The erection of the roof of the house is the final stage of construction. This is a responsible event, on which both the durability of the operation of the building and the safety of the people living here depend. You can't do without the right calculation in this matter.
Required element of the entire system is the rafter leg. It will have permanent and temporary loads. Therefore, before installing the roof yourself, you need to familiarize yourself with all the details of this process. There are certain norms and rules that govern the arrangement of the truss system.
General characteristics
The roof truss system is the main load-bearing structure. It bears the main load. To ensure the reliability of the system, each rafter leg is rigidly attached. This allows the roof to withstand gusts of wind, snow drifts and other impacts.
The material for such structural elements is most often wood. It is easier to correct, and the cost of work is significantly reduced. Special attention should be paid to special antiseptic and fire-fighting impregnations.
Tilt angletruss elements is equal to the slope of the roof slopes. The bottom of the rafter legs rests on the Mauerlat. This allows you to evenly distribute the load. The top of these elements rests on a beam under the ridge or intermediate fittings.
Rafter legs are sometimes also called a diagonal or oblique leg, as well as just a rafter.
Load
The rafter leg is exposed to various loads. These are permanent and temporary varieties. The first group includes the total weight that the truss system has, as well as other roofing materials (vapor barrier, waterproofing, roofing material, slate). This also includes elements of interior decoration of a room or attic.
Live loads can occur for a variety of reasons. They can only be calculated approximately. In this case, the maximum possible amount of precipitation that can be observed in this climatic zone is taken into account. Wind gusts can also affect the roof. If in this area they are long and have great strength, this feature should be taken into account when calculating.
It is necessary to take into account the weight of people who will carry out the construction or maintenance of the roof in the future, as well as the total value of their tool. Take into account the load that additional equipment will provide (chimney, antenna, aerator, ventilation, etc.). If additional structures are installed on the roof, their weight is also taken into account.
Calculation rules
To perform the calculation of the rafter leg, it follows after evaluating the loaddetermine the type of material, as well as the type of the roofing system itself. It can be suspended or layered. In the first case, the rafters have two points, but which are the extreme supports. This creates a bursting force horizontally. The legs of the rafters perform work in compression and bending. To reduce this effort, they are connected by stretching.
The layered type of construction is applicable in buildings with an average load-bearing wall or intermediate supports, the ends of which are adjacent to the outer walls. At the same time, the rafter leg performs the function only for bending. At the same time, the total material costs are reduced. But such a system is suitable only for those buildings in which the supports are separated from each other no further than 6.5 m.
When calculating, take into account also the angle of inclination of the roof. At this stage, all additional elements of the system are also considered.
Length
The length of the rafter leg is also calculated in accordance with all existing operating conditions of the roof. Initially, you should determine the size of the building itself. This takes into account all the ledges, verandas, attic, which contains the construction plan.
Next, the shape and angle of the roof slope are thought out. Further, based on the data obtained, choose the length of the rafter leg. Usually this indicator does not exceed 6 m. This is due to the standardization of sawn timber that goes on sale. To purchase longer varieties of products, you will have to shell out a decent amount of money.
If necessary, thesebuilding elements are increasing. The need for long rafter legs sometimes arises when arranging hip, half-hip or diagonal rafters.
Section
After calculating the length, it is required to determine the section of the rafter leg. Its type is influenced by several factors. All operating conditions specific to the roof will matter in this process. The level of loads, the slope of the roof, the type of roof must be taken into account when choosing a section. An important factor is the total area of \u200b\u200bthe building, its configuration. The more factors that affect the operation of the building, the wider the cross section of the rafters should be chosen.
Also, do not forget to take into account the peculiarities of the climate zone. It is important to immediately plan what material is used during the construction of the rafters. Most often it is wood. It must be of good quality. The moisture content of wood for rafters should be 20-22%.
Today, there are many special programs that allow you to calculate the cross section of the rafter leg. To avoid mistakes, you should use them. But it is better to entrust this work to a professional. The most popular section size is 50 x 150 mm.
Step spacing
The rafter leg, the dimensions of which were calculated in accordance with building regulations, requires proper installation. To do this, you will need to calculate the laying step of these structural elements.
In this case, an important role is played by the load that the factors listed above have on the roof. By choosing the right rafter parameters forusing special tables, you can calculate the laying step. With a standard section size (50 by 150 mm) and a length of 3 m, the distance between the rafters will be 1 m.
If the load level is high, it is better to reduce this indicator. This is especially true for slate roofs. In the case of using rafters with a standard section, but 4-4.5 m long, the step between structural elements is reduced to 60 cm.
Roof slope is also important in the calculations. For example, with a slope of 45 degrees, the pitch of the rafters can reach 120-140 cm. But in the event of a large amount of precipitation in this area, this figure is reduced to 60-80 cm.
Mounting basics
The rafter leg assembly consists of several elements. These include crossbar, racks and struts. Their participation in a system of small width is especially important. If this is not done, over time, the truss structure may sag. Therefore, in such cases, they equip a special lattice.
The legs of the rafters are known to rest on the Mauerlat. It is placed across the entire width of the building or placed only under the bottom of the structural elements. If the truss system is wooden, the Mauerlat is made of logs or timber. This is the top of the log. But in brick buildings, the mauerlat is set flush with the inner surface of the walls. A layer of waterproofing is laid between them.
Installation of a conventional roof
The rafter leg and Mauerlat are very important elements of the whole structure. From the correct installationdepends on the quality of the roof. They can be attached in two ways. Installation is rigid or sliding. The correct variety is chosen in accordance with the type of truss system (layered, hanging).
The rigid type of attachment ensures the immobility of the structure. At the same time, cuts are made on the rafters. Structural elements are fixed with metal brackets, corners, wire or long nails.
A sliding joint is also called a hinge joint. If it is necessary to ensure the freedom of settling of wooden elements on the frame, this type of installation is preferable. They make a gash on the rafter leg and fasten it with a Mauerlat with two nails. They are punched in diagonally. Another nail is driven in from above.
Hip roof installation
When arranging a hip roof, the rafter leg is often longer than 6 m. Here you need to build up. Two rafter boards pair. In this case, they need to be strengthened. This procedure involves the arrangement of struts. These are vertical racks, which are installed in the design no more than 2 pieces.
These reinforcements are supported by a wood lining. It is mounted on the ceiling or on the puff. Diagonal rafters are always longer than ordinary ones. They are subjected to a load that is 1.5 times greater than normal. Therefore, the amplification procedure in this case is simply irreplaceable.
Having become acquainted with such an element as a rafter leg, every novice builder will be able to delve deeper into the process of building a roof. Subject to allbuilding codes can achieve high quality construction.
