When building a roof, the first thing to choose is the type 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;
- element weight 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 that regulate 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
Calculation for pitched roof- simplest. The rafter system does not provide racks and braces - only the rafters themselves. Such a roof is most often installed in 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. Material used, length rafter legs and the cross-section of the beam 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 a significant number of 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 roofing 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 for the most part transmitted 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 ceramics weighs almost ten times more than 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 at the maximum length of the rafters, increased deflection loads are created. 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 for covering country houses, which often provide 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 roof is one of the main elements of the house, so it is worth paying attention Special attention correct calculation roof frame. Which will serve as a skeleton in your home. Incorrect calculation of all loads can lead to disastrous results in the form of roof deformation followed by its collapse.
Before proceeding with the installation of the roofing covering, it is necessary to calculate the rafter system, which will depend on the material used, design, and climatic conditions.
What you should pay attention to before making a calculation
Before starting roof construction, you must select the type of rafter system. Then calculate all the loads that will fall on the roof. The main loads include the weight of the frame, roofing material, insulation, ceiling, and temporary loads are also taken into account, among which are the weight of the snow cover, possible gusts of wind, and the weight of a person during installation and operation of the roof.
The distance between the rafters is calculated based on the selected type of rafters and the material with which the roof will be covered.
Types of rafters
During the construction of roofs various designs use hanging or layered rafters. Sloped - used when installing single- or double-pitched roofs. They have two points of support - load-bearing walls or a load-bearing wall and a ridge beam. Hanging rafters are used when it is necessary to cover large spans or a broken roof is created. In this case, the rafters rest with one end on the wall and the other on the opposing rafter. The quality of the material from which the frame is made will directly affect the reliability of the entire roof.
Material for rafters
Currently, wood and metal are used. Wooden beam or logs are used in the construction of residential buildings, garages and other buildings. Reinforced concrete or metal rafters are used in the construction of industrial facilities and shopping centers where wide spans are required.
Calculation method
The distance between the rafter legs is called the rafter pitch. It should not exceed one meter, and the minimum value is 60 cm. Before making the calculation, it is necessary to measure the size of the roof slope. Then we divide the resulting value by the approximate step size between the rafters. Add one to the result and round up to a whole number. This way we will know the number of rafters we will need. In order to find out the exact distance between the rafters, for this we need to divide the length of the roof slope by the number of rafter legs.
For greater clarity, consider an example calculation:
roof slope length – 28.5 m
select the pitch between the rafters to be 80 cm
add one to the resulting number: 35.625+1 = 36.625
As a result, we find that we need 37 rafter legs
the exact pitch of the rafters will be: 28.5/37 = 0.77 m
This is a general calculation method that requires adjustment depending on the roofing material.
Dependence of rafter pitch on roofing material
The most common roofing materials are slate, metal tiles, corrugated sheets, ondulin, and soft roofing.
Rafter structure for slate roofs
Slate has wide application as a roofing material, due to its low cost and resistance to temperature changes. Due to the heaviness of the material, it is necessary to install a powerful rafter system. The distance between the rafters in this case will depend on the cross-section of the beam. The optimal value is a distance of 80 cm, which will allow not only to withstand increased weight, but also significant snow and wind loads. In this case, the lathing is made with a board at least 3 cm wide. Depending on the type of slate, the lathing is made solid for smooth sheets or sparse for wave sheets.
Important: the slate must have at least three support points at the edges and in the center.
Step between rafters for metal tiles
Increasingly widespread among roofing materials purchases metal tiles. Which is characterized simple process installation, and will also help create your home its own unique look. Metal tile sheets are lightweight, which allows you to increase the distance between the rafters from 600 to 950 mm, with a beam cross-section of 150x50 mm. The lathing in this case will depend on the pitch of the sheet wave. So for a wave of 350 mm, a distance between the boards of 30-40 cm is possible.
Important: on eaves overhangs and bevel edges, the sheathing pitch is kept to a minimum for greater roof reliability.
