construction of residential buildings, garages and other buildings. Reinforced concrete or metal rafters are used in construction industrial facilities, shopping centers where wide spans are needed.

Calculation method

The distance between the rafter legs is called the rafter pitch. It should not exceed one meter, and minimum value- 60 cm. Before calculating it is necessary to measure the size of the roof slope. After that, the resulting value is divided by the approximate size of the step to the honey rafters. Add one to the result and round up to the nearest whole number. So we find out the number of rafters that we need. In order to find out the exact distance between the rafters, for this we need to divide the length of the roof slope by the number of rafter legs.

For clarity, consider an example of calculation:

roof bevel length - 28.5 m

the step between the rafters is chosen equal to 80 cm

add one to the resulting number: 35.625 + 1 = 36.625

as a result, we get that we need 37 rafter legs

the exact step size of the rafters will be: 28.5 / 37 = 0.77 m

This is a general calculation method that requires adjustment depending on the roofing material.

Dependence of the pitch of the rafters on the roofing material

The most common roofing materials are slate, metal, corrugated board, ondulin, soft roofing.

Slate roof truss

Slate has wide application as a roofing material, due to its low cost, resistance to temperature extremes. Due to the severity of the material, it is necessary to install a powerful rafter system. The distance between the rafters in this case will depend on the section of the timber. The optimal value is a distance of 80 cm, which will allow not only to withstand the increased weight, but also significant snow and wind loads. In this case, the lathing is performed with a board with a width of at least 3 cm. Depending on the type of slate, the lathing is performed solid for smooth sheets or sparse for wave sheets.

Important: the slate must have at least three support points along the edges and center.

Step between rafters for metal tiles

Metal tiles are becoming more and more common among roofing materials. Which is characterized simple process installation, and will also help to create your own unique view... Metal sheets are lightweight, which allows you to increase the distance between the rafters from 600 to 950 mm, with a bar section of 150x50 mm. The lathing in this case will depend on the step of the sheet wave. So for a wave of 350 mm, a distance between the boards of 30-40 cm is possible.

Important: on the overhangs of the eaves, the edges of the bevels, the step of the lathing is made minimal for greater reliability of the roof.

Step of rafters under corrugated board

Decking is a galvanized steel sheet covered with a special coating that protects it from harmful effects. environment. Big choice color scheme, the width of the corrugation, will allow you to create a reliable and aesthetically pleasing roof. The step of the rafters under the corrugated board will directly depend on the characteristics of the type of profile used, the angle of inclination of the roof, and its configuration. You should also take into account the fact that the crate under the profiled sheet is attached perpendicularly. The rafter system is made from beams with a cross section of 50-75 mm or from a board 20-50 mm thick and no more than 15 cm wide. The lathing can be solid with a gap between the boards no more than 10 mm, with the usual pitch of 20-40 cm, and sparse - the distance between the boards is 50-75 cm. The step of the rafters under the corrugated board is calculated by general scheme and is 60-90 cm.

Step of roof rafters from ondulin

Ondulin is corrugated sheets which have high strength and durability. With such a roof, the rafter system is made of pine boards with a section of 50x200 mm, with a step of 60-90 cm. A sparse lathing of 40x50 cm is made from above.

Important: if the roof has an inclination angle of more than 50 degrees, then the lathing must be solid.

Determining the pitch of the rafters for a pitched roof

A pitched roof is simple and does not require any special installation skills from you. Most often it is installed in garages, baths, outbuildings. The roof frame consists of beams that rest on the walls of the building. The distance between the rafters is one pitched roof will depend on the length of the rafters. Here you should correctly approach the choice of the cross-section of the timber, since the greater the distance, the greater the load on the rafters. For correct selection step shed roof you should use the data from the table:

Distance between rafters for a gable roof

The gable roof is the most common, not only because of the simplicity of the device, but also because of its high reliability. Rafter step gable roof calculated according to the general scheme. If the bevels are the same on both sides, then one part can be calculated. To do this, we determine the angle of inclination of the bevel, here you should take into account the material with which you will cover the roof. So at an angle of 45 degrees or more, all types of coatings can be used. For slate, tiles, the minimum angle of inclination is 22 degrees, for corrugated board and soft tiles- 12 degrees, for metal tiles - 14 degrees, for ondulin - 6 degrees. The length of the rafters for a gable roof is calculated using the Pythagorean theorem, in which the length is the hypotenuse, and the height of the roof and half of its width are legs. If the spans are more than 6 meters, then the rafter system is additionally reinforced with struts and headstock, which will not allow the rafter legs to deform under the weight of the roofing material.

