Through what distance do the rafters put in the construction of roofs. Step of gable roof rafters Distance between gable roof rafters for slate
The distance between the rafters is one of the key parameters that affect the strength of the structure. Competent calculation of the installation step of the rafters allows you to build a roof that is resistant to high operational loads.
Roof loads and rafter system calculation
Development of a project for a single or two pitched roof starts with type selection truss system, the angle of inclination of the slopes (roof height) and materials for the construction of the structure. The calculation of the distance between the rafter legs is carried out taking into account the loads that the roof will experience during operation. Permanent loads include:
- the weight of the materials from which the truss system is made;
- the weight roofing;
- weight of roofing cake materials (waterproofing, vapor barrier, insulation);
- the weight of the finishing elements of a residential attic or attic.
In addition to permanent loads, the roof also experiences temporary ones, which include:
A step is the distance between the rafters of one slope. When calculating a shed, gable or complex roof, the following scheme is usually followed:
- the length of the future roof slope is measured;
- the resulting value is divided by the optimal numerical value of the pitch of the rafters;
- one is added to the obtained value, the result is rounded off;
- the length of the roof slope is divided by the rounded result.
The final result will determine how far the rafter legs should be placed. The determination of the step cannot be extremely accurate, since it is necessary to take into account a number of additional factors, including the width of the insulation, the installation features of the crate under different kinds roofing material. If a roof with a chimney is being designed, the pitch can be adjusted according to its location so that it is not necessary to remove part of the rafter in the future and install a supporting structure, such as a special rafter system.
The distance between the rafters under the slate
Slate is a traditional roofing material. Its advantages include such characteristics as resistance to external influences (excluding mechanical ones) and low cost. Slate allows you to create a roofing, the repair of which can be reduced to the replacement of individual elements. Slate is heavy and requires the installation of a sufficiently powerful truss system. The calculation of the distance at which it is necessary to put the rafters under the slate is carried out taking into account the cross section of the beam for manufacturing rafter legs.
The optimal solution is to install the system under the slate, in which the gap between the rafters must be at least 800 mm. In order for the slate structure to withstand not only the weight of the material, but also increased external loads, the crate is made of timber or boards with a cross section of at least 30 mm. When calculating the truss system for slate, it should be read that this material has rather large restrictions on the choice of the angle of inclination of the slopes.
Rafters for metal roofing
Metal tiles are actively used as a practical and aesthetic roofing material when arranging a shed, gable, hip or complex roof. The frame for the metal tile is built according to standard principles. To calculate at what distance it is better to place the rafters, it is necessary to take into account the loads and the angle of the roof. The metal tile is characterized by relatively low weight, so it can serve as a replacement for the old roofing of slate or ceramic tiles. In this case, the rafters do not need to be strengthened or the pitch of their installation changed.
The standard step of rafters for metal tiles is 600-900 mm. The cross section of the elements can be 50-150 mm - this is enough to create a reliable frame for a metal tile. But if it is planned to use insulation, the layer of which in areas with low winter temperatures should be 200 mm, it is recommended to use a 200x50 beam for rafters under metal tiles so as not to mount an additional system that holds the insulation. The gap between the rafters under the metal tile is best adjusted to the width of the sheet or roll heat insulator.
Decking: rafters and crate
The professional flooring belongs to easy and convenient roofing materials in application. Galvanized or covered with a decorative and protective layer, corrugated board can be used both for mounting a pitched roof of a utility room or garage, and for gable roof residential building. How to calculate the distance required to install the rafters under the corrugated board?
To ensure the necessary rigidity of the structure, it is enough to install the rafters under the corrugated board in increments of 600-900 mm. In this case, it is necessary to pay attention to the angle of the roof. The calculation shows that with high external loads, it is better to lay the corrugated board on the system with a minimum step. But if the distance between the rafters under the corrugated board is close to the maximum, and the angle of the roof slope is small, then the structure is strengthened by using a more frequent crate. In this case, the step of the crate under the corrugated board should be about 50 mm, the width of the elements should be at least 100 mm.
Rafter system for soft roofing
Soft roofing includes bituminous and bitumen-polymer roll materials, roofing membranes, as well as soft tiles. A soft roof is characterized by relatively low weight and no need to install a massive roof structure.
The minimum distance between the rafters is 600 mm, the maximum is 1500 mm. When installing the support under soft roof it is important to take into account the angle of inclination of the slopes: the smaller the angle, the smaller the distance between the supports for a continuous crate should be. The choice of step is also influenced by the thickness of the material for the crate - the thicker the sheet of plywood or OSB, the greater the installation step of the rafter legs can be.
