Interrail distance: calculation technology. Calculation of the pitch of rafters for various roofing materials Maximum distance between rafters made of steel structures
So, in order for the structure to serve for a long period of time, to be strong and also reliable, it is worth thinking not only about the foundation, but also about the roof. The building system of such an element plays a huge role., because it is the roof that takes on negative aspects from changes in weather conditions, as well as other situations.
The shed roof rafter system must be characterized by certain requirements, including:
- Rigidity
- Little weight
- Quality material
Such requirements must be taken into account in order for the structure to serve for a long time.
The rigid characteristics of the element play an important role, because it is with the help of rigid elements that different parts are connected. Such elements should not undergo deformation processes.as well as spraying under no circumstances.
The basis of this design is a triangle, which is made using a special reliable frame. Each element of this frame is fixed to one another in parallel, and with the help of strong fixing, the stability of the entire structure is ensured.
Shed roof rafter system: diagram
But, if such frames are poorly attached, they will be movable, this will only lead to negative consequences... Such a roof can collapse not only from strong winds, but also by itself.
If we talk about weight, then this the roof should not be heavy... That is why this system is made, in most cases, from wood. In the event that the weight is large enough, it is necessary to make a supporting base of metal.
There are times when use coniferous trees, the humidity of which is at least 18 percent. Among the prerequisites for using trees, we note:
- Antiseptic treatment
- Use of flame retardants
Only in this case, the nodes in the area of \u200b\u200bwhich the entire system is precisely fastened will be distinguished by high strength and reliability.
The high quality of the materials used is one of the main rules... The tree must meet the following characteristics:
- 1-3 different grades are used... It is important to pay attention that there are as few cracks as well as knots. For one meter of material, 3 knots with a height of no more than 3 centimeters are allowed. Cracks are also allowed in a minimum amount, but not along the entire depth.
- It is advisable to make elements of a bearing nature from parts whose thickness is at least 5 cm, and an area of \u200b\u200b40 m2.
- Planks made from coniferous trees can only be used with a length not exceeding 6.5 meters, and from deciduous trees - up to 4.5 m.
- It is advisable to make pillows, purlins, and also a Mauerlat from trees that are hardwood... Such material should be pre-treated with one or another high-quality antiseptic.
Shed roof structure
So, before starting to manufacture the system, it is very important to know what are its main parts:
- Mauerlat, which can be called the foundation of the system. With this part load is distributed evenly and correctly.
- Run represents an element that is confident holds all the rafter legs... The ridge version is at the top, but the side elements are located on the sides.
- The rafter leg is installed to determine the angle of inclination of the slope, as well as for the reliability of the entire roof, its appearance. It is this product that fixes the individual parts of the system.
- Tightening helps the legs to stay in place, do not move apart. This piece connects them at the bottom.
- Racks, as well as struts give additional leg stability.
- Lathing represents boards, as well as trimmed beams. It is stuffed perpendicularly transfers the load to the rafter legs.
- The overhang of the entire roof protects against precipitation.
- Skate is the place where two roof slopes meet. It is along this element that the crate is stuffed, due to which there is reinforcement of one or another part of the roof.
- Filly are used when the leg length is short, as a result of which they create an overhang.
ATTENTION!
Only if you take into account the described parameters will you get a reliable roof.
A gable roof is characterized by the presence of one slope, which is characterized by an inclination angle of 14 to 26 degrees. In the case when the roof is made for a small house, the span will not exceed 5 cm, therefore it is recommended to make a layered version system.
The support of such a roof is made on external walls.as well as on a wall that exists inside the object. Rafter systems are used in truss rafter cases.
Roofing cake, or rather, its structure, depends on what kind of final coverage option will be chosen. But, regardless of the material, this element maximizes roof life, durability.
The single-slope type requires special attention, since it is this stage of construction that has the maximum effect on the climate that the structure will have.
The structure of the rafter system
Fastening the rafters of a pitched roof
The fastening scheme is quite simple, since it is a parallel laid out boards that rest on two walls. To install the legs, special transitional elements are used, which are made of wood.
Depending on the material used, the following can be used as a transition piece:
- Mauerlat... In the above single slope roof system, there are two wooden beams that lie separately and complete the walls.
- Upper part of the foot, which is composed of beams.
- Top harness the whole frame.
