The distance between the rafters of a gable roof. Rafter pitch for different types of roofs and roofing materials Rafter pitch of a gable roof with slate

The roof structure is one of the main enclosing elements of the building, the quality characteristics of which are subject to rather stringent requirements.

One of the most common roof sheathing materials is metal shingles, which are made from thin sheets of steel, aluminum, or copper.

From above, the elements are equipped with a polymer coating, which protects metal from aggressive external influences.

Externally, the metal tile is similar to ceramic, but it is more durable. This material is used to cover pitched roofs, the slope of which must be at least 14 degrees.

This is the national team roof frame structure, consisting of many wooden or metal parts. She is rests on load-bearing walls, which are a reliable basis for all overlying elements. The rafter system serves as a kind of skeleton, on the basis of which it is made, - and the roof, as well as laying the roofing finish roofing layer.

truss system

The constituent elements of the truss roof, and their main characteristics:

• Mauerlat. A softwood beam, which is a connecting element between the rafters and the underlying structures. It has a square cross section with a side of 100 or 150 mm. Mauerlat is laid along the load-bearing wall along its entire length. With the help of the Mauerlat, the loads from the roof are evenly distributed throughout the building.
• Sill. A beam having a square section similar to a Mauerlat. It is laid transversely to the bearing walls, as it serves to redistribute the load from the roof racks.
• Rafter leg. From these elements, the main triangular roof structure is created, which experiences the full burden of external atmospheric influences (rain, wind, snow, hail, etc.).
• Rack. Vertical connecting elements that distribute compressive loads from the ridge assembly over the entire area of ​​​​bearing walls. They are made of square bars, the length of the edge of which is determined by calculation.
• Puff. It is the final horizontal element of the triangle of rafter legs, which does not allow them to crawl under the pressure of external loads and the own weight of the roof. It is used in systems with hanging rafters.
• Struts. Perceive and redistribute bending loads from the ridge assembly.
• Crate. It consists of boards, bars or plywood sheets (in the case of subsequent laying of bituminous tiles), which are located at a right angle relative to the rafter legs, while being an additional rigid element.
• . The junction of two roof slopes.
• Overhang. A roofing element protruding from the load-bearing wall structures at a distance of about 0.4 m. Its purpose is to limit the penetration of moisture to the walls.
• Filly. These elements are attached to the ends of the rafters if they are not long enough to organize an overhang.

Varieties of pitched roofs

Depending on the number of inclined planes, roof structures can be divided into:

In private housing construction, the most commonly used option gable roof, since he has a number of advantages. These include:

1. Practicality. The gable roof has a significant angle of inclination, thanks to which rainwater does not accumulate on its surface, and snow and wind loads are distributed in the most optimal way.
2. Ease of device and operation. The assembly and joining of two pitched elements is much easier than with complex roof structures. In addition, the repair of such a roof will also be simple.
3. Aesthetics. A roof with a gable structure is organically written into the surrounding infrastructure.
4. Reliability(if done correctly).
5. Democratic price constituent materials.

Types of pitched roofs

Gable roof - truss system for metal tiles

Frame from rafters under a gable roof from a metal tile has no significant differences from structures with other covering roofing materials.

But, in view of the fact that metal thin sheets have a low specific gravity, the rafters will experience less constant load.

This allows you to reduce the value of their cross section, due to which can save a lot on the purchase of wood materials.

Ideal for metal roofing the angle of inclination must be at least 14 degrees.

For a roof with two pitched elements, the following apply: frame options:

Laminated rafters under a metal tile.

In this case, 2 load-bearing rafter legs are fastened together using lying down(horizontally) and racks(vertically). The bed is laid parallel to the Mauerlat element, while taking on some of the force effects. The rafter system under the metal tile is taken over only bending loads, which significantly affects the selection of the calculated cross section. Such a system can be used for buildings with large and small spans.

Types of rafters

Hanging rafters.

Unlike layered systems, in this embodiment, two rafter legs fastened together only in the ridge knot. In this case, significant bursting forces arise on the supporting elements, which limits the use of hanging rafters only for buildings with a span of not more than 6 m.

They can be made of wood or metal, as well as installed at the bottom (acting as a supporting beam) or at the top of a triangular structure. It is worth considering that the higher the puff is, the greater the effort it will take.

NOTE!

To ensure the quality of the tightening, care must be taken on the reliability of fastening with load-bearing rafter legs.

Combined variant

Used to create an original roof structure. Includes elements of both hanging and layered systems.

How to calculate the angle of inclination of the rafters?