Ondulin: calculation of rafters
Ondulin (bituminous slate) is laid on a flat, continuous crate made of sheet material. This allows the roofing to successfully resist wind and snow loads. The crate under the ondulin rests on the rafters, which should be located in increments of 600 - 1000 mm, depending on the angle of inclination of the gable or shed roof.
Rafters for ondulin are made of timber with a section of 200 × 50 mm. When choosing at what distance to put the rafter legs for the structure under the ondulin, it is recommended to take into account the width of the insulation material in order to simplify its installation. This calculation allows you to reduce the financial costs of arranging the roof.
Sandwich panel roof
Sandwich roofing is most often erected on sip-panel houses or hangar-type buildings. A feature of the sandwich is its bending rigidity, which makes it possible to dispense with the installation of traditional rafters. Small spans from the ridge of a gable roof to the upper part of the wall (or the distance between the supporting structures of a shed roof) allow the installation of a sandwich without additional supports.
If the span exceeds 4 meters, additional girders must be installed. To install a sandwich roof on a residential building, a traditional truss system is often installed, but in this case the rafters can be positioned with big step- they act as a support for the runs. The distance between the rafter legs is selected based on the length of the available material for the runs and the length bearing walls. Technical specifications sandwich allow the roof to withstand high operating loads.
Polycarbonate: erection of the supporting structure
Polycarbonate has recently been actively used as a roofing material. First of all, polycarbonate is in demand in the construction of gazebos, sheds, winter gardens. The crate and truss system for polycarbonate can be made of wood or metal.
Polycarbonate varies in weight depending on the thickness of the sheet. The crate for polycarbonate is recommended to be done in increments of 600-800 mm. The crate (wooden or metal) is mounted on rafters, which can be straight or arched. Usually the gap between the rafters for polycarbonate is from 1500 to 2300 mm. In order to correctly calculate at what distance it is better to bleed the rafters, it is necessary to take into account the area of glazing, the dimensions and thickness of the sheets, and take into account that polycarbonate is attached with gaps for thermal expansion.
The distance between the rafters of a gable and single-pitched roof
Find out what distance between the rafters you need to make for a gable and shed roof. The maximum distance between the rafters for metal tiles, ondulin and soft roofing.
The distance between the rafters: principles and examples of calculating the pitch of the truss system
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's why the whole point is to pick up optimal step rafters on 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:
- The shape of the roof (gable, single-pitched or multi-pitched).
- Roof angle.
- The parameters of the timber that is used for the manufacture of rafters (width, thickness).
- The design of the truss system (layered, hanging or sliding).
- The totality of all loads on the roof (covering weight, atmospheric phenomena, etc.).
- Lathing material (20x100 or 50x50) and its parameters (solid, with gaps of 10 cm, 20 cm or solid plywood)
And each of these parameters must be taken into account, which is exactly what this article is about.
Decorative rafters: 0% load
First of all, decide on the most important point: the type of roof and its purpose. The fact is that the roof of a residential building in winter can withstand a large cap of snow, a constant wind at a height, and it is often insulated from the inside, but to the rafter system small gazebo, hidden under the crowns of trees, have completely different requirements.
For example, if you are building a pergola in its classical sense, then it does not matter at all what exactly the distance between the rafters will be - this is already a purely aesthetic factor:
In the above illustration, it can be seen that even in such a building there is a step of rafters. After all, here it provides both an aesthetic factor and the rigidity of the structure itself. But the step is chosen arbitrarily.
Functional rafters: detailed calculation
We approach the main question: what distance should be between the roof rafters of a residential building? Here, be patient and carefully study all the nuances.
Item 1. Wall length and rafter spacing
First of all, the step of installing rafters on the roof of a residential building is usually chosen according to the structural size of the building, although taking into account many other factors.
For example, it is easiest to install rafters in increments of 1 meter, so for a wall 6 meters long, 7 rafters are installed as standard. At the same time, you can save money by placing them with a distance of 1 and 2 meters, and you get exactly 5 rafters. It can also be placed with a distance of 2 and 3 meters, but reinforced with a crate. But it is highly undesirable to make a step of rafters more than 2 meters.
Item 2. Influence of snow and wind loads on the shape of the roof
So, we settled on the fact that the average distance between the rafters of an ordinary roof is 1 meter. But, if there is a significant snow or wind load in the area, or the roof is more or less flat or simply heavy (for example, covered with clay tiles), then this distance must be reduced to 60-80 cm. But on a roof with a slope of more than 45 degrees, it can be even zoom to a distance of 1.2m-1.4m.
Why is it so important? Let's figure it out. The fact is that the air flow collides on its way with the wall under the roof of the building, and turbulence occurs there, after which the wind hits the eaves of the roof. It turns out that the wind flow, as it were, goes around the slope of the roof, but at the same time trying to raise it. And in the roof at this moment there are forces that are ready to rip or overturn it - these are two windward sides and one lifting.
