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.

For low-rise buildings, a rafter roof is perfect. It will decorate the facade of the house, and with a sufficient slope, snow does not accumulate on such a roof, unlike a flat structure.

One of the types of rafter roof - gable... This is a fairly simple system that is formed by two slopes. The roof slope is the entire inclined plane with which the drain is provided.

The structure rests on two parallel walls. This roof forms two triangular lateral gables. The pediment is the completion of the building's facade.

Advantages of the gable system

1. Ease of design.
   The calculation of the bearing capacity and the necessary materials for the construction of such a roof is quite simple, since there are few options for the types and sizes of supporting structures;
2. Ease of installation.
   The gable roof has no complex structural elements. A small number of standard sizes allows you to quickly install all the elements of the roof;
3. Ease of use.
   The fewer different kinks the roof has, the more reliably it protects the home. In the simplest version, a gable roof has only one break - a ridge. It is easier to repair such a roof in the event of defects;
4. Free space.
   For arranging the attic, a gable roof is preferable, since it “eats up” space less. For comparison, consider a 6x6 m house with an attic. At the outer walls, the height from the floor of the room to the roof is 1.5 m, at the ridge - 3 m. For a gable roof under such conditions, the volume of the room will be 81 cubic meters, and for a hip roof with four slopes, 72 cubic meters. For larger building sizes, the volume loss will increase.

Types of structures

There are four main types of gable roofs:

1. Symmetrical.
   Reliable, stable, easy to implement, based on an isosceles triangle;
2. Asymmetrical.
   The ridge is not located in the center, the roof slopes have different slopes;
3. Polyline symmetric.
   The roof slopes are kinked. Significantly increases the height of the room;
4. Polyline asymmetrical.
   The attic or attic space is smaller than in the previous case. The roof has a very unusual appearance.

The choice of the type of gable roof depends on the purpose of the room located directly below it and the architectural appearance of the building.

General principles for calculating the rafter system

The most important load-bearing parts of the gable roof rafter system of a building are the Mauerlat, the transom and the rafters. Mauerlat works in compression, so its cross section can be taken conditionally.

The crossbar and rafter legs experience a bending moment.

The calculation of such structures is made in terms of strength and rigidity. For small buildings, you can choose their cross-section approximately, but for serious buildings, for safety reasons and to save material, the calculation of the rafter system should be performed by a professional.

Roof deadweight load

To perform the calculation, you need to know the load for 1 sq. roofs.

To do this, add up the masses of 1 sq. all roofing materials:

1. filing(if there is one, it is most often made of drywall);
2. rafter legs... To calculate the weight of the rafters per square meter of the roof, you need to find the mass of the running meter of the rafter leg and divide this number by the step of the rafters in meters. For the calculation, you can take the approximate cross-section of the rafter, the area of ​​this section must be multiplied by the density of the wood;
3. insulation (if any)... The density of the insulation must be indicated by the manufacturer, it must be multiplied by the thickness;
4. crate... To provide a margin, you can take a solid crate into account. For example, 1 sq. M. battens made of a 32 mm thick board will weigh approximately 25 kilograms;
5. roofing material. Weight 1 sq. coatings are usually indicated by the manufacturer.

Snow load

The snow load is different for each area and is equal to the weight of the snow cover on the horizontal plane.

On the territory of Russia, it can receive values ​​from 80 to 560 kilograms per square meter. On the Internet, you can easily find a map of the distribution of snow load and select the desired number based on the area of ​​construction.

Roof slope

The angle of inclination of the roof is easy enough to calculate, knowing the geometry and having at hand an engineering calculator or a standard calculator on a personal computer.

If you divide the height of the roof rise by the distance from the ridge to the eaves in the plan, you get the slope of the roof in shares or the tangent of the angle of inclination. In order to calculate the angle, you just need to find the arctangent.

If you find it difficult to use an engineering calculator, the arctangent can be found using an online calculator.

Calculation of the pitch of the rafters

The step of the rafters of the attic roof should be chosen for reasons of ease of installation of insulation. Mats are usually 60 centimeters wide, so the pitch of the rafters should be chosen so that the distance between them is 58 or 118 centimeters clean. Two centimeters will allow the insulation plates to be installed very tightly, which will allow it to stick between the rafters and improve thermal insulation.