Step of rafters under corrugated sheets
Corrugated sheeting is a galvanized steel sheet coated with a special coating that protects it from harmful influences. environment. Big choice color scheme, the width of the corrugation, will allow you to create a reliable and aesthetically attractive roof. The pitch of the rafters under the corrugated sheeting will directly depend on the characteristics of the type of profile used, the angle of inclination of the roof, and its configuration. You should also take into account the fact that the sheathing under the corrugated sheet is attached perpendicularly. The rafter system is made from beams with a cross-section of 50-75 mm or from boards 20-50 mm thick and no more than 15 cm wide. The lathing can be solid with a gap between the boards of no more than 10 mm, with a usual pitch of 20-40 cm, and sparse - the distance between the boards is 50-75 cm. The pitch of the rafters under the corrugated board is calculated according to the general scheme and is 60-90 cm.
Roof rafter spacing made of ondulin
Ondulin is a wavy sheet that has high strength and durability. With such a roof, the rafter system is made of pine boards with a cross section of 50x200 mm, in increments of 60-90 cm. A sparse lathing of 40x50 cm is made on top.
Important: if the roof has an angle of inclination greater than 50 degrees, then the sheathing must be continuous.
Determining the rafter pitch for a pitched roof
A pitched roof is simple and does not require any special installation skills from you. Most often it is installed on garages, bathhouses, and extensions. The roof frame consists of beams that rest on the walls of the building. The distance between the rafters of a pitched roof will depend on the length of the rafters. Here you should correctly choose the section of the beam, since the greater the distance, the greater the load on the rafters. To correctly select the pitch of a pitched roof, you should use the data from the table:
Distance between rafters for a gable roof
The gable roof is most widespread, not only because of the simplicity of the device, but also because of its high reliability. Rafter pitch gable roof calculated according to the general scheme. If the bevels are the same on both sides, then you can calculate one part. To do this, we determine the angle of inclination of the bevel; here you should take into account the material with which you will cover the roof. So, at an angle of 45 degrees or more, all types of coatings can be used. For slate and tiles, the minimum tilt angle is 22 degrees, for corrugated sheets and soft tiles - 12 degrees, for metal tiles - 14 degrees, for ondulin - 6 degrees. The length of the rafters for a gable roof is calculated using the Pythagorean theorem, in which the length is the hypotenuse, and the height of the roof and half of its width are the legs. If the spans are more than 6 meters, then the rafter system is additionally strengthened with struts and headstocks, which will not allow the rafter legs to deform under the weight of the roofing material.
The distance between the rafters for metal tiles necessarily takes into account the forces resulting from wind and snow loads, the dead weight of the structures, and the roof. In addition, the following factors influence the pitch of rafters for metal tiles:
- pipe location - wooden roof elements should be 25-35 cm away from the chimney and should not interfere with straight trajectories ventilation ducts, fan pipes;
- roof configuration - it is necessary to have a rafter leg at the junction of the ridge of a gable or hip roof.
All wooden elements of the rafter system are made from coniferous trees, the humidity of which does not exceed 20%.
The pitch of the rafter legs is calculated at the design stage to prepare an estimate. This will significantly reduce the amount of waste and cuttings of lumber.
What do you need to know when choosing the optimal distance between rafters?
Roof scheme with hanging rafters.
Having collected the present loads during the strength calculation, the designer evenly distributes them onto the load-bearing walls. The principle of calculation is the same for layered, hanging rafters, only the schemes for fastening the elements in the ridge and on the mauerlat differ.
The minimum and maximum spacing of wooden rafters for metal tiles are regulated at 0.7 m and 1.2 m, respectively.
When choosing a pitch of 60 - 100 cm, the length of the rafters cannot exceed 6 m; if it is reduced, a spread of up to 1.2 m is allowed. If you place the legs more than 60 cm, this will unnecessarily weigh down the roof and increase the construction budget. If you increase the pitch by more than 1.2 m, the load-bearing capacity and service life of the structure will sharply decrease.
