The topic of snow in September is not very relevant even for us, residents of Siberia. However... the “sleigh” should already be ready, despite the fact that we still continue to ride on “carts”. Moments come to mind when after heavy snowfall in winter and before the snow melts in spring...
Owners various buildings- from bathhouses, sheds and greenhouses to huge swimming pools, stadiums, workshops, warehouses - they are puzzled by two questions arising from each other: “Will the roof withstand or not withstand the mass of snow accumulated on it? Should I throw this snow off the roof or not?”
Snow load on a roof is a serious issue and cannot tolerate an amateurish approach. I will try to present information about snow as briefly and clearly as possible and provide assistance in resolving the issues raised above.
How much does snow weigh?
Anyone who has had to shovel snow knows that snow can be very light and incredibly heavy.
Fluffy light snow that fell in relatively frosty weather with an air temperature of about -10˚C has a density of about 100 kg/m3.
At the end of autumn and at the beginning of winter, the specific gravity of snow lying on horizontal and slightly inclined surfaces is usually 160 ± 40 kg/m3.
During prolonged thaws, the specific gravity of snow begins to increase significantly (the snow “sits” like in spring), sometimes reaching values of 700 kg/m3. This is why in warmer areas the snow density is always greater than in cold northern areas.
By mid-winter, the snow thickens under the influence of the sun, wind and pressure upper layers snowdrifts on the lower layers. Specific gravity becomes equal to 280±70 kg/m3.
By the end of winter, under the influence of more intense sun and February winds, the density of snow crust can become 400±100 kg/m3, sometimes reaching 600 kg/m3.
In the spring, before heavy melting, the specific gravity of “wet” snow can be 750±100 kg/m3, approaching the density of ice - 917 kg/m3.
Snow that has been raked into heaps and thrown from place to place doubles its specific gravity.
The most probable average density of “dry” compacted snow is in the range of 200...400 kg/m3.
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To remove snow from roofs or not?
It is necessary to understand a simple thing - the mass of snow lying on the roof, in the absence of snowfalls, remains unchanged regardless of density!!! That is, the fact that the snow “became heavier” did not increase the load on the roof!!!
The danger is that a layer of loose snow can absorb precipitation in the form of rain like a sponge. Then the total mass of water in its various forms located on the roof will increase sharply - especially in the absence of drainage, and this is very dangerous.
To correctly answer the question about removing snow from the roof, you need to know what load it is designed for and built. You need to know what pressure distributed load- how many kilograms per square meter - roof can really hold before unacceptable deformations of the structure begin.
To answer this question objectively, it is necessary to examine the roof, draw up a new or confirm the design calculation diagram, perform a new calculation or take the results of the old design one. Next, you should experimentally determine the density of the snow - for this, a sample is cut out, weighed and its volume is calculated, and then the specific gravity.
If, for example, according to calculations, the roof must withstand a specific pressure of 200 kg/m2, the snow density determined experimentally is 200 kg/m3, then this means that snowdrifts should not be more than 1 m deep.
If there is a snow cover on the roof more than 0.2...0.3 m deep and there is a high probability of rain followed by cold weather, it is necessary to take measures to dump the snow.
Standard and design snow load.
during the design and construction of facilities? The answer to this question is set out for specialists in SP 20.13330.2011 Loads and impacts. Updated version of SNiP 2.01.07-85*. We will not “take bread” from construction designers and delve into the options for geometric types of coatings, slope angles, snow drift coefficients and other complexities. But let’s create a general algorithm and write a program that implements it. We will learn to determine the standard and calculated snow pressure on the horizontal projection of the surface for objects in any area of Russia that interests us.Let's remember a few “axioms”. If on a simple single-slope or gable roof cover slope angle more than 60˚ , then it is considered that There can be no snow on such a roof (μ =0) . He will all “roll off”. If the slope of the coating less than 30˚ , then it is considered that all the snow on such a roof lies in the same layer as on the ground (μ =1) . All other cases are intermediate values determined by linear interpolation. For example, at angle equal to 45˚ only 50% of the fallen snow will lie on the roof (μ=0.5).