The distance between the rafters under the metal tile necessarily takes into account the efforts resulting from the wind, snow load, the own weight of structures, and the roof. In addition, the following factors affect the pitch of the rafters under the metal tile:

• arrangement of pipes - wooden elements roofs should be 25-35 cm away from the chimney, should not interfere with straight paths ventilation ducts, fan pipes;
• roof configuration - a rafter leg is required at the junction of the ridge of the gable, hipped roof.

All wooden elements of the truss system are made from trees conifers, the humidity of which does not exceed 20%.

The step of the rafter legs is calculated at the design stage for budgeting. This will significantly reduce the amount of waste, cut sawn timber.

What do you need to know when choosing the optimal distance between the rafters?

Roof layout with hanging rafters.

Having collected the present loads during the strength calculation, the designer distributes them evenly to the load-bearing walls. The principle of calculation is the same for layered, hanging rafters, only the schemes for fastening the elements in the ridge, on the Mauerlat, differ.

The minimum, maximum pitch of wooden rafters for metal tiles is regulated by 0.7 m, 1.2 m, respectively.

When choosing a step of 60 - 100 cm, the length of the rafters cannot exceed 6 m, with its decrease, a run-up of up to 1.2 m is allowed. If you put your legs more than 60 cm, this will unnecessarily burden the roof and increase the construction budget. If the step is increased by more than 1.2 m, the bearing capacity and the resource of the structure will sharply decrease.

A solid lathing made of wood-containing slabs adds strength, rigidity to the rafter system. In this case, it is allowed to increase the step by 0.3 - 0.2 m in comparison with a periodic crate from a bar or edged boards... However, to save the construction budget, a solid crate for metal tiles is rarely used. The material has sufficient strength, rigidity due to the additional transverse ribs of the profile.

A step of more than 1.2 m is not used even when using metal rafters, despite the sufficient safety margin of the material. This is due to the possible deflection of roof sheets during heavy snowfalls, hurricane winds.

The cross-section of the timber from which the rafter legs are made also affects the step of the rafters, since the support area of ​​the sheathing and the weight of the roof change. The best option a beam of 150 x 50 mm is considered with a discharged crate with a step of 4 - 7 cm, depending on the step of the shear wave.

Calculation example for a gable roof

When carrying out a project, specialists at the initial stage know the roofing material. In order to find out the recommended pitch of the rafters, you can use the SNiP tables, and then adjust the value in accordance with the operating conditions. An example table is shown below:

The table values ​​correspond to the rafters of simple single-pitched roofs. First, the section of the leg is selected, the length of the element, the distance between the centers of the log, the beam is obtained automatically. In the next step, the length of the ramp in the ridge is divided by the rafter pitch, adding one. Thus, the number of legs is counted, rounded up. Then it remains to adjust the distance between wooden rafters in fact. For example, with a ridge length of 7.5 m, a rafter leg with a section of 16 x 2 cm (board) 4 m long, you get:

7.5 / 0.7 = 10.7 + 1 = 11.7 pcs. round up to 12 rafters.

Specifying the size allows you to calculate the center-to-center distance for installation after installing the outer legs:

7.5 / 12 = 62.5 cm.

Dormer windows are placed between adjacent rafters, in the places where pipes and chimneys pass, the legs are shifted to the distance specified in SNiP. All other elements of the system remain in place, the area of ​​abutment to the pipes, if necessary, is enhanced:

• a bed is cut into two adjacent legs;
• a short rafter is cut into it with one end, the second adjoins in the ridge to the element of the opposite slope;
• the shifted legs in the upper part rest on ridge run attached to at least two trusses.

Thus, the system obtains the required rigidity without loss of bearing capacity, fire safety requirements are met wooden parts roofs.

Rafter leg material

The material of the rafters is more often a beam of 25 x 10 cm - 15 x 4 cm, which allows you to reduce the construction budget.

