The frequency of the rafters on the roof. Shed roof truss system: use a calculator to calculate the truss system
The shed truss system came to us from the USA and Europe. Residents using it noted reliability and cheapness, so the popularity of this type spread very quickly. Despite the fact that a small amount of wood was required for the construction of one slope, few people dared to build such a construction. The fact is that most developers considered such a system too simple for residential buildings, while the other part simply did not know how to build it to prove the opposite. In this article I will try to explain to you how to easily and quickly create such systems and correctly select the pitch of the rafters of a pitched roof.
Basis of calculation
Despite its simplicity, one slope must meet all the installation rules. After all, if serious mistakes are made at the same time, then the roofing will deform, which will inevitably entail not only leaks, but also the collapse of the entire roof.
To achieve maximum stability of the roofing system, it is necessary to pay attention to four components:
- Reliability of fastening of the rafter legs to the support beam and ridge;
- Proper selection of auxiliary parts for the truss system;
- Durable lumber and auxiliary elements;
- Rafter step.
Do not think that by observing only four points you will achieve the most stable design. To do this, you will have to use all known methods and technologies.
Calculation values
You can’t perform calculations without knowing certain indicators, right? Therefore, before starting, you need to make sure that you have four basic values.
In addition to all these indicators, the main task of any project is to calculate the maximum allowable load on the roof. It includes quite a lot of values, and here is a list of elements whose mass is especially important in the calculation:
- rafter legs
- crate
- roofing cake
If you are far from the construction industry, then you will have to remember that the calculation of the maximum roof load consists of two parts. The first one takes into account all the materials used, and the second one contains the snow load of your region. Its meaning is written in a special reference book, which you can easily find on the net.
But even on this, the indicators will not be accurate, because you forgot about the wind load and the weight of the worker himself, who will carry out installation work and subsequent maintenance (repair, cleaning).
When developing a project by a construction organization, they use complex formulas of strength of materials, so if you don’t want to bother with this, you can use the recommendations of experienced people.
How to calculate the required distance between the rafters
The distance between the rafters of a shed roof largely depends on the previously calculated maximum possible step. To determine this value, you will need to have a total load value, roof parameters and data on the wood of the rafter legs.
You can calculate the optimal step of the rafter leg using the following method:
- First of all, you need to find the total length of the roof. This value must include any ends and overhangs;
- The resulting value is divided by the maximum allowable distance between the rafters;
- The answer is rounded up. This number will indicate the number of spans;
- Next, we take the value of the length of the roof and divide it into spans. So you will find the optimal step;
- And to find the number of rafter legs, you need to add one to the spans.
This rule works for the vast majority of roofs, but there are those that cannot be calculated in this way. If you have just such a case, then you will have to acquire an additional rafter on one of the ends. 
Rafter system depending on the roofing
It's no secret that the greater the mass of the roofing, the greater the number of rafter legs must be installed. Most manufacturers of this material in the instructions for their product indicate the optimal number of rafters and their dimensions.
You should not blindly trust these instructions, only if you do not live in the central strip of Russia, because they were written specifically for this territory. Before developing a drawing, it is necessary to carefully study the prevailing winds and draw a kind of rose, which will be a guide for future construction.
It is worth noting that in regions of the country where a large amount of precipitation in the form of snow falls, it is best to create steep roofs with a slope of 35-45 degrees. This will provide fast natural gathering snow cover from the surface.
In most cases, the truss system of private houses is created from logs with a diameter of 12 to 22 centimeters, timber or boards with thicknesses from 40 to 100 and widths from 150 to 220 millimeters.
Rafter system for corrugated board
Roofing corrugated board is a fairly light material and at the same time has good strength characteristics. Therefore, as rafter legs, you can use lumber of a small section, but with a frequent step: 0.6 - 1.2 meters. The roof slope should be at a slope of 12 to 45 degrees.
The required section can be selected based on the span distance between the supports. If the distance is about 3 meters, then the section can be taken 40x150 millimeters, at 4 meters this value increases to 50x180 millimeters, and at 6 meters it is necessary to use lumber whose section is 60x200 millimeters.
