Gable roof rafter pitch: dependence of the rafter pitch on the roof material. The step of the rafters of the gable roof At what distance should the rafters be

The gable roof is formed on the basis of a frame that combines the elementary structure of the device and unsurpassed reliability. But the backbone of the roof in two rectangular slopes can boast of these advantages only in the case of a careful selection of rafter legs.

Parameters of the gable roof truss system

It is worth starting the calculations if you understand that the rafter system of a gable roof is a complex of triangles, the most rigid elements of the frame. They are assembled from boards, the size of which plays a special role.

Rafter length

The formula will help determine the length of strong boards for the rafter systema² +b² =c², derived by Pythagoras.

The length of the rafter can be found by knowing the width of the house and the height of the roof.

Parameter "a" stands for height and is self-selected. It depends on whether the under-roof space will be residential; it also has certain recommendations if an attic is planned.

Behind the letter "b" is the width of the building, divided in two. And "c" represents the hypotenuse of the triangle, that is, the length of the rafter legs.

Let's say that the width of half of the house is three meters, and it is decided to make the roof two meters high. In this case, the length of the rafter legs will reach 3.6 m (c = √a² + b² = 4 + √9 = √13≈3.6).

60-70 cm should be added to the figure obtained from the Pythagorean formula. Extra centimeters will be needed to take the rafter leg over the wall and make the necessary cuts.

The six-meter rafter is the longest, therefore it is suitable as a rafter leg

The maximum length of a bar used as a rafter leg is 6 m. If a durable board of greater length is required, then they resort to the splicing technique - nailing a piece from another bar to the rafter leg.

Cross-section of rafter legs

For various elements of the rafter system, there are standard sizes:

• 10x10 or 15x15 cm - for the Mauerlat bar;
• 10x15 or 10x20 cm - for the rafter leg;
• 5x15 or 5x20 cm - for running and strut;
• 10x10 or 10x15 cm - for the rack;
• 5x10 or 5x15 cm - for the bed;
• 2x10, 2.5x15 cm - for crates.

The thickness of each part of the roof supporting structure is determined by the load that it has to experience.

A beam with a section of 10x20 cm is ideal for creating a rafter leg

The cross-section of the rafter legs of a gable roof is affected by:

The rafter pitch affects the cross-section of the rafter legs most significantly. An increase in the distance between the beams entails increased pressure on the supporting structure of the roof, and this obliges the builder to use thick rafter legs.

Table: cross-section of rafters depending on length and pitch

Variable effect on the rafter system

The pressure on the rafter legs is constant and variable.

From time to time and with varying intensity, wind, snow and precipitation affect the supporting structure of the roof. In general, the roof slope is comparable to a sail, which can break under the pressure of natural phenomena.

The wind tends to overturn or raise the roof, so it is important to make all the calculations correctly

The variable wind load on the rafters is determined by the formula W = Wo × kxc, where W is the wind load indicator, Wo is the value of the wind load characteristic for a certain part of Russia, k is a correction factor due to the height of the structure and the nature of the terrain, and c is the aerodynamic coefficient.

The aerodynamic coefficient can range from -1.8 to +0.8. A minus value is typical for a rising roof, and a plus value is for a roof on which the wind presses. In a simplified calculation with a focus on improving strength, the aerodynamic coefficient is considered equal to 0.8.

The calculation of the wind pressure on the roof is based on the location of the house

The normative value of wind pressure is recognized by map 3 of Appendix 5 in SNiP 2.01.07–85 and a special table. The coefficient taking into account the change in wind pressure with height is also standardized.

Table: guideline value of wind pressure

Table: value of the coefficient k

It is not just the terrain that affects the wind load. The area of ​​housing is of great importance. Behind a wall of tall buildings, the house is almost not threatened, but in an open space the wind can become a serious enemy for it.

The snow load on the rafter system is calculated according to the formula S = Sg × µ, that is, the weight of the snow mass per 1 m² is multiplied by a correction factor, the value of which reflects the degree of slope of the roof.

The weight of the snow layer is indicated in SNiP "Roof systems" and is determined by the type of area where the building is built.

Snow load on the roof depends on where the house is located

The correction factor, if the roof slopes are inclined by less than 25 °, is equal to one. And in the case of a roof slope of 25-60 °, this figure is reduced to 0.7.

When the roof is tilted more than 60 degrees, the snow load is discounted. Still, snow rolls down quickly from a steep roof, without having time to negatively affect the rafters.

