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At what distance are the rafters placed. Rafter pitch for different types of roofs and roofing materials. Roof structure for ceramic tiles

Distance between rafters pitched roof is one of the most important parameters in its construction. It is this distance that affects the strength of the frame and the truss system, respectively, the strength of the entire roof also depends on it. To correctly determine it, it is necessary to make quite complex calculations. In this case, it is strongly recommended to contact an architectural studio for their implementation. Incorrect calculations and, as a result, an incorrectly chosen distance between the slopes can lead to serious negative consequences, such as deformation of the supports of the truss system, deformation and violation of the integrity of the roofing, roof collapse. Therefore, in the process of designing a gable roof, it is extremely important to use the most accurate initial data, reference values ​​\u200b\u200bmust be taken strictly in accordance with the specific conditions of construction, and the calculation must be made according to the method indicated below.

The distance between the rafters of a gable roof is one of the most important parameters in its construction.

Primitive calculation method

Usually builders refer to the spacing between rafters as their pitch. Almost always, the rafters are separated by a maximum of 1 m (at the base), while the minimum allowable interval between them is usually within 0.5 m. The algorithm for calculating the required number of supports for the construction of a solid roof is as follows:

1. First, the length of the slope along the eaves of the roof is measured (actually the length of the wall parallel to the slope + the expected ledges).
2. The value obtained during the measurement is divided by the selected interval between the "legs" of the truss system. Next, choose the interval for which the "legs" will be divorced. For example, 80 cm. In this case, the denominator of the fraction will be 0.8.
3. The last stage: a unit is added to the resulting quotient, if the resulting number is not an integer, then it is increased to an integer, always upwards.

Such a simple calculation will allow you to determine the number of rafters, as well as the distance between the supports. It is important to remember that the values ​​obtained will determine the number of supports for only one of the two slopes. When the count is completed, the longitudinal size of the slope is divided by the estimated number of truss supports. The result of this will be the exact distance between the supports. Consider one example: the length of the slopes of a gable roof (not total) is 20 m. Initially, a step of 0.75 m was selected. We make a preliminary calculation: 20/0.75 = 26.7. We add 1 to the obtained value, we get 27.7. Then we round up to a larger one and as a result we have 28 pieces. rafters. That is how many "legs" the rafter system of one slope will have. Next, we determine the exact distance between them: 20/28 \u003d 0.72 m. Using this simple technique, you can determine the minimum interval at which the rafters will be placed. However, it is also important to consider which roofing material is selected.

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If decking is selected

The professional flooring is though not heavy, but at the same time very flexible material. Therefore, for it, the minimum allowable step should be 0.5 m, and the maximum should not exceed 0.9 m. At the same time, the frame of the truss system must withstand not only the mass of the profiled sheet, but also the battens. For a profiled sheet, the crate is stuffed from a bar or boards with minimum size 30x100, the average installation step of the crate should be 0.5 m (it depends only on the thickness of the sheet). The boards of the crate that go to the eaves when stuffing the corrugated board should be 1.5-2 cm thicker than the main crate. It is important not to forget about the need for ventilation of the structure.

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Ceramic tiles

The main feature of this material is that ceramic tiles are very heavy. This is logical, because the raw material is ordinary clay, which has a large specific gravity. If we compare metal tiles and ceramics, then they differ in mass by more than 12 times. The weighted average pressure of such a coating is 45-70 kg per square meter of crate.

Ceramic tiles are very heavy, because the raw material is ordinary clay, which has a large specific gravity.

The frame with supports for such material should be made of perfectly dried timber, with about 15% moisture. For mounting, use bars approximately 50x150 mm (recommended 60x180 mm). The step of supports for ceramic coating will be in the range of 0.8-1.25 m. This value is greatly influenced by the angle of inclination of the slopes.

For example, if the angle is 15 °, the minimum interval is taken - 0.8 m. With a slope of about 45 ° - all 1.25 m. For this type of roofing material, specialists also calculate the length of the rafters (when calculating the interval between supports).

So, if the length is maximum for a particular roof, then the step value should be minimal. Short rafters require the largest possible interval between them. In this case, it is possible to move along the roof only if the rafter pitch is not more than 0.8-0.9 m with a slope of 45 °. One should also not forget about the need for ventilation of such a design.

For this, holes in the insulation are usually provided, the diameter of which is in the range of 9-12 mm. The process of erecting a rafter system under a metal tile is similar to the process of building rafters for other types of coating.