A continuous lathing made of wood-containing slabs adds strength and rigidity to the rafter system. In this case, it is allowed to increase the pitch by 0.3 - 0.2 m compared to periodic lathing made of timber or edged boards. However, to save construction budgets, continuous sheathing for metal tiles is used extremely rarely. The material has sufficient strength and rigidity due to additional transverse profile ribs.
A step greater than 1.2 m is not used even when using rafters made of rolled metal, despite the sufficient safety margin of the material. This is due to the possible deflection of roofing sheets during heavy snowfalls and hurricane winds.
The cross-section of the timber from which the rafter legs are made also affects the pitch of the rafters, since the support area of the sheathing and the weight of the roof change. The best option a beam of 150 x 50 mm with a discharged sheathing with a pitch of 4 - 7 cm is considered, depending on the pitch of the transverse wave.
Calculation example for a gable roof
When carrying out a project by specialists initial stage known roofing material. In order to find out the recommended rafter pitch, you can use the SNiP tables, and then adjust the value in accordance with the operating conditions. An example table is shown below:
| Leg section (cm) | Rafter pitch (cm) depending on their length (m) | ||
| 5 | 4 | 3 | |
| board 20 x 2 | 70 | 120 | – |
| board 18 x 2 | – | 100 | – |
| board 16 x 2 | – | 70 | 130 |
| beam 22 x 6 | – | 120 | – |
| timber 20 x 5 | – | 110 | – |
| beam 18 x 5 | – | 90 | 150 |
| log 180 | 90 | 150 | – |
| log 150 | – | 90 | 150 |
| log 140 | – | 70 | 140 |
| log 130 | – | – | 110 |
The table values correspond to the rafters of simple single-pitched roofs. First, the section of the leg is selected, the length of the element, and the distance between the centers of the log or beam are obtained automatically. At the next stage, the length of the slope in the ridge is divided by the pitch of the rafters with the addition of one. Thus, the number of legs is calculated with the number rounded up. Then it remains to adjust the distance between wooden rafters in fact. For example, with a ridge length of 7.5 m, a rafter leg with a section of 16 x 2 cm (board) 4 m long, the result will be:
7.5/0.7 = 10.7 + 1 = 11.7 pcs. round up to 12 rafters.
Specifying the size allows you to calculate the center-to-center distance for installation after installing the outer legs:
7.5/12 = 62.5 cm.
Dormer windows are placed between adjacent rafters; in places where pipes and chimneys pass, the legs are shifted to the distance specified in SNiP. All other elements of the system remain in place, the area adjacent to the pipes is strengthened if necessary:
- a bench is cut into two adjacent legs;
- a short rafter is cut into it at one end, the second is adjacent at the ridge to the element of the opposite slope;
- the offset legs in the upper part rest on a ridge girder attached to at least two trusses.
Thus, the system receives the necessary rigidity without loss bearing capacity, fire safety requirements are met wooden parts roofs.
Material of rafter legs
The rafter material is often timber 25 x 10 cm – 15 x 4 cm, which allows reducing the construction budget.
When choosing lumber with natural moisture, the developer is guaranteed to experience shrinkage of the structure in the first year and a half by 5-7 cm in height. By increasing the estimate for the arrangement of the rafter system by 70%, you can purchase laminated veneer lumber, significantly reducing structural loads, and doubling the roof service life.
The distance between the rafters will remain unchanged, however, instead of planed timber 17.5 x 5 cm, recommended by building codes for five-meter legs spaced every 0.6 m, you can get by with glued laminated timber of a smaller section 15 x 4 cm. Transportation costs will be reduced and work at height will be easier , cut of material.
Prefabricated rafters from boards are used in the same scheme for attaching hip roof trusses. The upper slopes are made of single boards, the lower ones are made of three boards, sewn with self-tapping screws offset in rows.
