Construction calculator for calculating the rafter system. Calculation of the roof truss system

Online calculator gable roof will help you calculate the angles of inclination of the rafters, the required amount of sheathing, the maximum load on the roof, as well as the materials required to build a roof of this type with given dimensions. You can calculate the roof from such popular roofing materials as slate, ondulin, ceramic, cement-sand and bitumen shingles, metal tiles and other materials.

The calculations take into account the parameters given in TKP 45-5.05-146-2009 and SNiP “Loads and Impacts”.

A gable roof (also known as a gable or gable roof) is a type of roof that has two inclined slopes that extend from the ridge to the exterior walls of the building. This is the most common type of roof today. This is explained by its practicality, low construction costs, effective protection premises and aesthetic appearance.

Rafters in the structure gable roof lean on each other, connecting in pairs. On the end side, gable roofs have the shape of a triangle; such ends are called gables or gables. Usually, an attic is installed under such a roof, which is illuminated using small windows on the gables (attic windows).

When entering data into the calculator, be sure to check the additional information marked with the icon.

At the bottom of this page you can leave feedback, ask your own question to the developers, or suggest an idea to improve this calculator.

Explanation of calculation results

Roof angle

The rafters and roof slope are inclined at this angle. It is understood that it is planned to build a symmetrical gable roof. In addition to calculating the angle, the calculator will inform you how the angle complies with the standards for the roofing material you have chosen. If you need to change the angle, then you need to change the width of the base or the height of the roof, or choose a different (lighter) roofing material.

Roof surface area

Total roof area (including overhangs of a given length). Determines the amount of roofing and insulating materials that will be needed for the work.

Approximate weight of roofing material

Total weight roofing material required to completely cover the roof area.

Number of rolls of overlapping insulation material

The total amount of insulating material in rolls that will be required to insulate the roof. The calculations are based on rolls 15 meters long and 1 meter wide.

The maximum load on the rafter system. The calculations take into account the weight of the entire roofing system, roof shape, as well as wind and snow loads of the region you specified.

Rafter length

The full length of the rafters from the beginning of the slope to the ridge of the roof.

Number of rafters

The total number of rafters required to construct a roof at a given pitch.

Minimum section of rafters, Weight and Volume of timber for rafters

The table shows the recommended dimensions of rafter sections (according to GOST 24454-80 Lumber coniferous species). To determine compliance, the type of roofing material, the area and shape of the roof structure, and the loads placed on the roof are taken into account. The adjacent columns display total weight and the volume of these rafters for the entire roof.

Number of rows of sheathing

The total number of rows of sheathing for the entire roof. To determine the number of rows of sheathing for one slope, it is enough to divide the resulting value by two.

Uniform distance between sheathing boards

To install the sheathing evenly and avoid unnecessary overspending, use the value indicated here.

Number of sheathing boards standard length

To sheath the entire roof, you will need the number of boards indicated here. For calculations, a standard 6-meter board length is used.

Volume of sheathing boards

The volume of boards in cubic meters will help you calculate the cost of sheathing.

Approximate weight of sheathing boards

Estimated total weight of sheathing boards. The calculations use average values ​​of density and moisture content for coniferous wood.

A properly selected and installed roof will withstand any weather conditions and will last for decades. What will the roof be like? country house, and what materials it will consist of is determined at the design stage. Technical nuances Designing is best left to professionals. Before making the final choice, the future owner needs to get an idea of ​​the features various types roofs and (which is important) about the amount that the chosen structure and roofing material will cost. At this stage, a roofing calculator will help you calculate the material for a gable roof, or any other - this quick way get a detailed answer.

The calculator will help you estimate the cost of a roof in the early planning stages Source colourbox.com

Online roofing calculator

To find out the approximate cost of roofing of various types, use the following calculator:

Parameters for calculating roofs and roofing materials

Before calculating the roof of a house, the calculator will ask for certain data. One of them is the type of roof. There are two criteria by which you can determine the type of roof: the angle of the roof and the number of slopes (planes). If the angle of inclination of the roof is zero, the roof is called flat; if it is greater than zero, it is called pitched. Pitched structures, in turn, are divided into types, depending on the number of slopes. In private low-rise construction, several types of roofs are common, including:

Single-pitch. It looks rather modest, but it is the simplest in design and the least expensive to build. It is a plane supported by walls of different heights. A shed roof can be seen on a garage, shed or modern project in high-tech style. Such designs are described by a small number of parameters and are calculated for all online calculator Oh.

