Distance between rafters gable roof is one of the most important parameters during its construction. It is this distance that affects the strength of the frame and rafter system; accordingly, the strength of the entire roof depends on it. To determine it correctly, it is necessary to produce enough complex calculations. It is strongly recommended that you contact an architectural studio to carry them out. Incorrect calculations and, as a result, an incorrectly chosen distance between the slopes can lead to serious negative consequences, such as deformation of the supports of the rafter system, deformation and violation of integrity roofing, roof collapse. Therefore, during the design process gable roof It is extremely important to use the most accurate initial data; reference values must be taken strictly in accordance with the specific construction conditions, and the calculation must be made according to the methodology indicated below.
The distance between the rafters of a gable roof is one of the most important parameters during its construction.
Primitive method of calculation
Usually builders call the interval between rafters their spacing. Almost always, the rafters are separated by a maximum of 1 m (at the base), while the minimum permissible interval between them is usually within 0.5 m. The algorithm for calculating the required number of supports for constructing a strong roof is as follows:
- First, the length of the slope along the eaves of the roof is measured (actually the length of the wall parallel to the slope + estimated protrusions).
- The value obtained during the measurement is divided by the selected interval between the “legs” of the rafter system. Next, select the interval for which the “legs” will be separated. For example, 80 cm. In this case, the denominator of the fraction will be equal to 0.8.
- The last stage: one is added to the resulting quotient; if the resulting number is not an integer, then it is increased to an integer, always in the direction of increase.
Such a simple calculation will allow you to determine the number of rafters, as well as the distances between the supports. It is important to remember that the obtained values will determine the number of supports for only one of the two slopes. When the calculation is completed, the longitudinal size of the slope is divided by the estimated number of rafter supports. The result of this will be the exact distance between the supports. Let's consider one example: the length of the slopes of a gable roof (not total) is 20 m. Initially, a step of 0.75 m was selected. We make a preliminary calculation: 20/0.75 = 26.7. We add 1 to the resulting value, we get 27.7. Next, we round up and in the end we have 28 pieces. rafters This is exactly how many “legs” the rafter system of one slope will have. Next, we determine the exact distance between them: 20/28 = 0.72 m. Using this simple method, you can determine the minimum interval at which the rafters will be placed. However, it is important to take into account what roofing material is chosen.
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If corrugated board is selected
Corrugated sheeting is, although not heavy, but at the same time very flexible material. Therefore, the minimum allowable step for it should be 0.5 m, and the maximum should not exceed 0.9 m. At the same time, the frame of the rafter system must withstand not only the weight of the corrugated sheet, but also the sheathing. For profiled sheets, the sheathing is made of timber or boards with minimum size 30x100, the average installation step of the lathing should be 0.5 m (it depends only on the thickness of the sheet). The sheathing boards that extend onto the cornice when filling the corrugated board should be 1.5-2 cm thicker than the main sheathing. At the same time, it is important not to forget about the need for ventilation of the structure.
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Ceramic tiles
The main feature of this material is that ceramic tiles very heavy. This is logical, because the raw material is ordinary clay, which has a high specific gravity. If we compare metal tiles and ceramics, they differ in weight by more than 12 times. The weighted average pressure of such a coating is 45-70 kg per square meter battens.
Ceramic tiles are very heavy, because the raw material is ordinary clay, which has a high specific gravity.
The frame with supports for such material should be made of well-dried timber, with approximately 15% humidity. For installation, beams of approximately 50x150 mm should be used (recommended 60x180 mm). The pitch of the supports under the ceramic coating will be in the range of 0.8-1.25 m. This value is greatly influenced by the angle of inclination of the slopes.
For example, if the angle is 15°, the interval is taken to be minimal - 0.8 m. If the slope is inclined at about 45° - all 1.25 m. For this type of roofing material, specialists also calculate the length of the rafters (when calculating the interval between supports).
So, if the length is maximum for a particular roof, then the pitch value should be minimal. Short rafters require the largest possible spacing between them. In this case, you can move on the roof only if the rafter pitch is no more than 0.8-0.9 m with a slope of 45°. We should also not forget about the need for ventilation of such a structure.
For this purpose, holes are usually provided in the insulation, the diameter of which is in the range of 9-12 mm. The process of constructing a rafter system for metal tiles is similar to the process of constructing rafters for other types of covering.
It is important to remember that in addition to careful calculation required quantity The rafters should be calculated and the pitch for the sheathing.
It varies depending on the type of ceramic tiles. For example, the length of a ceramic tile is 0.4 m, while the joint overlaps 0.5-0.9 m. in this case the sheathing pitch will be 0.31-0.35 m. It is important to remember that for each slope it is necessary to make a separate calculation, since it is impossible to build a truss structure that is absolutely identical (even if it is so according to the design): errors and inaccuracies in the assembly can result in an error of 0.2 m.
The reliability of the roof and its service life mainly depend on how correctly the calculations are made.
One of the most important parameters of the rafter system is how far apart the rafters are located.
After all, the distribution of the load on the frame depends precisely on this desired parameter.
If the calculation is made incorrectly, deformation may occur and the roof will collapse.
Therefore, it is extremely important to accurately calculate the interval between rafter legs when drawing up a roof project.
Basic principles of calculation
The pitch of the rafters is the distance from one rafter leg to the other.
When constructing roofs of private houses, this value is 1 meter.
But this figure is approximate.
To obtain Exact size interval, it is necessary to calculate the load-bearing capacity of the rafter system of the selected type.
For execution correct calculation the following scheme should be used:
- first you need to determine the length of the roof slope;
- Now the resulting figure should be divided by the value of the approximately selected rafter pitch. If you previously selected its value as 1 meter, then you need to divide by 1. If you chose 0.8, then you should divide by 0.8, etc.;
- after that, one is added to the result obtained and the resulting value is rounded up. This action is necessary in order to receive exact amount rafters that will need to be installed on one slope;
- the total length of the slope must be divided by the number of rafter legs obtained in the previous calculation. And we get the exact distance between them.
