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 rafter 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 beam with a cross 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 step. 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 on the roof if the rafter pitch 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 transverse boards of large cross section.
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.
Before installing the truss system, the question arises with what step to put the floor beams. Correctly calculating the distance between the rafters means preventing later deformation or even destruction of the roof frame. After reading the article to the end, readers will find out what should be the distance between the rafters for various types of roofs and how to correctly calculate.
Even at the stage of designing a house made of wood, you need to make all load calculations. This also applies to the truss system. This is especially important in wooden housing construction, since the upper link is often used instead of the Mauerlat. Correcting errors in such a design is subsequently difficult. For the correct calculation of the distance between the beams, there is a technique.
The span of the roof frame for the construction of a house from a bar standardly exceeds 1 m, and the smallest allowable value is 60 cm, such indicators are indicated in GOSTs (see figure). Correctly calculate the length of the rafters, their step can be the following option:
Using a tape measure, the length of the roof slope is measured, the result is divided by the step size of the roof frame. For example, if the distance between the rafters is 1 m, then you need to divide by 1, if 70 cm, then by 0.7. The resulting figure is summed from 1 and rounded up to the nearest higher number. So you can determine the number of beams for one roof slope.
By the result you need to divide the length of the future slope. The result is the distance between each rafter.
For example, consider a roof whose slope is 25.5 m and a step of 0.6 m. You need to calculate the following indicators: 25.5: 0.6 \u003d 42.5, to 42.5 + 1 \u003d 43.5. We round this figure to the nearest larger integer, we get 44. This is the number of rafters per 1 slope of the future roof.
Now we calculate the span between the rafters: 25.5:44 \u003d 0.58 m. It turns out that you need to put the legs of the frame after 58 cm. So you can easily calculate the step of any roof frame, shed or complex, without taking into account the roof. But professionals recommend their calculations for a certain type of roof.
Rafter leg step depending on the material
Since each forging material has its own characteristics and features. Among the most common are:
- Decking. It has a different thickness and shape of a tropezoidal bend. It costs from 120 rubles.
- Ceramic tiles. Expensive material from 670 rubles. Has 12 color options.
- Metal tile. This is a cheaper material, unlike ceramic, and costs from 320 rubles.
- Ondulin. Soft roofing insulates the house from rain, hail, etc. It costs from 340 rubles.
- Slate. The most economical option from 90 rubles.
The step size for the most common types of coverage will be discussed below.
The step of the rafter beams under the corrugated board
Envy the distance between the roof beams on the size of the sheet that the corrugated board has. The step of the roof frame beams under the corrugated board is taken as a standard not less than 60 cm and not more than 90 cm.
If this distance is greater, then boards with a large section are attached between the rafters. The cross section of the rafter legs for corrugated board is selected 50x100 or 150 mm.
The most important thing to consider when planning to fix corrugated board is the crate. They make it from a board with a section of 30x100mm, you need to mount it with a span of 50 cm or more. It depends on the brand and thickness that the corrugated board and the slope of the roof have.
So a roof of 15º grade C 10 corrugated board is mounted on a solid crate, C 21 corrugated board is mounted on a crate with a span of 30 cm. The largest C 44 corrugated board is mounted on a crate in increments of 50 cm, up to 1 m. passage of a chimney, ventilation hood, etc.
Step of rafter beams under ceramic tiles
The specificity of the installation of a truss system for laying ceramic tiles is related to the weight of this roof. Ceramic tiles are made from clay, and this roof has a weight greater than that of a metal tile by 9-10 times. The calculation of the load on the roof system for ceramic tiles is 40-60 kg / m 2.
Beams are made for the roof truss system under ceramic tiles only from dried material. The cross section is suitable for 50x150 or 60x180 mm. The standard distance between the rafter legs when roofing tiles is 80-120 cm. The span depends on what kind of slope the roof has. At an angle of 15º, the span between the rafters is 80 cm, at 750 after 1 m 30 cm.
When calculating the step, you need to take into account the length of the beam. Taking the maximum length, the distance between the rafters is minimal. And, on the contrary, with a minimum length of rafters, the step is maximum.
When laying ceramic tiles, it is important to consider that you will need to move along the roof. The maximum safe step of the rafter legs for such a movement is 80 cm.