Rafter leg length

The leg length can be easily calculated using the formula:
L / cosα,
here L is the distance from the roof ridge to the inner surface of the outer wall in the plan, and cos α is the cosine of the roof slope angle. With a rigid mount, you need to add the size of the cut.

Rafter leg section

The cross-section of the rafter leg must be selected as a multiple of the size of the boards and beams.

An example of a simple calculation of the cross-section of a rafter leg:

1. we find the load on 1 running meter of the rafter.
   q =(1.1 * weight of 1 square meter of roof * cosα + 1.4 * standard snow load * cosα2) * rafter pitch;
2. find W.
   W = q * 1.25 * flight of rafters / 130;
3. we solve the equation:
   W = b * h2 / 6.
   In this equation, b is the cross-sectional width of the rafter leg, and h is the height.

To solve it, you need to set the width and find the height by solving a simple quadratic equation. The width can be assigned 5 cm, 7.5 cm, 10 cm, 15 cm. With small spans, a width of 15 cm is impractical.

To calculate rafter systems, there are all kinds of tables, programs, online calculators.

The main elements of the roof

The main elements of a gable roof, like any other rafter roof, are:

Rafter roof with attic

To make full use of the space under the roof, you can design an attic.

Attic floor Is a floor in the attic space. The attic façade is completely or partially formed by the roof surfaces. According to regulatory documents, in order for a room to be considered an attic, the line of intersection of the plane of the roof and the outer wall should not be higher than 1.5 m from the floor level. If this requirement is not met, the space will be considered a regular floor.

The roof of the attic floor differs from the roof of the attic by the presence of insulation in its structure. Most often, mineral wool slabs are used to insulate the attic roof.

Lighting of the attic space can be done in three ways:

1. window openings in the gables;
2. dormer windows;
3. roof windows.

Dormer window - it is a window structure that has a frame mounted simultaneously with the rafter system. This frame is made of wood. The dormer has its own small roof, which can be gable or cylindrical. The glass unit itself is installed vertically.

Roof window Is a window specially designed for use on truss roofs. It is installed in the plane of the slope in an inclined position. The roof window must be able to withstand the calculated snow load. It is best not to use this type of window on slightly sloped roofs.

Roof material selection

After the appearance of the roof has been determined, you can start choosing the material. There are several types of modern coatings. In the list below, material options are listed in descending order of average market value.

1. Ceramic tiles.
   Ceramics as a roofing material has a long history. The ceramic roof is reliable and durable. The disadvantages of this material are the price and high weight. Under the roof made of ceramic tiles, you will have to arrange a reinforced rafter system and lathing;
2. Cement-sand tiles.
   Has almost all the characteristics of ceramic, but costs a little less;
3. Flexible bituminous shingles.
   Possesses good sound insulation characteristics. Thanks to the rough surface, the tiles are able to prevent snow from sliding off the roof. Requires continuous sheathing, usually a layer of moisture-resistant plywood is used. Cannot be used on roofs with steep slopes;
4. Metal roof tiles.
   Compared to previous coatings, it is lighter. Easy to assemble. The downside of a metal roof is that it can be too noisy when it rains.
5. Seam roof.
   The most attractive option in terms of cost. Requires special qualifications during installation, since it will be difficult for a non-professional to make high-quality connections. Installation is more time consuming than metal and shingles. As "noisy" as metal tiles.

The roof material completely depends on the wishes and capabilities of the customer. An exception is roofs with a too large or too small slope, since all materials have restrictions on the slope angle.