To understand this better, let's look at an example.
Having measured the length of the roof slope, we got 27.5 meters.
We choose a step of 1 meter to make it more convenient to count.
Further calculations will look like this:
Now we add the unit 27.5 m +1 = 28.5 m.
Round up to the nearest value and get the number 29.
That is, 29 rafter legs must be installed on one slope of our roof.
Now we divide the length of the roof by their number: 27.5/29 = 0.95 m.
This means that in our case, the pitch of the rafter legs should be 0.95 meters.
This is a general calculation.
In which the peculiarities of a particular roofing material are not taken into account.
And he can significantly change this parameter.
When you know what kind of material you will use on the roof, you will have to make some changes to the calculation procedure.
Optimal and minimum value
The step is a unit of calculation.
After all, it depends, first of all, on the load on the roof frame and the cross-section of the rafter legs.
You can take a thick board for their construction and make the interval between them 120 cm.
At this distance, the sheathing may begin to sag.
And how to install the insulation?
After all, most materials have a width of 1 meter.
So when calculating, they take an approximate step of 1 meter.
The minimum distance between rafter legs is 70 cm.
And to obtain the optimal value for each material, it is necessary to perform a calculation.
Determining the pitch for a pitched roof
The pitched roof is the simplest.
After all, in the truss of such a roof there are only rafter legs.
There are no struts, racks, or braces in its design.
Such a roof is usually installed on garages, outbuildings, and bathhouses.
In order to determine the pitch of the rafters on a pitched roof, you can use the table:
As can be seen from the table, the rafter pitch depends on their length and cross-section.
Distance between rafters for a gable roof
A gable roof is much more common than a shed roof.
And it’s easy to explain such popularity: the design is very simple, but despite all its simplicity, the gable roof is distinguished by its reliability.
Its design can be easily adjusted to any climatic conditions and any roofing material.
When calculating the pitch of the rafters gable roof, everything is done according to common system calculation (see above).
If the slopes have the same length, then it is enough to perform calculations for one slope.
If the slopes are of different lengths, then the calculation is performed for each slope.
It should be remembered that the maximum pitch values for the rafter legs are 70 and 120 cm.
Ondulin
If ondulin is used as a roofing material, then the rafter system is constructed from pine boards with a cross section of 50 x 200 mm, and the rafters should be located at a distance of at least 60 cm and no more than 90 cm from each other.
A sheathing of timber with a cross-section of 40 x 50 mm is laid on top.
Metal tiles
Metal roofing during construction country houses is used most often.
Because this material is much lighter than ceramic or cement tiles.
Although appearance very similar to her.
The low weight of metal tiles makes it possible to use boards of a smaller cross-section when creating a rafter system, and to use thinner bars for sheathing.
More about the counter-lattice for metal tiles.
ABOUT hip roof with hanging rafters at the link. Also about the design of hanging rafters.
About the price of Viking metal tiles here. Technical characteristics, photographs, reviews.
Reducing the size of the elements of the rafter leg system, in turn, reduces the load on the walls of the building and its foundation.
When constructing a rafter system under metal tiles, the rafters are mounted in increments of 60–95 cm.
The cross-section of the material is 50 x 150 mm.
According to experts, if you place insulation with a thickness of 150 mm in the space between the rafters, then attic will be created the most comfortable conditions for accommodation.
To ensure ventilation of the space where the insulation is laid, when installing the rafter system, holes near the upper roof with a diameter of 12 mm are drilled.
The technology for manufacturing a rafter system for metal tiles does not differ significantly from the technology for manufacturing a frame for other roofing materials.
Its only difference is the installation at the top.
Mounting of the upper support is not carried out ridge beam on the side, and on ridge run.
The presence of a free zone between the rafters allows air to fully circulate under the flooring, which helps prevent condensation from forming.
Ceramic tiles
The design of the system for ceramic tiles has its own characteristics.
After all, clay is used to make such roofing material.
And this is very heavy material.
If you compare metal tiles and ceramic tiles, the latter weighs 10 times more.
Accordingly, the rafter system is significantly different.
For 1 square meter of roof surface there is a load of 40 - 60 kg, depending on the manufacturer and brand of the product.
Rafters for this frame system made from wood that has been dried for a long time.
Such wood should have a moisture content of no more than 15%.
A beam with a cross-section of 50 x 150 or 60 x 180 mm is used.
It's more reliable.
And the distance between the rafter legs can be 80 - 130 cm.
The exact value can be given if the angle of inclination of the slopes is known.
If the angle of inclination is 15 degrees, then the pitch of the rafters will be 80 cm.
And if the angle of inclination, for example, is 75 degrees, then the step may be larger - 130 cm.
The interval between rafters is not greater than 130 cm.
Also, when calculating the pitch of the rafters, their length is taken into account.
The greater the dyne, the less distance between them.
The shorter the rafter legs, the greater the distance can be made.
If the angle of inclination is 45 degrees, then the roofer can safely move on the roof if the rafter pitch is 80 cm.
Corrugated sheet
When creating a rafter system for corrugated sheets minimum distance between the rafter legs is 60 cm.
The maximum size is 90 cm.
If for some reason the pitch of the rafters is more than 90 cm, then it becomes necessary to install cross-section boards of large cross-section.
The rafter legs themselves can have a cross-section of 50 x 100 or 50 x 150 mm.
Slate
Despite the emergence of a large number of new roofing materials, asbestos-cement slate remains one of the most popular.
If you plan to lay slate on the roof, then the rafters should have a cross-section of 50 x 100 or 50 x 150 mm.
The distance between them is made no less than 60 and no more than 80 cm.
The lathing is made of timber with a cross-section of 50 x 50 mm or boards with a cross-section of 25 x 100 mm.
