The rafter system is the step of the rafters. Distance between rafters: principles and examples of calculating the pitch of the rafter system. Parameters of the gable roof truss system

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 (when determining the optimal width, one must take into account the dimensions of waterproofing materials and insulation).

The exact pitch of the rafters for a gable roof can be calculated according to the following diagram:

we measure the length of the slope along the eaves of the roof;
we divide the measurement data by a certain step (we determined the 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;
we round the total (upwards) - we see the number of rafters for installation on one slope of a gable roof;
the length of the ramp is divided by the resulting number and we get the exact step between the rafters.

For example, the length of the roof slope is 30.5 meters, taking into account the width of the rolls of insulation and waterproofing, a step of 1 meter is chosen.

30.5 m / 1 m = 30.5 + 1 = 31.5. Rounding up gives a result of 32. 32 rafters are required per roof frame.

30.5 m / 32 pcs. = 0.95 cm - the value of 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 consider how to calculate the correct pitch of the rafters for the most demanded coatings.

It is especially worth highlighting the rafter system when erecting 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 are then cut.

A hip that is over 6 m in length is often reinforced by stitching it in two pieces. 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.

System of rafters for ceramic and metal tiles

The use of metal tiles in the construction of private houses is the most common phenomenon, which is facilitated by a number of its positive qualities.

Firstly, it is the low weight of the coating, which facilitates installation and helps to reduce the load on the supporting structures.

Secondly, large roof areas can be quickly covered with sheets of metal tiles, which is very convenient, especially if you choose a gable roof option.

The pitch of the rafters under the metal tile is set in the range from 60 to 95 cm, since the relatively low 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 thermal insulation 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 accumulation.

This can be avoided by organizing ventilation during the installation of the rafters: for this, at a short distance from the top in the rafters, you need to drill several holes (about 10 mm in diameter).

As for the installation of a rafter frame under a coating such as natural (ceramic) tiles, you must remember about its high weight.

In comparison with other modern materials, tiles are 10 times heavier or more. Given this feature, experts recommend using exclusively dry wood under it in order to avoid sagging after drying.

For rafters, in this case, you need to use a bar with a section of 50 - 60 mm * 150 - 180 mm; the width of the step of the rafter legs is set in the range of 80 - 130 cm, while the greater the degree of the roof slope, the greater the distance between the axes of the rafters.

The step 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.

Taking into account the size of the tiles (as a rule, its length does not exceed 40 cm), it is necessary to correctly calculate the width of the step of the sheathing stuffed on 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

Such types of roofs as corrugated board and ondulin are relatively new on the market of materials. At the same time, they are successfully used both for gable and hip roofs.

The weight of these materials is practically equal to the weight of the metal tile, therefore, the calculation of the step width of the rafters will be similar to the calculation when laying metal sheets. The step of the rafters under the corrugated board is determined from the range of 60 - 90 cm, under the 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 the strength of the transverse lathing can be increased.

The rule for installing the lathing under the corrugated board is similar to installing the lathing under the metal tile: the last board must be taken wider than the others (as a rule, 15 cm thicker).

The lathing for ondulin must be made continuous 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 roof and bituminous shingles.

The name itself suggests that a very strong foundation is needed for a soft roof, which will allow it to withstand heavy snow cover, gusts of wind and torrential rains.

The main requirements for roof frames for soft roofs are that they must be strong and even.

The strength should be calculated for the thickness of the snow specific to the region in which the structure is being erected and the average weight of an adult male to allow for troubleshooting.

A flat roof should be for the reason that it excludes the possibility of sagging under the influence of the above-described 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 one will be mounted, solid.

The counter lattice will help the soft roof not to bend and will increase its service life by an order of magnitude. For a solid lathing, a 30 mm board or an OSB 20 mm 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, having thought over a filing for laying insulation, hydro and vapor barrier.

These are all the subtleties of the roof frame device for a soft roof.

Slate roof rafters

Despite the richness and variety of modern materials, the good old slate remains quite popular. The use of expensive roofing coatings is far from always justified, and this is when an asbestos-cement sheet comes to the rescue.

