The rafter system acts as the main bearing part of the entire roof structure. It determines the stability and strength of the upper part of the house. Rafters must withstand the weight of the roofing material, the pressure of snow and wind, therefore, when choosing the most appropriate variation of the system, the climatic features of the region should be taken into account. The main functional elements of the truss structure are inclined struts, vertical racks and rafter legs.
Materials for the manufacture of rafters
The manufacture of rafters can be carried out using metal elements or wood. Each of the existing variations of rafters has its own characteristics.
Metal rafters
The main functional elements of the metal rafters
Metal structures are manufactured from steel products by electric arc welding. This system is characterized by maximum rigidity. In most cases, the racks of the metal profile are installed under ridge runs and used as supports. For carrying out assembly work, special equipment may be required. It is most expedient to use a metal variation of the rafters in such cases:
- with a high wind load on the roof;
- if the roofing system has a complex geometry;
- with a large mass of roofing material;
- in the case of long span lengths.
If a mixed rafter system is to be installed, contacting of metal elements with wood should be prevented. Otherwise, rotting of the tree is possible due to overmoistening caused by condensation on the metal surface.
Elements of the metal rafter system are characterized by high thermal conductivity. This feature leads to rapid heating and instant cooling of the material. In this context, there is a need for more thorough insulation of the roof.
Wooden rafters
Wooden rafters must necessarily be subjected to fire and antibacterial treatment.
A good alternative to metal structures - rafters made of wood. They are extremely easy to install and can be assembled directly on site. Most often for the device of the system a pine beam with section 150х150 mm is used. It is quite suitable boards size 50h150 mm.
It should be noted here that under a prolonged exposure to mechanical stress, the tree may become deformed. To avoid this, it is recommended to pre-treat the material with waterproofing agents or resort to the use of film insulation. Also, care should be taken to ensure good ventilation of the subspace.
Processing of wooden rafters
Antibacterial and fire-fighting treatments are vital procedures that should be carried out at a preliminary stage. Treatment with antibacterial compounds helps to prevent rotting processes and increases the operational potential of the material. Fireproofing reduces the flammability of the material, making it as stable as possible to direct exposure to open flames.
Rigid systems of nylon and hanging type
All rafter structures are divided into two types - layered and hanging. The choice of the system is determined by the structural features of the building. Regardless of the chosen version, the finished structure should be as stable as possible to negative factors of various types, among which:
- atmospheric precipitation;
- wind load;
- increased humidity;
- temperature fluctuations;
- negative impact of living microorganisms.
Features of suspended rafters
Hanging rafters
Hanging type suspension system is used in the construction of single-span buildings made of brick or stone. Rafting legs of this design have only two points of support, which serve as bearing walls of the house. The system creates a bursting force, which is transmitted to the walls of the building.
In order to compensate for this load, it is best to resort to the arrangement of the tightening. It will be able to connect each rafter pair in the lower part, so that the pressure exerted on the walls will be minimal. To ensure maximum effect above the base of the rafters, an additional tightening can be installed - the bolt.
The rafters of the hanging type system are supported by a support beam - Mauerlat. At the same time, the connection of the rafter and the base of the structure is carried out by means of a cutting. Additionally, the design can be fixed with a bracket or bracket.
Features of layered rafters
roof rafters A characteristic feature of the layered rafters is the need for an intermediate bearing wall. They are used for all types of roofing structures, regardless of the material of the walls of the house. They are also widely used in the creation of roof skylights.
The upper part of the layered construction rests on the ridge beam. The latter is supported by special supports. At the bottom, the rafter's legs rest against the harness. This design feature contributes to the fact that the main load is transmitted vertically. As a result, overall weights tend to decrease and there is no need to mount a horizontal tightening.
Rafter legs create maximum bending force, and the compression load is almost completely removed. This is why thin slabs can be used in the work, which makes the whole structure easier. Here you can talk and considerable monetary savings.
Roof truss system
Roof truss system
Shaped roofs look like a pyramid. The basis of such a design can be a square or a rectangle. The plane of triangular skates here is joined at the top. A characteristic feature of such roofs is the absence of pediments.
The entire rafter system is supported by a Mauerlat, which must be as firmly attached to the wall as possible. From the horizontal shift in the further operation of the Mauerlat will protect the outer walls. Provided that the roof does not differ in size, you can resort to using a short bar. The connection of individual elements is carried out at an angle of 90 degrees.
Structurally, this system has four load-bearing rafters, which are fixed in the corner of the base of the roof. They can have a layered or hanging execution. At the top of the rafters converge at one point.
Hinged roofing system
Hinged roof
Hip roofs are also not equipped with gables. Two rajet planes of such a roof have the form of a trapezoid, and the other two are triangles. Raft legs in this system are arranged diagonally. The formation of stingrays of the hip roof occurs due to the intermediate rafters. For their fastening is used Mauerlat and beams skates. The distance between the individual elements must vary between 100-120 cm.
The basis for the rafters at the top is the run of the skates. It is presented in the form of a wooden beam, the section of which is identical to the section of the diagonal rafters. Cantilever rafters should be the longest. This allows them to withstand the maximum load that is transmitted from the workers.
Sloping roof sloping system
Sloping roof sloping system
When installing a suspended roof rafter system for a broken roof, it should be borne in mind that two kinds of loads - compression and bending - will end up on the rafter's legs. To minimize the influence of these factors, it is recommended to resort to using a tightening in the lower part of the structure. Subject to the installation work, the performer will have to solve the following tasks:
- Prepare the drawing.
- Determine the optimal slope of the roof structure.
- Choose the most suitable type of rafter system.
- Calculate the number of required materials.
- Assemble the main part of the structure on the ground.
- Lift the structure up and continue installation.
- Ensure the reliable fixation of individual elements of the system.
Raised trusses for wide spans
It is recommended to use rafter trusses in case of a large span. Through their use, you can create a roof of any configuration. The magnitude of the slope may vary depending on the individual preferences of the owner of the object. With their help, it is possible to design an attic floor. Rafting trusses can be made directly on the construction site or ordered ready-made structures.
Roof trusses for wide spans constructively include the following elements:
- puffs;
- braces;
- rafter feet;
- racks;
- crossbars.
System components are installed within the upper and lower belt. This eliminates the need for additional supports. The pressure on the structure is transmitted only vertically.
What in the end?
The roofing system is selected depending on the structural features of the roof and the building as a whole. From the literacy of the installation work depends directly on the reliability and lifetime of the roof. In order for it to be maximum, it is necessary to approach very carefully the resolution of this issue.