Choice metal rafters acquitted when complex configuration roofs, an abundance of ventilation pipes, chimneys, which are not possible to bypass in compliance with SNiP and fire safety requirements. In this case, the pitch between the rafters increases as much as possible, since rolled metal is much stronger than lumber.
If the rafters are attached at the bottom to the mauerlat, the step of the legs is not critical; the elements can, if necessary, be shifted to the required distance in any direction. If a support scheme is used on tie rods, which are floor beams, it is much more difficult to displace individual elements. In this case, the amount of cutting waste during sheathing increases draft ceiling, floor of the attic or attic space.
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
The development of a project for a single-pitch 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 attics.
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 numeric value 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 step cannot be extremely accurate, since it is necessary to take into account a number of additional factors, including the width of the insulation, installation features 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 replacing 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 plan 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 utility room or a garage, or 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. Calculations show that under 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 of 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 of the insulating material to simplify its installation. 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 supporting structures pitched 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 at larger intervals - 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 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 sheathing (wooden or metal) is mounted on the rafters, which can be straight or have arched shape. Typically, the gap between rafters for polycarbonate is from 1500 to 2300 mm. In order to correctly calculate at what distance it is better to lower the rafters, it is necessary to take into account the glazing area, the size 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 pitched roof
Find out what distance between the rafters needs to be made for a gable and shed roof. The maximum distance between rafters for metal tiles, ondulin and soft roofing.
What is the distance between the rafters of a gable roof?
Erection of the roof - The final stage any construction. This structural element is load-bearing structure, which takes on all the loads and then evenly distributes them over the surface of the load-bearing walls of the house.
Gable roof
A gable roof is rightfully considered the most common option for arranging suburban housing. And there is a completely logical explanation for this. It's no secret that the simpler the design, the easier it is to build and the higher its reliability and performance characteristics.
The gable roof has a triangular shape and consists of two pitched planes connected at the highest point by a ridge girder, and the same number and shape of gables.
In principle, the construction of a gable roof is not considered so complex operation. But, despite all its simplicity, it requires the most responsible and thoughtful approach.
Structurally, a gable roof has two slopes located in relation to the wall elements of the house at a certain angle, ensuring natural removal of precipitation from its surface. Also gable roofing structures can be attic or mansard type.
As a rule, gable roofs are installed on single-story, simple architectural plan structures. A huge advantage is that the rafters in this case will not be particularly difficult to install.
The angle of inclination of the roof slopes of gable roofs
The angle of inclination of a gable roof cannot be less than 5 degrees, and in some cases it can even reach 90 degrees. Only at this angle of inclination of the roof slopes will the rafters be able to adequately cope with the function assigned to them.
To choose the angle of inclination of the slopes for gable roof influences great amount factors such as climatic conditions, the type of roofing material chosen and the architectural style of the building.
For example, flat roofs are ideal for construction in areas where strong hurricane winds constantly blow, but structures with steep slopes are an excellent option for those areas where significant amounts of precipitation fall.
Also, the angle of the roof affects its cost, this is due to the fact that a roof with a small angle of roof slopes will use much more roofing material than one with a large one.
However, this is not the only important parameter when building a gable roof. Equally important when forming a gable roof is the correct installation and fastening of the rafter system, as well as the step size between its elements.
The quality of the structure is also affected by the fastening of the rafters to the Mauerlat and ridge run. Especially reliable fastening can be formed using cutting and additional fixation of connections with bolts.
The distance between the rafter legs (otherwise known as the pitch of the rafters) is considered one of the most important parameters when installing a roof, which affects its strength characteristics.
A correctly calculated pitch between the rafters of a gable roof allows you to create a roof that is resistant to the high loads to which it will be subjected during operation.
Let's take a closer look at what the distance between the rafter legs should be.
Rafter spacing for a gable roof
The distance between the rafters of a gable roof is calculated during design. Correcting any mistakes made at this stage is quite problematic, and therefore if you are not sure own strength, then it is better to entrust its implementation to professional architects.