To implement a gable roof, you need to know a few geometric values ​​of the building, namely:

• Half span - L;
• The distance from the load-bearing wall to the roof ridge (or the height of the support post) - H.

Standard formula: α = arctg(L/H)

Where α is the desired angle of inclination of the roof.

Knowing this value, you can calculate the length of the supporting rafter leg:

l = H/sinα.

Where l is the length of the truss element.

Rafter Angle

How to calculate the load?

To carry out the correct selection of parts of the roof frame, it is necessary calculate live and permanent load values acting on its structural elements.

The constant load includes the weight of all elements, as well as the mass of the load-bearing elements themselves and the crate.

The composition of temporary loading options includes force effects from wind, snow cover, rain masses, as well as the weight of a person (to take into account options for subsequent repairs).

Dead Load Calculation

Roofing cake weight.

It is determined by adding the masses of all its elements, namely steam, hydro and thermal insulation, as well as roofing from metal tiles. In this case, the weight of one linear meter (can be found in the regulatory documentation) is multiplied by the value of its length.

The weight of the truss system.

It is determined by adding the weight values ​​​​of the crate, rough flooring, as well as the supporting frame. The mass of each element is calculated by the formula:

M=V*p,

Where V is the volume of the element, calculated depending on the geometric characteristics of the cross section and the length of the element;

P - The density of the wood used (depending on the species).

Total permanent load \u003d weight of the rafter system + weight of the roofing pie.

Calculation of live loading

Conducted in accordance with regulatory documents ( SNiP 2.01.07-85 "Loads and impacts" or Eurocode "Actions on structures" part 1-4).

To determine the value of the wind effect, the roof structure is conventionally divided by height into several parts. For each of them, the value of the wind load is calculated. To obtain the total wind pressure, they must be summed.

Formula for calculation:

Wm=Wo×k×c,

Where Wm is the value of the wind load;

Wo is the normative value of wind pressure determined from zoning maps;

k - wind pressure coefficient (determined depending on the height according to the regulatory documentation);

c - aerodynamic coefficient (for a gable roof - 0.8).

Determined by the formula:

S = µ×So;

Where So is the normative value of the snow load, determined from the zoning map.

µ is a coefficient that is determined depending on the angle of the roof:

• For α≤30 deg. — µ=1
• For α≥60deg. -µ=0
• For 30≤α≤60 deg. – µ=0.033×(60-α)

Snow load areas

How to choose a beam and calculate the pitch of the rafters under the metal tile?

Determining the value of the cross section of the beam of the truss element is carried out in several stages.

Calculation of the load distributed on each linear meter of the structure:

Qр = L×Q;

L - Step of the rafters.

The L value is calculated as follows:

The length of the roof slope is divided by the estimated step of the structures (for convenience, it is most often taken equal to 1). Then 1 is added to the resulting value. The resulting value reflects the number of rafters that need to be installed on one pitched roof surface. At the last stage, the value of the axial distance between the rafter elements is determined by dividing the length of the roof slope by the number of rafters.

The distance between the rafters under the metal tile - the standard step is 0.6-0.95 m.

Rafter pitch

Then we determine the maximum working area of ​​\u200b\u200bthe rafter leg (Lmax). We proceed to the calculation of the cross section. To do this, we find its height using the formula:

H ≥ 8.6*lmax * sqrt(Qp/(b*r)), with roof slope α<30 град;

H ≥ 9.5*lmax * sqrt(Qp/(b*r)), with a roof slope α≥30 degrees;

Where b is the width of the cross section,

r - the value of the normative resistance of wood to bending loads (determined according to regulatory documentation, depending on the type of wood).

To simplify the calculations, you need to use the standardization table for truss elements (GOST 24454-80 “Softwood lumber. dimensions").

If the inequality is not observed, it is necessary to increase the value of the geometric characteristics of the section and repeat the calculation.

What is the difference between the truss system for cold and warm roofs?

The main difference between these two roofs is the support system of the truss elements. In the case of a warm attic, the main supporting element is the Mauerlat, as well as the supporting beam system. In a cold roof, rafters are installed directly on load-bearing walls.

Installation of rafters under the metal tile

All installation work on the installation of the roof is carried out at a sufficiently high height. To minimize the risk of falls, as well as greatly simplify work at height, you can assemble the frame of the supporting truss system on the ground.

To do this, you need to create a template from the boards, according to which further assembly will be carried out.

It is made in several stages:

• The boards are raised above the walls of the building, leveled, and then fasten together with the help of a nail.
• Align the angle of the boards in accordance with the project, by lowering and raising them. The elements are fixed.
• The result should be a structure that resembles in shape the future truss system, made in accordance with the estimated geometric dimensions of the roof.
• The template is lowered to the ground, in accordance with it, the finishing elements are fixed to each other. More details in the video below.