Common forms pitched structures Source remokna.in.ua

Gable (gable). The most common, classic version with two rectangular inclined planes connected by a ridge, and a centuries-old history. The vertical triangular planes between the slopes are called pediments (gables). In modern private construction, the symmetry of the slopes is an optional condition. They can have different slopes and vary in size (broken), which opens up great design possibilities roofing structures. Gable roof - ideal option for the installation of an attic. For calculations on the online calculator, parameters such as the length and width of the slopes, the length of the overhangs and the height of the structure are used.

Hip (hatched). The main slopes are called hips and have the form of trapezoids, and the pediments are not located vertically, but at an angle, turning into slopes. Hip system much more difficult to develop and install than the previous ones, but this is compensated by increased structural stability. In addition, the hip roof allows you to raise the ceiling for the attic, making it much more comfortable. Calculating a hip roof using an online calculator has certain subtleties (the base can be square or rectangular) and includes the angle of inclination of the slopes.

Multi-forceps. A complex structure consisting of several tongs (gable elements). Calculating such a roof is a job for an experienced architect. There are online calculators that calculate the roof area of ​​a three-gable roof, but the calculation results they give are very approximate.

The complexity of the rafter system of a multi-gable roof excludes independent planning Source yandex.ru

Attic. The slope consists of two elements: the lower, steeper one, and the upper, flatter one. This design allows you to increase usable area premises, but to calculate it using an online calculator, you will need at least a preliminary drawing and understanding of the structure of the rafter system.

Types of roofing materials

The issue of roofing material is also decided at the design stage. His choice is influenced not only by the designer’s preferences, but also by more realistic factors, including the amount of precipitation and wind strength in the region. The online calculator makes it possible to find out not only the quantity, but also the cost of the selected material. Typically a roof calculator is configured to calculate the following materials:

Corrugated sheet.

Metal tiles.

Soft (roll) roofing.

Seam covering(steel, aluminum or copper).

Roof tiles. Ceramic (piece), flexible (soft), cement-sand, composite.

Slate(mainly for outbuildings).

Calculator for calculating metal tiles (works with several types of roofs) Source amvita.ru

Basic elements of roofing structure

Roof country cottage- this is not only a decorative detail and a business card of the building, but also a complex engineering system. It consists of a variety of building parts, the main ones of which are the following:

Mauerlat. The beam that is laid on top load-bearing walls. It supports the rafter system and transfers the load from the roof to the building.

Rafters. Beams or boards located at an angle are the basis of the system. The online calculator allows you to calculate some parameters of the rafter system.

Auxiliary elements. Racks, beams, purlins and tie-downs serve to secure the rafters and strengthen the structure.

Horse. The top edge of the roof, the intersection of the slopes.

Lathing. A lattice structure onto which the roofing material is attached. Some types of roofing require a continuous deck. The sheathing parameters on the online calculator are calculated quite well, especially for roofs of simple construction.

Main structural elements of the rafter system Source kafmt.ru

On our website you can find contacts of construction companies that offer country house design services. You can communicate directly with representatives by visiting the “Low-Rise Country” exhibition of houses.

What is calculated on an online calculator: types and possibilities

Even with ready-made drawings in hand, the future owner will not always find the time to carefully study them and painstaking calculations on paper. Among all the ways to solve the question of how to calculate the roof of a house, an online calculator will become the best option. There are two types of calculators that perform a certain type of calculation:

Standard roof calculator

The most common type, which allows you to obtain the basic parameters, from the angle of the rafters to the permissible load on the roof. When calculating roofing materials, as a rule, there are all popular options (all kinds of tiles, slate, ondulin and other materials). There are a wide range of calculators for calculating single-, gable- and hip roofs; there are settlement services hip roof or attic. The online gable or shed roof calculator is designed for simple tasks; more advanced calculation programs must be downloaded and installed on your computer.