The weight of the slate is quite impressive, while its installation does not require any grandiose lathing. This is because such a roof itself is strong enough.

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 lathing 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 completing the drying process, it is necessary to determine the bend. The rafter legs are recommended to be installed with the concave part (tray) upwards - so the water, if it hits the rafters, will slide down, bypassing the attic space.

Before starting the installation, the beams are checked for knots in them and rejected, since the knotty material may not withstand the weight of the roof.

In this case, rafter fasteners are made with nails, the optimal length of which is 15 - 20 cm.

Nails should pierce the beam through, but the protruding ends should never be bent, since it is required to maintain the mobility of the structure.

When the wood dries out and deforms, this technique will prevent cracking of the slate sheets.

The lathing for the device of a slate roof can be solid or sparse. Solid 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 lathing step is about 80 cm. It makes no sense to make the lathing more frequent, since the slate has a sufficient margin of safety.

After analyzing the materials of the article, you can independently start erecting the frame of a gable and hip roof, having determined for yourself their features and properties of roofing materials.

It will not be superfluous to remind that the calculation of the rafter step is a very responsible occupation, and it is necessary to approach it responsibly, as this will avoid mistakes and speed up the progress of work in the future.

The rafters are one of the individual elements of the supporting structure of the roof, with the help of which its slope is formed. In the design, the rafters are attached with their upper end to the ridge, and the lower end rests on the Mauerlat, with a straight slope, or on a rack (with a broken roof). Rafters are made from edged boards with a section of 150x60 mm or a bar of 150x100 mm. The distance between the rafters, at which they are from each other after installation, is called a step, which can be in the range of 600 - 1200 mm.

Roof systems, their types

Depending on the type of installation of the rafter legs, systems are divided into 3 types:

Why the step of installing the rafters may depend

The pitch of the rafters on the roof depends on such factors, how:

Taking into account all these indicators when calculating, you can get a strong and reliable rafter structure, which for a long time will be a high-quality support for the roof.

It is the calculation, subject to the foundations of standard loads, allows you to choose the right distance between the rafters. As a rule, the guideline values can be determined by the Sheaves, and the calculated values are derived on their basis separately for each structure.

In this case, it is taken as a template value to use rafter legs with a section of 150x50 mm with an optimal distance between rafters within 0.8 - 1.8 m / p. but it should be remembered that when the slope of the roof slope changes, the distance between the rafters also changes.

Calculation of the rafter structure

The strength and stability of the entire roof directly depends on the quality of the calculation for the selection of the cross-section of the rafter legs and the distance between them. Regardless of what type of coating will be chosen: profiled sheet, slate or metal tile, the initial calculation should remain unchanged. Indeed, each calculation is based on the structural strength under mechanical loads, and the rest of the effects are no longer important.

When calculating the choice of the optimal distance between the rafters for the roof, the following parameters are taken as a basis:

Roof covering type.
View of the rafter system and the design features of the roof.
Feasibility and economy.

For a small house, the calculation of the structure for the roof can be done by yourself. True, the method of calculating the elements for the roof truss system is rather difficult, and it is recommended to do it using programs specially created for this. Especially if you need to calculate a complex sloping roof with a large area, most likely, you will not be able to do without a specialist. In this case, the calculation of the step of the rafters will also be repelled by the standards - the minimum step is 0.6 m, the maximum is 1.2 m.

Calculation method

Produced in this way.

- The length of the building is measured along the cornice.

- The resulting length is divided by the estimated distance between the rafters. For example, the estimated pitch of the rafters will be 0.8 m / p. (The average distance is considered to be 950 mm).

- After performing this action, add one to the result obtained, and round the resulting amount. Thus, the required number of rafters is obtained on one side of the ramp. After that, the length of the building must be divided by the number of rafters obtained, and as a result, the exact axial pitch of the rafters is determined.

Example, - the length of the building is 26.5 m / p. the distance between the rafters is supposed to be 0.8 m. So:

- 26.5 m ˸ 0.8 m = 33.1 33.1 + 1 = 34.1. As a result, after rounding, it turns out that 34 rafters need to be installed on one slope.

26.5 m / n ˸ 34 Art. = 0.77 m - this value is the distance between the rafters along their central axes.