When choosing lumber natural moisture the developer is guaranteed to receive a shrinkage of the structure in the first year and a half by 5-7 cm in height. By increasing the cost estimate for arranging the rafter system by 70%, you can purchase glued beams, significantly reducing the structural loads, and doubling the life of the roof.

The distance between the rafters will remain unchanged, however, instead of the planed timber of 17.5 x 5 cm, recommended by building codes for five-meter legs, spaced 0.6 m apart, you can do with glued laminated timber of a smaller section of 15 x 4 cm.Transportation costs will decrease, work at height will be easier , cut material.

Prefabricated rafters from boards are used with the same scheme for fastening hip roof trusses. Upper slopes are made of single boards, the lower of three boards, sewn with self-tapping screws with an offset in the rows.

The choice of metal rafters is justified with a complex roof configuration, an abundance of ventilation pipes, chimneys, which cannot be bypassed in compliance with SNiP requirements, fire safety. In this case, the step between the rafters increases as much as possible, since the rolled metal is much stronger than lumber.

If the rafters are attached at the bottom to the Mauerlat, the step of the legs is not critical, the elements can, if necessary, move the required distance to either side. If a scheme is used to support the braces, which are floor beams, displace individual elements much more difficult. In this case, the amount of cutting waste increases when sheathing the rough ceiling, floor of the attic or attic.

The gable roof is formed on the basis of a frame that combines the elementary structure of the device and unsurpassed reliability. But the backbone of the roof in two rectangular slopes can boast of these advantages only in the case of a careful selection of rafter legs.

Parameters of the gable roof truss system

It is worth starting the calculations if you understand that the rafter system of a gable roof is a complex of triangles, the most rigid elements of the frame. They are assembled from boards, the size of which plays a special role.

Rafter length

The formula will help determine the length of strong boards for the rafter systema² +b² =c², derived by Pythagoras.

The length of the rafter can be found by knowing the width of the house and the height of the roof.

Parameter "a" stands for height and is self-selected. It depends on whether the under-roof space will be residential; it also has certain recommendations if an attic is planned.

Behind the letter "b" is the width of the building, divided in two. And "c" represents the hypotenuse of the triangle, that is, the length of the rafter legs.

Let's say that the width of half of the house is three meters, and it is decided to make the roof two meters high. In this case, the length of the rafter legs will reach 3.6 m (c = √a² + b² = 4 + √9 = √13≈3.6).

60-70 cm should be added to the figure obtained from the Pythagorean formula. Extra centimeters will be needed to take the rafter leg over the wall and make the necessary cuts.

The six-meter rafter is the longest, therefore it is suitable as a rafter leg

The maximum length of a bar used as a rafter leg is 6 m. If a durable board of greater length is required, then they resort to the splicing technique - nailing a piece from another bar to the rafter leg.

Cross-section of rafter legs

For various elements of the rafter system, there are standard sizes:

• 10x10 or 15x15 cm - for the Mauerlat bar;
• 10x15 or 10x20 cm - for the rafter leg;
• 5x15 or 5x20 cm - for running and strut;
• 10x10 or 10x15 cm - for the rack;
• 5x10 or 5x15 cm - for the bed;
• 2x10, 2.5x15 cm - for crates.

Thickness of each piece supporting structure the roof is determined by the load that it has to experience.

A beam with a section of 10x20 cm is ideal for creating a rafter leg

The cross-section of the rafter legs of a gable roof is affected by:

The rafter pitch affects the cross-section of the rafter legs most significantly. An increase in the distance between the beams entails increased pressure on the supporting structure of the roof, and this obliges the builder to use thick rafter legs.

Table: cross-section of rafters depending on length and pitch

Variable effect on the rafter system

The pressure on the rafter legs is constant and variable.

From time to time and with varying intensity, wind, snow and precipitation affect the supporting structure of the roof. In general, the roof slope is comparable to a sail, which can break under the pressure of natural phenomena.

The wind tends to overturn or raise the roof, so it is important to make all the calculations correctly

The variable wind load on the rafters is determined by the formula W = Wo × k x c, where W is the wind load indicator, Wo is the value of the wind load characteristic for a certain part of Russia, k is a correction factor due to the height of the structure and the nature of the terrain, and c is aerodynamic coefficient.