Constant loads

Loads acting continuously are considered the weight of the roofing cake, including the sheathing, insulation, films and finishing materials for arranging the attic.

The roofing cake creates constant pressure on the rafters

Roof weight is the sum of the weight of all materials used in the construction of the roof. On average, it is equal to 40–45 kg / sq. M. According to the rules, 1 m² of the rafter system should not account for more than 50 kg of the weight of roofing materials.

So that there is absolutely no doubt about the strength of the rafter system, 10% should be added to the calculation of the load on the rafter legs.

Table: weight of roofing materials per 1 m²

Number of beams

How many rafters will be needed to equip the gable roof frame is set by dividing the width of the roof by a step between the beams and adding one to the resulting value. It denotes an additional rafter that will need to be placed on the edge of the roof.

Let's say it was decided to leave 60 cm between the rafters, and the length of the roof is 6 m (600 cm). It turns out that 11 rafters are needed (taking into account the additional beam).

The rafter system of a gable roof is a structure made of a certain number of rafters

The pitch of the beams of the roof supporting structure

To determine the distance between the beams of the roof supporting structure, you should pay close attention to such points as:

• weight of roofing materials;
• the length and thickness of the timber - the future rafter leg;
• degree of roof slope;
• level of wind and snow loads.

After 90-100 cm, rafters are usually placed in the case of choosing a light roofing material

A step of 60-120 cm is considered normal for rafter legs. The choice in favor of 60 or 80 cm is made in the case of building a roof sloped by 45˚. The same small step should be, if desired, to cover the wooden roof frame with heavy materials such as ceramic tiles, asbestos-cement slate and cement-sand tiles.

Table: rafter pitch depending on length and section

Formulas for calculating the rafter system of a gable roof

The calculation of the rafter system is reduced to establishing the pressure on each beam and determining the optimal section.

When calculating the rafter system of a gable roof, proceed as follows:

1. According to the formula Qr = AxQ, they find out what the load per linear meter of each rafter leg is. Qr is the distributed load per linear meter of the rafter leg, expressed in kg / m, A is the distance between the rafters in meters, and Q is the total load in kg / m².
2. Go to the definition of the minimum cross-section of the timber-rafter. To do this, study the data of the table entered in GOST 24454-80 “Lumber of coniferous species. Dimensions ".
3. Based on the standard parameters, the section width is selected. And the section height is calculated using the formula H ≥ 8.6 Lmax sqrt (Qr / (B Rben)) if the roof slope is α< 30°, или формулу H ≥ 9,5·Lmax·sqrt(Qr/(B·Rизг)), когда уклон крыши α >30 °. H is the height of the section in cm, Lmax is the working area of ​​the rafter leg of maximum length in meters, Qr is the distributed load per linear meter of the rafter leg in kg / m, B is the width of the section, cm, Rben is the resistance of wood to bending, kg / cm². If the material is made from pine or spruce, then Rben can be equal to 140 kg / cm² (1 grade of wood), 130 kg / cm 2 (2 grade) or 85 kg / cm 2 (3 grade). Sqrt is the square root.
4. Check if the deflection value complies with the standards. It should not be more than the number that is obtained by dividing L by 200. L is the length of the working section. Correspondence of the deflection value to the L / 200 ratio is feasible only if the inequality is correct 3.125 · Qr · (Lmax) ³ / (B · H³) ≤ 1. Qr denotes the distributed load per linear meter of the rafter leg (kg / m), Lmax - the working area of ​​the rafter leg maximum length (m), B - section width (cm), and H - section height (cm).
5. When the above inequality is violated, the B and H scores increase.

Table: nominal dimensions of thickness and width of sawn timber (mm)

An example of the calculation of the supporting structure

Suppose that α (angle of inclination of the roof) = 36 °, A (distance between rafters) = 0.8 m, and Lmax (working section of the rafter leg of maximum length) = 2.8 m. Material from first grade pine is used as the beams , which means that Rben = 140 kg / cm².

Cement-sand tiles have been chosen for the roofing, and therefore the roof weight is 50 kg / m². The total load (Q) experienced by each square meter is 303 kg / m². And for the construction of the rafter system, beams with a thickness of 5 cm are used.

The following computational steps follow from this:

1. Qr = A · Q = 0.8 · 303 = 242 kg / m - distributed load per running meter of rafter timber.
2. H ≥ 9.5 Lmax sqrt (Qr / B Rben).
3. H ≥ 9.5 2.8 sqrt (242/5 140).
4. 3.125 · Qr · (Lmax) ³ / B · H³ ≤ 1.
5. 3.125 · 242 · (2.8) ³ / 5 · (17.5) ³ = 0.61.
6. H ≥ (approximate height of the rafter section).