But this is only a general calculation method, which does not take into account the peculiarity of the planned roofing. Therefore, experts recommend calculating the step between the rafters for a certain roofing material and insulation, for example, for the most popular roofing metal tile today.

Roof structure for metal tiles

Metal tile visually imitates ceramic roof tiles. It is made from thin sheet steel by cold stamping. Thanks to the polymer coating, it has a high resistance to weathering and a rather attractive visual appearance, is not afraid of sudden temperature changes.

The advantage of metal tiles

Often used in the construction of most mansard roofs.

The section of rafters made of wood for a roof made of metal tiles is usually standard 150-50 mm, but the distance between them can be from 600 mm, but not exceed 900 mm (depending on their angle of inclination, which can range from 22 to 45 degrees). This limitation of the pitch of the rafters is due to the fact that the lathing for the metal tile is mounted with a distance from each other within 300 mm. The standard timber used for the lathing has a cross section of 30x50 mm or 50x50 mm. This means that each rafter is subject to additional stress.

Stability of the roof structure against various mechanical loads depends on four factors:

An important factor when calculating a rafter structure, is the estimated maximum roof load, the formation of which includes:

The weight of the entire rafter structure.
The weight of the lathing under the cover.
Insulation and roofing weight.
Snow load (determined by a special, unique for each region, reference book).
Wind load (also according to a special reference book for the region).
Weight of a person with a tool (repair work, estimated weight - 175 kg / m²).

When installing the rafter system, the distance of the rafter legs should not exceed an average value of 0.9 m / p. except for certain cases stipulated in advance.

If, when calculating the loads, any inaccuracy is made in the selection of material for the roof and the location of the rafters, it may occur its deformation and destruction of the roofing... A reliable roof structure will be guaranteed only with the correct calculation of the cross-section of the rafters and their installation pitch.

It should be remembered. There is no universal value for calculating rafter structures. When building each house, an individual calculation is required.

Shed roof rafters

Shed roofs can often be found on small outbuildings. They can also be used on private residential buildings, but quite rarely. In such cases, the angle of inclination of the roof is quite small, and with such an arrangement of the load-bearing floor beams, there is a very great pressure on them, especially in winter.

Therefore, for a pitched roof, load-bearing floor beams are installed from a bar of large cross-section from 60x150 to 100x220 mm, depending on the width of the span to be covered. In this case, the distance at which the rafters are stacked from each other should be within 400 - 800 mm, depending on the angle of inclination of the roof.

For a pitched roof no complex rafter construction required, they can be simply laid on the walls, without even using the Mauerlat. In regions where winters are rather snowy with a lot of snow, it is recommended to erect the roof slope at a maximum angle of 35 ⁰ and place the roof in the "wind". This reduces the windage and leads to its self-cleaning.

Gable roof

Represents a structure assembled from rafters, connected to each other in the form of a triangle. The upper part, which rests on the ridge, and the lower part on the Mauerlat, located parallel to each other on opposite walls. In simple terms, this is a roof consisting of two opposite slopes, connected by a ridge.

Gable roof structure, depending on its area, is mounted from separate rigid elements that increase the strength of the roof. These include struts that support the rafters, ties that connect the rafters to each other, jibs, purlins, support beams, etc.

For a gable roof, often the rafters are mounted taking into account the insulation in increments of 0.9 - 1.2 m / p. In this case, the strength of the mounted structure will be the highest if the formed triangle is isosceles. In regions with strong winds, it is recommended to install rafters with a slope of about 20 ⁰, and in snowy areas, the optimal angle should be 45 ⁰.

Although the gable roof is considered a classic, it has several alternative "related" types.

Roof roof

For mansard roof, for the calculated parameter for determining the step between the rafters and their number, the load is taken in the range of 40-60 kg for each 1 m / p. rafters, and the maximum deflection from its length is 1/250. Usually, with a properly selected section, this distance along the centers of the rafters is, as for a gable roof, 0.6 - 1.2 m / p.

It should be noted that the average load on the attic is approximately 200 kg / m2. So, with the standard calculation of the cross-section of the rafters, it is recommended to add a small percentage of the safety factor.