Although the design of this roof is simple, there are some subtleties of fastening the rafters that are important to know about.
The fact is that the nodes that are applied must take into account all the negative aspects of a material such as wood.
When designing, the following tasks should be considered:
- The ability to easily move wood parts from one another
- Adaptation to the consequences that may occur after the subsidence of each wall, to take a stable position
- Elimination of all possible reasons for the violation of one or another connection
The triangles are fastened according to the scheme: the horizontal side is installed on the Mauerlat, fixed. It is very important that it has enough space for docking. with other elements.
It is important to set the rafter legs at a certain angle to the supporting elements. It should be understood that two points are small enough for a strong attachment, so there are methods that are used to avoid negative consequences.
First of all, it is important to increase the total area of \u200b\u200binteraction of the raftersas well as a support part with:
- Select cuttings
- Saw down the upper and lower edges of the legs. With the help of such actions, you can easily create a support platform, increase stability.
Fastening the rafters
Rafter step
The distance between the rafters of a pitched roof is calculated depending on whether what material is chosen, as well as the section... Such calculations should be done at the stage, building codes and rules are used.
The calculation for the above roof option is very simple. There are no racks, as well as braces, as a result, only the rafters of a shed roof are taken into account.
Usually, for such a roof, softwood material is used, the moisture factor of which is approximately 20-22 percent. Such boards should be characterized by evenness, the absence of blue.
Each roofing material is characterized by its own characteristics, therefore, the step of the rafters is also different:
- Using distance depends on the size of the sheet... Usually, the spacing of the beams is at least 60 cm and up to 90 cm. With a greater distance, boards with a large section - 150 mm are additionally used. It is important to take into account the use of the lathing, the cross section of which should be 30 * 100 mm, and the installation is carried out taking into account the span of at least 50 cm.
- often used, but its weight is taken into account... The beams for such a system are pre-dried. When determining the step size, consider the length of the boards. At the maximum length, it is worth making the minimum distance between the rafters. The same rule is used with the minimum length of the beams - a large step distance. Usually, 80 cm is considered a safe step.
- Under , which is used much more often than the two above materials, beams with a small section are used... The step in this case is equal to a number from 60 to 90 centimeters. The bar should be used with a cross section of about 50 * 150 mm.
- Using it is worth understanding that this in the form of sheets... Beams should be placed with a distance that will not be less than 60 centimeters, but not more than 90 centimeters. The section of the bar is 50 * 200, and you can also use 50 * 150 mm. When using a smaller section, negative aspects can be expected, since such a section will not be able to provide high strength to the legs.
- Under which is used very rarely, rafter legs with a section of 50 * 100,50 * 150 are used. The step is not less than 60 centimeters, and also not more than 80. In this case, the step differs depending on the roof structure.
Rafter pitch table
Installation of the rafter system
When deciding to independently install the rafters of a pitched roof, you should first prepare all the elements, and also process them with special means.
Boards should be laid on both sides of a certain roof and laid in the grooves.
Only then is it important to attach several extreme rafters.
CAUTION!
Consider that it is important to hammer in one or two nails per joint... The legs are set taking into account the previously stretched strings, after which they are nailed in the same way. After that, the lathing is installed, and the roof is also laid.
After calculation, design, there are certain installation stages:
- Installation of the supporting beam... A large timber is laid along the wall of the object. Previously, it should be cursed, soaked with an antiseptic... It is important to lay roofing material along the end of the wall; mount the beam on it at the level with the help of anchor bolts.
- Processing of timber, roofing elements... It is planned to leave the board above the roof overhang - a level of about 40 cm on each side, depending on. It is important to consider that the steeper the angle, the less it costs to fly... When using metal tiles, as well as corrugated board, the step is 120 centimeters. In the case when the width is more than 6 meters, it is recommended to reduce the step to 1 meter. The board cuts for strength into the Mauerlat.In contact with
The gable roof is the most popular construction in private housing. The gable roof rafter system must provide a support area for the installation of the roof. A correctly calculated pitch of the rafters of a gable roof allows you to ensure the strength and stability of the structure to all external loads, to create a durable and reliable roof covering. This article discusses the structural features of the rafter system, the procedure for calculation and installation. This information will allow you to correctly understand the methodology for creating a gable roof, so as not to ask workers unnecessary questions during construction.
