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When designing the roof rafters of a private house, you need to be able to correctly calculate the angle of the roof. How to navigate in various units of measurement, what formulas to calculate and how the angle of inclination affects the wind and snow load of the roof, we will talk in this article.
The roof of a private house built according to individual project, can be very simple or surprisingly whimsical. The slope angle of each slope depends on architectural solution the whole house, the presence of an attic or attic, used roofing material, the climatic zone in which it is located household plot. In a compromise of these parameters, you need to find optimal solution combining the strength of the roof with beneficial use roof space and the appearance of the house or complex of buildings.
Roof angle units
The angle of inclination is the value between the horizontal part of the structure, slabs or floor beams, and the roof surface or rafters.
In reference books, SNiP, technical literature, there are various units for measuring angles:
- degrees;
- aspect ratio;
- interest.
Another unit for measuring angles - radians - is not used in such calculations.
What are degrees, everyone remembers from school curriculum. The ratio of the sides of a right-angled triangle, which is formed by the base - L, height - H (see the figure above) and the roof deck is expressed as H: L. If α = 45°, the triangle is equilateral and the ratio of sides (legs) is 1:1. In the case when the ratio does not give a clear idea of the slope, they speak of a percentage. This is the same ratio, but calculated in shares converted to percentages. For example, with H = 2.25 m and L = 5.60 m:
- 2.25 m / 5.60 m 100% = 40%
The digital expression of some units through others is clearly shown in the diagram below:
Formulas for calculating the angle of inclination of the roof, the length of the rafters and the area covered by the roofing material
To easily calculate the dimensions of the elements of the roof and truss system, you need to remember how we solved problems with triangles at school, using the basic trigonometric functions.
How does this help in calculating the roof? We break complex elements into simple right-angled triangles and find a solution for each case using trigonometric functions and the Pythagorean theorem.
More complex configurations are more common.
For example, you need to calculate the length of the rafters of the end part of the hip roof, which is an isosceles triangle. From the vertex of the triangle we lower the perpendicular to the base and get right triangle, whose hypotenuse is the midline of the end of the roof. Knowing the width of the span and the height of the ridge, from a structure divided into elementary triangles, you can find the angle of the hip - α, the angle of the roof - β and get the length of the rafters of a triangular and trapezoidal slope.
Calculation formulas (length units must be the same - m, cm or mm - in all calculations to avoid confusion):
Attention! The calculation of the lengths of the rafters according to these formulas does not take into account the size of the overhang.
Example
The roof is hipped, hipped. Ridge height (CM) - 2.25 m, span width (W / 2) - 7.0 m, depth of inclination of the end part of the roof (MN) - 1.5 m.
Having obtained the values of sin(α) and tg(β), you can determine the value of the angles using the Bradis table. A complete and accurate table with an accuracy of up to a minute is a whole brochure, and for rough calculations, which in this case valid, you can use a small table of values.
Table 1
| Roof pitch, in degrees | tg(a) | sin(a) |
| 5 | 0,09 | 0,09 |
| 10 | 0,18 | 0,17 |
| 15 | 0,27 | 0,26 |
| 20 | 0,36 | 0,34 |
| 25 | 0,47 | 0,42 |
| 30 | 0,58 | 0,50 |
| 35 | 0,70 | 0,57 |
| 40 | 0,84 | 0,64 |
| 45 | 1,00 | 0,71 |
| 50 | 1,19 | 0,77 |
| 55 | 1,43 | 0,82 |
| 60 | 1,73 | 0,87 |
| 65 | 2,14 | 0,91 |
| 70 | 2,75 | 0,94 |
| 75 | 3,73 | 0,96 |
| 80 | 5,67 | 0,98 |
| 85 | 11,43 | 0,99 |
| 90 | ∞ | 1 |
For our example:
- sin(α) = 0.832, α = 56.2° (obtained by interpolating neighboring values for angles of 55° and 60°)
- tg(β) = 0.643, β = 32.6° (obtained by interpolation of neighboring values for angles of 30° and 35°)
Remember these numbers, they will be useful to us when choosing a material.