Then you should take care of installing the support element - Mauerlat. As mentioned earlier, it is laid on load-bearing walls in the longitudinal direction. Fastening is carried out using studs (on an armored belt or masonry) or using a wire rod (for buildings with a small roof height).

CAREFULLY!

When using a hairpin connection, connecting elements do not need to be tightly sealed into the wall. They should protrude from the wall by 30-40 mm, as the nut will be screwed onto the studs.

The next step is to create ridge run, serving as a supporting part for the entire structure of a gable roof. It is made from timber or hewn logs. If the span of the building is not more than 6 m, it can be supported without additional supporting elements. Otherwise, construction trusses must be used for installation.

Mounting. Part 1

After installing these elements, it is possible to carry out the lifting and installation of the main truss element, assembled according to the template. Fastening with a Mauerlat can be carried out in 2 ways:

Rigid connection. It is carried out with the help of corners and beams. Less often, fastening is used by means of washing down on rafter legs, followed by fixation with nails or staples.

Features: in addition to the main connection, it is necessary to tie the rafters to the wall using anchors or a wire structure.

Sliding. It is based on the creation of a swivel joint. It is made by joining elements using cuts. The elements are connected with a metal embedded part with holes for bolts, or with 2 nails that need to be hammered in at an angle.

It is necessary to carry out the installation of wooden trusses in a certain sequence. First, extreme trusses are installed, located at the ends of the building. Then a cord or rope is pulled between them, with the help of which the verticality of their installation is checked. Further, under the cord, further installation of truss structures is carried out in accordance with the specified design step.

Mounting. Part 2

Creating a roof from a metal tile is a rather laborious process that requires certain skills and a full hand. Therefore, for proper installation, you must at least work under the supervision of a competent specialist.

Useful video

Video instruction for self-installation of rafter legs:

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

The device of the truss system under the metal tile

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

Calculation of the distance between the rafters for metal tiles

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

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

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

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

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

Installation of rafters under the metal tile

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

The whole process is carried out in stages:

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

Do not forget about the installation of supporting elements, namely, Mauerlat. Laying is carried out on load-bearing walls in a longitudinal position. As fasteners, special studs or wire rods are used.

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

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

Mauerlat can be fixed in several ways:

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

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

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

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

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

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

An interval of 1.2 m is almost never used during installation work. This is due to the fact that despite the rather high level of strength, the metal tile will begin to sag under the weight of snow in the winter or with strong gusts of wind.

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

Conclusion

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

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.

What determines the pitch of the rafters?

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

1. The shape of the roof (gable, single-pitched or multi-pitched).
2. Roof angle.
3. The parameters of the timber that is used for the manufacture of rafters (width, thickness).
4. The design of the truss system (layered, hanging or sliding).
5. The totality of all loads on the roof (covering weight, atmospheric phenomena, etc.).
6. 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. Therefore, we advise you to make all the calculations manually.

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.

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:

1. Static, which includes the weight of the rafter system itself, the weight of the roof, snow lying on the roof and additional elements.
2. 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!

Before the construction of the truss system and the organization of the roof, a number of simple measures must be carried out, which will be the key to the integrity of the structure. This includes choosing the type of roof.

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

Live loads are snow cover on the roof in winter, water flows from rain in summer, wind, the load that a person exerts while carrying out maintenance work during the operation of the roof, etc.

Permanent loads include the weight of the rafter system itself, the weight of the roofing material and the roofing pie, the mass of interior decoration, if it is planned to organize an attic in the attic of the building.

When creating a project for a single-pitched or dual-pitched roof, first of all, they choose the type of truss structure, the angle of inclination of the roof slopes, as well as materials for the construction of the structure. When calculating the distance between the rafters, one should take into account the loads that will affect the roof of the building during operation.

• The weight of the roofing material;

• The weight of the building materials from which the roof truss frame is built;

• Weight of insulation, vapor barrier, waterproofing;

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

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

• Snow weight;

• The weight of a worker performing maintenance and repair of the roof.

For the correct calculation of the pitch of the rafters, it is necessary to take into account the cross section of the elements of the structure under construction, the presence of thermal insulation of the roof, the type of lathing and roofing. Calculations should be performed on the basis of SNiP 2.01.85 "Loads and impacts".

