Snow load on the roof. Snow load. Find the total calculated value of the wind load W

The roof constantly protects the building from all weather and climatic manifestations, excluding the contact of all materials with atmospheric or rainwater and being a boundary layer that cuts off the effect of frosty air on the attic.

These are the main and most important functions of the roof in the mind of an unprepared person, they are quite correct, but do not reflect the full list of functional loads and stress experienced.

At the same time, the reality is much harsher than it looks at first glance, and the impact on the roof is not limited to certain material wear.

It is transmitted to almost all load-bearing elements of the building - first of all, to the walls of the building, on which the entire roof directly rests, and ultimately to the foundation.

It is impossible to neglect all the loads that are created, this will lead to a quick (sometimes sudden) destruction of the building.

The main and most dangerous effects on the roof and on the entire structure as a whole are:

• Snow loads.
• Wind loads.

At the same time, the snow acts during certain winter months, absent in warm weather, while the wind creates an effect all year round. Wind loads, having seasonal fluctuations in strength and direction, are constantly present to one degree or another and are dangerous by periodically occurring squall amplifications.

In addition, the intensity of these loads is of a different nature:

• Snow creates constant static pressure which can be adjusted by cleaning the roof and removing clumps. The direction of the acting efforts is constant and never changes.
• The wind acts inconsistently, in jerks, suddenly increasing or abating. The direction can be changed, which makes all roof structures have a solid margin of safety.

Large masses of snow from a roof can suddenly cause damage to property or people in the area where it falls. Besides, intermittent but extremely destructive atmospheric phenomena occur periodically- hurricane winds, heavy snowfalls, especially dangerous in the presence of wet snow, which is an order of magnitude heavier than usual. It is almost impossible to predict the date of such events, and as protective measures, you can only increase the strength and reliability of the roof and rafter system.

Collection of roof loads

Dependence of loads on the angle of inclination of the roof

The angle of inclination of the roof determines the area and power of the roof contact with wind and snow. At the same time, the snow mass has a vertically directed force vector, and the wind pressure, regardless of the direction, is horizontal.

Therefore, taking the angle of inclination steeper, it is possible to reduce the pressure of the snow masses, and sometimes completely eliminate the occurrence of snow accumulations, but at the same time, the "windage" of the roof increases, and the wind stresses increase.

It's obvious that to reduce wind loads, a flat roof would be ideal, whereas it is she who will not allow the masses of snow to slide down and will contribute to the formation of large snowdrifts, which, when melting, can wet the entire building. The way out of the situation is the choice of such an angle of inclination at which the requirements for both snow and wind loads are maximally satisfied, and they have individual values ​​in different regions.

Load versus roof angle

Snow weight per square meter of roof depending on the region

Rainfall is an indicator that directly depends on geography region. More southern regions hardly see snow, more northern regions have a constant seasonal amount of snow masses.

At the same time, high-mountainous areas, regardless of latitude, have high rates of snowfall, which, in combination with frequent and strong winds, creates a lot of problems.

Building Norms and Rules (SNiP), compliance with the provisions of which is mandatory, contain special tables, showing the standard indicators of the amount of snow per unit surface in different regions.

NOTE!

Consideration should be given to the usual state of snow masses in the area. Wet snow is several times heavier than dry snow.

These data are the basis for calculating snow loads, since they are quite reliable, and are also given not in average, but in limiting values ​​that provide an adequate margin of safety during roof construction.

Nevertheless, it is necessary to take into account the structure of the roof, its material, as well as the presence of additional elements that cause accumulation of snow, since they can significantly exceed the standard indicators.

The weight of snow per square meter of roof, depending on the region, is shown in the diagram below.

Snow load region

Calculation of snow load on a flat roof

The design of load-bearing structures is carried out according to the method of limit states, that is, those when the forces being tested cause irreversible deformations or destruction. Therefore, the strength of a flat roof must exceed the value of the snow load for a given region.

There are two types of limit states for roof elements:

• The structure collapses.
• The structure is deformed, breaks down without complete destruction.

Calculations are carried out for both states, with the aim of obtaining a reliable structure that is guaranteed to withstand the load without consequences, but also without unnecessary costs of building materials and labor. For flat roofs, the values ​​of snow loads will be maximum, i.e. the slope correction factor is 1.

