Calculation of rafter pitch for various roofing materials. The distance between the wooden rafters under the metal tile The step between the rafters of a pitched roof

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

Important. The house has two main architectural 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.

Design and construction truss system can only be done by professionals. 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.

Physical Properties roofing materials, together and 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 a bunch of various 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. mineral wool can have a width of 120 cm to 100 cm. Accordingly, their installation requires a different pitch 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 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 performance characteristics roofing or their design appearance, namely structural and physical differences.

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

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

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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. It means weight 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 buildings, 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 the city or in open areas), the number of storeys, the shape of the roof, etc. It must be borne in mind that in Lately the climate is 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

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Snow guard

Engineers use the formula

Formula 1. Determination of snow load

We have already mentioned that the normative load may 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. Distributed load on running meter legs is determined by the formula

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

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

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

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

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

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

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

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

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When you need to calculate the distance between the rafter legs

Such a need arises very rarely and mainly concerns non-residential premises. For example, the developer already has boards for the manufacture of the truss system, he needs to know at what distance to fix the rafters so that the roof can withstand the calculated loads. That is, you need to do the reverse calculation. If in the standard situation the distance is known and the dimensions of the boards are selected taking into account these parameters, then in the second case the opposite is true. 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 distance between the rafters is one of the key parameters that affect the strength of the structure. Competent calculation of the installation step of the rafters allows you to build a roof that is resistant to high operational loads.

Roof loads and rafter system calculation

Development of a single-slope or gable roof begins with the choice of the type of truss system, the angle of inclination of the slopes (roof height) and materials for the construction of the structure. The calculation of the distance between the rafter legs is carried out taking into account the loads that the roof will experience during operation. Permanent loads include:

the weight of the materials from which the truss system is made;
roofing weight;
weight of roofing cake materials (waterproofing, vapor barrier, insulation);
the weight of the finishing elements of a residential attic or attic.

In addition to permanent loads, the roof also experiences temporary ones, which include:

snow cover weight;

the weight of a person during the maintenance and repair of the roof.

A step is the distance between the rafters of one slope. When calculating a shed, gable or complex roof, the following scheme is usually followed:

the length of the future roof slope is measured;
the resulting value is divided by the optimal numerical value of the pitch of the rafters;
one is added to the obtained value, the result is rounded off;
the length of the roof slope is divided by the rounded result.

The final result will determine how far the rafter legs should be placed. The determination of the step cannot be extremely accurate, since it is necessary to take into account a number of additional factors, including the width of the insulation, the installation features of the crate under different kinds roofing material. If a roof with a chimney is being designed, the pitch can be adjusted according to its location so that it is not necessary to remove part of the rafter in the future and install a supporting structure, such as a special rafter system.

The distance between the rafters under the slate

Slate is a traditional roofing material. Its advantages include such characteristics as resistance to external influences (excluding mechanical ones) and low cost. Slate allows you to create a roofing, the repair of which can be reduced to replacement individual elements. Slate is heavy and requires the installation of a sufficiently powerful truss system. The calculation of the distance at which it is necessary to put the rafters under the slate is carried out taking into account the cross section of the beam for the manufacture of rafter legs.

The optimal solution is to install the system under the slate, in which the gap between the rafters must be at least 800 mm. In order for the slate structure to withstand not only the weight of the material, but also increased external loads, the crate is made of timber or boards with a cross section of at least 30 mm. When calculating the truss system for slate, it should be read that this material has rather large restrictions on the choice of the angle of inclination of the slopes.

Rafters for metal roofing

Metal tiles are actively used as a practical and aesthetic roofing material when arranging a shed, gable, hip or complex roof. The frame for the metal tile is built according to standard principles. To calculate at what distance it is better to place the rafters, it is necessary to take into account the loads and the angle of the roof. The metal tile is characterized by relatively low weight, so it can serve as a replacement for the old roofing of slate or ceramic tiles. In this case, the rafters do not need to be strengthened or the pitch of their installation changed.

The standard step of rafters for metal tiles is 600-900 mm. The cross section of the elements can be 50-150 mm - this is enough to create a reliable frame for a metal tile. But if it is planned to use insulation, the layer of which in areas with low winter temperatures should be 200 mm, it is recommended to use a 200x50 beam for rafters under metal tiles so as not to mount an additional system that holds the insulation. The gap between the rafters under the metal tile is best adjusted to the width of the sheet or roll heat insulator.

Decking: rafters and crate

The professional flooring belongs to easy and convenient roofing materials in application. Galvanized or coated with a decorative and protective layer, corrugated board can be used both for mounting a shed roof of a utility room or garage, and for a gable roof of a residential building. How to calculate the distance required to install the rafters under the corrugated board?

To ensure the necessary rigidity of the structure, it is enough to install the rafters under the corrugated board in increments of 600-900 mm. In this case, it is necessary to pay attention to the angle of the roof. The calculation shows that with high external loads, it is better to lay the corrugated board on the system with a minimum step. But if the distance between the rafters under the corrugated board is close to the maximum, and the angle of the roof slope is small, then the structure is strengthened by using a more frequent crate. In this case, the step of the crate under the corrugated board should be about 50 mm, the width of the elements should be at least 100 mm.