Distance between rafters for a gable roof
Among people engaged in the construction of a private or country house, there are constant discussions about the most successful roof structure and the number of supporting elements. To understand these opinions and take one side or the other, it is necessary to consider the general structure of the roof.
There are two types of rafter construction:
Hanging.
Fortified.
They are used on relatively small houses with supporting elements no more than 6 m long. The structure consists of a number of truss trusses in the shape of an isosceles triangle. The trusses are installed on a lathing from a bar (mauerlat), interconnected by lathing strips. The bearing capacity of hanging rafters is relatively low, but the simplicity of the structure, the economy and the high speed of installation are their advantages. There are quite a few options for the implementation of hanging rafters, which is explained by the prevalence of small buildings that do not need a complex and massive roof structure.
Design layered rafter system somewhat more complicated. A strong timber - Mauerlat - is laid along the perimeter of the ceiling of the upper floor. Two (or more) vertical posts are installed along the longitudinal central axis, the height of which determines the angle of inclination of the slopes. A ridge girder is installed between the posts, which runs along the entire length of the roof and serves as a reference line for the rafter legs. Each of them has two points of support - at the bottom it is a Mauerlat, and at the top is a ridge run.
To form additional support, excluding the sagging of the supports, struts are used - inclined strips attached to the rafter legs at an angle close to a straight line and abutting in the lower part against the central lower bar - a bed.
The lag step for the roof is the distance between two adjacent rafters. It is determined by the number of lags evenly distributed along the length of the longitudinal axis of the roof. The main supporting structures for the roof are rafters and lathing, which form inclined surfaces with a given geometry and area. The angle of inclination determines the wind and snow loads, and, with an increase in the angle, the wind load increases, and with a decrease, the snow load on the roof.
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What determines the pitch of the rafters
Consider the factors that determine the step between the rafters of a gable roof in more detail. It must be taken into account immediately that the number of rafters determines the bearing capacity. A decrease in their number complicates the installation of insulation, contributes to the sagging of the battens and the roof installed on them.
At the same time, too frequent placement of rafters also creates difficulties in the installation of insulation. It has to be adjusted in width, which creates waste, i.e. waste of material. Therefore, the size of the heat insulator is often used as a criterion for determining the pitch of the rafters. For example, many types of mineral wool are 60 cm wide, which is suitable for most gable roof structures.
In addition, the step of the rafters directly depends on their number. This is a calculated value, which is determined based on the bearing capacity of the supporting elements. The loads acting on the roofing, as well as the weight of the coating itself, are quite large, therefore, to accept them, a stable and durable structure is needed. It should be borne in mind that the type of rafter system also matters, since layered rafters are much heavier than hanging ones, they form a noticeable load on the walls and foundation of the house.
Wind and snow loads are external factors that affect the roof structure. The weight of snow in winter can push through or even break a roof if its structure is not properly designed. SNiP applications contain special data on the average annual amount of snow in different regions. Some of them have up to half a ton of snow for every square meter.
In addition to snow, wind creates serious loads. Moreover, if the snow load is static, then the wind effects are sudden and uneven. The wind can rise at any time of the year, both in winter and in summer, which makes us take it seriously. When choosing the angle of inclination, one should find out the strength and direction of the prevailing winds in the region, learn about the possibility of hurricane gusts. SNiP annexes are available.
All these factors determine the parameters of the rafter system and the distance between the individual supports.
Dependence of the pitch of the rafters on the roof material
There are many types of roofing. Most of them are noticeably outdated and are little used in modern construction. The most popular today are:
Professional list.
Metal tile.
It should be noted that the profiled sheet and the profiled flooring represent one group of profiled coating. Some sources consider them to be different names for the same material, others divide them by wave height. At the profiled sheet, the wave height is greater, and the profiled flooring is somewhat flatter. The first type can be used not only as a roof covering, but also as a material for the construction of fences, enclosures, metal garages, etc.
The corrugated board has a smaller wave and is intended for laying as a roof. Both materials have a common specific feature - profiling is performed only in the longitudinal direction, which expands their capabilities and allows you to make a roof for round roofs and awnings.