Thus, according to the SNiP tables, the total weight of snow on a flat roof will be the value of the standard multiplied by the roof area. Values ​​can reach tens of tons, therefore, buildings with flat roofs in our country are practically not built, especially in regions with high precipitation rates in winter.

Calculation of snow load on the roof online

An example of calculating the snow load will help to clearly demonstrate the procedure, and also show the possible magnitude of snow pressure on the structure of the house.

The snow load on the roof is calculated using the following formula:

S = Sg * µ;

where S- snow pressure per square meter of the roof.

Sg- standard value of snow load for a given region.

µ - a correction factor that takes into account the change in load at different angles of inclination of the roof. From 0 ° to 25 ° the value of µ is taken equal to 1, from 25 ° to 60 ° - 0.7. At angles of inclination of the roof over 60 °, the snow load is not taken into account although in reality there are accumulations of wet snow on steeper surfaces.

Let's calculate the load on the roof with an area of ​​50 square meters, the angle of inclination is 28 ° (µ = 0.7), the region is the Moscow region.

Then the standard load is (according to SNiP data) 180 kg / sq.m.

Multiply 180 by 0.7 - we get a real load of 126 kg / m2.

The total snow pressure on the roof will be: 126 multiplied by the roof area - 50 sq. M. Result - 6300 kg... This is the estimated weight of the snow on the roof.

Snow impact on the roof

The calculation of the wind load is done in a similar way. It is based on the normative value of the wind load in effect in the given region, which is multiplied by the correction factor for the height of the building:

W = Wo * k;

Wo- standard value for the region.

k- a correction factor that takes into account the height above the ground.

Rose of Wind

There are three groups of values:

• For open areas of the earth's surface.
• For woodlands or urban areas with obstacle heights from 10 m.
• For urban settlements or areas with difficult terrain with an obstacle height of 25 m.

All standard values, as well as correction factors, are contained in the SNiP tables and must be taken into account when calculating loads.

CAREFULLY!

When carrying out calculations, one should take into account the independence of snow and wind loads from each other, as well as the simultaneity of their impact. The total roof load is the sum of both values.

In conclusion, it is necessary to emphasize the large magnitude and unevenness of the loads created by snow and winds. Values ​​comparable to the dead weight of the roof cannot be ignored, these values ​​are too serious. The inability to regulate or eliminate their presence forces a response by increasing strength and choosing the right angle of inclination.

All calculations should be based on SNiP, to clarify or check the results, it is recommended to use online calculators, of which there are many on the network. The best way would be to use several calculators and then compare the values ​​obtained. Correct calculation is the basis for a long-term and reliable service of the roof and the entire building.

Useful video

You can learn more about roof loads in this video:

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Various forces act on the roof structure. Calculation of the load on the roof includes such influences as: the weight of the roofing material, rafters and battens, insulation, underlay, snow and wind load. Let's consider separately each of these loads.

Calculation of rafters

If you are building a house yourself, and you do not have sufficient knowledge in the field of engineering and architecture, then the calculation of the roof load can be ordered from a specialized organization or from a private designer. If the building is not so demanding on technical calculations, then everything can be done on your own.

Impact of wind force

Snow load can destroy the roof, but the wind load can also tear the roof off. The greater the angle of the roof slopes, the greater the wind load on the structure. The smaller the angle, the stronger will be the lifting force tending to tear off the roof. That is why the calculation of the gable roof area is so important. To begin with, determine the length of the rafter leg. Here, knowledge of the school geometry course will come in handy, since the rafter makes a right-angled triangle with the adjacent walls, therefore, by calculating the length of the hypotenuse, you can determine the required indicator.

It is a little more difficult to calculate the cross-section of the rafters and the distance between them. To do this, we will calculate the wind load on the roof using the formula: Wр = W * k * C. W - wind pressure, which is taken from the SNiP tables. k is a coefficient depending on the height of the building, it is also indicated in the above-mentioned normative document. C is the aerodynamic coefficient used to calculate the upwind and leeward lift.

Coefficient C can have both positive and negative values. The first case occurs if the wind presses on the surface of the slopes, this is true for large angles. The second case occurs on sloping roofs, when the wind "flows" along the slopes. To counteract these forces, depending on the pitch of the rafters, so-called "ruffs" are installed in the walls of the house. These are metal pins to which the rafter legs are tied with wire. In windy regions, each rafter is tied, under normal conditions this is done through one beam, having previously performed according to available data.