To calculate the amount of roofing material, you will need to determine the area of \u200b\u200bcoverage. Slope area gable roof- rectangle. Its area is the product of the sides. For our example - a hip roof - this comes down to determining the areas of a triangle and a trapezoid.
For our example, the area of one end triangular slope with CN = 2.704 m and W / 2 = 7.0 m (the calculation must be performed taking into account the extension of the roof beyond the walls, we take the length of the overhang - 0.5 m):
- S \u003d ((2.704 + 0.5) (7.5 + 2 x 0.5)) / 2 \u003d 13.62 m 2
The area of one side trapezoidal slope at W = 12.0 m, H c = 3.905 m (trapezoid height) and MN = 1.5 m:
- L k \u003d W - 2 MN \u003d 9 m
We calculate the area, taking into account overhangs:
- S \u003d (3.905 + 0.5) ((12.0 + 2 x 0.5) + 9.0) / 2 \u003d 48.56 m 2
The total area covered by four slopes:
- S Σ \u003d (13.62 + 48.46) 2 \u003d 124.16 m 2
Roof slope recommendations depending on the purpose and material
An unused roof may have minimum angle tilt 2-7°, which provides immunity to wind loads. For normal snow melting, it is better to increase the angle to 10 °. Such roofs are common in the construction of outbuildings, garages.
If the under-roof space is supposed to be used as an attic or attic, the slope of a single or gable roof must be large enough, otherwise a person will not be able to straighten up, and effective area will be "eaten" by the truss system. Therefore, it is advisable to apply in this case broken roof, for example, attic type. Minimum Height ceilings in such a room should be at least 2.0 m, but it is desirable for a comfortable stay - 2.5 m.
Options for arranging the attic: 1-2. Double pitched roof classic. 3. Roof with a variable angle of inclination. 4. Roof with remote consoles
When accepting this or that material as a roofing material, it is necessary to take into account the requirements for the minimum and maximum slope. Otherwise, there may be problems that require repair of the roof or the entire house.
table 2
| roof type | Range of permissible mounting angles, in degrees | Optimal slope roof, in degrees |
| Roofing with roofing | 3-30 | 4-10 |
| Tole roof, two-layer | 4-50 | 6-12 |
| Zinc roofing with double standing seams (zinc strips) | 3-90 | 5-30 |
| Tole roof, simple | 8-15 | 10-12 |
| Sloping roof covered with roofing steel | 12-18 | 15 |
| Groove tile with 4 grooves | 18-50 | 22-45 |
| shingle roof | 18-21 | 19-20 |
| Grooved tiles, normal | 20-33 | 22 |
| Decking | 18-35 | 25 |
| Corrugated Asbestos Cement Sheet | 5-90 | 30 |
| artificial slate | 20-90 | 25-45 |
| Slate roof, double layer | 25-90 | 30-50 |
| Slate roof, normal | 30-90 | 45 |
| glass roof | 30-45 | 33 |
| Roof tiles, two-layer | 35-60 | 45 |
| Grooved Dutch tile | 40-60 | 45 |
The tilt angles obtained in our example are in the range of 32-56°, which corresponds to slate roof, but does not exclude some other materials.
Determination of dynamic loads depending on the angle of inclination
The design of the house must withstand static and dynamic loads from the roof. Static loads are weight truss system and roofing materials, as well as under-roof space equipment. This is a constant value.
Dynamic loads are variable values depending on the climate and season. In order to correctly calculate the loads, taking into account their possible compatibility (simultaneity), we recommend studying SP 20.13330.2011 (sections 10, 11 and Appendix G). In full, this calculation, taking into account all possible factors in a particular construction, cannot be presented in this article.
The wind load is calculated taking into account the zoning, as well as the location features (leeward, windward side) and the angle of the roof, the height of the building. The calculation is based on wind pressure, the average values of which depend on the region of the house under construction. The remaining data are needed to determine the coefficients that correct a relatively constant value for the climatic region. The larger the angle of inclination, the more serious wind loads the roof experiences.
