Roof is an important element of any building. Its main purpose is to protect the internal space of the house from adverse environmental factors. It takes on all possible external loads and evenly distributes them to all walls. Roofs of various designs can be erected on buildings. But in Russia, the most popular is, of course, a gable roof. The calculation of such a structure is not difficult. Its advantages are ease of design and construction.
Basic elements
Such a roof, as you can already judge by its name, consists of only two slopes located on both sides of the building. The main elements of the roof of this design are:
- Mauerlat;
- skate;
- rafters;
- racks and struts;
- sheathing.
A gable roof is usually erected in the following order:
- A Mauerlat is fixed on the anchors previously cast into the walls.
- A skate is mounted on the racks.
- The rafters and struts are being installed.
- The crate is being installed.
Further, the resulting structure is sheathed with insulating material, waterproofing 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 should, of course, be drawn up. This will avoid wasting material and save time and effort.
When drawing up a gable roof drawing, calculations are usually performed as follows:
- slope angle;
- lengths and cross-sections of timber for rafters;
- step between rafters.
In order to determine the required amount of insulation, waterproofing and roofing material, you will also have to calculate the area of \u200b\u200bthe slopes and gables. It is with all these indicators in mind that the roof of a gable roof is calculated.
Tilt angle limits
It is from the angle of inclination of the slopes that you should start calculating the gable roof when building a house. This indicator in this case may depend on several factors:
- of the type of roofing material chosen for sheathing;
- estimated wind load;
- snow load.
In the first case, the recommendations of the material manufacturer are taken into account first of all. So, for example, the minimum tilt angle:
- for metal tiles will be 14 degrees;
- for roll materials - 5 - 15 gr;
- corrugated board - 15 gr;
- Ondulina - 6 gr.
Depending on the wind and snow load, the maximum permissible values for the angle of inclination of the slopes are determined by special maps of the areas. Also in this case, special tables are used. For example, with strong wind loads, it is recommended to make slopes more gentle - 15 - 25 degrees. With an abundance of precipitation in the area where the house is being built, they, on the contrary, should be equipped with steeper - 45-60 degrees.
Gable roof rafters: calculating the angle of inclination
So, having learned the maximum allowable indicators, you can actually start drawing up a drawing of the roof. The first step 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 ridge too much above the level of the walls. This will save on material. If it is planned to equip a dwelling under the roof (which is rare), it is worth building it high enough. In any case, the optimal slope angle in most areas of Russia is 30 - 45 degrees.
In addition to the height of the ridge, to calculate the slope of a 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=1/2LtgA. A is the actual angle of inclination of the slope, H is the height of the ridge, L is the width of the pediment. The tangent of an angle can be determined usingMathematical table Bradis.
Calculation of gable roof rafters: length and section
It is these elements in the design of a gable roof that are the main ones. The cross-section and length of the rafters should be calculated, first of all, based on the fact that for 1 m2 of the slope area, the weight of materials should not exceed 45 kg.
Most often, a beam with a section of 100 x 150 cm is used to assemble a gable roof. Such material would be ideal with a step between the rafters of 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 thinner rafters.
The length of the beam is determined depending on the height of the ridge and the width of the gable (divided by 2). The rafters in this case in a right triangle will play the role of the hypotenuse. Determining 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 simply need to be multiplied by the sine of the angle of inclination. You can find out this indicator from the Bradis table.
To the final result, add about 20 - 40 cm for overhangs. It is a must to set them up. Otherwise, in the future, during the operation of the house, rainwater will fall on its walls. And this, in turn, will significantly reduce the life of the building.
Sami lumber for rafters should choose only high quality. After all, it is this roof element that is load-bearing. Bars with a large number of knots for rafters cannot be used. These elements should be fastened to the mauelat and the ridge using only galvanized corners or high-quality nails.
Calculate the area of the slopes and the amount of material needed
Thus, calculations are made for the angle of inclination of a 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 \u200b\u200bthe slopes. In this case, no particularly complex formulas will also have to be used. You can find out the area of one slope by simply multiplying the length of the rafter by the length of the building itself.
It is easy to determine when designing and the amount of material needed for sheathing. For example, when using roofing felt, you must first calculate the area of one roll. To do this, multiply its width by its length. Further, the area of \u200b\u200bthe slope is simply divided by the area of \u200b\u200bthe roll. When calculating in this case, it is also necessary to take into account the expected number of skin layers. Calculations are also made when using sheet materials, for example, metal tiles or corrugated board.
Calculation of gable area
This part of the roof structure is usually covered with boards. To calculate the gables of a gable roof, you will need indicators such as the height of the ridge and the width of the span of the house. By determining the area of this part of the roof structure, you canwill 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.
Helpful advice
Having calculated the area of \u200b\u200bthe slopes and the gable, it is easy to determine the amount of material needed for sheathing. However, you should definitely purchase roofing sheets and boards with a margin. After all, when sheathing the roof, part of the material will certainly be damaged. Waste in such a case is usually inevitable. And cutting boards or sheets as rationally as possible is far from always possible.
Features of assembling a gable roof: how to avoid mistakes
Thus, having correctly drawn up the project and performed all the necessary calculations, the roof can be built as reliable as possible. However, in order for the roof of two slopes to be durable, certain recommendations should be followed directly during its assembly:
- ventilation must be provided before the insulation layer in the roofing cake;
- the plates of heat-insulating material themselves should adjoin each other and the structures of the truss system as tightly as possible;
- The vapor barrier film in the cake is fixed with adhesive tape, not nails;
- the crate should be stuffed in increments corresponding to the selected material.
To assemble the roof in order to make it reliable, it should be without violating any technology. The gable roof pie is mounted as followsway:
- Insulation boards are laid between the installed rafters. From the side of the attic, so that they do not fall out, a rare mesh of steel or aluminum wire is pulled.
- A waterproofer 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 when the roof moves, as well as equip the ventilation layer.
- A crate is mounted above the waterproofer.
The vapor barrier of a gable roof is being installed from the side of the attic. Sheathing material is mounted above the film, fixed with a tape. It can be, for example, plywood, lining, plastic panels, etc.
Basic for roofing material
To calculate the crate when drafting a gable roof, factors such as the weight of the roofing material and the possible snow load should be taken into account. Under a metal tile, for example, supporting boards can be packed in increments of 230 - 400 mm. Under the roofing material, the crate is equipped with a solid one, etc.
Lumber for the base under the roofing material is also selected taking into account the weight of the latter. Both a bar and a board can be used to assemble the crate. In any case, it is not recommended to take too wide lumber for mounting the base. Otherwise, the elements of the crate during the operation of the roof may twist. Also, wide boards often crack, which can make the fastening of sheets of sheathing material not very reliable. The best option for cratestimber or boards are considered to be 150 mm wide.