Calculation of floor beams, see the video:

Roof weight load

The weight of the roofing material itself has a serious impact on the characteristics of the rafter system. At the same time, different materials can differ significantly in their weight. The more the roof weighs, the greater the angle of inclination of the slopes should be. You also need to know how to calculate the square meters of the roof, since the larger its area, the more it will depend on the influence of external loads.

The force of roof pressure on the rafters can be calculated by knowing the characteristics of the material. They are often indicated in the technical data or instructions from the manufacturer. Depending on the type of roofing material, a certain sheathing option is selected. So, to create it, OSB board, plywood or edged board is used. The average weight of these materials can be obtained from regulatory tables or technical data from the manufacturer. For example, under a slate roof, bars with a cross section of 4 * 6 or 6 * 6 cm are used, while under bituminous shingles - OSB boards or plywood.

The calculation of the square of the roof depends on its type. very easy for pitched roofs. In more complex structures, the roof should be divided into elementary figures - rectangles and triangles, the area of ​​which is easily determined (for more details: ""). It is also important to consider the roof overhangs on the eaves. The distance between the rafters is determined based on the thickness of the roofing material.

No less important is the heat engineering calculation of the roof, on the basis of which the insulation and its thickness are selected. These two factors greatly influence the total weight of the roof structure. In addition, this includes the weight of the vapor and waterproofing, as well as the inner lining of the attic room. The thickness of the insulation is calculated by the formula: T = R * L. Where R is the thermal resistance of the structure that will be insulated, L is the thermal conductivity of the selected insulation (selected according to SNiP II-3-79).

Suppose that the roof is insulated with URSA M-20 glass wool, the house is located in the central region. Then the thickness of the insulation will be: T = 4.7 * 0.038 = 0.18 m = 18 cm. In this case, 4.7 is the thermal resistance taken from the SNiP standards, and 0.038 is the thermal conductivity coefficient, which was specified by the manufacturer of the material. Knowing the density of the insulation (indicated in the technical data) equal to 18-21 kg / m2, you can calculate the weight of the material.

Similarly, the weight of the waterproofing and vapor barrier, as well as the finishing material, is calculated. The calculation of roof heating is also important, since it affects the thickness of the insulation. Also, the heating system that will be installed in the attic will be added to the weight of the roof structure.

In order to take into account the weight of the rafter structure itself, you should draw its plan. The calculation takes into account the average values ​​for layered rafters and girders - 5-10 kg / sq. M, for hanging rafters - 10-15 kg / sq. M. To obtain a certain margin of safety of the structure, the resulting loads are multiplied by a factor of 1.1.

In order to more accurately determine the weight loads on the roof, it is necessary to carry out a thermal calculation of the roof, an example of which can be found on the pages of our portal.

When designing a roof, it is necessary to take into account the loads acting on it - snow and wind. To determine the indicators of these values, you can contact a special construction organization, where engineers will help you with calculations. But if you want to do everything yourself and do not doubt your abilities, then here you will find the necessary formulas with a detailed description of the quantities that will be needed in the calculation. So, first, let's figure out what these loads are and why they must be taken into account.

The Russian climate is very diverse. It is important to understand that the roof of a house under construction will be influenced by temperature changes, wind pressure, precipitation and other physical and mechanical factors. Moreover, the degree of their influence will directly depend on the construction area. All this will put pressure not only on the roof railing - the roof, but also on supporting structures such as rafters and battens. You have to understand that a house is a single structure. Through a chain reaction, the load from the roof is transferred to the walls, and from them to the foundation. Therefore, it is important to calculate everything to the smallest detail.

The snow cover that forms on the roof of the house during the winter periods puts a certain pressure on it. The further north the area, the more snow. It seems that the threat of breakdowns is higher, but you should be more careful when designing a house in an area where there is a periodic change in temperatures that can cause snow to melt and its subsequent freezing. The average weight of snow is 100 kg / m3, but in a wet state it can reach 300 kg / m3. In such cases, the snow mass can cause deformation of the rafter system, waterproofing and thermal insulation, which will lead to roof leaks. Such weather conditions will also affect the rapid and uneven snow cover from the roof, which can be dangerous for humans.