Table 3
Snow load, unlike wind load, is related to the angle of the roof in the opposite way: the smaller the angle, the more snow lingers on the roof, the lower the probability of snow cover convergence without the use of additional means, and the greater the load the structure experiences.
Table 4
Approach the issue of determining loads seriously. The calculation of sections, designs, and hence the reliability and cost of the truss system depends on the values obtained. If you are not confident in your abilities, it is better to order a load calculation from specialists.
Houses with flat roofs are found in multi-storey buildings, in private houses and cottages they are more often sloping. Roof slope - a surface that has a certain slope, which plays an important role together with the truss system, rafter sheathing, properly selected roofing materials.
In this article
What determines the slope of the roof
An indicator characterizing the slope with respect to the horizon is the slope. It shows as a percentage how the roof height relates to ½ of the building.
However, the value of the slope in percentage is not the same as in degrees, and this is important when designing roofs. Given that 1° equals 1.7%, the equivalent of a 30° angle, as opposed to the math, would be 57.7%.
An accurate result can be obtained with a surveying tool. A value of 0° corresponds to a flat roof, more often it is from 11° to 45°.
When choosing a slope, the determining factors are:
- the influence of climatic loads (wind pressure on steep slopes is higher, although atmospheric precipitation descends from them faster);
- the purpose of the attic located under the roof of the attic (for residential, a larger angle of inclination is required, then the room will be spacious, the ceilings are high);
- type of roofing building material (it is necessary to take into account the permissible slope value that exists for each coating);
- financial costs (they increase even when doing the work yourself, if the angle of inclination exceeds 45 °);
- architectural solutions, local traditions.
Table: roof slope dimension
This parameter is measured in percent or degrees. Using a special table, you can quickly translate values.
| Degrees, ° | Interest, % | Degrees, ° | Interest, % | Degrees, ° | Interest, % |
| 1 | 1.7 | 16 | 28.7 | 31 | 60.0 |
| 2 | 3.5 | 17 | 30.5 | 32 | 62.4 |
| 3 | 5.2 | 18 | 32.5 | 33 | 64.9 |
| 4 | 7.0 | 19 | 34.4 | 34 | 67.4 |
| 5 | 8.7 | 20 | 36.4 | 35 | 70.0 |
| 6 | 10.5 | 21 | 38.4 | 36 | 72.6 |
| 7 | 12.3 | 22 | 40.4 | 37 | 75.4 |
| 8 | 14.1 | 23 | 42.4 | 38 | 78.9 |
| 9 | 15.8 | 24 | 44.5 | 39 | 80.9 |
| 10 | 17.6 | 25 | 46.6 | 40 | 83.9 |
| 11 | 19.3 | 26 | 48.7 | 41 | 86.0 |
| 12 | 21.1 | 27 | 50.9 | 42 | 90.0 |
| 13 | 23.0 | 28 | 53.1 | 43 | 93.0 |
| 14 | 24.9 | 29 | 55.4 | 44 | 96.5 |
| 15 | 26.8 | 30 | 57.7 | 45 | 100 |
The influence of natural factors on the slope of the roof
The choice of the angle of inclination is influenced by local weather. When lowering or increasing the slope, the negative effect of the elements may affect.
In case of dominance strong winds it is not recommended to choose a project with a sharp roof. High windage with a strong slope will be more exposed to the damaging effects of the wind. It is better if the roof turns out to be more gentle (less slope gives more security) with reinforced rafters.
The direction of the wind also matters. For a roof made of metal, it is preferable that the wind force be directed into the plane of the sheets. With gusts coming from the ends, the likelihood increases that the sheets will bend and tear off.
In a climate zone with heavy snow cover, a minimum slope of 45° (or more) is required. In this case, the snow will begin to slide off the roof, and not cake on it. In sunny areas with little rain, the roof may be flat or with a minimal slope.
With regular cleaning of the roof, drainage system, peaks from snow, the load on the roof structure is reduced.
An increase in the angle of inclination entails an increase in the natural convergence of the snow cover from the roof. It is allowed to reduce the calculated snow load with a slight slope (12-20%) by the drift coefficient.