When laying ceramic tiles, it is important to calculate the span of the crate. This distance is directly related to the size of the roofing material. A standard tile sheet is 40 cm long. Laying occurs with an overlap of 50 to 90 mm. When calculating the step of the crate, the size of the overlap is subtracted from the length of the tiles. The result is a step of 305-345 mm.
For a shed roof for the construction of a house from a profiled beam, it is not difficult to make a calculation. If the roof is of a complex multi-pitched shape, then each distance between the rafters is calculated separately for the step of the crate. By fixing the cord on the opposite side of the roof slope, you can easily mark the rows.
Features of the roof frame under the metal tile
Metal tiles are used more often than ceramic or corrugated board. Externally, the roof resembles ceramic tiles, but unlike it, it is easier to install and lighter.
The metal tile weighs from 35 kg / m 2 of the roof. This makes it possible to lighten the design of the rafters and use beams of a smaller section. In this case, the step between the rafter legs of the roof frame increases and is equal to 60 to 90 cm. A beam is used with a section of 50x150 mm.
To create a ventilated space in the beams under the roof, holes are drilled with a diameter of 12-13 mm.
The design of the roof frame for metal tiles is not much different from corrugated board or ceramic tiles. But there is a small peculiarity: the support from above is attached to the ridge run from above, and not from the side, as in other cases. So a ventilated gap will appear under the metal tiles, which will eliminate the accumulation of condensate.
Features of rafter legs for ondulin
Ondulin is a soft roof used for the construction of a house made of glued laminated timber or other material. Ondulin is produced in the form of sheets, it looks like painted slate, but light. This material is great for wooden houses, both low-rise and large.
Rafter beams under ondulin are placed with a distance of at least 60 cm, maximum 90 cm. For the rafter system, a beam of coniferous wood with a section of 50x150 or 50x200 mm is used. A smaller section will not provide sufficient strength to the rafters.
The crate on the rafters is made of a material with a section of 40x50 mm in increments of 60 cm. This is quite enough for fastening sheets of ondulin with an overlap of 30 cm. Ondulin is fastened with special nails that are sold in the kit.
Features of the truss system for slate
Slate is rarely used to cover the roofs of modern houses. But in summer cottage construction and households. buildings, this material is indispensable. It is low cost and easy to install.
Rafter under slate
Rafter legs for slate are used with a section of 50x100 or 50x150 mm. The fastening step between the rafters is not less than 60 cm and not more than 80 cm.
The crate for slate is made of bars 50x50 mm or a wide board 30x100 mm. The crate is laid from the steps, depending on the slope of the roof. For a steep shed roof, it is 45 cm. The consumption is 4 bars per 1 sheet of slate. For a flat shed or gable roof 63-65 cm, so the consumption is reduced to 4 bars per sheet.
The step of the rafter system under the slate roof structure differs. For the host buildings are often mounted shed.
A feature of the size between the rafters of a shed and gable roof
Whether a safety margin is needed during installation depends on what shape the roof is. And the distance between the beams of the rafters directly depends on this.
single truss system
Shed roofing is more durable and easier to assemble. The thickness of the rafters is selected depending on the type of wood, its strength and the specifics that this or that design has. The step between them can be 60-140 cm. The distance also takes into account whether the structure will be insulated. If yes, then the step should correspond to the width of the insulation.
The thickness of the rafters must be calculated depending on the slope of the roof. For a slight slope of 15-20º, you can use a material with a section of 50x100 mm. For a steep slope of 45º, stronger ones with a section of 50x150 mm are needed.
Gable truss system
If the calculation of the leg pitch of the frame of a shed or other type of roof is not correct, then the roof can be taken away, and the beams will sag and bend due to the severity of the structure. In this case, simple repairs are not enough, you will have to redo the entire structure. Therefore, it is so important to correctly calculate the distance between the legs of the rafters, depending on the roofing material used: corrugated board, ceramic or metal tiles, ondulin or slate, etc.
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 distribution of the load 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 the 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 organizing 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.
truss system, undoubtedly, is the most important structural element of any pitched roof. The consequence of its improper installation can be not only the deformation of the roof, requiring expensive repairs, but also the complete collapse of the roof on the head of an insolvent builder.
The following four main factors influence the stability of the truss system to various loads:
- fastening strength rafters to the ridge and Mauerlat;
- correct calculation of the supporting structure for rafters, depending on the length of the span;
- choice roofing material;
- step between the rafters.
The topic of this article is the choice of material and pitch between the rafters, taking into account the intended type of roof.