There is another force that arises from wind pressure and acts perpendicular to the slope, trying to push the roof slope inwards. And the greater the angle of inclination of the roof slope, the more important are the safe wind forces and the less tangential. And the larger the angle of the slope, the less often you need to put rafters.
To understand whether you should make a high roof or a flat one, this map of the average wind load will help:
The second point: in the Russian region, such an atmospheric phenomenon as snow constantly affects the standard roof of a house. And here, too, you need to consider that the snow bag usually accumulates more on one side of the roof than on the other.
That is why in such places where such a bag is possible, it is necessary to insert paired rafter legs or make a continuous crate. The easiest way to determine such places is by the wind rose: single rafters are placed on the windward side, and paired rafters on the leeward side.
If you are building a house for the first time, then you will not find your own worldview, but determine the average snow load for your area according to official data:
Point 3. The issue of insulation and the standard width of mats
If you will insulate the roof, then it is advisable to put the step of the rafters under standard sizes insulation plates, and these 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 normative documents, 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 roof trusses connected to each other, and their lower belt is used simultaneously as floor beams, then the distance between the trusses must be made within 60-75 cm to take into account the design of the future floor.
Item 6. Loads on truss nodes
So, here are the main loads that act on the roof truss system:
- Static, which includes the weight of the rafter system itself, the weight of the roof, snow lying on the roof and additional elements.
- Dynamic, which includes wind force, unexpected damage to the roof, the weight of a person and equipment for repairs, and similar factors.
And all these factors are 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 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 along the edges you need to fasten directly into the rafter or crate, and it is important that they match. Otherwise, roofing work will easily turn into a living hell at a height, believe me.
That is why, even before starting installation, it is necessary to make a layout, check everything several times. And to know some important subtleties for each type of coating.
Determining the totality of loads on the roof as a whole and the rafters separately
So, we have determined that, in addition to other design factors, a whole set of loads simultaneously acts on the roof truss system: the weight of the truss system, a snow cap, wind pressure. After you add all the loads together, be sure to multiply them by a factor of 1.1. So you all count on unexpected favorable conditions, that is, lay an additional 10% percent strength.
And now you just have to divide the total load by the planned number of rafters and see if each of them will cope with its task. If it seems that the design will be frail - feel free to add 1-2 rafters to the total, and you will be calm for your home.
You need to make a calculation for destruction, i.e. to the full load that acts on the roof. All these loads are determined by technical specifications materials and SNiPam.
The standard roof structure is rafters, lattice runs, and each of these elements works only on the load that presses on it, and not on common roof generally. Those. each individual rafter has its own load, total, but divided by the number of rafter legs, and by changing the step of their location, you change the load collection area on the rafters - reducing it or increasing it. And, if it is inconvenient for you to change the pitch of the rafters, then work with the parameters of the section of the rafter legs, and the total bearing capacity of the roof will increase significantly:
In this calculation, try to ensure that the longest rafter in your project is no more than six and a half meters, otherwise, splice along the length. Now let's explain in more detail. So, on roofs with a slope of up to 30 degrees, the rafters are the so-called "bendable elements". Those. they work specifically for bending, and there are certain requirements for them. And the possibility of deflection of the rafters is calculated according to a special formula, and if the result exceeds the norm, then the rafters are increased in height and a new calculation is made again.
But on the roof with a warehouse slope of more than 30 degrees, which rafters are already considered “bendable-compressed” elements. That is, they are affected not only by a uniformly distributed load, which causes the rafters to bend, but also by forces that are already acting along the axis of the rafter. talking plain language, here the rafters not only bend a little under the weight of the roof, but are also squeezed from the ridge to the Mauerlat. In addition, the crossbar, which usually holds back two rafter legs, must also be checked for tension.
As you can see, even a person who is far from construction can cope with such calculations. The main thing is to take everything into account, be attentive and ready to spend a little more time on design, so that later all the work goes like clockwork!
The distance between the rafters: what step should be between the rafters
Detailed instructions on how to correctly calculate the distance between roof rafters different designs, taking into account the amount of loads and the material used.
truss system is undoubtedly the most important structural element any pitched roof. The consequence of its improper installation can be not only the deformation of the roof, requiring expensive repairs, but also the complete collapse of the roof on the head of an insolvent builder.
The following four main factors influence the stability of the truss system to various loads:
- fastening strength rafters to the ridge and Mauerlat;
- correct calculation of the supporting structure for rafters, depending on the length of the span;
- choice roofing material;
- step between the rafters.
The topic of this article is the choice of material and pitch between the rafters, taking into account the intended type of roof.
What are the calculations based on?