When installing any building structure It should be remembered that there are still unforeseen situations.
And, therefore, when calculating the sections of rafters and the distance between them, it is necessary to provide a safety margin.
about the installation of the rafter system.
Sergey Novozhilov is an expert in roofing materials with 9 years of experience practical work in area engineering solutions in construction.
Source: http://ProRoofer.ru/montaz/stropilnye-sistemy/rasstoyanie-mezhdu-stropilami.html
The distance between the rafters of a gable roof and the pitch of the rafters
The quality and durability of the roof largely depend on the correct calculation of the rafter pitch. It affects the installation of insulation, fastening of roofing material and installation of additional parts.
Pay attention only to the requirements for the distance under the roofing sheets, then problems may arise with the insulation boards. Conversely, adjusting the insulation to fit the dimensions can make the frame too weak, and in winter there is a risk of collapse.
Basics of determining rafter pitch
As a rule, the pitch between the rafters depends on several factors. But usually the distance ranges between 0.6 and 1.2 meters. These figures are rounded; in practice, the distance may differ by several centimeters downwards. For an accurate determination, the following calculations must be performed:
- Determine the length of the slope by measuring along the eaves of the house. Let's assume that it turns out to be 17.8 meters.
- Divide the resulting figure by the planned pitch of the rafters. If it was decided that the distance between the beams would be 0.8 meters, then 17.8/0.8 = 22.25.
- Next, round the result up and add one: 23 + 1 = 24. At this stage, the number of required rafters is determined.
- Now we calculate the distance between the axes of the beams. To do this, the length of the slope must be divided by the number of rafters: 17.8/24 = 0.74 m.
So, you will determine the actual distance at which the rafters should stand for a roof made of metal tiles or some other material.
Often, when planning a roof frame, specialized calculators are used. They enter basic data and get the finished result. However, you should not completely trust the program, since some conditions can only be taken into account by a person. When calculating, you can understand how the system works, what loads are applied. If necessary, adjustments are made to strengthen or lighten the structure. Self-calculation will help you more accurately determine the required pitch of gable rafters and pitched roof.
Calculation of pitch depending on roofing material
For each coating, its own standards and dimensions are developed for rafter system. The main factors are the strength of the material, its weight and resistance to external loads. Let's look at the main types of coatings.
Corrugated sheet
The pitch of the rafters under the corrugated sheet can vary from 0.6 to 0.9 m. The final result depends on additional conditions, which we will discuss below. If for some reason the step should be larger, add a cross-section board with a larger cross-section. In this case, the rafters themselves are usually chosen with dimensions of 50x100 or 50x150 mm.
In addition to the rafters, 30x100 mm sheathing 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 sheet and the height of the wave. The sheathing boards protruding beyond the boundaries of the cornice should be 1.5 cm thicker than usual. This is done based on the need to attach ventilation, chimney or drainage.
Ceramic tiles
The main difficulty of design rafter frame under ceramic tiles is a large weight of roofing material. It is 10 times heavier than corrugated sheeting and weighs from 40 to 60 kg per square meter.
Dry beams with a moisture content of only 15% are used for this coating. Their cross-section should be either 50x150 or 60x180 mm. With such indicators, the maximum permissible distance there can be 1.3 meters between the rafters. The minimum permissible step through which rafters can be placed is 0.8 m. The final decision is influenced by the slope of the roof: at 15° the step is 0.8 m, at 75° - 1.3 m.
The length of the rafter leg is also taken into account; the shorter it is, the larger the gap, and vice versa. In addition, if the slope is less than 45°, and movement on the surface is planned, the beams are placed in increments of no more than 0.85 m.
The distance between the sheathing boards is selected so that each intersection of the tiles has own foundation. The standard length of the material is 400 mm, and the amount of overlap during installation ranges between 55 and 90 mm. It turns out that the distance between the central axes of the sheathing can be either 310 or 345 millimeters.
Metal tiles
IN last years A particularly pressing question is: how to determine the distance between the rafters for metal tiles? It imitates a more expensive one 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 metal tiles is less than ceramic tiles, so a simpler frame is required. The cross-section of the beams is reduced to 50x150 mm and the pitch between the sheathing is increased. The pitch of the rafters for metal tiles varies between 0.6 and 0.95 m.
Ondulin
The permissible step for ondulin coating is 0.6-0.9 meters. The standard rafter section is 50x200 millimeters. These dimensions will allow you to withstand the created load. roofing pie on a gable roof.
A lathing made of bars measuring 40x50 millimeters is attached on top of the counter-lattice. The pitch between the central axis is 600 mm.
Additional factors
When calculating the pitch of the rafters, attention is paid not only to the type of roofing. Many other points are taken into account, data on which can be found in reference books and SNiPs. Here are some of the factors:
- Snow and wind loads. The more snow falls in winter and the stronger the winds blow, the smaller the distance between the beams should be. But, if you increase the roof pitch above 45°, then you are allowed to increase the pitch.
- 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 we neglect this condition, then it appears a large number of undercuts, cold bridges and construction will be delayed.
- Quality of lumber. Here the type of wood, grade and section are taken into account. As mentioned above, strength is affected by how well the beam was dried. When purchasing wood, pay attention to the evenness and presence of defects in the form of knots and traces of pests.
- Floor beams and tie rods. If you are installing under a gable roof attic floor, then the maximum distance between the rafters should be 0.75 meters.
The calculation of the distance between the beams for a gable and saddle roof is different. Even if he makes several slopes, for each it is necessary to make the calculation individually. This especially applies to buildings with different lengths cornices
Taking into account all these factors, you can determine at what distance to install the rafters. Although all calculations can be done independently, since reference data is freely available, it is better to turn to professionals. They have experience in design and will quickly determine the required distance between the rafters. Yes, you will avoid possible errors and you will be sure of safety.