In the table of standard sizes, you need to find the height of the rafter section close to the indicator of 15.6 cm.A parameter equal to 17.5 cm is suitable (with a section width of 5 cm).

This value is quite consistent with the deflection indicator in regulatory documents, and this is proved by the inequality 3.125 · Qr · (Lmax) ³ / B · H³ ≤ 1. Substituting the values ​​(3.125 · 242 · (2.8) ³ / 5 · (17, 5) ³), it turns out that 0.61< 1. Можно сделать вывод: сечение пиломатериала выбрано верно.

Video: detailed calculation of the rafter system

The calculation of the gable roof rafter system is a whole complex of calculations. In order for the bars to cope with the task assigned to them, the builder needs to accurately determine the length, quantity and cross-section of the material, find out the load on it and find out what should be the step between the rafters.

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

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

What determines the pitch of the rafters?

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

1. Roof shape (gable, single-pitched or multi-pitched).
2. Roof inclination angle.
3. Parameters of the timber used for the manufacture of rafters (width, thickness).
4. The structure of the rafter system (layered, hanging or sliding).
5. The aggregate of all loads on the roof (coating weight, atmospheric phenomena, etc.).
6. Sheathing 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

For the correct calculation of the cross-section of the rafters and the step of their installation, there are many complex formulas today. But remember that such formulas were at one time developed more so that it was possible not so much to ideally calculate the roof structures, but to study the work of such elements.

For example, today simple online programs are popular that calculate the parameters of rafters well. But it's ideal if you can set specific tasks yourself and calculate everything you need. It is important to understand to the smallest detail what exactly happens in the rafter system during operation, what forces are acting 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 do 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 withstands a large cap of snow, a constant wind at a height and 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 distance between the rafters it will have - this is already a purely aesthetic factor:

In the above illustration, it can be seen that even such a building has its own rafter pitch. Indeed, here it provides both the aesthetic factor and the rigidity of the structure itself. But they choose a step in an arbitrary way.

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

Point 1. The length of the wall and the choice of the pitch of the rafters

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

For example, the easiest way is to install rafters in 1 meter increments, so 7 rafters are standard for a 6 meter long wall. 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 take a step of the rafters more than 2 meters.

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

So, we stopped at the fact that the average distance between the rafters of a conventional roof is 1 meter. But, if there is a significant snow or wind load in the area, or the roof is more or less sloping or just 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 increase 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 there are turbulences, after which the wind hits the eaves overhang of the roof. It turns out that the wind flow, as it were, bends around the slope of the roof, but at the same time trying to raise it. And at this moment, forces arise in the roof that are ready to rip it off or overturn it - these are two windward sides and one lifting side.

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

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

The second point: in the Russian region, an atmospheric phenomenon such as snow constantly affects a 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 places where such a bag is possible, you need to insert paired rafter legs or make a solid crate. The easiest way to identify such places is by the wind rose: single rafters are placed on the windward side, and paired 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:

Clause 3. Issue of insulation and standard width of mats

If you are going to insulate the roof, then it is advisable to place the rafter pitch under the standard dimensions of the insulation plates, which are 60, 80 cm and 120 cm.

Modern insulation today is sold in a standard width, usually at the same standard rafter pitch. If you then take them and adjust to the already existing parameters, then there will be a lot of waste, cracks, cold bridges and other problems.

Item 4. The quality and strength of the lumber used

It is also of great importance what kind of material you use for the construction of the rafter system. So, for each type of wood there is its own regulatory documentation that relates to its bearing capacity:

Because for the manufacture of roof truss systems in Russia, pine and spruce are most often used, their bending strength and features of use have long been spelled out. If you use wood of other species, then it will be possible to display a correction factor.

In addition, if there are sections, cuts or bolt holes on the rafters, at this point you need to calculate the bearing capacity of the bar with a factor of 0.80.

Item 5. Distance between tie rods and floor beams

Another point: if the roof is built with trusses connected to each other, and their lower chord is used simultaneously as floor beams, then the distance between the trusses must be made within 60-75 cm in order to take into account the design of the future floor.

Item 6. Loads on roof truss assemblies

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 repair, and similar factors.

And all these factors are capable of simultaneously affecting the roof at a certain moment, and therefore there is such a thing as critical value. This is exactly the value of the loads at which the roof does not withstand and deforms.