By the way, the crate in this matter also plays an important role. In the case when the rafter step is a decent value, you will have to use wider boards. For example, for a step of 0.6 meters, elements with a section of 25x100 millimeters will be needed, and for 1.2 meters - 40x100.
The crate for corrugated board is arranged discharged method, and the step of its elements should be 50-80 centimeters. However, these values \u200b\u200bmay go beyond due to the characteristics of the roofing itself. You can also find tips on how to arrange these parts in the instructions that came with the purchased material.
Rafter system for ceramic tiles
Ceramic tiles are a unique roofing material. It is made of clay, which makes this material very heavy. The designed truss systems must necessarily follow the following requirements:
In the roofing sphere, there are only 3 types of crates. One of them can be arranged at an angle of 12-60 degrees, and the other two at an angle of 20-45 degrees. As elements of the crate for clay tiles, you can most often see a beam with a section of 50x50 millimeters.
Rafters for metal tiles
Due to the fact that metal sheets have a much smaller thickness, you do not have to arrange a serious truss system. Therefore, you can safely follow the advice and recommendations of roofing material manufacturers.
It is worth saying a few words about the only nuance that will allow you to save some lumber. So, it lies in the fact that the minimum step of the crate can be increased to 1 meter. This is due to the dimensions of the sheet material. When a metal tile is tripled, then, as a rule, it is supported by a crate in only a few places, and with a rafter pitch of 0.6 meters, it is impossible to create an “economical” crate, so you have to change it along with the rafter system. 
Rafter structure for ondulin
To date, ondulin has given way to more modern coatings, but despite this, developers whose roofs were laid with asbestos slate began to look at this material as a profitable alternative. It is made on the basis of bitumen and fiberglass, has a low weight and high quality.
The truss system for ondulin must comply with the following parameters:
- The slope of the slope should be in the range from 5 to 45 degrees;
- With a small slope, the step of the rafter legs should be minimal: 0.6 meters, and with a steeper roof, this distance increases to 0.9 meters;
- With a sloping roof, say up to 10 degrees, it is necessary to arrange a continuous crate. To do this, it is best to use moisture-resistant plywood, OSB boards or edged boards with a section of 30x100 or a beam of 40x50 millimeters.
As for the section of the rafter legs themselves, it is selected according to the same rules as for corrugated board.
Rafter system for corrugated asbestos-cement sheets (slate)
Surprisingly, everyone knows the roofing material called "slate", because the vast majority of private houses are covered with this particular product. Due to its rigidity and components, this material has a fairly solid weight, so it is necessary to follow the recommendations for the construction of the truss system so that it does not collapse even before the start of operation.
- The low tightness of the finished plane does not allow the use of slate with a slope of less than 22 degrees, this will lead to leaks. If you cannot find any recommendations for the installation of asbestos-cement sheets (which is unlikely), then you can always use the instructions that came with ondulin;
- The maximum possible slope of the rafters with a slate roof is less than 60 degrees;
- The optimal step of the rafter legs lies in the range from 0.8 to 1.5 meters. Here everything will depend on the load and cross-section of lumber;
- As a rule, a wooden system for slate requires a slightly larger section of the legs than with a light roof. An example is the situation when the pitch of the rafters is 1.2 meters. For the rafters, you will have to take a bar with a section of 75x150 or 100x200;
- As for the crate, its elements will also differ from the step of the rafter legs. If it is up to 1.2 meters, then a bar of 50x50 millimeters will do, and with a larger step - 60x60 millimeters;
- The step of the crate beam should be selected so that one sheet is supported by 3 elements. The slate should extend beyond the edges by 15 centimeters on both sides. For example, if we consider the standard dimensions of an asbestos-cement sheet (175 centimeters), then we can use a crate step of 80 centimeters.
It is probably worth remembering that asbestos is harmful substance, therefore, when working with a material that contains its particles, safety precautions must be observed. Which states that the worker must wear personal protective equipment. 
Rafter system of one and two slopes
Recently, the shed roof is gaining more and more sympathy. It is understandable, because materials are only getting more expensive, and you want to save money. Due to the simple design, this can be done. The rafter system of one slope is quite primitive. To do this, you just need to put the beams on the crown and secure. Of course, do not forget about the insulating material.