When making calculations, four main indicators are taken into account:
The most important is the calculation of the maximum roof load, consisting of:
- rafter weights,
- crate weight,
- weight of roofing material and insulation,
- snow load (reference information unique to each region),
- wind load (also reference information),
- person's weight (if repair or cleaning is necessary, 175 kg/sq.m).
To carry out accurate calculations, experts use special formulas from strength of materials, but when building a private one, you can use approximate recommendations.
Method for calculating the distance between the rafters
Accurate Distance Calculation between rafters is based on the results of a preliminary calculation of the maximum allowable step. To make this calculation, the total load, the roof structure and the material used on the rafter legs are taken into account.
Method for calculating the step of the roof frame:
- Measure the length of the roof from end to end.
- Received distance divided by the maximum step size.
- The resulting value is rounded up to a larger integer.. This is the number of inter-rafter spans.
- Divide the total length of the roof by the number of spans. This is the required rafter step size.
- Add one to the number of spans.It required amount rafters.
For some types of roofing material it is desirable to use fixed distances between the rafters, in which case an additional rafter with a non-standard pitch is installed on one of the ends of the roof.
Rafter leg step depending on the material
Can be increased as the strength of the material from which they are made increases. Most often, for each roofing material, the step of the rafters required for it and the permissible sections of the rafter legs, taking into account the load, are indicated.
These recommendations are regional character and are applicable to the central strip 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 cross section of the rafters.
In those regions where the snow load significantly exceeds the wind load, the use of roofs with a slope is recommended. 35 – 45 degrees.
truss system in private houses, it is most often made of logs with a diameter 12 - 22 cm, beam/board thickness 40 – 100 mm and width 150 - 220 mm. When calculating, it is possible to allow the use instead of logs of a certain diameter of bars of the same width, thickness 100 mm.
Rafter structure for corrugated board
Roof structure for ceramic tiles
Ceramic tiles has significant differences from other types of roofing materials, which must be taken into account when designing a truss systems for it:
- 5 to 10 times the weight resulting in doubling the weight of the entire roof. This leads to the need to use the frequent step ( 0.6-0.8 meters) and increased by 25% cross-sectional area of the rafters.
- Fine-grained nature of the material. Increases the requirements for the accuracy of the installation of the transverse battens. The step of the sheathing beam, the permissible sections and installation angles are always indicated in the instructions for each specific tile model.
There are models of tiles designed for installation at an angle. 12 - 60 degrees, ordinary models are recommended to be mounted at an angle 20 - 45 degrees. For crates most often use timber 50x50 mm.
Roof structure for metal roofing
metal tile essentially a less rigid and lighter decorative option corrugated board, so the requirements for the rafter system, in particular for the recommended sections of the rafter legs, are largely the same.
A feature of the truss structure under the metal tile can be called a significant reduction in the pitch of the crate, 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 for the crate. The angle of the roof slope is selected from 22 to 45 degrees.
Rafter structure for ondulin
Ondulin- slate based on fiberglass and bitumen, produced by only one manufacturer and has unified technological installation standards:
- permissible mounting angle - 5 - 45 degrees;
- distance between rafters - 60 cm at a slope angle of up to 15 degrees, up to 90 cm - at an angle of more than 15 degrees;
- crate - solid plywood on a slope up to 10 degrees, board 30x100 mm step by step 45 cm on the slope 10 - 15 degrees, beam 40x50 mm step by step 60 cm on the slope above 15 degrees.
Given the low weight of the material, the cross section of the rafter legs is selected based on the same recommendations as for corrugated board.
Rafter construction under a covering from slate
Slate- traditional, rather rigid and heavy roofing material, fragile, but resistant to constant loads. Such properties change the recommendations for the optimal design of the truss system towards the use of more durable elements and increasing the step between them:
- Due to 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, you can use the recommendations for installing an ondulin as an instruction, adjusted for the universal batten pitch - 55 cm.
- Permissible angle for installing rafters under slate - up to 60 degrees.
- The installation step is selected from 0.8 to 1.5 m, depending on the section of the rafter leg, the load and the presence of the crate material.
- The material for the rafters is selected with a slightly larger section than for light roofs. For the most popular move 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.
- Material for the crate selected in accordance with the distance between the rafters - timber 50x50 mm up to 1.2 m, beam 60x60 mm - 1.2 m and more.
- Lathing step is selected in such a way that each sheet lies on three bars, and has an overlap on 15 cm with neighboring. Considering the standard sheet length 1.75 m, step is used 80 cm.
Rafters for single-pitched and double-pitched 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, directly on the crown.
No extra ribs stiffness sets the maximum slope angle - 30 degrees and allowable span length - less than 6 m(for wooden rafters). The optimal angle 15 - 20 degrees.