The relationship of roofing material and the slope of the slopes
Roofing materials can be smooth or rough (in this case, water will linger on the surface). There are other factors that affect slope.
The minimum angle of inclination when using metal tiles should be 15°. With a small slope, water that does not have time to drain from the roof during heavy showers is under the joints.
For corrugated sheet roofing, the minimum slope can reach 12 °, when installed with an overlap, it should be 20 cm. Minimum slope for roofing shingles, ondulin should not be less than 11 °.
With a decrease in the angle of inclination, it is necessary to increase the number of roof layers, since flat roofs require good moisture protection. There is a relationship that should be taken into account when choosing roofing materials: the denser the structure of the coating, the smaller the slope should be.
Bitumen shingles are the most wind-resistant material suitable for buildings with a complex polygonal configuration (for example, in the shape of a trapezoid). In areas with a predominance of strong and frequent winds, it is recommended soft tiles glue first, and then fasten to the base with nails.
Coatings are mastic, piece and rolled, natural tiles have high reliability, but with an erroneously chosen slope strong wind can break pieces. For sheet coverings, a large windage is considered a disadvantage.
The dependence of the height of the ridge on the slope of the roof
You can make simple calculations using a mathematical formula. The height of the ridge is ½ the width of the building divided by 2 times 100.
Since it is impossible to change the width of the building, it is necessary to change the height of the ridge (provided that the foundation and walls of the building are reliable and have a margin of safety).
To determine the height of the ridge mark 2 external walls(along which the slope will be located). Rub the cord with chalk, pull between the marks. Then the center is determined at the cord, a bar is placed at the resulting point (perpendicular to the plane of overlap).
By changing the cord, the desired slope is achieved. After obtaining the desired result, a mark is placed on the bar. The resulting piece is sawn off, a template is made that is required for the skate supports.
How to correctly calculate the angle of inclination
An inclinometer is used to calculate the slope of the roof (there are many types of devices, ranging from analog to digital). The mechanical device is simple and convenient, it can be applied to the surface and take readings. The accuracy of the electronic goniometer is higher, the values are displayed on the display, which is located on the panel.
When the protractor is in a horizontal position, the division indicates the zero mark. To determine the angle of inclination, place the device perpendicular to the ridge and record the readings (they are indicated in degrees).
The goniometer should be used only in cases where it can be attached to the base (if the rafter system is ready). Otherwise, use the table above.
To determine the angle of inclination, it is required to divide the height of the under-roof space by ½ the width of the building (including gable and cornice overhangs).
Video: universal goniometer
The video shows the Semenov goniometer and the principle of working with it.
Video: how to calculate the angle of inclination and roof height
This video tutorial shows how to calculate the angle of inclination and height of the roof.
Calculation of the total load on the roof
In the absence of knowledge in the field of architecture and engineering, you can order a load calculation from private designers or from an organization that offers such services.
When determining the total impact on the roof, it is necessary to take into account:
- snow load;
- wind load;
- weight of roofing material;
- insulation weight;
- weight of films (waterproofing, polyethylene, vapor barrier);
- crate weight;
- total roof load.
The load on the truss system should not exceed 300 kg / m² (otherwise, a change in the angle of inclination will be required or the coating will have to be replaced).
Knowing the total design load, it is easier to select the section of lumber intended for the truss frame.
Table: rafter cross section and installation step depending on the total load on the roof
Note: * indicates 2 boards connected to each other.
The minimum angle of inclination for different types of roofs
The most stable is tented (more common in square-shaped buildings). It is easy to assemble, but if the roof of the house is slightly tilted, then this does not allow you to make the space that the attic occupies comfortable.
In a 4-pitched roof, especially a Dutch half-hip roof, load resistance increases several times due to truncated end slopes.
When arranging 1-pitched surfaces, the direction of the wind must be taken into account in order to maintain the strength of the structure and solve the problem with precipitation. For flat roofs, slope and drainage are important, then the roof will be reliable, despite the minimum slope.
All types of roofing have such a value as a minimum slope. Manufacturers inform about it, you should only study the instructions for the coating.