The step of the rafters of the gable roof under the corrugated board is selected taking into account this material feature. If the value is too high, it will be possible for the roof to sag between the rafters. In addition, there will be an excessive load on the battens, which may not be ready for it. The area of \u200b\u200bthe slope is also becoming an important parameter. The pitch of the rafters of a single-pitched roof under the corrugated board is much less than that of a gable roof, since the length of the supporting elements and the magnitude of the load on it increase significantly and require an increased number of supports.
The metal tile looks like a natural ceramic tile. In all its performance characteristics, it is very similar to a corrugated board or a corrugated sheet, but physically it has an important feature - the presence of not only longitudinal, but also transverse waves. This allows you to slightly increase the step between the rafters of a gable roof under the metal tile, or be guided by the size of the heat insulator.
When using slate or ondulin, the step of the rafters is taken according to the degree of rigidity of these materials. Alternatively, they increase the packing density of the battens, or install a solid version of thick plywood.
Method for calculating the distance between the rafters
There are two calculation options:
Engineering calculation using the appropriate formulas and techniques.
Using online calculatorsgiving the answer after entering their own initial data.
The first method is only suitable for a professional roofing system designer. It is extremely difficult for an unprepared person to perform such calculations, since various specific data, coefficients, tabular values \u200b\u200bare needed, which are difficult to find and must be used correctly. Calculations obtained using online calculators are also not recommended for real construction, but use as an option for clarifying or checking the calculation results performed by specialized organizations.
Video description
In the video you can see what the step of the rafters should be:
Conclusion
In conclusion, it should be recalled that all design and calculation activities must be performed by trained and specially trained specialists. The step of the rafters is an important and responsible value that determines the bearing capacity of the roof. The destruction caused by the inability to accept existing loads is serious enough and can call into question the possibility of living in a house, therefore it is necessary to take this issue as seriously as possible.
The distance between the rafters (rafter legs) is called the rafter pitch. When arranging a roof, it is customary to use a rafter leg pitch of no more than 100 and at least 60 cm. The reliability of the roof structure depends entirely on how correctly the distance is calculated.
Incorrect determination of the loads on the rafters and the parameters of the materials used as them can cause deformation not only of the roof, but of the entire building. The roof can collapse and cause walls to collapse. Given this, the calculation of the structure of the rafter system must be given the same close attention as the general design of the building.
Methodology for calculating the distance between the bars
- moving along the eaves of the slope, measure its length;
- divide the resulting number by the selected step (from 60 to 100 cm);
- add 1 to the resulting quotient and round the number up.
As an example, take a slope 30 m long and a distance between the rafters of 0.6 m.
50 + 1 \u003d 51 - 51 rafters are required to build a roof.
Then we determine the step between the beams that will be used as a supporting structure:
30: 51 \u003d 0.58 m - the distance between the axes of the beams that will be installed on the roof slope as rafters.
This example shows a general methodology for calculating a supporting structure, but does not take into account the specifics of a particular roofing material. Experts recommend calculating the distance based on the characteristics of the roofing.
In addition, the calculations should be carried out taking into account the materials from which the truss system of the house will be made. Here the step largely depends both on the type of material and on its dimensions.
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The specifics of laying rafters under ceramic tiles
Despite the fact that ceramic tiles are one of the elite and environmentally friendly roofing materials, their installation is fraught with certain difficulties. And the main one is a large mass. Thus, the weight of ceramic tiles is almost 10 times the weight of metal tiles. This means that for every m2 of the structure, pressure from 40 to 60 kg will be exerted. These conditions imply the creation of a reinforced supporting system that can support the weight of the roof.
To create a rafter system under a ceramic tile roof, a bar with a cross section of at least 5x15 cm, and better - 6x18 cm, is usually used. The moisture content of the wood should not exceed 15%.
The distance between the beams depends on the slope of the ramp and the length of the rafters. So, the steeper the roof, the greater the distance between the rafter legs. If, with a slope of 15 o, the step is 80 cm, then with a slope of 75 o, it will be 130 cm. Long bars will be located at the maximum distance from each other, and short ones - at the minimum.
In order for the installation of ceramic tiles to be performed correctly, the step is not only of the rafter legs, but also of the sheathing. When creating a house structure, it is necessary to take into account the parameters of each roofing element (in this case, tiles). Typically, a tile tile does not exceed a length of 40 cm, and during installation it forms an overlap with the previous row of about 9 cm.This determines the pitch of the sheathing, which should be at least 31 and not more than 35 cm.