It is important to remember that in addition to carefully calculating the required number of rafters, the step for the crate should also be calculated.

It differs depending on the type of ceramic tiles. For example, the length of a ceramic tile tile is 0.4 m, while the joint overlaps 0.5-0.9 m. In this case, the sheathing step will be 0.31-0.35 m. It is important to remember that for each slope it is necessary make a separate calculation, since it is impossible to build an absolutely identical truss structure (even if it is the same according to the project): errors and inaccuracies in the assembly can give an error of 0.2 m.

truss structure is a fundamental element of a pitched roof. Incorrectly calculated distance between the rafters, incorrect calculation of the load on the erected system of beams, their incorrect installation most likely to lead to deformation and collapse. The stability of the truss 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 length of the span;
3. wood quality;
4. rafter steps.

Obviously, the main condition for the reliability of the roof structure is a correctly calculated distance between the rafters. How to determine this value for single-slope, gable, hip roof, you can figure it out.

What are span length calculations based on?

A competent design calculation, in which the pitch 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 tile, slate, etc.);
2. distance (span) between adjacent supports;
3. the angle at which the legs of the rafter 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 the repair, maintenance of the roof itself and the objects located on it.

Snow and wind - the values ​​\u200b\u200bfor each region are different, you need to look for these indicators in background information specific locality or region.

How to calculate truss gaps

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

• measure the length of the roof;
• divide the result 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 to the other leg of the rafter system, usually a standard value, approximately selected, is taken into account);
• add one to the result, round the resulting value;

After that, the length of the roof slope should be divided by the obtained value (the number of trusses) - the required step of the rafters will be obtained.

Calculation example. The slope has a length of 27m, the selected step is 0.8m.

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

We determine the distance between the rafters: 27: 35 \u003d 0.8. That is, the leg is set one from the other at a distance of 80 cm.

The generally accepted standard is a value equal to 1 meter, 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.

Intervals between rafters used for different types of roofing materials

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

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

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

Decking

Profiled modern durable material, made of galvanized sheet, formed into a specific profile. The material is light, 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 large cross-section board that fastens the rafters. The crate for corrugated board is made from a board of thirty, mounted 50 cm apart, if the roof angle is 15 °, the corrugated board is laid on the crate, laid 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 a 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 rafters for ceramic tiles, a heavy, expensive material, is somewhat different from others. For a material whose weight is large, only dried strong beams with a section of 50x150, 60x180 cm are used. The optimal distances between the rafters taken as standards are 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 of the rafter beam. For the longest rafter, a minimum step is required, and vice versa, the short length of the rafter allows you to use a step of maximum width.

metal tile

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

Ondulin

This type of soft roof is becoming more and more popular, lightweight, easy to install, strong and durable. Sheets of ondulin are fastened with an overlap on the crate 40x50 from boards conifers trees (step 60 cm).

The pitch 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 farm buildings, baths, houses, garages. Therefore, what should be the distance between the rafters when using this roofing material, many people know. The use of this particular material created a system of rafter pitch 60-80, battens 50x50. The crate is made of bars 50x50 or the thirtieth board, depending on the slope. For gentle shed roof a crate step of 45 cm is used, for a gable - 65 cm.

How do the steps of the rafters of gable and shed roofs differ?

Each type of roof has its own strength. The pitch of the rafter beams depends on what margin of safety should be laid during the installation of a particular type of roof.

Shed roof structures, which are typical for simple buildings for household purposes, are made of beams fixed to 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 timber used, based on the fact that the longer the gap, the greater the load.

The gable system, which includes gable, tent, hip and other structures, is always mounted with thermal insulation. The standard step for such roofs is 1-1.2 meters. In each 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 impacts. The step is calculated according to the usual scheme given above. Be sure to take into account the angle of inclination. An angle of 45° allows the use of all types of roofing. With the same roof slopes, the pitch of one side is calculated.

Stick to the following tips:

• If a decision is made to independently arrange the roof, 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 rolled or sheet insulation shrinks over time. Remember about ventilation holes, waterproofing.
• If the slope of the roof is 45° or more, the weight of the person is subtracted from the sum of the maximum load, which allows the use of fewer rafters (by 20%).
• Decide which 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.

An attic is an attic space that can be used as a living space. The mansard roof should ensure the normal functioning of such a room. In the construction of the roof, a truss structure is usually used, and the pitch between the rafters of the mansard roof is an important indicator of its reliability.

Huge loads caused by the weight of the roof, wind, climatic factors are perceived by the rafter system. Distance between roof rafters attic type determines how much of the load falls on each element. Only the right choice of distance will ensure the stability of the entire roof.