Hip roof

Among all the rafter structures, it is considered one of the most difficult ... It's practically a hipped roof, while the rafters of the end slopes are attached with their upper ends to the corner bowstrings, and not to the ridge. Therefore, certain requirements may be imposed on this type of roof during construction. In this case, the rafters are installed similarly to a gable roof at a distance of 60 cm - 1.2 m / p.

Mansard rooms under such a roof are made in rare cases, since its slopes "eat up" some area of the attic, especially in height.

Before the construction of the rafter system and the organization of the roof, it is necessary to carry out a number of simple measures that will act as a guarantee of the integrity of the structure. This includes the choice of roof type.

It can be hanging or layered, or it can be a combined version. This is when two types are combined in one building.

Temporary 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 service 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 cake, the weight of the interior decoration, if an attic is supposed to be organized in the attic of the building.

When creating a project of a shed or gable roof, first of all, the type of rafter structure, the angle of inclination of the roof slopes, as well as materials for the construction of the structure are chosen. When calculating the distance between the rafters, one should take into account the loads that will act on the roof of the building during operation.

Roofing material weight;

Weight of building materials from which the roof truss frame is built;

Insulation, vapor barrier, waterproofing weight;

The weight of the finishing material of the attic or residential attic.

The following live loads also affect the roof of the structure:

Snow weight;

The weight of a worker performing roof maintenance and repair.

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 being erected, the presence of roof insulation, 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 rafter system:

Scheme for calculating the distance between the rafters

All calculations are carried out at the stage of building design. They are carried out by design engineers of the organization where the project of the house was ordered.

If the project was not 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.

Next, 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, then the loads on the rafters will be different, and, therefore, the course of calculations also changes.

The calculations must take into account the climatic zone where the work is carried out, the structural material of the rafters and its section.

So, the step of the rafters is the distance between the rafter legs. It can vary from 0.6 m to 1.0 m.

Calculation progress:

the length of the roof slope is measured first. Further, this value is divided by the length of the step of the rafters of the selected material. This indicator is taken from SNIP and for each building material it is unique and also depends on the used section of the beam;
add one to the result of previous calculations and round 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 steep roofs. 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.

Distance between rafters for different types of roofing

However, the calculation of the distance between the rafters cannot be done so unambiguously. After all, this indicator also depends on the type of roof construction material used.

Distance between beams for metal roofing

The average weight on the roof is 35 kg / m². To withstand it, the roof must have a pitch of 0.6-0.9 m. In this case, a bar 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 is often equipped with a living room.

This leads to the installation of a roofing cake 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 the beams. This is especially true for regions with low air temperatures in winter. Recommended rafter dimensions 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.

Distance between beams for corrugated roofing

The recommended pitch of the rafters for the roof is 0.6 m - 0.9 m.However, here you need to take into account the operational characteristics of the corrugated board itself. If the step is large, the corrugated board will "sag" under its 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 perform in some way the role of rafters.

The cross-section of the rafters for a roof made of corrugated board is 50x100 mm or 50x150 mm. The lathing is made of a board with a section of 30x100 mm.

Distance between beams for ceramic tile roofing

Ceramic shingles are a heavy roofing material. 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 inclination of the roof. The larger it is, the less often beams can be mounted.

Installation of a 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 rafter frame.

It should be noted that for this roofing material it is necessary to make a continuous sheathing. Due to this, the material will better resist snow loads and solar exposure.

Sometimes a thinned type of lathing is used. For its manufacture, a wooden beam is used. The distance between adjacent elements should be less than 30 centimeters. This option is usually more costly than solid sheathing.

Roofing system for slate

Slate roofing is considered the most widespread in Russia. The main reason is the low cost of this roofing material, the ease and speed of installation work. Another important advantage is the ability to replace 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 slate lathing should be thinned out. For its manufacture, a board or bar 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, you should remember about a constant margin of safety. It may be needed in case of bad weather and mechanical stress.

Rafter frame for a soft roof

Soft roofing includes soft tiles, bitumen-polymer and bitumen 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 less the slope of the roof slopes, the less you need to make the distance between the rafter legs for a continuous sheathing.