Types of rafter systems

Structural rafter roof systems can be of three types:

1. Rafters.
   The rafters are supported on two sides. From below - to the Mauerlat, from above - to the crossbar. Racks and struts can be used as intermediate supports. Most often they are used in buildings with a small distance between the ends or, if possible, place racks or a wall in the middle of the attic.
   For large rafter spans (large distances between longitudinal walls), additional posts, struts or braces can be used.
   Roof rafters are easy to calculate.
   Usually the most powerful element of such a system is the girder, which carries half the load of the entire roof structure.
2. Hanging rafters.
   In the absence of the possibility of using the crossbar as an upper support, it is reasonable to use this rafter system.
   Hanging rafters rest only on the Mauerlat, and at the top point they are connected to each other using a lining.
   This truss system works like a truss under load. The greatest pressure is on the outer walls. A horizontal force arises - a thrust, which can lead to displacement of the walls. In the construction of hanging rafters, the spacer force is perceived by a tightening that tightens the rafter legs and prevents them from moving apart.
   Hanging rafters are classified according to the tightening location:
   1) Triangular three-articulated arch.
   Tightening and rafters form a triangle. The tightening is located at the level of the overlap;
   2) Triangular three-articulated arch with suspension.
   With a large span of rafters, the tightening may not pass according to the deflection requirements. To prevent it from sagging, the puff is suspended from the ridge. But with such a system, as well as with a system of layered rafters, a number of racks are formed in the middle of the attic;
   3) Triangular three-pivot arch with a raised latch.
   The tightening is most often located at the level of the ceiling of the attic room. Such a scheme is less advantageous from the point of view of the structure's operation. The higher the puff is located, the more thrust it perceives.
   Hanging rafters must be considered a triangular truss, which complicates the calculation.
3. Combined rafters.
   The combined system includes spacer rafters. They need both bolt installation and tightening. Unlike previous options, in which the rafters are pivotally attached to the Mauerlat, here the rafter leg is rigidly attached, so a strut appears in the system. For such a system, the Mauerlat must be securely attached to the wall, and the wall itself must be strong and thick. An excellent option for the mill is execution along the perimeter of a reinforced concrete belt.

Installation of the rafter system

Installation takes place in the following order:

1. laying Mauerlat;
2. installation of the crossbar (if any);
3. the layout of the rafters;
4. insulation (if any);
5. crate;
6. roofing material.

Attaching the rafter leg to the Mauerlat can be rigid and articulated.

Hinge fastening

It makes it possible to compensate for the expansion of wood under the influence of humidity and temperature changes.

Fastening can be done in several ways:

1. with the help of special fasteners, a metal "slide";
2. using a mounting plate;
3. a gash is performed on the rafter leg. The junction of the rafter leg and the Mauerlat is fixed with nails.

Rigid anchorage

The rafter is attached to the Mauerlat with a cut and securely fixed with nails hammered at an angle in relation to each other. One nail is driven vertically to the surface of the Mauerlat. Such a connection excludes displacement in any plane.

The gable rafter system has undeniable advantages. It can be designed and assembled on your own, you just need to take a responsible attitude to this issue and think over everything to the smallest detail.

When designing a private house, many different parameters must be taken into account. If they are calculated incorrectly, then the strength of the structure will be in great doubt. The same goes for the roof of the house. Here, even before the start of construction, you need to find out the height of the ridge, and the area of ​​the roof and much more, including calculating the length of the rafters. And how to make the last calculations will be discussed in this article.

What type of roof

How to calculate the length of the rafters? This question will interest everyone who builds a house on their own. But in order to answer it, it is worthwhile to first find out many other parameters. First of all, it is worth deciding on the type of roof, because the length of the slope and rafters will depend on this. The most common option is considered to be a gable design. But even here there are several options, namely:

1. Symmetrical is the most common type of gable roof. Its popularity is due to its simplicity of design and uncomplicated calculation of all the necessary parameters. Another plus is the even distribution of loads on the rafter system. But there are also disadvantages. Not a very rational use of space. This is especially important if you are thinking. A large number of sharp corners creates a lot of "blind" zones, which cannot be rationally used.
   
2. Asymmetrical. In this case, the slopes are located at different angles. As a result, the rational area increases. But here, too, there were some drawbacks. Such a gable roof requires more complex calculations. If done with a mistake, then the structure may not withstand the loads that are not evenly distributed.
   
3. A polyline is the most effective construction if you want to make an attic floor. In this case, the rafter legs will "break" at a certain distance from the ridge. As a result, more free space under the roof will be obtained, and the entire area will be used more rationally. In this case, it will be even more difficult to calculate the parameters of the rafters, including their length.
   