Such roofs usually not subject to wind loads, but require protection from precipitation. In regions where wind pressure is comparable to snow load, correct installation shed roof "downwind" can lead to self-cleaning of the roof.
gable roof is a system of parallel triangles interconnected 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, ties, jibs, support beams, and so on.
Step between rafters gable roof make taking into account the size of the heat insulator, which is placed 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 lead to an increase in material consumption and to a multiple increase in the windage of the roof. The optimal slope angle for snowy regions is 45 degrees, for windy - 20 degrees.
Distance between rafters roofs attic type determines how much of the load falls on each element. When designing hip roofing 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 self-assembly the roof is worth taking a lesson from an experienced carpenter and reading educational literature.
- When choosing a rafter pitch, do not forget about thermal insulation. All types of insulation can shrink a little, so you can buy them by 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 a person on the roof can be ignored. This removes 175 kilograms of the calculated load on square meter and allows you to put rafters on average 20% less often.
- Snow and wind load in Russian regions can be found by regulatory documents- maps in the application AND to .
- There are many online roof calculators on the web., capable of, if not correctly calculating all the nuances, then at least advise on the selection of the correct section for the rafters.
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 when carrying out maintenance work during the operation of the roof, etc.
Constant loads include - the weight of the rafter system itself, the weight of the roofing material and the roofing pie, the mass 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 finishing material 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 correct calculation 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 detailed diagram conducting calculations and a map of the climatic zones of the country.
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:
- 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;
- one is added to the result of previous calculations and rounded up more. Thus, an integer value is obtained and it indicates the required number of beams;
- the length of the roof slope is divided by the resulting integer. The result will show how many beams are needed to build a high-quality and durable roof.
Experts point to the following feature of 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 roof construction material used.
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 construction. 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 you need to take into account performance characteristics 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 implementation. 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
A roof 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 construction of the roof truss system and the subsequent roofing - milestones in any construction. This matter is very complicated, associated with comprehensive preparation, which includes the calculation of the main elements of the system and the acquisition of materials of the desired section. Not every novice builder will be able to design and sanitize a complex structure.
However, often in the construction of adjoining buildings, utility or auxiliary buildings, garages, sheds, gazebos and other objects, the special complexity of the roof is not required at all - the simplicity of design, the minimum amount of material costs and the speed of work, which are quite feasible, come first. for independent performance. It is in such situations that the rafter system becomes a kind of "lifesaver"
In this publication, the main focus is on the calculations of a shed roof structure. In addition, the most typical cases of its construction will be considered.
The main advantages of shed roofs
Despite the fact that not everyone likes the aesthetics of a building over which a shed roof is mounted (although the question itself is ambiguous), many owners of suburban areas, when building buildings, and sometimes even a residential building, choose this option, guided by a number of advantages similar design.
- Materials for a shed truss system, especially if it is being built over a small outbuilding, will require very little.
- The most "rigid" flat figure is a triangle. It is he who underlies almost any truss system. In a shed system, this triangle is rectangular, which greatly simplifies the calculations, since all geometric relationships are known to everyone who graduated from high school. But this simplicity does not affect the strength and reliability of the entire structure.
- Even if the owner of the site, who is leading an independent construction, has never previously encountered the construction of a roof, the installation of a shed truss system should not cause him excessive difficulties - it is quite understandable, not so complicated. Often, when blocking small outbuildings or other adjoining structures, it is quite possible to do not only without calling a team of specialists, but even without inviting assistants.
- When erecting a roof structure, the speed of work is always important, naturally, without loss of quality - you want to protect the building from the vagaries of the weather as quickly as possible. For this setting shed roof is unequivocally a "leader" - in its design there are practically no complex connecting nodes that take a lot of time and require high-precision adjustment.
How significant are the shortcomings of a single-pitched truss system? Alas, they exist, and they also have to be reckoned with:
- An attic with a shed roof is either not supposed at all, or it turns out to be so small that you have to forget about its wide functionality.
- Based on the first point, there are certain difficulties in ensuring sufficient thermal insulation of the premises located under a pitched roof. Although, of course, this can be corrected - nothing prevents the roof slope itself from being insulated or from placing an insulated attic floor under the rafter system.
- Shed roofs, as a rule, are made with a slight slope, up to 25 ÷ 30 degrees. This has two implications. First, not all types of roofing are suitable for such conditions. Secondly, the significance of the potential snow load increases sharply, which must be taken into account when calculating the system. But on the other hand, with such slopes, the influence of wind pressure on the roof is significantly reduced, especially if the slope is correctly positioned - to the windward side, in accordance with the prevailing winds in this area.