Fragment of an online calculator for calculating a hip roof Source citymang.ru

Construction calculator

Complex calculation algorithms are used for calculations; as a result, you can get not only tables of numbers, but also a set of detailed drawings, as well as 3D visualization. In a construction calculator, as a rule, you can calculate any type of roof. In addition to the basic parameters, you can find out how much lumber you will need, select optimal insulation and vapor barrier. The drawings will show the layout of the rafter system and sheathing and will allow you to check the correct angle of inclination and location of the rafters.

Online calculator device for calculating a gable roof

The gable roof rafter system calculator is an easy-to-use mechanism that allows you to perform basic structural calculations. The interface of any service has a convenient and intuitive appearance and looks like a set of empty fields with an explanation. For the convenience of visitors, schematic images are placed nearby on the page. various types roofs with parameters marked on them.

Before starting calculations, you should familiarize yourself with the designation of the fields Source stankotec.ru

The user needs to enter in each field desired value(size) or select an option from the available ones. When filling out, you should pay attention to the dimensions - parameters can be entered in cm or mm. After filling in the fields, you press the calculation button and get the desired result in the form of the following data:

Number of roofing materials. The calculator will allow you to calculate the amount of metal tiles (or other material) for a country house with a gable, hip or other roof.

Calculation of the rafter system and roof gable. Based on the specified wall width and height to the ridge, the service will help determine the length of the rafters and the area of ​​the roof gable.

To calculate the material for the roof of a house, the “gable” program will require you to enter the following values:

Roof dimensions. There are separate fields for entering height, width (on each side) and overhang.

Rafter dimensions. The width and thickness are set, as well as the distance between the rafters and the distance to the edge of the roof.

Video description

About calculating the roof using a construction calculator in the following video:

Sheathing parameters. Enter the width and thickness of the boards, the distance between them.

Roofing material parameters. If a roofing sheet is selected, specify the height, width and overlap of the sheet.

The result of the calculation will be the following parameters:

Roof size. Height and width of the canvas, total area.

Rafters. Number and length of rafters. The volume of required material (in cubic meters) is also calculated.

Lathing. The calculation shows the number of rows of boards, the length of each part and the volume of the sheathing boards.

Roofing material. The area of ​​hydro- and vapor barrier is calculated. So, if roofing felt or glassine is selected as the under-roofing material, the calculator shows the required number of rolls (based on the size of the roll), taking into account the overlap.

Roofing material. The calculator determines not only the coverage area, but also the weight and required amount of the selected material.

Calculator for calculating the main elements of a gable roof Source stankotec.ru

Calculation of additional parameters

Many online services calculate additional, no less useful quantities:

Roof angle. The calculator will determine not only the optimal angle, but also tell you whether it is suitable for the selected roofing material. By changing the height of the rise or the width of the base, you can achieve full compliance of the angle with the material.

Calculation of wind and snow load . For some areas, this load may be a determining factor in choosing a roof type. You will need to enter into the calculator additional information: region of construction, type of terrain, height to the ridge of the building, type of wood for the rafters.

Chimney calculation. For safe operation it is necessary to determine the height of the chimney relative to the roof ridge. Incorrect design can affect the stable operation of heating devices and lead to unplanned financial expenses (if rework is required).

When calculating the chimney, the presence of obstacles near the home is taken into account Source stroim-dom.radiomoon.ru

Limitations in using the online calculator

Roofing calculators offered by online resources are an affordable and very fast way to get the necessary information. But like any mechanisms designed for the mass user, such calculators tend to use generalized calculation techniques. The worst thing is that the calculation process is hidden from the person using the calculator; It is very difficult to double-check the output information.

The calculator for calculating the roof of a house may contain certain (acceptable) variations in parameters, which, nevertheless, will affect the final result. Possible results that may contain inaccurate (approximate) values ​​include:

Determining the total amount of roofing material

Building materials are never laid joint-to-joint, so the roof surface area and roofing area will always be different. When calculating, the roof area is usually increased by 15% - this provides a margin when forming an overlap.

Video description

About calculating a gable roof free calculator in the following video:

If the roof has complex design, the calculation also becomes more complicated, since an experienced designer simultaneously solves the additional problem of waste minimization. For such purposes, different algorithms are used (with different accumulating errors and with different results), which of them is included in the calculator is known only to its developers.

