As you know, the roof of any building is its upper part, which can combine protective and decorative functions. It protects the roof mainly from atmospheric precipitation getting inside the building from above, at the same time, with its appearance, material and color of the roof, it can emphasize the architectural features of the building.
The wooden beams that make up the rigid roof frame are called rafters; the selected roofing material is already mounted directly on them.
As buildings carry different functional contents (for example, residential buildings or industrial and technological buildings), so the roofs of various buildings differ from each other. Their shape can directly depend on climatic conditions: on the wind load or the amount of snowfall. It is difficult to clean the roof from the latter if its slope is 30 0 or less, and the large “sail” of a high roof can be a serious problem with wind gusts of more than 18 m / s.
Among the huge variety of roofs, most usually consists of a roof and a set of building structures that hold this roof.
One of the main elements of these structures are, as a rule, wooden beams, on which the roofing is mounted. These beams are called rafters or trusses. They are also the stiffening elements that determine the mechanical strength of the roof, as well as those guides that determine the angle of inclination of the roofing.
The rafters can be located either from one to the other outer wall of the building, with a certain slope, or from the center (ridge) of the roof to the outer wall. According to the first method, single-pitched roofs are arranged, according to the second - gable roofs.
It can be assumed that the closer these truss trusses are located to each other, the more reliable the base for roofing will be.
However, the excessive use of materials makes the structure heavier and leads to higher construction costs. Therefore, the question of how to install rafters is one of the fundamental when designing a roof.
There are two types of rafters: the so-called "hanging", resting with their ends only on the outer load-bearing walls, and those that rest with one of their ends on the inner load-bearing wall of the building or the inner column. Farms of the latter type are called "layered".
Proper placement and fastening of these elements of the building is the basis for the fact that its upper part is not deformed under the influence of possible loads.
How to properly install rafters
General provisions
When designing the roof of a building, determining the number of trusses and the distance between them, they must take into account the required section of the beam used for the construction of the rafters, determine its material and the optimal length of the rafter. Usually, a bar made of coniferous trees is used for the device of rafters, with a section of 50x150 mm (considered the most used) or more.
The length of the trusses directly depends on the size of the building box, the type of roof, and also on its height. The cross section of the timber used and the distance between the rafters determine the strength of the supporting structure for the roof. The distance between the axes of adjacent trusses is called and calculated when designing the roof. In practice, the applied pitch can take a value from 600 to 2000 mm. The specified step is interconnected with the length of the trusses: the shorter they are, the greater the distance between them can be installed.
There is a generalized method for calculating the specified distance. It lies in the fact that the table determines the preliminary step of the rafters. Having then measured the length of the roof overhang of one slope along the lower edge, the resulting distance must be divided by the step determined from the table. The result obtained and the unit added to it, after rounding up, will correspond to the number of rafters required for one slope of the projected roof.
The exact distance between the axes of the "legs" of neighboring farms will be obtained by dividing the length of one roof slope by the number of rafters calculated for it.
In this way, it is possible to determine at what minimum distance the rafters can be installed so that the roof supporting structure meets the design load requirements.
However, the above method does not take into account possible additional loads on the structure associated with the use of various types of roofing, from slate to ondulin. Does not take into account the need to organize free space between trusses to accommodate sheets or slabs of roofing insulation used.
In the case when it is planned to use insulating agents, the width of the canvases or panels of which is known, you can immediately determine at what distance the rafters should be installed. It is recommended in such cases to equate the step to the width of the insulation, minus 1.5 to 2 mm.
Recommendations for choosing a rafter pitch for different roofing
For corrugated roofing, the pitch is selected in the range from 600 to 900 mm. At the same time, the beam is recommended with an optimal section - 50x150 mm.
A heavy roof made of ceramic tiles is characterized by an increased load on the rafters, about 60 - 70 kg / m 2. The step is recommended in the range from 800 to 1300 mm. Moreover, it can increase in proportion to the increase in the angle of inclination of the roof. For example, the distance between trusses should be no more than 800 mm if the angle of inclination of the roof does not exceed 15 0. By increasing the specified angle to 70 0 the step can be increased to the maximum. The cross section of the timber for such a roof is recommended from 50x150 to 60x180 mm.
The device of the supporting structure of the roofing for metal tiles is not much different from the standard one. The material, in comparison with ceramics, is almost twice as light: the load per 1 m 2 does not exceed 30 kg. A bar with dimensions of 50x150 mm is recommended for use. Some features of fastening the upper ends of the rafters are associated with the provision of ventilation of the metal roof to prevent condensation.
Slate roofing is the optimal solution for numerous buildings, despite the fact that this material is recognized as harmful and banned for use in European countries.