- Another drawback, perhaps, can be attributed to very conditional and subjective - this appearance shed roof. It may not appeal to lovers of architectural delights, they say, it greatly simplifies the appearance of the building. This can also be objected to. Firstly, the simplicity of the system and the cost-effectiveness of erection often play a decisive role in the construction of auxiliary structures. And three times - if you look at the overview of projects of residential buildings, you can find very interesting design options, in which the emphasis is on a shed roof. So, as they say, tastes differ.
How is a shed truss system calculated?
General principles of system calculation
In any scenario, a shed roof system is a structure of rafter legs installed parallel to each other. The name itself - “layered” indicates that the rafters rest (lean) on two rigid points of support. For ease of perception, we turn to a simple scheme. (By the way, we will return to the same scheme more than once - when calculating the linear and angular parameters of the system).
So, two points of support of the rafter leg. One of the points (AT) located above the other (BUT) to a certain excess value (h). Due to this, a slope of the slope is created, which is expressed by the angle α.
Thus, as already noted, the construction of the system is based on a right-angled triangle ABC, in which the base is the horizontal distance between the support points ( d) - most often this is the length or width of the building being built. Second leg - excess h. Well, the length of the rafter leg between the fulcrum becomes the hypotenuse - L. Base angle (α) determines the slope of the roof slope.
Now let's consider the main aspects of choosing a design and performing calculations in more detail.
How will the required slope of the slope be created?
The principle of the location of the rafters - parallel to each other with a certain step, with the required slope angle of the slope - is common, but this can be achieved in various ways.
- The first is that even at the stage of developing a building project, the height of one wall (shown in pink) is immediately laid in excess of h relative to the opposite ( yellow). The two remaining walls, running parallel to the roof slope, are given a trapezoidal configuration. The method is quite common, and although it somewhat complicates the process of building walls, it extremely simplifies the creation of the roof truss system itself - almost everything is already ready for this.
- The second method can, in principle, be considered a variation of the first. In this case, it is about frame construction. Even at the stage of project development, it is laid in it, then the vertical racks of the frame on one side are higher by the same amount h compared to the opposite.
In the illustrations above and in those that will be placed below, the diagrams are made with simplification - the Mauerlat passing along the upper end of the wall, or the strapping beam - on the frame structure is not shown. This does not fundamentally change anything, but in practice, this element, which is the basis for the installation of the truss system, cannot be dispensed with.
What is a Mauerlat and how is it attached to the walls?
The main task of this element is to evenly distribute the load from the rafter legs to the walls of the building. Rules for the selection of material and on the walls of the house - read in a special publication of our portal.
- The following approach is practiced when the walls are of equal height. The excess of one side of the rafter legs over the other can be ensured by installing vertical racks of the required height h.
The solution is simple, but the design is, at first glance, somewhat unstable - each of the "rafter triangles" has a certain degree of freedom to the left - to the right. This is quite simply eliminated by fastening the transverse bars (boards) of the crate and sewing the rectangular gable part of the roof from the front side. The remaining pediment triangles on the sides are also sewn up with wood or other material convenient for the owner.
rafter mount
- Another solution to the problem is the installation of a roof using shed trusses. This method is good because, after carrying out the calculations, it is possible to perfectly assemble and fit one truss, and then, taking it as a template, make the required number of exactly the same structures on the ground.
It is convenient to use such technology when, due to their large length, they require a certain amplification (this will be discussed below).
The rigidity of the entire truss system is already embedded in the design of the truss - it is enough to install these assemblies on the Mauerlat with a certain step, gain a foothold on it, and then connect the trusses with a strapping or transverse bars of the crate.
Another advantage of this approach is that the truss performs both the role of the rafter leg and the floor beam. Thus, the problem of thermal insulation of the ceiling and filing of the flow is greatly simplified - everything for this will be ready right away.
- Finally, one more case - it is suitable for the situation when a shed roof is planned over an extension being built near the house.
On the one hand, the rafter legs rest on the racks of the frame or on the wall of the extension being built. On the opposite side is the main wall of the main building, and the rafters can rest on a horizontal run fixed on it, or on individual fasteners (brackets, embedded bars, etc.), but also aligned horizontally. The attachment line of this side of the rafter legs is also made in excess h.
Please note that despite the differences in approaches to the installation of a shed system, the same “rafter triangle” is present in all options - this will be important for calculating the parameters of a future roof.
In which direction should the roof slope be provided?
It would seem - an idle question, however, it is necessary to decide on it in advance.
In some cases, for example, if there are no special options, the slope should be located only in the direction from the building in order to ensure free flow of storm water and melted snow.
On a stand-alone building, there are already certain choices. Of course, the option is rarely considered in which the truss system is positioned in such a way that the direction of the slope falls on the front part (although such a solution is not excluded). Most often, the slope is organized back or to one side.
Here it is already possible to take the external design of the building under construction, the features of the territory of the site, the convenience of laying communications for the storm water collection system, etc. as selection criteria. But you should still keep in mind certain nuances.
