Interrafter distance: calculation technology. Calculation of rafter spacing for various roofing materials Maximum distance between steel rafters
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 the negative aspects from changes in weather conditions, as well as other situations.
truss system pitched roof must meet certain requirements, including:
- Rigidity
- Little weight
- quality material
Such requirements must be taken into account so that the structure serves for a long time.
Rigid item characteristics play important role, because it is with the help of rigid elements that the connection of different parts occurs. Such elements should not be subjected to deformation processes., as well as raspor under any circumstances.
The basis of this design is a triangle, which is made using a special reliable frame. Each element of this frame is fixed one to the other in parallel, and with the help of a strong fixation, the stability of the entire structure is ensured.
Shed roof truss system: scheme
But, if such frames are poorly attached, if they are movable, this will only lead to negative consequences.. Such a roof can collapse not only from a strong wind, but also by itself.
If we talk about weight, then this the roof should not be heavy. That's why this system 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 cases when use coniferous trees, the humidity of which is not less than 18 percent. Among the prerequisites for the use of 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, as well as reliability.
The high quality of the materials used is one of the main rules. The tree must meet the following characteristics:
- Applies 1-3 different varieties . It is important to pay attention to the fact that there are fewer cracks as well as knots. For one meter of material, 3 knots with a height of not more than 3 centimeters are allowed. Cracks are also allowed in a minimal amount, but not over the entire depth.
- It is desirable to make elements of a bearing nature from parts whose thickness is not less than 5 cm, and the area is from 40 m2.
- Boards from coniferous trees can only be used with a length of not more than 6.5 meters, and from deciduous trees- up to 4.5 m.
- Pillows, girders, as well as Mauerlat, it is desirable to make from trees that are hardwoods. Such material should first be treated with the help of one or another high-quality antiseptic.
Shed roof construction
So, before starting the manufacture of the system, it is very important to know what its main parts are:
- Mauerlat which can be called the foundation of the system. With this part the load is distributed evenly and correctly.
- Run is an element that is confidently fastens all the legs of the rafters. The ridge option 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. This product fixes individual parts systems.
- Tightening helps feet stay in place, do not move apart. This detail connects them at the bottom.
- Racks, as well as struts give additional leg stability.
- crate represents boards, as well as bars in a cropped form. She is stuffed perpendicularly, transfers the load to the rafters.
- The overhang of the entire roof protects against rainfall.
- Skate is the place where two roof slopes meet. It is along this element that the crate is stuffed, due to which the reinforcement of one or another part of the roof.
- Filly are used when the length of the legs is small, as a result of which they create an overhang.
ATTENTION!
Only if you take into account the described parameters, you will get a reliable roof.
Shed roof is characterized by the presence of one slope, which is characterized by an angle of inclination from 14 to 26 degrees. In the case when the roof is made for a small house, the span will not exceed 5 cm, so it is recommended to make a layered system.
The supports of such a roof are made on the walls of an external nature., as well as a wall that exists inside the object. Truss systems are used in truss truss cases.
roofing cake, or rather, its device, depends on which final version of the coating will be chosen. But, regardless of the material, this element maximizes roof life, durability.
The shed type requires special attention, since it is this stage of construction that has the greatest impact on the climate that the structure will be.
Design truss system
Shed roof rafters
The mounting scheme is quite simple, as it is a parallel spread out boards that rest on two walls. To install the legs, special transition elements are used, which are made of wood.
Depending on what material is used, the following can be used as a transition piece:
- Mauerlat. In the above roof system with one slope, these are two wooden beams, which lie separately and complete the walls.
- Upper part of the foot, which is composed of bars.
- Top harness the entire 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 solution of the following tasks should be taken into account:
- Ability to easily move wood parts from one another
- Adapting to the consequences that may be after the subsidence of each wall in order to take a stable position
- Exclusion of all possible causes 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 not 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 interaction of the rafters, as well as the reference part using:
- Select cuts
- File the top as well as the bottom edges of the legs. With the help of such actions, you can easily create a support platform, increase stability.
Rafter fastening
Rafter pitch
The distance between the rafters of a shed roof is calculated depending on whether what material is chosen, as well as the cross 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 used, whose moisture factor is approximately 20-22 percent. Such boards should be characterized by evenness, the absence of blue.
