Shed roof truss system: use a calculator to calculate the truss system. Through what distance do the rafters put in the construction of roofs The distance between the rafters of a gable roof under the slate

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 with its subsequent collapse.

Before proceeding with the installation roofing it is necessary to calculate the truss 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 truss 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 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

In the construction of roofs of various designs, hanging or layered rafters are used. Sloped - used when installing one- or two-slope roofs. They have two points of support - bearing walls or load-bearing wall and ridge beam. Hanging rafters are used when it is necessary to cover large spans or create a sloping roof. In this case, the rafters rest with 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.

Material for rafters

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

Method of calculation

Distance between rafter legs called rafter step. It should not exceed one meter, and the minimum value - 60 cm. Before making a calculation, it is necessary to measure the size of the roof slope. Then we divide the obtained value by the approximate value of the step between the rafters. One is added to the result and rounded up to the next 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 bevel by the number of rafter legs.

For greater clarity, consider an example 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 \u003d 36.625

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

the exact step 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.

The dependence of the pitch of the rafters on the material of the roof

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

Roof truss structure for slate roofs

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 truss system. The distance between the rafters in this case will depend on the cross section of the timber. The optimal value is a distance of 80 cm, which will not only withstand increased weight, but also significant snow and wind loads. In this case, the crate is made with a board at least 3 cm wide. Depending on the type of slate, the crate is made continuous for smooth sheets or sparse for wave ones.

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

Step between rafters for metal tiles

Increasingly widespread among roofing materials acquires a metal tile. Which is characterized by a simple installation process, and will also help to create your own unique look for your home. Sheets of metal tiles are lightweight, which allow you to increase the distance between the rafters from 600 to 950 mm, with a beam section of 150x50 mm. The crate in this case will depend on the pitch 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 cornices, the edges of the bevels, the step of the lathing is made minimal for greater reliability of the roof.

Rafter pitch under corrugated board

Decking is a galvanized steel sheet coated with a special coating that protects it from harmful effects. environment. A large selection of colors and corrugation widths will allow you to create a reliable and aesthetically attractive 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 the roof, 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 of beams with a section of 50-75 mm or from a board 20-50 mm thick and no more than 15 cm wide. sparse - the distance between the boards is 50-75 cm. The step of the rafters under the corrugated board is calculated according to the general scheme and is 60-90 cm.

Step of roof rafters from ondulin

Ondulin is a wavy sheet that has high strength and durability. With such a roof, the truss system is made of pine boards with a section of 50x200 mm, in increments of 60-90 cm. A sparse crate of 40x50 cm is made from above.

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

Determining the pitch of the rafters for a pitched roof

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

The distance between the 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 pitch 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, you can use all types of coatings. 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 the legs. If the spans are more than 6 meters, then the rafter system is additionally reinforced with struts and headstocks, which will not allow the rafter legs to deform under the weight of the roofing material.

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 from changes in 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 is 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 the prerequisites for the use of trees, we note:

Antiseptic treatment
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:

Mauerlat which can be called the foundation of the system. With this part the load is distributed evenly and correctly.
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.
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. It is this product that fixes the individual parts of the system.
Tightening helps feet stay in place, do not move apart. This detail connects them at the bottom.
Racks, as well as struts give additional leg stability.
crate represents boards, as well as bars in a cropped form. She is stuffed perpendicularly, transfers the load to the rafters.
The overhang of the entire roof protects against rainfall.
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.
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 shed type requires special attention, since it is this stage of construction that has the greatest impact on the climate that the structure will be.

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.

Primarily, it is important to increase the total area of interaction of the rafters, 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:

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.
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 the maximum length, it is worth making 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.
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.
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.
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

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 playing decisive role in durability and operational safety: foundation and 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 extensive practical experience in performing such work, only practice allows you to make the best decisions during 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 rafter 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?