Recommendations for the installation of rafters for corrugated slate roofing are typical: they are placed in intervals from 600 to 800 mm, they can be 50x100 or 50x150 mm.
For roofing from ondulin, it is proposed to perform according to the recommendations in force for slate roofing. The modern innovative material ondulin looks like slate, but it is five times lighter than the last one.
The determination of the inter-rafter distance for multi-pitched (tented) roofs is made separately for each slope. For buildings in which the “box” is assembled from logs or timber, the lower end of the rafters is attached directly to the upper part of the outer load-bearing wall, and not to a special timber laid along the perimeter of the upper part of the building (Mauerlat). This installation method makes the price of an error especially high when determining the pitch of the rafters, since it can be very difficult to eliminate such an error.
Bearing truss structure for a mansard roof
For such roofs, the supporting structures for the roof are usually made of timber. The pitch of the rafters for a slope no longer than 15 m can be selected in the range from 800 to 1000 mm. For attics with slopes longer than 15 m, it is recommended to use metal rafters.
It should be noted that for all types of roofs, when determining the pitch of the rafters, the presence of existing vertical structural elements of the building passing through the attic and roof should be taken into account. These elements include chimneys and air ducts. If the design point of the truss installation coincides with the passage of the existing pipe or other building elements that cannot be transferred to another part of the attic, the rafter placement plan should be changed accordingly.
If for some reason it is not advisable to change the specified plan, it is recommended that the rafter, which coincides in place with the building element, be arranged so that it is interrupted at the place where the pipe passes. Moreover, the ends of this truss, cut off before and after the passed pipe, must rest on the corresponding jumpers connecting adjacent rafters.
It must be borne in mind that the nodes of such an "interception" of the truss should be performed with the necessary reliability and quality, which makes it possible to correspond to the calculated reliability of the supporting structure of the roofing.
It should be noted that the installation of rafters is part of a whole complex of very serious and very important construction work on the roof of a building. As a structural element of the load-bearing roofing system of a building, rafters are specified in the roof design plan, which reflects the results of calculations of various possible loads.
Such calculations should take into account all sorts of factors that affect the designed structure in the complex:
- necessary and sufficient height and slope of the roof;
- optimal material for roofing;
- the parameters of its placement on the required crate and the total weight of the roofing;
- the necessary bearing capacity of the truss structure in general and the corresponding parameters of the rafters in particular;
- method of attaching the roof to the walls of the building and the condition of the walls.
And other equally important data, without taking into account which the constructed building and its roof may not withstand various loads.
Therefore, in order not to have distressing consequences as a result of inept actions, it is better to entrust issues related to the design and construction of buildings to professional specialists with the necessary experience and knowledge. At least in the part that concerns the calculation of the load on the truss structures.
The service life and the final reliability of the roof lie in the correct preparatory work, which includes the correctly chosen distance between the rafters. It is from this element of the supporting frame that the load distribution on the supporting frame directly depends, an error in the calculations of which can lead to deformation and collapse of the entire roof. So, the calculation of the total distance between the truss elements is one of the most important tasks in planning and calculating the load-bearing house.
Basic calculation technology
Rafter pitch is the exact distance between two legs of one truss truss. Most often, in private construction, the distance between the legs is about one meter, but the exact figures should come from a detailed calculation of the bearing capacity of the selected type of roofing system. In order to independently perform such a calculation, you must adhere to the following scheme of actions:
- Having measured the eaves of the roof structure, it is necessary to determine the total length of the roof slope.
- The resulting value must be divided by the selected and most optimal step of the rafters. In other words, if exactly one m is chosen in the rafters, then the length of the slope must be divided by this unit of measurement.
- One is added to the result, after which you can round the finished value. It is this method that allows you to determine the number of roof trusses on one roof slope.
- Now it’s worth dividing the length of the roof slope by the resulting number of trusses, which will allow you to determine the pitch of the rafters.
It is worth recalling that this method of calculating such a building element as the pitch of the rafters cannot be considered extremely accurate, because in such calculations it is necessary to take into account the features of the selected roofing material, which can be a problem in the absence of proper experience in this matter. It is for this reason that methods will be described below that will allow you to choose the right rafter pitch for popular roofing materials.
Ceramic tiles and rafter installation
The main feature of the manufacture and installation of a truss bearing system for ceramic tiles is the extremely large weight of the roofing material, which in its totality is ten times greater than the weight of any roofing material.
As a rule, this type and size of roofing material provides for up to 60 kg per square m of the truss bearing system. All this becomes the reason for the use of only dry lumber on the roof, which eliminates the possibility of further deformation during drying and pressure.
When using a wooden beam on the roof, the cross section of which is 150x50 mm, the step between can vary from 70 to 120 cm.