The maximum slope of a shed roof can be 30 degrees, and the span is 6 meters (this rule applies to lumber). The most optimal slope is 15-20 degrees. At this angle, the wind load will not cause much harm, but the snow cover will cause some inconvenience. The solution to this problem can be to place your building "downwind", which will allow it to remove the snow mass from the roof in a natural way.
An alternative option for a single-pitched roof is a double-pitched one. It is a number of rectangles connected together with a Mauerlat and a ridge. It is worth noting one interesting fact. When the shape of a triangle approaches an isosceles one, its rigidity increases. In this regard, with a roof slope of up to 60 degrees, it is possible to expand the step between the rafter legs.
But do not flirt with calculations, because this can lead to an increase in windage and lumber consumption. The most optimal slope of the slopes for a gable system is 45 degrees.
If you decide to build a roof yourself, then you will certainly need some tips that will not only make your work easier, but also increase the operational period of your roof as a whole.
- Calculating the structure correctly is not an easy task, but even if it is done correctly, it can be broken if it is incorrectly fastened. Therefore, mounting the rafter legs in their places, do the work with all responsibility. To improve your skills, you can read information on the network, or invite a knowledgeable person to the facility;
- The step of the rafter legs should not affect the thermal insulation in any way. It is worth remembering that the plates can vary slightly in size. Take advantage of this and push them as tightly as possible. In a hardware store, there are standard sizes of insulation boards of 60, 80, 100 and 120 centimeters;
- For most roofs with a slope of less than 45 degrees, it is necessary to include the weight of the worker in the calculation. As for sharper roofs, this is not necessary, therefore, it is possible to reduce the pitch of the rafter legs by 20%;
- Take advantage of modern technology and calculate your roof with online calculators. All you need is to enter the exact parameters;
- Regulatory documents regarding wind and snow load you can find on the net or from the craftsmen at the construction site;
- Any wood used for construction purposes should be dried as much as possible. This will avoid its deformation in the future.
The roof of a building is one of the most important elements of the entire building. If you start saving on a roofing pie, then soon you will face costly repairs that will affect not only this site, but the entire building as a whole. Therefore, if you want to get the maximum operating period from your comfort, then you should not use low-quality materials.
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 elements that 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 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 made and fixed in 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.
There are many different elements in the construction of the roof of a wooden house, 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 of 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 at the 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 pitch 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. The mass of a square meter of a tile reaches 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 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
The construction of the roof of a building is an important stage in the construction of a house, while it is necessary to calculate the pitch of the rafters as accurately as possible, since the reliability and service life of the roof will depend on this.
If the master does not pay attention to the calculations and installs the rafters, focusing only on his own eye, then the frame will turn out to be either too heavy, moreover, expensive, or fragile.
General calculation rules
The step of the rafters is the distance from one to the other rafter leg. It is believed that such a distance is set in the range from 60 cm to 100 - 120 cm (determining the optimal width, you need to take into account the dimensions of waterproofing materials and insulation).
The exact installation step of the rafters for a gable roof can be calculated according to the following scheme:
- measure the length of the slope along the cornice of the roof;
- we divide the measurement data by a certain step (we determined a step of 1 m - we divide by 1, if the step is 0.8 m - we divide by 0.8, etc.);
- add 1 to the resulting number;
- the result is rounded up (in the direction of increase) - we see the number of rafters for installation on one slope of a gable roof;
- we divide the length of the slope by the resulting number and get the exact step between the rafters.
For example, the length of the roof slope is 30.5 meters, given the width of the insulation and waterproofing rolls, a step of 1 meter is selected.
30.5 m / 1 m = 30.5 + 1 = 31.5. Rounding up gives a result of 32. 32 rafters are required for the frame for the roof slope.
30.5 m / 32 pcs. \u003d 0.95 cm - the distance (step) between the centers of the rafters.
However, this formula does not take into account the nuances of certain roofing materials, therefore, in the future, the article will discuss how to calculate the correct pitch of the rafters for the most popular coatings.