It is believed that the calculator helps you save on the purchase of building materials. But when installing the roof complex shape in this case, it often turns out that extra (often expensive) materials were purchased. The opposite situation, when there is not enough material and you have to pay for an unplanned purchase and delivery, is no less annoying.

Determining the slope for a roof

Building codes require minimum slopes for each roofing material. They are calculated taking into account the slope of the roof and additional indicators (wind and snow load). Specialists perform calculations according to SNiP “Loads and Impacts” standards and additional design standards. It is not possible to check what indicators the roofing calculator uses in its work.

Some calculators take into account additional options(presence of skylights and drainage systems) Source stankotec.ru

Roof calculation: how to avoid mistakes

In calculations you can go one of the following ways:

Calculate the roof manually. If you have basic knowledge of geometry, do preliminary calculations You can also do it manually. To do this, just stock up on paper, a pencil, a regular calculator, and remember that any roof is a set of simple shapes (rectangles and triangles), the calculation of the area of ​​which is described by the simplest formulas from school course. The method does not work well if the calculations become more complicated. They take a lot of time and increase the risk of error.

Roof calculations should be carried out in online service . It should be taken into account that the values ​​are always averaged; Your planned home may require a custom solution.

Check the roof calculation manually using a calculator. Roofing online calculators are in a convenient way simulate the roof structure and find out the required amount of building materials. The calculation of simple structures is quite easy to check, but if you do not have a specialized education, confusion with coefficients and percentages is inevitable. Differing results will cause lengthy double-checks and searches for errors, as well as mistrust in the abilities of the calculator (or your own).

Checking the calculation results will require time and care Source transsib6.ru

Professional roof calculation. For preliminary calculations in order to determine the materials and design of the roof, this method is clearly not suitable. But when ordering a turnkey house, construction company will prepare a full-fledged project, which will indicate all calculations and estimates. In addition, specialists can make preliminary calculations for you even at the stage of discussing the project.

Conclusion

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

One of the varieties rafter roof – gable. That's enough simple system, which is formed by two slopes. The roof slope is the entire inclined plane through which drainage is provided.

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

Advantages of a gable system

1. Ease of design.
   Calculation bearing capacity And necessary materials for the installation of such a roof is quite simple, since there are options for types and sizes load-bearing structures A little;
2. Easy to install.
   A gable roof does not have complex structural elements. A small number of standard sizes allows you to quickly install all roof elements;
3. Ease of use.
   The fewer different kinks a roof has, the more reliably it protects the home. In the very simple design The gable roof has only one break - the ridge. Such a roof is easier to repair in case of defects;
4. Free space.
   For arranging an attic, a gable roof is preferable, since it “eats up” less space. 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, which has four slopes, 72 cubic meters. For large sizes building volume losses 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. Broken symmetrical.
   The roof slopes have a kink. Significantly increases the height of the room;
4. Broken asymmetrical.
   The attic or attic space turns out to be 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 rafter system of a gable roof of a building are the Mauerlat, crossbar and rafters. The Mauerlat works in compression, so its cross-section can be taken conditionally.

The crossbar and rafter legs experience a bending moment.

Such structures are calculated based on strength and rigidity. For small buildings, you can choose their cross-section approximately, but for serious buildings, for the sake of safety and saving material, the calculation of the rafter system should be performed by a professional.

Load from the roof's own weight

To perform the calculation you need to know the load per 1 square meter. roofs.

To do this, you need to add up masses of 1 square meter. all roofing materials:

1. binder(if it exists, it is most often made of plasterboard);
2. rafter legs. To calculate the weight of the rafters square meter roofing, you need to find the mass of a linear meter of a rafter leg and divide this number by the pitch of the rafters in meters. For calculation, you can take the approximate cross-section of the rafters; the area of ​​this cross-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. sheathing. To ensure a reserve, you can take into account a continuous sheathing. For example, 1 sq.m. sheathing made from boards 32 mm thick will weigh approximately 25 kilograms;
5. roofing material. Weight 1 sq.m. coatings are usually specified by the manufacturer.

Snow load

The snow load is different for each area and is equal to the weight of the snow cover on a 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 snow load distribution map and select the right number based on the construction area.

Roof angle

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

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

If using an engineering calculator is difficult, the arctangent can be found using an online calculator.