Attic: system features

Rafters are called load-bearing beams, on which protective, additional and external coverings of the mansard roof are attached.

Elements are usually made in the form of a durable wooden beam or boards with a thickness of at least 50 mm. Sometimes a log can be used. For particularly durable buildings, metal and reinforced concrete beams are used.

For the roof of the attic, one of two options for truss systems (layered or hanging) is used, as well as a combination of both options in one design. The layered type is characterized by the support of each of the rafters on the wall of the structure. The hanging type implies linking the elements into a common frame, which is fixed only on the extreme supports.

According to what type of truss system is used, mansard roofs are conventionally divided into the following types: single-pitched, double-pitched, broken, hip, hipped and vaulted. In private construction, the most wide application has a single-pitched, double-pitched or sloping roof. In a shed roof, the rafters rest on walls of different heights, which ensures that the roof slopes (slope) in one direction. The gable roof has two inclined planes, with each of the rafters resting at one end on the wall, and at the other end connected to another beam. This design forms a triangle, and the angle between the elements determines the slope of the slope. The sloping roof also has two slopes, but each of them has a break line in which the laying angle changes.

Mounting Features

When installing the rafter system of the attic roof, fastening and installation of rafters in the form of simple geometric shapes. The greatest rigidity (strength) has a linkage into a triangle, which is used in the construction of a mansard roof. So, the most common gable roof includes a series of triangles of rafters, connected by longitudinal lags (girders). The linkage of the rafters into a triangle is provided by the lower transverse beam (Mauerlat). To facilitate the fastening of the outer roof covering and the redistribution of its weight on the rafters, a lattice is made in the form of transverse bars or boards.

A sloping roof combines two types of rafter connections. The lower rafters with the help of a Mauerlat and a rack are connected into right-angled triangles, which, in turn, are fastened with a longitudinal run between themselves at the top. At the bottom, the attic rafters rest on the wall of the house. The upper ones are connected into a triangle by analogy with a gable design.

Figure 1. Table for selecting the section of a beam for rafters.

The lower end of the rafter is fixed to transverse log, and the upper ends are connected together through a longitudinal upper run. The lower corners of the bonded triangle are interconnected using a longitudinal lower run. The system formed is fixed on the lower truss system. To strengthen the upper triangles, additional vertical racks are used. Thus, the mansard roof is a surface with a break on each side. From the wall, a slope with greater steepness begins, and then it takes on a more gentle appearance.

Mansards with longitudinal bars (including floor beams) are made by cutting rafters into a bar by a third of its height. Fastening to the cross beams is advisable to produce a screw connection. With such fastenings, the functions of two different truss systems are separated, and they are calculated as separate systems.

Parameters taken into account when choosing rafters

When choosing the design of the rafter system, the size of the beam and the number of elements, it is important to take into account all the loads acting on the rafters. These loads can be divided into permanent and temporary, periodic or short-term nature. Under a permanent load, the weight of all elements should be taken mansard roof: the truss structure itself with a grate, external roofing, additional protective and insulating layers, elements of a suspended attic interior. The weight of the external roof can vary greatly depending on the type and material of the coating.

Natural factors should be taken into account as temporary or periodic loads. This is, first of all, the weight of snow in winter time. The wind has a significant impact, and the direction of such a load can be different. For some areas, this factor may be decisive. The possibility of storm water flows cannot be ignored either. In addition, it is necessary to take into account the weight of people and materials when carrying out repair work on the roof.

The geometry of the roof and rafter system has a significant impact on the distribution of loads. The main parameters include the length and width of the roof, as well as the steepness of the slope. The length of the roof greatly affects the distribution of the load, so for long lengths it is necessary to use reinforcing vertical posts. An increase in the width of the roof leads to an increase in the load on all attic rafters, as their length increases and total weight all elements. For wide roofs, a broken type is more suitable due to the presence of intermediate vertical racks in them and the redistribution of loads between different truss systems.

Changing the slope slope affects the parameters ambiguously. An increase in steepness, on the one hand, reduces the accumulation of snow cover and redistributes the load on the load-bearing walls of the house, on the other hand, the length of the rafters and the windage of the roof increase, which is dangerous in windy areas. The concentration of loads on the walls can also adversely affect the reliability of the house, because with a decrease in loads on the rafters, permanent loads on wall laying.

