The roof is an important element of any building. Its main purpose is to protect the internal space of the house from adverse environmental factors. She takes on all possible external loads and evenly distributes them to all walls. Roofs of different designs can be erected on buildings. But in Russia, the most popular is, of course, a gable roof. The calculation of this design is simple. Its advantages are the simplicity of design and construction.
Essential elements
Such a roof consists, as can already be judged by its name, of only two slopes located on both sides of the building. The main elements of a roof of this design are:
- Mauerlat;
- horse;
- rafters;
- struts and struts;
- crate.
A gable roof is usually erected in the following order:
- Mauerlat is fixed to the ones previously poured into the walls of the anchor.
- A skate is mounted on racks.
- Rafters and struts are installed.
- Mounted crate.
Next, the resulting design is sheathed with insulation material, a waterproofing material and roofing sheets.
What is important to consider when designing
Thus, the gable roof structure is extremely simple. However, the project before assembling the roof, of course, follows. This will avoid overuse of the material and save time and effort.
When drawing up a gable roof, the calculations are usually performed as follows:
- slope angle;
- lengths and sections of a bar for rafters;
- step between the rafters.
In order to determine the right amount of insulation, waterproofing and roofing material, you will also have to calculate the area of slopes and gables. It is with all these indicators that the calculation of the gable roof is performed .
Tilt Angle Limits
It is from the angle of inclination of the slopes that you should start calculating the gable roof during the construction of the house. In this case, this indicator may depend on several factors:
- the type of roofing material selected for cladding;
- estimated wind load;
- snow load.
In the first case, the recommendations of the material manufacturer are taken into account primarily. So, for example, the minimum angle of inclination:
- for metal will be 14 degrees;
- for rolled materials - 5 - 15 g;
- corrugated board - 15 gr;
- ondulin - 6 gr.
Depending on the wind and snow load, the maximum permissible values of the slope angle are determined by special terrain maps. Also in this case, special tables are used. For example, with strong wind loads, slopes are recommended to be made more gentle - 15 - 25 degrees. With an abundance of rainfall in the area where the house is being built, they, on the contrary, are supposed to equip with more abrupt - 45-60 degrees.
Rafters of a gable roof: calculation of the angle of inclination
So, having learned the maximum permissible indicators, you can proceed to the actual drawing up of a roof drawing. The first thing to do with this is to determine the height of the ridge. If it is decided to make an ordinary attic under a gable roof, it is not worth raising the skate too much above the level of the walls. This will save on material. If it is planned to equip a living space under the roof (which is rare), it is worth building it quite high. In any case, the optimal slope angle indicators in most areas of Russia are 30 - 45 degrees.
In addition to the height of the ridge, to calculate the slope of the gable roof, or rather the angle of inclination of its slopes, you will need such an indicator as the width of the pediment. It can be determined by simply measuring the short wall of the house, then you need to add the length of the overhangs to the result. Further, the calculation is performed using the following formula: H = 1 / 2L * tgA. A is the slope angle itself, H is the height of the ridge, L is the width of the pediment. The tangent of the angle can be determined using the Bradis mathematical table.
Calculation of rafters of a gable roof: length and section
It is these elements in the construction of the gable roof that are the main ones. The cross section and length of the rafters should be calculated primarily on the basis that the weight of materials should not exceed 45 kg per 1 m 2 of slope area.
Most often, a beam with a cross section of 100 x 150 cm is used to assemble a gable roof. Such a material will be ideal when the pitch between rafters is 80 - 100 cm. If the project provides for a greater distance between these two elements, it is worth using a thicker beam. With a smaller step, on the contrary, it is allowed to install the rafters thinner.
The length of the beam is determined depending on the height of the ridge and the width of the pediment (divided by 2). The rafters in this case in a right triangle will play the role of a hypotenuse. Determine the length of the beam is not difficult. You can also calculate the length of one beam, simply focusing on the angle of inclination of the gable roof. In this case, you will additionally need such an indicator as the height of the ridge. This figure will just need to be multiplied by the sine of the angle of inclination. You can find out this indicator from the Bradis table.