Reliable rafters are the basis of any house roof.
The rafter pitch is calculated taking into account the loads to which the structure will be subjected during operation and the angle of inclination of the roof slopes.
When making a competent calculation, the presence or absence of an insulating layer, the cross-section of the structural elements of the rafter system, the type of sheathing and roofing must be taken into account. It is necessary to correctly calculate the loads, as this will help you avoid making mistakes when choosing the rafter section.
The rafter pitch is the distance between two adjacent trusses.
Step-by-step instructions for calculating rafter pitch for a gable roof:
- We calculate the estimated length of the roof slopes.
- Divide the resulting number by optimal sizes step.
- We add one to the resulting number and round the result.
- We divide the length of the slopes by the rounded result.
As a result of these simple calculations, you will get the distance at which the rafters should be installed.
The pitch between the rafters cannot be calculated accurately, since to obtain more accurate data it is necessary to take into account a huge number of parameters, ranging from the width of the insulating layer, the type of roofing material and even the distance between the gable roof sheathing elements. Rafters installed correctly will serve you faithfully for decades.
Rafter spacing under asbestos-cement slate
An important parameter of asbestos-cement slate is its significant weight, due to which it requires the installation of powerful rafters that can withstand heavy loads. The distance between the rafters is selected based on the cross-section of the timber used to make the rafters.
It is equally important that the rafters of a gable roof are fastened correctly, as this will provide it with a high degree of reliability and a long service life.
The optimal pitch between the rafters when using asbestos-cement slate should not be less than 800 mm. Thanks to this, the rafters will be able to easily cope with the task assigned to them.
Rafters for metal tiles
We will not talk about all the advantages and disadvantages of this material; a lot has already been said about this. Let's take a better look at what the pitch should be between the load-bearing elements of the structure. Rafters for metal tiles are installed in accordance with existing standards and requirements.
Due to its low weight, this coating can be used to cover roofs that previously had ceramic tiles or asbestos-cement slate laid on them.
The size between the rafters in this case ranges from 600 to 900 mm, and the cross-section of the lumber is 50 by 150 mm. This step between the rafters will create the most reliable load-bearing frame for the roof.
However, in areas characterized by snowy winters, it is preferable to arrange a distance between rafters of 200 mm, and to use timber with a section of 50 by 200 mm for the manufacture of structural elements.
In order not to install a special system to maintain the insulation, you can adjust the distance between the rafters to the width of the thermal insulation material.
Rafters for ondulin
Ondulin or flexible tiles must be laid on a continuous, perfectly flat sheathing, and it is better if it is made of some kind of sheet material, which will allow the roof to withstand all loads.
The sheathing is attached to the rafter legs, located in increments of 600 to 1000 mm, depending on the angle of inclination of the roof slopes of the gable roof.
The correctly selected distance between the elements of the rafter system guarantees the entire supporting frame a high degree of strength and durability of the entire structure.
What is the distance between the rafters of a gable roof, YouSpec Construction Encyclopedia
The correctly selected distance between the elements of the rafter system guarantees the entire supporting frame a high degree of strength and durability of the entire
Distance between rafters: correct calculation
The reliability of the roof and its service life mainly depend on how correctly the calculations are made.
One of the most important parameters 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 the rafters 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 the exact size of the 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 obtain the exact number of rafters that will need to be installed on one slope;
- the total length of the slope must be divided by the number of rafter legs obtained in the previous calculation. And we get the exact distance between them.
To 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.
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 receive optimal value For each material it is necessary to perform calculations.
Determining the pitch for a pitched roof
The pitched roof is the simplest.
After all, in roof truss Such a roof has only rafter legs.
There are no struts, racks, or braces in its design.
Such a roof is usually installed on garages, outbuildings, and bathhouses.
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 of a 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.
What is the pitch depending on the roofing material
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 is most often used in the construction of country houses.