Also, this indicator can be determined according to the following scheme:
- the length of the lower row is subtracted from the length of the slope;
- then the distance between the first row of the lathing and the last rafter is subtracted.
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Specificity of mounting the supporting structure for metal tiles and corrugated board
Installation of metal tiles does not require reinforcement of the supporting structure due to its low weight. The wood will not resist the loads exerted, which means that the step between the beams may not be wide. So, with metal roofing, the rafters can be located at a distance of 60-95 cm from each other.
Profiled sheeting is another roofing material that is lightweight. And according to other characteristics, the corrugated board is as close as possible to the metal tile. Therefore, the step of the rafter legs is similar to the above - from 60 to 90 cm.
Distance parameters determine the characteristics of building materials. For example, if a board with a width of less than 10 cm is used to equip a structure on the roof, the distance should be reduced to 50 cm.
Do not forget about the distance between the elements of the sheathing, which can be from 0 to 400 cm. The pitch of the sheathing is chosen taking into account the brand of the profiled sheet and the slope of the slope. For example, a professional sheet of the C-21 brand with a thickness of 0.5 to 0.7 mm with a slope of the roof slope of more than 15 o should be attached to the crate, the step of which will be no more than 65 cm.
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 from each other the rafters are located.
After all, the distribution of the load on the frame depends precisely on this desired parameter.
If the calculation is not correct, deformation may occur and the roof will collapse.
Therefore, it is extremely important to perform an accurate calculation of the interval between when drawing up a roof project.
Basic provisions of the calculation
The step of the rafters is the distance from one rafter leg to the other.
When building roofs of private houses, this value is equal to 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 rafter system of the selected type.
To perform the correct calculation, use the following scheme:
- first it is necessary to determine what is the length of the roof slope;
- now the resulting figure should be divided by the value of the approximately selected rafter step. If you pre-selected its value of 1 meter, then it must be divided by 1.
If 0.8 was chosen, then it should be divided by 0.8, etc.;
- after that, add one to the result obtained and round the resulting value up. This action is necessary in order to get the exact number of rafters that need to be installed on one slope;
- the total length of the ramp must be divided by the number of rafter legs obtained in the previous calculation. And we get the exact distance between them.
To understand it better, 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 easier to count.
Further calculations will look like this:
Now add a unit of 27.5 m +1 \u003d 28.5 m.
Round up to the nearest value and get the number 29.That is, it is necessary to install 29 rafter legs on one slope of our roof.
Now we divide the length of the roof by their number: 27.5 / 29 \u003d 0.95 m.
This means that 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, you will have to make some changes to the calculation procedure.
Optimum 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 bend.
And how to lay the insulation?
After all, most materials have a width of 1 meter.
So they take an approximate step of 1 meter when calculating.
The minimum distance between 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
A pitched roof is the simplest.
Indeed, in the truss of such a roof, there are only rafter legs.
There are no braces, struts, braces in its structure.
Such a roof is usually arranged in garages, outbuildings, baths.
In order to determine the pitch of the rafters on a pitched roof, you can use the table:
As you can see from the table, the rafter pitch depends on their length and section.
Distance between rafters for a gable roof
A gable roof is much more common than a pitched 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 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 performed according to the general calculation system (see above).
If the slopes are of 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 \u200b\u200bare 70 and 120 cm.
What is the step depending on the roofing material
Ondulin
If ondulin is used as a roofing material, then the rafter system is constructed of 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 crate of timber with a section of 40 x 50 mm is laid on top.
Metal tile
Metal roofing 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.
A small one makes it possible to use boards of a smaller section when creating a rafter system, and use thinner bars for the crate.
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 with a thickness of 150 mm is placed in the gap 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 are drilled near the upper roof with a diameter of 12 mm.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 mounting at the top.
The mounting of the upper support is carried out not on the ridge beam on the side, but on the ridge girder.
The presence of a free zone between the rafters allows the air to fully circulate under the deck, which helps to prevent condensation.
Ceramic roof 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 a very difficult material.
If we compare metal and ceramic tiles, the latter weighs 10 times more.
Accordingly, the rafter system is significantly different.
For 1 square meter of the roof surface, there is a load of 40 - 60 kg, depending on the manufacturer and brand of the product.