Factors affecting the distance between the rafters	Short description
	This factor has an impact only if it is planned to make the roof insulated. The terms of reference for the design should indicate the type and size of the heaters used, and they are different. For example, the standard width of foam plastic and pressed mineral wool is 60 cm. In order to eliminate the formation of cold bridges, facilitate and speed up the process of installing insulation and minimize the amount of unproductive waste, the span between the rafters should be within 56–58 cm. Rolled mineral wool may have width from 120 cm to 100 cm. Accordingly, their installation requires a different step of the rafter legs.
	The greater the distance, the more load each rafter leg takes. This affects its dimensions and the total amount of lumber for the roof. Currently, the tree belongs to a very expensive category of building materials, it is necessary to achieve a reduction in consumption. This is done both by using additional stops of the rafter system for optimal load distribution, and by adjusting the number of rafter legs, which allows to reduce the cross section of the roof elements and save expensive boards.
	Each house has its own architectural features. This refers to the location and number of chimneys and ventilation outlets, the layout of attic spaces, materials for the manufacture of load-bearing walls, the presence of a wooden Mauerlat or a concrete reinforcing belt. Rafters cannot be located above chimneys and ventilation pipes, interfere with the installation skylights etc. Such nuances must be thought out during the design of the building, they also affect the distance between the rafters.

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 the performance characteristics of roofing or their design appearance, but structural and physical differences.

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

All these materials have fundamentally different methods of fixing to the truss system. But they do not have any effect on the step of the rafters.
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.
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 meanings and their own characteristics of influence on the strength of the system.

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.
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 regulatory 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 in the range of 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. The distributed load per linear meter of the leg 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 the standard dimensions of lumber (thickness and width).

Nominal dimensions for thickness and width of edged sawn timber with parallel edges and thicknesses of unedged and edged sawn timber 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, it is necessary to install various types of 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 wood resistance to bending.

They depend on the quality of lumber and the type of wood, taken from the tables of 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 step is 80 cm, the slope angle is 35 °, the length of the working area is 280 cm. The truss system is made of pine, the bending radius of this material of the first grade 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.

Bar prices

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. The dimensions of the rafter boards are known, it is necessary to determine the pitch of the rafters. It is done in this order.

Knowing total load on the roof and the maximum load on one rafter, by a simple arithmetic operation we determine the number of rafter legs. 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

It is pointless to argue about the importance of the roof for any building. It is not for nothing that over a dozen different types of roofs have been invented in the history of mankind, from simple to quite complex in design and construction. An important element when planning the construction of a roof, there is a step between the rafters - strong bars that are the basis of the structure. This will be discussed in this article.

The distance between the base of the roof slopes is not a constant value and depends on the following components:

type of roof;
slope angle;
the type of roofing material to be installed;
rafter section dimensions.

Before proceeding with the process of erecting the upper structure of the house, a calculation should be performed by determining the optimal distance between the rafters.

Gable roof rafter pitch

The most widespread in our country are gable roofs. They are a structure that has two parallel planes, with an angle of inclination relative to the horizon from 20 to 50 degrees.

With an insufficient slope of the gable roof in snowy areas, there is a danger of accumulation of large snow masses, which can lead to the destruction of the structure. An increase in the slope angle in regions with a predominance of strong winds is also fraught with a high load and the risk of breaking not only the roof, but the entire structure as a whole.

Mansard roof truss system

Most private houses have an exploited under-roof space called an attic. This design is characterized by an increased height of the slope, which is caused by the need to create a living space of a comfortable height. Typically, stingrays mansard roof broken lines with a varying angle of inclination. For their installation, a double truss system is used.

The steepness of the lower slopes of the mansard roof significantly exceeds the slope of their upper extensions. The plane load perceived by them is not great. Thanks to this, the rafters in the lower part can be installed with a maximum pitch. The upper ridge slopes are recommended to be mounted with a reduced gap from each other.

Rafters in a shed roof

For outbuildings and some private houses, roofs with one slope are used. Due to the limitation of the angle of inclination, they are high pressure. Experts recommend using lumber of increased cross-section for the rafters of a single-pitched roof, with the installation of a minimum step from each other.