The aerodynamic coefficient can range from -1.8 to +0.8. A minus value is typical for a rising roof, and a plus value is for a roof on which the wind presses. In a simplified calculation with a focus on improving strength, the aerodynamic coefficient is considered equal to 0.8.

Payment wind pressure to the roof based on the location of the house

The normative value of wind pressure is recognized by map 3 of Appendix 5 in SNiP 2.01.07–85 and a special table. The coefficient taking into account the change in wind pressure with height is also standardized.

Table: guideline value of wind pressure

Table: value of the coefficient k

It is not just the terrain that affects the wind load. Great importance has a housing area. Behind a wall of tall buildings, the house is almost not threatened, but in an open space the wind can become a serious enemy for it.

The snow load on the rafter system is calculated according to the formula S = Sg × µ, that is, the weight of the snow mass per 1 m² is multiplied by a correction factor, the value of which reflects the degree of slope of the roof.

The weight of the snow layer is indicated in SNiP "Roof systems" and is determined by the type of area where the building is built.

Snow load on the roof depends on where the house is located

The correction factor, if the roof slopes are inclined by less than 25 °, is equal to one. And in the case of a roof slope of 25-60 °, this figure is reduced to 0.7.

When the roof is tilted more than 60 degrees, snow load discounted. Still, snow rolls down quickly from a steep roof, without having time to provide negative impact on the rafters.

Constant loads

Loads acting continuously are considered to be the weight roofing cake, including crate, insulation, films and Decoration Materials for arranging the attic.

The roofing cake creates constant pressure on the rafters

Roof weight is the sum of the weight of all materials used in the construction of the roof. On average, it is equal to 40–45 kg / sq. M. According to the rules, 1 m² of the rafter system should not account for more than 50 kg of the weight of roofing materials.

So that there is absolutely no doubt about the strength of the rafter system, 10% should be added to the calculation of the load on the rafter legs.

Table: weight of roofing materials per 1 m²

Number of beams

How many rafters are needed to equip a gable roof frame is set by dividing the width of the roof by a step between the beams and adding one to the resulting value. It denotes an additional rafter that will need to be placed on the edge of the roof.

Let's say it was decided to leave 60 cm between the rafters, and the length of the roof is 6 m (600 cm). It turns out that 11 rafters are needed (taking into account the additional beam).

Rafter system gable roof- this is a structure made of a certain number of rafters

The pitch of the beams of the roof supporting structure

To determine the distance between the beams of the roof supporting structure, you should pay close attention to such points as:

• weight of roofing materials;
• the length and thickness of the timber - the future rafter leg;
• degree of roof slope;
• level of wind and snow loads.

After 90-100 cm, rafters are usually placed in the case of choosing a light roofing material

A step of 60-120 cm is considered normal for rafter legs. The choice in favor of 60 or 80 cm is made in the case of building a roof sloped by 45˚. The same small step should be, if desired, to cover wooden frame roofs with heavy materials like ceramic tiles, asbestos-cement slate and cement-sand tiles.

Table: rafter pitch depending on length and section

Formulas for calculating the rafter system of a gable roof

The calculation of the rafter system is reduced to establishing the pressure on each beam and determining the optimal section.

When calculating the rafter system of a gable roof, proceed as follows:

1. Using the formula Qr = AxQ, they find out what is the load on running meter each rafter leg. Qr is the distributed load per linear meter of the rafter leg, expressed in kg / m, A is the distance between the rafters in meters, and Q is the total load in kg / m².
2. Go to the definition of the minimum cross-section of the timber-rafter. To do this, study the data of the table entered in GOST 24454-80 “Lumber of coniferous species. Dimensions ".
3. Based on the standard parameters, the section width is selected. And the section height is calculated using the formula H ≥ 8.6 Lmax sqrt (Qr / (B Rben)) if the roof slope is α< 30°, или формулу H ≥ 9,5·Lmax·sqrt(Qr/(B·Rизг)), когда уклон крыши α >30 °. H is the height of the section in cm, Lmax is the working area of ​​the rafter leg of maximum length in meters, Qr is the distributed load per linear meter of the rafter leg in kg / m, B is the width of the section, cm, Rben is the resistance of wood to bending, kg / cm². If the material is made from pine or spruce, then Rben can be equal to 140 kg / cm² (1 grade of wood), 130 kg / cm 2 (2 grade) or 85 kg / cm 2 (3 grade). Sqrt is the square root.
4. Check if the deflection value complies with the standards. It should not be more than the number that is obtained by dividing L by 200. L is the length of the working section. Correspondence of the deflection value to the L / 200 ratio is feasible only if the inequality is correct 3.125 · Qr · (Lmax) ³ / (B · H³) ≤ 1. Qr denotes the distributed load per linear meter of the rafter leg (kg / m), Lmax - the working area of ​​the rafter leg maximum length (m), B - section width (cm), and H - section height (cm).
5. When the above inequality is violated, the B and H scores increase.

