When it comes to the roof of buildings, the word "slope" means the angle of inclination of the roof sheath to the horizon. In geodesy, this parameter is an indicator of the steepness of the slope, and in the design documentation this is the degree of deviation of straight elements from the baseline. The slope in degrees does not cause any questions, but the slope in percent sometimes causes confusion. The time has come to deal with this unit of measurement in order to clearly understand what it is and, if necessary, easily translate it into other units, for example, in the same degrees.
Percentage slope calculation
Try to imagine a right triangle ABC lying on one of its legs AB. The second BC leg will be directed vertically upward, and the AC hypotenuse will form a certain angle with the lower leg. Now we have to recall a little trigonometry and calculate its tangent, which will precisely characterize the slope formed by the hypotenuse of the triangle with the lower leg. Suppose that the leg AB = 100 mm and the height BC = 36.4 mm. Then the tangent of our angle will be 0.364, which according to the tables corresponds to 20Λ. What then will the percent bias be equal to? To translate the obtained value into these units of measurement, we simply multiply the tangent value by 100 and we get 36.4%.
How to understand the slope angle in percent?
If the road sign shows 12%, then this means that on every kilometer of such ascent or descent, the road will rise (fall) 120 meters. To translate the percentage value into degrees, you just need to calculate the arctangent of this value and, if necessary, convert it from radians to familiar degrees. The same goes for construction drawings. If, for example, it is indicated that the slope angle in percent is 1, then this means that the ratio of one leg to the other is 0.01.
Why not in degrees?
Many are probably interested in the question: βWhy use some other percentages for the slope?β Indeed, why not just do it by degrees. The fact is that in any measurement there always occurs some error. If degrees are used in the project documentation , then installation difficulties will inevitably arise. Take at least the same sewer pipe. An error of several degrees with a length of 4-5 meters can lead it to a completely different direction from the desired position. Therefore, the instructions, recommendations and design documentation usually apply interest.
Practical application
Suppose that a country house construction project involves a pitched roof. It is required to check its slope in percent and degrees, if it is known that the height of the ridge is 3.45 meters, and the width of the future dwelling is 10 meters. Since the roof in front is an equilateral triangle, it can be divided into two right-angled triangles, in which the height of the ridge will be one of the legs. We find the second leg, dividing the width of the house in half.
Now we have all the necessary data for calculating the slope. We get: atan
-1 (0.345) β 19Λ. Accordingly, the percentage bias is 34.5. What does this give us? Firstly, we can compare this value with the parameters recommended by specialists, and secondly, check the requirements of SNiPa when choosing a roofing material. Referring to the directories, you can find out that for laying
natural tiles such a level of inclination will be too small (the minimum level is 33 degrees), but such a roof is not afraid of powerful gusts of wind.