Rafter system for soft roofing

Soft roofing includes bituminous and bitumen-polymer roll materials, roofing membranes, as well as soft tiles. A soft roof is characterized by a relatively low weight and no need to install a massive truss structure.

The minimum distance between the rafters is 600 mm, the maximum is 1500 mm. When installing the support under soft roof it is important to take into account the angle of inclination of the slopes: the smaller the angle, the smaller the distance between the supports for a continuous crate should be. The choice of step is also influenced by the thickness of the material for the crate - the thicker the sheet of plywood or OSB, the greater the installation step of the rafter legs can be.

Ondulin: calculation of rafters

Ondulin (bituminous slate) is laid on a flat continuous crate made of sheet material. This allows the roofing to successfully resist wind and snow loads. The crate under the ondulin rests on the rafters, which should be located in increments of 600 - 1000 mm, depending on the angle of inclination of the gable or pitched roof.

Rafters for ondulin are made of timber with a section of 200 × 50 mm. When choosing at what distance to put the rafter legs for the structure under the ondulin, it is recommended to take into account the width of the insulation material in order to simplify its installation. This calculation allows you to reduce the financial costs of arranging the roof.

Sandwich panel roof

Sandwich roofing is most often erected on sip-panel houses or hangar-type buildings. A feature of the sandwich is its bending rigidity, which makes it possible to dispense with the installation of traditional rafters. Small spans from the ridge of a gable roof to the upper part of the wall (or the distance between the supporting structures of a shed roof) allow the installation of a sandwich without additional supports.

If the span length exceeds 4 meters, additional purlins must be installed. To install a sandwich roof on a residential building, a traditional rafter system is often installed, but in this case the rafters can be positioned with a large step - they serve as a support for the girders. The distance between the rafter legs is selected based on the length of the available material for the runs and the length of the load-bearing walls. The technical parameters of the sandwich allow the roof to withstand high operating loads.

Polycarbonate: erection of a supporting structure

Polycarbonate has recently been actively used as a roofing material. First of all, polycarbonate is in demand in the construction of gazebos, sheds, winter gardens. The crate and truss system for polycarbonate can be made of wood or metal.

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 (determined by optimum width, you need to take into account the dimensions of waterproofing materials and insulation).

The exact installation step of the rafters for gable roof can be calculated as follows:

measure the length of the slope along the eaves 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 thermal insulation material, used for insulating roofs made of metal tiles, 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 is more often used or OSB board 20 mm.

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 wealth and diversity modern materials, 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.

The reliability of the roof and its service life mainly depend on how correctly the calculations are made.

One of the most important parameters of the rafter system is how far apart the rafters are located.

After all, the distribution of the load on the frame depends precisely on this desired parameter.

If the calculation is made incorrectly, then deformation may occur and the roof will collapse.

Therefore, it is extremely important to perform an accurate calculation of the interval between the rafter legs when drawing up a roof project.

Basic provisions of the calculation

The pitch of the rafters is the distance from one rafter leg to the other.

In the construction of roofs of private houses, this value is 1 meter.

But this figure is approximate.

To obtain Exact size interval, it is necessary to calculate the bearing capacity of the truss system of the selected type.

To perform the correct calculation, the following scheme should be used:

first you need to determine the length of the roof slope;
now the resulting figure should be divided by the value of the approximately selected rafter step. If you previously chose its value of 1 meter, then you need to divide by 1. If you chose 0.8, then you should divide by 0.8, etc.;
after that, one is added to the result obtained and the resulting value is rounded up. This action is necessary in order to get the exact number of rafters that will need to be installed on one slope;
the total length of the slope must be divided by the number of rafter legs obtained in the previous calculation. And we get the exact distance between them.

To better understand everything, let's look at an example.

By measuring the length of the roof slope, we got 27.5 meters.

We choose a step of 1 meter to make it more convenient to count.

Further calculations will look like this:

Now we add the unit 27.5 m + 1 = 28.5 m.

We round up to the nearest value and get the number 29.

That is, 29 rafter legs must be installed on one slope of our roof.

Now we divide the length of the roof by their number: 27.5 / 29 \u003d 0.95 m.

So, in our case, the step of the rafter legs should be 0.95 meters.

This is a general calculation.

In which the peculiarity of a particular roofing material is not taken into account.

And he can significantly change this parameter.

When you know what kind of material you will use on the roof, some changes will have to be made to the calculation procedure.

Optimal and minimum value

The step is the unit of account.

After all, it depends, first of all, on the load on the roof frame and the section of the rafter legs.

You can take a thick board for their construction and make the interval between them 120 cm.

At this distance, the crate may begin to sag.

Yes, and how to lay the heater?

Indeed, for most materials, the width is 1 meter.

So they take an approximate step of 1 meter when calculating.

The minimum distance between the rafter legs is 70 cm.

And to obtain the optimal value for each material, it is necessary to perform a calculation.

Determining the pitch for a pitched roof

Shed roofing is the simplest.