Table: nominal dimensions of thickness and width of sawn timber (mm)

An example of the calculation of the supporting structure

Suppose that α (angle of inclination of the roof) = 36 °, A (distance between rafters) = 0.8 m, and Lmax (working section of the rafter leg of maximum length) = 2.8 m. Material from first grade pine is used as the beams , which means that Rben = 140 kg / cm².

Cement-sand tiles have been chosen for the roofing, and therefore the roof weight is 50 kg / m². The total load (Q) that everyone experiences square meter, is equal to 303 kg / m². And for the construction of the rafter system, beams with a thickness of 5 cm are used.

The following computational steps follow from this:

1. Qr = A · Q = 0.8 · 303 = 242 kg / m - distributed load per linear meter of rafter timber.
2. H ≥ 9.5 Lmax sqrt (Qr / B Rben).
3. H ≥ 9.5 2.8 sqrt (242/5 140).
4. 3.125 · Qr · (Lmax) ³ / B · H³ ≤ 1.
5. 3.125 · 242 · (2.8) ³ / 5 · (17.5) ³ = 0.61.
6. H ≥ (approximate height of the rafter section).

In the table standard sizes you need to find the height of the section of the rafters close to the indicator of 15.6 cm. A parameter equal to 17.5 cm is suitable (with a section width of 5 cm).

This value is quite consistent with the deflection index in regulatory documents, and this is proved by the inequality 3.125 · Qr · (Lmax) ³ / B · H³ ≤ 1. Substituting the values ​​(3.125 · 242 · (2.8) ³ / 5 · (17.5) ³) into it, we will find that 0.61< 1. Можно сделать вывод: сечение пиломатериала выбрано верно.

Video: detailed calculation of the rafter system

The calculation of the gable roof rafter system is a whole complex of calculations. In order for the bars to cope with the task assigned to them, the builder needs to accurately determine the length, quantity and cross-section of the material, find out the load on it and find out what should be the step between the rafters.

The distance between the rafters (rafter legs) is called the rafter pitch. When arranging a roof, it is customary to use a rafter leg pitch of no more than 100 and at least 60 cm. The reliability of the roof structure depends entirely on how correctly the distance is calculated.

Incorrect determination of the loads on the rafters and the parameters of the materials used as them can cause deformation not only of the roof, but of the entire building. The roof can collapse and cause walls to collapse. Given this, the calculation of the structure of the rafter system must be given the same close attention as the general design of the building.

Methodology for calculating the distance between the bars

• moving along the eaves of the slope, measure its length;
• divide the resulting number by the selected step (from 60 to 100 cm);
• add 1 to the resulting quotient and round the number up.

As an example, let's take a slope 30 m long and a distance between the rafters of 0.6 m.

50 + 1 = 51 - 51 rafters are required to build a roof.

Then we determine the step between the beams that will be used as a supporting structure:

30: 51 = 0.58 m - the distance between the axes of the beams, which will be installed on the roof slope as rafters.

This example shows a general method for calculating a supporting structure, but does not take into account the specifics of a particular roofing material. Experts recommend calculating the distance based on the characteristics of the roofing.

In addition, the calculations should be carried out taking into account the materials from which the roof system of the house will be made. Here the step largely depends on both the type of material and its dimensions.

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The specifics of laying rafters under ceramic tiles

Despite the fact that ceramic tiles are one of the elite and environmentally friendly roofing materials, their installation is fraught with certain difficulties. And the main one is large mass... So, the weight of ceramic tiles is almost 10 times the weight of metal tiles. This means that for each m2 of the structure, a pressure of 40 to 60 kg will be exerted. These conditions imply the creation of a reinforced supporting system that can support the weight of the roof.