Therefore, if a building is being built with significant spans, then steel trusses are necessarily used. The fact is that there is no stress 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 trusses is calculated depending on the type of roof and the structure 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 nodes of the truss in 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 support the entire roof, and its weight is critical in this case:

Item 8. Convenience 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 the solid crate? 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 along the edges need to be fastened directly to the rafter or crate, and it is important that they match. Otherwise, the work on roofing will easily turn into a living hell at a height, believe me.

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

Determination of the totality of loads on the roof as a whole and the rafter separately

So, we have determined that, in addition to other design factors, a whole set of loads simultaneously acts on the roof rafter system: the weight of the rafter system, a cap made of snow, wind pressure. After you add all the loads together, be sure to multiply them by a factor of 1.1. So you all rely 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 structure will be frail - feel free to add 1-2 rafters to the total, and you will be calm about your home.

You need to do the calculation for destruction, i.e. full load on the roof. All these loads are determined by the technical characteristics of materials and SNiPs.

The standard roof structure is rafters, lattice girders, and each of these elements is triggered only by the load that presses 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 pitch of their location, you change the collection area of ​​the load on the rafters - by 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 load-bearing capacity of the roof will increase significantly:

With this calculation, try to ensure that the longest rafter in your project is no more than six and a half meters, otherwise, splicate along the length. Let's explain in more detail now. So, on roofs with a slope of up to 30 degrees rafters are the so-called "bendable elements". Those. they work precisely in bending, and there are certain requirements for them. And the possibility of deflection of the rafters is calculated using 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 "bend-compressed" elements. That is, they are affected not only by a uniformly distributed load, which causes the bending of the rafters, but also by the forces that are already acting along the axis of the rafter. In simple terms, here the rafters not only sag slightly under the weight of the roof, but also squeeze from the ridge to the Mauerlat. In addition, the crossbar, which usually holds the two rafter legs, must be checked for tension.

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

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

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

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

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

What are the calculations based on?

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

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

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

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

Method for calculating the distance between the rafters

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

Method for calculating the pitch of the roof frame:

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

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

Rafter leg step depending on material

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

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

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

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

Roof structure for corrugated board

Roof structure for ceramic tiles

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

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

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

Roof structure for metal tiles

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

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

Roof structure for ondulin

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

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

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

Roof structure for slate covering

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

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

Rafters for shed and gable roofs

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

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

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

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

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

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

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

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

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

It is pointless to argue about the importance of a roof for any building. It is not for nothing that in the entire history of mankind, more than a dozen different types of roofs have been invented, from simple to quite complex in design and construction. An important element when planning the construction of a roof is the step between the rafters - strong bars that are the basis of the structure. This is what will be discussed in this article.

The distance between the base of the roof slopes is not constant and depends on the following components:

• type of roof;
• slope angle;
• the type of roofing material intended for installation;
• the dimensions of the rafter section.

Before proceeding with the process of erecting the upper structure of the house, a calculation should be performed, having determined the optimal distance between the rafters.

Gable roof rafter pitch

The most widespread in our country are gable roofs. They represent a structure having two parallel planes with an inclination angle relative to the horizon from 20 to 50 degrees.

If the slope of the gable roof is insufficient in snowy areas, there is a risk of accumulation of large snow masses, which can lead to the destruction of the structure. An increase in the angle of slopes in regions with a predominance of strong winds is also fraught with high loads and the danger of breaking not only the roof, but the entire structure as a whole.

Mansard roof rafter system

Most private homes have an exploited under-roof space called an attic. This design is characterized by an increased slope height, which is caused by the need to create a living space of a comfortable height. As a rule, the slopes of the attic roof are broken, with a varying slope angle. For their installation, a double rafter system is used.

The steepness of the lower half slopes of the attic roof significantly exceeds the slope of their upper extensions. The plane load perceived by them is not great. Thanks to this, the rafters in the lower part can be installed with a maximum pitch. It is recommended to mount the upper ridge slopes with a reduced distance from each other.

Rafters in a pitched roof

For outbuildings and some private houses, roofs with one slope are used. Due to the limitation of the angle of inclination, high pressure is exerted on them. Experts recommend using lumber with an increased cross-section for the rafters of a pitched roof, with the installation of a minimum step from each other.

When calculating the distances at which the roof beams are installed, special attention should be paid to the amount of snow load in a particular area. With a small slope, this characteristic is of great importance. It is better to choose roofing material for such roofs with a minimum own weight, which will reduce the bending load.