Indeed, in the truss farm of such a roof there are only rafter legs.

There are no struts, racks, braces in its design.

Such a roof is usually arranged on garages, outbuildings, baths.

In order to determine the pitch of the rafters on a pitched roof, you can use the table:

As can be seen from the table, rafter step depends on their length and cross section.

Distance between rafters for a gable roof

A gable roof is much more common than a shed roof.

And to explain such popularity is simple: the design is very simple, but for all its simplicity, the gable roof is distinguished by its reliability.

Its design is easy to adjust to any climatic conditions and any roofing material.

When calculating the pitch of the rafters of a gable roof, everything is performed according to the general calculation system (see above).

If the slopes have the same length, then it is enough to perform calculations for one slope.

If the slopes are of different lengths, then the calculation is performed for each slope.

It should be remembered that the limit values for the pitch of the rafter legs are 70 and 120 cm.

Ondulin

If ondulin is used as a roofing material, then the rafter system is constructed from pine boards with a section of 50 x 200 mm, and the rafters should be located at a distance of at least 60 cm and not more than 90 cm from each other.

A crate of timber with a section of 40 x 50 mm is laid on top.

metal tile

Metal roofing during construction country houses used most often.

Because this material is much lighter than ceramic or cement tiles.

Although according to appearance very similar to her.

The light weight of the metal tile makes it possible to use boards of a smaller section when creating the rafter system, and to use thinner bars for the crate.

More about the counter-lattice under the metal tile.

About the hip roof with hanging rafters at the link. Also about the design of hanging rafters.

About the price of Viking metal tiles here. Specifications, photos, reviews.

Reducing the size of the elements of the rafter leg system, in turn, reduces the load on the walls of the building and its foundation.

During the construction of the rafter system under the metal tile, the rafters are mounted in increments of 60 - 95 cm.

The cross section of the material is 50 x 150 mm.

According to experts, if a heater having a thickness of 150 mm is placed between the rafters, then the most comfortable living conditions will be created in the attic.

To ensure ventilation of the space where the insulation is laid, when installing the rafter system, holes will be drilled near the upper roof with a diameter of 12 mm.

The technology for manufacturing a truss system for metal tiles does not differ significantly from the technology for manufacturing a frame for other roofing materials.

Its only difference is the installation at the top.

The upper support is mounted not on the side of the ridge beam, but on the ridge run.

The presence of a free zone between the rafters allows the air to fully circulate under the flooring, which helps to protect against the formation of condensate.

Ceramic tiles

The design of the system for ceramic tiles has its own characteristics.

After all, clay is used to make such a roofing material.

And this is very heavy material.

If we compare metal and ceramic tiles, the latter weighs 10 times more.

Accordingly, the truss system is significantly different.

On 1 square meter of the roof surface there is a load of 40 - 60 kg, depending on the manufacturer and brand of the product.

The rafters for such a frame system are made from wood that has been dried for a long time.

Such wood should have a moisture content of no more than 15%.

A beam with a section of 50 x 150 or 60 x 180 mm is used.

So more reliable.

And the distance between the rafter legs can be 80 - 130 cm.

The exact value can be called if the angle of inclination of the slopes is known.

If the angle of inclination is 15 degrees, then the pitch of the rafters will be 80 cm.

And if the angle of inclination, for example, is 75 degrees, then the step can be larger - 130 cm.

More than 130 cm interval between the rafters do not.

Also, when calculating the pitch of the rafters, their length is taken into account.

The larger the dyne, the smaller the distance between them.

The shorter the rafter legs, the greater the distance can be.

If the angle of inclination is 45 degrees, then the roofer can safely move along the roof if the pitch of the rafters is 80 cm.

Decking

When creating a rafter system for corrugated board, the minimum distance between the rafter legs is 60 cm.

The maximum value is 90 cm.

If for some reason the pitch of the rafters was more than 90 cm, then it becomes necessary to install large cross-section boards.

The rafter legs themselves can have a section of 50 x 100 or 50 x 150 mm.

Slate

Despite the emergence of a large number of new roofing materials, asbestos-cement slate remains one of the most popular.

If it is planned to lay slate on the roof, then the rafters should have a section of 50 x 100 or 50 x 150 mm.

The distance between them is made not less than 60 and not more than 80 cm.

The crate is made from a bar having a section of 50 x 50 mm or a board with a section of 25 x 100 mm.

When device any building structure It should be remembered that there are still unforeseen situations.

And, therefore, when calculating the sections of the rafters and the distance between them, it is necessary to provide for a margin of safety.

about the installation of the truss system.

Sergey Novozhilov is an expert in roofing materials with 9 years of experience practical work in the field of engineering solutions in construction.

Source: http://ProRoofer.ru/montaz/stropilnye-sistemy/rasstoyanie-mezhdu-stropilami.html

The distance between the rafters of a gable roof and the pitch of the rafters

The quality and durability of the roof largely depend on the correct calculation of the pitch of the rafters. It affects the laying of insulation, the fastening of roofing material and the installation of additional parts.