The distance between the rafters also depends on the material from which the lathing will be made. The thicker the plywood or OSB sheet, the more you can step the rafters.

Sandwich panel roof

Roofing of this type, as a rule, is erected on hangar-type buildings or houses from sip-panels. Sandwich panels have bending stiffness, so their installation does not require the installation of traditional rafter legs.

If the spans from the upper part 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 a sandwich panel, a traditional truss frame is often erected on a residential building. However, in this case, the distance between the rafter legs can be made large, since they serve as a support for the girders.

The distance between the rafters is chosen based on the length of the bearing walls and the length of the material for the purlins. Sandwich panel roofing is able to withstand high operational loads.

Erection of a rafter frame for polycarbonate

Recently, polycarbonate is often used in the construction of roofing. It is used in the construction of sheds, conservatories and gazebos. The rafter frame and lathing are made of metal or wood.

Polycarbonates differ in weight, which depends on the thickness of the sheet. The step of the lathing for polycarbonate should be from 60 to 80 cm. The lathing 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, you need to take into account the glazing area, thickness and dimensions of the sheets. It should also be remembered that polycarbonate sheets are mounted with small gaps.

Rafter system is undoubtedly the most important structural element of any pitched roof. The consequence of its incorrect installation can be not only deformation of the roof, requiring expensive repairs, but also a complete collapse of the roof on the head of an insolvent builder.

The following four main factors affect the stability of the rafter system to various loads:

fastening strength rafters to the ridge and Mauerlat;
correct calculation of the supporting structure for rafters, depending on the length of the span;
choice rafter material;
step between the rafters.

The topic of this article is the choice of material and the pitch between the rafters, taking into account the intended type of roof.

What are the calculations based on?

When carrying out calculations, four main indicators are taken into account:

design features of the roofing material;

span length between supports;

mounting angle of the rafter leg.

The most important is the calculation of the maximum roof load, consisting of:

rafter weight,
the weights of the crate,
weight of roofing material and insulation,
snow load (background information, unique for each region),
wind load (also background information),
weight of a person (if necessary, repair or cleaning, 175 kg / m2).

To carry out accurate calculations, specialists use special formulas from the strength of materials, but when building a private one, you can use approximate recommendations.

Method for calculating the distance between the rafters

Calculating the exact distance between rafters is based on the results of a preliminary calculation of the maximum allowable pitch. To make this calculation, take into account the total load, the roof structure and the material used on the rafter legs.

Method for calculating the pitch of the roof frame:

Measure the length of the roof from end to end.
Distance obtained divided by the maximum step size.
Round up the resulting value to a larger integer... This is the number of spans.
Divide the total length of the roof by the number of spans... This is the desired step size of the rafters.
Add one to the number of spans.This is the required number of rafters.

For some types of roofing material it is advisable to use fixed distances between the rafters, in which case an additional rafter with a non-standard pitch is installed at one of the ends of the roof.

Rafter leg step depending on material

Can be increased as the strength of the material from which they are made increases. Most often, for each roofing material, the pitch of the rafters required for it and the permissible sections of the rafter legs, taking into account the load, are indicated.

These guidelines are regional in nature and applicable to the central zone of Russia and more southern regions. Before developing a drawing, you should definitely check the level of wind pressure and snow cover in your region, and adjust the pitch and / or section of the rafters.

In those regions where the snow load significantly exceeds the wind load, the use of pitched roofs is recommended. 35 – 45 degrees.

Rafter system in private houses, it is most often made of logs with a diameter 12 - 22 cm, timber / boards thick 40 - 100 mm and width 150 - 220 mm... When calculating, it can be assumed that instead of logs of a certain diameter, beams of the same width, thickness 100 mm.

Roof structure for corrugated board

Roof structure for ceramic tiles

Ceramic roof tiles has significant differences from other types of roofing materials that must be taken into account when designing a rafter systems for it:

5 to 10 times the weight, doubling the weight of the entire roof... This leads to the need to use a frequent step ( 0.6-0.8 meters) and a 25% increased cross-sectional area of the rafters.
Small-scale nature of the material. Increases the requirements for the accuracy of the installation of the transverse lathing. The pitch of the battens, the permissible sections and angles of installation are always indicated in the instructions for each specific tile model.