Hip roof rafter system

The most difficult in construction is the rafter system of the hip roof. This type is called four-slope, since the roof is formed not only by the side, but also by additional end slopes, where the installation of the rafters is carried out not on the ridge, but on the corner bowstrings. This places special demands on the organization of the roof frame.

Under a hip roof, an attic is not often arranged. This is due to the small angle of inclination of the rafters and the roof as a whole. In the case of an increase in the angle of the slopes to the horizon, the distance between the rafters is increased, with a decrease, on the contrary. An additional aspect of the calculation is the used roofing material.

Dependence of the pitch of the rafters on the roofing material

In addition to snow and wind loads, which are variable, a constant (static) also acts on the roof, the force of which depends on the used roofing material. It is no secret that different types of roofs have their own weight, which can differ by a factor of 10 or more.

The correct choice of material affects not only the upper, but also all other parts of the structure of a residential building and other buildings. No wonder, when designing a foundation, it is necessary to decide in advance on the choice of a roof.

Roof from profiled sheet

Currently, one of the most common roofing materials is profiled sheet, produced in galvanized or with subsequent polymer coating. The distinctive features of the profiled sheet include the following parameters:

1. High corrosion resistance;
2. As a result, a long (more than 15 years) service life;
3. Easy installation even without the required qualifications;
4. Small sheet weight (weight of 1 m 2 is 4-5 kg).

Since this roofing material does not exert a high load on the rafter system, the distance between the elements is chosen as much as possible for a particular angle of inclination. In addition, the profiled sheet does not require high strength characteristics from the roof lathing. All this together allows you to minimize the overall load on the foundation and walls.

Metal roofing

The second common type of steel roofing material is metal. This type of profiled sheet, which successfully imitates natural clay material, but with a lower weight (10 or more). A feature of the rafters for metal tiles is the smaller section size.

When choosing at what distance to install the rafters, first of all, you should be guided by the dynamic load. Like the profiled sheet, the metal tile is not demanding on the size of the rafter legs and is well mounted on a crate made of an inch board of coniferous species. All this makes the metal roof cost effective.

Rafter system for ondulin

In the 21st century, wavy sheet materials have been replaced by a more durable and lightweight analogue - ondulin. Among others - the lightest material. Sheet weight does not exceed 6 kg.

The small thickness of the sheets of ondulin at the angles of the slopes of less than 15 ° requires the arrangement of a continuous sheathing of plywood sheets, for example, which will require an appropriate step of the rafters. You should pay attention to this when calculating.

Slate roof

Not so long ago, a corrugated material from an asbestos-cement mixture called slate was widespread. High weight and fragility are the main disadvantages, however, to this day, he finds his fans in the construction of various outbuildings.

A high mass, comparable to the weight of clay tiles, will not allow using the same rafter system as for metal tiles. Building codes determine the minimum slope angle of a slate roof of 22 degrees or more. Otherwise, the load from the material itself and the rafter system with a crate exceeds the permissible parameters. The pitch of the inclined beams, as well as their section, are selected individually in each case.

Roof polycarbonate

In recent years, an artificial polymer material - polycarbonate - has been increasingly used on the roofs of verandas and gazebos. Produced in two versions - monolithic and honeycomb. The first is similar in properties to ordinary quartz glass, but significantly surpasses it in strength. The second one has less mechanical properties, but high thermal insulation and light transmittance.

Cellular polycarbonate is usually much lighter than its monolithic counterpart. It is used as a roof without the use of lathing, provided that the step does not exceed ½ the width of the sheet of material. The high strength of the monolithic analogue also allows you to avoid elements transverse to the rafters. Sufficient flexibility allows you to cover semicircular roofs on a metal frame, the pitch of which does not exceed 0.9 meters.

Thematic material:

Rafters under a soft roof

The original pattern can be obtained through the use of soft roofing materials, spread with an adhesive layer. They are installed on a solid crate made of plywood or OSB. The step of the rafters should allow the sheets to be fixed, so it is chosen to be a multiple of ½ of the width. Provided the standard dimensions of plywood are 1520x1520 mm, the center distance between the rafters will be: 1520: 3 = 506 mm.

Step rafters under insulation

The installation of residential under-roof spaces is often combined with the laying of insulation sheets in the rafter gap. The most common slabs with dimensions of 600x1000mm. We use these parameters as starting points.