Source: https://build-experts.ru/shag-stropil/
The distance between the rafters is one of the key parameters affecting the strength of the structure. Proper calculation of the installation pitch of the rafters allows you to build a roof that is resistant to high operating loads.
Roof loads and calculation of the rafter system
Development of a project for a single-pitched or gable roof begins with choosing the type of rafter system, the angle of inclination of the slopes (roof height) and materials for constructing the structure. Calculation of the distance between the rafter legs is carried out taking into account the loads that the roof will experience during operation. Constant loads include :
- the weight of the materials from which the rafter system is made;
- roofing weight;
- weight of roofing materials (waterproofing, vapor barrier, insulation);
- weight of finishing elements residential attic or attic.
In addition to permanent loads, the roof also experiences temporary loads, which include :
The pitch refers to the distance between the rafters of one slope. When calculating a single slope, gable or complex roof, usually follow the following scheme :
- the length of the future roof slope is measured;
- the resulting value is divided by the optimal numerical value of the rafter pitch;
- one is added to the resulting value, the result is rounded;
- the length of the roof slope is divided by the rounded result.
The final result will allow you to determine at what distance the rafter legs should be placed.
Determining the pitch cannot be extremely accurate, since it is necessary to take into account a number of additional factors, including the width of the insulation, features of installation of the sheathing under different kinds roofing material.
If a roof with a chimney is being designed, the pitch can be adjusted taking into account its location, so that you do not have to subsequently remove part of the rafters and install a supporting structure, such as a special rafter system.
Distance between rafters under slate
Slate is a traditional roofing material. Its advantages include characteristics such as resistance to external influences(excluding mechanical) and low cost. Slate allows you to create a roofing covering, the repair of which can be reduced to replacement individual elements. Slate is heavy and requires the installation of a fairly powerful rafter system. Calculation of the distance at which it is necessary to place the rafters under the slate is carried out taking into account the cross-section of the beam for the manufacture of rafter legs.
The optimal solution is to install a system under slate, in which the gap between the rafters should 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 sheathing is made of timber or boards with a cross-section of at least 30 mm. When calculating the rafter system for slate, you should read that this material has quite large restrictions on the choice of slope angle.
Rafters for metal tiles
Metal tiles are actively used as a practical and aesthetic roofing material when arranging a pitched, gable, hip or complex roof. The frame for metal tiles is built according to standard principles.
To calculate at what distance it is better to install the rafters, it is necessary to take into account the loads and the angle of the roof. Metal tiles are characterized by their relatively low weight, thanks to which they can serve as a replacement for old slate or ceramic tile roofing.
In this case, the rafters will not need to be strengthened or the pitch of their installation changed.
The standard pitch 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 metal tiles.
But if you intend to use insulation, the layer of which in areas with low winter temperatures should be 200 mm, for rafters under metal tiles it is recommended to use 200x50 timber so as not to install additional system holding the insulation.
It is better to adjust the gap between the rafters for metal tiles to the width of the sheet or roll insulation.
Corrugated sheeting: rafters and sheathing
Corrugated sheeting is a lightweight and easy-to-use roofing material. Galvanized or coated with a decorative protective layer, corrugated sheets can be used for installation pitched roof a utility room or garage, as well as for a gable roof of a residential building. How to calculate the distance required to install rafters under corrugated sheeting?
To ensure the necessary structural rigidity, it is enough to install the rafters under the corrugated sheets in increments of 600-900 mm. In this case, you need to pay attention to the angle of the roof.
The calculation shows that at high external loads It is better to lay corrugated sheets on the system with a minimum step.
But if the distance between the rafters under the corrugated sheet is close to the maximum, and the roof slope angle is small, then the structure is strengthened by using more frequent sheathing. In this case, the pitch of the sheathing under the corrugated sheet should be about 50 mm, the width of the elements should be at least 100 mm.
Rafter system for soft roofing
Soft roofs include bitumen and bitumen-polymer roll materials, roofing membranes, as well as soft tiles. Soft roofing is characterized by relatively low weight and the absence of the need to install a massive rafter structure.
The minimum distance between the rafter legs is 600 mm, the maximum is 1500 mm. When installing a 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 sheathing should be. The choice of step is also influenced by the thickness of the material for the sheathing - the thicker the sheet of plywood or OSB, the larger the installation step of the rafter legs can be.
Ondulin: calculation of rafters
Ondulin (bitumen slate) is laid on a flat continuous sheathing made from sheet material. This allows the roofing covering to successfully resist wind and snow loads. The sheathing for 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 pitched roof.
Rafters for ondulin are made of timber with a section of 200×50 mm. When choosing at what distance to place the rafter legs for the structure under the ondulin, it is recommended to take into account the width insulation material to make it easier to install. This calculation allows us to reduce financial expenses for the installation of the roof.
Sandwich panel roof
Sandwich roofing is most often erected on houses made of sip panels or hangar-type buildings. A special 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 top of the wall (or the distance between the supporting structures of a gable roof) allow the installation of a sandwich without additional supports.
If the span exceeds 4 meters, additional purlins must be installed. To install a sandwich roof on a residential building, a traditional rafter system is often installed, but in this case the rafters can be positioned big step– they serve as a support for the purlins. The distance between the rafter legs is selected based on the length of the available material for the purlins and the length of the load-bearing walls. Technical specifications sandwich allow the roof to withstand high operating loads .
Polycarbonate: construction of a supporting structure
Polycarbonate in Lately is actively used as a roofing material. First of all, polycarbonate is in demand in the construction of gazebos, canopies, winter gardens. The lathing and rafter system for polycarbonate can be made of wood or metal.
Polycarbonate varies in weight depending on the thickness of the sheet. It is recommended to perform lathing under polycarbonate in increments of 600-800 mm. The lathing (wooden or metal) is mounted on rafters, which can be straight or arched.