- in the case of an underestimated angle, accumulation of moisture will be noted at the docking points, over time, leaks and deformations will appear;
- in the process of laying roll coatings, it will be necessary to reduce the number of layers of insulation or insulation, which, in turn, will lead to an increase in heating costs;
- a continuous crate may be required instead of a sparse one (in some cases, gluing the seams);
- with an increase in slope, the coverage area will increase, at the same time, the weight of the roof will increase, the load on the truss system will increase and costs will increase;
- if the slope is exceeded, swelling may form, which can lead to the destruction of the truss frame.
Video: minimum slope for a flat roof, ramping
It is imperative to deal with the calculation of the slope, because not only the strength of the building, but also the safety of people depends on this indicator.
What affects the angle of the roof
The construction of the roof is the last stage in the construction of the house. But no less important than building walls. After all, the roof protects our housing from bad weather, and the aesthetic side of our home depends a lot on the type of roof.
It just so happened, but flat roofs in our country can only be found near high-rise buildings. Cottages and private houses are crowned with pitched roofs. And one of the main design indicators in the construction of a house, builders consider the angle of inclination of the roof. Let's look at how to correctly calculate this indicator, what it depends on and how it affects the construction of the roof as a whole.
Types of roofs and their dependence on the angle of inclination
Depending on the device of the roof, there are several types of roofs:
- shed roof. The roof is an inclined plane that rests on the walls different heights. For such a roof, any material is suitable.
- Gable roof. This is a fairly reliable and easy to install roof. Consists of two slopes. You can also choose absolutely any material for the roof.
- Shaft cover. The roof is a structure in which several isosceles triangles close at one point with their vertices. The rafter system of such a roof is quite complicated, but Supplies it needs a minimum.
- hip roof. It has four slopes (two triangular and two trapezoidal). The tops of the roof have been cut off. By their design, the roofs are very complex, but very economical in terms of material consumption.
- Vaulted cover. Such roofs are made only of brick or stone. And since they are very heavy, today they are almost never used in individual construction
- Multi-gable roofs. A very complex but beautiful configuration of many junctions and edges.
So, the roof is considered pitched if the angle of inclination of the roof exceeds 10 degrees.
Allocate exploited and non-exploited roofing.
An unused roof is when there is almost no space between the roof itself and the upper ceiling, or this space is intended for technical purposes. Such roofs can be flat roofs with a slope angle of 2 to 7 degrees. In such roofs, the height of the space between the roof and the ceiling is not more than one and a half meters.
Building flat roofs is profitable. Minimum cost for materials and labor. The wind won't blow. Again, you can equip an additional place to relax. Recently, it is very popular to lay green roofs on such roofs. But precipitation can ruin such a roof. Therefore, it is unprofitable to make completely flat roofs. Precipitation in puddles will accumulate on the surface of the roof and destroy it. 
In order to create a natural outflow of water, a layer of ceramite is poured onto flat roofs under a certain slope.
Pitched roofs allow you to use the space under the roof for household needs - attic, attic, or even equip them with careful insulation and living rooms.
Factors on which the angle of inclination of the roof most depends
The main factors affecting the slope of the roof include:
- natural factors. The slope of the roof depends on the climate of the area where the construction will take place. The wind puts a huge strain on roofing roofs and on the truss system as a whole. A slight increase in the slope angle (by about 30 degrees) increases the wind load by almost 5 times. But even a slight angle can also play into the hands of the elements. So it will be easier for him to get into the roof through the joints of the coating and easily tear off the roof. Precipitation can also be detrimental to roof performance. But with the help of a well-chosen bias, you can avoid these troubles.
Remember that the maximum snow load on the roof of the roof is achieved by observing the roof slope angle of 30 degrees. And at 45 degrees, snow and rain do not linger on the roof at all.
Thus, it is obvious that if you are going to build a house in a region where rainfall is very frequent, then a roof slope of 45 degrees is just right. But if there is not so much precipitation, but the wind blows all year round, then best option– Roof with a slope of 30 degrees.
How to calculate slope angle
How to determine the roof slope that will be optimal for your new home?
