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During the construction of a new house, the question often arises about the amount of lumber for the roof. And this question is really important. After all, various materials for the roof are not at all cheap and if you buy too much, then the money will simply fly into the chimney. At the same time, if there is not enough material, then this will cause construction downtime and, possibly, additional costs for the delivery of a new batch. That is why the calculation of materials for the roof is a burning issue on which the final stage of building a house depends.

As you know, when designing a house, a preliminary calculation of the forest for the roof is made. At this stage of work, the strength of the structure and its resistance to climatic conditions are determined. If calculations of the strength of the structure have not been carried out, then the roof may eventually turn out to be unstable to the action of wind and snow, which can lead to inevitable consequences.

Well, let's take a closer look at the calculation of the material for the roof of the house. In preliminary calculations, the thickness and type of insulation, the material for creating the lathing must be taken into account.

Types of roofs, materials

Roofs can be performed both in a classic form and in a completely fantastic one, but basically these are:

• classic single or multi-slope;
• broken;
• hip, half-hip, hip;
• oblique;
• domed;
• folded;
• cruciform;
• flat;
• spherical;
• steeple.

The rafters are affected by various loads - the own weight and the weight of the roofing material, wind loads and the effect of precipitation. For the arrangement of rafters, lathing and Mauerlat, high-quality and well-dried coniferous lumber is used. It is such wood that is most resistant to moisture and decay.

The roof is laid on the rafters, the calculation of materials and the method of fastening of which depends on the selected type. These can be nails, dowels or special glue. As a roof, you can use different materials - aluminum, copper, ondulin, ceramic or metal tiles, bitumen, polymers, etc. As insulation, foam and glass wool are most often used.

How to calculate materials for the roof

After the rafters are installed on the waterproofing, you can start laying the counter battens. It is designed to drain condensate and circulate air. can be either continuous or with a certain step. It all depends on the selected roof material and the angle of its slope. The step should be counted carefully so as to avoid deformation or collapse of the roof.

Calculation of lumber on the roof

The calculation of the material for the roof of the house is influenced by the step or distance between the beams. In order to define it, it is necessary in advance (primary and secondary). In this case, the main point is to ensure a certain margin of safety to maintain the integrity of the roof in extreme conditions (heavy snowfall, hurricane).

The main load is the weight of the roof elements and the weight of the roofing cake. The secondary load is wind force, rain, snow, etc.

The calculation of the roof is carried out according to the following scheme:

It is better to calculate the roofing material for the roof and the main loads using a calculator or Excel program. This will help you avoid mistakes. Also on the Internet you can find various calculator programs that help to calculate the various characteristics of the roof.

Below we give some examples of calculations of various roof parameters for several types of materials. Suppose that we have already calculated the parameters of the Mauerlat, as well as us, the slope and height of the roof. Using the standard table, it can be determined that the total load on the roof structure will be 2400 kg / m, while the permissible load per 1 linear meter of wood is 100 kg. Thus, it can be done by calculating the required footage of the rafters. To do this, we simply divide the first indicator by the second: 2400/100 = 24 m.

If the length of one rafter is 3 meters, then their total number will be: 24/3 = 8 pcs. Naturally, the number of pairs will then be 8/2 = 4. The maximum step is calculated based on the length of the roof (in our case, it is 4.5 m) and the number of pairs: 4.5 / (4-1) = 1.5 m. In this formula we have subtracted the very first from the number of pairs, that is, in total, there are three gaps between the rafters.

In order to provide the roof with greater stability and strength, the rafters are installed in a smaller pitch. To do this, you can add a few more pairs to the estimated number of rafters so that the distance between them does not exceed 100 cm.

Calculation of materials for construction, detailed video:

Based on this, to fill one row, you must use 6 sheets of metal. Next, the number of rows of material from the ridge to the cornice is calculated.

• the distance from the eaves to the ridge is measured;
• the overhangs of the cornice are calculated;
• the value of the vertical overlap is determined (no more than 15 cm).

For example, the width of the slope is 4 m, and the overhangs are 30 cm.Thus, the total distance from the bottom edge of the roof to the top is 4.3 m.The standard length of a sheet of metal tile is 1 m.This means that the effective indicator of this parameter will be 85 cm ( subtract the amount of overlap). We divide the indicator of the total length of the roof by the effective length of one sheet and we get that for laying it is necessary to use 4.3 / 0.85 = 5.05 sheets. Since rounding to the bottom side we will have a shortage of material, then in reality we will have to use 6 rows.