There are tile models designed for installation at an angle 12 - 60 degrees, ordinary models are recommended to be mounted at an angle 20 - 45 degrees... For the lathing, timber is most often used. 50x50 mm.

Roof structure for metal tiles

Metal tile in fact, it is a less rigid and lighter decorative version of corrugated board, therefore, the requirements for the rafter system, in particular for the recommended sections of rafter legs, largely coincide.

A feature of the rafter structure for metal tiles can be called a significant reduction in the pitch of the sheathing, which should be equal to the length of the longitudinal wave (30 cm for most species). This leads to the need to reduce the distance between the rafters. up to 0.6 - 1 m, to reduce the cost of lumber on the crate. Roof slope angle is selectable from 22 to 45 degrees.

Roof structure for ondulin

Ondulin- slate based on fiberglass and bitumen, produced by only one manufacturer and has unified technological installation standards:

permissible mounting angle - 5 - 45 degrees;
distance between rafters - 60 cm at a slope angle of up to 15 degrees, up to 90 cm - at an angle of more than 15 degrees;
crate - solid plywood on a slope up to 10 degrees, board 30x100 mm step by step 45 cm on the slope 10 - 15 degrees, timber 40x50 mm step by step 60 cm on the slope above 15 degrees.

Given the low weight of the material, the cross-section of the rafter legs is selected based on the same recommendations as for corrugated board.

Roof structure for slate covering

Slate- traditional, rather rigid and heavy roofing material, fragile, but resistant to constant loads. Such properties change the recommendations for the optimal structure of the rafter system towards the use of more durable elements and increasing the step between them:

Due to the low tightness, it is undesirable to use slate roofs with a slope angle of less than 22 degrees. If it is necessary to install such a roof, as an instruction, you can use the recommendations for installing ondulin, adjusted for the universal pitch of the lathing - 55 cm.
Acceptable angle for installing rafters under slate - up to 60 degrees.
The installation step is selectable from 0.8 to 1.5 m, depending on the cross-section of the rafter leg, load and the presence of lathing material.
The material for the rafters is selected with a slightly larger section than for light roofs... For the most popular step 1.2 m a bar is taken with a section from 75x150 to 100x200 mm, depending on the length of the span between the supports.
Lathing material selected in accordance with the distance between the rafters - timber 50x50 mm up to 1.2 m, bar 60x60 mm - 1.2 m and more.
Sheathing step is selected in such a way that each sheet lies on three beams, and has an overlap on 15 cm with the neighbor. Given the standard sheet length 1.75 m, step is used 80 cm.

Rafters for shed and gable roofs

What is the distance of the rafters for a pitched roof? Shed roof does not require a complex truss structure. The rafters are laid from wall to wall, most often without using a Mauerlat, right on the crown.

No extra ribs stiffness sets the maximum slope angle - 30 degrees and the permissible span length - less than 6 m(for wooden rafters). The optimal angle is 15 - 20 degrees.

Such roofs usually not subject to wind loads, but require protection from precipitation. In regions where the wind pressure is comparable to the snow load, the correct installation of a pitched roof "downwind" can lead to self-cleaning of the roof.

Gable roof is a system of parallel triangles connected by a Mauerlat and a ridge. There are many elements for firmly fastening the sides of the triangle to each other and transferring loads from the rafter legs to the walls - racks, screeds, jibs, support beams, and so on.

The step between the rafters of the gable roof is made taking into account the size of the heat insulator, which is laid between them. Approximate step between rafter legs 1-1.2 meters

Rigid triangle strength increases as its shape approaches isosceles, therefore, as the slope angle increases up to 60 degrees you can expand the step between the rafters.

However, this will also result in to an increase in material consumption and to a multiple increase in the windage of the roof. The optimal slope angle for snowy regions is 45 degrees, for windy ones - 20 degrees.

Distance between rafters roofs attic type determines how much of the load falls on each element. When designing hip roofs step rafters should be between 60 cm and 1 m.