Typically, the gap between rafters for polycarbonate is from 1500 to 2300 mm.
Source: http://krovlya-mp.ru/shag-stropil-dvuskatnoj-kryshi.html
Distance between rafters: what step should be between rafters
The task of correctly calculating the distance between the rafters is a very important one. How seriously you begin to solve this problem will determine not only the reliability and durability of the roof, but also all subsequent work on it: laying insulation, installing roofing, installing additional elements. If you manipulate the pitch of the rafters under the roofing sheets, as many do, then it is not a fact that insulation will then fit between the rafters.
If you focus only on insulation, the very first winter with its abundant Russian snow will crush the rafter system. That's why the whole point is to pick optimal step rafters for all slopes, and this is the skill we will teach you now.
Here is a good video tutorial on how to independently calculate the distance between the rafters:
What determines the pitch of the rafters?
So, the distance between the rafters is determined by the following important factors:
- Roof shape (gable, single-slope or multi-slope).
- Roof angle.
- Parameters of the timber used to make rafters (width, thickness).
- The design of the rafter system (sloping, hanging or sliding).
- The totality of all loads on the roof (weight of covering, 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 needs to be taken into account, which is exactly what this article is about.
Online calculators vs. notepad and pencil
To correctly calculate the cross-section of rafters and the step of their installation, today there are many complex formulas. But remember that such formulas were at one time developed more so that it would be possible not so much to perfectly calculate roof structures, but to study the operation of such elements.
For example, today simple online programs are popular that do a good job of calculating rafter parameters. But it’s ideal if you can set specific tasks yourself and calculate everything you need.
It is important to understand down to the smallest detail what exactly happens in the rafter system during operation, what exact forces are exerted on it and what loads. A computer program cannot always take into account everything that the human brain notices.
Decorative rafters: 0% load
First of all, decide on the most important point: the type of roof and its purpose. The fact is that the roof of a residential building in winter can withstand a large cap of snow, a constant wind at height, and it is also often insulated from the inside, but to the rafter system small gazebo, hidden under the canopy 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 a purely aesthetic factor:
The illustration above shows that even such a building has its own pitch of rafters. After all, here it provides both the aesthetic factor and the rigidity of the structure itself. But they choose a step arbitrarily.
Functional rafters: detailed calculation
We come to the main question: what distance should be between the rafters of the roof of a residential building? Here, be patient and carefully study all the nuances.
Point 1. Wall length and choice of rafter spacing
The first step in installing rafters on the roof of a residential building is usually chosen structurally based on 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 for a wall 6 meters long, 7 rafters are installed as a standard. At the same time, you can save money by placing them at a distance of 1 and 2 meters, and you will get exactly 5 rafters. It can also be placed at a distance of 2 and 3 meters, but reinforced with lathing. But it is extremely undesirable to make the rafter spacing more than 2 meters.
Point 2. The 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 a regular 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 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 even be increased by a distance of 1.2 m-1.4 m.
Why is this 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 seems to bend around the slope of the roof, but at the same time trying to lift it. And at this moment forces arise in the roof that are ready to tear it off or overturn it - these are two windward sides and one lifting side.
There is another force that arises from wind pressure and acts perpendicular to the slope, trying to press 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 tangential ones. And the greater the angle of the slope, the less often you need to install rafters.
This map of the average wind load will help you understand whether to make a high roof or a flat one:
The second point: in the Russian region, the standard roof of a house is constantly exposed to such atmospheric phenomena as snow. Here too, you need to take into account 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 continuous sheathing. The easiest way to identify such places is by the wind rose: single rafters are placed on the windward side, and paired rafters are placed on the leeward side.
If you are building a house for the first time, then you won’t have to decide on your own worldview, but rather determine the average snow load for your area according to official data:
Point 3. The issue of insulation and standard width of mats
If you will be insulating the roof, then it is advisable to set the pitch of the rafters to the standard sizes of insulation boards, which are 60, 80 cm and 120 cm.
Modern insulation materials are sold today standard width, usually at the same standard rafter pitch. If you then take them and adjust them to fit existing parameters, then there will be a lot of waste, cracks, cold bridges and other problems.
Point 4. Quality and strength of the lumber used
It is also of great importance what kind of material you use to build the rafter system. Thus, for each type of wood there is its own regulatory documentation that concerns its load-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 prescribed. If you use wood of other species, you can derive a correction factor.
In addition, if the rafters have sections, notches or holes for bolts, in this place the load-bearing capacity of the beam must be calculated with a coefficient of 0.80.
Point 5. Distance between tie rods and floor beams
One more point: if the roof is built with interconnected trusses, and their lower chord is used simultaneously as floor beams, then the distance between the trusses should be within 60-75 cm in order to take into account the design of the future floor.
Point 6. Loads on rafters
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, the 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 influencing the roof simultaneously at a certain moment, and therefore there is such a thing as critical value. This is exactly the load value at which the roof cannot withstand and becomes deformed.
Therefore, if a building is being built with significant spans, then steel roof trusses. The fact is that there is no longer any 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 trusses is calculated depending on the type of roof and the design of the roof itself.
Typically, a unified truss is installed with a span that is a multiple of six, and therefore a distance that is a multiple of one and a half meters is made between the nodes of the truss.
Point 7. Weight of the rafter system and roofing pie
Do not forget that the main purpose of the rafters is to support the entire roof, and its weight is crucial:
Point 8. Ease of installation of roofing
The distance between the rafters is also influenced by factors such as the selected roofing covering. The higher the roof slope, 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 continuous sheathing? 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 the edges need to be fixed directly into the rafter or sheathing, and it is important that they coincide. Otherwise, the work of covering the roof will easily turn into a living hell at altitude, believe me.
That is why, even before starting installation, you must make a layout and 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 rafters 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, the 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 plan for the unexpected favorable conditions, that is, to provide an additional 10% percentage strength.