We multiply the indicator of the number of sheets vertically and horizontally and we get the total amount of material per slope: 6 * 6 = 36 sheets.

All parameters must be specified in millimeters.

B- Roof length.

Y- Height.

C- Overhang distance.

X- Roof width.

Y2- Additional height.

X2- Additional width.

This program will help you to perform an accurate calculation of building materials for the construction of a roof: the number of rafters and battens, roofing material (roofing felt, glassine), the amount of sheet material (metal, slate, nulin or ondulin).
Our online calculator will calculate other useful roof dimensions.

The presented program performs the calculation in two versions: type 1 - simple gable roofs, type 2 - gable roofs with 2 side gables.

If the projected roof has only one side gable, then in this case we perform the calculation by type - 1, and then by type - 2. Based on the results of the calculations, you can determine the required amount of materials: roofing, sheet, rafters and lathing board.

Otherwise, you will make a mistake in the calculation, since the program takes into account the cutouts for the side edges when calculating the parameters of the main roof.

Based on the results of the calculation, you get the volume and size of the material for one roof slope, and the entire volume and size will be indicated in brackets.

When calculating the volume and useful dimensions of an additional roof, you get two parameters in brackets: the volume and the size of one or two additional roofs.

Important! It is worth considering that the program performs a calculation over the entire roof area, when determining the number of sheets of roofing material.

For example, 7.7 sheets are used per row, and only 2.8 rows. Based on the calculation results, you will receive 3 real building rows.

In the event that you want to get the exact number of sheets for the future roof, you need to reduce their height until you get an integer number of rows.

Do not forget to set the exact length of the overlap.

Important! In type 2 mode, in the process of calculating the volume of material for the rafters of the main roof, the program does not take into account the cutouts for the side gables. This calculation of the gable roof rafter system is associated with the device of the program itself.

Also, the remaining building material for the rafters, you can use for the construction or repair of the house, otherwise you can make corrections to the calculations.

The exact calculation of the approximate cost of the roof depends on the correct basic measurements.

Important! Do not forget to purchase building materials with a margin of 5-10% for waste.

Do-it-yourself gable roof

First of all, we need a diagram (drawing or design) of a gable roof, according to which we will perform all calculations (indicated above).

The procedure for erecting a roof is quite simple, but a sequence of certain stages must be followed.

Before you install beams or transfers for the future overlap, you need to determine whether the attic or just an attic room will be equipped. As a rule, for a simple attic, it is enough to choose a board of 150x150 mm. In the event that you plan to build an attic, then it is most correct to choose a bar with the same size. To increase the strength of the frame, beams or boards should be mounted exclusively on the walls.

The process of fixing the beams is carried out taking into account the release from the outer edge by about 400 mm in order to prevent precipitation or wind from entering under the roof.

We will use a board edged for 50X150 mm when arranging the attic frame, and fixation is carried out with roofing nails. To give the gable roof stability, it is necessary to carry out all measurements correctly, trying to exclude an error.

Now we turn to the assembly of the rafter structure, starting the installation from the gables, already using the above method. At the same time, we saw off the lower parts of the boards, which will give our rafter structure additional stability.

When the structure is fully erected for the gable roof, we begin to perform the overlap with roofing materials.

Advantages of a gable roof:

• This design is quite simple to build, which allows you to do all the work yourself without the costly help of specialists;
• The building materials used are available;
• The large slope of the roof perfectly removes water during precipitation;
• The absence of complex structures and kinks greatly facilitates the construction and cladding of the roof.

A gable roof or gable roof is a roof with two slopes, i.e. having 2 inclined surfaces (slopes) of a rectangular shape.

The gable roof frame, due to its design features, ideally combines simplicity of construction and maintenance with reliability and durability. These and many other parameters make the construction of a gable roof a practical and rational solution for private and commercial housing construction.

As part of this article, we will consider how to make a gable roof rafter system with your own hands. For effective perception of the material, it is presented in the form of step-by-step instructions from A to Z, from selection and calculations, to the installation of the Mauerlat and the lathing under the roof. Each stage is accompanied by tables, diagrams, drawings, pictures and photos.