   

You can consider even more complex designs, such as multi-level. These roofs will look very attractive. But to make a calculation, and especially to build a rafter system, in this case it will be almost impossible without the help of professionals. Therefore, in most cases, they are limited to the three above-mentioned options for a gable roof.

System type

The calculation of the length of the gable roof rafters will also depend on the system used. Here experts distinguish the following two main types:

1. ... This is the easiest option. In this case, the rafter legs rest only on the Mauerlat. Their upper part is simply connected to each other. This system is used if the width of the house is small. In this case, the length of the rafters should not exceed six meters. The hanging version is undesirable for use with an asymmetrical gable roof.
2. - This is a more durable rafter system. It is used if there is an axial load-bearing wall in the middle of the house. In this case, supports and a ridge girder are installed, on which the upper part of the rafter legs is attached.

You can also use a combined option. It is often used in the construction of houses with complex geometry. Here it will be more difficult to calculate the length of the rafters and other parameters of the system. If you have exactly this option, then it is better to entrust everything to a specialist to calculate. In this case, there will be fewer mistakes, which means that the roof will last longer and will not cause you problems during operation.


What else needs to be considered

The type of roof and the system used are not all the parameters that will be required in order to calculate the length of the gable roof rafters. Before calculating everything, you need to find out a lot more information, namely:




In addition, when calculating the length of the rafters, you should find out what the overhangs should be. More than one roof can do without this "additional" element. Overhangs play the role of protection that protects the walls of the house and its foundation from being washed away by water flowing from the roof.

They can be a continuation of the rafters or made as independent elements. In the latter case, boards called "filly" are attached to the main structure. At their core, they are an extension of the rafters.

How long to choose overhangs is up to the owners of the house. According to existing building codes, this parameter should be in the range from 50 to 60 centimeters. Do not do less, otherwise the walls and foundation may suffer. Sometimes overhangs are made more than one meter. In this case, a small canopy is obtained along the wall, which can be used for resting or storing things.


Making calculations

How is the length of the rafters calculated? If the roof has a symmetrical shape, then it is not difficult to calculate this parameter. For this, the formula of the Pythagorean theorem is used, namely: C is equal to the square root of A squared plus B squared, where:

• C is the desired length of the rafter;
• A is the height at which the ridge is located (from the base of the roof);
• B is half the width of the house.

Moreover, using this formula, you can calculate the length of the rafters only up to. The length of the overhangs is not taken into account here. If they are a continuation of the rafters, then their length must be added to the calculated parameter.

And how to make a calculation if the roof is asymmetrical? In this case, the slopes will be different. But even here you can use the Pythagorean theorem. You can calculate the rafters on the roof using the same formula, but first find out the value of the "B" parameter (in the first case, it is equal to half the width of the house). If the roof is asymmetrical, then even at the design stage you will calculate at what distance the ridge will be located from the walls. It is this value that is taken as the "B" parameter. As a result of the calculation, you will receive the length of each of the rafter legs (on the left and right slope). As you can see, there are no problems with calculations here either.

There is another way to calculate the rafters. In this case, the angle of inclination of the ramp is used. This formula is a little more complicated than the previous one. The length of the rafters (for a gabled symmetrical roof) will be equal to the sum of 0.5 and the height from the base of the roof to the ridge divided by the cosine of the slope angle.

Before proceeding with the construction of the roof, it is of course desirable that it be designed for strength. Immediately after the publication of the last article "", I began to receive questions in the mail regarding the choice of the section of rafters and floor beams.

Yes, it is really quite difficult to understand this issue on the vastness of our beloved Internet. There is a lot of information on this topic, but, as always, it is so scattered and sometimes even contradictory that an inexperienced person, who in his life may not even have encountered such a subject as "Strength" (someone was lucky), can easily get confused in these wilds.

I, in turn, will now try to draw up a step-by-step algorithm that will help you independently calculate the rafter system of your future roof and finally get rid of constant doubts - and suddenly it will not stand, but suddenly it will fall apart. I must say right away that I will not delve into the terms and various formulas. Well, why? There are so many useful and interesting things in the world that you can fill your head with. We just need to build a roof and forget about it.