Pay attention only to the requirements for the distance under the roofing sheets, then there may be problems with the insulation boards. And vice versa, adjusting the size of the insulation can make the frame too weak, and in winter there will be a threat of collapse.

The basics of determining the pitch of the rafters

As a rule, the pitch between the rafters depends on several factors. But usually the distance fluctuates between 0.6 and 1.2 meters. These figures are rounded, in practice the distance may differ by several centimeters downwards. For an accurate determination, the following calculations must be performed:

Determine the length of the slope by measuring along the eaves of the house. Suppose that it turned out 17.8 meters.
Divide the figure obtained by the planned step of the rafters. If it was decided that the distance between the beams would be 0.8 meters, then 17.8 / 0.8 = 22.25.
Further, we round the result up and add one: 23 + 1 = 24. At this stage, the number of rafters required is determined.
Now we calculate the distance between the axes of the beams. To do this, the length of the slope must be divided by the number of rafters: 17.8 / 24 \u003d 0.74 m.

So, you will determine the actual distance at which the rafters for a roof made of metal or some other material should stand.

Often, when planning a roof frame, specialized calculators are used. They enter basic data and get the finished result. Nevertheless, you should not completely trust the program, since only a person can take into account some conditions. When calculating, you can understand how the system works, what loads are acting. If necessary, adjustments are made to strengthen or facilitate the design. Self-calculation will help to more accurately determine the required pitch of the rafters of a gable and single-pitched roof.

Step calculation depending on the roofing material

For each coating, its own standards and dimensions are developed for the truss system. The main factors are the strength of the material, its weight and resistance to external loads. Consider the main types of coatings.

Decking

The step of the rafters under the corrugated board can vary from 0.6 to 0.9 m. The final result depends on additional conditions, which we will discuss below. If for some reason the step should be larger, a transverse board with a large section is added. In this case, usually the rafters themselves are chosen with dimensions of 50x100 or 50x150 mm.

In addition to the rafters, a crate of 30x100 millimeters is used. The gap between the boards should be about 0.5 meters. It can be more, it all depends on the type of corrugated board and the height of the wave. Sheathing boards protruding beyond the boundaries of the eaves should have a thickness of 1.5 cm more than usual. This is done based on the need to mount ventilation, a chimney or a drain.

Ceramic tiles

The main difficulty in designing a roof frame for ceramic tiles is the large weight of the material for the roof. It is 10 times heavier than corrugated board and accounts for 40 to 60 kg per square meter.

Under such a coating, dry beams are used, with a moisture content of only 15%. Their cross section should be either 50x150 or 60x180 mm. With such indicators, the maximum allowable distance between the rafters can be 1.3 meters. The minimum allowable step through which rafters can be placed is 0.8 m. The roof slope affects the final decision: at 15 °, the step is 0.8 m, at 75 ° - 1.3 m.

The length of the rafter leg is also taken into account, the shorter it is, the larger the gap, and vice versa. In addition, if the slope is less than 45 °, and movement is planned on the surface, the beams are placed in increments of no more than 0.85 m.

The distance between the boards of the crate is selected so that each intersection of the tiles has its own base. The standard length of the material is 400 mm, and the amount of overlap during installation varies between 55 and 90 mm. It turns out that the distance between the central axes of the crate can be either 310 or 345 millimeters.

metal tile

In recent years, the question has been particularly acute: how to determine the distance between the rafters under the metal tile? It imitates more expensive ceramic material, but at the same time it has the positive properties of corrugated board. Installation of such a coating is simple and does not require large financial costs. All this makes the material attractive for the roofs of private houses.

The mass of metal tiles is less than ceramic, so a simpler frame is required. The section of the beams is reduced to 50x150 mm and the step between the crate is increased. The step of the rafters under the metal tile varies between 0.6 and 0.95 m.

Ondulin

The allowable step for covering from ondulin is 0.6-0.9 meters. The standard section of the rafters is 50x200 millimeters. Such dimensions will allow to withstand the load of the roofing pie on the gable roof.

On top of the counter-lattice, a crate of bars measuring 40x50 millimeters is attached. The pitch between the central axis is 600 mm.

Additional factors

When calculating the pitch of the rafters, attention is paid not only to the type of roofing. Many other points are taken into account, data on which can be found in reference books and SNiPs. Here are some of the factors:

Snow and wind loads. The more snow falls in winter and the stronger the winds blow, the smaller the distance between the beams should be. But, if you increase the angle of the roof slope over 45 °, then it is allowed to increase the step.
Choice of heater. To reduce the cost of insulation boards, it is recommended to take into account their standard sizes. They produce mats with a width of 600, 800 and 1200 mm. If this condition is neglected, then a large number of undercuts will appear, cold bridges and construction will be delayed.
lumber quality. It takes into account the type of wood, grade and section. As mentioned above, strength is affected by how well the beam was dried. When buying wood, pay attention to evenness and the presence of defects in the form of knots and traces of pests.
Floor beams and puffs. If you equip under a gable roof attic floor, then the maximum distance between the rafters should be 0.75 meters.