Designers carry out calculations based on limit states, which are divided into two groups. The transition beyond the limiting states of the first group is the destruction and loss of the object. The transition beyond the limit states of the second group is an excess of deflections permissible limits and, as a consequence, the need to repair the facility, possibly a major one. In the first case, the calculation uses a calculated snow load equal to the standard load increased by 40%. In the second case, the calculated snow load is the standard snow load.
Calculation in Excel of snow load according to SP 20.13330.2011.
If you do not have MS Excel on your computer, you can use a freely available, very powerful alternative - the OOo Calc program from the Open Office package.
Before you start, search the Internet and download SP 20.13330.2011 with all applications.
Part important materials from SP 20.13330.2011 are in the file that site subscribers can download from the link located at the very end of this article.
We turn on the computer and start calculating the snow load on the surfaces in Excel.
In cells with a light turquoise fill we will write the initial data selected by SP 20.13330.2011. We calculate the results in cells with a light yellow fill. In cells with a pale green fill we will place the original data, which is little subject to change.
In the notes for all cells in a column C put formulas and links to points SP 20.13330.2011!!!
1. We open Appendix G in SP 20.13330.2011 and according to the map “Zoning of the territory Russian Federation by weight of snow cover” we determine the number of the snow region for the area where the building was built (or will be built). For example, for Moscow, St. Petersburg and Omsk this is the III snow region. Select the corresponding line with entry III in the drop-down list box located on top
You can read in detail about how the INDEX function works together with a combo box.
2. We read the mass of snow cover per 1 m2 of horizontal surface of the earth Sg in kg/m2 for the selected area
3. In accordance with clause 10.5-10.9 of SP 20.13330.2011, we accept the value of the coefficient that takes into account the removal of snow from building surfaces by the wind Ce
in cell D4: 1,0
Ce- write 1.0.
4. We assign, in accordance with clause 10.10 SP 20.13330.2011, the value of the thermal coefficient Ct
in cell D5: 1,0
If you don't understand how to prescribe Ct- write 1.0.
5. We assign, in accordance with clause 10.4 of Appendix G SP 20.13330.2011, the value of the coefficient of transition from the weight of the snow cover of the ground to the snow load on the surface μ
in cell D6: 1,0
Let us recall the “axioms” from the previous section of the article. If you don’t remember and don’t understand anything, write 1.0.
6. We read the standard value of the snow load on the horizontal projection of the coating S0 in kg/m2, calculated
in cell D7: =0.7*D3*D4*D5*D6 =128
S0 =0.7*Ce *Ct *μ * Sg
7. In accordance with clause 10.12 of SP 20.13330.2011, we record the value of the reliability coefficient for snow load γ f
in cell D8: 1,4
8. And finally, we read the calculated value of the snow load on the horizontal projection of the coating S in kg/m2, calculated
in cell D9: =D7*D8 =180
S = γ f * S0
Thus, for “simple” buildings of the third snow region withμ =1 calculated snow load is 180 kg/m2. This corresponds to a snow cover height of 0.90...0.45 m with a snow density of 200...400 kg/m3, respectively. Let each of us draw conclusions!
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TO THE REST can be downloaded just... - there are no passwords!
I look forward to your comments, dear readers!!! I ask professional builders to “not hit too hard.” The article was written not for specialists, but for a general audience.
When building a roof, one of the important technical solutions is the calculation of the maximum snow load that determines the design rafter system, element thickness load-bearing structure. For Russia, the standard value of the snow load is determined using a special formula, taking into account the area where the house is located and SNiP standards. To reduce the likelihood of consequences from excessive weight of snow mass, when designing a roof, it is necessary 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 placing excessive load on the roof, the snow mass sometimes causes leaks in the roof. Thus, when a strip of ice forms, the free flow of water becomes impossible and melted snow will most likely end up in the under-roof space. The heaviest snowfalls occur in mountainous areas, where the snow cover reaches several meters in height. But most Negative consequences from load occur during periodic thawing, ice and freezing. In this case, deformation of the roofing materials and incorrect operation are possible. drainage system and an avalanche-like flow of snow from the roof of the house.