What are the calculations based on?
When making calculations, four main indicators are taken into account:
The most important is the calculation of the maximum roof load, consisting of:
- rafter weights,
- crate weight,
- weight of roofing material and insulation,
- snow load (reference information unique to each region),
- wind load (also reference information),
- person's weight (if repair or cleaning is necessary, 175 kg/sq.m).
To carry out accurate calculations, experts use special formulas from strength of materials, but when building a private one, you can use approximate recommendations.
Method for calculating the distance between the rafters
Accurate Distance Calculation between rafters is based on the results of a preliminary calculation of the maximum allowable step. To make this calculation, the total load, the roof structure and the material used on the rafter legs are taken into account.
Method for calculating the step of the roof frame:
- Measure the length of the roof from end to end.
- Received distance divided by the maximum step size.
- The resulting value is rounded up to a larger integer.. This is the number of inter-rafter spans.
- Divide the total length of the roof by the number of spans. This is the required rafter step size.
- Add one to the number of spans.This is the required number of rafters.
For some types of roofing material it is desirable to use fixed distances between the rafters, in which case an additional rafter with a non-standard pitch is installed on one of the ends of the roof.
Rafter leg step depending on the material
Can be increased as the strength of the material from which they are made increases. Most often, for each roofing material, the step of the rafters required for it and the permissible sections of the rafter legs, taking into account the load, are indicated.
These recommendations are regional character and are applicable to the central strip of Russia and more southern regions. Before developing a drawing, you should definitely check the level of wind pressure and snow cover in your region, and adjust the pitch and / or cross section of the rafters.
In those regions where the snow load significantly exceeds the wind load, the use of roofs with a slope is recommended. 35 – 45 degrees.
truss system in private houses, it is most often made of logs with a diameter 12 - 22 cm, beam/board thickness 40 – 100 mm and width 150 - 220 mm. When calculating, it is possible to allow the use instead of logs of a certain diameter of bars of the same width, thickness 100 mm.
Rafter structure for corrugated board
Roof structure for ceramic tiles
Ceramic tiles has significant differences from other types of roofing materials, which must be taken into account when designing a truss systems for it:
- 5 to 10 times the weight resulting in doubling the weight of the entire roof. This leads to the need to use the frequent step ( 0.6-0.8 meters) and increased by 25% cross-sectional area of the rafters.
- Fine-grained nature of the material. Increases the requirements for the accuracy of the installation of the transverse battens. The step of the sheathing beam, the permissible sections and installation angles are always indicated in the instructions for each specific tile model.
There are models of tiles designed for installation at an angle. 12 - 60 degrees, ordinary models are recommended to be mounted at an angle 20 - 45 degrees. For crates most often use timber 50x50 mm.
Roof structure for metal roofing
metal tile in fact, it is a less rigid and lighter decorative version of corrugated board, therefore the requirements for the rafter system, in particular for the recommended sections of the rafter legs, are largely the same.
A feature of the truss structure under the metal tile can be called a significant reduction in the pitch of the crate, which should be equal to the length of the longitudinal wave (30 cm for most species). This leads to the need to reduce the distance between the rafters. up to 0.6 - 1 m, to reduce the cost of lumber for the crate. The angle of the roof slope is selected from 22 to 45 degrees.
Rafter structure for ondulin
Ondulin- slate based on fiberglass and bitumen, produced by only one manufacturer and has unified technological installation standards:
- permissible mounting angle - 5 - 45 degrees;
- distance between rafters - 60 cm at a slope angle of up to 15 degrees, up to 90 cm - at an angle of more than 15 degrees;
- crate - solid plywood on a slope up to 10 degrees, board 30x100 mm step by step 45 cm on the slope 10 - 15 degrees, bar 40x50 mm step by step 60 cm on the slope above 15 degrees.
Given the low weight of the material, the cross section of the rafter legs is selected based on the same recommendations as for corrugated board.
Rafter construction under a covering from slate
Slate- traditional, rather rigid and heavy roofing material, fragile, but resistant to constant loads. Such properties change the recommendations for the optimal design of the truss system towards the use of more durable elements and increasing the step between them:
- Due to low tightness, it is undesirable to use slate roofs with a slope angle of less than 22 degrees. If it is necessary to install such a roof, you can use the recommendations for installing an ondulin as an instruction, adjusted for the universal batten pitch - 55 cm.