When calculating the distances at which roof beams are installed, special attention should be paid to the amount of snow load in a particular area. With a small slope, this characteristic has great importance. Roofing material for such roofs is best chosen with a minimum dead weight, which will reduce the bending load.

Hip roof truss system

The hip roof truss system is considered the most difficult in construction. This type called four-slope, since the roof is formed not only by the side, but also by additional end slopes, where the installation of the rafters is carried out not on the ridge, but on the corner bowstrings. This places special demands on the organization of the roof frame.

Under hip roof the attic is not often arranged. This is due to the small angle of inclination of the rafters and the roof as a whole. In the case of an increase in the angle of the slopes to the horizon, the distance between the rafters is increased, with a decrease, vice versa. An additional aspect of the calculation is the roofing material used.

The dependence of the pitch of the rafters on the roofing material

In addition to variable snow and wind loads, a constant (static) one also acts on the roof, the force of which depends on the roofing material used. It's no secret that different kinds roofs have their own weight, which can differ by 10 or more times.

The right choice of material affects not only the top, but also all other parts of the structure of a residential building and other buildings. Not without reason, when designing the foundation, it is necessary to decide in advance on the choice of the roof.

Roofing from profiled sheet

Currently, one of the most common roofing materials is a profiled sheet, which is produced galvanized or with subsequent polymer coated. TO distinctive features profiled sheet will include the following parameters:

High corrosion resistance;
As a result, a long (more than 15 years) service life;
Easy installation even without the necessary qualification;
Small sheet weight (weight 1 m 2 is 4-5 kg).

Since this roofing material does not exert a high load on the rafter system, the distance between the elements is chosen as much as possible for a particular angle of inclination. In addition, the profiled sheet does not require high strength characteristics from the roof lathing. All this together allows minimizing the total load on the foundation and walls.

Roofing from a metal tile

The second common type of steel roofing materials is metal tiles. This type of profiled sheet, which successfully imitates natural clay material, but with a lower mass (10 or more). A feature of the rafters under the metal tile is the smaller section size.

When choosing at what distance to install the rafters, first of all, you should be guided by the dynamic load. Like a profiled sheet, a metal tile is not demanding on the size of the rafter legs and is well mounted on a crate made of an inch coniferous board. All this makes a metal roof low-cost.

Rafter system for ondulin

In the 21st century, corrugated sheet materials were replaced by a more durable and lightweight analogue - ondulin. Among others - the most lightweight material. The weight of the sheet does not exceed 6 kg.

The small thickness of ondulin sheets at slope angles of less than 15 ° requires the construction of a continuous crate of plywood sheets, for example, which will require an appropriate rafter pitch. This should be taken into account in the calculations.

slate roof

Not so long ago, a wavy material from an asbestos-cement mixture, called slate, was widespread. High mass and fragility are the main disadvantages, however, even today he finds his fans in the construction of various outbuildings.

A high mass, comparable to the weight of a clay tile, will not allow the use of the same truss system as under a metal tile. Building codes define a minimum angle of slope for a slate roof of 22 degrees or more. Otherwise, the load from the material itself and the truss system with the crate exceeds the permissible parameters. The step of the inclined bars, as well as their cross section, are selected individually in each case.

Polycarbonate roof

V last years Increasingly, on the roofs of verandas and gazebos, an artificial polymer material, polycarbonate, has been used. Produced in two versions - monolithic and honeycomb. The first in its properties is similar to ordinary quartz glass, but significantly exceeds it in strength. The second one has less mechanical properties, but high thermal insulation and light transmission.

Cellular polycarbonate is standardly much lighter than a monolithic counterpart. It is used as a roof without the use of lathing, provided that the step does not exceed ½ of the width of the sheet of material. The high strength of the monolithic analogue also makes it possible to avoid elements transverse to the rafters. Sufficient flexibility allows you to cover semi-circular roofs on a metal frame, the pitch of which does not exceed 0.9 meters.