Each blood material is characterized by its own characteristics, so the pitch of the rafters is also different:
- Using distance depends on sheet size. Usually, the spacing of the beams is at least 60 cm and up to 90 cm. For larger distances, additional boards with a large cross section of 150 mm are used. It is important to take into account the use of the crate, the cross section of which should be 30 * 100 mm, and the mounting is carried out taking into account the span of at least 50 cm.
- often used, but its weight is taken into account. Beams for such a system are pre-dried. When determining the step size, the length of the boards should be taken into account. At maximum length it is necessary to make the minimum distance between the rafters. The same rule is used for the minimum length of beams - long distance step. 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 beam should be used with a cross section of about 50 * 150 mm.
- Using it should be understood 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 cross section of the beam is 50 * 200, and 50 * 150 mm can also be used. 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 truss system
When deciding to independently install the rafters of a shed roof, you should first prepare all the elements, as well as process them with special means.
Boards should be laid on both sides of a certain roof and laid in grooves.
Only after that it is important to attach a few extreme rafters.
CAREFULLY!
Keep in mind that it is important to hammer in one or two nails for each joint. The legs are installed taking into account the previously stretched strings, after which they are similarly nailed. After that, the crate is installed, and the roof is laid.
After calculation, design, there are certain stages of installation:
- Installation of the bearing beam. A large beam is laid along the wall of the object. It should first be scoured, soaked with an antiseptic. It is important to lay the roofing material along the end of the wall, to mount the beam on it in level with the help of anchor bolts.
- Processing timber, building elements. It is planned to fly the board over 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, the step is recommended to be reduced to 1 meter. The board crashes into the Mauerlat for strength.In contact with
The gable roof is the most popular design in private housing construction. The truss system of a gable roof should provide a support platform for mounting the roof. Properly calculated pitch of the rafters of a gable roof allows you to ensure the strength and stability of the structure to all external loads, create a durable and reliable roofing. This article discusses design features truss system, calculation and installation procedure. This information will allow you to correctly understand the methodology for creating a gable roof so that you do not ask unnecessary questions to workers during construction.
The distance between the rafters for a gable roof
Among people employed in the construction of a private or country house, there are ongoing discussions about the most successful design roof and quantity supporting elements. In order to understand these opinions and take one side or another, it is necessary to consider general device roofs.
There are two types of rafter construction:
hanging.
Layered.
Applied to relatively small houses with a length of supporting elements of not more than 6 m. The structure consists of a number of truss trusses having the shape of an isosceles triangle. The trusses are installed on a strapping made of timber (Mauerlat), interconnected by batten strips. The bearing capacity of hanging rafters is relatively small, but the simplicity of design, economy and high speed of installation are their advantages. There are quite a few options for implementing hanging rafters, which is explained by the prevalence small buildings that do not require complex and massive construction roofs.
Design layered truss system somewhat more difficult. Along the perimeter of the ceiling of the upper floor, a strong timber is laid - Mauerlat. Along the longitudinal central axis, two (or more) vertical racks, the height of which determines the angle of inclination of the slopes. Installed between racks ridge run, which runs along the entire length of the roof and serves as a reference line for rafter legs. Each of them has two points of support - at the bottom it is a Mauerlat, and at the top - a ridge run.
To form additional support, which excludes 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- bed.
The step lag 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, forming 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 gable roof, details. It must be immediately taken into account that the number of rafters determines the bearing capacity. Reducing their number complicates the installation of insulation, contributes to the sagging of the laths of the crate 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 mineral wool have a width of 60 cm, which is quite suitable for most designs of gable roofs.
In addition, the pitch of the rafters directly depends on their number. This is a calculated value based on bearing capacity supporting elements. The loads acting on the roofing, as well as the weight of the roofing itself, have enough big values, therefore, their adoption requires a stable and solid construction. It must be borne in mind that the type of rafter system also matters, since layered rafters are much heavier than hanging rafters, they form a noticeable load on the walls and foundation of the house.