To create a rafter system under a ceramic tile roof, a bar with a cross section of at least 5x15 cm, and preferably 6x18 cm, is usually used. The moisture content of the wood should not exceed 15%.

The distance between the beams depends on the slope of the ramp and the length of the rafters. So, the steeper the roof, the greater the distance between the rafter legs. If, with a slope of 15 o, the step is 80 cm, then with a slope of 75 o, it will be 130 cm. Long bars will be located at the maximum distance from each other, and short ones at the minimum.

In order for the installation of ceramic tiles to be performed correctly, the step of not only the rafter legs, but also the sheathing is important. When creating a house structure, you need to take into account the parameters of each roofing element(in this case, tiles). Typically, a tile tile does not exceed a length of 40 cm, and during installation it forms an overlap with the previous row of about 9 cm.This determines the pitch of the sheathing, which should be at least 31 and not more than 35 cm.

Also, this indicator can be determined according to the following scheme:

• the length of the lower row is subtracted from the length of the slope;
• then the distance between the first row of the lathing and the last rafter is subtracted.

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Specificity of mounting the supporting structure for metal tiles and corrugated board

Installation of metal tiles does not require reinforcement of the supporting structure due to its low weight. The wood will not resist the applied loads, which means that the step between the beams may not be wide. So, for roofing from metal roofing rafters can be located at a distance of 60-95 cm from each other.

Decking is another roofing material that is lightweight. And according to other characteristics, the corrugated board is as close as possible to the metal tile. Therefore, the step of the rafter legs is similar to the above - from 60 to 90 cm.

Distance parameters define characteristics building materials... For example, if a board with a width of less than 10 cm is used to equip a structure on a roof, the distance should be reduced to 50 cm.

Do not forget about the distance between the elements of the lathing, which can be from 0 to 400 cm. The step of the lathing is selected taking into account the brand of the profiled sheet and the slope of the slope. For example, a professional sheet of the C-21 brand with a thickness of 0.5 to 0.7 mm with a slope of the roof slope of more than 15 o should be attached to the crate, the step of which will be no more than 65 cm.

The rafter structure is the fundamental element of the pitched roof. Incorrectly calculated distance between the rafters, incorrect accounting of the load on the erected system of beams, their incorrect installation, most likely, will lead to deformation and collapse. The stability of the rafter system depends on:

1. from strength at the bottom to the ridge at the top;
2. the validity of the drawing of the support for the rafters, taking into account the span length;
3. quality of wood;
4. step of the rafters.

Obviously, the main condition for the reliability of the roof structure is the correctly calculated distance between the rafters. You can figure out how to determine this value for a gable, gable, hip roof.

What are the spans length calculations based on?

A competent calculation of the structure, in which the step of all rafter legs is calculated according to the same principle for any type of roof, is based on the following indicators:

1. type of roofing material (metal, slate, etc.);
2. distance (span) between adjacent supports;
3. the angle at which the rafter legs are attached.

• rafter weight;
• insulation weight;
• roof weight;
• crate weight;
• snow;
• wind;

the weight of a person or people who will subsequently be engaged in repairs, maintenance of the roof itself and the objects on it.

Snow and wind - the values ​​for each region are different, you need to look for these indicators in reference information specific area, region.

How to calculate rafter gaps

The exact distance between the rafter legs is calculated using complex mathematical formulas, strength materials, but many craftsmen cope with this task in their own way. After the calculation of the maximum load has been carried out, the following actions should be performed:

• measure the length of the roof;
• divide the result obtained by the span of the roof frame or the approximate step for installing the rafters, (the step of the rafters is the distance from one leg to the other leg of the rafter system, usually the standard value, approximately selected, is taken into account);
• add one to the result obtained, round off the resulting value;

After that, the length of the roof slope should be divided by the obtained value (the number of rafter trusses) - you get the desired rafter pitch.

Calculation example. The ramp is 27m long, the chosen step is 0.8m.

27:0,8=33,75
33,75+1= 34,75
round up = 35, The number 35 means that you need to put 35 rafters.

Determine the distance between the rafters: 27: 35 = 0.8. That is, the leg is set at a distance of 80 cm from one another.

The generally accepted standard is a value equal to 1 meter, and a step of eighty, seventy, ninety cm can also be optimal. Obviously, the calculation procedure cannot be called accurate, because the type of roofing material is not taken into account.