In addition, the distance between the rafters may depend on the overall slope of the roof.
Do not forget about the length of the rafter-type legs themselves. The longer this length is, the smaller the distance should be between the legs of the rafters, otherwise the supporting frame of the roof will be deprived of maximum strength and stability.
Experts recommend using no more than 80 centimeters of pitch between trusses if the roof slope is up to 45 degrees. Special attention should be paid to the lathing system when using ceramic roofing material on the roof.
To determine such a step, it is necessary to take into account the characteristics of each individual element of the roofing material, namely each tile. In order to perform the correct calculation of the crate step for such material, it is necessary to subtract the length of the lowest row and the distance between the last bar and the row of the crate from the pitched length.
As a rule, all varieties of such roofing material have a length of no more than 40 cm. When laying tiles, they are overlapped, which takes up to 9 cm from the bottom row. In other words, the correct step in this calculation is from 31 to 35 cm.
Metal tiles and laying methods
As a rule, the use of metal tiles in private construction is considered the most common, for which there are a number of reasons and positive characteristics of this roofing material on the roof.
If we compare such a roofing type material with the one described above, then several striking differences can be noted, each of which can be safely considered a positive feature of the material. First, it is worth recalling the simplicity and speed of installation of such material, which is made in a sheet type, allowing you to cover a significant area of \u200b\u200bthe roof at a time.
The second feature of metal roof tiles can be considered the extremely low weight of the material, which has a positive effect on installation, work on the roof and the load on the supporting frame of the roofing system.
This feature can be considered the most important, because it is responsible for the lower costs of labor and time in the organization of the truss carrier system. When using this roofing material, the pitch of the rafter bearing legs is from 60 to 95 cm, because the reduced weight and size of the roof does not require high load resistance parameters.
With such indicators, it is worth using a heat-insulating material, the thickness of which is at least 15 cm, which is placed between the rafters. When organizing, the thickness of the insulating material should or may be greater, because this is necessary for arranging a residential floor in the attic. This also affects such an element as the thickness of the material that is used to make the rafter load-bearing legs.
All this indicates the absence of significant differences in the truss system for metal roof tiles. This roofing material provides standard knowledge about the construction of truss and roofing systems, which is simply necessary to install. The main difference of such a system may be the fastening of the upper type support to the ridge run, and not through the ridge type beam itself.
The free space at the top of the system, obtained through the installation of rafter legs, is ideal for ventilation of the entire under-roof space, which is often covered with condensate in metal roofing material.
In the event that changes are made to the roof of an old wooden house, it is necessary to completely remove the mauerlat, replacing it with a common top-type crown. In such a crown, it is necessary to put marks and make selections with the desired step, into which the elements of the rafter bearing legs will be installed. This allows you to more accurately calculate the pitch of the rafter bearing legs and install them.
Decking and determining the distance between the racks
When using such a roofing material as corrugated board, the calculation of the correct pitch of the rafter bearing legs is 60-90 cm, which practically coincides with all the types of structures and roofing materials described.
If necessary, put more distance between the elements of the rafter legs, it is necessary to insure the transverse elements of the crate with a greater thickness and cross section. This will strengthen the entire supporting structure, which will extend the life of the entire roof. The step between is about 50 centimeters, when using a board that is at least 10 centimeters in size.
When it comes to such a moment as calculating the crate on the truss system, then do not forget that the last board should be 1.5 centimeters thicker than all the other elements of the system. Before installing the elements of the crate, it is worth remembering the presence of a chimney and a special system that should be on each roof. This will save time on the calculation and alteration of the truss system, and the crate as a whole.
Ondulin and construction installation methods
As in the cases described above, ondulin provides for the calculation of the pitch of the rafter bearing legs from 60 to 100 cm, which makes such sizes standard when using the most popular roofing materials.
The truss trusses themselves are made of lumber with a section of 200x50 millimeters, which is quite enough to ensure that the strength and reliability of the truss system are at the maximum level, and it is easy to install them. It is immediately worth noting the fact that the described roofing material needs a continuous lathing system, which will allow the material to qualitatively resist the loads from snow thicknesses, as well as solar exposure.
In some cases, a thinned type of crate can also be used, the calculation of which is quite simple if a wooden beam is used for this, the step between the elements of which is no more than 30 cm. As a rule, this option is more expensive than necessary for a continuous crate. In other words, it is irrelevant to use the thinned type of system in this case.
Slate and truss structure under it
As a rule, slate coating is considered the most common in our country. The reason for this indicator can be considered the extremely low cost of the material, the simplicity and speed of installation, as well as the possibility of replacing individual sheets in case of damage to individual sections of the roof.