The popularity of the roof of the house is due to a number of advantages:

• design variability;
• simplicity in calculations;
• natural water flow;
• the integrity of the structure reduces the likelihood of leaks;
• profitability;
• preservation of the usable area of ​​the attic or the possibility of arranging the attic;
• high maintainability;
• strength and durability.

Types of gable roof

Installation of the gable roof truss system depends primarily on its design.

There are several options for gable roofs (types, types):

The most common version of the roof device due to its simplicity and reliability. Thanks to symmetry, an even distribution of loads on the load-bearing walls and the Mauerlat is achieved. The type and thickness of the insulation do not affect the choice of material.

The cross-section of the timber makes it possible to provide a reserve of bearing capacity. There is no chance of bending the rafters. Supports and spacers can be placed almost anywhere.

An obvious drawback is the impossibility of arranging a full-fledged attic floor. Sharp corners create blind spots that are unusable.

The arrangement of one angle more than 45 ° leads to a decrease in the amount of unused area. It becomes possible to make living rooms under the roof. At the same time, the requirements for the calculation are increasing, since the load on the walls and foundation will be unevenly distributed.

This roof structure allows you to equip a full second floor under the roof.

Naturally, a simple gable roof rafter differs from a broken one, not only visually. The main difficulty lies in the complexity of the calculations.

The structure of the rafter system of a gable roof

Do-it-yourself roof construction of any complexity presupposes knowledge of the purpose of the main structural elements.

The locations of the elements are shown in the photo.

• Mauerlat... Designed to distribute the load from the rafter system to the load-bearing walls of the building. For the arrangement of the Mauerlat, a bar of solid wood is selected. Preferably larch, pine, oak. The cross-section of the timber depends on its type - solid or glued, as well as on the supposed century of the construction. The most popular sizes are 100x100, 150x150 mm.

  Advice. For a metal rafter system, the Mauerlat must also be metal. For example, a channel or I-profile.

• Rafter leg... The main element of the system. For the manufacture of rafter legs, a durable beam or log is used. Legs connected from above form a truss.

The silhouette of the truss determines the appearance of the structure. Examples of farms in the photo.

The parameters of the rafters are important. They will be discussed below.

• Tightening- connects the rafter legs and gives them rigidity.

• Run:

• Ridge run, mounted at the junction of one rafter to another. In the future, a roof ridge will be installed on it.

• Side girders, they provide the truss with additional rigidity. Their number and size depend on the load on the system.

• Rafter rack- vertically located timber. Part of the load from the weight of the roof is also taken over. In a simple gable roof, it is usually located in the center. With a significant span - in the center and on the sides. In an asymmetrical gable roof - the installation location depends on the length of the rafter. With a broken roof and the arrangement of one room in the attic, the racks are located on the sides, leaving free space for movement. If there are two rooms, the racks are located in the center and on the sides.

The position of the pillar depending on the length of the roof is shown in the figure.

• Brace... Serves as a support for the rack.

Advice. Installing the brace at an angle of 45 ° significantly reduces the risk of deformation from wind and snow loads.

In regions with significant wind and snow loads, not only longitudinal struts (located in the same plane with the rafter pair) are installed, but also diagonal ones.

• Sill... Its purpose is to serve as a support for the rack and as an attachment point for the strut.

• Lathing... Designed for movement during construction work and for fixing the roofing material. Installed perpendicular to the rafter legs.

Advice. An important purpose of the lathing is to redistribute the load from the roofing material to the rafter system.

The presence of a drawing and a diagram indicating the location of all the listed structural elements will help in the work.

Advice. Be sure to add data on the device for the passage of the ventilation shaft and chimney to the gable roof truss system diagram.

The technology of their device is determined by the type of roof.

The choice of material for rafters

When calculating the material for a gable roof, you need to choose high-quality wood without damage and wormholes. The presence of knots for beams, mauerlat and rafters is not allowed.

For boards, there should be a minimum of knots, and they should not fall out. The wood must be durable and treated with the necessary preparations that will enhance its properties.

Advice. The length of the knot should not exceed 1/3 of the thickness of the bar.

Calculation of the rafter system of a gable roof

The calculation of the parameters of the material is an important stage, therefore, we present the calculation algorithm step by step.