Wind and snow loads are external factors affecting roof structure. Snow weight in winter period capable of pushing through or even breaking the roof if its design is not properly designed. The SNiP applications contain special data on the average annual amount of snow in different regions. In some of them, for each square meter accounts for up to half a ton of snow.
In addition to snow, wind creates serious loads. At the same time, 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, you should find out the strength and direction of the prevailing winds in the region, find out about the possibility of hurricane gusts. Available in SNiP applications.
All these factors determine the parameters of the truss system and the distance between the individual supports.
The dependence of the pitch of the rafters on the material of the roof
There are many types of roofing. Most of them are noticeably outdated and little used in modern construction. The most popular today are:
profiled sheet.
metal tile.
It should be noted that profiled sheet and corrugated board are one group of profiled coating. Some sources consider them to be different names for the same material, others separate them by wave height. The profiled sheet has a higher wave height, and the corrugated board 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, fences, 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 canopies.
The step of the rafters of the gable roof under the corrugated board is selected taking into account this feature of the material. 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. An important parameter also becomes the area of the slope. The pitch of the rafters of a shed roof under corrugated board is much less than that of gable roof, since the length of the supporting elements and the magnitude of the load in it increase significantly and require an increased number of supports.
The metal tile looks like a canvas made of natural ceramic tiles. For all your performance it is very similar to corrugated board or profiled sheet, but physically it has 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 a metal tile, or be guided when choosing the size of a heat insulator.
When using slate or ondulin, the pitch of the rafters is taken according to the degree of rigidity of these materials. Alternatively, increase the density of the lathing, or install a solid version of thick plywood.
Method for calculating the distance between the rafters
There are two calculation options:
Engineering calculation using appropriate formulas and techniques.
Using online calculators, giving an answer after entering their own initial data.
The first method is only suitable for a professional roof system designer. For unprepared person it is extremely difficult to perform such calculations, since various specific data, coefficients, table values, which are difficult to find and must be used correctly. Calculations obtained using online calculators are also not recommended for use in real construction, but as an option to refine or verify the results of calculations 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 carried out by trained and specially trained specialists. The pitch of the rafters is an important and crucial value that determines the bearing capacity of the roof. The damage caused by the inability to take on existing loads is quite serious and can call into question the possibility of living in a house, so it is necessary to take this issue as seriously as possible.
The distance between the rafters (rafter legs) is called the pitch of the rafters. When arranging the roof, it is customary to use a rafter 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 the destruction of the walls. Given this, the calculation of the design of the truss system must be given the same close attention as the overall design of the building.
Method for calculating the distances 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 = 51 - 51 rafters are required to build a roof.
Then we determine the step between the bars, which will be used as load-bearing structure:
30: 51 \u003d 0.58 m - the distance between the axes of the bars that will be installed on the roof slope as rafters.
This example shows the general methodology for calculating the supporting structure, but does not take into account the specifics of a particular roofing material. Experts recommend calculating the distance based on the characteristics of roofing.
In addition, calculations should be performed taking into account the materials from which the truss system of the house will be made. Here the step largely depends on both the type of material and its dimensions.
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The specifics of laying rafters under ceramic tiles
Despite the fact that ceramic tiles are one of the elite and environmentally friendly roofing materials, its installation is associated with certain difficulties. And the main one is a large mass. Thus, the weight of a ceramic tile is almost 10 times higher than the mass of a metal tile. And this means that for each m 2 of the structure, pressure from 40 to 60 kg will be exerted. These conditions imply the creation of a reinforced carrier system that can withstand the weight of the roof.
To create a truss system for a roof made of ceramic tiles, a beam with a cross section of at least 5x15 cm, and preferably 6x18 cm, is usually used. The moisture content of the wood should not exceed 15%.
The distance between the bars depends on the slope of the slope 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 °, the step is 80 cm, then with a slope of 75 ° it will be 130 cm. Long bars will be located at the maximum distance from each other, and short ones at the minimum.
In order for the installation of ceramic tiles to be carried out correctly, the step of not only the rafter legs, but also the crate is important. When creating a house structure, it is required 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 forms an overlap with the previous row of about 9 cm. This determines the pitch of the crate, which should be at least 31 and not more than 35 cm.