Calculation of rafter pitch

The pitch of the attic roof rafters should be chosen based on the convenience of installing the insulation. Mats usually have a width of 60 centimeters, so the pitch of the rafters should be chosen so that the clear distance between them is 58 or 118 centimeters. Two centimeters will allow you to install the insulation boards very tightly, which will allow it to stay between the rafters and improve thermal insulation.

Rafter leg length

Leg length can be easily calculated using the formula:
L/cosα,
here L is the distance from the roof ridge to inner surface outer wall in plan, and cosα is the cosine of the roof inclination angle. For rigid fastening, you need to increase the size of the notch.

Section of the rafter leg

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. find the load on 1 linear meter rafters
   q =(1.1*weight of 1 sq.m. roof*cosα + 1.4*normative snow load*cosα2)* rafter spacing;
2. we find W.
   W= q*1.25*rafter flight/130;
3. 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, you need to set the width and find the height by solving a simple quadratic equation. The width can be set to 5 cm, 7.5 cm, 10 cm, 15 cm. For small spans, a width of 15 cm is not practical.

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

Basic roof elements

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

Rafter roof with attic

To fully utilize the space under the roof, you can design an attic.

Attic floor- this is the floor in attic space. The attic façade is formed entirely or partially by the roof surfaces. According to regulatory documents In order for a room to be considered an attic, the line of intersection of the roof plane 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.

Roof attic floor differs from attic roofing in the presence of insulation in its design. Most often for insulation mansard roof mineral wool boards are used.

Lighting the attic space can be done in three ways:

1. window openings in gables;
2. dormer windows;
3. attic windows.

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

Dormer window - This is a window specifically designed for use on rafter roofs. It is installed in the plane of the slope in an inclined position. The roof window must withstand the calculated snow load. It is better not to use this type of window in roofs with a slight slope.

Selection of roofing material

Once the appearance of the roof has been determined, you can begin to select the material. There are several types modern coatings. In the list below, material options are listed in descending order of average market cost.

1. Ceramic tiles.
   Ceramics, as a roofing material, has long history. The ceramic roof is reliable and durable. The disadvantages of this material are the price and large mass. Under the roof from ceramic tiles you will have to install a reinforced rafter system and sheathing;
2. Cement-sand tiles.
   It has almost all the characteristics of ceramic, but costs a little less;
3. Flexible bitumen shingles.
   Has good soundproofing characteristics. Thanks to the rough surface, the tiles are able to prevent snow from moving off the roof. Requires continuous sheathing; usually a layer of moisture-resistant plywood is used. Cannot be used on roofs with large slopes;
4. Metal tiles.
   Compared to previous coatings, it is lighter in weight. Easy to install. Minus metal roofing is that when it rains it can be too noisy.
5. Seam roofing.
   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 labor-intensive than metal and flexible tiles. The same “noisy” as metal tiles.

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

Types of rafter systems

Structural roof truss systems can be of three types:

1. Layered rafters.
   The rafters rest on two sides. From below - on the mauerlat, from above - on the crossbar. Racks and struts can be used as intermediate supports. Most often used in buildings with a small distance between the ends or where it is possible to place racks or a wall in the middle of the attic.
   For large rafter spans (large distances between longitudinal walls), racks, struts or tie rods can be additionally used.
   Layered rafters are easy to calculate.
   Typically, the most powerful element of such a system is the crossbar, which carries half the load of the entire roof structure.
2. Hanging rafters.
   If it is not possible to use the crossbar as an upper support, it is reasonable to use this rafter system.
   The hanging rafters rest only on the mauerlat, and at the top point they are connected to each other using an overlay.
   This rafter system operates under load like a truss. The greatest pressure occurs on the outer walls. A horizontal force arises - thrust, which can lead to displacement of the walls. In the design of hanging rafters, the spacer force is absorbed by the tightening, which tightens the rafter legs and prevents them from moving apart.
   Hanging rafters are classified depending on the location of the tie:
   1) Triangular three-hinged arch.
   The tie and rafters form a triangle. The tightening is located at the ceiling level;
   2) Triangular three-hinged arch with suspension.
   With a large span of rafters, the tightening may not meet the deflection requirements. To prevent it from sagging, the tie is suspended from the ridge. But with such a system, just as with the system of layered rafters, a row of racks is formed in the middle of the attic;
   3) Triangular three-hinged arch with a raised drawstring.
   The tightening is most often located at the ceiling level attic room. This scheme is less beneficial from the point of view of the operation of the structure. The higher the tightening is located, the more thrust it absorbs.
   Hanging rafters must be treated as a triangular truss, which complicates the calculation.
3. Combined rafters.
   TO combined system can be attributed to spacer layered rafters. They require both bolt installation and tightening. Unlike previous options, in which the rafters are hinged to the mauerlat, here the rafter leg is rigidly attached, so a thrust 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 would be to build around the perimeter of a reinforced concrete belt.

