Truss leg: description, calculation features, dimensions

The erection of the roof of the house is the final stage of construction. This is a responsible event, on which depends both the durability of the operation of the building, and the safety of the people living here. Without proper calculation in this matter is indispensable.

An obligatory element of the whole system is the rafter's leg. It will have constant and temporary loads. Therefore, before you make the installation of the roof yourself, you need to familiarize yourself with all the details of this process. There are certain rules and regulations that govern the arrangement of the rafter system.

general characteristics

Roof rafters are the main bearing structure. She has the main load. To ensure the reliability of the system, each rafter is fixed rigidly. This allows the roof to withstand wind gusts, snow drifts and other impacts.

The material for such structural elements is mostly wood. It is easier to adjust, and the cost of work is significantly reduced. Special attention should be given to special antiseptic and fireproof impregnations.

The angle of slope of the rafters is equal to the slope of the roof slopes. The bottom of the rafters rests against the Mauerlat. This allows you to evenly distribute the load. The top of these elements rests on a bar under the ridge or intermediate adjustments.

Rafting legs are sometimes called a diagonal or foot foot, as well as simply a rafter.

Load

The rafter's leg is subjected to various loads. These are permanent and temporary varieties. The first group includes the total weight, which has a raft system, as well as other roofing materials (vapor barrier, waterproofing, roofing material, slate). Also here include the elements of interior decoration of the room or attic.

Temporary loads can occur due to a variety of reasons. They can be calculated only approximately. In this case, consider the maximum possible amount of precipitation, which can be observed in this climatic zone. Also on the roof can be affected by gusts of wind. If in this area they are long and have great strength, this feature should be taken into account in the calculations.

It is necessary to take into account the weight of people who will perform the construction or maintenance of the roof in the future, as well as the total value of their tools. Consider the load that will be provided by additional equipment (chimney, antenna, aerator, ventilation, etc.). If additional structures are installed on the roof, their weight is taken into account.

Calculation rules

To perform the calculation of the rafter leg, you should determine the type of material after the load evaluation, as well as the type of the roofing system itself. It can be suspended or strung. In the first case, the rafters have two points, but which have extreme supports. This creates a bursting force horizontally. Legs of rafters perform work on compression and bending. To reduce this effort, they are connected by stretching.

The layered type of construction is applicable in structures with an average supporting wall or intermediate supports, the ends of which are adjacent to the outer walls. The rafter leg thus performs a function only for bending. At the same time, the total costs of the material are reduced. But such a system is suitable only for those structures in which the supports are not more than 6.5 m apart.

Performing the calculation, take into account also the angle of the roof. At this stage, also consider all the additional elements of the system.

Length

The length of the rafter is also calculated in accordance with all existing roof operating conditions. Initially, determine the size of the building itself. This takes into account all the ledges, verandas, attics, which contains the plan of construction.

Further, the shape and angle of the roof slope are considered. Further, based on the received data, the length of the rafter is chosen. Usually, this figure does not exceed 6 m. This is due to the standardization of sawnwood for sale. To buy longer types of products, you will have to pay a decent amount of money.

If necessary, these elements of the construction increase. The need for long rafter legs sometimes arises in the arrangement of hip, half-wool or diagonal rafters.

Section

After calculating the length it is required to determine the cross-section of the rafter leg. Several factors influence its type. All the operating conditions, characteristic of the roof, will have significance in this process. The level of loads, the slope of the roof, the type of the roof must be taken into account when choosing a section. An important factor is the total area of the building, its configuration. The more factors will influence the operation of the building, the wider the cross-section of the rafters should be selected.

Also do not forget to take into account the peculiarities of the climatic zone. It is important to immediately plan what material is used during the construction of rafters. Most often it is wood. It should be of good quality. The humidity of wood for rafters should be 20-22%.

To date, there are many special programs that allow you to calculate the cross-section of the rafter. To avoid mistakes, you should use them. But it is more correct to entrust this work to a professional. The most popular section size is 50 by 150 mm.

Paving step

The rafter leg, the dimensions of which were calculated in accordance with the building rules, requires proper installation. To do this, you need to calculate the step of laying these elements of the structure.

In this case, an important role is played by the load exerted by the factors listed above on the roof. Correctly selecting the parameters of rafters using special tables, you can calculate the laying step. With a standard section size (50 to 150 mm) and a length of 3 m, the distance between the rafters will be 1 m.

If the load level is high, this figure is better reduced. This is especially true for roofing from slate. In the case of using rafters with a standard cross-section, but 4-4.5 m in length, the step between the structural elements is reduced to 60 cm.

The slope of the roof is also important in the calculations. For example, with a slope of 45 degrees, the rafter step can reach 120-140 cm. But in the case of a large amount of precipitation in this area, this figure is reduced to 60-80 cm.

Basics of installation

The rafter assembly consists of several elements. These include bolt, struts and struts. Particularly important is their participation in a system of small width. If this is not done, in time the rafter structure can sag. Therefore, in such cases, a special grid is arranged.

The legs of the rafters, as is known, are based on the Mauerlat. It is placed over the entire width of the structure or placed only under the bottom of the structural elements. If the rafter system is wooden, the mauerlatt is made from a log or a beam. This is the top of the frame. But in the brick buildings of the Mauerlat, the level of the inner surface of the walls is leveled. A layer of waterproofing is laid between them.

Installation of a regular roof

The rafter and mauerlat are very important elements of the whole structure. From the correctness of their installation depends the quality of the roof. They can be mounted in two ways. Installation is hard or slippery. The correct variety is chosen in accordance with the type of rafter system (nylon, hanging).

The rigid type of attachment ensures the immovability of the structure. At the same time on the rafters do zapily. Elements of the construction are fixed with metal staples, 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. On the rafter, they make a drink and fasten it with a mauerlat with two nails. They are hammered obliquely. Another nail is driven from above.

Installation of the hip roof

When equipping a hip roof, the rafter's foot often turns out to be longer than 6 m. Two rafters are paired. In this case, it is required to perform their amplification. This procedure involves the arrangement of struts. This is a vertical rack, which in the design set no more than 2 pieces.

These reinforcement elements are supported by a lining of wood. It is mounted on the ceiling or on the puff. The diagonal rafter elements are always longer than the ordinary ones. They are exposed to a load that is 1.5 times larger than usual. Therefore, the amplification procedure in this case is simply irreplaceable.

Having become acquainted with such an element as a rafter's leg, every novice builder will be able to delve deeper into the process of erecting the roof. With all building codes and rules, it is possible to achieve a high quality construction.