Also, this indicator can be determined as follows:
- the length of the bottom row is subtracted from the length of the slope;
- then the distance between the first row of the crate and the last rafter is taken away.
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The specifics of the installation of the supporting structure under the metal tile and corrugated board
Installation of a metal tile does not require strengthening of the supporting structure due to its low weight. The wood will not resist the loads exerted, which means that the step between the bars may not be wide. Yes, at roofing rafters from metal tiles can be located at a distance of 60-95 cm from each other.
Decking 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 define characteristics building materials. For example, if a plank with a width of less than 10 cm is used to equip the structure on the roof, the distance should be reduced to 50 cm.
Do not forget about the distance between the elements of the crate, which can be from 0 to 400 cm. The pitch of the crate is selected taking into account the grade of the profiled sheet and the slope of the slope. For example, a profiled sheet of grade S-21 with a thickness of 0.5 to 0.7 mm with a roof slope of more than 15 ° 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 The rafter system is how far apart the rafters are.
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 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 obtain Exact size 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 exact amount rafters that will need to be installed on one slope;
- the total length of the slope must be divided by the number of rafter legs obtained in the previous calculation. And we get the exact distance between them.
To 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.
Further calculations will look like this:
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 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.
In order to determine the pitch of the rafters on a pitched roof, you can use the table:
As can be seen from the table, the rafter 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 common system calculation (see above).
If the slopes have the same length, then it is enough to perform calculations for one slope.
If the slopes are of different lengths, then the calculation is performed for each slope.
It should be remembered that the limit values \u200b\u200bof 70 and 120 cm.
What is the step depending on the material of the roof
Ondulin
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
Metal roofing during construction country houses used most often.
Because this material is much lighter than ceramic or cement tiles.
Although according to appearance very similar to her.
A small one makes it possible to use boards of a smaller section when creating a truss 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 having a thickness of 150 mm is placed between the rafters, then the most comfortable conditions for living.
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
System design under 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.
So more reliable.
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 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 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.
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 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 device any building structure It should be remembered that there are still unforeseen situations.
And, therefore, at and distances 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 the roof for any building. It is not for nothing that over a dozen different types of roofs have been invented in the history of mankind, from simple to quite complex in design and construction. An important element when planning the construction of a roof, there is a step between the rafters - strong bars that are the basis of the structure. This will be discussed in this article.
The distance between the base of the roof slopes is not a constant value and depends on the following components:
- type of roof;
- slope angle;
- the type of roofing material to be installed;
- rafter section dimensions.
Before proceeding with the process of erecting the upper structure of the house, a calculation should be performed by determining the optimal distance between the rafters.
Gable roof rafter pitch
The most widespread in our country are gable roofs. They are a structure that has two parallel planes, with an angle of inclination relative to the horizon from 20 to 50 degrees.
With an insufficient slope of the gable roof in snowy areas, there is a danger of accumulation of large snow masses, which can lead to the destruction of the structure. Increasing the angle of the slopes in regions with a predominance of strong winds It is also fraught with a high load and the risk of breaking not only the roof, but the entire structure as a whole.
Mansard roof truss system
Most private houses have an exploited under-roof space called an attic. This design is characterized by an increased height of the slope, which is caused by the need to create a living space of a comfortable height. Typically, stingrays mansard roof broken lines with a varying angle of inclination. For their installation, a double truss system is used.
The steepness of the lower slopes of the mansard 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. The upper ridge slopes are recommended to be mounted with a reduced gap from each other.
Rafters in a shed roof
For outbuildings and some private houses, roofs with one slope are used. Due to the limitation of the angle of inclination, they are high pressure. Experts recommend using lumber of 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 roof beams are installed, Special attention should be given to the magnitude of the snow load in a particular area. With a small slope, this characteristic is of great importance. Roofing material for such roofs is best chosen with a minimum dead weight, which will reduce the bending load.
Hip roof truss system
The hip roof truss system is considered the most difficult in construction. This type 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 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, vice versa. An additional aspect of the calculation is the roofing material used.
The dependence of the pitch of the rafters on the roofing material
In addition to variable snow and wind loads, a constant (static) one also acts on the roof, the force of which depends on the roofing material used. It's no secret that different kinds roofs have their own weight, which can differ by 10 or more times.