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 the hip roof with hanging rafters, follow 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.
The upper support is mounted not on the side of the ridge beam, but on the ridge girder.
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
System design under 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.
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 larger the dyne, the smaller the 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.
Despite the appearance large quantity 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.
Distance between rafters: single-pitched, gable roof
One of the most important parameters when calculating a rafter system is the distance between the rafters. After all, it depends on it how strong and stable it will be.
There is no point in arguing about the importance of a roof for any building. It is not for nothing that over the entire history of mankind, more than a dozen different types of roofs have been invented, from simple to quite complex in design and construction. An important element When planning the construction of a roof, there is a step between the rafters - strong bars that are the basis of the structure. This will be discussed in this article.
The distance between the base of the roof slopes is not a constant value and depends on the following components:
- type of roof;
- slope angle;
- the type of roofing material to be installed;
- rafter section sizes.
Before starting the process of erecting the upper structure of the house, you should perform a calculation, determining the optimal distance between the rafters.
Gable roof rafter spacing
Gable roofs are most widespread in our country. They are a structure with two parallel planes, with an angle of inclination relative to the horizon from 20 to 50 degrees.
If the roof slope of a gable roof is insufficient in snowy areas, there is a risk of accumulation of large snow masses, which can lead to the destruction of the structure. Increasing the slope angle in regions with predominant strong winds is also fraught with high loads and the danger of breaking not only the roof, but the entire structure as a whole.
Mansard roof rafter system
Most private houses have a usable under-roof space called an attic. This design is characterized by an increased height of the slope, which is caused by the need to create a living space of a comfortable height. As a rule, stingrays mansard roof broken lines with varying slope angles. For their installation, a double rafter system is used.
The steepness of the lower slopes of the attic roof significantly exceeds the slope of their upper extensions. The plane load perceived by them is not large. Thanks to this, the rafters in the lower part can be installed with maximum spacing. It is recommended to install the upper ridge slopes with a reduced gap from each other.
Rafters in a pitched roof
For outbuildings and some private houses, roofs with one slope are used. Due to the limitation of the angle of inclination, they are exposed to high pressure. Experts recommend using lumber with a larger cross-section for the rafters of a pitched roof, setting a minimum spacing from each other.
When calculating the distances at which roof beams are installed, special attention should be paid to the amount of snow load in a particular area. At a small slope this characteristic has great importance. It is better to choose roofing material for such roofs with a minimum dead weight, which will reduce the bending load.
Hip roof rafter system
The hip roof rafter system is considered the most complex in construction. This type is called hipped, since the roof is formed not only by side, but also by additional end slopes, where the rafters are installed not on the ridge, but on the corner bowstrings. This places special demands on the organization of the roof frame.
Under hip roof An attic is not often installed. It's connected with small angle the slope of the rafters and the roof as a whole. If the angle of the slopes to the horizon increases, the distance between the rafters increases; if it decreases, vice versa. An additional aspect of the calculation is the roofing material used.
Dependence of rafter pitch on roofing material
In addition to snow and wind loads, which are variable, the roof is also subject to constant (static) loads, the force of which depends on the roofing material used. It is no secret that different types of roofing have their own weight, which can differ by 10 or more times.
The correct choice of material affects not only the upper, but also all other parts of the structure of a residential building and other buildings. It is not without reason that when designing the foundation it is necessary to decide in advance on the choice of roof.
Corrugated sheet roofing
Currently, one of the most common roofing materials is profiled sheets, produced galvanized or followed by a polymer coating. TO distinctive features profiled sheet will include the following parameters:
- High corrosion resistance;
- As a result, a long (more than 15 years) service life;
- Easy installation even without the necessary qualifications;
- Low leaf mass (weight of 1 m2 is 4-5 kg).
Since this roofing material does not place a high load on the rafter system, the distance between the elements is selected as much as possible for a particular angle of inclination. In addition, the profiled sheet does not require high strength characteristics from the roof sheathing. All this together allows us to minimize the overall load on the foundation and walls.