Installation of the rafter system

Installation occurs in the following order:

1. laying the Mauerlat;
2. installation of a crossbar (if there is one);
3. rafter layout;
4. insulation (if any);
5. sheathing;
6. roofing material.

Attaching the rafter leg to the mauerlat can be rigid and hinged.

Hinge fastening

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. using special fasteners, a metal “sled”;
2. using a mounting plate;
3. A cut is made on the rafter leg. The junction of the rafter leg and the Mauerlat is fixed with nails.

Rigid fastening

The rafter is attached to the mauerlat with a notch and is securely fixed with nails driven at an angle relative to each other. One nail is driven vertically onto the surface of the Mauerlat. This connection eliminates displacement in any plane.

The gable rafter system has undeniable advantages. You can design and install it yourself, you just need to take this issue responsibly and think through everything down to the smallest detail.

X- width of the house
Y- roof height
C- overhang size
B- roof length
Y2- extra height
X2- extra width

Reference

The program works in two modes: a simple gable roof and a roof with two side gables (side roofs), type 1 and type 2.

Attention! If you have a roof with one side gable, then for the calculation use first type 1, then type 2. And from the data obtained, calculate the quantity building materials: rafters, sheathing boards, roofing and sheet materials.
Otherwise there may be an error in the calculation. After all, the program takes into account the cutouts in the main roof for the roofs of the side gables.

In the calculation you will see several numbers: the size or volume of the building material of half the roof and in brackets - the full size or volume.
In calculation additional roof- the full size and volume, and two numbers in parentheses: the size and volume of one and two additional roofs.

Attention! When calculating sheet roofing material, keep in mind that the program calculates by roof area.
For example, 2.8 rows times 7.7 sheets per row. During actual construction, 3 rows are laid.
For more accurate calculation the number of roofing sheets, the height of the sheet must be reduced in the calculation until a whole number of rows is obtained.
Don't forget to set the amount of overlap more precisely.

When calculating the volume of material for the rafters of the main roof, in mode type 2, the program does not take into account the cutout for the side gable. This is due to some implementation difficulties in the program.
Maybe I'll solve this in the future.
However, the excess rafter material is unlikely to disappear, or make some adjustments to your calculations.
There will also be a separate program for more intelligent calculation of sheet roofing materials.

And don’t forget that you need to buy building materials with some reserve for waste.

Do you want to calculate the rafter system quickly, without studying theory and with reliable results? Take advantage online calculator on the website!

Can you imagine a person without bones? In the same way, a pitched roof without a rafter system is more like a structure from a fairy tale about the three little pigs, which can easily be swept away by natural elements. A strong and reliable rafter system is the key to the durability of the roof structure. In order to design a high-quality rafter system, it is necessary to take into account and predict the main factors affecting the strength of the structure.

Take into account all the bends of the roof, correction factors for uneven distribution of snow over the surface, snow drift by the wind, slope of the slopes, all aerodynamic coefficients, forces of influence on the structural elements of the roof, and so on - calculate all this as close as possible to the real situation, and also take into account everything loads and skillfully assembling their combinations is not an easy task.

If you want to understand it thoroughly, a list of useful literature is given at the end of the article. Of course, a strength of strength course for a complete understanding of the principles and impeccable calculation of the rafter system cannot be fit into one article, so we will present the main points for simplified versioncalculation.

Load classification

Loads on the rafter system are classified into:

1) Basic:

• permanent loads: the weight of the rafters and roof themselves,
• long-term loads- snow and temperature loads with a reduced design value (used when it is necessary to take into account the influence of load duration when testing endurance),
• variable short-term influence- snow and temperature effects at the full calculated value.