And now all you have to do is share total load for 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 have peace of mind for your home.
You need to make calculations for destruction, i.e. for the full load acting on the roof. All these loads are determined by technical specifications materials and SNiPs.
The standard roof structure consists of rafters, lattice purlins, and each of these elements responds only to the load that puts pressure on it, and not on common roof generally. Those.
Each individual rafter is subject to its own load, total, but divided by the number of rafter legs, and by changing the step of their location, you change the area where the load is collected on the rafters - reducing it or increasing it.
And, if changing the pitch of the rafters is inconvenient for you, then work with the parameters of the section of the rafter legs, and the overall load bearing capacity the roof will increase significantly:
When making 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 slopes up to 30 degrees, the rafters have so-called “bending elements”. Those. they work specifically for bending, and there are certain requirements for them.
And the possibility of rafter deflection 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 a roof with a warehouse slope of more than 30 degrees, which rafters are already considered “bending-compressed” elements. That is, they are affected not only evenly distributed load, which causes bending of the rafters, but also forces that are already acting along the axis of the rafters. Speaking in simple language, here the rafters not only bend a little under the weight of the roof, but are also compressed from the ridge to the mauerlat. In addition, the crossbar, which usually holds the two rafter legs, must also be checked for tension.
As you can see, even a person far from construction can handle 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 then all the work goes like clockwork!
The distance between the rafters (rafter legs) is called the rafter pitch. When arranging a roof, it is customary to use a rafter pitch of no more than 100 and no less than 60 cm. The reliability of the roof structure depends entirely on how correctly the distance is calculated.
Incorrect determination of the loads on the rafters and the parameters of the materials used as them can cause deformation of not only the roof, but the entire building. The roof may collapse and cause the walls to collapse. Taking this into account, the design calculation of the rafter system must be given the same close attention as overall project building.
Methodology for calculating the distances between bars
- moving along the eaves of the slope, measure its length;
- divide the resulting number by the selected step (from 60 to 100 cm);
- add 1 to the resulting quotient and round the number up.
As an example, let's take a slope 30 m long and a distance between the rafters of 0.6 m.
50 + 1 = 51 - 51 rafters will be required to build the roof.
Then we determine the step between the bars that will be used as load-bearing structure:
30: 51 = 0.58 m - the distance between the axes of the beams that will be installed on the roof slope as rafters.
This example shows general methodology calculation of the supporting structure, but does not take into account the specifics of a particular roofing material. Experts recommend calculating the distance based on the characteristics of roofing coverings.
In addition, calculations should be performed taking into account the materials from which the rafter system of the house will be made. Here the step largely depends on both the type of material and its dimensions.
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Specifics of laying rafters under ceramic tiles
Despite the fact that ceramic tiles are one of the elite and environmentally friendly roofing materials, their installation is fraught with certain difficulties. And the main one is a large mass. Thus, the weight of ceramic tiles is almost 10 times the weight of metal tiles. This means that for every m 2 of the structure a pressure of 40 to 60 kg will be exerted. These conditions imply the creation of a reinforced load-bearing system capable of supporting the weight of the roof.
To create a rafter system for a roof made of ceramic tiles, a beam with a cross-section of at least 5x15 cm, or better yet 6x18 cm, is usually used. The moisture content of the wood should not exceed 15%.
The distance between the beams depends on the slope of the slope and the length of the rafters. So, the steeper the roof, the greater the distance between the rafters will be. If, with a slope slope of 15 o, the step is 80 cm, then with a slope of 75 o it will be 130 cm. Long bars will be located at the maximum distance from each other, and short ones at the minimum.
In order for the installation of ceramic tiles to be carried out correctly, the pitch of not only the rafter legs, but also the sheathing is important. When creating a house structure, it is necessary to take into account the parameters of each roofing element (in this case, tiles). Typically, tile tiles do not exceed a length of 40 cm, and during installation they overlap with the previous row by about 9 cm. This determines the pitch of the sheathing, which should be no less than 31 and no more than 35 cm.
This indicator can also be determined according to the following scheme:
- The length of the bottom row is subtracted from the length of the slope;
- then the distance between the first row of sheathing and the last rafter is subtracted.
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Specifics of installation of a supporting structure under metal tiles and corrugated sheets
Installation of metal tiles does not require reinforcement of the supporting structure due to its low weight. The wood will not resist the loads exerted, which means that the step between the beams may not be wide. So, with metal roofing, the rafters can be located at a distance of 60-95 cm from each other.
Corrugated sheeting is another roofing material that is lightweight. And according to other characteristics, corrugated sheeting is as close as possible to metal tiles. Therefore, the pitch of the rafter legs is similar to the above - from 60 to 90 cm.
Distance parameters determine characteristics building materials. For example, if a board less than 10 cm wide is used to construct a structure on the roof, the distance should be reduced to 50 cm.
Do not forget about the distance between the elements of the sheathing, which can range from 0 to 400 cm. The pitch of the sheathing is selected taking into account the grade of the corrugated sheet and the slope of the slope. For example, a profiled sheet of grade C-21 with a thickness of 0.5 to 0.7 mm with a roof slope of more than 15 o should be attached to the sheathing, the pitch of which will be no more than 65 cm.
The content of the articleWhen building a roof, the first thing to choose is the type of rafter system. This means that the rafters must be hanging or layered, or the entire rafter system will consist of both rafters, i.e., combined. It is not difficult to calculate the distance between the rafters, knowing the magnitude of the loads that will act on the entire roof.
Loads can be temporary or permanent. Constant loads include:
- the weight of the materials of the rafter system itself;
- weight of roofing material;
- the weight of the elements of the roofing pie, if the roof is insulated;
- weight of the interior finishing of the attic ceiling.
Temporary loads include: weight of snow cover, weight of a person during production roofing works and roof maintenance during operation, wind load and the weight of possible water flows in the summer.