Metal roofing
The second common type of steel roofing materials is metal tiles. This type of profiled sheet successfully imitates natural clay material, but with less mass (10 or more). A special feature of rafters for metal tiles is their smaller cross-sectional size.
When choosing at what distance to install the rafters, you should first of all be guided by the dynamic load. Like corrugated sheets, metal tiles are not demanding on the size of rafter legs and can be easily mounted on a sheathing made of inch board coniferous species. All this makes metal roofing low-cost.
Rafter system for ondulin
In the 21st century, wavy ones are replacing sheet materials a more durable and lighter analogue has arrived - ondulin. Among others, it is the lightest material. The weight of the sheet does not exceed 6 kg.
The small thickness of ondulin sheets with slope angles of less than 15° requires the construction of a continuous sheathing made of plywood sheets, for example, which will require an appropriate spacing of the rafters. This should be taken into account when making calculations.
Slate roofing
Not so long ago, a wavy material made from an asbestos-cement mixture, called slate, was widespread. High mass and fragility are the main disadvantages, however, even today it finds its fans in the construction of various outbuildings.
The high mass, comparable to the weight of clay tiles, will not allow the use of the same rafter system as for metal tiles. Building codes determine the minimum slope angle of a slate roof to be 22 degrees or more. Otherwise, the load from the material itself and the rafter system with sheathing exceeds valid parameters. The pitch of the inclined beams, as well as their cross-section, are selected individually in each specific case.
Polycarbonate on the roof
IN last years Increasingly, artificial polymer material - polycarbonate - has begun to be used on the roofs of verandas and gazebos. Available in two versions - monolithic and cellular. The first one is similar in its properties to the ordinary one. quartz glass, but significantly exceeds it in strength. The second has smaller mechanical properties, but with high thermal insulation and light transmittance.
Cellular polycarbonate is usually much lighter than its monolithic counterpart. It is used as a roof without the use of lathing, provided that the pitch does not exceed ½ the width of the sheet of material. High strength a monolithic analogue also allows you to avoid elements transverse to the rafters. Sufficient flexibility allows you to cover semicircular roofs on metal frame, the step of which does not exceed 0.9 meters.
Thematic material:
Rafters for soft roofing
An original pattern can be obtained through the use of soft roofing materials, spread with an adhesive layer. They are installed on a continuous sheathing made of plywood or OSB. The pitch of the rafters should allow the sheets to be secured, so it is chosen as a multiple of ½ the width. Given that standard sizes plywood 1520x1520 mm, the center distance between the rafters will be equal to: 1520:3=506 mm.
Rafter spacing for insulation
The installation of residential under-roof spaces is often combined with the laying of insulation sheets in the rafter gap. The most common slabs with dimensions are 600x1000mm. We use these parameters as starting points.
Scheme for calculating rafter pitch
By building regulations The pitch of the roof rafters is in the range of 0.6 - 1 meter. Its final calculation is performed using a simple formula depending on the total length of the roof. To calculate, you need to perform the following list of actions:
- determine what distance should be between the rafters for your specific construction conditions. The reference book determines the magnitude of wind and snow loads in the area.
- The length of the roof is divided by the desired distance, adding one. The result obtained will be equal to the number of rafter legs that are installed on one roof slope. If the value is not a whole number, it is rounded.
- The length of the roof is divided by the number of rafters calculated above, we get the final pitch in meters.
For example, with a slope slope of 30 degrees, the maximum distance between the rafters of a gable roof under metal tiles is 0.6 measures. The length is assumed to be 16 meters. Hence:
- 16:0,6+1=27,66;
- rounding the result, we get 28 rafters per slope;
- 16:28 = 0.57 meters - the center distance of the rafter legs for these specific conditions.
As you can see, the calculation technology is not complicated, but it is only approximate diagram. Taking into account many of the other parameters mentioned above can make certain adjustments.