The distance between the rafters for this type of roof should be 80 cm. It is this distance that is considered the most optimal solution when combining the load from the weight of slate sheets.
The crate in such a system needs a thinned type using a board or timber of any type, but of a certain section, which should not be less than 30 mm. Such a thickness of a board or timber is needed for high-quality and correct distribution of weight from the roofing material itself, as well as from winter precipitation.
Do not forget about the constant margin of safety when organizing the truss system, which may be required in case of unforeseen circumstances associated with mechanical loads and bad weather. All other features of the truss and crate system do not have any special differences from the options listed above. In other words, for all other types of coatings, we determine the distance in the same way as for the above roof.
The distance between the rafters is one of the key parameters that affect the strength of the structure. Competent calculation of the installation step of the rafters allows you to build a roof that is resistant to high operational loads.
Roof loads and rafter system calculation
The development of a single-pitched or dual-pitched roof project begins with the choice of the type of truss system, the angle of inclination of the slopes (roof height) and materials for the construction of the structure. The calculation of the distance between the rafter legs is carried out taking into account the loads that the roof will experience during operation. Permanent loads include:
- the weight of the materials from which the truss system is made;
- roofing weight;
- weight of roofing cake materials (waterproofing, vapor barrier, insulation);
- the weight of the finishing elements of a residential attic or attic.
In addition to permanent loads, the roof also experiences temporary ones, which include:
A step is the distance between the rafters of one slope. When calculating a shed, gable or complex roof, the following scheme is usually followed:
- the length of the future roof slope is measured;
- the resulting value is divided by the optimal numerical value of the pitch of the rafters;
- one is added to the obtained value, the result is rounded off;
- the length of the roof slope is divided by the rounded result.
The final result will determine how far the rafter legs should be placed. The determination of the step cannot be extremely accurate, since it is necessary to take into account a number of additional factors, including the width of the insulation, the particular installation of the crate for various types of roofing material. If a roof with a chimney is being designed, the pitch can be adjusted according to its location so that it is not necessary to remove part of the rafter in the future and install a supporting structure, such as a special rafter system.
The distance between the rafters under the slate
Slate is a traditional roofing material. Its advantages include such characteristics as resistance to external influences (excluding mechanical ones) and low cost. Slate allows you to create a roofing, the repair of which can be reduced to the replacement of individual elements. Slate is heavy and requires the installation of a sufficiently powerful truss system. The calculation of the distance at which it is necessary to put the rafters under the slate is carried out taking into account the cross section of the beam for the manufacture of rafter legs.
The optimal solution is to install the system under the slate, in which the gap between the rafters must be at least 800 mm. In order for the slate structure to withstand not only the weight of the material, but also increased external loads, the crate is made of timber or boards with a cross section of at least 30 mm. When calculating the truss system for slate, it should be read that this material has rather large restrictions on the choice of the angle of inclination of the slopes.
Rafters for metal roofing
Metal tiles are actively used as a practical and aesthetic roofing material when arranging a shed, gable, hip or complex roof. The frame for the metal tile is built according to standard principles. To calculate at what distance it is better to place the rafters, it is necessary to take into account the loads and the angle of the roof. The metal tile is characterized by relatively low weight, so it can serve as a replacement for the old roofing of slate or ceramic tiles. In this case, the rafters do not need to be strengthened or the pitch of their installation changed.
The standard step of rafters for metal tiles is 600-900 mm. The cross section of the elements can be 50-150 mm - this is enough to create a reliable frame for a metal tile. But if it is planned to use insulation, the layer of which in areas with low winter temperatures should be 200 mm, it is recommended to use a 200x50 beam for rafters under metal tiles so as not to mount an additional system that holds the insulation. The gap between the rafters under the metal tile is best adjusted to the width of the sheet or roll heat insulator.
Decking: rafters and crate
The professional flooring belongs to easy and convenient roofing materials in application. Galvanized or coated with a decorative and protective layer, corrugated board can be used both for mounting a shed roof of a utility room or garage, and for a gable roof of a residential building. How to calculate the distance required to install the rafters under the corrugated board?
To ensure the necessary rigidity of the structure, it is enough to install the rafters under the corrugated board in increments of 600-900 mm. In this case, it is necessary to pay attention to the angle of the roof. The calculation shows that with high external loads, it is better to lay the corrugated board on the system with a minimum step. But if the distance between the rafters under the corrugated board is close to the maximum, and the angle of the roof slope is small, then the structure is strengthened by using a more frequent crate. In this case, the step of the crate under the corrugated board should be about 50 mm, the width of the elements should be at least 100 mm.