- The optimal location of a shed roof is to the windward side. This allows you to minimize the wind effect, which can work with the lifting application of the force vector, when the slope turns into a kind of wing - the wind tries to tear the roof up. It is for shed roofs that it has essential. When the wind blows into the roof, especially at small angles of steepness of the slopes, the value of the wind effect will be minimal.
- The second aspect of the choice is the length of the slope: with a rectangular building, it can be placed along it or across it. It is important to consider here that the length of the rafters without reinforcement cannot be unlimited. In addition, the longer the span of the rafters between the support points, the thicker the lumber used for the manufacture of these parts should be in cross section. This dependence will be explained a little later, already during the calculations of the system.
However, they practice the rule that the free length of the rafter leg should usually not exceed 4.5 meters. With an increase in this parameter, additional elements of structural reinforcement are necessarily provided. Examples are shown in the illustration below:
So, with a distance between opposite walls from 4.5 to 6 meters, it will already be necessary to install a rafter leg (strut), located at an angle of 45 °, and resting from below on a rigidly fixed support beam (lying). At distances up to 12 meters, it will be necessary to install a vertical rack in the center, which should be based either on a reliable ceiling, or even on a capital partition inside the building. The rack also rests on the bed, and in addition, a strut is also installed on each side. This is all the more relevant due to the fact that the standard length of lumber usually does not exceed 6 meters, and the rafter leg will have to be made composite. So without additional support to do in any case will not work.
A further increase in the length of the slope leads to an even greater complication of the system - it becomes necessary to install several vertical racks, with a step of no more than 6 meters, based on capital walls, and with tying these racks with contractions, with the installation of the same struts both on each rack and on both outer walls.
Thus, you should think carefully about where it will be more profitable to orient the direction of the roof slope also for reasons of simplifying the design of the truss system.
wood screws
What angle of slope will be optimal?
In the vast majority of cases, when it comes to a pitched roof, an angle of up to 30 degrees is chosen. This is due to a number of reasons, and the most important of them has already been mentioned - the strong vulnerability of the single-slope structure to the wind load from the front side. It is clear that, following the recommendations, the direction of the slope is oriented to the windward side, but this does not mean at all that the wind on the other side is completely excluded. The steeper the angle of inclination, the greater the resulting lifting force becomes, and the greater the shear load will be experienced by the roof structure.
In addition, shed roofs with a large angle of inclination look somewhat awkward. Of course, this is sometimes used in bold architectural and design projects, but we are talking about more “mundane” cases ...
Too gentle slope, with a slope angle of up to 10 degrees, is also not very desirable, for the reason that the load on the truss system from snow drifts increases sharply. In addition, with the onset of snowmelt, it is very likely that ice will appear along the lower edge of the slope, making it difficult for the free flow of melt water.
An important criterion for choosing the slope angle of the slope is the intended one. It is no secret that for various roofing materials there are certain "frameworks", that is, the minimum allowable roof slope angle.
The slope angle itself can be expressed not only in degrees. It is more convenient for many masters to operate with other parameters - proportions or percentages (even in some technical sources you can find a similar system of measurements).
Proportional calculus is the ratio of the span length ( d) to the slope height ( h). It can be expressed, for example, in a ratio of 1:3, 1:6, and so on.
The same ratio, but in absolute terms and reduced to percentages, gives a slightly different expression. For example, 1:5 - this will be a slope of 20%, 1:3 - 33.3%, etc.
To simplify the perception of these nuances, below is a table with a graph-diagram showing the ratio of degrees and percentages. The scheme is fully scaled, that is, it can be easily converted from one value to another.
The red lines show the conditional division of roofs: up to 3 ° - flat, from 3 to 30 ° - roofs with a small slope, from 30 to 45 ° - medium steepness, and above 45 - steep slopes.
The blue arrows and their corresponding numerical designations (in circles) show the established lower limits for the use of a particular roofing material.