Video on how to calculate the truss system:

Scheme for calculating the distance between the rafters

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

If the project has not been drawn up and the person relies only on the experience of the masters who are entrusted with the construction of the roof, then in this case you need to familiarize yourself with the relevant documentation. These are SNiP 2.01.85 "Loads and Impacts" and "Changes from SNiP 2.01.85".

There is a detailed calculation scheme and a map of the country's climatic zones.

Further, they are determined with the type of roofing system and the purpose of the attic space. Indeed, depending on whether it is an unheated attic or a living room, the loads on the rafters will be different, and, consequently, the course of calculations also changes.

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

So, the pitch of the rafters is the distance between the rafter legs. It can vary within 0.6 m - 1.0 m.

Calculation progress:

1. First, the length of the roof slope is measured. Further, this value is divided by the step length of the rafters of the selected material. This indicator is taken from the SNIP and is unique for each building material and also depends on the beam section used;
2. one is added to the result of previous calculations and rounded up. Thus, an integer value is obtained and it indicates the required number of beams;
3. the length of the roof slope is divided by the resulting integer. The result will show how many beams are needed to build a high-quality and durable roof.

Experts point to the following feature of roofs with a steep slope. When erecting them, you can reduce the distance between the rafters. This is due to the transfer of the load from the beams to the wall of the house.

The distance between the rafters for different types of roofs

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

The distance between the beams for a roof made of metal

The average weight exerted on the roof is 35 kg/m². To withstand it, the roof must have a step of 0.6-0.9 m. In this case, a beam with a section of 50x150mm is used.

However, metal tiles are often used in the construction of country houses and cottages. And in such structures, the attic space is often equipped as a living room.

This leads to the installation of a roofing pie and all kinds of heaters, which, in turn, put an additional load on the rafters. Therefore, it is recommended to increase the cross section of the beam for beams. This is especially true for regions with low air temperatures in winter. The recommended dimensions of the rafters are 50x200mm.

In addition, the distance between the rafters can be adjusted to the width of the insulation. This will not only increase the bearing capacity of the roof, but also simplify the arrangement of the heat-insulating layer, and reduce the consumption of insulation.

The distance between the beams for the roof of corrugated board

The recommended rafter pitch for a roof is 0.6 m - 0.9 m. However, here it is necessary to take into account the operational characteristics of the corrugated board itself. If the step is large, then the corrugated board will “sag” under its own weight, thereby changing the geometry of the roof and its technical characteristics.

To prevent this, you need to mount additional boards with a large section as a crate. They will act in some way as rafters.

The cross section of the rafters for roofing from corrugated board is 50x100 mm or 50x150 mm. The crate is made of a board with a section of 30x100 mm.

The distance between the beams for a roof made of ceramic tiles

Ceramic tiles are a heavy material for roofing. It exerts a load on the rafters in the range of 40-60 kg per m². That is why the distance between the rafters in this case will be minimal - 80-130 cm. The greater the weight, the smaller the distance. However, the latter indicator may decrease, depending on the angle of the roof. The larger it is, the less often you can mount beams.

Installation of the structure for ondulin

The step of the rafter legs under the ondulin should be 60-100 centimeters. For the manufacture of rafters, lumber with a section of 200 × 50 mm is used. This is enough to create the most durable and reliable truss frame.

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

Sometimes a thinned type of crate is used. For its manufacture, a wooden beam is used. The distance between adjacent elements should be less than 30 centimeters. This option, as a rule, is more expensive compared to a continuous crate.

Rafter system under slate

Slate roofing is considered the most common in Russia. The main reason is the low cost of this roofing material, the ease and speed of installation work. Also an important advantage is the possibility of replacing individual damaged slate sheets with new ones.

The distance between the rafter legs for a slate roof should be 80 centimeters. This distance is considered the most optimal.

The crate under the slate should be thinned out. For its manufacture, a board or timber with a cross section of at least 30 millimeters is used. It is this thickness of the timber or board that is required for the qualitative distribution of the weight of the roofing and winter precipitation.

When erecting a rafter system, one should remember about a constant margin of safety. It may be needed in case of bad weather and under mechanical stress.

Rafter frame for a soft roof

Soft roofing includes soft tiles, bitumen-polymer and bituminous roll materials, as well as roofing membranes. The main advantages of this type of roof include low weight, as well as the absence of the need to build a massive rafter system.

The minimum pitch of the rafters is 60 centimeters, and the maximum is 150 centimeters. When erecting a rafter frame under a soft roof, the angle of inclination of the slopes should be taken into account. In other words, the smaller the slope of the roof slopes, the less you need to make the distance between the rafter legs for a continuous crate.

The distance between the rafters also depends on the material from which the crate will be made. The greater the thickness of the plywood or OSB sheet, the greater the pitch of the rafters can be.