Requirements for the material of the truss system

The calculation of the number of rafters and installation parameters is based on the fact that high-quality material was used during construction. In this regard, the material for the truss system should be selected based on the following conditions.

Only high-quality timber with a section of at least 50x100 mm should be used as the main rafters.

All wooden elements during installation must be well dried (permissible moisture content - no more than 15%). The number of even small defects on the beam cannot exceed 3 pieces per 1 m. The tree is treated with an antiseptic before installation. Coniferous wood performed the best. Vertical racks are made of a bar with a size of at least 100x100 mm with a check of their vertical location using a plumb line.

Features of the calculation of rafters

After choosing the design of the mansard roof (based on the recommendations of experts and in accordance with the reference data), the main design parameters are the distance between the rafters () and their number. Usually the distance between the rafters is from 0.6 to 1.5 m. The calculations are based on the fact that the optimal load should be 40-60 kg per 1 m of the rafter length, and the maximum allowable beam deflection is 1/250 of its length.

The number of rafters per slope is calculated after measuring the length of the slope and selecting. The length of the slope is divided by the step value, 1 (one) is added to the result. The result is rounded up to the nearest whole number.

A specialist can calculate the distance between the rafters, taking into account all factors, but in practice they use reference recommendations. So, for example, for rafters from a board measuring 50x180 mm and a slope length of 3 m, the average step is 1.5 m; with a length of 3.5 m - 1.2 m; and with a length of 4 m - 0.9 m.

Distance between rafters for different roofs

The distance between the rafters varies significantly for roofs with different coating. Ceramic tiles are one of the heaviest roofing materials. For rafters from a bar measuring 50x150-60x180 mm, the recommended distance between them is 80-130 mm (depending) on ​​the steepness of the slope. With a slope of 15 °, the step is chosen to be 80 cm. With an increase in the length of the rafter, the step is increased within the recommended range.

The distance between the rafters for roofs with metal roofing is set smaller than for natural tiles. The optimal step is 60-95 cm for a bar measuring 50x150 mm. When using a corrugated board coating, the step is in the range of 60-90 cm with a sufficient cross-section of the beam from 50x100 mm to 50x150 mm.

The lightest coating is obtained when using ondulin. The optimal distance between rafters measuring 50x50 mm is 60-80 cm and decreases when installing a beam bigger size. When covering the roof of the attic with slate, a beam measuring from 50x100 mm to 50x150 mm is used. The step is set in the range of 60-80 cm.

Required Tools

When installing rafters on mansard roof the following tools are used:

• Bulgarian;
• drill;
• hacksaw;
• saw;
• axe;
• chisel;
• hammer;
• plane.

When installing a truss system on a mansard roof, it is important to determine optimal distance between the rafters. Right choice this parameter will allow you to calculate the optimal amount of material and ensure the reliability of the entire roof.

A gable roof is one of the most common and versatile roof structures for buildings. for various purposes. They can be made both cold for non-residential attic spaces, and insulated for attic rooms.

Important. The house has two main architectural element, which play a decisive role in the durability and safety of operation: the foundation and the roof. During their design, it is necessary to strictly comply with all the requirements of building codes and regulations.

Only professionals can deal with the design and construction of the truss system. They must have deep theoretical knowledge and great practical experience performing such work, only practice allows you to take optimal solutions in the course of construction.

Each house has its own individual characteristics, each batch of lumber is different in strength, each load-bearing unit can be manufactured and fixed different ways. All this affects the stability of the truss system, increases or reduces the estimated cost of the roof, etc. It is necessary to achieve such an option that the truss system is as simple as possible to build and at the same time reliable and cheap.

There are so many different opinions from inexperienced developers about how to choose the distance between the rafters. Some in all seriousness give advice on choosing this parameter for each type of roofing material: natural or artificial piece tiles, metal tiles and corrugated board, soft bitumen or slate coatings. In fact, all this is not so, architects never put in the initial data when calculating the step rafter system type of roof.

The physical properties of roofing materials, together with other factors, do not affect the distance between the rafters, but their dimensions and additional structural elements of the truss system to increase the stability of the structure, including:

• vertical supports;
• horizontal runs;
• corner supports;
• crossbars and other special elements.

In roof structure wooden house many different elements, each of which performs its function and is fixed in a certain way. To find out in detail what elements the roof of a wooden house consists of,. You will find not only the description of the elements, but also the best practical tips!

Before starting calculations, engineers have initial data (terms of reference) for the entire system, taking into account these values, other parameters are calculated. Among the initial data there is also a rafter step, it is known before the start of design and does not change in the final project. What exactly influences this parameter?

