Any construction is accompanied by a number of different calculations related to a variety of parameters, for example, the calculation of the strength of the structure or the required amount of building materials. This article will talk about how the calculation of the roof of the house and its individual elements is performed.

When performing such a calculation, a number of auxiliary data are used, for example, various sizes and dimensions.

The calculation of materials for the roof we are considering will require the following information:

The calculation of lumber for a roof requires the cross-sections of the beams and the approximate weight of the entire roof structure, including the covering material;
In order to calculate the material for the roof, its dimensions must be known, as well as the dimensions of the material itself.

First of all, consider the calculation of the rafter system, that is, the roof structure made of wood.

Content

Calculation of the truss system

truss system - This is a set of logs or beams that together make up the roof frame. There are different types of roofs, respectively, and truss systems may differ from each other.

So, for example, roofs can be one-, two-, three- or four-pitched.

The number of slopes affects the results obtained when calculating the strength and finding the most suitable thickness of a log or beam, which also affects the amount of material used.

Therefore, the calculation of the scaffolding for the roof first of all begins with the choice of the type of material.

If the rafter system is made of beams, the calculation can be done in two ways:

The cross section of the beam is known, we calculate the laying parameters;
The installation parameters of the beams are known, it is necessary to calculate the cross section.

Calculation of the step of laying the beams requires a preliminary calculation of the load on the roof, consisting of individual loads, the main of which are the own weight of the roof and the weight of its covering.

The snow cover is considered a secondary temporary load, the pressure of which on the rafter system may at certain moments exceed the load created by the ceilings.

In addition, when calculating the load, you can take into account the weight of people performing various repair or maintenance work on the roof. The wind load is also taken into account when performing the calculation.

Important: when calculating the roof, it is recommended to leave a small safety margin to ensure the safety of the roof in emergency situations, for example, during a hurricane.

After calculating the total load, you should calculate how many rafters need to be distributed at the right angle in order to provide the necessary strength of the roof structure.

This calculation is performed as follows:

With the help of special tables that can be found in specialized reference books, the maximum possible load per linear meter of the rafter beam is determined.
The total footage is calculated, which makes it possible to provide the required strength with a margin.
Given the length of one do-it-yourself rafters their total number is calculated.
The number of rafter pairs is calculated, which are then distributed along the entire length of the roof.

Useful: A roof calculation calculator can also be used to calculate loads, reducing the risk of errors or inaccuracies.

Let's give an example of a specific calculation: let's say that the calculation of the roof has already been completed - height, length and other parameters. The length of the roof is 4.5 meters, the slope angle is 30°.

The cross section of the existing rafters 3 meters long allows you to withstand no more than 100 kg per linear meter.

The calculation of snow and wind loads shows that the total load is 2400 kg.
Taking into account the available data, the step of the rafters, which allows you to create a load per meter that does not exceed 100 kg of force, is calculated quite easily: we divide 2400 by 100, we get 24 as a result. Accordingly, the minimum allowable footage of the rafters is 24 m.
Given that the length of one rafter is known, the required number of rafters is also calculated quite simply - 24/3 = 8 pieces.. Since rafters are installed in pairs, the number of pairs is calculated by simply dividing the number of rafters by two - 8/2 = 4 pairs of rafters.
The minimum distance between the rafters is calculated by dividing the total length of the roof by a number one less than the number of pairs (since one pair is on the edge): 4.5 / (4 - 1) \u003d 1.5 m. Given the initial data, the maximum rafter installation step is 1.5 m, but the greatest reliability is ensured by their installation at a shorter distance, for example, every 90 cm.
This distance will be optimal for laying rafters taking into account the fact that 4.5 m is divided into 90 cm without a trace, that is, 5 pairs of rafters are required. Taking into account the extreme pair, we obtain the desired result: six pairs of three-meter rafters.

Next, the amount of material required to cover the roof is calculated. To do this, you also need to know how to correctly calculate the area of \u200b\u200bthe roof.

Roof coverage calculation

calculation of materials for the roof — Gable roof

The calculation of the material for the roof requires data such as the surface area to be covered and the dimensions of the material used. Assume that a metal tile is used as a roofing material. Consider the calculation of the dimensions of this material.

Useful: to facilitate the calculation of the area, you can also use a special calculator program for calculating the area of \u200b\u200bthe roof.

For metal tiles, similarly to slate, there are two sizes, more precisely two widths - real and effective:

Under the real width understand the actual distance between the edges of the sheet;

The effective width is the width covered by one sheet of material.

Important: when calculating the roof covering, it should be remembered that the value of the effective width is always less than the value of the real width.

This difference appears due to the fact that in the process of laying tiles, each next sheet slightly covers the previous one, both from the side, and from below and from above. Accordingly, the length of the sheet can be classified according to the same criterion.

The standard dimensions of a tile sheet are as follows:

The actual width is 1180mm;
Effective - 1100 mm.

Now that everything is clear with the width, you can proceed directly to the measurements, the purpose of which is to establish the length of the roof that you plan to cover. To do this, the length of the entire roof is measured along the ridge or eaves.

Let's say that the resulting length is six meters. We divide this value by 1.1 m, we get 5.45 as a result. The result is rounded up - we get 6 sheets. This is the required number of sheets of material to lay one row of tiles along the entire length of the roof.

Next, we calculate how many sheets are required to lay one vertical row from the ridge to the eaves. For this, the length of the row is measured, which includes the following parameters:

The distance between the ridge and the eaves;
The length of the cornice overhang;
The size of the overlap, which is usually about 150 mm.

Let us assume that the distance between the ridge and the eaves is 4 m, the sheet protrudes from below by 30 cm. Thus, the total distance is 4.3 m.

Let's also assume that the length of one sheet is 1 meter. Subtracting 15 cm from each overlapping sheet gives an effective sheet length of 85 cm. Therefore, 4.3/0.85 = 5.05 sheets are required to cover the entire row.

Useful: in this case, you can round the resulting value to 5 sheets, since the remaining space can be covered with ridge tiles.

Other calculations

The amount of vapor and waterproofing material is calculated by dividing the area covered by the area of the material used.

Consider at the same time how to calculate the area of \u200b\u200bthe roof: let's say that the roof is gable, the length of one slope is 5 m, the width is 4 m. The total area covered in this case will be 5 x 4 x 2 = 40 m².

Next, the area of \u200b\u200bsteam and waterproofing material in a roll is calculated. Let's say that in one roll 80 m² material, 15% of them are deducted for elements such as overlaps and overlaps. We get as a result 70 m², respectively, one roll of material will be enough.

When performing a cost calculation, both the main materials used and spares should be taken into account.

The cost is calculated by multiplying the required amount of material by the cost of this material, and, in the case of back-to-back material calculation, the calculated cost should be increased by about 10%.

The total cost of a roof also includes the cost of performing roofing work and possible consulting and transport services.

That's all I wanted to talk about the calculation of the roof. When starting construction, it is important to remember that it is better to spend time calculating before the roof is erected than to spend much more time and money later on correcting various shortcomings identified during operation.

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