It is important to know: the entire rafter system consists of many triangles, as the most rigid element. In turn, if the slopes have a different shape, i.e. are an irregular rectangle, then you need to divide it into separate components and calculate the load and the amount of materials for each. Summarize the data after calculations.

1. Calculation of the load on the rafter system

The load on the rafters can be of three types:

• Constant loads... Their action will always be felt by the rafter system. Such loads include the weight of the roof, lathing, insulation, films, additional roofing elements, finishing materials for. The weight of the roof is the sum of the weight of all its constituent elements; such a load is easier to take into account. On average, the value of the constant load on the rafters is 40-45 kg / sq.

Advice. To make a margin of safety for the rafter system, it is better to add 10% to the calculation.

For reference: The weight of some roofing materials per 1 sq. M. presented in the table

Advice. It is desirable that the weight of the roofing material per 1 sq. roof area, did not exceed 50 kg.

• Variable loads... They act in different periods and with different strengths. Such loads include: wind load and its strength, snow load, precipitation intensity.

Basically, a roof slope is like a sail and when wind load is taken into account, the entire roof structure can be destroyed.

The calculation is carried out according to the formula: the wind load is equal to the indicator for the region, multiplied by the correction factor. These indicators are contained in the SNiP "Loads and Impacts" and are determined not only by the region, but also by the location of the house. For example, a private house surrounded by multi-storey buildings has less stress. A detached country house or summer cottage is experiencing increased wind loads.

2. Calculation of snow load on the roof

The calculation of the roof for snow load is carried out according to the formula:

The total snow load is equal to the weight of the snow multiplied by the correction factor. The coefficient takes into account wind pressure and aerodynamic influence.

The weight of snow, which falls on 1 sq. roof area (according to SNiP 2.01.07-85) is in the range of 80-320 kg / sq.

The coefficients showing the dependence on the slope of the slope are shown in the photo.

Nuance. At an angle of inclination of the slope over 60 ° the snow load does not affect the calculation. Since the snow will quickly slide down and will not affect the strength of the timber.

• Special loads... Such loads are taken into account in places with high seismic activity, tornadoes, and stormy winds. For our latitudes, it is enough to make a margin of safety.

Nuance. The simultaneous action of many factors causes a synergistic effect. This is worth considering (see photo).

Assessment of the condition and bearing capacity of walls and foundations

It should be borne in mind that the roof has a significant weight that can harm the rest of the building.

Determination of the roof configuration:

• simple symmetrical;
• simple asymmetric;
• broken line.

The more complex the shape of the roof, the greater the number of trusses and trusses needed to create the necessary safety margin.

The angle of inclination of a gable roof is determined primarily by the roofing material. After all, each of them puts forward its own requirements.

• soft roof - 5-20 °;
• metal tile, slate, corrugated board, ondulin - 20-45 °.

It should be noted that increasing the angle increases the area of ​​space under the roof, but also the amount of material. What affects the total cost of work.

Nuance. The minimum angle of inclination of the gable roof must be at least 5 °.

5. Calculation of the step of the rafters

The pitch of the rafters of a gable roof for residential buildings can be from 60 to 100 cm. The choice depends on the roofing material and the weight of the roof structure. Then the number of rafter legs is calculated by dividing the length of the ramp by the distance between the rafter pairs plus 1. The resulting number determines the number of legs per ramp. For the second, the number needs to be multiplied by 2.

The length of the rafters for the attic roof is calculated according to the Pythagorean theorem.

Parameter "a"(roof height) is set independently. Its value determines the possibility of arranging a dwelling under the roof, the convenience of being in the attic, and the consumption of material for the construction of the roof.

Parameter "b" equal to half the width of the building.

Parameter "c" represents the hypotenuse of the triangle.

Advice. To the resulting value, you need to add 60-70 cm. For sawing and carrying the rafter leg over the wall.

It should be noted that the maximum length of the bar is 6 lm. Therefore, if necessary, the rafter beam can be spliced ​​(building, joining, joining).

The method of splicing the rafters along the length is shown in the photo.

The width of the roof rafters depends on the distance between the opposing load-bearing walls.