The calculation of the distance between the beams for a gable and single-pitched roof is different. Even if he makes several slopes, for each it is necessary to make a calculation individually. This is especially true for buildings with different lengths of cornices.

Taking into account all these factors, it is possible to determine how far the rafters should be installed. Although all calculations can be done independently, since reference data is freely available, it is better to turn to professionals. They have experience in designing, they will quickly determine the required distance between the rafters. So, you will avoid possible mistakes and be sure of safety.

Source: https://build-experts.ru/shag-stropil/

Roof loads and rafter system calculation

The development of a single-pitched or dual-pitched roof project begins with the choice of the type of truss system, the angle of inclination of the slopes (roof height) and materials for the construction of the structure. The calculation of the distance between the rafter legs is carried out taking into account the loads that the roof will experience during operation. Permanent loads include :

the weight of the materials from which the truss system is made;
roofing weight;
weight of roofing cake materials (waterproofing, vapor barrier, insulation);
the weight of the finishing elements of a residential attic or attic.

In addition to permanent loads, the roof also experiences temporary ones, which include :

snow cover weight;

the weight of a person during the maintenance and repair of the roof.

A step is the distance between the rafters of one slope. When calculating a shed, gable or complex roof, the following scheme is usually followed :

the length of the future roof slope is measured;
the resulting value is divided by the optimal numerical value of the pitch of the rafters;
one is added to the obtained value, the result is rounded off;
the length of the roof slope is divided by the rounded result.

The final result will determine how far the rafter legs should be placed.

The determination of the step cannot be extremely accurate, since it is necessary to take into account a number of additional factors, including the width of the insulation, the particular installation of the crate for various types of roofing material.

If a roof with a chimney is being designed, the pitch can be adjusted according to its location so that it is not necessary to remove part of the rafter in the future and install a supporting structure, such as a special rafter system.

The distance between the rafters under the slate

Slate is a traditional roofing material. Its advantages include such characteristics as resistance to external influences (excluding mechanical ones) and low cost. Slate allows you to create a roofing, the repair of which can be reduced to the replacement of individual elements. Slate is heavy and requires the installation of a sufficiently powerful truss system. The calculation of the distance at which it is necessary to put the rafters under the slate is carried out taking into account the cross section of the beam for the manufacture of rafter legs.

Rafters for metal roofing

Metal tiles are actively used as a practical and aesthetic roofing material when arranging a shed, gable, hip or complex roof. The frame for the metal tile is built according to standard principles.

To calculate at what distance it is better to place the rafters, it is necessary to take into account the loads and the angle of the roof. The metal tile is characterized by relatively low weight, so it can serve as a replacement for the old roofing of slate or ceramic tiles.

In this case, the rafters do not need to be strengthened or the pitch of their installation changed.

The standard step of rafters for metal tiles is 600-900 mm. The cross section of the elements can be 50-150 mm - this is enough to create a reliable frame for a metal tile.

But if it is planned to use insulation, the layer of which in areas with low winter temperatures should be 200 mm, it is recommended to use a 200x50 beam for rafters under metal tiles so as not to mount an additional system that holds the insulation.

The gap between the rafters under the metal tile is best adjusted to the width of the sheet or roll heat insulator.

Decking: rafters and crate

The calculation shows that with high external loads, it is better to lay the corrugated board on the system with a minimum step.

But if the distance between the rafters under the corrugated board is close to the maximum, and the angle of the roof slope is small, then the structure is strengthened by using a more frequent crate. In this case, the step of the crate under the corrugated board should be about 50 mm, the width of the elements should be at least 100 mm.

Rafter system for soft roofing

The minimum distance between the rafters is 600 mm, the maximum is 1500 mm. When installing a support under a soft roof, it is important to take into account the angle of inclination of the slopes: the smaller the angle, the smaller the distance between the supports for a continuous crate should be. The choice of step is also influenced by the thickness of the material for the crate - the thicker the sheet of plywood or OSB, the greater the installation step of the rafter legs can be.

Ondulin: calculation of rafters

Ondulin (bituminous slate) is laid on a flat, continuous crate made of sheet material. This allows the roofing to successfully resist wind and snow loads. The crate under the ondulin rests on the rafters, which should be located in increments of 600 - 1000 mm, depending on the angle of inclination of the gable or shed roof.

Sandwich panel roof

Polycarbonate: erection of a supporting structure

Polycarbonate varies in weight depending on the thickness of the sheet. The crate for polycarbonate is recommended to be done in increments of 600-800 mm. The crate (wooden or metal) is mounted on rafters, which can be straight or arched.

Usually the gap between the rafters for polycarbonate is from 1500 to 2300 mm.

Source: http://krovlya-mp.ru/shag-stropil-dvuskatnoj-kryshi.html

The distance between the rafters: what step should be between the rafters

The task of correctly calculating the distance between the rafters is very responsible. Not only the reliability and durability of the roof, but also all subsequent work on it will depend on how seriously you begin to solve it: laying insulation, installing roofing, installing additional elements. If you manipulate the step of the rafters under the roof sheets, as many do, then it is not a fact that a heater will then enter between the rafters.