The greater the slope of the roof, the less snow deposits will linger on it. But if your roof has a complex shape, then at the joints of the roof, where internal corners are formed, snow can collect, which will contribute to the formation of an uneven load. It is best to install snow guards in areas where the amount of precipitation is high enough so that snow collected near the edge of the eaves cannot damage the drainage system. Snow removal can be done independently, but this process cannot be called 100% safe.

In order to ensure a safe snow melt and prevent the formation of icicles, a cable heating system is used. It can be controlled automatically or manually. Depends on your desire and choice. The heating elements of such a system are located along the entire edge of the roof in front of the gutter.

For Russia, the value of the snow load will depend on the construction area. A special map will help determine how much snow cover will be in your area.

The technology for calculating the snow load: S = Sg * m, where Sg is the calculated value of the weight of the snow cover on 1 m2 of the horizontal surface of the earth, taken from the table, and m is the coefficient of transition from the weight of the snow cover of the earth to the snow load on the cover.

The calculated value of the weight of the snow cover Sg is taken depending on the snow region of the Russian Federation.

Determination of the snow load of the area

Coefficient m depends on the angle of inclination of the roof slope, at the angles of inclination of the roof slope:

less than 25 degrees m is taken equal to 1

from 25 to 60 degrees, the value of m is taken equal to 0.7 (approximately, for each slope its own value)

more than 60 degrees, the value of m, in the calculation of the total snow load, is not taken into account.

The wind exerts lateral pressure on the walls of the house and the roof. The air flow, colliding with an obstacle, is distributed, going down to the foundation and up to the eaves overhang of the roof. If you do not calculate the wind pressure, then the roofing can simply be ripped off by the hurricane wind. Such destruction cannot always be corrected with some kind of cosmetic repair, often this leads to the need to replace the roof. An important indicator when calculating the effect of wind is the aerodynamic coefficient. It depends on the slope angle of the roof. The steeper the slope, the greater the load will be, and the wind will try to "knock over" the roof. If the angle of your roof is small, then the wind will act on the roof like a lifting force, trying to rip it off and carry it away. In order to prevent this from happening, you need to properly observe the roof structure. The stability of the rafter system depends on the provision of spatial rigidity, which consists of the correct combination of braces, struts and diagonal ties in it, as well as their rigid attachment to each other. In addition, the wind can carry objects that, when they collide with the roof, will leave mechanical damage. To prevent this from happening, you need to carefully choose the roofing and properly organize the crate for its installation.

The wind pressure, as well as the weight of the snow cover, will depend on the construction area. You can determine the zoning on the map below.

Wind load calculation technology

The coefficient k, taking into account the change in wind pressure along the height z, is determined from the table below, depending on the type of terrain. The following terrain types are accepted:

A - open coasts of seas, lakes and reservoirs, deserts, steppes, forest-steppe, tundra;

B - urban areas, woodlands and other areas, evenly covered with obstacles over 10 m high;

C - urban areas with buildings with a height of more than 25 m.

A structure is considered to be located in an area of ​​this type if this area is preserved from the windward side of the structure at a distance of 30h - with a structure height h up to 60 m and 2 km. - at a higher height.

Note: when determining the wind load, the terrain types can be different for different calculated wind directions.

Wind and snow loads when designing canopies

Particular attention should be paid to the calculation for those who are thinking about designing a canopy - for example, for a gazebo or parking lot. Usually, in such cases, an economical design is used that does not have sufficient rigidity. Therefore, the pressure of the snow cannot be ignored. It is recommended to clean the snow on time, avoiding the formation of a snow cover more than 30 cm thick. For a canopy made of wood, it will be more reliable to make a solid sheathing and reinforced rafters. If you have chosen a metal structure, then it must have an appropriate profile thickness. In any case, to select materials of the required stiffness, it is better to use the calculation results.