- Permissible angle for installing rafters under slate - up to 60 degrees.
- The installation step is selected from 0.8 to 1.5 m, depending on the section of the rafter leg, the load and the presence of the crate material.
- The material for the rafters is selected with a slightly larger section than for light roofs. For the most popular move 1.2 m a bar is taken with a section from 75x150 to 100x200 mm, depending on the length of the span between the supports.
- Material for the crate selected in accordance with the distance between the rafters - timber 50x50 mm up to 1.2 m, timber 60x60 mm - 1.2 m and more.
- Lathing step is selected in such a way that each sheet lies on three bars, and has an overlap on 15 cm with neighboring. Considering the standard sheet length 1.75 m, step is used 80 cm.
Rafters for single-pitched and double-pitched roofs
What is the distance of the rafters for a pitched roof? shed roof does not require a complex truss structure. The rafters are laid from wall to wall, most often without the use of a Mauerlat, directly on the crown.
No extra ribs stiffness sets the maximum slope angle - 30 degrees and allowable span length - less than 6 m(for wooden rafters). The optimal angle 15 - 20 degrees.
Such roofs usually not subject to wind loads, but require protection from precipitation. In regions where wind pressure is comparable to snow load, the correct installation of a shed roof "in the wind" can lead to self-cleaning of the roof.
gable roof is a system of parallel triangles interconnected by a Mauerlat and a ridge. There are many elements for firmly fastening the sides of the triangle to each other and transferring loads from the rafter legs to the walls - racks, ties, jibs, support beams, and so on.
The step between the rafters of a gable roof is made taking into account the size of the heat insulator that is laid between them. Approximate step between rafter legs 1-1.2 meters
Rigid Triangle Strength increases as its shape approaches isosceles, therefore, with an increase in the slope angle up to 60 degrees you can expand the step between the rafters.
However, this will also lead to an increase in material consumption and to a multiple increase in the windage of the roof. The optimal slope angle for snowy regions is 45 degrees, for windy - 20 degrees.
Distance between rafters roofs attic type determines how much of the load falls on each element. When designing hip roofing step rafters should be between 60 cm and 1 m.
- The correct fastening of the rafters is no less important than the correct calculation of the structure. Before installing the roof yourself, you should take a lesson from an experienced carpenter and read educational literature.
- When choosing a rafter pitch, do not forget about thermal insulation. All types of insulation can shrink a little, so you can buy them by approximate size. The most commonly produced sizes are 60, 80, 100, 120 cm.
- For roofs with a slope of 45 degrees or more, the weight of a person on the roof can be ignored. This removes 175 kilograms of design load per square meter and allows you to put rafters on average 20% less often.
- Snow and wind load in Russian regions can be found by regulatory documents - maps in the application F to .
- There are many online roof calculators on the web., capable of, if not correctly calculating all the nuances, then at least advise on the selection of the correct section for the rafters.
The roof is one of the main elements of the house, so you should pay special attention to the correct calculation of the roof frame. Which will serve as a skeleton in your home. Incorrect calculation of all loads can lead to disastrous results in the form of deformation of the roof with its subsequent collapse.
Before proceeding with the installation of the roofing, it is necessary to calculate the truss system, which will depend on the material used, construction, and climatic conditions.
What you should pay attention to before making a calculation
Before starting the construction of the roof, it is necessary to choose the type of truss system. Then calculate all the loads that will fall on the roof. The main loads include the weight of the frame, roofing material, insulation, ceiling, and temporary loads are taken into account, among which are the weight of the snow cover, possible gusts of wind, the weight of a person during the installation and operation of the roof.
The distance between the rafters is calculated based on the selected type of rafters and the material with which the roof will be covered.
Types of rafters
In the construction of roofs of various designs, hanging or layered rafters are used. Sloped - used when installing one- or two-slope roofs. They have two points of support - load-bearing walls or a load-bearing wall and a ridge beam. Hanging rafters are used when it is necessary to cover large spans or create a sloping roof. In this case, the rafters rest with one end on the wall, and the other on the opposite rafter. The quality of the material from which the frame is made will directly affect the reliability of the entire roof.
Material for rafters
Currently, wood and metal are used. A wooden beam or log is used in the construction of residential buildings, garages and other buildings. Reinforced concrete or metal rafters are used in the construction of industrial facilities, shopping centers, where wide spans are needed.