If you focus only on insulation, the very first winter with its abundant Russian snow will crush the truss system. That is why the whole point is to choose the optimal rafter pitch for all slopes, and now we will teach you this skill.

Here is a good video tutorial on how to independently calculate the distance between the rafters:

What determines the pitch of the rafters?

So, the distance between the rafters is determined by such important factors:

The shape of the roof (gable, single-pitched or multi-pitched).
Roof angle.
The parameters of the timber that is used for the manufacture of rafters (width, thickness).
The design of the truss system (layered, hanging or sliding).
The totality of all loads on the roof (covering weight, atmospheric phenomena, etc.).
Lathing material (20x100 or 50x50) and its parameters (solid, with gaps of 10 cm, 20 cm or solid plywood)

And each of these parameters must be taken into account, which is exactly what this article is about.

Online calculators vs. notebook and pencil

Today, there are many complex formulas for the correct calculation of the cross section of the rafters and the step of their installation. But remember that such formulas were at one time developed more in order to be able not only to ideally calculate the roof constructs, but to study the work of such elements.

For example, simple online programs that calculate the parameters of rafters are popular today. But ideally, if you can independently set specific tasks and calculate everything you need.

It is important to understand to the smallest detail what exactly happens in the truss system during operation, what kind of forces act on it and what loads. And a computer program cannot always take into account everything that the human brain notices.

Decorative rafters: 0% load

First of all, decide on the most important point: the type of roof and its purpose. The fact is that the roof of a residential building in winter can withstand a large cap of snow, a constant wind at a height, and it is often insulated from the inside, but to the rafter system small gazebo, hidden under the crowns of trees, have completely different requirements.

For example, if you are building a pergola in its classical sense, then it does not matter at all what exactly the distance between the rafters will be - this is already a purely aesthetic factor:

In the above illustration, it can be seen that even in such a building there is a step of rafters. After all, here it provides both an aesthetic factor and the rigidity of the structure itself. But the step is chosen arbitrarily.

Functional rafters: detailed calculation

We approach the main question: what distance should be between the roof rafters of a residential building? Here, be patient and carefully study all the nuances.

Item 1. Wall length and rafter spacing

First of all, the step of installing rafters on the roof of a residential building is usually chosen according to the structural size of the building, although taking into account many other factors.

For example, it is easiest to install rafters in increments of 1 meter, so for a wall 6 meters long, 7 rafters are installed as standard. At the same time, you can save money by placing them with a distance of 1 and 2 meters, and you get exactly 5 rafters. It can also be placed with a distance of 2 and 3 meters, but reinforced with a crate. But it is highly undesirable to make a step of rafters more than 2 meters.

Item 2. Influence of snow and wind loads on the shape of the roof

So, we settled on the fact that the average distance between the rafters of an ordinary roof is 1 meter. But, if there is a significant snow or wind load in the area, or the roof is more or less flat or simply heavy (for example, covered with clay tiles), then this distance must be reduced to 60-80 cm. But on a roof with a slope of more than 45 degrees, it can be even zoom to a distance of 1.2m-1.4m.

Why is it so important? Let's figure it out. The fact is that the air flow collides on its way with the wall under the roof of the building, and turbulence occurs there, after which the wind hits the eaves of the roof. It turns out that the wind flow, as it were, goes around the slope of the roof, but at the same time trying to raise it. And in the roof at this moment there are forces that are ready to rip or overturn it - these are two windward sides and one lifting.

There is another force that arises from wind pressure and acts perpendicular to the slope, trying to push the roof slope inwards. And the greater the angle of inclination of the roof slope, the more important are the safe wind forces and the less tangential. And the larger the angle of the slope, the less often you need to put rafters.

To understand whether you should make a high roof or a flat one, this map of the average wind load will help:

The second point: in the Russian region, such an atmospheric phenomenon as snow constantly affects the standard roof of a house. And here, too, you need to consider that the snow bag usually accumulates more on one side of the roof than on the other.

That is why in such places where such a bag is possible, it is necessary to insert paired rafter legs or make a continuous crate. The easiest way to determine such places is by the wind rose: single rafters are placed on the windward side, and paired rafters on the leeward side.

If you are building a house for the first time, then you will not find your own worldview, but determine the average snow load for your area according to official data:

Point 3. The issue of insulation and the standard width of mats

If you will insulate the roof, then it is advisable to set the pitch of the rafters under the standard dimensions of the insulation boards, which are 60, 80 cm and 120 cm.

Modern heaters today are sold in standard widths, usually at the same standard rafter spacing. If you then take them and adjust them to existing parameters, then there will be a lot of waste, cracks, cold bridges and other problems.

Point 4. The quality and strength of the lumber used

Of great importance is also what kind of material you use to build the truss system. So, for each type of wood there is its own regulatory documentation, which concerns its bearing capacity:

Because for the manufacture of the roof truss system in Russia, pine and spruce are most often used, their bending strength and features of use have long been prescribed. If you use wood of other species, then you can display the correction factor.

In addition, if there are sections, cuts or bolt holes on the rafter, in this place it is necessary to calculate the bearing capacity of the bar with a factor of 0.80.