About 20–40 cm per overhang should be added to the final result. Arranging them is a must. Otherwise, later in the operation of the house, rainwater will fall on its walls. And this, in turn, will significantly reduce the life of the building.
Lumber for rafters themselves should be selected only high-quality. After all, it is this roof element that is the bearing. Bars with a large number of knots for rafters can not be used. Fasten these elements to the Mauelat and the ridge using only galvanized corners or high-quality nails.
Calculation of the area of slopes and the amount of necessary material
Thus, calculations are made of the slope of the gable roof, the length and cross section of its rafters. But in order to determine the amount of material needed for sheathing, you also need to know such an indicator as the area of slopes. In this case, you will not have to use any particularly complex formulas. You can find out the area of one slope by simply multiplying the length of the rafters by the length of the building itself.
When designing, it is easy to determine the amount of material required for sheathing. For example, when using roofing material, you must first calculate the area of one roll. To do this, multiply its width by length. Further, the area of the ramp is simply divided by the area of the roll. In the calculation in this case, it is also necessary to take into account the estimated number of skin layers. Calculations are also made when using sheet materials, for example, metal tiles or corrugated board.
Calculation of the area of the gables
This part of the roof structure is usually covered with boards. To calculate the gables of a gable roof , indicators such as the height of the ridge and the span of the house will be needed. Having determined the area of this part of the roof structure, it will be possible to find out the number of boards needed for sheathing. The calculation in this case is made according to the formula: S = 1 / 2ah, where S is the area, a is the width of the pediment, h is the height of the ridge.
Useful advice
Having made the calculation of the area of slopes and pediment, it is easy to determine the amount of material required for sheathing. However, it is imperative to purchase roofing sheets and boards with a margin. After all, when covering the roof, part of the material will necessarily be spoiled. Waste in such a case is usually inevitable. And cutting boards or sheets as rationally as possible is far from always possible.
Features of the assembly of a gable roof: how to avoid mistakes
Thus, having correctly designed the project and having completed all the necessary calculations, the roof can be built as reliable as possible. However, in order for the roof of two slopes to turn out to be durable, certain recommendations should be observed directly during its assembly:
- before the insulation layer in the roofing pie ventilation must be equipped;
- the plates of the insulating material themselves should adjoin each other and the structures of the rafter system as tightly as possible;
- the vapor barrier film in the cake is fixed with adhesive tape, not nails;
- the crate should be packed in increments corresponding to the selected material.
To collect the roof so that it turns out reliable, it should, without violating any technology. The gable roof cake is mounted as follows:
- Between the installed rafters, insulation boards are laid. From the attic side, so that they do not fall out, a rare mesh of steel or aluminum wire is pulled.
- An insulator is mounted above the insulation. It is best to fix it with a slight sag on the bars. This method will avoid tearing the material during roof movements, as well as equip the ventilation layer.
- Over the waterproofing, a crate is mounted.
The vapor barrier of the gable roof is arranged from the attic. Over the film, fixed with a tape, the sheathing material is mounted. This can be, for example, plywood, lining, plastic panels, etc.
Base for roofing material
To calculate the crate, when designing a gable roof, factors such as the weight of the roofing material and possible snow load should be taken into account. Under the metal tile, for example, the supporting boards can be filled in increments of 230 - 400 mm. Under the roofing material, the crate is solid, etc.
Lumber for the base under the roofing material is also selected taking into account the weight of the latter. To assemble the lathing, both a beam and a board can be used. In any case, taking too wide lumber for mounting the base is not recommended. Otherwise, the elements of the lathing during the operation of the roof can twist. Also, wide boards often crack, which may make the fastening of sheets of sheathing material not very reliable. The best option for the lathing is a bar or board with a width of 150 mm.