Examples of calculating snow and wind loads for Moscow and the Moscow region

Example # 1: Calculating snow load

Initial data:

region: Moscow

roof slope: 35 degrees

Let us find the total calculated value of the snow load S:

the total calculated value of the snow load is determined by the formula: S = Sg * m

according to the map of the snow cover zones of the territory of the Russian Federation, we determine the number of the snow region for Moscow: in our case, it is III, which corresponds to the weight of the snow cover according to the table Sg = 180 (kgf / m2);

conversion factor from the weight of the ground snow cover to the snow load on the cover for a roof angle of 35 degrees m = 0.7

we get: S = Sg * m = 180 * 0.7 = 126 (kgf / m2)

Example # 2: Calculation of wind load

Initial data:

region: Moscow

roof slope: 35 degrees

building height: 20 meters

type of terrain: urban areas

Let us find the total calculated value of the wind load W:

The calculated value of the average component of the wind load at a height z above the earth's surface is determined by the formula: W = Wo * k,

Based on the map of wind pressure zones across the territory of the Russian Federation, we determine region I for Moscow

The normative value of the wind load corresponding to the I region, we take Wo = 23 (kgf / m2)

The coefficient k, taking into account the change in wind pressure along the height z, is determined from Table. 6 k = 0.85

We get: W = Wo * k = 23 * 0.85 = 19.55 (kgf / m2)

When building a roof, special attention should be paid to calculating its bearing capacity, since a huge amount of forces are constantly acting on the structure. One of the forces that acts on the roof is the snow load, respectively, with which the roof is built. It is she who determines how thick the supporting elements will be and how to build the rafter system. Its value is calculated using a special formula, according to SNiP.

Snow load and its negative impact

Usually, up to 5% of the snow cover is removed from the pitched roof during the day. It is blown away by the wind, slides down or becomes covered with ice. But the remaining amount negatively affects not only the design, but also the person:

1. The weight of the snow can increase during a bitter frost after warming. In this case, deformations of the rafter system, waterproofing and thermal insulation are possible.
2. The snow load on complex roofs tends to be unevenly distributed.
3. Snow sliding to the cornice can be dangerous for people nearby, so the installation of snow guards is mandatory.
4. Sliding snow, in addition to being a danger to humans, can harm the drainage system. That is why you need to clean it off or install snow protectors in time.

Cleaning the roof from the snow mass

The most effective way to remove snow from the roof is by hand. But it is very dangerous to carry out independently without preliminary preparation. That is why, correctly calculated snow load can help not to remove snow all the time.

The slope of the roof slope has a positive effect on snow removal. The best roofing option for regions where there is a high probability of a large amount of snow is from 45 to 60 degrees.

In order to reduce frost and prevent the formation of icicles, cable heating can be installed around the perimeter of the roof. It can be automated or manual.

Calculation of the snow load on the roof

Even at the design stage of the roof, in order to exclude damage to its structure during heavy precipitation, design measures are carried out. The average weight of snow is 100 kg per cubic meter. meter, and wet precipitation weighs even more, which is 300 kg per 1 cubic meter. meter. Knowing these approximate values, it is quite simple to calculate the permissible snow load.

But this also requires knowledge of the thickness of the falling snow layer. You can measure this indicator on a flat area, and the resulting number can be multiplied by a coefficient that assumes a margin and is equal to 1.5. In order to take into account the regional indicator, you can use a special map. It became the basis for obtaining SNiP rules and other standards. In general, the indicator is determined by the following formula:

S = S calc. * μ

In accordance with this formula, its components are deciphered as follows:

• S calc - the value of the weight per square meter of the horizontal platform.
• μ is the roof slope coefficient.

Usually, as mentioned earlier, calculations are made using the snow load map, which is presented below:

In accordance with SNiP, there are such indicators of the roof slope coefficient:

• If the roof slope is less than 25 degrees, then the coefficient is 1.
• If the roof slope is in the range from 25 to 60 degrees, then the coefficient will be 0.7.
• With a slope of more than 60 degrees, the coefficient may not be taken into account at all.

In this case, the side from which the wind is blowing is also taken into account. This is necessary, since there will be less snow on the windward side than on the leeward side.

In order to better understand how the snow load is calculated, let us present an illustrative example for the Moscow region. The calculated roof has a slope of 30 degrees. So, according to the requirements of SNiP, we make a calculation:

1. In the map we find the location of the Moscow region and reveal that it belongs to the third climatic region. Here the value of the roof load is 180 kg per 1 sq. meter.
2. According to the formula, we calculate the total weight of the snow. To do this, multiply 180 by a factor of 0.7. We get the number 126 kg per sq. meter.
3. Already for this indicator, a rafter system is created, which is calculated according to the maximum numbers.