Item 5. Distance between puffs and floor beams

One more thing: if the roof is built with interconnected roof trusses, and their lower belt is used simultaneously as floor beams, then the distance between the trusses must be made within 60-75 cm to take into account the design of the future floor.

Item 6. Loads on truss nodes

So, here are the main loads that act on the roof truss system:

Static, which includes the weight of the rafter system itself, the weight of the roof, snow lying on the roof and additional elements.
Dynamic, which includes wind force, unexpected damage to the roof, the weight of a person and equipment for repairs, and similar factors.

And all these factors can certain moment affect the roof at the same time, and therefore there is such a thing as a critical value. This is exactly the value of the loads at which the roof does not withstand and deforms.

Therefore, if the building is being built with significant spans, then steel truss trusses are necessarily used. The fact is that there is no tension in such rods, and the entire load falls on the nodes - here they are affected by compressive and tensile forces. And the distance between such farms is calculated depending on the type of roof and the design of the roof itself.

Usually, a unified truss is placed with a span that is a multiple of six, and therefore a distance is made between the truss nodes that is a multiple of one and a half meters.

Item 7. Weight of the rafter system and roofing cake

Do not forget that the main purpose of the rafters is to hold the entire roof on itself, and its weight is crucial:

Point 8. Ease of installation of roofing

The distance between the rafters is also influenced by such a factor as the selected roofing. The higher the slope of the roof, the more roofing materials will be used. And the heavier they are, the more often you will have to put rafters under them. But what about a full slab? The fact of the matter is that it also has its own weight:

Each type of roof has its own optimal rafter pitch. After all, many standard sheets at the edges need to be fixed directly to the rafter or crate, and it is important that they match. Otherwise, roofing work will easily turn into a living hell at a height, believe me.

That is why, even before starting installation, it is necessary to make a layout, check everything several times. And to know some important subtleties for each type of coating.

Determining the totality of loads on the roof as a whole and the rafters separately

So, we have determined that, in addition to other design factors, a whole set of loads simultaneously acts on the roof truss system: the weight of the truss system, a snow cap, wind pressure. After you add all the loads together, be sure to multiply them by a factor of 1.1. So you all count on unexpected favorable conditions, that is, lay an additional 10% percent strength.

And now you just have to divide the total load by the planned number of rafters and see if each of them will cope with its task. If it seems that the design will be frail - feel free to add 1-2 rafters to the total, and you will be calm for your home.

You need to make a calculation for destruction, i.e. to the full load that acts on the roof. All these loads are determined by technical specifications materials and SNiPam.

The standard roof structure is rafters, lattice runs, and each of these elements works only on the load that puts pressure on it, and not on the overall roof as a whole. Those.

each individual rafter has its own load, total, but divided by the number of rafter legs, and by changing the step of their location, you change the load collection area on the rafters - reducing it or increasing it.

And, if it is inconvenient for you to change the pitch of the rafters, then work with the parameters of the section of the rafter legs, and the total bearing capacity of the roof will increase significantly:

In this calculation, try to ensure that the longest rafter in your project is no more than six and a half meters, otherwise, splice along the length. Now let's explain in more detail.

So, on roofs with a slope of up to 30 degrees, the rafters are the so-called "bendable elements". Those. they work specifically for bending, and there are certain requirements for them.

And the possibility of deflection of the rafters is calculated according to a special formula, and if the result exceeds the norm, then the rafters are increased in height and a new calculation is made again.

But on the roof with a warehouse slope of more than 30 degrees, which rafters are already considered “bendable-compressed” elements. That is, they are affected not only by a uniformly distributed load, which causes the rafters to bend, but also by forces that are already acting along the axis of the rafter. talking plain language, here the rafters not only bend a little under the weight of the roof, but are also squeezed from the ridge to the Mauerlat. In addition, the crossbar, which usually holds back two rafter legs, must also be checked for tension.

As you can see, even a person who is far from construction can cope with such calculations. The main thing is to take everything into account, be attentive and ready to spend a little more time on design, so that later all the work goes like clockwork!

When carrying out installation work, it is very important to correctly determine the pitch of the rafters under the metal tile. It is important to understand that it is quite difficult to make such calculations, and the level of strength of the roof directly depends on how correctly everything will be done. Many experts argue that the operational life of not only the roof, but also the structure itself depends on the level of reliability of attaching the metal tile to the rafters. As a result of the fact that the metal tile has a rather large weight, the truss system must be strong. In addition, beginners will not be able to lay roofing material. In order to properly carry out installation work, it is recommended to responsibly approach the calculation of the step of the truss system.

The device of the truss system under the metal tile

Do-it-yourself rafter system for metal tiles is not as difficult to perform as it is to make the appropriate calculations. It is important to understand that the type of system used depends entirely on the type of roof. To date, the truss system for a gable roof under a metal tile is considered the most popular option. Such truss systems, as practice shows, are great for installing metal tiles on the roof of a dwelling. To equip the rafters, wooden blocks of different lengths are used - the choice, as a rule, directly depends on the length of the legs. Many experts recommend paying attention to the fact that it is necessary to choose the right angle of inclination, which can vary from 15 to 30 degrees - this value is considered optimal.

