The roof is one of the most important elements of any building or structure, providing reliable protection from external environmental influences, in particular from precipitation. The correct implementation of the roof structure provides for its waterproofing and high-quality rainwater drainage, which requires that the calculation of the roof slope angle be carried out correctly and accurately, which will be discussed in this article.
In order to correctly calculate the angle of the roof, many factors should be taken into account, the most important of which include:
- Wind. The greater the angle of inclination of the roof, the greater its resistance to wind gusts, but too large values of the angle of inclination can also be dangerous for the roof.For example, the wind load on a roof with a pitch of 45° is 5 times higher than the load on a roof with a pitch of 11°, but at a very small pitch there is a possibility of the roof being torn off by a strong gust of wind.
- Precipitation in the form of snow and rain. It is clear that the greater the angle of the roof slope, the better the snow will fall off it under the action of its own weight. For example, an angle exceeding 45° ensures that all snow masses roll off the roof. In addition, a larger pitch angle provides better roof tightness due to the fact that the wind forces atmospheric water under the roof joints, but increasing the pitch angle reduces the likelihood of water penetrating under the joints of the materials with which the roof is covered.
The above factors help to understand how to calculate the angle of the roof. In regions with strong winds, a slope of 15-20° is recommended, and for areas where winds are not very strong, 35-40°.
At the same time, one should not forget that the calculation is made for each building individually.
When calculating what the roof slope should be, it is also necessary to take into account the design features of the building along with the climatic features of the area.
Calculation methods
The calculation of the roof slope is an important part of the design process of its structure. Most often, the angle of inclination is selected in the range from 11 to 45 °, but other values \u200b\u200bare also found.
Increasing the angle of inclination reduces the load of snow on the roof, but increases the impact of wind currents, requiring reinforcement of the rafters and battens and the acquisition of more durable building materials for this, which increases the overall cost of construction.
Important: in addition to quality, the amount of materials required for its construction also depends on the angle of the roof. Increasing the angle of inclination affects the increase in the cost of the roof.
The minimum roof slope depends on the climatic conditions of the area and on the material chosen for roofing. In a region with a high amount of precipitation, a larger slope angle should be chosen.
To calculate the minimum and optimal roof slope, it is necessary to calculate the load that is expected on the roof during use.
When calculating it, two indicators are taken into account:
- The mass of the structure under construction;
- Load of snow masses in the region.
The calculation is made as follows: for each layer, the mass of one square meter is specified, the values obtained for all laid layers are added together. Further, the result is multiplied by a factor of 1.1.
Roof Slope Calculation Example
Let's give an example of how to calculate the slope of the roof, if the thickness of the crate is 2.5 cm, and 1 sq. a meter of roofing weighs 15 kg. It is planned to lay insulation with a thickness of 10 cm, the weight of which is about 10 kg per square meter. In addition, ondulin will be used for coating, the weight of which is 3 kg per square meter.
The calculation will look like this: (15 + 10 + 3) x1.1 = 30.8 kg / sq.m. According to average statistics, the load on the roof of residential buildings is usually no more than 50 kg per square meter, although the permissible load for many coatings is significantly overestimated, which should also be taken into account.
Useful: a safety factor of 1.1 serves to be able to re-roof later, making the carpet heavier.
Bradis table for calculating the slope of the roof
The coefficient for the snow load depends on the slope angle selected for the roof. If it does not exceed 25°, then the coefficient is 1; when the angle of inclination is from 25 to 60°, a coefficient equal to 1.25 is selected. With a larger roof slope, the snow load is not taken into account.
To calculate the angle of the roof slope, a table of tangents (Bradis table) can be used: the height of the roof in the ridge is divided by half the length of the gable, after which the table contains the angle corresponding to the value obtained.
The height of the ridge is calculated as follows:
- The span width is calculated;
- The span width is divided by 2;
- The resulting value is multiplied by the individual value for the angle of inclination.
Useful: the angle of inclination and the height of the ridge can also be calculated using a square.
For example: let the width of the building be 8 meters. Half of this value is 4 m, it is required to calculate the height of the rafters with a roof slope of 25 °. In the table we find the corresponding indicator, which is 0.47.
We multiply half the width of the building by the value obtained from the table: 4x0.47 = 1.88, i.e. rafters should be raised to a height of 1.88 meters.
The choice of material for the roof in accordance with the angle of inclination
The materials used to cover the roof are grouped according to such criteria as physical and technical parameters, as well as price characteristics.
When choosing a coating material, you can use the following recommendations:
- With a small roof slope, ranging from 2.5 to 10 °, coatings of coarse stone chips or gravel are most often used. The thickness of the top layer of the coating is 3-5 mm for stone chips and 10-15 mm for gravel.
- In case the roof slope exceeds 10° and bituminous base waterproofing is used, the top layer is made of coarse-grained materials. If a roll film material is chosen, an additional layer of color should be used for protection.
- If the angle of inclination in a design such as hip roof, does not exceed 20 °, and the coating is made of corrugated board or asbestos cement sheets, all joints must be sealed.
- With an angle of inclination not exceeding 60 ° and roofing with steel or copper sheets, it is also necessary to seal the joints, which, moreover, must be double.
The use of all the above requirements and recommendations when calculating the roof structure allows you to build a reliable hipped hipped roofcapable of lasting for several decades.
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