Important. The step of the rafter legs is measured between the axes, when choosing the final parameter, the thickness of the boards must be taken into account. For the installation of insulation, the distance between the side planes, and not the axes of the rafters, is important.

What effect does the type of roofing material have on the distance of the rafters

It is necessary to dwell on this issue in detail, quite a lot of developers do not fully understand the problem. To answer, you need to know the fundamental differences between materials and their effect on the distance and calculation of rafters. We emphasize that we do not mean performance characteristics roofing or their design appearance, namely structural and physical differences.

1. Linear dimensions. Most of all, the dimensions of metal coatings can reach eight meters.

   

   

   All of these materials are fundamentally different methods fixing to the truss system. But they do not have any effect on the step of the rafters.

2. Bending strength. There is an erroneous opinion that for flexible roofing materials you need to reduce the pitch, this is not so. Not a single roof covering is fixed directly to the rafter legs; for this, a crate is made, and when it is arranged, fastening methods are taken into account. Moreover, for some types of roofing, it is necessary to control very accurately - the materials have precisely fixed places provided during manufacture.

   

3. Weight. The calculation of the truss system is influenced only by heavy coatings: piece tiles and asbestos-cement slate. All other types of roofs have such an insignificant mass that it is not taken into account when designing a structure.

   

Prices for different types of tiles

Roof tiles

Algorithm for calculating the truss system

As mentioned above, the distance between the rafters is set to initial stage and depends on the characteristics of the heaters. They affect another important parameter - the width of the boards.

It should take into account the minimum thickness of the insulation layer, taking into account the climatic zone of the building. If in cold regions the insulation should have a thickness of 20 cm or more, then for a warmer climate, 10 cm of insulation is enough. Accordingly, the width of the board for rafters is from 20 cm to 10 cm.

Practical advice. You always need to consider the cost of lumber. There are options when it is much more profitable for rafter legs to use boards 10 cm wide, and to increase the depth of the niche for insulation by building up ordinary thin low-quality ones. But in all cases, the main size criterion is the ability to hold the maximum design loads.

The calculation of rafters is carried out in several stages.

Determination of roof forces

Several types of loads act on the roof slope, they have different meaning and its features of influence on the strength of the system.

1. Constant loads. This refers to the weight of building materials for the truss system and the mass of roofing. If heavy types of materials are used as coatings, then their mass must be taken into account.

   

   As for light metal sheets, this is optional.

   

   The fact is that the roof is one of the most important structural element of the building, and they have a safety margin of at least 140%. This means that the structure can withstand loads almost one and a half times more than the calculated ones. The maximum load on the roof is created by snow and wind. The values ​​of these efforts are measured in hundreds of kilograms, and the mass of metal sheets is only a few kilograms per square meter. The safety factor fully covers the possible increase in effort.

   

2. Variable loads. These include snow and wind forces, they are placed in the tables available in building codes and regulations. This takes into account the location of the building (in a city or in an open area), the number of storeys, the shape of the roof, etc. It must be borne in mind that recently the climate has been changing rapidly, and in the tables the information is fifty years old. It is not very correct to use them, it is better to take data from the reports of the hydrometeorological center of your region.

   

   

The maximum permanent and temporary loads are summed up and increased by approximately 40% to create a margin of safety for all load-bearing elements. The safety factor can also be taken into account by another method. After performing all engineering calculations, the linear parameters of the rafters are determined, in the final version they are multiplied by a factor of 1.4, the results are used during the creation of working drawings of the truss system. It does not matter which method to use, the main thing is to observe the accuracy of mathematical calculations, and only a specialist with a special technical education can perform them.

The methodology is prescribed in SNiP 2.01.07-85, it has been amended by some formulas adopted in 2008. Before taking into account the distance between the rafters, you should know all the loads acting on them.

Snow loads

Prices for snow guards

Snow guard

Engineers use the formula

Formula 1. Determination of snow load

We have already mentioned that the normative load can differ significantly from the actual one, in this regard, it is recommended to use more modern data. As for the angle of inclination of the roof α, this parameter is set in the initial specifications for the design of the truss system. The coefficient µ is determined by the formula

Formula 2. Definition of µ

One component of several efforts on the rafters has been determined, now you should move on to other types of loads.

Important. Please note that snow loads, depending on the climatic region, range from 120–180 kg/m2. Now it should be clear why the weight of light roofs can be ignored, their efforts are approximately 5–7 kg / m2, this is within the limits of a mathematical error. In addition, a safety factor is applied. 40% of 180 kg is 72 kg, this value is much larger than the mass of metal roofs and has already been taken into account when calculating the strength of the rafters.