Thematic material:

Rafters under a soft roof

The original pattern can be obtained through the use of soft roofing materials, which are spread with an adhesive layer. They are installed on a continuous crate made of plywood or OSB. The step of the rafters should allow you to fix the sheets, so it is chosen as a multiple of ½ of the width. Provided standard sizes plywood 1520x1520 mm, the center distance between the rafters will be: 1520: 3 = 506 mm.

Rafter step for insulation

Installation of residential roof spaces often combined with laying sheets of insulation in the rafter gap. The most common plates with dimensions of 600x1000mm. These parameters are used as starting points.

Rafter pitch calculation scheme

By building codes the pitch of the roof rafters is in the range of 0.6 - 1 meter. Its final calculation is performed according to a simple formula, depending on the total length of the roof. For the calculation, you must perform the following list of actions:

determine how much distance should be between the rafters for your specific building conditions. According to the reference book, the magnitude of wind and snow loads in the area is determined.
the length of the roof is divided by the desired distance by adding one. The result will be equal to the number of rafter legs that are installed on one roof slope. If the value is not an integer, it is rounded off.
the length of the roof is divided by the number of rafters calculated above, we get the final step in meters.

For example, with a slope of 30 degrees, the maximum distance between the rafters of a gable roof under a metal tile is 0.6 measure. The length is assumed to be 16 meters. Hence:

16:0,6+1=27,66;
rounding the result, we get 28 rafters per slope;
16:28 \u003d 0.57 meters - the center gap of the rafter legs for these specific conditions.

As you can see, the calculation technology is not complicated, but this is just an approximate scheme. Taking into account many other parameters mentioned above can make certain adjustments.

One of milestones any construction is the construction of the roof of the building, the basis of which is the installation of a truss system. The uniform distribution of the weight of the roof on the frame, the reliability of the roof and the duration of its operation as a whole will completely depend on how correctly the pitch of the rafters is chosen, that is, the distance between them. With any slight calculation error, damage and collapse of the entire roof can occur.

Collection of the required calculated values \u200b\u200bto establish the pitch of the rafters

The rafter system includes the following components:

farms;
ridge and side runs;
Mauerlat;
diagonal elements.

Farms consist of a crossbar, base, rafter legs, binding and fastening elements. The rafter legs are beams located along the slopes, the lower ends of which are connected to the Mauerlat, and the upper ends to the girders.

Rafter pitch is the exact distance between two rafter legs.

To get the exact indicated value, you must first find out the values of some quantities important for this.
All calculations for the roof covering system should be correctly made at the design stage of the house. Such a responsible business can be carried out by yourself or entrusted to its specialists. The more accurate the calculations are, the stronger the base for the roof will be.

In order to correctly make all the required calculations, including the rafter pitch, you need to know:
permanent and temporary loads;

their size;

slope angle;

type of roofing;

material for the manufacture of rafters;

roof type.

One of the indicators that must be taken into account when calculating the pitch of the rafters are permanent and temporary loads. These include:

the weight of the roofing and truss structure;

weight interior decoration roofs;

snow cover weight;

the weight of the person carrying out the maintenance of the roof.

It should be noted that these data are taken in special tables developed by scientists, depending on climatic zones, for various territorial regions.

The angle of the slope can be determined by knowing the length of the wall of the house and the height of the roof. The steeper the roof, the more installed, since the load on such roofs will be transferred mainly to the load-bearing walls. After making further calculations, the length of the rafters is easily calculated. Most often they have standard sizes: 4 and 6 m.

Coniferous wood is well suited for the manufacture of a roofing system. Lumber must be of high quality, without knots, rot. Before work, all wooden elements must be treated with antiseptic special compounds.

The step of the rafters will also depend on the type of roof, that is, on the functional features and its shape. The value of simple and complicated roof will be different.

How the type of roofing will affect the pitch of the rafters should be considered in more detail.