Rafter system for soft roofing
Soft roofing includes bituminous and bitumen-polymer roll materials, roofing membranes, as well as soft tiles. A soft roof is characterized by a relatively low weight and no need to install a massive truss structure.
The minimum distance between the rafters is 600 mm, the maximum is 1500 mm. When installing a support under a soft roof, it is important to take into account the angle of inclination of the slopes: the smaller the angle, the smaller the distance between the supports for a continuous crate should be. The choice of step is also influenced by the thickness of the material for the crate - the thicker the sheet of plywood or OSB, the greater the installation step of the rafter legs can be.
Ondulin: calculation of rafters
Ondulin (bituminous slate) is laid on a flat, continuous crate made of sheet material. This allows the roofing to successfully resist wind and snow loads. The crate under the ondulin rests on the rafters, which should be located in increments of 600 - 1000 mm, depending on the angle of inclination of the gable or shed roof.
Rafters for ondulin are made of timber with a section of 200 × 50 mm. When choosing at what distance to put the rafter legs for the structure under the ondulin, it is recommended to take into account the width of the insulation material in order to simplify its installation. This calculation allows you to reduce the financial costs of arranging the roof.
Sandwich panel roof
Sandwich roofing is most often erected on sip-panel houses or hangar-type buildings. A feature of the sandwich is its bending rigidity, which makes it possible to dispense with the installation of traditional rafters. Small spans from the ridge of a gable roof to the upper part of the wall (or the distance between the supporting structures of a shed roof) allow the installation of a sandwich without additional supports.
If the span exceeds 4 meters, additional girders must be installed. To install a sandwich roof on a residential building, a traditional truss system is often installed, but in this case the rafters can be positioned with a large step - they serve as a support for the girders. The distance between the rafter legs is selected based on the length of the available material for the runs and the length of the load-bearing walls. The technical parameters of the sandwich allow the roof to withstand high operating loads.
Polycarbonate: erection of the supporting structure
Polycarbonate has recently been actively used as a roofing material. First of all, polycarbonate is in demand in the construction of gazebos, sheds, winter gardens. The crate and truss system for polycarbonate can be made of wood or metal.
Polycarbonate varies in weight depending on the thickness of the sheet. The crate for polycarbonate is recommended to be done in increments of 600-800 mm. The crate (wooden or metal) is mounted on rafters, which can be straight or arched. Usually the gap between the rafters for polycarbonate is from 1500 to 2300 mm. In order to correctly calculate at what distance it is better to bleed the rafters, it is necessary to take into account the glazing area, the dimensions and thickness of the sheets, and take into account that polycarbonate is attached with gaps for thermal expansion.
The distance between the rafters of a gable and single-pitched roof
Find out what distance between the rafters you need to make for a gable and shed roof. The maximum distance between the rafters for metal tiles, ondulin and soft roofing.
What is the distance between the rafters of a gable roof
The erection of the roof is the final stage of any construction. This structural element is a load-bearing structure that 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 perfectly 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.
The gable roof has a triangular shape and consists of two pitched planes connected at the highest point by a ridge run, and the same number and shape of gables.
In principle, the construction of a gable roof is not considered such a complicated operation. But, despite all the simplicity, it requires the most responsible and thoughtful approach.
Structurally, a gable roof has two slopes located at a certain angle relative to the wall elements of the house, providing it with a natural removal of precipitation from its surface. Also, gable roof structures can be attic or attic type.
As a rule, gable roofs are installed on one-story, architecturally simple structures. A huge plus is that the rafters in this case will not be particularly difficult to install.
The angle of inclination of the roof slopes of the 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 with such an angle of inclination of the roof slopes, the rafters will be able to adequately cope with the function assigned to them.
The choice of slope angle for a gable roof is influenced by a huge number of factors, such as climatic features, the type of roofing material chosen and the architectural style of the building.
For example, sloping roofs are ideal for building in areas where strong gale-force winds constantly blow, but steep-sloped structures are a great option for areas that receive an impressive amount of rainfall.
Also, the angle of inclination of the roof affects its cost, this is due to the fact that much more roofing material will go to the roof with a small angle of roof slopes than with a large one.
However, this is not the only important parameter in the construction of a gable roof. Equally important in the formation of a gable roof is the correct installation and fastening of the truss system, as well as the step size between its elements.
Also, the quality of the structure is affected by the fastening of the rafters to the Mauerlat and the ridge run. Particularly reliable fastening can be formed with the help of cutting and additional fixation of the joints with bolts.
The distance between the rafter legs (otherwise, 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 step between the rafters of a gable roof allows you to form a roof that is resistant to the high loads that it will be subjected to during operation.
Let's take a closer look at what the distance between the legs of the rafters should be.