Wind loads

These efforts can reach significant values ​​and must be taken into account when calculating the parameters of the rafter legs. There are two types of wind loads. When the slopes are more than 30 °, the wind tries to overturn them, with great effort it presses on the leeward side of the roof. If the slope is small, then due to differences in the speed of air flow, a lifting force appears, tearing the roof from the Mauerlat. Wind loads are determined by the formula

The wind pressure coefficient by height includes several factors. All of them have a complex method of calculations, which are performed by competent thermodynamic engineers.

To facilitate calculations in normative documents there is a ready-made table, a specific coefficient is selected depending on:

• building height;
• terrain type (open or closed);
• urban building heights.

The aerodynamic coefficient may be greater than one or less than one. In the first case, the wind load increases, in the second it decreases slightly. For most buildings, simplified calculations are made for wind loads, it is assumed that the coefficient is 0.8.

The mass of elements of the truss system and roofing

Taking into account the peculiarities of the crate and materials for the manufacture of rafter legs, their total mass can increase the values ​​​​of the loads on the system within 30–50 kg / m2. As already mentioned, this parameter can be ignored. A large safety factor makes the roofs universal, they can be covered with any kind of roofing materials.

Calculation of rafter legs

The distance between them is available in the design specification, is a stable value and is specified in the design specification. Next, you should find out the linear dimensions of the rafters so that they can withstand the maximum possible effort during operation. Distributed load on running meter legs is determined by the formula

We have all the initial data for calculating the distributed load.

Now you can proceed to the selection of the optimal section of the rafter leg. In this case, one should be guided by the GOST 24454-80 table, which indicates standard sizes lumber (thickness and width).

Nominal thickness and width dimensions of edged sawn timber with parallel edges and thicknesses of unedged and edged lumber with non-parallel edges

Be sure to familiarize yourself with the table, this is necessary to understand the methodology for choosing boards. For example, with a thickness of 16 mm, the maximum board width is 150 mm, and with a thickness of 75 mm, the maximum width increases to 275 mm.

It is necessary to set the width of the board section and, taking into account this parameter, calculate the height. Formula used

It is suitable for cases where the roof slope α< 30°.

If the slope angle α > 30°, then you need to use the formula

• H- the desired height of the board for the rafters;
• Lmax- the distance between the most distant points of the abutment of the rafter. For small slopes, it is equal to the distance from the ridge to the Mauerlat; in other cases, you need to set various types stops and measure the distance, taking into account their location;
• QR- distributed load on the rafter leg, it was calculated earlier;
• B- the thickness of the board, is chosen arbitrarily, taking into account the individual characteristics of the truss system;
• Rizg- normative indicators of resistance of wood to bending.

Depend on the quality of lumber and type of wood, taken from the tables state standards. The quality of lumber plays a decisive role in the bending resistance of lumber.

For example, if for the first grade of pine Rizg = 140 kg/cm2, then for the third grade this parameter is reduced to 85 kg/cm2. The standards strictly regulate the bending radius of the roof, if it is too small, then there are high risks of leakage due to a violation of the integrity of the roofing. For all roof elements, the deflection cannot exceed L (length of the working section) / 200.

In SNiP there is a formula for checking the condition under which the deflection does not exceed the established norms

If the sum exceeds one, then it is necessary to increase the thickness or width of the rafter leg.

Calculation example

The number of rafters is known, this value is always determined taking into account the required distance between them. In our case, the pitch is 80 cm, the slope angle is 35°, the length of the working area is 280 cm. truss system made of pine, the bending radius of this first grade material is 140 kg/cm2. Piece cement-sand tiles will be used as roofing material. This is a very heavy material, its weight is recommended to be taken into account. Weight square meter tiles up to 50 kg. Now all the initial data are known, you can start the calculations.

Taking into account the climatic zone, the total wind and snow load is 253 kg / m2, the weight of the tiles should be added to them, for a total of 303 kg / m2. The distributed load on the rafter is calculated by the formula and in our case is 242 kg / m2. It is planned to make rafters 5 cm thick, you need to find their width.

Applying the formula

It is this formula that is used due to the fact that the angle of inclination of the slope is more than thirty degrees. Now it remains to check whether the maximum allowable deflection radius of the rafter will not be exceeded. If the value is less than one, everything is normal. If it is more than one, then it is necessary to increase the linear dimensions of the boards.