Factors influencing snow load
When calculating the load from snow masses on 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 crust. As a result of these transformations, the following negative consequences arise:
Methods for clearing snow from a roof
The best way out of this situation is manual cleaning. But, based on human safety, performing such work is extremely dangerous. For this reason, load calculation has a significant impact on the design of the roof, rafter system and other roof elements. It has long been known that the steeper the slopes, the less snow will stay on the roof. In regions with big amount precipitation in winter period year, the roof slope ranges from 45° to 60°. In this case, the calculation shows that a large number of junctions and complex connections provide uneven load.
To prevent the formation of icicles and ice, cable heating systems are used. A heating element installed around the perimeter of the roof directly in front of the gutter. To control the heating system use automatic system controls or manually control the entire process.
Calculation of snow mass and load according to SNiP
During 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, a design calculation is performed depending on the impact 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 regional terrain features in Russia, a special snow load map is used. The requirements of SNiP and other rules are based on it. The total snow load on the roof is calculated using the formula:
S=S calc. ×μ;
S calc. – calculated value of snow weight per 1 m 2 of horizontal surface of the earth;
μ – calculated coefficient taking into account the slope of the roof.
On the territory of Russia, the calculated value of the weight of snow per 1 m 2 in accordance with SNiP is accepted according to a special map, which is presented below.
SNiP stipulates following values coefficient μ:
- if the roof slope is 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, Hooray, it’s happened and we are pleased to present you with an online calculator for calculating snow and wind loads, now you don’t need to figure anything out on a piece of paper or in your mind, you just indicated your parameters and got the load right away. In addition, the calculator can calculate the depth of soil freezing if you know its type. Here is a link to the calculator -> Online Snow and Wind Load Calculator. In addition to this, we have many other construction calculators You can see a list of them all on this page:
An illustrative example of calculation
Let's take the roof of a house that is located in the Moscow region and has a slope of 30°. In this case, SNiP stipulates the following procedure for calculating the load:
- Using a map of Russian regions, we determine that the Moscow region is located in the 3rd climatic region, where the standard value of snow load is 180 kg/m2.
- Using the formula from SNiP, we determine the full load: 180 × 0.7 = 126 kg/m 2.
- 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 done correctly, then there is no need to remove snow from the roof surface. And to combat it from sliding off the eaves, snow retainers are used. They are very easy to use and eliminate the need to remove snow from the roof of the house. In the standard version, tubular structures are used, which are capable of operating if the standard snow load does not exceed 180 kg/m2. For denser weights, install snow guards in several rows. SNiP stipulates the use of snow guards:
- with a slope of 5% or more with external drainage;
- snow guards are installed at a distance of 0.6-1.0 meters from the edge of the roof;
- When using tubular snow retainers, a continuous roof sheathing must be provided underneath them.
SNiP also describes the basic designs and geometric dimensions of snow guards, their installation locations and operating principles.
Flat roofs
The maximum possible amount of snow accumulates on a flat horizontal surface. The calculation of loads in this case should provide the necessary margin of safety of the supporting structure. Flat horizontal roofs are practically not built in regions of Russia with a large amount of precipitation. Snow can accumulate on their surface and create an excessively large load that was not taken into account in the calculation. When organizing a drainage system from a horizontal surface, they resort to installing a heating system, which ensures water drains from the roof.
The slope towards the drainage funnel must be at least 2°, which will make it possible to collect water from the entire roof.
When building a canopy for a gazebo, parking a car, country house Special attention pay attention to load calculation. The canopy in most cases has a budget design that does not provide for the influence of large loads. In order to increase the reliability of operation of the canopy, continuous lathing, reinforced rafters and other structural elements. Using the calculation results, you can definitely obtain known value loads and use materials of the required rigidity for the construction of the canopy.
Calculation of the main loads makes it possible to optimally approach the issue of choosing the design of the rafter system. This will ensure long service life roofing, will increase its reliability and operational safety. Installing snow guards near the eaves allows you to protect people from the sliding of snow masses that are dangerous to humans. In addition to this, there is no need for manual cleaning. An integrated approach to roof design also includes the option of installing a cable heating system, which will ensure stable operation of the drainage system in any weather.