Rafter spacing for a gable roof
The distance between the rafters of a gable roof is calculated at the time of design. Correcting any mistakes made at this stage is quite problematic, and therefore if you are not confident in your own abilities, then it is better to entrust its implementation to professional architects.
Reliable rafters are the basis of any roof of the house.
The rafter step 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.
With a competent calculation, the presence or absence of an insulating layer, the cross section of the structural elements of the truss system, the type of crate and roofing are necessarily taken into account. It is necessary to correctly calculate the load, as this will help not to make a mistake when choosing a rafter section.
The rafter step is the distance between two adjacent truss trusses.
Step-by-step instructions for calculating the pitch of rafters for a gable roof:
- We calculate the estimated length of the roof slopes.
- The resulting number is divided by the optimal step sizes.
- 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 step between the rafters cannot be calculated exactly, since in order to obtain more accurate data, it is necessary to take into account a huge number of parameters, ranging from the width of the insulation layer, the type of roofing material, and even the distance between the elements of the gable roof lathing. Rafters installed correctly will serve you faithfully for decades.
Step of rafters 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 section of the timber used to make the rafters.
It is equally important that the gable roof rafters are properly fastened, as this will provide it with a high degree of reliability and a long service life.
The optimal step 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 should be the step between the supporting structural elements. Rafters for metal tiles are installed in accordance with existing norms and requirements.
Due to its low weight, this coating can be used to cover roofs on which ceramic tiles or asbestos-cement slates have previously been laid.
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. Such a step between the rafters will allow you to create the most reliable supporting frame for the roof.
However, in areas characterized by snowy winters, it is preferable to equip the distance between the rafters of 200 mm, and for the manufacture of structural elements, use a bar with a section of 50 by 200 mm.
In order not to mount a special system to support 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 should be laid on a solid, perfectly even crate, and it is better if it is made of some kind of sheet material, which will allow the roof to endure all loads.
The lathing 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 chosen distance between the elements of the truss 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 Building Encyclopedia
The correctly chosen distance between the elements of the truss system guarantees the entire supporting frame a high degree of strength and durability of the entire structure.
The distance between the rafters: the 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 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, then deformation may occur and the roof will collapse.
Therefore, it is extremely important to perform an accurate calculation of the interval between the rafter legs when drawing up a roof project.
Basic provisions of the calculation
The pitch of the rafters is the distance from one rafter leg to the other.
In the construction of roofs of private houses, this value is 1 meter.
But this figure is approximate.
To get the exact size of the interval, it is necessary to calculate the bearing capacity of the truss system of the selected type.
To perform the 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 chose its value of 1 meter, then you need to divide by 1.
If 0.8 was chosen, then it should be divided 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 get 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 better understand everything, let's look at an example.
By measuring 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.
We 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 \u003d 0.95 m.
So, in our case, the step of the rafter legs should be 0.95 meters.
This is a general calculation.
In which the peculiarity of a particular roofing material is not taken into account.
And he can significantly change this parameter.
When you know what kind of material you will use on the roof, some changes will have to be made to the calculation procedure.
Optimal and minimum value
The step is the unit of account.
After all, it depends, first of all, on the load on the roof frame and the 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 crate may begin to sag.
Yes, and how to lay the heater?
Indeed, for most materials, the width is 1 meter.
So they take an approximate step of 1 meter when calculating.
The minimum distance between the 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
Shed roofing is the simplest.
Indeed, in the truss farm of such a roof there are only rafter legs.
There are no struts, racks, braces in its design.
Such a roof is usually arranged on garages, outbuildings, baths.
As can be seen from the table, the rafter step 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 to explain such popularity is simple: the design is very simple, but for all its simplicity, the gable roof is distinguished by its reliability.
Its design is easy to adjust to any climatic conditions and any roofing material.
When calculating the pitch of the rafters of a gable roof, everything is performed according to the general calculation system (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 limit values for the pitch of the rafter legs are 70 and 120 cm.
What is the step depending on the material of the roof
If ondulin is used as a roofing material, then the rafter system is constructed from pine boards with a section of 50 x 200 mm, and the rafters should be located at a distance of at least 60 cm and not more than 90 cm from each other.
A crate of timber with a section of 40 x 50 mm is laid on top.
metal tile
Roofing from metal tiles is most often used in the construction of country houses.
Because this material is much lighter than ceramic or cement tiles.
Although in appearance it is very similar to her.
The light weight of the metal tile makes it possible to use boards of a smaller section when creating the rafter system, and to use thinner bars for the crate.
More about the counter-lattice under the metal tile.
About the hip roof with hanging rafters at the link. Also about the design of hanging rafters.
About the price of Viking metal tiles here. Specifications, photos, 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.