Scheme for calculating the pitch of the rafters

According to building codes, the pitch of the roof rafters is in the range of 0.6 - 1 meter. Its final calculation is performed according to a simple formula, depending on the total length of the roof. To calculate, you must perform the following list of actions:

1. determine how much distance should be between the rafters for your specific building conditions. The reference book determines the value of wind and snow loads in the area.
2. the length of the roof is divided by the desired distance by adding one. The result will be equal to the number of rafter legs that are installed on one roof slope. In the event that the value is not an integer, it is rounded up.
3. the length of the roof is divided by the number of rafters calculated above, we get the final step in meters.

For example, with a slope of 30 degrees, the maximum distance between the rafters of a gable roof under the metal tile is 0.6 measure. The length is assumed to be 16 meters. Hence:

1. 16:0,6+1=27,66;
2. rounding the result, we get 28 rafters per slope;
3. 16: 28 = 0.57 meters - the center distance of the rafter legs for these specific conditions.

As you can see, the calculation technology is not complicated, but this is just a rough diagram. Taking into account many of the other parameters mentioned above can make certain adjustments.

The quality and durability of the roof largely depends on the correct calculation of the pitch of the rafters. It affects the installation of insulation, fastening of the roofing material and the installation of additional parts. Pay attention only to the requirements for the distance under the roofing sheets, then problems with the insulation plates may arise. And vice versa, adjusting the insulation to the size of the insulation can make the frame too weak, and in winter there will be a threat of collapse. How to correctly calculate the distance between the roof rafters? We will talk about this in our article.

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 a few centimeters downward. For an accurate determination, the following calculations must be performed:

1. Determine the length of the slope by measuring along the eaves of the house. Let's assume that this is 17.8 meters.
2. Divide the resulting figure by the planned pitch of the rafters. If it was decided that the distance between the beams will be 0.8 meters, then 17.8 / 0.8 = 22.25.
3. Next, round the result up and add one: 23 + 1 = 24. At this stage, the number of required rafters is determined.
4. Now we calculate the distance between the axes of the beams. To do this, the length of the ramp must be divided by the number of rafters: 17.8 / 24 = 0.74 m.

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

Often, when planning the 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 lighten the structure. Self-calculation will help to more accurately determine the required pitch of the rafters of the gable and shed roof.

Calculation of the step depending on the roofing material

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

Corrugated board

The step of the rafters under the corrugated board can vary from 0.6 to 0.9 m. The end result depends on additional conditions, which we will talk about below. If, for some reason, the step should be larger, add a transverse board with a large section. In this case, the rafters themselves are usually 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 borders of the eaves should be 1.5 cm thicker than usual. This is done on the basis of the need to mount ventilation, chimney or drain.

Ceramic roof tiles

The main difficulty in designing a rafter 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.

For such a coating, dry beams are used, with a moisture content of only 15%. Their section should be either 50x150 or 60x180 mm. With such indicators, the maximum permissible 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 final decision is influenced by the slope of the roof: at 15 °, a step is made 0.8 m, at 75 ° - 1.3 m.

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

The distance between the lathing boards is selected so that each tile intersection has its own base. The standard length of the material is 400 mm, and the overlap during installation ranges 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 the more expensive ceramic material, but at the same time 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 the metal tile is less than the ceramic one, therefore, a simpler frame is required. The cross-section of the beams is reduced to 50x150 mm and the step between the battens is increased. The step of the rafters under the metal tile ranges between 0.6 and 0.95 m.

Ondulin

The permissible pitch for the ondulin coating is 0.6-0.9 meters. The standard section of the rafters is 50x200 millimeters. These dimensions will allow you to withstand the generated load of the roofing cake on the gable roof.

On top of the counter-lattice, a lathing made of bars measuring 40x50 millimeters is attached. The pitch between the center 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. Some of the factors are:

1. 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 inclination of the roof over 45 °, then it is allowed to increase the step.
2. The choice of insulation. To reduce the cost of insulation boards, it is recommended to take into account their standard sizes. Mats are produced in widths of 600, 800 and 1200 mm. If this condition is neglected, then a large number of undercuts will appear, cold bridges and construction will drag on.
3. The quality of the lumber. Here, the species of wood, grade and section are taken into account. As discussed above, strength is influenced by how well the beam has been dried. When purchasing wood, pay attention to the evenness and presence of defects in the form of knots and traces of pests.
4. Floor beams and ties. If you equip an 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 a pitched roof is different. Even if he makes several ramps, for each it is necessary to make the calculation individually. This is especially true for buildings with different eaves lengths.

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