Remember that the greater the angle of the roof, the more costs you will incur for construction work.
The slope value is calculated as the ratio of the size of the ridge to half the width of the building and multiplied by 100. Professional builders have their own instructions and calculations in case of calculating the roof slope indicators. Most of them use calculation matrices and special charts. You can find them on the World Wide Web.
The influence of the slope of the roof on the choice of roofing material (and not only)
An ideal roof that would suit all regions and roofing materials has not yet been invented.
So, the slope was calculated. Now we select the roofing material. Slate and shingles are suitable for roofs with an angle of more than 20 degrees. If the slope is smaller, then water will run into the joints, snow will clog, which means that the life of the roof itself will decrease.
Roll materials on the basis of bitumen is used when covering flat roofs or the angle of inclination of the roof, which exceeds 30 degrees. At high level heating such roofs by the sun and with a greater slope, the roof can simply slide off.
Metal profiles and metal tiles are used on roofs with a slope of at least 10 degrees.
And here is a list of the most common roofing materials:
- Tiling. Today it is almost wildly popular. There are many varieties of this material. These roofs are easy to repair. But to give finance for given material will have a lot But this material is very durable. Its service life can be calculated not only in decades, but also in centuries.
- Roof panels. Such panels are made directly at factories and in the final form they represent almost finished roof. The panels immediately contain several layers - both thermal insulation and vapor barrier and the plate itself. Installing these boards is very easy. Don't need any special equipment. The panels are attached to each other with a special tape. But such material is very expensive.
- Metal profile. Galvanized steel sheets. Relatively light and durable material. Rust resistant and environmentally friendly. Today you can choose any color and size and direction of the waves. Manufacturers give a guarantee for this material for a period of 75 years.
- piece materials from wood, such as shingles, shavings and shingles. Usually, similar materials in modern construction no one is using it anymore. This material is not durable, can rot, micro-organisms multiply and is easily flammable.
- Slate. This material has long been reliable in operation, easy to install and inexpensive to purchase. Moisture-resistant, frost-resistant, fireproof. Yes and appearance today manufacturers have improved. You can choose a slate of any desired color.
When choosing a roofing material, remember that the denser its structure, the smaller the roof slope should be.
When using sheets of metal profiles and metal tiles on sloping roofs, it is recommended to pass the joints with a moisture-resistant and frost-resistant sealant. As well as the size of the overlap of the sheets during the installation of the roof of these materials also depends on the angle of the roof. The steeper the roof, the less overlap. This also applies to slate.
When installing the roof, do not forget about the ventilation of the space under it. Pitched roofs also need to be equipped with a drainage system.
Thus, we can conclude that the angle of the roof is a very important indicator. Not only the quality of work depends on it, but also the life of the roof itself. The main thing is to correctly calculate the value, choose desired design roofs, high-quality roofing material and a good team of workers. And, of course, not all of this will require some voluminous budget. Good luck with your building!
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The foundation and the roof are the two most important and complex architectural elements of any building. The load-bearing elements of the roof are the truss system, and its performance largely depends on the angle of inclination of the slopes. Ordinary developers choose the optimal roof slope based on criteria other than designers.
They are not entirely interested in calculations for the strength of bearing nodes, they are of little interest in the influence of the angle of inclination gable roof on the cost and complexity of the truss system, etc.
What do ordinary developers pay attention to?
| Roof Angle Options | Short description |
|---|---|
| Every owner wants to have beautiful house with their individual differences. On the outside of the house big influence renders the angle of inclination of the slopes. Architects have their own requirements for buildings, houses must organically fit into the style of existing buildings. This parameter is especially strictly applied when the house is located within the city. Quite often, local governments make decisions prohibiting the violation of the traditional architectural appearance. It is impossible, for example, to build a house with a roof slope of 45 °, if all the buildings on this street have a slope of no more than 20 °. |
| This factor has very little effect on the optimum angle. Roofing materials have only general recommendations for installation on flat and sloping roofs. flat roofs have a slope angle of less than 10 °, all structures with an angle of inclination exceeding these values are considered inclined. The technology of installation of roofing materials with an angle of inclination of 15 ° is no different from the technology roofing works on slopes with a slope of 45 °. There is, however, a limitation for piece tiles, it can be installed on roofs with an inclination angle of at least 22 °. |
| The greater the angle of inclination of the slopes, the higher attic space. Such roofs are built for buildings with attics. Developers pay great attention to this factor, but not everything is as simple as it might seem at first glance. |
These wishes are taken into account by architects during the design and calculation of elements of roof systems. But a fairly large number of purely engineering factors are added to them, which have a decisive influence during the calculation of the parameters of the truss system. And the angle of inclination of the slopes is not the only one among them, all values depend on each other and cannot be ignored when developing a project.