During the construction of the rafter system under the metal tile, 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 a heater having a thickness of 150 mm is placed between the rafters, then the most comfortable living conditions will be created in the attic.
To ensure ventilation of the space where the insulation is laid, when installing the rafter system, holes will be drilled near the upper roof with a diameter of 12 mm.
The technology for manufacturing a truss 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 run.
The presence of a free zone between the rafters allows the air to fully circulate under the flooring, which helps to protect against the formation of condensate.
Ceramic tiles
The design of the system for ceramic tiles has its own characteristics.
After all, clay is used to make such a roofing material.
And this is very heavy material.
If we compare metal and ceramic tiles, the latter weighs 10 times more.
Accordingly, the truss system is significantly different.
On 1 square meter of the roof surface there is a load of 40 - 60 kg, depending on the manufacturer and brand of the product.
The rafters for such a frame system are 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 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 called 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 can be larger - 130 cm.
More than 130 cm interval between the rafters do not.
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.
If the angle of inclination is 45 degrees, then the roofer can safely move along the roof if the pitch of the rafters is 80 cm.
Decking
When creating a rafter system for corrugated board, the minimum distance between the rafter legs is 60 cm.
The maximum value is 90 cm.
If for some reason the pitch of the rafters was more than 90 cm, then it becomes necessary to install large cross-section boards.
The rafter legs themselves can have a section of 50 x 100 or 50 x 150 mm.
Despite the emergence of a large number of new roofing materials, asbestos-cement slate remains one of the most popular.
If it is planned to lay slate on the roof, then the rafters should have a section of 50 x 100 or 50 x 150 mm.
The distance between them is made not less than 60 and not more than 80 cm.
The crate is made from a bar having a section of 50 x 50 mm or a board with a section of 25 x 100 mm.
When constructing any building structure, it should be remembered that there are still unforeseen situations.
And, therefore, when calculating the sections of the rafters and the distance between them, it is necessary to provide for a margin of safety.
The distance between the rafters: shed, gable roof
One of the most important parameters in the calculation of the truss system is the distance between the rafters. After all, it depends on him how strong and stable it will be.
The distance between the rafters under the metal tile without fail takes into account the efforts made up of wind, snow load, own weight of structures, roofing. In addition, the following factors affect the pitch of the rafters under the metal tile:
- the location of the pipes - the wooden elements of the roof should be 25-35 cm from the chimney, should not interfere with the direct paths of the ventilation ducts, fan pipes;
- roof configuration - it is necessary to have a rafter leg at the junction of the ridge of a gable, hipped roof.
All wooden elements of the truss system are made from coniferous trees, the humidity of which does not exceed 20%.
The step of the rafter legs is calculated at the design stage for budgeting. This will significantly reduce the amount of waste, cuttings of sawn timber.
What you need to know when choosing the optimal distance between the rafters?
The scheme of the roof with hanging rafters.
Having collected the loads present during the strength calculation, the designer evenly distributes them on 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, on the Mauerlat, differ.
The minimum, maximum step of wooden rafters under the metal tile is regulated by 0.7 m, 1.2 m, respectively.
When choosing a step of 60 - 100 cm, the length of the rafters cannot exceed 6 m, with its decrease, a run-up of up to 1.2 m is allowed. If you put your feet more often than 60 cm, this will unnecessarily make the roof heavier and increase the construction budget. If you increase the step more than 1.2 m, the bearing capacity and the resource of the structure will sharply decrease.
A solid crate of wood-containing boards adds strength and rigidity to the truss system. In this case, it is allowed to increase the step by 0.3 - 0.2 m compared to a periodic crate made of a bar or edged board. However, to save the construction budget, a continuous crate for metal tiles is used extremely rarely. The material has sufficient strength and rigidity due to additional transverse profile ribs.
A step of more than 1.2 m is not used even when using rolled metal rafters, despite a sufficient margin of safety of the material. This is due to the possible deflection of the roof sheets during heavy snowfalls, hurricane winds.
The cross section of the beam from which the rafter legs are made also affects the pitch of the rafters, since the area of \u200b\u200bsupport of the crate and the weight of the roof change. The best option is considered to be a beam of 150 x 50 mm with a discharged crate in increments of 4 - 7 cm, depending on the pitch of the transverse wave.
Calculation example for a gable roof
During the implementation of the project, specialists at the initial stage know the roofing material. In order to find out the recommended pitch of the rafters, 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 |
| timber 22 x 6 | – | 120 | – |
| timber 20 x 5 | – | 110 | – |
| timber 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-gable roofs. First, the section of the leg, the length of the element, the distance between the centers of the log, the beam is 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 counted, rounding the number up. Then it remains to adjust the distance between the 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, you get:
7.5 / 0.7 \u003d 10.7 + 1 \u003d 11.7 pcs. round up to 12 rafters.