Rafters for such a frame system are made from wood that has undergone a long drying.
Such wood should have a moisture content of no more than 15%.
A bar is used with a cross section of 50 x 150 or 60 x 180 mm.
It's safer this way.
And the distance between 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 step of the rafters will be 80 cm.
And if the angle of inclination, for example, is 75 degrees, then the step can be more - 130 cm.
More than 130 cm the interval between the rafters is not made.
Also, when calculating the step of the rafters, their length is taken into account.
The more dyne, the smaller the distance between them.
The shorter the rafter legs, the more distance you can make.
If the angle of inclination is 45 degrees, then the roofer can move safely along the roof if the rafter pitch is 80 cm.
Corrugated board
When creating a rafter system for corrugated board, the minimum distance between 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 a large section.
The rafter legs themselves can have a cross section of 50 x 100 or 50 x 150 mm.
Slate
Despite the emergence of a large number of new roofing materials, asbestos-cement slate remains one of the most popular.
If it is planned 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 not less than 60 and not more than 80 cm.
The lathing is made from a bar with a cross section of 50 x 50 mm or a board with a cross section of 25 x 100 mm.
When constructing any building structure, it should be remembered that there are still unforeseen situations.
And, therefore, at and the distance between them, it is necessary to provide a margin of safety.
Video about the installation of the truss system.
It is pointless to argue about the importance of a roof for any building. It is not for nothing that in the entire history of mankind, more than a dozen different types of roofs have been invented, from simple to quite complex in design and construction. An important element when planning the construction of a roof is the step between the rafters - strong bars that are the basis of the structure. This is what this article will discuss.
The distance between the base of roof slopes is not constant and depends on the following components:
- type of roof;
- slope angle;
- the type of roofing material intended for installation;
- the dimensions of the rafter section.
Before proceeding with the process of erecting the upper structure of the house, a calculation should be performed, having determined the optimal distance between the rafters.
Gable roof rafter pitch
The most widespread in our country are gable roofs. They are a structure having two parallel planes with an inclination angle relative to the horizon from 20 to 50 degrees.
If the slope of the gable roof is insufficient in snowy areas, there is a risk of accumulation of large snow masses, which can lead to the destruction of the structure. An increase in the angle of slopes in regions with a predominance of strong winds is also fraught with a high load and the danger of breaking not only the roof, but also the entire structure as a whole.
Mansard roof rafter system
Most private homes have an exploited under-roof space called an attic. This design is characterized by an increased slope height, which is caused by the need to create a living space of a comfortable height. As a rule, the slopes of the attic roof are broken, with a varying slope angle. For their installation, a double rafter system is used.
The steepness of the lower half slopes of the attic roof significantly exceeds the slope of their upper extensions. The plane load perceived by them is not great. Thanks to this, the rafters in the lower part can be installed with a maximum pitch. It is recommended to mount the upper ridge slopes with a reduced 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, high pressure is exerted on them. Experts recommend using lumber with an increased cross-section for the rafters of a single-pitched roof, with the installation of a minimum step from each other.
When calculating the distances at which the roof beams are installed, special attention should be paid to the amount of snow load in a particular area. With a small slope, this characteristic is of great importance. It is better to choose a roofing material for such roofs with a minimum own weight, which will reduce the bending load.
Hip roof rafter system
The most difficult in construction is the rafter system of the hip roof. This type is called four-slope, since the roof is formed not only by the side, but also by additional end slopes, where the installation of the rafters is carried out not on the ridge, but on the corner bowstrings. This places special demands on the organization of the roof frame.
Under the hip roof, the attic is not often arranged. This is due to the small angle of inclination of the rafters and the roof as a whole. In the case of an increase in the angle of the slopes to the horizon, the distance between the rafters is increased, with a decrease, on the contrary. An additional aspect of the calculation is the used roofing material.
Dependence of the pitch of the rafters on the roofing material
In addition to snow and wind loads, which are variable, a constant (static) also acts on the roof, the force of which depends on the used roofing material. It is no secret that different types of roofs have their own weight, which can differ by 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. No wonder, when designing a foundation, it is necessary to decide in advance on the choice of a roof.