7. Calculation of the cross-section of the rafters

The cross-section of the gable roof rafters depends on several factors:

• load, we have already written about it;

• type of material used. For example, a log can withstand one load, a beam - another, a glued beam - a third;

• rafter leg length;

• the type of wood used in construction;

• distance between rafters (rafter pitch).

You can determine the cross-section of the timber for the rafters, knowing the distance between the rafters and the length of the rafters, using the data below.

Rafters section - table

Advice. The larger the step of installing the rafters, the greater the load falls on one rafter pair. This means that the cross-section of the rafters needs to be increased.

Dimensions of lumber (timber and boards) for a gable rafter system:

• thickness (section) of the Mauerlat - 10x10 or 15x15 cm;

• the thickness of the rafter leg and tightening is 10x15 or 10x20 cm. Sometimes a 5x15 or 5x20 cm bar is used;

• run and brace - 5x15 or 5x20. Depending on the width of the leg;

• rack - 10x10 or 10x15;

• bed - 5x10 or 5x15 (depending on the width of the rack);

• thickness (section) of the roof lathing - 2x10, 2.5x15 (depending on the roofing material).

Types of gable roof truss system

For the roof structure under consideration, there are 2 options: layered and hanging rafters.

Let's consider each type in detail in order to make an informed choice.

Hanging rafters

They are used with a roof width of no more than 6 lm. Installation of hanging rafters is carried out by attaching the leg to the load-bearing wall and ridge girder. The design of the hanging rafters is special in that the rafter legs are under the influence of a bursting force. Hanging rafters with a tie between the legs reduce its influence. The tightening in the rafter system can be wooden or metal. Often the braces are placed at the bottom, then they play the role of load-bearing beams. It is important to ensure that the fastener is securely attached to the rafter leg. Because a bursting force is also transmitted to it.

Advice.
The higher the tightening is, the more strength it should have.
If the tightening is not installed, the load-bearing walls can simply "disperse" from the pressure created by the rafter system.

Rafters

They are used for arranging roofs of any size. The design of the layered rafters provides for the presence of a bed and a stand. The bed lying parallel to the Mauerlat takes on part of the load. Thus, the rafter legs are, as it were, inclined to each other and are supported by a stand. The rafter legs of the layered system work only for bending. And the ease of installation also tilts the scales in their favor. The only drawback is the presence of a rack.

Combined

Due to the fact that modern roofs are distinguished by a large variety of shapes and complexity of configurations, a combined type of rafter system is used.

After choosing the type of rafter system, you can accurately calculate the amount of materials. Record the calculation results. At the same time, professionals recommend drawing up drawings for each element of the roof.

Installation of the rafter system of a gable roof

After the rafters of the gable roof have been calculated, you can proceed with the installation. We will divide the process into stages and give a description of each of them. You will get a kind of step-by-step instructions containing additional information on each stage.

1. Mounting the Mauerlat to the wall

The beam is installed along the length of the wall on which the rafters will rest.

In log cabins, the upper crown plays the role of Mauerlat. In buildings constructed of porous material (aerated concrete, foam concrete) or brick, the Mauerlat is installed along the entire length of the load-bearing wall. In other cases, it can be installed between the rafter legs.

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Since the length of the Mauerlat exceeds the standard dimensions of lumber, it has to be spliced.

The connection of the Mauerlat to each other is done as shown in the figure.

How to connect the Mauerlat?

The bars are washed down only at an angle of 90 °. The connection is made using bolts. Nails, wire, wooden pins are not used.

How to mount the Mauerlat?

The Mauerlat is installed on the top of the wall. The mounting technology provides for several ways of attaching the Mauerlat:

• strictly in the center of the bearing wall;
• offset to one side.

Advice.
Mauerlat cannot be placed closer than 5 cm to the outer edge of the wall.

To protect the timber for the Mauerlat from damage, it is laid on a layer of waterproofing material, which is most often an ordinary roofing material.

The reliability of the Mauerlat fastening is an important aspect of construction. This is because the roof slope is like a sail. That is, it is experiencing a strong wind load. Therefore, the Mauerlat must be firmly fixed to the wall.

Methods for attaching the Mauerlat to the wall and rafters

Anchor bolts. Ideal for monolithic construction.

Wooden dowels. They are used for log cabins and beams. But, they are always used with additional fasteners.

Staples.

Hairpin or fittings. It is used if the cottage is built of porous materials (aerated concrete, foam concrete).