What are the calculations based on?
The distance between the roof rafters is also calculated based on the selected material and the cross-section of the rafters. All calculations are carried out at the house design stage by specialists from design organizations. To do this, they use reference documents and building codes and rules regulating this or that rafter pitch, sheathing pitch and other calculated values.
When building a private house, rarely does anyone order a project where, based on calculations, it is recommended what distance between the rafters should be maintained. Most often, developers rely on the experience of the craftsmen and trust them to carry out all the calculations on site. However, there are those who want to calculate the rafter system themselves and build the roof themselves.
In this case, they must first decide on the type of roof, choose what kind of attic it will be - heated residential or cold, since the type of rafter system and the calculation of the distance between the rafters directly depend on these parameters
Distance between rafters of a pitched roof
The calculation for a pitched roof is the simplest. The rafter system does not provide racks and braces - only the rafters themselves. This type of roof is most often installed on utility rooms, garages, bathhouses, etc.
The pitch of the rafters of a pitched roof is presented in the table below and depends on the cross-section of the timber:
If the developer wants to independently calculate the loads on the rafter system, it will be useful for him to familiarize himself with documents such as SNiP 2.01.85 “Loads and impacts” and “Changes from SNiP 2.01.85”, which contains maps of the climatic regions of Russia.
Wood is chosen as the material for the construction of the rafter system. coniferous species, the humidity of which is 20-22%. Boards, beams and other types of lumber must be smooth without curling, rot, knots or blue stains.
All wooden elements should be treated with antiseptics and fire retardants to protect the wood from rotting and fire. The material used, the length of the rafters and the cross-section of the timber also affects the calculations (see table):
Approximate calculation
The pitch of the rafters is nothing more than the distance between the rafter legs. As a rule, for residential private houses this figure is 0.6-1.0 m.
The pitch of the rafters is influenced by significant amount factors. Calculation required quantity rafter legs are produced in the following way:
- The length of the roof slope is measured. After this, the resulting value is divided by the selected pitch between the rafters.
- Then one is added to the resulting value and rounded up to get a whole number. This is how the number of rafters required for a given length of one roof slope is obtained.
- After this, the entire length of the roof slope is divided by the resulting integer (the number of rafter legs) and as a result, the distance between the axes of the future rafters is obtained, which is called the rafter pitch.
- The axis should run through the center of the rafter. However for different types roof covering, the pitch of the rafters can vary, and it also changes depending on the slope of the roof slope.
For example: the length of the roof slope is 16 meters, and the pitch between the rafters is 0.6 meters. Therefore, 16/0.6 + 1 = 27.66 = 28 meters (rafters are necessary for the installation of the slope)
The greater the slope angle, i.e., the steeper the roof, the larger the pitch of the rafters can be made. This is explained by the fact that the load on steep roofs is not distributed over the entire roof plane, but is mostly transferred to load-bearing walls.
Rafters for ceramic tiles
Ceramic tiles are a material that has a decent weight. Therefore, to install a tile roof, you should calculate the cross-section and length of the rafters, taking into account that one square meter of ceramics weighs almost ten times more than the weight of metal tiles.
- If the design of the rafter system involves tightening the rafters, then its cross-section should be increased.
- The rafters themselves should be made of dry, healthy wood, their cross-section should be 50x150 or 60x180 mm.
- The pitch of the rafters is made in the range of 0.8 -1.3 m for ceramic tile coverings, and its exact determination depends on the slope angle of the slopes.
The higher the roof, the wider the rafter spacing can be. For example, with a slope angle of 15 degrees, the step will be 80 cm, and if the slope angle increases to 75 degrees, the distance between the rafter legs will increase to 1.3 m.
Another circumstance affects the pitch of the rafters - the length of the rafter legs. The longer they are, the shorter their step. This is explained by the fact that when maximum length rafters create increased deflection loads. They can be reduced by installing a system of supporting posts, struts and other elements of the rafter system, which take on part of the loads from the rafters.
Metal roof rafters
The rafter system for metal tiles is not much different from others truss structures. But due to the fact that it weighs several times less than ceramic tiles, rafters and all other elements of the roof structure can be made with a smaller margin of safety, i.e., a smaller cross-section. The difference in weight of clay and metal tiles is about 35 kg per 1 m2.
The rafter spacing for metal tiles is usually 0.6-0.9 m. Metal tiles are widely used to cover country houses, which often include attic rooms, so the roof is made insulated. The pitch of the rafters in such structures is adjusted to the size of the insulation, which is inserted between the rafter legs.
The distance between the rafters is a fundamental parameter on which the strength and reliability of the roof structure, its service life, and the possibility of using certain roofing materials depend.
The strength and service life of the roof depend on many factors: the quality of building materials, climatic conditions, and the reliability of the sheathing.
But the supporting structure of the roof is the foundation on which the entire structure rests.
The rafter system must be accurately calculated, correctly installed and reliably protected from destructive external influences.
General scheme for calculating rafter pitch
The rafter system is the supporting structure of the entire roof. It consists of rafter legs, vertical racks and inclined struts.
Each rafter is located at a certain distance from the next - this distance is called the “rafter step”.
The strength of the roofing structure depends on it, the maximum permissible load per square meter and materials that can be used for roofing work.
According to GOSTs, the minimum permissible value the rafter pitch is 60 cm, the average is more than 1 m.
To determine the approximate pitch, you can use the following formula: D/(D/m+1), where D is the length of the roof from ridge to ridge, m is the approximate rafter pitch.
All results obtained must be rounded to the nearest higher integer. Obviously, this formula serves only for approximate calculations.
To determine the exact step size, the following factors must be taken into account:
- own weight of the rafter system, i.e. the materials from which it is made;
- the weight of the material with which you plan to cover the roof;
- weight additional insulation, seals, hydro- and vapor barrier systems;
- sheathing weight;
- weight finishing materials attic;
- climatic loads (wind, snow accumulation).