It is especially worth highlighting the rafter system during the construction of a hip roof (envelope). The construction of such a roof begins to be built precisely from the hip legs, into which the rest of the rafters then crash.
The hip, which has a length of over 6 m, is often reinforced by sewing it together from two elements. Otherwise, the installation and calculation of the pitch of the rafters for a hip roof are similar to the installation and calculation of a gable roof.
Rafter system for ceramic and metal tiles
The use of metal tiles in the construction of private sector houses is the most common phenomenon, which is facilitated by a number of its positive qualities.
Firstly, this is a small weight of the coating, which facilitates installation and helps to reduce loads on supporting structures.
Secondly, sheets of metal tiles can quickly cover large areas of the roof, which is very convenient, especially if you choose a gable version of the roof.
The step of the rafters under the metal tile is set in the range from 60 to 95 cm, since the relatively small weight of the roof does not require increased resistance. Due to the low weight of the coating, the thickness of the rafters can also be reduced.
As for the thickness of the heat-insulating material used to insulate metal roofs, experts believe that when installing an attic under it, for greater confidence in reliability, thermal insulation of 20 cm can be used, in other cases 15 cm is enough.
A feature of roofs covered with metal tiles is the possibility of condensation.
This can be avoided by organizing ventilation during the installation of the rafters: for this, several holes (about 10 mm in diameter) must be drilled in the rafters at a short distance from the top.
As for the installation of a frame made of rafters under a coating such as natural (ceramic) tiles, it is necessary to remember its large weight.
In comparison with other modern materials, tiles are 10 times heavier or more. Given this feature, experts recommend using exclusively dry wood for it in order to avoid sagging after drying.
For rafters in this case, you need to use a beam with a section of 50 - 60 mm * 150 - 180 mm; the step width of the rafter legs is set in the range of 80 - 130 cm, while the greater the degree of roof slope, the greater the distance between the axes of the rafters.
The pitch of the rafters is also dependent on their length: the greatest length will require the smallest distance, and vice versa. Otherwise, the roof frame will lose the necessary stability.
Given the size of the tile (as a rule, its length does not exceed 40 cm), it is necessary to correctly calculate the width of the step of the crate stuffed onto the rafters.
From the length of the slope, you need to subtract the length of the bottom row and the number of centimeters between the crate and the last bar.
Frame for ondulin, corrugated board and soft roof
Relatively new on the market of materials are such types of roofing as corrugated board and ondulin. At the same time, they are successfully used both in the construction of a gable and hip roof.
The weight of these materials is almost equal to the weight of the metal tile, so the calculation of the width of the rafter pitch will be similar to the calculation when laying metal sheets. The pitch of the rafters for corrugated board is determined from the range of 60 - 90 cm, for ondulin - 60 - 100 cm.
The sufficient thickness of the rafters themselves when covering the roof with ondulin and corrugated board is 50 * 200 mm.
If it is necessary to increase the distance between the centers of the rafters, then you can increase the strength of the transverse crate.
The rule for installing a batten under a corrugated board is similar to installing a batten for a metal tile: the last board must be taken wider than the rest (usually 15 cm thicker).
The crate for ondulin must be made solid to increase the resistance of the material to various weather conditions.
Speaking about the device of the truss system for a soft roof, it is worth remembering the types of such material presented on the markets: this is a roll type of roofing and bituminous tiles.
The name itself suggests that a soft roof requires a very strong foundation that will withstand heavy snow, gusts of wind and heavy rains.
The main requirements for roof frames for soft roofing are that they must be strong and even.
Strength must be calculated for the thickness of the snow typical for the region in which the structure is being built, and for the average weight of an adult male, so that troubleshooting is possible.
A flat roof should be for the reason that to exclude the possibility of sagging under the influence of the above weather phenomena.
Between the axes of the rafters for a roof frame with a soft roof, the step should be small, no more than 50 cm.
If the step is still larger, you will need to make a rough crate, on which the main, solid one will already be mounted.
The counter-lattice will help the soft roof not to bend and increase its service life by an order of magnitude. For a continuous crate, a 30 mm board or a 20 mm OSB board is more often used.