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When you need to calculate the distance between the rafter legs

Such a need arises very rarely and mainly concerns non-residential premises. For example, the developer already has boards for the manufacture of the truss system, he needs to know at what distance to fix the rafters so that the roof can withstand the calculated loads. That is, you need to do the reverse calculation. If in the standard situation the distance is known and the dimensions of the boards are selected taking into account these parameters, then in the second case the opposite is true. Sizes known rafter boards, you need to determine the step of the rafters. It is done in this order.

Knowing the total load on the roof and the maximum load on one rafter, we determine the number of rafter legs with a simple arithmetic operation. Of course, all roundings are done upwards; an excess margin of safety will never hurt the truss system. The last stage - the length of the roof slope is divided by the minimum number of rafters and the distance between them is obtained. Rounding should be done in the direction of decreasing the step.

Video - Choosing the distance between the rafters

So, in order for the structure to serve for a long period of time, to be strong and also reliable, it is worth thinking not only about the foundation, but also about the roof. The building system of such an element plays a huge role, because it is the roof that takes on the negative aspects of the changes weather conditions, as well as other situations.

The truss system of a shed roof must be characterized by certain requirements, including:

• Rigidity
• Little weight
• quality material

Such requirements must be taken into account so that the structure serves for a long time.

The rigid characteristics of the element play an important role, because it is with the help of rigid elements that the connection of different parts occurs. Such elements should not be subjected to deformation processes., as well as raspor under any circumstances.

The basis of this design is a triangle, which is made using a special reliable frame. Each element of this frame is fixed one to the other in parallel, and with the help of a strong fixation, the stability of the entire structure is ensured.

Shed roof truss system: scheme

But, if such frames are poorly attached, if they are movable, this will only lead to negative consequences.. Such a roof can collapse not only from a strong wind, but also by itself.

If we talk about weight, then this the roof should not be heavy. That is why this system made, in most cases, from wood. In the event that the weight is large enough, it is necessary to make a supporting base of metal.

There are cases when use coniferous trees, the humidity of which is not less than 18 percent. Among mandatory conditions when using trees, note:

1. Antiseptic treatment
2. Use of flame retardants

Only in this case, the nodes, in the area of ​​\u200b\u200bwhich the entire system is precisely fastened, will be distinguished by high strength, as well as reliability.

The high quality of the materials used is one of the main rules. The tree must meet the following characteristics:

• Applies 1-3 different varieties . It is important to pay attention to the fact that there are fewer cracks as well as knots. For one meter of material, 3 knots with a height of not more than 3 centimeters are allowed. Cracks are also allowed in a minimal amount, but not over the entire depth.
• It is desirable to make elements of a bearing nature from parts whose thickness is not less than 5 cm, and the area is from 40 m2.
• Boards from coniferous trees can only be used with a length of not more than 6.5 meters, and from deciduous trees- up to 4.5 m.
• Pillows, girders, as well as Mauerlat, it is desirable to make from trees that are hardwoods. Such material should first be treated with the help of one or another high-quality antiseptic.

Shed roof construction

So, before starting the manufacture of the system, it is very important to know what its main parts are:

1. Mauerlat which can be called the foundation of the system. With this part the load is distributed evenly and correctly.
2. Run is an element that is confidently fastens all the legs of the rafters. The ridge option is at the top, but the side elements are located on the sides.
3. The rafter leg is installed to determine the angle of inclination of the slope, as well as for the reliability of the entire roof, its appearance. This product fixes individual parts systems.
4. Tightening helps feet stay in place, do not move apart. This detail connects them at the bottom.
5. Racks, as well as struts give additional leg stability.
6. crate represents boards, as well as bars in a cropped form. She is stuffed perpendicularly, transfers the load to the rafters.
7. The overhang of the entire roof protects against rainfall.
8. Skate is the place where two roof slopes meet. It is along this element that the crate is stuffed, due to which the reinforcement of one or another part of the roof.
9. Filly are used when the length of the legs is small, as a result of which they create an overhang.

ATTENTION!

Only if you take into account the described parameters, you will get a reliable roof.

Shed roof is characterized by the presence of one slope, which is characterized by an angle of inclination from 14 to 26 degrees. In the case when the roof is made for a small house, the span will not exceed 5 cm, so it is recommended to make a layered system.

The supports of such a roof are made on the walls of an external nature., as well as a wall that exists inside the object. Truss systems are used in truss truss cases.

roofing cake, or rather, its device, depends on which final version of the coating will be chosen. But, regardless of the material, this element maximizes roof life, durability.