In addition to this option, there is a complete calculation, which is also presented in SNiP and has a corresponding table there. The calculation is carried out according to the following formula:

Q1 = m * Q

Here m, which is calculated by the interpolation method, is used as an indicator of the coefficient. With a roof slope of 30 degrees, it is 1, and at 60 degrees - 0.

The calculation of the standard indicator can be made. To do this, you need to use an atlas in which changes in SNiP are recorded, or calculate the indicator using the formula: Q2 = 0.7 * Q * m. If the calculation is made for the structure that is mounted in areas with constant winds blowing snow from the roof, then it is necessary to add the C coefficient to the formula. It is equal to 0.85. But there are a number of conditions for adding this indicator. This wind speed is not lower than 4 m / s, the average monthly temperature in the winter months is not higher than -5 degrees, and the slope should be in the range from 12 to 20 degrees.

Important! If it is not clear how to calculate the load yourself, then it is better to contact a specialist.

Features of installing snow guards

If the roof structure is correctly executed, taking into account the calculations, then the snow from the roof may not be removed. And in order to avoid strong slipping, snow holders are installed without fail. Such structures are very convenient and help not to remove snow from the roof during heavy rainfall.

Usually, tubular-type snow guards are installed, which can be used with a snow load of no more than 180 kg per 1 sq. meter. If the weight of the snow cover is greater, then the structures are installed in several rows. SNiP regulates the cases and rules when the installation of snow guards is necessary:

1. The slope is more than 5%, and there is also an external drain.
2. The distance from the edge of the roof to the installed snow guard must be at least 0.6 m.
3. If tubular structures are installed, then only a solid crate is provided under them.

Features of calculating snow load for flat roofs

A sufficiently large amount of snow accumulates on a flat-type roof, therefore, all requirements for calculating the snow load must be met so that the roof can withstand such a weight for a long time.

In most of Russia, flat roofs are not created, since a layer of snow can create an excessive load on the rafter structure. But, if, nevertheless, the project of the house provides for just such a reinforced concrete or other roof and it cannot be replaced, then during installation it is necessary to provide a heating system in order to ensure high-quality drainage of water from it.

Important! A flat roof should have a minimum slope of 2 degrees so that water from the entire surface can drain without problems.

Conclusion

Calculation of the snow load on the roof will help to create an optimal structure of the rafter system, as well as keep the roofing in good condition. The correctness of the calculation depends on the theoretical knowledge in this area, which can be obtained by reading this article.

When building a roof, one of the important technical solutions is the calculation of the maximum snow load, which determines the design of the rafter system, the thickness of the elements of the supporting structure. For Russia, the normative value of the snow load is found according to a special formula, taking into account the area where the house is located and the norms of SNiP. To reduce the likelihood of consequences from excessive weight of the snow mass, when designing the roof, it is imperative to calculate the load value. Particular attention is paid to the need to install snow guards to prevent snow from falling off the roof overhang.

In addition to exerting excessive stress on the roof, the snow mass sometimes causes leaks in the roof. So, with the formation of a strip of ice, free flow of water becomes impossible and melted snow is likely to fall into the under-roof space. The largest snowfalls occur in mountainous regions, where the snow cover reaches several meters in height. But, the most negative consequences from the load occur with periodic thawing, ice and freezing. In this case, deformations of roofing materials, improper operation of the drainage system and an avalanche-like stream of snow from the roof of the house are possible.

Factors of influence of snow load

When calculating the load from snow masses on a pitched roof, one should take into account the fact that up to 5% of the snow mass evaporates during the day. At this time, it can slide, be blown away by the wind, and become covered with an infusion. As a result of these transformations, the following negative consequences arise.:

Methods for cleaning the roof from snow

A reasonable way out of the situation is manual cleaning. But, based on safety for humans, it is extremely dangerous to perform such work. For this reason, the calculation of the load has a significant impact on the structure of the roof, rafter system and other elements of the roof. It has long been known that the steeper the slopes, the less snow will linger on the roof. In regions with a large amount of precipitation in the winter period of the year, the angle of inclination of the roof is from 45 ° to 60 °. At the same time, the calculation shows that a large number of abutments and complex connections provide an uneven load.

To prevent the formation of icicles and ice, cable heating systems are used. The heating element is installed around the perimeter of the roof directly in front of the gutter. To control the heating system, an automatic control system is used or the entire process is manually controlled.