Calculation of the distance between the rafters for metal tiles

The step of the rafter under the metal tile is the distance from one rafter leg to the other, to put it differently, then the roofers call this distance the step of the rafter system. This distance directly depends on the type of roofing chosen. As practice shows, for all roofing materials, including metal tiles, this size varies from 0.6 to 1.2 m. However, it is important to understand that it is best to carry out accurate distance calculations for each material separately - it must be individual approach.

Before proceeding with the installation work, it is necessary not only to determine the distance between the rafters, but also to understand how much material is required for the legs. To find out the pitch of the rafters of a gable roof under a metal tile or a shed, it is recommended to adhere to the following recommendations:

First of all, calculate the length of the roof slope from the metal tile. Measurements, as a rule, are carried out along the eaves of the roof.
After that, it is possible to choose an arbitrary step. It is important to take into account the fact that the step limits for metal tiles can vary from 0.6 to 1 m. For example, initially it became necessary to adhere to a distance of 0.8 m. The length of the slope should be divided by the selected value for the pitch of the truss system. Let's say that the length of the slope is 12 m, it turns out that 12 / 0.8 and it turns out 15. After that, you will need to add 1 to the resulting value. In the case when the number turns out to be fractional, then it should definitely be rounded up. Thus, it turns out 15+1=16. This value shows exactly how many rafter legs should be installed on the roof. Then you need to take the length of the slope and divide it by the resulting number of legs. It turns out that 12/16 and it turns out 0.75 m.

Many experts recommend entrusting these works to professionals, which will allow you to get the desired result in the future. It is important to understand that there is a high probability that mistakes will be made, which will ultimately negatively affect finished construction roofs.

Attention! As practice shows, such calculations can be used for any roofing materials.

Installation of rafters under the metal tile

Since installation work is carried out at a great height, if necessary, it is possible to assemble the frame for the supporting truss system on the ground, and then lift and fix it on the roof. For these purposes, it is best to create a special template or scheme of the truss system for metal tiles from boards, according to which the installation will be carried out.

The whole process is carried out in stages:

First of all, the boards are raised above the wall of the building, leveled and fixed with nails.
According to the project, the boards must be aligned at a certain angle of inclination, after which all elements are securely fixed.
Ultimately, a structure should be obtained that, in appearance and shape, resembles a truss system. Manufacturing must be carried out taking into account the calculations made.
Then you need to lower the template to the ground and install all the finishing elements.

Don't forget to install supporting elements, namely, Mauerlat. Laying is carried out on bearing walls in a longitudinal position. As fasteners, special studs or wire rods are used.

The next step is the installation of the ridge run, which is used as a supporting part for all roofs. For work, you will need to use a beam or a hewn log. In cases where the length of the slope does not exceed 6 m, then additional supporting elements can be dispensed with.

When the installation of all elements has come to an end, you can proceed with the installation and further installation work on the arrangement of the truss system according to the attached template.

Mauerlat can be fixed in several ways:

rigid connection- in this case, a beam or corners should be used, nails and staples are used much less often, a feature is the fact that it will be necessary to additionally tie the rafters to the wall, using anchors for this purpose;
sliding way- in such cases, an articulated connection must be created, it can be done by joining the elements with cuts.

During operation, the step distance of the truss system must be observed.

When choosing a rafter pitch for a metal tile, you should pay attention that the distance should not be less than the minimum allowable value and more than the maximum allowable value, that is, it can vary from 0.6 m to 1.2 m.

If it was decided to choose a distance from 0.6 to 1 m, then the length of the rafters in this case should not be more than 6 m. In the event that it is reduced, it is allowed to make a run up to 1.2 m.

If the legs of the truss system are installed more often than after 0.6 m, then this will only contribute to a significant weighting of the roof and, as a rule, an increase in costs. If necessary, the distance can be 1.2 m, but it is important to understand that in this case the level of bearing capacity will be significantly reduced, which will negatively affect the structure of the metal tile.

If necessary, you can increase the level of strength, then for this you will need to perform a continuous crate of wood boards. In such situations, the step can vary from 0.2 to 0.3 m. This option is used extremely rarely, since its implementation requires much more investment.

Spacing of 1.2m almost never during exercise installation work not used. This is due to the fact that despite the rather high level of strength, the metal tile will begin to sag under the weight of snow in winter period time or strong wind gusts.

An important value is the cross section of the timber used for arranging the truss system. It depends on him what distance will be chosen. The best option the choice of wooden bars with a cross section of 150 * 150 mm is considered, while the crate can be installed at intervals of 4 to 7 cm. In this case, it is recommended to take into account the step of the transverse wave.

Conclusion

The pitch of the rafters under the metal tile can only be determined after the appropriate calculations have been made. It is important to understand that if the distance is quite small, this can significantly increase the material consumption and project budget, and if the distance is made too large, the roofing material will begin to sag during operation, which will lead to deformation of the metal tile.