The whole calculation will be described using the example of a gable roof, which I wrote about in

So Step # 1:

Determine the snow load on the roof. For this we need a map of snow loads of the Russian Federation. To enlarge the picture, click on it with the mouse. Below I will give a link where you can download it to your computer.

Using this map, we determine the number of the snow region in which we are building the house and from the following table we select the snow load corresponding to this region (S, kg / m²):

If your city is on the border of regions, choose a higher load value. It is not necessary to correct the resulting figure depending on the angle of inclination of the slopes of our roof. The program we are going to use will do it itself.

Let's say in our example we are building a house in the suburbs. Moscow is located in the 3rd snow region. The load for it is 180 kg / m².

Step # 2:

Determine the wind load on the roof. For this we need a map of the RF wind loads. It can also be downloaded from the link below.

Using this map, we also select the corresponding region number and determine the value of the wind load for it (the values ​​are shown in the lower left corner):

Here, column A - open coasts of seas, lakes and reservoirs, deserts, steppes, forest-steppe and tundra; Column B - urban areas, forests and other areas evenly covered with obstacles. It should be noted that in some cases the type of terrain may differ in different directions (for example, the house is located on the outskirts of a settlement). Then we select values ​​from column "A".

Let's go back to our example. Moscow is located in the 1st wind region. The height of our house is 6.5 meters. Suppose that it is being built in a populated area. Thus, we take the value of the correction factor k = 0.65. Those. the wind load in this case will be equal to: 32x0.65 = 21 kg / m².

Step # 3:

You need to download to your computer a calculation program made in the form of an Excel table. Further we will work in it. Here is the download link: “. It also contains maps of snow and wind loads of the Russian Federation.

So, download and unpack the archive. Open the file "Calculation of the rafter system", while we get into the first window - "Loads":

Here we need to change some values ​​in the cells filled with blue. All calculations are done automatically. Let's continue with our example:

In the plate "Initial data" we change the angle of inclination by 36 ° (what angle you will have, write this, well, I think everyone understands this);

We change the pitch of the rafters to the one we chose. In our case, this is 0.6 meters;

Load roof (load from the own weight of the roofing material) - we select this value from the table:

For our example, we select a metal tile with a weight of 5 kg / m².

Snow. region - here we enter the sum of the values ​​of snow and wind loads that we received earlier, i.e. 180 + 21 = 201 kg / m²;

Insulation (mans.) - we leave this value unchanged if we lay insulation between the rafters. If we make a cold attic without insulation, we change the value to 0;

Enter the required dimensions of the lathing in the "Crate" plate. In our case, for metal tiles, we will change the pitch of the lathing by 0.35 m and the width by 10 cm. Leave the height unchanged.

All other loads (from the own weight of the rafters and lathing) are automatically taken into account by the program. Now let's see what we got:

We see the inscription "The load-bearing capacity of the crate is provided!" We do not touch anything else in this window, there is even no need to understand what the numbers are in other cells. If, for example, we choose another step of the rafters (more), it may turn out that the bearing capacity of the lathing will not be provided. Then it will be necessary to select other dimensions of the crate, for example, to increase its width, etc. In general, I think you will figure it out.

Step # 4:

Lanyard 1»And go to the rafter calculation window with two support points. Here, all the input data we entered earlier have already been substituted by the program automatically (this will be the case in all other windows).

In our example from the article "Do-it-yourself gable roof of a house", the rafters have three points of support. But let's imagine that there are no intermediate racks and let's make a calculation:

Change the length of its horizontal projection on the rafter diagram (the cell is filled with blue). In our example, it is 4.4 meters.

In the plate "Calculation of rafters" we change the value of the thickness of the rafters B (given) to our choice. We put 5 cm.This value must necessarily be greater than that indicated in the cell Tue (steady);

Now the line “ Accept H»We need to enter the selected rafter width in centimeters. It must be greater than the values ​​specified in the lines " Ntr., (Durable)" and " Ntr., (Deflection)". If this condition is met, all the inscriptions at the bottom under the rafter scheme will look like "Condition met". In the line “ H, (by grade)"The value that the program itself suggests to us is indicated. We can take this figure, or we can take another. Usually we select the sections available in the store.