The single-sided type requires special attention, since it is precisely this stage construction has the greatest impact on the climate that will be the construction.

Construction of the truss system

Shed roof rafters

The mounting scheme is quite simple, as it is a parallel spread out boards that rest on two walls. To install the legs, special transition elements are used, which are made of wood.

Depending on what material is used, the following can be used as a transition piece:

• Mauerlat. In the above roof system with one slope, these are two wooden beams, which lie separately and complete the walls.
• Upper part of the foot, which is composed of bars.
• Top harness the entire frame.

Although the design of this roof is simple, there are some subtleties of fastening the rafters that are important to know about.

The fact is that the nodes that are applied must take into account all the negative aspects of a material such as wood.

When designing, the solution of the following tasks should be taken into account:

• Ability to easily move wood parts from one another
• Adapting to the consequences that may be after the subsidence of each wall in order to take a stable position
• Exclusion of all possible causes violation of one or another connection

The triangles are fastened according to the scheme: the horizontal side is installed on the Mauerlat, fixed. It is very important that it has enough space for docking. with other elements.

It is important to set the rafter legs at a certain angle to the supporting elements. It should be understood that two points are not enough for a strong attachment, so there are methods that are used to avoid negative consequences.

First of all, important to increase total area rafter interactions, as well as the reference part using:

• Select cuts
• File the top as well as the bottom edges of the legs. With the help of such actions, you can easily create a support platform, increase stability.

Rafter fastening

Rafter step

The distance between the rafters of a shed roof is calculated depending on whether what material is chosen, as well as the cross section. Such calculations should be done at the stage, building codes and rules are used.

The calculation for the above roof option is very simple. There are no racks, as well as braces, as a result, only the rafters of a shed roof are taken into account.

Usually, for such a roof, softwood material used, whose moisture factor is approximately 20-22 percent. Such boards should be characterized by evenness, the absence of blue.

Each blood material is characterized by its own characteristics, so the pitch of the rafters is also different:

1. Using distance depends on sheet size. Usually, the spacing of the beams is at least 60 cm and up to 90 cm. For larger distances, additional boards with a large cross section of 150 mm are used. It is important to take into account the use of the crate, the cross section of which should be 30 * 100 mm, and the mounting is carried out taking into account the span of at least 50 cm.
2. often used, but its weight is taken into account. Beams for such a system are pre-dried. When determining the step size, the length of the boards should be taken into account. At maximum length it is necessary to make the minimum distance between the rafters. The same rule is used for the minimum length of the beams - a large step distance. Usually, 80 cm is considered a safe step.
3. Under, which is used much more often than the two above materials, beams with a small section are used. The step in this case is equal to a number from 60 to 90 centimeters. The beam should be used with a cross section of about 50 * 150 mm.
4. Using it should be understood that this in the form of sheets. Beams should be placed with a distance that will not be less than 60 centimeters, but not more than 90 centimeters. The cross section of the beam is 50 * 200, and 50 * 150 mm can also be used. When using a smaller section, negative aspects can be expected, since such a section will not be able to provide high strength to the legs.
5. Under , which is used very rarely, rafter legs with a section of 50 * 100.50 * 150 are used. The step is not less than 60 centimeters, and also not more than 80. In this case, the step differs depending on the roof structure.

Rafter pitch table

Installation of the truss system

When deciding to independently install the rafters of a shed roof, you should first prepare all the elements, as well as process them with special means.

Boards should be laid on both sides of a certain roof and laid in grooves.

Only after that it is important to attach a few extreme rafters.

CAREFULLY!

Keep in mind that it is important to hammer in one or two nails for each joint. The legs are installed taking into account the previously stretched strings, after which they are similarly nailed. After that, the crate is installed, and the roof is laid.

After calculation, design, there are certain stages of installation:

• Installation of the bearing beam. A large beam is laid along the wall of the object. It should first be scoured, soaked with an antiseptic. It is important to lay the roofing material along the end of the wall, to mount the beam on it in level with the help of anchor bolts.
• Processing timber, building elements. It is planned to fly the board over the roof overhang - a level of about 40 cm on each side, depending on. It is important to consider that the steeper the angle, the less it costs to fly. When using metal tiles, as well as corrugated board, the step is 120 centimeters. In the case when the width is more than 6 meters, the step is recommended to be reduced to 1 meter. The board crashes into the Mauerlat for strength.In contact with