If a soft roof is provided as a covering for a hip roof with the organization of an attic space, then it is necessary to think about its insulation by thinking over a filing for laying insulation, hydro and vapor barrier.
These are all the subtleties of the roof frame device for a soft roof.
Rafter for slate roof
Despite the richness and variety of modern materials, the good old slate remains quite popular. The use of expensive roofing is far from always justified, and it is then that an asbestos-cement sheet comes to the rescue.
The weight of slate is quite impressive, while its installation does not require any kind of grandiose crate. This is because such a roof in itself is quite strong.
For the construction of the roof frame, in this case, rafters with a section of 150 * 40 mm and a bar with a section of 35 * 35 mm for the crate are required.
Lumber for the construction of the frame should be stacked and kept for some time to give the same level of moisture. 
After the drying process is completed, the bend must be determined. Rafter legs are recommended to be installed with the concave part (tray) up - so if water gets on the rafters, it will slide down, bypassing the attic space.
Before starting the installation, the beams are checked for the content of knots in them and rejected, since the knotted material may not withstand the weight of the roof.
Rafter fasteners in this case are produced with nails, the optimal length of which is 15 - 20 cm.
Nails should pierce the timber through, however, the peeking ends should never be bent, since it is necessary to maintain the mobility of the structure.
With drying and deformation of the tree, this technique will prevent cracking of the slate sheets.
The lathing for the device of a slate roof can be continuous or sparse. A solid one is made from a sheet of OSB or plywood and is more often used when laying flat slate.
Sparse is typical for laying wave slate on it. For a sheet with a standard size of 1.75 m, the crate pitch is about 80 cm. There is no point in making the crate more frequent, since the slate has a sufficient margin of safety.
After analyzing the materials of the article, you can independently engage in the construction of a gable and hip roof frame, determining for yourself their features and properties of roofing materials.
It would not be superfluous to recall that the calculation of the rafter pitch is a very responsible task, and it is necessary to approach its markup responsibly, since this will avoid mistakes and speed up the progress of work in the future.
Before the construction of the truss system and the organization of the roof, a number of simple measures must be carried out, which will be the key to the integrity of the structure. This includes choosing the type of roof.
It can be hanging or layered, or maybe a combined version. This is when two types are combined in one building.
Live loads are snow cover on the roof in winter, water flows from rain in summer, wind, the load that a person exerts when carrying out maintenance work during the operation of the roof, etc.
Permanent loads include the weight of the rafter system itself, the weight of the roofing material and the roofing pie, the mass of interior decoration, if it is planned to organize an attic in the attic of the building.
When creating a project for a single-pitched or dual-pitched roof, first of all, they choose the type of truss structure, the angle of inclination of the roof slopes, as well as materials for the construction of the structure. When calculating the distance between the rafters, one should take into account the loads that will affect the roof of the building during operation.
- The weight of the roofing material;
- The weight of the building materials from which the roof truss frame is built;
- Weight of insulation, vapor barrier, waterproofing;
- The weight of the finishing material of the attic or residential attic space.
The following temporary loads also affect the roof of the structure:
- Snow weight;
- The weight of a worker performing maintenance and repair of the roof.
For the correct calculation of the pitch of the rafters, it is necessary to take into account the cross section of the elements of the structure under construction, the presence of thermal insulation of the roof, the type of lathing and roofing. Calculations should be performed on the basis of SNiP 2.01.85 "Loads and impacts".
Video on how to calculate the truss system:
Scheme for calculating the distance between the rafters
All calculations are carried out at the design stage of the building. They are carried out by design engineers of the organization where the house project was ordered.
If the project has not been drawn up and the person relies only on the experience of the masters who are entrusted with the construction of the roof, then in this case you need to familiarize yourself with the relevant documentation. These are SNiP 2.01.85 "Loads and Impacts" and "Changes from SNiP 2.01.85".
There is a detailed calculation scheme and a map of the country's climatic zones.
Further, they are determined with the type of roofing system and the purpose of the attic space. Indeed, depending on whether it is an unheated attic or a living room, the loads on the rafters will be different, and, consequently, the course of calculations also changes.