Sliding mount (articulated). A bundle in this way allows you to ensure the displacement of the rafter legs when the house shrinks.

Annealed wire (knitting, steel). Used as an additional mount in most cases.

2. Manufacturing of roof trusses or pairs

Installation is carried out in two ways:

• installation of beams directly on the roof. It is not often used, since it is problematic to carry out all work, measurements, trimming at height. But it allows you to completely complete the installation yourself;

• assembly on the ground. That is, individual elements (triangles or pairs) for the rafter system can be assembled below, and then raised to the roof. The advantage of such a system is the faster execution of work at height. And the disadvantage is that the weight of the assembled truss structure can be significant. To lift it, you need special equipment.

Advice. Before assembling the rafter legs, you need to apply the markings. It is very convenient to use templates for these purposes. The rafter pairs assembled according to the template will be exactly the same. To make a template, you need to take two boards, the length of each of which is equal to the length of one rafter, and are connected to each other.

3. Installation of rafter legs

The collected pairs go upstairs and are installed on the Mauerlat. To do this, at the bottom of the rafter legs, you need to make a wash.

Advice. Since the slots on the Mauerlat will weaken it, you can only make cuts on the rafter leg. In order for the saw to be the same and fit snugly to the base, you need to use a template. It is cut from plywood.

The ways of attaching the rafter leg are shown in the figure.

You need to start the installation of rafter pairs from opposite ends of the roof.

Advice. To properly position the rafter legs, it is best to use temporary struts and struts.

A string is pulled between the fixed pairs. It will simplify the installation of subsequent rafter pairs. And also, it will indicate the level of the skate.

If the rafter system is mounted directly on the roof of the house, then after installing the two outer rafter legs, the ridge support is installed. Further, half of the rafter pairs are attached to it.

It is worth noting that the opinions of professionals differ on this issue. Some advise using a staggered fastening order, which will evenly distribute the increasing load on the walls and foundation more evenly. This order involves the installation of one rafter in a checkerboard pattern. After part of the rafter legs are installed, the missing parts of the pair are mounted. Others insist that you need to do sequential editing of each pair. Depending on the size of the structure and the configuration of the truss, the rafter legs are reinforced with struts and uprights.

Nuance. Additional structural elements are connected by cutting. It is preferable to fix them with construction brackets.

If necessary, you can lengthen the rafter leg.

Methods for splicing rafter legs are shown in the photo.

Advice. The way in which the Mauerlat is lengthened (washed down at 90 °) cannot be used in this case. This will loosen the rafter.

4. Installation of the gable roof ridge

The roof ridge assembly is made by connecting the rafter legs at the top.

Roof ridge device:

• Method without using a support bar (see fig.).

• The method using a rafter bar. The beam is needed for large roofs. In the future, it can become a support for the rack.

• Timber overlay method.

• A more modern version of making a ridge knot can be considered the method shown in the photo.

• Cutting method.

After the rafter system has been installed, we make the capital fastening of all structural elements.

5. Installation of roof battens

The lathing is mounted in any case, and is designed for more convenient movement on the roof during work, as well as for fastening the roofing material.

The pitch of the lathing depends on the type of roofing material, for example:

• for metal tiles - 350 mm (the distance between the two lower boards of the sheathing should be 300 mm).
• for corrugated board and slate - 440 mm.
• we lay a continuous crate under the soft roof.

The rafter system of a gable roof with an attic - video:

Conclusion

As you can see, despite the apparent simplicity, the installation of the gable roof truss system contains many pitfalls. But, based on the recommendations given, you can easily build a reliable structure with your own hands.

Building a roof on your own is a very real task. Of course, this requires a certain amount of knowledge, and first of all it concerns the rafter system - the main element of the roof, which perceives and resists all types of loads.

The rafter system actually provides the rigidity of the roof structure, since it distributes the load from the battens with the laid roofing material to the external and internal supports. Therefore, the reliability of the roof, its ability to withstand all influences, depends on how to calculate the rafter system.

