If you decide to remodel the roof of your private home, or build it from scratch and it comes to building it, you have two options: either resort to the services of professionals, or do it yourself. In the second case, almost every homeowner is faced with the problem of how to calculate the roof of the house so that it does not form a house of cards from the slightest gust of wind. It will allow you not only to calculate the required strength of the structure, but also to find out the required amount of material for its implementation. Below we will consider in detail all the stages of designing such an important element as the roof of the house with your own hands. The calculation should be extremely accurate.
Initial data
To perform the correct calculation, you will need supporting information about the size of the house and the dimensions of some of its elements. To make calculations for the roof as described below, you need information about the approximate weight of the entire structure, including the material that will cover its frame. The cross-sectional size of the beams on which the roof will be held is also important. Calculating the
size of the house can simplify the task somewhat if the roof has no more than 2 slopes.
Rafter system
The roof frame is a
rafter system consisting of a set of wooden beams. Such systems can be very diverse, and their arrangement depends primarily on one or another type of roof that you are going to build.
As a rule, the type of roof is determined by the number of slopes on it, which can vary from one to four. To calculate the required amount of building materials, you need to correctly calculate the strength of the structure, and, consequently, the most optimal length and thickness of the bars. This information, in turn, depends on the number of alleged slopes of the future roof.
The calculation of the required amount of wood material begins with the determination of the type of wood from which the beam will be made. Depending on the source data, the calculation is performed in the following ways:
- with a known value of the cross-section of the bars , the method of their installation is calculated;
- with the already defined method of laying the bars, the required size of their section is calculated.
Load calculation
In order to calculate at what distance from each other it is necessary to stack the bars (laying step), it is necessary to calculate the load on the roof itself. The total load consists of all individual loads. These include the main ones, that is, the weight of the coating and the own weight of the roof, and minor ones: snow cover in the winter season, wind load, the weight of people who from time to time will repair or maintain the roof, being directly on it. We highly recommend that you also provide a sufficient margin of safety in case of extreme situations like hurricanes.
Calculation of the roofs of private houses - the number of rafters
After calculating the total load, you can begin to calculate the required number of rafters to ensure optimal strength of the frame base of the roof. Remember that it is also necessary to take into account the angle at which these rafters will be built.
To determine the maximum permissible load, which will act on one linear meter of timber, use specialized references containing special tables. To ensure sufficient strength with a small margin, calculate the total footage. Next, knowing this indicator, as well as the length of one rafter, calculate the required number of bars. Finally, break their total number into pairs and distribute them along the entire length of the roof structure.
This is how the calculation of the roof of the house is done. A program that automatically calculates loads on structures of this kind can significantly increase the accuracy of your calculations. Finding such a program is not a problem, there are enough of them on the network, and their use is free. Enter in it initial data such as the type of roofing material, the type of timber of the beams, the length and width of the base, the height of the roof, the length of the overhang and the pitch of the rafters, and at the output you will get a lot of useful information, such as the total surface area of the roof, the approximate weight of the rafters and roofing, the required length, section and number of rafters.
The formula for calculating the roof of the house: an example
Suppose that you have already calculated the length, height and other necessary parameters of the future design. Let's say the roof slope is 45 degrees, and the length is 6 meters. The length of the rafters is 4 meters and the maximum load per linear meter of the beam is 100 kg. Calculations of the total load, including wind and snow, led us to the figure of 2000 kg.
In order to calculate the optimal distance at which the pairs of rafters should be from each other and withstand a load of not more than 100 kg per linear meter, divide the total load by the load per linear meter. As a result, you get an acceptable minimum total rafter length. Those. 2000 is divided by 100 and we get 20 meters.
Calculate the required number of rafters now is not difficult, for this, divide the total length by the length of one beam. 20 divided by 4, we get 5 pieces. But this is not all - since the bars are installed in pairs, 5 must be divided into two and rounded to the nearest whole number in a larger direction, if necessary. In our case, it will be 3 pairs. Keep in mind that this is not the final number.
Finally, to get the desired maximum allowable step, divide the total length of the roof by the number of rafter pairs minus one pair, which will be located on the edge. That is, 6 is divided by (3 - 1), we get 3 meters. Note that 3 meters is the maximum permissible distance between the rafters, and for greater reliability, it is recommended to place them closer to each other, for example, every 2 meters.
With a step between the rafters of 2 meters, we will try to re-calculate the required number of rafter pairs. To do this, divide the total roof length of 6 m by a step of 2 m, and get 3 pairs. Do not forget to take into account the pair that will be located at the edge of the roof, so we need 4 pairs of four-meter rafters.
Calculation of the material for the roof
First you need to correctly calculate the surface area of the roof. As in the case of rafters, to perform the calculation of the roof of the house - a program for calculating the area of such complex surfaces is the best solution that will allow you to avoid many mistakes and errors. These programs include 3D Max and Arcon. If you are a confident PC user, understanding them is not difficult. If you are far from 3D modeling, you can use simpler online services.
Suppose you decide to cover your roof with metal tiles. For this material, two types of width are characteristic - real and effective. From the name you can understand that the actual width of the sheet is its actual size. By effective is meant the width of the roof surface, which is covered with a sheet of metal tile, taking into account the overlap of adjacent sheets on it. Actually this is the reason why the effective width is always less than the real one. Suppose the actual width of the sheet of material is 1180 mm. Then its effective width will be approximately 1100 mm.
Having understood the width, you can begin to calculate the length of the roof. It can be measured by the eaves of the roof or by its ridge. We calculate the number of sheets of material needed to lay one row from edge to edge of the roof. Divide the length of the roof by the effective width of one sheet and, if necessary, round the result to a larger integer. Assume that the length of the roof is 7 meters. Then the number of sheets will be equal to 7 / 1,1 or 7 sheets.
Next, we will do the same operation, but now relative to the width of the roof, that is, the distance from the cornice to the roof ridge. In this case, it is important to take into account such additional parameters as the length of the overhang of the cornice and the width covered by the adjacent sheet (as a rule, it is 150 mm).
Let the roof width be 4 m, the eaves 30 cm and the sheet length 1 m. The effective sheet length is 1 m - 15 cm = 85 cm. The total width that needs to be covered is 4 m + 30 cm = 4.3 m. To get the required number of sheets, divide the total width of 4.3 m by the effective sheet length of 0.85 m, and get 5.05. Since the ridge tile partially covers the roof area, the resulting number can be rounded to 5 sheets. Finally, we get their total number to cover the entire surface: 5 * 7 = 35 sheets. Thus, the calculation of the roof of the house. The program (4 pitched roof construction is very difficult for manual calculations) will do most of the computing operations for you.
Insulation material calculation
Since insulating material is usually sold in rolls, the roof area must be divided by the material area in one roll to calculate its quantity. Let us take the simplest case of a gable roof with a length of 7 m and a slope of 4 m wide. We calculate the area of one slope, multiplying the length and width of 28 m 2 . The total roof area is 56 m 2 . Suppose that 80 m 2 of material is wrapped in one roll. About 10 m 2 of them will go to the floors. But even in this case it is already clear that one roll is enough for work.
In cases with more complex forms, use online calculators to calculate the roof of the house. The program will greatly facilitate your work.
Cost calculation
To calculate the approximate cost of the material, you need to multiply the price per unit by its required amount. It is recommended to increase the resulting value by 10%. You should also consider the various spare materials, the cost of transport and other services that you are going to use.
Conclusion
In the end, I would like to remind you that before you start any work, spend more time calculating the roof of the house - a program that can perform calculations with its complex forms will greatly simplify your life and save money.