Roof from profiled sheet
Currently, one of the most common roofing materials is a profiled sheet, produced in galvanized or with subsequent polymer coating. The distinctive features of the profiled sheet include the following parameters:
- High corrosion resistance;
- As a result, a long (more than 15 years) service life;
- Easy installation even without the required qualifications;
- Small sheet weight (weight of 1 m 2 is 4-5 kg).
Since this roofing material does not exert a high load on the rafter system, the distance between the elements is chosen as much as possible for a particular angle of inclination. In addition, the profiled sheet does not require high strength characteristics from the roof lathing. All this together allows you to minimize the overall load on the foundation and walls.
Metal roofing
The second common type of steel roofing material is metal roofing. This type of profiled sheet, which successfully imitates natural clay material, but with a lower weight (10 or more). A feature of the rafters under the metal tile is the smaller section size.
When choosing at what distance to install the rafters, first of all, one should be guided by the dynamic load. Like the profiled sheet, the metal tile is not demanding on the size of the rafter legs and is well mounted on a crate made of an inch board of coniferous species. All this makes the metal roof cost effective.
Rafter system for ondulin
In the 21st century, wavy sheet materials have been replaced by a more durable and lightweight analogue - ondulin. Among others - the lightest material. Sheet weight does not exceed 6 kg.
The small thickness of ondulin sheets at slope angles less than 15 ° requires the arrangement of a continuous sheathing of plywood sheets, for example, which will require an appropriate rafter pitch. You should pay attention to this when calculating.
Slate roof
Not so long ago, a corrugated material from an asbestos-cement mixture, called slate, was widespread. High weight and fragility are the main disadvantages, however, to this day, he finds his fans in the construction of various outbuildings.
A high mass, comparable to the weight of clay tiles, will not allow using the same rafter system as for metal tiles. Building codes define a minimum slope angle of a slate roof of 22 degrees or more. Otherwise, the load from the material itself and the rafter system with a crate exceeds the permissible parameters. The pitch of the inclined beams, as well as their section, are selected individually in each case.
Roof polycarbonate
In recent years, an artificial polymer material - polycarbonate - has been increasingly used on the roofs of verandas and gazebos. Available in two versions - monolithic and honeycomb. The first is similar in properties to ordinary quartz glass, but significantly surpasses it in strength. The second one has less mechanical properties, but high thermal insulation and light transmittance.
Cellular polycarbonate is usually much lighter than its monolithic counterpart. It is used as a roof without the use of lathing, provided that the step does not exceed ½ the width of the sheet of material. The high strength of the monolithic analogue also allows you to avoid elements transverse to the rafters. Sufficient flexibility allows you to cover semicircular roofs on a metal frame, the pitch of which does not exceed 0.9 meters.
Thematic material:
Rafters under a soft roof
The original pattern can be obtained through the use of soft roofing materials, spread with an adhesive layer. They are installed on a solid crate made of plywood or OSB. The step of the rafters should allow the sheets to be fixed, so it is chosen to be a multiple of ½ of the width. Provided the standard dimensions of plywood are 1520x1520 mm, the center distance between the rafters will be: 1520: 3 \u003d 506 mm.
Step of rafters under insulation
The installation of residential under-roof spaces is often combined with the laying of insulation sheets in the rafter gap. The most common slabs with dimensions of 600x1000mm. We use these parameters as starting points.
Scheme for calculating the pitch of the rafters
According to building codes, the pitch of the roof rafters is in the range of 0.6 - 1 meter. Its final calculation is performed according to a simple formula depending on the total length of the roof. To calculate, you must perform the following list of actions:
- determine how much distance should be between the rafters for your specific building conditions. The reference book determines the value of wind and snow loads in the area.
- the length of the roof is divided by the desired distance by adding one. The result will be equal to the number of rafter legs that are installed on one roof slope. In the event that the value is not an integer, it is rounded up.
- the length of the roof is divided by the number of rafters calculated above, we get the final step in meters.
For example, with a slope of 30 degrees, the maximum distance between the rafters of a gable roof under the metal tile is 0.6 measure. The length is assumed to be 16 meters. Hence:
- 16:0,6+1=27,66;
- rounding the result, we get 28 rafters per slope;
- 16: 28 \u003d 0.57 meters - the center distance of the rafter legs for these specific conditions.
As you can see, the calculation technology is not complicated, but this is just a rough diagram. Taking into account many of the other parameters mentioned above can make certain adjustments.