So, what we got is shown in the figure:

In our example, in order to comply with all strength conditions, it is necessary to choose rafters with a cross section of 5x20 cm. But the roof scheme shown by me in the last article has rafters with three support points. Therefore, to calculate it, we proceed to the next step.

Step # 5:

Click at the bottom of the working screen on the tab " Lanyard 2"Or" Lanyard. 3 ″... This opens a window for calculating rafters with 3 support points. The choice of the tab we need is made depending on the location of the middle support (rack). If it is located to the right of the middle of the rafter, i.e. L / L1<2, то пользуемся вкладкой "Lanyard 2"... If the post is located to the left of the middle of the rafter, i.e. L / L1> 2, then we use the tab "Lanyard 3"... If the rack is exactly in the middle, you can use any tab, the results will be the same.

In the rafter diagram, we forward the dimensions in the cells filled with blue (except for Ru);

By the same principle as described above, we select the dimensions of the rafter section. For our example, I took the dimensions 5x15 cm. Although it could have been 5x10 cm. I'm just used to working with such boards, and the margin of safety will be more.

Now it is important: from the figure obtained during the calculation, we will need to write out the value of the vertical load acting on the rack (in our example (see the figure above) it is 343.40 kg) and the bending moment acting on the rack (Mop. = 78.57 kghm). We will need these figures further when calculating the racks and floor beams.

Further, if you go to the tab " Arch“, The window for calculating the rafter system will open, which is a ridge arch (two rafters and a tightening). I will not consider it, it will not fit our roof. We have too large a span between the supports and a small angle of inclination of the slopes. There you will get rafters with a section of about 10x25 cm, which is certainly unacceptable for us. For smaller spans, such a scheme can be used. I am sure whoever understood what I wrote about above will figure it out on their own with this calculation. If you still have questions, write in the comments. And we move on to the next step.

Step 6:

Go to the "Rack" tab. Well, everything is simple here.

The previously determined values ​​of the vertical load on the rack and the bending moment are entered in the figure, respectively, in the cells "N =" and "M =". We have them written in kilograms, we enter them in tons, while the values ​​are automatically rounded;

Also, in the figure, we change the height of the rack (in our example, it is 167 cm) and set the dimensions of the section we have chosen. I chose a 5x15 cm board. Below, in the center, we see the inscription "Central provided!" and "Vnecenter. provided. " So everything is in order. The safety factors "Kz" are very large, so you can safely reduce the cross-section of the racks. But we will leave it as it is. The calculation result in the figure:

Step # 7:

Go to the tab "Beam". A distributed load and a concentrated load act on the floor beams at the same time. We need to consider both. In our example, beams of the same cross-section cover spans of different widths. We of course make calculations for a wider span:

- in the plate "Distributed load" we indicate the step and span of the beams (from the example we take 0.6 m and 4 m, respectively);

- we take the values ​​Load (normal) = 350 kg / m² and Load (calculated) = 450 kg / m². The values ​​of these loads in accordance with SNiP are averaged and taken with a good margin of safety. They include the load from the own weight of the floors and the operating load (furniture, people, etc.);

- to the line “ B given»Enter the selected width of the section of the beams (in our example, it is 10 cm);

In the lines “ H, strength" and " H, deflection»The minimum possible cross-section heights of the beams will be indicated at which it will not break and its deflection will be acceptable. We are interested in the largest of these numbers. We take the height of the section of the beam proceeding from it. In our example, a 10x20 cm beam is suitable:

So, if we did not have racks resting on floor beams, the calculation would be over at this point. But there are racks in our example. They then create a concentrated load, so we continue to fill in the plates "" and " Distribution + concent.«:

In both plates we enter the dimensions of our spans (here I think everything is clear);

In the plate "" we change the values ​​of Load (normal) and Load (calculated) by the figure that we received above when calculating rafters with three support points - this is the vertical load on the rack (in our example, 343.40 kg);

In both plates we enter the accepted width of the beam section (10 cm);

The height of the section of the beam is determined by the plate " Distribution + focus. " ... Focusing on a higher value again. For our roof, we take 20 cm (see the picture above).