Do you want to calculate the rafter system quickly, without studying theory and with reliable results? Take advantage online calculator Online!
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. Strong and reliable system rafters are 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, the 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 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 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 rafter spacing to a minimum in this place, and also pay close attention to the manufacturers’ recommendations roofing material- 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:
- the volume of wood (m3) used as sheathing is multiplied by the density of the wood (500 kg/m3)
- weight of the rafter system
- weight of 1m2 roofing material
- weight 1m2 of insulation weight
- weight 1m2 finishing material
- 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 calculating, 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:
10 - 15 kg/m² |
|
Ceramic tiles | 35 - 50kg/m² |
Cement-sand tiles | 40 - 50 kg/m² |
Bituminous shingles | 8 - 12 kg/m² |
Metal tiles | |
Corrugated sheet | |
Subfloor weight | 18 - 20 kg/m² |
Sheathing weight | 8 - 12 kg/m² |
Rafter system weight | 15 - 20 kg/m² |
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.
falls on each rafter leg separately, convert kg/m2 to kg/m.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 truss 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, take into account maximum torque bending, 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 flexural and compressive
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 that the deflection does not exceed the permitted value.
The deflection of the rafters should be less L/200- length of the thing being checked longest span 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 on linear meter 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:
- SNiP 2.01.07-85 Loads and impacts with latest changes 2008
- SNiP II-26-76 “Roofs”
- SNiP II-25-80 “Wooden structures”
- SNiP 3.04.01-87 “Insulating and finishing coatings”
- A.A. Savelyev “Rafter systems” 2000
- K-G. Goetz, Dieter Hoor, Karl Möhler, Julius Natterer “Atlas of wooden structures”
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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 sheathing, insulation, underlayment, snow and wind load. Let us consider each of these loads separately.
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 a roof load calculation can be ordered from a specialized organization or from a private designer. If the construction is not so demanding on technical calculations, then everything can be done on your own.
Impact of wind force
A snow load can destroy the roof, and a wind load can also tear off the covering. The greater the angle of the roof slopes, the greater the wind load on the structure. The smaller the angle, the stronger the lifting force will be, tending to tear off the roof. This is why calculating the area is so important gable roof. First, determine the length of the rafter leg. This is where knowledge comes in handy school course geometry, since the rafter is in line with the adjacent walls right triangle, 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 SNiP tables. k is a coefficient depending on the height of the building, it is also indicated in the above regulatory document. C is the aerodynamic coefficient used to calculate leeward and windward 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 flat roofs, when the wind “flows” down the slopes. To counteract these forces, depending on the pitch of the rafters, so-called “ruffs” are installed in the walls of the house. This metal pins, to which they are tied with wire rafter legs. In windy regions, each rafter is tied; under normal conditions, this is done through one beam, having previously completed it according to the available data.
Calculation of the floor beam, see the video:
Roof weight load
The weight of the roofing material itself has a serious impact on the characteristics of the rafter system. Wherein various materials may vary significantly in weight. The more the roof weighs, the greater the slope of the slopes should be. You also need to know how to count square meters roof, since the larger its area, the more it will depend on the influence of external loads.
The pressure force of the roof 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 specific lathing option is selected. So, to create it, OSB board, plywood or edged board. The average weight of these materials can be found from standard tables or technical data from the manufacturer. For example, for a slate roof, bars with a cross section of 4*6 or 6*6 cm are used, while for bitumen shingles - OSB boards or plywood.
The calculation of the roof square footage depends on its type. very easy for single-pitched roofs. In more complex structures the roof should be divided into elementary shapes - rectangles and triangles, the area of which is easily determined (more details: " "). It is also important to take into account the roof overhangs at the eaves. The distance between the rafters is determined based on the thickness of the roofing material.
No less important is the thermal engineering calculation of the roof, on the basis of which the insulation and its thickness are selected. These two indicators significantly influence total weight roof structures. In addition, this includes the weight of vapor and waterproofing, as well as internal lining attic room. The thickness of the insulation is calculated using the formula: T=R*L. Where R is the thermal resistance of the structure that will be insulated, L is the thermal conductivity coefficient of the selected insulation (selected according to SNiP II-3-79 standards).