The right choice of material affects not only the top, but also all other parts of the structure of a residential building and other buildings. Not without reason, when designing the foundation, it is necessary to decide in advance on the choice of the roof.
Roofing from profiled sheet
Currently, one of the most common roofing materials is a profiled sheet, which is produced galvanized or with subsequent polymer coated. TO distinctive features profiled sheet will include the following parameters:
- High corrosion resistance;
- As a result, a long (more than 15 years) service life;
- Easy installation even without the necessary qualification;
- Small sheet weight (weight 1 m 2 is 4-5 kg).
Since this roofing material does not exert a high load on the truss 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 minimizing the total load on the foundation and walls.
Roofing from a metal tile
The second common type of steel roofing materials is metal tiles. This type of profiled sheet, which successfully imitates natural clay material, but with a lower mass (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, you should be guided by the dynamic load. Like a profiled sheet, a metal tile is not demanding on the size of the rafter legs and is well mounted on a crate made of an inch coniferous board. All this makes metal roof low-cost.
Rafter system for ondulin
In the 21st century, to replace wavy sheet materials a more durable and lightweight analogue came - ondulin. Among others - the most lightweight material. The weight of the sheet does not exceed 6 kg.
The small thickness of ondulin sheets at slope angles of less than 15 ° requires the construction of a continuous crate of plywood sheets, for example, which will require an appropriate rafter pitch. This should be taken into account in the calculations.
slate roof
Not so long ago, wide use had a corrugated material of asbestos-cement mixture called slate. High mass and fragility are the main disadvantages, however, even today he finds his fans in the construction of various outbuildings.
A high mass, comparable to the weight of a clay tile, will not allow the use of the same truss system as under a metal tile. Building codes define a minimum angle of slope for a slate roof of 22 degrees or more. Otherwise, the load from the material itself and the truss system with the crate exceeds the permissible parameters. The step of the inclined bars, as well as their cross section, are selected individually in each case.
Polycarbonate roof
IN last years Increasingly, on the roofs of verandas and gazebos, artificial polymer material- polycarbonate. Produced in two versions - monolithic and honeycomb. The first in its properties is similar to ordinary quartz glass, but significantly exceeds it in strength. The second one has less mechanical properties, but high thermal insulation and light transmission.
Cellular polycarbonate is standardly much lighter than a monolithic counterpart. It is used as a roof without the use of lathing, provided that the step does not exceed ½ of the width of the sheet of material. The high strength of the monolithic analogue also makes it possible to avoid elements transverse to the rafters. Sufficient flexibility allows you to cover semicircular roofs on metal frame, the step of which does not exceed 0.9 meters.
Thematic material:
Rafters under a soft roof
The original pattern can be obtained through the use of soft roofing materials, which are spread with an adhesive layer. Which are installed on solid crate plywood or OSB. The step of the rafters should allow you to fix the sheets, so it is chosen as a multiple of ½ of the width. On condition standard sizes plywood 1520x1520 mm, the center distance between the rafters will be: 1520: 3 = 506 mm.
Rafter step for insulation
The installation of residential under-roof spaces is often combined with the laying of insulation sheets in the rafter gap. The most common plates with dimensions of 600x1000mm. These parameters are used as starting points.
Rafter pitch calculation scheme
According to building codes, the pitch of the roof rafters is in the range of 0.6 - 1 meter. Its final calculation is carried out according to a simple formula, depending on overall length roofs. For the calculation, you must perform the following list of actions:
- determine how much distance should be between the rafters for your specific building conditions. According to the reference book, the magnitude of wind and snow loads in the area is determined.
- 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. If the value is not an integer, it is rounded off.
- 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 a metal tile is 0.6 measure. The length is assumed to be 16 meters. Consequently:
- 16:0,6+1=27,66;
- rounding the result, we get 28 rafters per slope;
- 16:28 \u003d 0.57 meters - the center gap of the rafter legs for these specific conditions.
As you can see, the calculation technology is not complicated, but this is only exemplary scheme. Taking into account many other parameters mentioned above can make certain adjustments.
