The strength, as well as the stability of the roof, depends directly on the supporting structure, which is presented in the form of a rafter system. The basis of the rafter system is, respectively, rafters. Roof — the outer surface of the roof, which is laid directly on the structure consisting of a crate and a system formed by rafters. The rafters must withstand not only the weight of the roofing material laid on them, but also the load on it of snow masses in winter and gusts of wind. The rafter structure is selected based on the chosen roofing material, and the level of snow loss, and the strength of the wind gusts characteristic of this type of area are important here, are important here.
Design
The main element in the rafter system is a triangle. This triangle is usually formed using two standard rafter legs. These are the so -called upper and lower farm belts.
The main element of each farm is the so -called rafter legs. They are solid elements and lay strictly along the slope of the roof, their task is to maintain the crate.
The crate is called the totality of bars laid at an angle of 90 degrees on construction legs. She assumes the pressure of roofing material, and directly presses on the rafters. They, in turn, direct the pressure of the roof itself to the supporting walls. The crate, depending on the distance between the bars, may be: continuous, the distance between the individual bars does not exceed one centimeter, and the distance between the bars is 3-4 centimeters. The bars forming a crate are nailed to the rafters with special nails. Typically, the length of such nails is two thicknesses of bars. The rafter structure with two belts can withstand only the lightest roof. Heavy roofing materials require hard thoroughly support. Therefore, almost all rafter systems are equipped with all kinds of supports, for example, racks, fights or struts. In order to get a hard frame, the rafters are fixed with each other, and so that in the future the roof is not torn by the wind, the frame itself is firmly associated with the very box of the house. Beams are attached to the wall, and in brick houses a strong wire clamp is usually put on the rafters, which is tied to the pins driven into the wall.
Types of rafter structures
There are two main types of rafter structures: hanging and lounge (not to be confused with inclined!) rafters.
The rafters of the first type are based on extreme supports, the work of their rafter legs is aimed, respectively, at the bend and compression.
Named rafters, in turn, are installed in houses with a central carrying wall or intermediate support. With the ends of the rafters they rest on the outer walls, and their central part on the support. Unlike hanging rafters, layers work, exclusively on bending.
As the main material for rafters, wood is most often used. This is because they can be easily installed and, so to speak, adjusted to the required size. This means that they can be increased or trimmed, pushed. Such manipulations may be needed in cases of low -quality construction of walls, which, for example, cannot be done with metal structures. Reinforced concrete structures are used for the construction of massive stone, reinforced concrete or brick houses and cottages, the roofs of which are heavy and require special attention.
In order to make the life of the wood work as long as possible, it is necessary to take protective measures at the design stage. The rafters are subjected to antiseptic and fire impregnation. The life of the wood will depend in the future on the quality of the work performed. For the manufacture of rafters from wood, only the first varieties are taken, which contain the smallest amount of all kinds of roughnesses. Preference is given to coniferous species of wood, larch and pine. Humidity should not exceed 22 %. The thickness of the bar, the boards or the plate used for the manufacture of the rafters are directly dependent on the size of the rafter legs, the weight of the roof itself, the loads of the winds and the snow masses, the retreats between the rafters themselves, and so on and so on and so on and so on.
Recently, metal elements have been added to wooden rafter structures. It is necessary to take into account the fact that serious problems can occur due to significant differences in the coefficients of thermal conductivity of the tree and thermal conductivity of metal structures. The condensate formed at the daily temperature difference can cause rotting of wooden beams. In the event that the use of metal elements cannot be avoided in any way, it is necessary to take care of the thorough insulation of them from contact with wood. Wooden rafters can be obtained using two ways: the first is to purchase ready -made rafters, or the second — to make them yourself.
But there are not only wooden rafters, they can also be metal and combined. Rafters of steel can also be obtained using two ways — purchased in the market (today there are a lot of construction companies specialize in their production), or make them independently, directly on the construction site.
The design of the rafter structure is carried out in accordance with calculations, the deviation from which can lead to serious or even destructive consequences.