How designers choose the optimal angle
Calculations are made on the basis of SNiP 2.01.07-85. Placed norms are used during calculations taking into account permanent, temporary and special loads and their various combinations.
SNiP 2.01.07-85. The PDF file will open in a new tab
What loads are taken into account when determining the angle of the roof
Loads are divided into several categories depending on the duration of their impact: long-term, short-term and special.
- Long-term (permanent) loads on the truss system. These include the weight of roofing materials, insulation, wooden elements truss structure. This category should include loads arising from thermal expansion and changes in linear dimensions due to changes in the relative humidity of lumber. Regulatory temperature changes are determined by formulas separately for heated and unheated premises. The weight of the snow cover is also considered a long-term load on the truss system and, in without fail taken into account when determining optimal angle slope of the rafter legs.
- short-term. The rafter system is influenced by the weight of workers, stored building materials, the mass of special equipment and tools used during construction, and wind loads.
- Special loads. The effort that occurs during natural Disasters, earthquakes, explosions, with a sharp loss of the bearing capacity of one or more loaded nodes of the truss system.
Special loads include earthquakes and natural disasters
When determining the angle of inclination of the roof, the maximum possible combination of loads is taken into account. Both of these parameters affect the thickness and length of the rafter legs. The calculation of the truss system and the angle of inclination of the slopes is done according to the limit states, taking into account all adverse factors.
The maximum deflections and movement of the rafter legs are regulated regardless of their linear dimensions and should not lead to partial depressurization of the roof. For all types of roofs, regardless of the angle of inclination, the following conditions are put forward:
- should be guaranteed safe operation buildings;
- structural integrity cannot be compromised even during short-term peak loads;
- the appearance of the roof should not change the entire period of operation.
Moreover, each requirement must be fulfilled independently of the others. The limiting values of the deflection of the rafters are limited taking into account performance characteristics roofing materials. If the standard values do not have a noticeable effect on the appearance, then they are not adjusted.
Practical advice. Much easier integrity roofing cake Roofs are provided not by increasing the strength of the truss system, but by using special structural compensators.
a is one of most used roof structures, having two inclined planes separated by a rib - a ridge.
The slopes can be either the same, creating an isosceles triangle in cross section, or different, having different angles of inclination and area.
In addition, widespread attic construction gable roof, when the slopes consist of two planes with different angles of inclination.
This design allows more effective use attic space for commercial or residential purposes.
The main advantage of two pitched roofs counts simplicity of construction and reliability in operation, the absence or small number of valleys or grooves that contribute to the accumulation of water or snow.
The design as a whole ensures optimal distribution of the weight of the rafters and roofing on the walls, contributing to the maximum life of the roof.
You will read in detail about how to make a gable roof yourself.
During the life of the roof constantly experiencing stress different kind. The problem is not their presence - this issue is easily solved amplification. The point is the diversity and unevenness of these loads.
Constant and unchanging- the weight of the roofing cake and the roof itself, they create continuous pressure on the elements due to its weight. Additional factors include wind load and the weight of precipitation.
NOTE!
These factors dangerous in their unpredictability and a large spread of values.
If moderate winds of a certain direction prevail in the region, then a one-time gust of hurricane force can cause significant damage or completely tear off the roof. In winter, with abnormal in large numbers snowfall load on the roof can exceed the allowable values, which is fraught with deformations or violation of the integrity of the coating and the formation of leaks.