General technology for calculating the distance between the rafters

Having made all the necessary measurements, it is possible to make a constructive calculation of the pitch of the rafters. Based on practice, this indicator is in the range from 0.6 to 1.0 m.

In order to correctly perform this calculation on your own, you must adhere to the following technology:

The total length of the roof slope is taken.

The optimal step of the truss truss is selected.

The length of the slope must be divided by the pitch of the rafters.

One is added to the resulting value.

To get a whole number, the result is rounded up.

This calculation is the number of trusses (rafter legs) located on one roof slope.

Now the entire length of the roof slope is divided by the resulting value, showing the number of trusses. This determines the pitch of the rafters.

It should be noted that this calculation is made in the center of future rafters. However, the calculations cannot be considered accurate and constant. In each case of the construction of the roof of a house, the angle of the roof slope, the features of the selected roofing material, and other indicators are taken into account. In this regard, it is necessary to consider the features of choosing a rafter pitch for the most common roofing materials: metal and ceramic tiles, corrugated board, slate and ondulin.

Features when choosing the distance between the rafters for metal and ceramic tiles

Metal tiles as roofing are extremely common in both urban and suburban construction. The very design of the roof truss system when using metal tiles will differ little from the general scheme. However, due to the fact that this construction material has a small weight, rafters and other elements of the system can be taken with a smaller section, i.e. with a smaller margin of safety. The distance between the rafters when using metal tiles is 60-95 cm. All work on the installation of roofing from metal tiles is much easier than from other roofing materials. A feature of the lathing device of this material is that the board near the cornice should be about 1.5 cm thicker than the others. Usually, the cross section of metal rafters is 50x150 mm.

Ceramic tile is a roofing material that has a significant weight, which is 10 times the weight of a metal tile. In this regard, it is necessary to more thoroughly approach the calculation of the roof truss system. should be slightly increased - up to 60x180 mm. The average distance between the rafters for covering ceramic tiles is set in the range of 0.8-1.3 m. The angle of the slopes of the slopes is necessarily taken into account: the distance between the rafters is made larger, the higher the roof.

The length of the rafter legs in this case will have a strong influence on the result. The distance between the rafters decreases with increasing their length.. With their long length, increased deflection loads may occur, which can be significantly reduced if an additional system of struts, supporting racks and other elements is installed.

Features when choosing a rafter pitch for slate, corrugated board and ondulin

The most common roofing material is slate. This is due to its low cost, ease of installation, and the possibility of replacement if individual elements of the roof are damaged.

The features of the crate for slate is its thinned type, consisting of any type of board or timber, but with a mandatory cross section of at least 30 mm. This is necessary for the correct and high-quality distribution of the weight of the slate on the crate.

The optimal distance between the rafters, when combined with the load from the weight of the slate sheets, should be 80 cm. It is worth constantly taking care of the margin of safety of the truss system, which may be due to various unforeseen circumstances. Otherwise, its installation under a slate roof does not differ from other options.

Now you should pay attention to some features when installing a truss system for roofing materials such as corrugated board and ondulin.

The weight of corrugated board and ondulin is much lighter than that of ceramic tiles or slate, so the technology for installing rafters for these materials is practically no different from installing metal tiles. The distance between the rafters for a corrugated roof is 60-90 cm, and from ondulin - 60-100 cm.

If it is necessary to increase the distance between the rafter legs, it is necessary to strengthen the structure of the system with transverse elements of the crate.

The sheathing device for corrugated board is very similar to the sheathing device made of metal tiles. It is important to remember that in this case, the last board should also be slightly thicker than all the others.

A feature of the installation of the crate for ondulin should be considered the need for its continuous type for high-quality resistance to various loads. In some cases, a thinned type crate can also be used, but then the step between the rafters should be no more than 30 cm.

Thus, being able to produce everything necessary measurements, knowing the basics of installing a truss system for basic roofing materials (tiles, corrugated board, slate and ondulin), you can correctly calculate the distance between the rafters.