 |
|||
|---|---|---|---|
| № | Slope | Type of acceptable roofing (minimum slope) | Illustration |
| 1 | 0 to 2° | Absolutely flat roof or with an angle of inclination up to 2°. At least 4 layers of rolled bituminous coating applied using a "hot" technology, with a mandatory top dressing of fine gravel embedded in molten mastic. | |
| 2 | ≈ 2° 1:40 or 2.5% | Same as in point 1, but 3 layers of bituminous material will be enough, with obligatory sprinkling | |
| 3 | ≈ 3° 1:20 or 5% | At least three layers of bituminous roll material, but without gravel backfill | |
| 4 | ≈ 9° 1:6.6 or 15% | When using rolled bituminous materials - at least two layers glued to the mastic in a hot way. It is allowed to use some types of corrugated board and metal tiles (according to the manufacturer's recommendations). | |
| 5 | ≈ 10° 1:6 or 17% | Asbestos-cement slate corrugated sheets of reinforced profile. Euroslate (single line). | |
| 6 | ≈ 11÷12° 1:5 or 20% | Soft bituminous tile | |
| 7 | ≈ 14° 1:4 or 25% | Flat asbestos-cement slate with reinforced profile. Decking and metal tiles - practically without restrictions. | |
| 8 | ≈ 16° 1:3.5 or 29% | Sheet steel roofing with folded connection of adjacent sheets | |
| 9 | ≈ 18÷19° 1:3 or 33% | Slate asbestos-cement corrugated regular profile | |
| 10 | ≈ 26÷27° 1:2 or 50% | Natural ceramic or cement tiles, slate or composite resin tiles | |
| 11 | ≈ 39° 1:1.25 or 80% | Roofing from wood chips, shingles, natural shingle. For lovers of special exotics - reed roofing | |
Having such information and having outlines for the future roofing, it will be easier to determine the slope angle of the slope.
metal tile
How to set the desired slope angle?
Let's go back to our basic scheme"rafter triangle" above.
So, to set the required slope angle α , it is necessary to ensure the elevation of one side of the rafter leg by an amount h. The ratios of the parameters of a right-angled triangle are known, that is, it will not be difficult to determine this height:
h = d × tg α
The value of the tangent is a tabular value that is easy to find in reference literature or in tables published on the Internet. But in order to simplify the task for our reader as much as possible, a special calculator is placed below, which will allow you to perform calculations in just a few seconds.
In addition, the calculator will help to solve, if necessary, the inverse problem - by changing the slope angle in a certain range, select the optimal value of the excess when this criterion becomes decisive.
Calculator for calculating the excess of the upper point of the installation of the rafter leg
In building a house, it is important that the roof frame and its rafter structure are reliable. For this you need to know optimal dimensions gap between rafters. How to correctly carry out calculations for the gable roof truss system, taking into account various roofing materials, our experts will tell in this article.
How to correctly calculate the distance between the rafters (for a gable roof)
Distance for various roofing materials
Experts advise: when determining the step between the rafter supports, consider the roofing material from which the roof of the gable roof will be created. Consider the most common roofing options suitable for private residential buildings.
- Decking - for this roofing material, the distance we need for a digital indicator is from 60 to 90 centimeters (if you increase the step to at least one meter, you will have to install additional cross boards with a large section - 5 × 10 cm). At the same time, under the corrugated board, it will be necessary to install the crate, which will provide the possibility of attaching the mandatory vertical components - the chimney, the ventilation system.
- Ceramic tiles - a roof made of such material has enough heavy weight, therefore, the load on the truss system will be higher than when the roof is covered with corrugated board. Accordingly, the distance that we calculate will be different: from 80 centimeters to 1 meter 30 centimeters. But in this option, the steepness of the roof slope is also taken into account (if the angle of inclination is 15 degrees, then the gap will be minimal - 80 cm, at 75 degrees - 130 cm).
- Metal tile - this roofing material is lighter than the previous one and is sold immediately in sheet form, therefore, the thickness of the components of the truss system is reduced, and, consequently, the distance between the elements in it is also reduced. For roofing material with a cross section of 15 × 5 centimeters, the gap should be selected from 60 centimeters to 95 centimeters. Such a distance will make it possible to qualitatively insulate the attic space (for this, it is necessary to place the insulation material directly between the rafters). The peculiarity of the installation of the truss structure under the metal tile is that the supports are installed on top of the ridge run (usually they are mounted on the side of the ridge beam). But in this case, do not forget about the ventilation holes near the upper roof.
- Ondulin - this material is called "Euroslate", and it is perfect for the roof of private residential buildings. For the truss structure under the ondulin, rafters from boards of 5 × 20 centimeters are used, which provides a certain margin of safety (this also takes into account the rafter runs). The distance between these rafter boards standard - from 60 to 90 centimeters, and the wooden beam for the crate should be a section of 4 × 5 cm, with an interaxal pitch of 60 cm.
- Slate is one of the most common roofing materials in our country; under it, rafters should be selected with a section of 5 × 10 / 5 × 150 centimeters. The distance between them will be in a slightly smaller range - 60-80 cm. wooden beam has its own gap between the elements, which directly depends on the angle of the slope of the roof slope: with a small slope - from 45 cm, with a larger one - from 60 cm.
Thus, the general digital indicators for determining the distance between the rafters (depending on the roofing material) will fluctuate within the following limits: the minimum is 60 cm, and the maximum is 130 cm. If you yourself cannot decide on the choice of such a digital indicator, then you should contact to qualified professionals for help.