2) Additional- wind pressure, weight of builders, ice loads.

3) Force majeure- explosions, seismic activity, fire, accidents.

To carry out the calculation of the rafter system, it is customary to calculate the maximum loads in order to then, based on the calculated values, determine the parameters of the elements of the rafter system that can withstand these loads.

Calculation of the rafter system pitched roofs produced according to two limit states:

a) The limit at which structural failure occurs. The maximum possible loads on the structural strength of the rafters should be less than the maximum permissible.

b) Limit state at which deflections and deformations occur. The resulting deflection of the system under load should be less than the maximum possible.

For more simple calculation Only the first method applies.

Calculation of snow loads on the roof

To count snow load use the following formula: Ms = Q x Ks x Kc

Q- the weight of the snow cover covering 1 m2 of a flat horizontal roof surface. Depends on the territory and is determined from the map in Figure No. X for the second limit state - calculation of deflection (when the house is located at the junction of two zones, a snow load with a large value is selected).

For strength calculations according to the first type, the load value is selected according to the area of ​​residence on the map (the first digit in the indicated fraction is the numerator), or is taken from table No. 1:

The first value in the table is measured in kPa, in parentheses the desired converted value is in kg/m2.

Ks- correction factor for the roof slope angle.

• For roofs with steep slopes with an angle of more than 60 degrees, snow loads are not taken into account, Ks=0 (snow does not accumulate on steeply pitched roofs).
• For roofs with an angle from 25 to 60, the coefficient is taken 0.7.
• For others it is equal to 1.

The angle of the roof can be determined online roof calculator the appropriate type.

Kc- coefficient of wind removal of snow from roofs. Assuming a flat roof with a slope angle of 7-12 degrees in areas on the map with a wind speed of 4 m/s, Kc is taken = 0.85. The map shows zoning based on wind speed.

Drift factor Kc is not taken into account in areas with January temperatures warmer than -5 degrees, since an ice crust forms on the roof and snow does not blow off. The coefficient is not taken into account if the building is blocked from the wind by a taller neighboring building.

The snow falls unevenly. Often, a so-called snow bag is formed on the leeward side, especially at joints and kinks (valley). Therefore, if you want strong roof, keep the pitch of the rafters to a minimum in this place, and also pay close attention to the recommendations of the roofing material manufacturers - snow can break off the overhang if it is of the wrong size.

We remind you that the calculation given above is presented to your attention in a simplified form. For a more reliable calculation, we recommend multiplying the result by the load safety factor (for snow load = 1.4).

Calculation of wind loads on the rafter system

We've sorted out the snow pressure, now let's move on to calculating the wind influence.

Regardless of the angle of the slope, the wind has a strong impact on the roof: it tries to throw off a steeply pitched roof, more flat roof- lift from the leeward side.

To calculate the wind load, its horizontal direction is taken into account, while it blows bidirectionally: on the facade and on the roof slope. In the first case, the flow is divided into several - part goes down to the foundation, part of the flow tangentially from below vertically presses on the roof overhang, trying to lift it.

In the second case, acting on the roof slopes, the wind presses perpendicular to the slope, pressing it in; a vortex is also formed tangentially on the windward side, going around the ridge and turning into a lifting force on the leeward side, due to the difference in wind pressure on both sides.

To calculate the average wind load use the formula

Mv = Wo x Kv x Kc x strength factor,

Where Wo- wind pressure load determined from the map

Kv- wind pressure correction factor, depending on the height of the building and the terrain.

Kc- aerodynamic coefficient, depends on the geometry of the roof structure and wind direction. Values ​​are negative for the leeward side, positive for the windward side

For pitched roof it is necessary to take the coefficient from the table for Ce1.

To simplify the calculation, it is easier to take the maximum value of C, equal to 0.8.

Calculation of own weight, roofing pie

To calculate permanent load you need to calculate the weight of the roof ( roofing pie-see Figure X below) per 1 m2, the resulting weight must be multiplied by a correction factor of 1.1 - the rafter system must withstand this load throughout its entire service life.

The weight of the roof consists of:

1. the volume of wood (m3) used as sheathing is multiplied by the density of the wood (500 kg/m3)
2. weight of the rafter system
3. weight of 1m2 roofing material
4. weight 1m2 of insulation weight
5. weight of 1m2 of finishing material
6. weight 1m2 of waterproofing.