The intervals between the rafters used for different types of roofing materials

When calculating the step of the rafter legs, it is necessary to take into account the characteristics and dimensions of the roofing material. The most popular are the following types of roofing:

• corrugated board;
• ceramic tiles;
• metal tiles;
• ondulin;
• slate.

These types of roofs are used for the installation of roofs of residential buildings, baths, outbuildings. For each type of roof and roof shape, pitched, gable or otherwise, a certain gap between the rafters is used.

Corrugated board

Decking is a modern durable material made of galvanized sheet formed into a specific profile. The material is lightweight, durable. When using it, the calculation of the distance between adjacent rafters is 60-90 centimeters. A greater distance is possible only if there is a board of a large section fastening the rafters. The lathing for the corrugated board is made from a board of thirty, mounted 50 cm apart, if the roof angle is 15 °, the corrugated sheet is laid on the lathing, covered without gaps.

The step of the rafters under the corrugated board does not depend on its brand. So, C44, the heaviest material, is attached to the crate with a span of 30 cm, but the pitch of the rafters does not change.

Ceramic tile

The calculation of the pitch of the rafter beams for ceramic tiles, a material of large weight, expensive, is somewhat different from others. For a material that is heavy, only dried strong beams with a section of 50x150, 60x180 cm are used. The optimal spacing between the rafters, taken as standards, is from 80 to 120 cm.The choice of interval depends on the slope and type of roof. The calculation must be made taking into account the length rafter beam... The longest rafter requires a minimum pitch, and vice versa, the short rafter length allows you to use the maximum pitch.

Metal tile

Metal tiles can be safely called the leader among all roofing materials. It is used for complex, hip, gable, hip, pitched roofs. Its installation is much easier than ceramic tiles. Metal roofing can be placed on old roof, replace the ceramic tile, slate, using the old step. The metal tile is 10 times less, therefore, beams of a smaller section 50x150 are used, the pitch between the rafters is from 60-90 cm, standard values. It is especially convenient to insulate such a roof, taking into account the width of the roll or sheet insulation.

Ondulin

This kind soft roof becomes more and more popular, lightweight, easy to install, strong and durable. Ondulin sheets are fastened with an overlap on a 40x50 crate made of coniferous boards (step 60 cm).

The step of the rafter legs is from 60 to 90 cm. Beams are needed with a section of 50x150 or 50x200.

Slate

Slate is widely used to cover outbuildings, baths, houses, garages. Therefore, many people know what the distance between the rafters should be when using this roofing material. The use of this particular material has created a rafter pitch system 60-80, lathing 50x50. The crate is made from 50x50 bars or the thirtieth board, depending on the slope. For a flat shed roof, a sheathing step of 45 cm is used, for a gable roof - 65 cm.

How the steps of the rafters of a gable and a pitched roof differ

Each type of roof has its own strength. The pitch of the rafter beams depends on what margin of safety should be laid when installing this or that type of roof.

Single-pitched roof structures, which are characteristic of simple household buildings, are made of beams reinforced on the walls. The distance between the roof rafters directly depends on their length. It is also important to take into account the cross-section of the beam used, based on the fact that the longer the gap, the greater the load.

The gable system, which includes the gable, hip, hip and other structures, is always mounted with thermal insulation. The standard pitch for such roofs is 1-1.2 meters. In each specific case, the calculation is carried out taking into account, as already mentioned, the weight of the roofing material and other things, SNiP 2.01.85 is taken as the basis, which considers all types of loads and influences. The step is calculated according to the usual scheme given above. The angle of inclination must be taken into account. The 45 ° angle allows the use of all types of roofing. With the same roof slopes, the step of one side is calculated.

Follow these tips:

• If a decision is made about self-arrangement roofs, check the correctness of your calculations with specialists or, at worst, use the services online calculators construction companies.
• When determining the pitch of the rafters, remember about thermal insulation, any roll or sheet insulation shrinks over time. Remember about ventilation holes, waterproofing.
• If the roof slope is 45 ° or more, the person's weight is deducted from the sum of the maximum load, which allows the use of fewer rafters (by 20%).
• Decide what type: layered or required for the selected roof geometry.
• Take your time with the choice of timber, it must be dry (residual moisture not more than 20%), made of coniferous wood.