The correct fastening of the rafters is no less important than the correct calculation of the structure. Before installing the roof yourself, it is worth taking a lesson from an experienced carpenter and reading educational literature.
When choosing the pitch of the rafters, do not forget about thermal insulation. All types of insulation are capable of shrinking a little, so you can buy them at an approximate size. The most commonly produced sizes are 60, 80, 100, 120 cm.
For roofs with a slope of 45 degrees or more, the weight of the person on the roof can be disregarded. This removes 175 kilograms of the design load per square meter and allows the rafters to be installed on average 20% less frequently.
Snow and wind load in the regions of Russia can be found in regulatory documents - maps in the appendix F To .
There are many online roof calculators online, capable, if not to calculate all the nuances correctly, then at least advise the selection of the correct section for the rafters.

As you know, the roof of any building is its upper part, which can combine protective and decorative functions. Protects the roof mainly from precipitation from above inside the building, at the same time, with its appearance, material and color of the roof, it can emphasize the architectural feature of the building.

Wooden beams that make up a rigid roof frame are called rafters; the selected roofing material is already mounted on them.

As buildings carry different functional contents (for example, residential buildings or industrial and technological buildings), so the roofs of various buildings differ from each other. Their shape can directly depend on climatic conditions: on the wind load or the amount of snow falling. It is difficult to clean the roof from the latter if its slope is 30 0 or less, and the large "windage" of a high roof can be a serious problem in case of wind gusts of more than 18 m / s.

Among the huge variety of roofs, most usually consist of a roof and a set of building structures that support this roof.

One of the main elements of these structures are, as a rule, wooden beams, on which the roof covering is mounted. These beams are called rafters or trusses. They are also the elements of rigidity that determine the mechanical strength of the roof, as well as those guides that determine the angle of inclination of the roofing.

The rafters can be located either from one to the other outer wall of the building, with a certain slope, or from the center (ridge) of the roof to the outer wall. According to the first method, single-pitched roofs are arranged, according to the second, gable roofs.

It can be assumed that the closer these trusses are located to each other, the more reliable the base for the roofing will be.

However, excessive use of materials makes the structure heavier and leads to higher construction costs. Therefore, the question of how to install the rafters is one of the fundamental in designing a roof.

There are two types of rafters: the so-called "hanging", resting with their ends only on the outer load-bearing walls, and those that rest with one of their ends on the internal load-bearing wall of the building or an internal column. Farms of the latter type are called "layered".

Correct placement and fastening of these building elements is the basis for the fact that its upper part does not deform under the influence of possible loads.

How to put the rafters correctly

General Provisions

When designing the roof of a building, determining the number of trusses and the distance between them, it is imperative to take into account the required section of the timber used for the device of rafters, determine its material and the optimal length of the rafters. Usually, a bar made of coniferous trees is used for the rafter device, with a cross section of 50x150 mm (considered the most used) or more.

The length of the trusses directly depends on the size of the building box, the type of roof, and also on its height. The cross-section of the timber used and the distance between the rafters set the strength of the supporting structure for the roof. The distance between the axes of adjacent trusses is called and calculated when designing the roof. In practice, the applied step can take a value from 600 to 2000 mm. This step is interrelated with the length of the trusses: the shorter they are, the greater the distance between them they can be installed.

There is a generalized method for calculating the specified distance. It consists in the fact that the preliminary step of the rafters is determined according to the table. Having then measured the length of the roof overhang of one slope along the lower edge, the resulting distance must be divided by the step determined from the table. The resulting result and the unit added to it, after rounding up, will correspond to the number of required rafters for one slope of the projected roof.

The exact distance between the axes of the "legs" of neighboring trusses will be obtained by dividing the length of one roof slope by the number of rafters calculated for it.

In this way, it is possible to determine at what minimum distance the rafters can be installed in order for the roof supporting structure to meet the design load requirements.

However, the above method does not take into account possible additional loads on the structure associated with the use of various kinds of roofing, from slate to ondulin. Does not take into account the need to organize free space between the trusses for placing canvases or slabs of the used insulation for the roof.