All these parameters can be easily obtained by checking this data with the seller, or looking at the main characteristics on the label: m3, m2, density, thickness - perform simple arithmetic operations.

Example: for insulation with a density of 35 kg/m3, packed in a roll 10 cm or 0.1 m thick, 10 m long and 1.2 m wide, weight 1 m2 will be equal to (0.1 x 1.2 x 10) x 35 / (0.1 x 1.2) = 3.5 kg/m2. The weight of other materials can be calculated using the same principle, just do not forget to convert centimeters to meters.

More often the roof load per 1 m2 does not exceed 50 kg, therefore, when making calculations, this value is used, multiplied by 1.1, i.e. use 55 kg/m2, which itself is taken as a reserve.

More data can be taken from the table below:

Collecting loads

According to the simplified version, now it is necessary to add up all the loads found above by simple summation, we will get the final load in kilograms per 1 m2 of roof.

Calculation of the rafter system

After collecting the main loads, you can already determine the main parameters of the rafters.

We calculate using the formula: N = rafter spacing x Q, Where

N - uniform load on the rafter leg, kg/m
rafter pitch - distance between rafters, m
Q - final roof load calculated above, kg/m²

It is clear from the formula that by changing the distance between the rafters, you can regulate the uniform load on each rafter leg. Typically, the pitch of the rafters is in the range from 0.6 to 1.2 m. For a roof with insulation, when choosing a pitch, it is reasonable to focus on the parameters of the insulation sheet.

In general, when determining the installation pitch of the rafters, it is better to proceed from economic considerations: calculate all the options for the location of the rafters and choose the cheapest and optimal in terms of quantitative consumption of materials for the rafter structure.

• Calculation of the cross-section and thickness of the rafter leg

In the construction of private houses and cottages, when choosing the section and thickness of the rafters, they are guided by the table below (the cross section of the rafters is indicated in mm). The table contains average values ​​for the territory of Russia, and also takes into account the sizes of building materials on the market. In general, this table is enough to determine what cross-section of timber you need to purchase.

However, we should not forget that the dimensions of the rafter leg depend on the design of the rafter system, the quality of the material used, constant and variable loads exerted on the roof.

In practice, when building a private residential building, boards with a cross section of 50x150 mm (thickness x width) are most often used for rafters.

Independent calculation of rafter cross-section

As mentioned above, rafters are calculated based on maximum load and deflection. In the first case, the maximum bending moment is taken into account, in the second, the section of the rafter leg is checked for resistance to deflection over the longest section of the span. The formulas are quite complex, so we have chosen for you simplified version.

The section thickness (or height) is calculated using the formula:

a) If the roof angle< 30°, стропила рассматриваются как изгибаемые

H ≥ 8.6 x Lm x √(N / (B x Rben))

b) If the roof slope is > 30°, the rafters are flexurally compressed

H ≥ 9.5 x Lm x √(N / (B x Rben))

Designations:

H, cm- rafter height
Lm, m- working section of the longest rafter leg
N, kg/m- distributed load on the rafter leg
B, cm- rafter width
Rizg, kg/cm²- bending resistance of wood

For pine and spruce Rizg depending on the type of wood is equal to:

It is important to check whether the deflection exceeds the permitted value.

The deflection of the rafters should be less L/200- length of the largest span being tested between supports in centimeters divided by 200.

This condition is true if the following inequality is satisfied:

3,125 xNx(Lm)³ / (BxH³) ≤ 1

N (kg/m) - distributed load per linear meter of rafter leg
Lm (m) - working section of the rafter leg of maximum length
B (cm) - section width
H (cm) - section height

If the value is greater than one, it is necessary to increase the rafter parameters B or H.

Sources used:

1. SNiP 2.01.07-85 Loads and impacts with latest changes 2008
2. SNiP II-26-76 “Roofs”
3. SNiP II-25-80 “Wooden structures”
4. SNiP 3.04.01-87 “Insulating and finishing coatings”
5. A.A. Savelyev “Rafter systems” 2000
6. K-G. Götz, Dieter Hoor, Karl Möhler, Julius Natterer “Atlas of wooden structures”