In addition to the above loads, the roof must support the weight of at least one adult person, so that in the event of repairs or antenna installation, the installer can safely climb onto the roof.
If you are planning to install a chimney pipe, then its location must initially be included in the calculations so that in the future you will not need to remove part of the roof and install additional support points.
Single-pitch and gable roof: the difference in rafter systems
For a pitched roof, erecting a rafter system is quite simple. Most often, rafters are laid directly on the crown, without the use of additional supports and supporting structures.
That is why the maximum angle of inclination of a pitched roof is limited to 30 degrees: the absence of additional load-bearing structures and support beams means that the entire load falls on the building walls and foundation.
The optimal tilt angle is 15 – 25 degrees. Maximum permissible length The span of the rafters does not even reach 6 m.
When erecting a pitched roof, be sure to take into account the direction of the wind and the possible additional load from the weight of snow accumulated on the roof.
For houses located in regions with strong winds and little precipitation, you can choose a slope angle at which the roof is cleared of snow due to gusts of wind.
A gable roof is a system of two inclined slopes connected by a ridge. One of the main advantages of this design is the possibility of more evenly distributing the load between the rafter system and the load-bearing walls of the building.
Besides, gable frame allows the rafters to rest on each other, which gives it additional strength.
The overall strength of the roof structure increases as the slope angle approaches 45 degrees. It is this slope that is considered optimal for regions with heavy rainfall.
As the angle of inclination increases, on the one hand, stability increases significantly, so you can take a larger rafter pitch.
On the other hand, the windage of the roof increases, so for windy regions optimal angle the inclination does not exceed 20 degrees.
Slate rafter system
Despite the appearance large selection modern roofing materials, classic version– slate – is still very popular, mainly due to its low cost and ease of installation.
The distance between roof rafters under slate is calculated taking into account the characteristics of the material: slate is quite fragile, but at the same time it can withstand heavy weight loads.
The permissible range of rafter pitch for slate is from 80 cm to 1.5 m. Most often, the average pitch length is used, 120 cm.
Since slate itself weighs quite a lot, the material for the supporting structure must be chosen durable, for example, beams with a cross-section of at least 75 mm by 150 mm.
The length of the rafter pitch and the thickness of the sheathing are interrelated: the stronger the sheathing you plan to install, the smaller the pitch, and vice versa.
The slate sheet has a standard length of 175 mm, the sheathing pitch is selected so that each slate sheet has at least three support points (one in the center of the sheet and two closer to the edges).
The sheathing pitch depends on the degree of roof slope: for a flat single- or gable roof, 63–67 cm is sufficient. The minimum gap for a steep roof is 45 cm.
You can determine the exact length of the rafter pitch for slate only by taking accurate measurements and calculating the total weight of all roofing materials.
Don’t forget to take into account weather conditions (possibility of snow accumulation, strong gusts of wind) and load additional equipment(antenna or chimney). If the attic will be equipped with an attic, then take into account the weight of the insulation.
Nuances of the system for metal tiles
Metal tiles are one of the most popular roofing materials on the market. It is easy to handle, durable, and looks beautiful.
In addition, metal tiles are one of the lightest roofing materials (only 35 kg per square meter); they can be laid on a fairly light support, thereby reducing the load on the building walls and foundation.
The average distance between the rafters for metal tiles is 60–95 cm for a gable roof with a slope of 20–45 degrees.
The size of the beams is chosen taking into account the insulation and waterproofing materials. For a simple metal roof, a cross-section of 50 – 150 mm is sufficient.
But in most cases, to create mansard roof Under the metal tiles you will have to lay insulation with a thickness of 150 - 200 mm.
Taking into account the weight of the insulation, the rafter system must be more durable; the recommended size of the beams increases to 200 mm by 50 mm.
When calculating the distance between the rafters, take into account not only the length of the metal tile sheets, but also the insulation.
At correct location rafters you can save significantly on timber.
Do not forget about the peculiarities of installing a roof made of metal tiles: this material does not allow air to pass through well, as a result of which condensation often accumulates under the roof.
Attach the top support of the rafter system to the ridge purlin instead of the side part. This will create a small air gap, will increase ventilation and help protect the roof from destructive moisture.
Rafter system for corrugated sheets and ondulin
Distinctive feature corrugated sheeting is light and rigid, therefore, as in the case of metal tiles, the requirements for the rafter system are not so high.
The distance between the rafters under the corrugated sheet should be in the range from 60 cm to 120 cm. Optimal cross section rafter leg depends on the span between the supports.
So, for a span of 3 m, a beam measuring 40 mm by 150 mm is chosen, for a span of 5 m, a beam measuring 50 mm by 180 mm is chosen.
What distance is permissible between the rafter legs depends directly on the cross-section of the beams: the larger the rafter pitch, the more durable material must be used for rafters. When choosing a pitch of more than 80 cm, increase the thickness of the beams by 20 - 25%.
Do not forget to take into account the weight of the sheathing under the corrugated sheet. The distance between the rafters of a pitched roof of 60 cm will require lathing with minimum cross-section beams 25 mm by 100 mm.
With a rafter pitch of 80 cm, it is 30 mm per 100 mm, etc. The angle of inclination of the roof also plays an important role: with a slope of less than 15 degrees, it is recommended to lay a continuous sheathing under the corrugated sheet, which is much heavier than the sparse one.
Since both are relatively light in weight, supporting structure can be quite light, which reduces the load on the load-bearing walls and foundation of the building.
The higher the degree of inclination, the greater the distance between the rafters is allowed.
On a gable roof with a slope of less than 10 degrees, it is recommended to install continuous sheathing, which increases the load on the roof structure.
In this case, it is better to use more thick timber measuring 40 mm by 50 mm, and keep the rafter pitch to a minimum (60 cm).