How to correctly calculate the rafter system

The calculation of the elements of the rafter system is performed in order to determine the optimal parameters of the structure, which ensure its ability to withstand the effect of the total weight of the roof, including the coating and thermal insulation, under conditions of maximum exposure to external loads, wind and snow. In this regard, the question naturally arises of how to calculate the rafter system for the total effect of possible loads. For example, the weight of the coating, interior finishing of ceilings, hail, wind, ice on the roof during the period, etc. In the calculations, safety factors are used, say, 1.1 and 1.4. The first increases the strength of the calculated roof by 10%, and the second - by 40%.

As a rule, the design scheme that is taken in the calculations is “idealized”. It is considered that the roof is under the influence of a uniformly distributed load, that is, it experiences the same and even force, which equally acts on all slopes. In fact, such a picture practically does not occur. For example, when the wind sweeps snow bags onto a slope, it simultaneously blows it off the other. The force on the slopes is thus uneven.

Rafter loads

Rafters experience two types of impact - temporary and permanent. The latter include the weight of the roof elements, including roofing, battens, purlins, and rafters. To the second - snow and wind. Temporary - also include useful, if any.

Snowy

This type of impact can pose a serious threat to the reliability of the structure, since large amounts of snow accumulated on the roof have a significant impact on it. The amount of snow load is determined in a horizontal projection by the formula:

S = Sg * µ,

• Sg is the mass of snow cover per unit area of ​​the horizontal plane. This parameter depends on the location of the building.
• µ is a coefficient that expresses the dependence on the angle of inclination of the roof. For example, for flat roofs up to 25⁰ - 1.0, for pitched roofs with a slope of more than 25 ⁰< α < 60⁰ – 0,7. При крутом уклоне, свыше 60°, снеговая нагрузка не учитывается.

Wind

To calculate the average wind load at a given height, the following formula is used:

W = W o x k,

wherein

• W o - standard value, it is selected according to the table, according to the wind region;
• k - coefficient of dependence of wind pressure on height, it differs depending on the area where the construction is carried out:

Correction for the wind in the calculation of rafters is made only when the roof slope is more than 30 °.

The choice of the type of terrain depends on the direction of the wind, which is used in the calculation.

How to calculate with wind and snow

Let us calculate climatic loads using the example of the Moscow region, which is part of the middle zone of the Russian Federation. The calculated values ​​are selected from SNiP 2.01.07-85 *, namely “Loads and Impacts”.

(1.1 MiB, 1,547 hits)

Let's say the roof slope is 22⁰. This is the third snow region, for which the calculated one is 180 kg / m 2, and µ = 1.0, then 180 x 1.0 = 180 kg / m 2. For pitched roofs with a coefficient µ = 0.7, this value decreases to 126 kg / m 2.

With the formation of a snow bag, the value of this indicator can increase to 400-500 kg / m 2.

The calculated wind load for the same region is 32 kg / m 2. If we assume that we are talking about a 10-meter house, then the magnitude of the wind effect will be 32 x 0.65 = 20.8 kg / m 2.

Other

• The load created by the roof structure and the roof itself is calculated according to the size of the structure and the volume of materials used.
• Useful is taken into account for structures "connected" with trusses. For example, ceilings suspended from them, ventilation chambers or water tanks located on farms, etc.

When designing a roof, two types of calculations are carried out:

• by strength, which excludes damage to the rafter legs;
• by deformation, which determines the maximum degree of deflection of such a beam. So, the calculation of the rafter system of a sloping roof should take into account that the deflection of the rafters for such a structure should not be more than 0.004 of the length of the section, that is, for example, the maximum deflection of a 6-meter beam reaches 2 cm.At first glance, it may seem that this is not so there are too many, however, even if the deformation value is slightly exceeded, it will become visually noticeable. Large deflections will make the roof look like a Chinese pagoda.

Calculation of elements

The design of the system is determined taking into account the following parameters:

• roof slope,
• the size of the span to be covered,
• cross-section of rafters and battens,
• cumulative load from roofing, wind and snow,
• the distance between the rafters, its optimal value is determined by the method of the limit, that is, the value, upon reaching which, partial or complete destruction can be expected.

The cut (section) of the rafters is selected based on their length and the magnitude of the loads being tested.

The values ​​given in this table, of course, are not the result of a full-fledged calculation, they are only recommended for use when carrying out rafter work for simple structures.

A full-fledged calculation of the system is possible with a sufficient baggage of theoretical knowledge, certain drawing and drawing skills. Fortunately, the design task today is greatly facilitated thanks to convenient computer programs designed specifically for the development of projects of all kinds of building elements. They are suitable not only for professionals, but also for private users.