The specification of the size allows you to calculate the center-to-center distance for mounting after installing the outer legs:
7.5/12 = 62.5 cm.
Dormer windows are located between adjacent rafters, in the places where pipes and chimneys pass, the legs are displaced by the distance specified in SNiP. All other elements of the system remain in place, the area of adjacency to the pipes, if necessary, is enhanced:
- a bed is cut into two adjacent legs;
- a short rafter cuts into it at one end, the second adjoins the element of the opposite slope in the ridge;
- the offset legs in the upper part rest on a ridge run attached to at least two roof trusses.
Thus, the system receives the necessary rigidity without loss of bearing capacity, the fire safety requirements of wooden roof parts are met.
Rafter leg material
The material of the rafters is often a beam of 25 x 10 cm - 15 x 4 cm, which allows to reduce the construction budget.
When choosing lumber of natural moisture, the developer is guaranteed to shrink the structure in the first year and a half by 5-7 cm in height. By increasing the cost estimate for the arrangement of the truss system by 70%, you can purchase glued laminated timber, significantly reducing structural loads, and doubling the roof resource.
The distance between the rafters will remain unchanged, however, instead of a planed beam of 17.5 x 5 cm, recommended by building codes for five-meter legs spaced every 0.6 m, you can get by with a glued beam of a smaller section of 15 x 4 cm. Transportation costs will decrease, work at height will be facilitated , cut material.
Prefabricated rafters from boards are used with 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 with an offset in the rows.
The choice of metal rafters is justified with a complex configuration of the roof, an abundance of ventilation pipes, chimneys, which cannot be bypassed in compliance with the requirements of SNiP, fire safety. In this case, the step between the rafters is maximized, 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, move to the desired distance in any direction. If the scheme of support on puffs, which are floor beams, is used, it is much more difficult to displace individual elements. In this case, the amount of cutting waste increases when sheathing the draft ceiling, the floor of the attic or attic space.
The roof frame must be reliable and durable. But without well-conducted calculations, this is difficult to achieve. In the process of carrying out the calculations, it is determined at what distance to put the rafters on the roof.
What can lead to an incorrect or inaccurate calculation of the loads that the truss structure will undergo? To the most negative consequences, ranging from deformation of the rafter legs and damage to the roof covering and ending with the collapse of the base of the roof frame. Therefore, when designing buildings, the list of mandatory calculations contains data on what should be the distance between the roof rafters. There is a certain technique that allows you to calculate this value.
Method for calculating the distance between the rafters
The distance between the rafters on the roof is called the pitch of the rafters. As a rule, the step of the rafters in the roof structure usually exceeds one meter, and the minimum gap varies within 60 centimeters.
The calculation of the required number of rafters for a roof of a certain length and the pitch of the rafters is carried out as follows:
Roof structure for metal roofing
During the construction of suburban private real estate, metal roofing can be found most often. This roofing material is similar to the flooring made of clay tiles, but in comparison with it has a number of advantages. Sheet metal tiles are easy to install, so you can build a roof in a shorter time, the rafter system for metal tiles is also not difficult.
Metal tiles are lighter than ceramic products, the difference in weight sometimes reaches 35 kilograms per square meter, depending on the thickness of the products (read also: ""). Due to a significant reduction in the weight of the roofing, it becomes possible to reduce the thickness of the elements of the truss structure and the cross-sectional dimensions of the lathing bars, and increase the installation step of the rafters.
Under the metal-tiled coating, the rafter legs are mounted with a distance of 600 to 950 millimeters, while the cross section of the construction material is 150 by 50 millimeters. According to experts, in this case, if a heater 150 millimeters thick is placed between the rafters, then such thermal insulation will create comfortable conditions for staying in the attic room. At the same time, for greater reliability, it is advisable to choose a 200 mm insulation.
When installing rafters, to ensure ventilation of the space that is filled with insulation, holes with a diameter of 10-12 millimeters are drilled in the rafters near the upper roof.
The technology for creating a truss system for metal tiles does not differ significantly from structures for other types of roofing materials. The only feature is that at the rafters, the upper support is mounted on the ridge run from above, and not on the side of the ridge beam. The presence of a free zone between the rafters ensures air circulation under the roofing, and this, due to the use of metal material, reduces the risk of condensation.
Shed roof truss system, main advantages and characteristics ").
The distance between the rafters of a gable roof is made taking into account the size of the heat insulator that is laid between them. An approximate step between the rafter legs is 1-1.2 meters (read: ""). Rafters regulate the size of the roof overhang.