Calculation of snow mass and load according to SNiP

In case of snowfall, the load can deform the elements of the supporting structure of the house, the rafter system, and roofing materials. In order to prevent this, at the design stage, structural analysis is performed depending on the effect of the load. On average, snow weighs about 100 kg / m 3, and when wet, its weight reaches 300 kg / m 3. Knowing these values, it is quite simple to calculate the load on the entire area, guided only by the thickness of the snow layer.

The thickness of the cover should be measured in an open area, after which this value is multiplied by a safety factor of 1.5. To take into account the regional features of the terrain in Russia, a special snow load map is used. On its basis, the requirements of SNiP and other rules are built. The total snow load on the roof is calculated using the formula:

S = S calc. × μ;

S calc. - the estimated value of the weight of snow per 1 m 2 of the horizontal surface of the earth;

μ is a design factor that takes into account the slope of the roof.

On the territory of Russia, the calculated value of the weight of snow per 1m 2 in accordance with SNiP is taken according to a special map, which is presented below.

SNiP stipulates the following values ​​of the coefficient μ:

• with a roof slope of less than 25 °, its value is equal to one;
• with a slope from 25 ° to 60 °, it has a value of 0.7;
• if the slope is more than 60 °, the design factor is not taken into account when calculating the load.

Friends, U-ra, it happened and we are glad to present you an online calculator for calculating snow and wind loads, now you do not need to figure out anything on a piece of paper or in your mind, everything just indicated your parameters and received a load right away. In addition, the calculator can calculate the depth of soil freezing if you know its type. Here is the link to the calculator -> Online Snow and Wind Load Calculator. In addition, we have many other construction calculators, you can see a list of all on this page:

An illustrative example of calculation

Let's take the roof of a house located in the Moscow region and has a slope of 30 °. In this case, SNiP stipulates the following procedure for the production of load calculation:

1. According to the map of the regions of Russia, we determine that the Moscow region is located in the 3rd climatic region, where the standard value of the snow load is 180 kg / m 2.
2. Using the formula from SNiP, we determine the total load: 180 × 0.7 = 126 kg / m 2.
3. Knowing the load from the snow mass, we calculate the rafter system, which is selected based on the maximum loads.

Installation of snow guards

If the calculation is performed correctly, then the snow can not be removed from the roof surface. And to combat its sliding from the eaves, snow holders are used. They are very easy to use and free from the need to remove snow from the roof of the house. In the standard version, tubular structures are used that are capable of operating if the standard snow load does not exceed 180 kg / m 2. With a denser weight, the installation of snow guards in several rows is used. SNiP stipulates the cases of using snow holders:

• with a slope of 5% or more with an external drain;
• snow holders are installed at a distance of 0.6-1.0 meters from the edge of the roof;
• when operating tubular snow holders, a continuous roof lathing should be provided under them.

SNiP also describes the basic structures and geometric dimensions of snow holders, their installation locations and the principle of operation.

Flat roofs

The maximum possible amount of snow accumulates on a flat horizontal surface. The calculation of loads in this case must provide the necessary safety margin of the supporting structure. Flat horizontal roofs are practically not built in regions of Russia with a large amount of atmospheric precipitation. Snow can accumulate on their surface and create an excessive load, which was not taken into account in the calculation. When organizing a drainage system from a horizontal surface, they resort to installing heating, which ensures that water flows from the roof.

The slope towards the drain funnel should be at least 2 °, which will make it possible to collect water from the entire roof.

When building a shed for a gazebo, a car park, a country house, special attention is paid to calculating the load. In most cases, the canopy has a budget design that does not provide for the influence of large loads. In order to increase the reliability of the operation of the canopy, a continuous crate, reinforced rafters and other structural elements are used. Using the results of the calculation, you can get a known value of the load and use materials of the required stiffness for the construction of the canopy.

The calculation of the main loads makes it possible to optimally approach the issue of choosing the design of the rafter system. This will ensure a long service life of the roof covering, increase its reliability and operational safety. Installation of snow holders near the eaves allows you to protect people from slipping snow masses dangerous for humans. In addition, there is no need for manual cleaning. An integrated approach to the design of the roof also includes the option of installing a cable heating system, which will ensure the stable operation of the drainage system in any weather.