The calculations must necessarily take into account the climatic zone where the work is carried out, the structural material of the rafters and its cross section.
So, the pitch of the rafters is the distance between the rafter legs. It can vary within 0.6 m - 1.0 m.
Calculation progress:
- First, the length of the roof slope is measured. Further, this value is divided by the step length of the rafters of the selected material. This indicator is taken from the SNIP and is unique for each building material and also depends on the beam section used;
- one is added to the result of previous calculations and rounded up. Thus, an integer value is obtained and it indicates the required number of beams;
- the length of the roof slope is divided by the resulting integer. The result will show how many beams are needed to build a high-quality and durable roof.
Experts point to the following feature of roofs with a steep slope. When erecting them, you can reduce the distance between the rafters. This is due to the transfer of the load from the beams to the wall of the house.
The distance between the rafters for different types of roofs
However, the calculation of the distance between the rafters cannot be carried out so unambiguously. After all, this indicator also depends on the type of structural material used for the roof.
The distance between the beams for a roof made of metal
The average weight exerted on the roof is 35 kg/m². To withstand it, the roof must have a step of 0.6-0.9 m. In this case, a beam with a section of 50x150mm is used. 
However, metal tiles are often used in the construction of country houses and cottages. And in such structures, the attic space is often equipped as a living room.
This leads to the installation of a roofing pie and all kinds of heaters, which, in turn, put an additional load on the rafters. Therefore, it is recommended to increase the cross section of the beam for beams. This is especially true for regions with low air temperatures in winter. The recommended dimensions of the rafters are 50x200mm.
In addition, the distance between the rafters can be adjusted to the width of the insulation. This will not only increase the bearing capacity of the roof, but also simplify the arrangement of the heat-insulating layer, and reduce the consumption of insulation.
The distance between the beams for the roof of corrugated board
The recommended rafter pitch for a roof is 0.6 m - 0.9 m. However, here it is necessary to take into account the operational characteristics of the corrugated board itself. If the step is large, then the corrugated board will “sag” under its own weight, thereby changing the geometry of the roof and its technical characteristics.
To prevent this, you need to mount additional boards with a large section as a crate. They will act in some way as rafters.
The cross section of the rafters for roofing from corrugated board is 50x100 mm or 50x150 mm. The crate is made of a board with a section of 30x100 mm.
The distance between the beams for a roof made of ceramic tiles
Ceramic tiles are a heavy material for roofing. It exerts a load on the rafters in the range of 40-60 kg per m². That is why the distance between the rafters in this case will be minimal - 80-130 cm. The greater the weight, the smaller the distance. However, the latter indicator may decrease, depending on the angle of the roof. The larger it is, the less often you can mount beams.
Installation of the structure for ondulin
The step of the rafter legs under the ondulin should be 60-100 centimeters. For the manufacture of rafters, lumber with a section of 200 × 50 mm is used. This is enough to create the most durable and reliable truss frame.
It should be noted that under this roofing material it is necessary to make a continuous crate. Due to this, the material will better resist snow loads and solar exposure.
Sometimes a thinned type of crate is used. For its manufacture, a wooden beam is used. The distance between adjacent elements should be less than 30 centimeters. This option, as a rule, is more expensive compared to a continuous crate.
Rafter system under slate
Slate roofing is considered the most common in Russia. The main reason is the low cost of this roofing material, the ease and speed of installation work. Also an important advantage is the possibility of replacing individual damaged slate sheets with new ones.
The distance between the rafter legs for a slate roof should be 80 centimeters. This distance is considered the most optimal.
The crate under the slate should be thinned out. For its manufacture, a board or timber with a cross section of at least 30 millimeters is used. It is this thickness of the timber or board that is required for the qualitative distribution of the weight of the roofing and winter precipitation.
When erecting a rafter system, one should remember about a constant margin of safety. It may be needed in case of bad weather and under mechanical stress.
Rafter frame for a soft roof
Soft roofing includes soft tiles, bitumen-polymer and bituminous roll materials, as well as roofing membranes. The main advantages of this type of roof include low weight, as well as the absence of the need to build a massive rafter system.