Let's assume that the roof is insulated with URSA M-20 glass wool and 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 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.
The weight of hydro- and vapor barrier, as well as finishing material, is calculated in the same way. 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 add 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 average values for layered rafters and purlins are taken into account - 5-10 kg/sq.m., for hanging rafters - 10-15 kg/sq.m. To obtain a certain safety margin 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 engineering calculation of the roof, an example of which can be found on the pages of our portal.
Snow is a pleasant joy for many, but sometimes it is a great disaster for them, especially when there is a lot of it. It is important to understand the determination of weight based on its calculations, primarily for builders, so that the roofs do not collapse.
Weight of specific gravity of snow per 1m³ depending on characteristics |
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| Snow characteristics | Specific gravity (g/cm³) | Weight 1 m³ (kg) |
| Dry snow | 0.125 | 125 |
| Freshly fallen fluffy dry | from 0.030 to 0.060 | from 30 to 60 |
| Wet snow | up to 0.95 | up to 950 |
| Wet freshly fallen | from 0.060 to 0.150 | from 60 to 150 |
| Freshly fallen settled | from 0.2 to 0.3 | from 200 to 300 |
| Wind (blizzard) transfer | from 0.2 to 0.3 | from 200 to 300 |
| Dry settled old | from 0.3 to 0.5 | from 300 to 500 |
| Dry firn (dense snow) | from 0.5 to 0.6 | from 500 to 600 |
| Wet firn | from 0.4 to 0.8 | from 400 to 800 |
| Wet old | from 0.6 to 0.8 | from 600 to 800 |
| glacier ice | from 0.8 to 0.96 | from 800 to 960 |
| Lying snow for more than 30 days | 340-420 | |
In some countries the snow is excellent building materials, for example, during the construction of Igloos among the Eskimos, and on holidays for the construction of original sculptures.
Formation of snow as a natural phenomenon
Snow - a natural phenomenon, formed due to the crystallization of small droplets of water in the atmosphere and falling to the ground in the form of precipitation. Snow is formed in the atmosphere when microscopic particles of water begin to group around similarly sized dust particles and crystallize. Initially, the size of the resulting ice crystals does not exceed 0.1 mm. But in the process of falling to the earth's surface, depending on the temperature external environment, they begin to “overgrow” with other frozen water crystals and increase proportionally.
The patterned shape of snowflakes is formed due to the specific structure of water molecules. These are usually six-pointed patterned figures, with a possible angle between the edges of either 60 or 120 degrees. In this case, the main “central” crystal forms a hexagon shape with regular edges. And the crystalline rays added during the fall can give the snowflake a wide variety of shapes. Considering that in the process of falling, snowflakes are exposed to wind, temperature changes, and can repeatedly increase the number of crystals; ultimately, they become not only flat, but also volumetric shape. At first glance, this may seem like a pile of frozen droplets of water, but if you look closely, then in the original structure all such connections will have correct angles.
As a rule, the color of snow is white. This is due to the presence of air in its internal structure. In fact, snow is 95% air. This is what determines the “lightness” of snowflakes, as well as their smooth landing on hard surfaces. Subsequently, when light passes through crystallized water, taking into account air gaps and begins to dissipate, the snowflake becomes visible White color. But this classic version. If there are other elements in the atmosphere, including tiny particles of dust, smoke, polluted by industrial emissions and air mixtures, the snow may take on other shades.
Typically, snowflakes are no larger than 5 mm in diameter. But in history there are known cases of the formation of “giant” snowflakes, when the size of each “instance reached up to 30 cm in diameter. At the same time, taking into account the many factors influencing the process of formation of these natural creations, it is believed that it is simply impossible to find two identical snowflakes. And even if visually it seems to you that they are completely similar, when you look at them under a microscope you will realize that this is far from the case. Variations of them possible forms today unlimited quantity.
How much does 1 cube of snow weigh - depending on dependencies
- From temperature environment
- From time since precipitation
- From additional precipitation in the form of rain
- From caking density
Have great weather at home!
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