This completes the calculation of the rafter system.

I almost forgot to say: the calculation program we use is applicable for roof systems made of pine (except for Weymouth), spruce, European and Japanese larch. All used wood is of the 2nd grade. When using other woods, some changes will need to be made to the program. Since other types of wood are rarely used in our country, I will not describe now what needs to be changed.

Specify the parameters of wooden rafters:

B- the width of the rafter, an important parameter that determines the reliability of the rafter system. The desired cross-section of the rafter (in particular, the width) depends on: loads (constant - the weight of the lathing and roofing cake, as well as temporary - snow, wind), the material used (quality and its type: board, timber, glued beams), the length of the rafter leg, the distance between the rafters. You can determine the approximate cross-section of the timber for the rafters using the data in the table (the width value is the larger value from column 3, for example, with a rafter length of up to 3000 mm and a step of 1200 mm, the desired width is 100 mm). When choosing the width of the rafters, it is imperative to take into account the recommendations given in SP 64.13330.2011 "Wooden structures" and SP 20.13330.2011 "Loads and influences".

Rafters length, mm	Rafter pitch, mm	Rafters section, mm
Up to 3000 mm	1200	80x100
Up to 3000 mm	1800	90x100
Up to 4000 mm	1000	80x160
Up to 4000 mm	1400	80x180
Up to 4000 mm	1800	90x180
Up to 6000 mm	1000	80x200
Up to 6000 mm	1400	100x200

Y- the height of the roof, the distance from the ridge to the ceiling of the attic. Affects the angle of inclination of the roof. If you plan to equip a non-residential attic, you should choose a small height (less material is required for rafters, waterproofing and roofing), but sufficient for inspection and maintenance (at least 1500 mm). If it is necessary to equip a living space under the arch of the roof, to determine its height, it is necessary to focus on the growth of the tallest family member plus 400-500 mm (approximately 1900-2500 mm). In any case, you must also take into account the requirements of SP 20.13330.2011 (updated edition of SNiP 2.01.07-85 *). It should be remembered that precipitation can linger on a roof with a small angle of inclination (low height), which negatively affects its tightness and durability. However, a high roof becomes more vulnerable to strong wind gusts. The optimum tilt angle is within 30-45 degrees.

X- The width of the roof (without overhangs) is determined by the width of the outer perimeter of your house.

C- the size of the overhang, an important structural element of the roof that protects the walls and foundation from precipitation, is determined taking into account the climatic conditions of your region (SP 20.13330.2011) and the general architectural idea. For one- and two-story houses without the organization of an external water drain, not less than 600 mm. If you arrange a drainage system, you can reduce it to 400 mm (SNB 3.02.04-03). According to the requirements of IRC-2012, paragraph R802.7.1.1 (International Building Code for 1-2 apartment individual residential buildings), the maximum length of the free overhang of the rafters, which does not require the arrangement of additional support struts, is 610 mm. The optimal overhang is 500 mm.

Z Is the distance from the top edge of the rafter to the saw. The size Z connected with the width of the rafter by a simple ratio - no more than 2/3 of its width (neglect of this rule significantly reduces the bearing capacity of the rafter). A gash is necessary for attaching the rafters to the Mauerlat - a support that absorbs loads from the roof and redistributes to the load-bearing walls.

Checking the item "Black and white drawing" you will receive a drawing close to the requirements of GOST and you can print it without wasting color paint or toner.

Calculation results:

Length to the overhang of the rafter- this size should be used to mark the sawn rafters to the Mauerlat.

Overhang length will show how far it is necessary to release the rafter outside the perimeter of the house to obtain a given roof overhang ( WITH) protecting from bad weather.

Having calculated the total length of the rafter and overhang it is not difficult to find out the required amount of lumber of the required length and estimate how many reagents are needed for processing wood from decay.

Calculation of the angle and section of the rafters: the cut angle is the angle at which the ends of the rafters must be cut to connect to each other. At the same angle to the edge of the rafter, the start of the saw should be measured. To maintain the same angle, it is advisable to use a template on all rafters.