The optimal distance between the rafters of a gable roof. Distance between rafters for different types of roofs and materials Rafter spacing

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 get the exact size of the 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, the 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

Roofing from metal tiles is most often used in the construction of country houses.

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

Although in appearance it is 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 transverse boards of large cross section.

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 constructing 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 practical experience 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 the 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 the attic floor under a gable roof, 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/

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

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.

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 rafter 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 a relatively small 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?

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 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.

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 exceeds 4 meters, additional girders 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 the 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.

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 completely different requirements are imposed on the rafter system of a small gazebo hidden under the crowns of trees.

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 are able at a certain moment to act on 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 the technical characteristics of materials and SNiPs.

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. In simple terms, 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!

Roof loads and rafter system calculation

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

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 a relatively small 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

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

Ondulin: calculation of rafters

Sandwich panel roof

Polycarbonate: erection of the supporting structure

The distance between the rafters (rafter legs) is called the pitch of the rafters. When arranging the roof, it is customary to use a rafter pitch of no more than 100 and at least 60 cm. The reliability of the roof structure depends entirely on how correctly the distance is calculated.

Incorrect determination of the loads on the rafters and the parameters of the materials used as them can cause deformation not only of the roof, but of the entire building. The roof can collapse and cause the destruction of the walls. Given this, the calculation of the design of the truss system must be given the same close attention as the overall design of the building.

Method for calculating the distances between the bars

moving along the eaves of the slope, measure its length;
divide the resulting number by the selected step (from 60 to 100 cm);
add 1 to the resulting quotient and round the number up.

As an example, take a slope 30 m long and a distance between the rafters of 0.6 m.

50 + 1 = 51 - 51 rafters are required to build a roof.

Then we determine the step between the bars, which will be used as a supporting structure:

30: 51 \u003d 0.58 m - the distance between the axes of the bars that will be installed on the roof slope as rafters.

This example shows the general methodology for calculating the supporting structure, but does not take into account the specifics of a particular roofing material. Experts recommend calculating the distance based on the characteristics of roofing.

In addition, calculations should be performed taking into account the materials from which the truss system of the house will be made. Here the step largely depends on both the type of material and its dimensions.

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The specifics of laying rafters under ceramic tiles

Despite the fact that ceramic tiles are one of the elite and environmentally friendly roofing materials, their laying is associated with certain difficulties. And the main one is a large mass. Thus, the weight of a ceramic tile is almost 10 times higher than the mass of a metal tile. And this means that for each m 2 of the structure, pressure from 40 to 60 kg will be exerted. These conditions imply the creation of a reinforced carrier system that can withstand the weight of the roof.

To create a truss system for a roof made of ceramic tiles, a beam with a cross section of at least 5x15 cm, and preferably 6x18 cm, is usually used. The moisture content of the wood should not exceed 15%.

The distance between the bars depends on the slope of the slope and the length of the rafters. So, the steeper the roof, the greater the distance between the rafter legs. If, with a slope of 15 °, the step is 80 cm, then with a slope of 75 ° it will be 130 cm. Long bars will be located at the maximum distance from each other, and short ones at the minimum.

In order for the installation of ceramic tiles to be carried out correctly, the step of not only the rafter legs, but also the crate is important. When creating a house structure, it is required to take into account the parameters of each roofing element (in this case, tiles). Typically, a tile tile does not exceed a length of 40 cm, and during installation forms an overlap with the previous row of about 9 cm. This determines the pitch of the crate, which should be at least 31 and not more than 35 cm.

Also, this indicator can be determined as follows:

the length of the bottom row is subtracted from the length of the slope;
then the distance between the first row of the crate and the last rafter is taken away.

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The specifics of the installation of the supporting structure under the metal tile and corrugated board

Installation of a metal tile does not require strengthening of the supporting structure due to its low weight. The wood will not resist the loads exerted, which means that the step between the bars may not be wide. So, with metal roofing, the rafters can be located at a distance of 60-95 cm from each other.

Decking is another roofing material that is lightweight. And according to other characteristics, the corrugated board is as close as possible to the metal tile. Therefore, the step of the rafter legs is similar to the above - from 60 to 90 cm.

Distance parameters determine the characteristics of building materials. For example, if a plank with a width of less than 10 cm is used to equip the structure on the roof, the distance should be reduced to 50 cm.

Do not forget about the distance between the elements of the crate, which can be from 0 to 400 cm. The pitch of the crate is selected taking into account the grade of the profiled sheet and the slope of the slope. For example, a profiled sheet of grade S-21 with a thickness of 0.5 to 0.7 mm with a roof slope of more than 15 ° should be attached to the crate, the step of which will be no more than 65 cm.

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

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

Attic: system features

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

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

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

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

Mounting Features

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

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

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

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

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

Parameters taken into account when choosing rafters

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

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

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

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

Requirements for the material of the truss system

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

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

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

Features of the calculation of rafters

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

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

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

Distance between rafters for different roofs

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

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

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

Required Tools

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

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

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

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

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

Primitive calculation method

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

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

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

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If decking is selected

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

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Ceramic tiles

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

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

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

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

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

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

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

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