Method of calculation
The distance between the rafter legs is called the pitch of the rafters. It should not exceed one meter, and the minimum value - 60 cm. Before making a calculation, it is necessary to measure the size of the roof slope. Then we divide the obtained value by the approximate value of the step between the rafters. One is added to the result and rounded up to the next whole number. So we find out the number of rafters that we need. In order to find out the exact distance between the rafters, for this we need to divide the length of the roof bevel by the number of rafter legs.
For greater clarity, consider an example calculation:
roof bevel length - 28.5 m
the step between the rafters is chosen equal to 80 cm
add one to the resulting number: 35.625 + 1 \u003d 36.625
as a result, we get that we need 37 rafter legs
the exact step of the rafters will be: 28.5 / 37 = 0.77 m
This is a general calculation method that requires adjustment depending on the roofing material.
The dependence of the pitch of the rafters on the material of the roof
The most common roofing materials are slate, metal tiles, corrugated board, ondulin, soft roofing.
Roof truss structure for slate roofs
Slate is widely used as a roofing material, due to its low cost, resistance to temperature extremes. Due to the severity of the material, it is necessary to install a powerful truss system. The distance between the rafters in this case will depend on the cross section of the timber. The optimal value is a distance of 80 cm, which will allow not only to withstand increased weight, but also significant snow and wind loads. In this case, the crate is made with a board at least 3 cm wide. Depending on the type of slate, the crate is made continuous for smooth sheets or sparse for wave ones.
Important: the slate must have at least three support points along the edges and in the center.
Step between rafters for metal tiles
Metal tiles are becoming more and more common among roofing materials. Which is characterized by a simple installation process, and will also help to create your own unique look for your home. Sheets of metal tiles are lightweight, which allow you to increase the distance between the rafters from 600 to 950 mm, with a beam section of 150x50 mm. The crate in this case will depend on the pitch of the sheet wave. So for a wave of 350 mm, a distance between the boards of 30-40 cm is possible.
Important: on the overhangs of the cornices, the edges of the bevels, the step of the lathing is made minimal for greater reliability of the roof.
Rafter pitch under corrugated board
Decking is a galvanized steel sheet coated with a special coating that protects it from the harmful effects of the environment. A large selection of colors and corrugation widths will allow you to create a reliable and aesthetically attractive roof. The step of the rafters under the corrugated board will directly depend on the characteristics of the type of profile used, the angle of the roof, its configuration. You should also take into account the fact that the crate under the profiled sheet is attached perpendicularly. The rafter system is made of beams with a section of 50-75 mm or from a board 20-50 mm thick and no more than 15 cm wide. sparse - the distance between the boards is 50-75 cm. The step of the rafters under the corrugated board is calculated according to the general scheme and is 60-90 cm.
Step of roof rafters from ondulin
Ondulin is a wavy sheet that has high strength and durability. With such a roof, the truss system is made of pine boards with a section of 50x200 mm, in increments of 60-90 cm. A sparse crate of 40x50 cm is made from above.
Important: if the roof has an angle of inclination greater than 50 degrees, then the crate must be solid.
Determining the pitch of the rafters for a shed roof
A shed roof is simple and does not require any special installation skills from you. Most often it is installed on garages, baths, extensions. The roof frame consists of beams that rest on the walls of the building. The distance between the rafters of a shed roof will depend on the length of the rafters. Here you should correctly approach the choice of the section of the beam, since the greater the distance, the greater the load on the rafters. For the correct selection of the pitch of a shed roof, use the data from the table:
The distance between the rafters for a gable roof
The gable roof is the most common, not only because of the simplicity of the device, but also because of its high reliability. The pitch of the rafters of a gable roof is calculated according to the general scheme. If the bevels are the same on both sides, then one part can be calculated. To do this, we determine the angle of inclination of the bevel, here you should take into account the material with which you will cover the roof. So at an angle of 45 degrees or more, you can use all types of coatings. For slate, tiles, the minimum angle of inclination is 22 degrees, for corrugated board and soft tiles - 12 degrees, for metal tiles - 14 degrees, for ondulin - 6 degrees. The length of the rafters for a gable roof is calculated using the Pythagorean theorem, in which the length is the hypotenuse, and the height of the roof and half of its width are the legs. If the spans are more than 6 meters, then the rafter system is additionally reinforced with struts and headstocks, which will not allow the rafter legs to deform under the weight of the roofing material.