It is possible to deal with such natural manifestations only by preventive measures:
- Creation of a margin of safety in calculations.
- Taking into account the prevailing winds in the region, their strength and direction.
- Taking into account the average annual amount of precipitation, their composition and quality indicators.
- The correct choice of the angle of inclination of the slopes.
Choice right angle the slope of the slopes is one of the most effective methods of neutralizing harmful effects to the truss system. It allows you to reduce the pressure of snow by eliminating its accumulation, adjust the wind load by reducing the windage of the roof and ensure the runoff of rainwater, excluding its freezing at night in the autumn.
Wind loads on truss systems
The dependence of the angle of inclination on the choice of roofing material
From the point of view of saving material and reducing the windage of the roof, 
slope angle should be minimal.
At the same time, a roof that is too sloping will hold large masses of snow or prevent the effective outflow of water.
But most main criterion the angle of inclination is .
Its characteristics determine the optimum, based on the following indicators:
- Rigidity. A quantity that specifies the allowable weight or pressure on a surface without causing deformation.
- Plastic. The ability of a material to change shape under load without breaking.
- Waterproof. Water absorption contributes to rapid destruction material.
- Surface quality. Snow masses easily slide off smooth surfaces, freeing the roof from pressure. At the same time, the gathering of large volumes can cause certain harm people or property caught in the snowfall area.
Based on these parameters, each type of roofing material has its own slope limits. Simplifying somewhat, we can say that materials with a smoother and more water-resistant surface allow the smallest angle of inclination, while rougher and more water-absorbing materials require a steeper slope. Basically dominated values from 20° to 45°.
The dependence of the angle on the angle and roofing material
How to measure the pitch of a gable roof
First of all, you should decide what the angle of inclination is. This is the angle between the slope plane and the horizontal.
The slope of the slopes is usually measured in degrees or percentage. If everything is clear with degrees, then the percentages are obtained from the ratio of the height of the ridge above the ceiling of the upper floor to half the width of the building.
The use of percentages is introduced for simplicity - complex trigonometric calculations error-prone, and dividing one value by another is easier and more accurate. However, they often resort to Bradys tables, to find out the exact value in degrees.
When calculating the angle of inclination of a broken slope, the values \u200b\u200brelated to the areas being determined are used. This applies both to the width - the part that is covered by the roof section is taken into account, and to the height above the ceiling.
All subsequent calculations are made for each section separately, display and use some average value is not possible.
This applies both to the determination of loads and the power of load-bearing elements, and to the calculation required amount material.
How to measure the angle of a gable roof
Minimum slope angle of a gable roof
It is necessary to immediately determine the correct understanding of the term "minimum". This refers to the smallest permissible value of the angle of inclination of the roof, taking into account wind and snow loads.
It is in this moment that many difficulties lie. : indicated values in different regions very different from each other, so need to know the average annual rainfall, volumes of snow and its qualitative composition(wet snow is much heavier than dry snow and can cause destruction incorrectly calculated roof).
In addition, one should have an idea of the prevailing winds, their strength and direction, and, most importantly, the presence of periodic hurricane-force wind gusts in the region.
CAREFULLY!
Ignore such extreme weather manifestations for reasons of “maybe it will blow over” by no means, since one single case is capable of destroy the entire roof.
Given these circumstances, the minimum angle can be defined as smallest value declared in SNIPs adjusted for climatic conditions. Experts clearly see for pitched roofs at least 20°, which applies only to non-residential or unused attics.
Finding the minimum angle
The optimal angle of inclination of a gable roof
The corner of a regular gable roof lies within 20°-45°, which corresponds to the scatter in the values of material properties and averaged climatic parameters.
The angle of inclination of the gable roof - important indicator, affecting the durability and integrity of the entire building, and it is impossible to treat it as a secondary factor.
Accounting for all possible loads, both permanent and one-time extreme, will help ensure safety and comfort of your home.
More exact values are selected based on factors such as:
- Designation of the attic.
- roofing used.
- Climatic conditions.
The optimal angle of inclination of a gable roof