The minimum pitch of the rafters is 60 centimeters, and the maximum is 150 centimeters. When erecting a rafter frame under a soft roof, the angle of inclination of the slopes should be taken into account. In other words, the smaller the slope of the roof slopes, the less you need to make the distance between the rafter legs for a continuous crate.
The distance between the rafters also depends on the material from which the crate will be made. The greater the thickness of the plywood or OSB sheet, the greater the pitch of the rafters can be.
Roof made of sandwich panels
Roofing of this type, as a rule, is erected on hangar-type buildings or houses made of sip panels. Sandwich panels have bending rigidity, so their installation does not require the installation of traditional rafter legs.
If the spans from the top of the wall to the ridge of the gable roof are small, then the sandwich panels are mounted without additional supports.
With a span length of more than 400 centimeters, it is necessary to install additional runs. When building a roof from sandwich panels on a residential building, a traditional truss frame is often erected. However, in this case, the distance between the rafter legs can be made large, since they serve as a support for the runs.
Choose the distance between the rafters based on the length of the bearing walls and the length of the material for the runs. Roofing made of sandwich panels is able to withstand high operational loads.
Construction of a truss frame for polycarbonate
Recently, polycarbonate is often used in the construction of roofing. It is used in the construction of sheds, winter gardens and arbors. The rafter frame and crate are made of metal or wood.
Polycarbonate differ in weight, which depends on the thickness of the sheet. The step of the crate for polycarbonate should be from 60 to 80 cm. The crate made of metal or wood is attached to the rafters (straight or arched).
The distance between the rafter legs for polycarbonate, as a rule, is 150-230 cm. To correctly calculate the distance between the rafters, it is necessary to take into account the glazing area, the thickness and dimensions of the sheets. It should also be remembered that polycarbonate sheets are mounted with small gaps.
The gable roof is the most popular design in private housing construction. The truss system of a gable roof should provide a support platform for mounting the roof. Properly calculated pitch of the rafters of a gable roof allows you to ensure the strength and stability of the structure to all external loads, create a durable and reliable roofing. This article discusses the design features of the truss system, the calculation and installation procedure. This information will allow you to correctly understand the methodology for creating a gable roof so that you do not ask unnecessary questions to workers during construction.
The distance between the rafters for a gable roof
Among the people involved in the construction of a private or country house, there are constant discussions about the most successful roof design and the number of supporting elements. In order to understand these opinions and take one side or another, it is necessary to consider the general structure of the roof.
There are two types of rafter construction:
hanging.
Layered.
They are used on relatively small houses with a length of supporting elements of not more than 6 m. The structure consists of a number of truss trusses having the shape of an isosceles triangle. The trusses are installed on a strapping made of timber (Mauerlat), interconnected by batten strips. The bearing capacity of hanging rafters is relatively small, but the simplicity of design, economy and high speed of installation are their advantages. There are quite a few options for implementing hanging rafters, which is explained by the prevalence of small buildings that do not need a complex and massive roof structure.
Design layered truss system somewhat more difficult. Along the perimeter of the ceiling of the upper floor, a strong timber is laid - Mauerlat. Two (or more) vertical racks are installed along the longitudinal central axis, the height of which determines the angle of inclination of the slopes. A ridge run is installed between the posts, which runs along the entire length of the roof and serves as a reference line for the rafter legs. Each of them has two points of support - at the bottom it is a Mauerlat, and at the top - a ridge run.
For the formation of additional support, which excludes sagging of the supports, struts are used - inclined strips attached to the rafter legs at an angle close to a straight line and abutting in the lower part against the central lower bar - lying.
The step lag for the roof is the distance between two adjacent rafters. It is determined by the number of lags evenly distributed along the length of the longitudinal axis of the roof. The main supporting structures for the roof are rafters and lathing, forming inclined surfaces with a given geometry and area. The angle of inclination determines the wind and snow loads, and, with an increase in the angle, the wind load increases, and with a decrease, the snow load on the roof.