An example of calculation using programs

Step 1. Calculation of loads

At the first stage, the "Loads" window is selected from the menu and the necessary changes are made to the cells of the blue tables:

"Initial data"

• Change the slope of the ramp and the pitch of the rafters to the intended ones. The next line of the table “Load. Roofs ”are filled with data from the table below.

• The sum of the preliminary calculated wind and snow loads is entered into the next cell. Next comes “ Warming (mans.)"- the cell is left unchanged for a warm attic or 0 is entered for a cold one.
• The values ​​in the "Crate" table are also corrected.

If the filled-in data is correct, the message "The load-bearing capacity of the battens is provided!" Should appear at the bottom of the window. Otherwise, you will need to change the dimensions of the battens or the distance between the rafters.

Step 2 Rafters with two supports

At this stage, work with the tab “Lanyard. 1".

Starting from this tab, the data already entered in the table will be inserted by the program into the cells automatically.

What edits do you make at this stage?

• Changes are made to the value of the horizontal projection of the rafters in the diagram and proceed to filling in the table "Calculation of rafters".
• The value of the thickness of the rafter, which is entered into the cell "B (preset)", must be greater than the specified "Wtr (stable)".
• The width of the rafters entered in the line "Accept N" must exceed the values ​​indicated in the lines "Ntr. (Deflection)" and "Ntr. (Strength)". If all values ​​are substituted correctly, then the program under the scheme will "write": "The condition is fulfilled."

The line "H, (by grade)" is filled in by the program itself, but you should know that you can change the data yourself.

Step 3 Rafters with three supports

Such rafters are calculated on the tab "Slings 2" or "Slings 3".

Which one to choose depends on the location of the intermediate support. The tabs differ in the location of the B-pillar (support). In case of L / L1<2, иначе говоря, она находится правее середины стропила, пользуются «Строп.2 », в противном случае – «Строп.3 ». Стойка может располагаться точно посередине, тогда не принципиально, какую из них выбрать – результат будет тот же. С этими вкладками работают аналогично «Строп. 1 ».

Step 4 Stand

The value of the bending moment of the rack and the vertical impact on it is entered (in tons), respectively, in the cells "M =" and "N =". The inscriptions “Vnecenter. provided "and" Central provided! " in the center means admission to the next stage.

We offer a professional free calculation of the gable roof truss system using an online calculator site, 3D visualization and detailed drawings. Detailed calculations of the roof and roof, all materials, lathing, rafters, Mauerlat. Try calculating a gable roof now!

Our online calculator rafter system will calculate the gable roof:

• calculation of the length of the gable roof rafters
• number of rafters and step
• calculation of the gable roof area and the angle of inclination
• calculation of the roof lathing
• the number of sheet roofing materials (for example, corrugated board, metal tiles, slate)
• parameters of vapor barrier and insulation

To form the calculation of the gable roof calculator, you need to measure and enter the following dimensions in the appropriate windows:

The cross-section (thickness x width) and the pitch of the rafters depend on the angle of inclination of the roof, its type, the length of the rafter leg, the maximum withstand basic loads, as well as on the type and weight of the roof covering, and even to some extent on the width of the insulation. If you don't know where to get the standard parameters of rafters and battens, our article will help you " Optimal cross-section, pitch of the lathing and rafter legs, depending on the type of roof ».

The calculator calculates the materials for the roof, starting from the dimensions of the roofing sheet you entered and from the calculated value of the roof area. We advise you to buy the amount of roofing materials for the roof, boards and beams for the rafter system with a small margin, it is always better to hand over the leftovers to a hardware store than pay a lot of money for the delivery of a missing pair of boards.

Be careful! From how accurate the values ​​you enter, the online calculator will be able to calculate the gable roof so reliably.

Simplify your calculations and save time, the program will draw itself rafter plangable roof and will display the results of calculating a gable roof according to the data you entered in the form of a drawing of a gable roof in different viewing angles, and its interactive 3d model.

On the tab “ 3 D- View»You can better see your future gable roof in 3D. In our opinion, visualization in construction is a very necessary feature.

If you have a gable roof with different slopes in your project, you should calculate with the calculator twice - for each slope separately.