Roof made of sandwich panels

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

If the spans from the top of the wall to the ridge of the gable roof are small, then the sandwich panels are mounted without additional supports.

With a span length of more than 400 centimeters, it is necessary to install additional runs. When building a roof from sandwich panels on a residential building, a traditional truss frame is often erected. However, in this case, the distance between the rafter legs can be made large, since they serve as a support for the runs.

Choose the distance between the rafters based on the length of the bearing walls and the length of the material for the runs. Roofing made of sandwich panels is able to withstand high operational loads.

Construction of a truss frame for polycarbonate

Recently, polycarbonate is often used in the construction of roofing. It is used in the construction of sheds, winter gardens and arbors. The rafter frame and crate are made of metal or wood.

Polycarbonate differ in weight, which depends on the thickness of the sheet. The step of the crate for polycarbonate should be from 60 to 80 cm. The crate made of metal or wood is attached to the rafters (straight or arched).

The distance between the rafter legs for polycarbonate, as a rule, is 150-230 cm. To correctly calculate the distance between the rafters, it is necessary to take into account the glazing area, the thickness and dimensions of the sheets. It should also be remembered that polycarbonate sheets are mounted with small gaps.

The rafter is 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 rafter is attached with its upper end to the ridge, and the lower end rests on the Mauerlat, with a straight slope, or on a rack (with a sloping roof). Rafters are made from edged boards with a section of 150x60 mm or a beam of 150x100 mm. The distance between the rafters at which they are located from each other after installation is called a step, which can be in the range of 600 - 1200 mm.

Rafter systems their types

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

What may determine the installation step of the rafters

The step of the roof rafters depends on such factors, as:

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

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

At the same time, it is customary to use rafter legs with a section of 150x50 mm with an optimal distance between the 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 truss structure

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

When calculating the choice of the optimal distance between the rafters for the roof, are based on the following parameters:

1. Type of roofing.
2. View of the truss system and design features of the roof.
3. feasibility and economy.

For a small house, the design calculation for the roof can be done by yourself. True, the method of calculating the elements for the roof truss system is rather complicated, 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. At the same time, the calculation of the step of the rafters will also be based on the standards - the minimum step is 0.6 m, the maximum step is 1.2 m.

Method of calculation

Produced in this way.

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

- 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. (mean distance is considered to be 950 mm).

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

Example, - building length 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/s ˸ 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, it is recommended by experts to calculate 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 roofing

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

The advantage of metal tiles

Often used in the construction of most mansard roofs.

The cross section of wooden rafters under a metal roof 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 vary between 22 - 45 degrees). This limitation of the pitch of the rafters is due to the fact that the crate under the metal tile is mounted with a distance from each other within 300 mm. The standard timber, which is used for the crate, has a section of 30x50 mm or 50x50 mm. And this means that each rafter is subjected to additional load.

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

An important factor in the calculation of the truss structure, is the estimated maximum load on the roof, the formation of which includes:

1. The weight of the entire truss structure.
2. The weight of the crate under the cover.
3. Weight of insulation and roofing.
4. Snow load (determined according to a special, unique for each region, reference book).
5. Wind load (also according to a special guide for the region).
6. The 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, foreseen in advance cases.

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 step.

It should be remembered. There is no universal value for the calculation of truss structures. Each building requires an individual calculation.

Rafters for a shed roof

Shed roofs can often be found on small outbuildings. They can also be used in private residential buildings, but quite rarely. In such cases, the angle of inclination of the roof is rather small, and with this arrangement of the load-bearing beams of the floor, they are under a lot of pressure, especially in winter.

Therefore, for a shed roof, load-bearing floor beams are installed from a beam of large section from 60x150 to 100x220 mm, depending on the width of the overlapped span. At the same time, the distance at which the rafters are laid from each other should be within 400 - 800 mm, depending on the angle of the roof.

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

Gable roof

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

Double pitched roof structure, depending on its area, is mounted from separate rigid elements that enhance the strength of the roof. These include racks that support rafters, puffs that connect rafters to each other, jibs, girders, 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 resulting triangle is isosceles. In regions with strong winds, it is recommended to mount rafters with a slope of approximately 20⁰, and in snowy areas, the optimal angle should be 45⁰.

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

mansard roof

For mansard roof, for the calculated parameter for determining the step between the rafters and their number, a load is taken in the range of 40-60 kg for every 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 section of the rafters, it is recommended to add a small percentage of the margin of safety.

hip roof

Among all roof structures, it is considered one of the most difficult . It's almost 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.

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