An important stage in the design of a house and the preparation of an estimate for its construction is the calculation of the roof being erected, on the correctness of which both the cost of materials and the cost of arranging the roof, as well as the subsequent costs of repair and maintenance of the roof, depend. This article will talk about how to calculate the roof, namely, the calculation of its area and angle of inclination.
Before you correctly calculate the roof, it should be borne in mind that the shape of the roof has a direct impact on the complexity of the calculation, especially for a large number of broken lines and complex elements, such as attics.
To understand how to calculate the area of \u200b\u200bthe roof, the following points should be understood:
- Various roof elements such as ventilation holes, chimney pipes, attic windows, etc. included in the calculation of the total area;
- The length of the roof slope from the edge of the eaves to the lower element of the ridge must be determined with maximum accuracy;
- It is mandatory to calculate such roofing elements as firewall walls, parapets, overhangs, etc.;
- When calculating, the type of coating used should be taken into account;
- Take into account the reduction in the length of the slopes by 70 centimeters when using roofing materials such as rolls or tiles.
In order to calculate the roof on your own, it is recommended to conditionally divide the area of \u200b\u200bthe entire roof into separate parts and calculate each of them separately, and then add the resulting values together.
To calculate the area of each of the parts, mathematical formulas are used to calculate the areas of geometric shapes, such as a trapezoid, triangle, rectangle, etc.
After the calculations of the slope areas are completed, their angle of inclination should be calculated by multiplying each element by the cosine of the slope angle of the corresponding roof element.
Important: it should be borne in mind that only the overhangs of the cornices are used in the calculation.
In the case of simple roof structures, such as gable roofs, the slope of which is 30º, the calculation is greatly simplified: it is enough to multiply the cosine of the angle and the area of the slope. For more complex designs, it is recommended to use special calculator programs, which can be found in large numbers on the Internet.
The calculation of the roof slope and its area performed in this way will turn out to be the most accurate, gross errors will not be made in it, which can lead to a re-covering of the roof in the future.
Roof area calculation
To calculate the roof area, the first step is to take into account the type of roof itself:
- The calculation of the area of \u200b\u200ba combined roof, which is most often used in outbuildings, is the easiest: just multiply the length and width of the roof together.
- Attic and mansard roofs are used in residential buildings, the area of \u200b\u200bwhich is much more difficult to calculate due to the wide variety of structures, such as gable, four-slope, flat, hip, etc. In this case, the angle of the roof slope is first calculated, which is from 11 to 70º, depending on the conditions of the area in which the building is built.
In order to purchase the right amount of roofing material, it is necessary to correctly calculate the area of the roof, while taking into account a sufficiently large number of different elements, and often specific features of a particular type of roof are also provided.
In addition, other units are used to calculate many materials, such as sheets, pieces, rolls, etc.
To perform a calculation roof material in pieces, you need to know the exact values \u200b\u200bof the slope and height of the roof. A simple mathematical formula is used for the calculation; for a galvanized or soft roof, the following formula is used:
Roof area = (2 x eaves width + building length) x (2 x eaves width + building width) / cos (roof slope), all values used for this formula should be taken by slopes.
It is advisable to calculate the area of more complex roof structures (hipped, broken, four-pitched, etc.) not manually, but using special calculators.
Calculation of the angle of the roof
Let's talk about how to calculate the slope of the roof, which is a very important stage in the design of the roof. Most often, an angle from 11 to 45º is chosen for the construction of a roof, but other angles are also found depending on climatic conditions and design decisions.
Increase roof pitch angle allows you to reduce the load of the snow cover, but at the same time the impact of wind currents increases, requiring increased costs for the use of more durable materials, battens and rafters.
In addition, it should be remembered that in addition to the quality, the amount of material required for the construction of the roof also depends on the angle of inclination: a larger angle requires more material costs.
Roof slope should be chosen on the basis of the material chosen for the construction of the roof, as well as the climate of the area in which the construction is carried out: the more often precipitation falls in the area, the greater the slope of the roof should be.
To calculate the required angle of inclination, the planned roof load should be calculated, for the calculation of which two main parameters are used:
- The weight of the erected structure;
- Snow loads in the region.
The calculation is made as follows: you should find out the weight of 1 m2 each of the layers of the roof, add up these indicators and multiply the resulting amount by a factor equal to 1.1.
Let's give an example of calculation: let's say that the thickness of the crate is 25 mm, and 1m2 of this material weighs 15 kg. For the roof, it is planned to use insulation, the layer thickness of which is 10 cm, and the weight is 10 kg per 1 m2. Ondulin is used as a roofing, the weight of which is 3 kg per 1 m2.
We perform the calculation according to the formula, we get (15 + 10 + 3) * 1.1 = 30.8 kg per 1 m2.
According to average indicators, in the case of residential buildings, the roof load is usually no more than 50 kg per 1 m2, and the allowable loads for many floors are significantly overestimated.
Useful: if after a certain long period of time the roofing will be replaced, and the new carpet will be much heavier. It is as a margin for such a case that a safety factor of 1.1 is used.
Next, we calculate the load created by the weight of the roof itself, denoting it for simplicity as H:
H = 50 kg/m2 x 1.1 = 55 kg/m2.
Important: when calculating the cross section of the rafter leg, the weight of the rafter itself must be added to the weight of the roofing carpet.
Did the article help you?