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What determines the pitch of the rafters
Consider the factors that determine the step between the rafters of a gable roof, in more detail. It must be immediately taken into account that the number of rafters determines the bearing capacity. Reducing their number complicates the installation of insulation, contributes to the sagging of the laths of the crate and the roof installed on them.
At the same time, too frequent placement of rafters also creates difficulties in the installation of insulation. It has to be adjusted in width, which creates waste, i.e. waste of material. Therefore, the size of the heat insulator is often used as a criterion for determining the pitch of the rafters. For example, many types of mineral wool are 60 cm wide, which is quite suitable for most gable roof designs.
In addition, the pitch of the rafters directly depends on their number. This is a calculated value, which is determined based on the bearing capacity of the supporting elements. The loads acting on the roofing, as well as the weight of the roofing itself, are quite large, so a stable and durable structure is needed to accept them. It should be borne in mind that the type of rafter system also matters, since layered rafters are much heavier than hanging rafters, they form a noticeable load on the walls and foundation of the house.
Wind and snow loads are external factors that affect the roof structure. The weight of snow in winter can crush or even break a roof if its design is not properly designed. The SNiP applications contain special data on the average annual amount of snow in different regions. Some of them have up to half a ton of snow per square meter.
In addition to snow, wind creates serious loads. At the same time, if the snow load is static, then the wind effects are sudden and uneven. The wind can rise at any time of the year, both in winter and in summer, which makes us take it seriously. When choosing the angle of inclination, you should find out the strength and direction of the prevailing winds in the region, find out about the possibility of hurricane gusts. Available in SNiP applications.
All these factors determine the parameters of the truss system and the distance between the individual supports.
The dependence of the pitch of the rafters on the material of the roof
There are many types of roofing. Most of them are noticeably outdated and are little used in modern construction. The most popular today are:
profiled sheet.
metal tile.
It should be noted that profiled sheet and corrugated board are one group of profiled coating. Some sources consider them to be different names for the same material, others separate them by wave height. The profiled sheet has a higher wave height, and the corrugated board is somewhat flatter. The first type can be used not only as a roof covering, but also as a material for the construction of fences, fences, metal garages, etc.
The corrugated board has a smaller wave and is intended for laying as a roof. Both materials have a common specific feature - profiling is performed only in the longitudinal direction, which expands their capabilities and allows you to make roofs for round roofs and canopies.
The step of the rafters of the gable roof under the corrugated board is selected taking into account this feature of the material. If the value is too high, it will be possible for the roof to sag between the rafters. In addition, there will be an excessive load on the battens, which may not be ready for it. An important parameter also becomes the area of the slope. The pitch of the rafters of a shed roof under corrugated board is much less than that of a gable roof, since the length of the supporting elements and the magnitude of the load in it increase significantly and require an increased number of supports.
The metal tile looks like a canvas made of natural ceramic tiles. In all its operational qualities, it is very similar to corrugated board or profiled sheet, but physically it has an important feature - the presence of not only longitudinal, but also transverse waves. This allows you to slightly increase the step between the rafters of a gable roof under a metal tile, or be guided when choosing the size of a heat insulator.
When using slate or ondulin, the pitch of the rafters is taken according to the degree of rigidity of these materials. Alternatively, increase the density of the lathing, or install a solid version of thick plywood.
Method for calculating the distance between the rafters
There are two calculation options:
Engineering calculation using appropriate formulas and techniques.
Using online calculators, giving an answer after entering their own initial data.
The first method is only suitable for a professional roof system designer. For an unprepared person, it is extremely difficult to perform such calculations, since various specific data, coefficients, tabular values are needed, which are difficult to find and must be used correctly. Calculations obtained using online calculators are also not recommended for use in real construction, but as an option to refine or verify the results of calculations performed by specialized organizations.
Video description
In the video you can see what the step of the rafters should be:
Conclusion
In conclusion, it should be recalled that all design and calculation activities must be carried out by trained and specially trained specialists. The pitch of the rafters is an important and crucial value that determines the bearing capacity of the roof. The damage caused by the inability to take on existing loads is quite serious and can call into question the possibility of living in a house, so it is necessary to take this issue as seriously as possible.