In the case when it is planned to use insulation products, the width of the canvases or panels of which is known, you can immediately determine through what distance the rafters should be installed. It is recommended in such cases to equate the step to the width of the insulation, minus 1.5 to 2 mm.

Recommendations for choosing the pitch of the rafters for different roofing

For roofing made of corrugated board, the pitch is selected in the range from 600 to 900 mm. In this case, the timber is recommended with an optimal section - 50x150 mm.

For a heavy roof made of ceramic tiles, an increased load on the rafters is characteristic, of the order of 60 - 70 kg / m 2. The step is recommended in the range from 800 to 1300 mm. Moreover, it can increase in proportion to the increase in the angle of inclination of the roof. For example, the distance between the trusses should be no more than 800 mm, if the angle of inclination of the roof does not exceed 15 0. By increasing the specified angle to 70 0, the step can be increased to the maximum. The cross-section of the timber for such a roof is recommended from 50x150 to 60x180 mm.

The device of the supporting structure of the roofing for metal tiles is not much different from the standard one. The material, in comparison with ceramics, is almost two times lighter: the load per 1 m 2 does not exceed 30 kg. A bar with dimensions of 50x150 mm is recommended for use. Some of the features of fastening the upper ends of the rafters are associated with the provision of ventilation of the metal roof to prevent condensation.

Slate roofing is an optimal solution for numerous buildings, despite the fact that this material is recognized as harmful and is prohibited for use in European countries.
Recommendations for the installation of rafters for corrugated slate roofing are typical: they are placed in the intervals from 600 to 800 mm, they can be 50x100 or 50x150 mm.

For ondulin roofing, it is proposed to follow the recommendations for slate roofing. Modern innovative material ondulin looks like slate, but lighter than the last one five times.

Determination of the inter-rafter distance for multi-slope (hipped) roofs is carried out separately for each slope. For buildings in which the "box" is assembled from logs or beams, the lower end of the rafters is attached directly to the upper part of the external load-bearing wall, and not to a special beam laid along the perimeter of the upper part of the building (mauerlatu). This method of installation makes an especially high cost of error in determining the pitch of the rafters, since it can be very difficult to eliminate such an error.

Mansard roof truss structure

For such roofs, the supporting structures for the roof are usually made of timber. The pitch of the rafters for a slope no longer than 15 m can be selected in the range from 800 to 1000 mm. For attics with slopes longer than 15 m, it is recommended to use metal rafters.

It should be noted that for all types of roofs, when determining the pitch of the rafters, the presence of existing vertical structural elements of the building passing through the attic and the roof should be taken into account. These elements include chimneys and air ducts. If the calculated point of installation of the truss coincides with the place of passage of the existing pipe or other building elements, the transfer of which to another part of the attic is impossible, the plan for placing the rafters should be changed accordingly.

If changing the specified plan for some reason is impractical, it is recommended that the rafter, which coincides in place with the building element, be arranged so that it is interrupted at the place where the pipe passes. Moreover, the ends of this truss, cut off before and after the passed pipe, must rest on the corresponding jumpers connecting adjacent rafters.

It should be borne in mind that the nodes of such a "interception" of the truss should be made with the necessary reliability and quality, allowing them to correspond to the calculated reliability of the supporting structure of the roof covering.

It should be noted that the installation of rafters is part of a whole complex of very serious and very important construction work on the construction of the roof of the building. As a structural element of the supporting system of the roof covering of a building, rafters are indicated in the roof design plan, which reflects the results of calculations of various possible loads.

Such calculations should take into account all sorts of factors that affect the designed structure in the complex:

the necessary and sufficient height and slope of the roof;
optimal material for roofing;
the parameters of its placement on the required crate and the total weight of the roofing;
the necessary bearing capacity of the rafter structure in general and the corresponding parameters of the rafters in particular;
the method of fastening the roof to the walls of the building and the condition of the walls.

And other equally important data, without taking into account which the constructed building and its roof may not withstand various loads.

Therefore, in order not to have upsetting consequences as a result of inept actions, it is better to entrust the issues related to the design and construction of buildings to professional specialists with the necessary experience and knowledge. At least in the part that concerns the calculation of the load on the truss structures.