In addition to decorative features, the roofing of any buildings must have a qualitative type of construction and be of high strength. These factors are of paramount importance for the reliability of the roof, they are achieved by installing the rafters and the frame, transmitting the necessary pressure on the walls of the building.
In the construction of houses with supporting walls it is necessary to use naps and rafters.
In buildings with the presence of supporting walls, rafters of a slant type are used. They are divided into several types, the features of which are discussed below.
The main advantage of such rafters is a long service life, since they are located in places where there is constant air exchange. This circumstance does not allow dampness to be preserved in the wood structure of the structural elements, thus protecting them from rotting and destruction. Suspended rafters have the simplest design, so their device does not cause any problems.
Scheme of nodes connecting truss system.
The joints of the truss system include the following parts:
The design features of the nacelle carriers for a single-slope type of roof are equipped with additional supports, the side of which is located on opposite sides of the walls of the building. For the dual-slope type of roof, double rafter legs with a slope are additionally used. Their lower part is placed against the wall, and the upper part rests on the girder, supported by special racks.
If the passage distance is increased, there is a risk of bending, breaking, and further failure of the rafter foot. This can be prevented by bearing parts located under the rafters. They consist of special racks and props of boards, which are placed during the connection of supports. This approach allows us to strengthen the naslonnuyu design, giving it more reliability.
Support systems are divided into 2 main types: non-displacement and expansion.
Supporting units and the method of fixing the truss base allow you to determine whether a strut is created on the supporting walls.
Layout of nasal rafters for dual-pitch roofs.
In this design, the support base is mounted on a bend; it does not redistribute the expanding reinforcement onto the supporting walls. Arrangement of an impassable system involves 3 different variations.
In the first case, a support bar is fixed at the bottom of the support base or a recess is created and connected to the power plate. In the upper part of the support a recess is created with a large size and a slight slope. This is necessary to prevent an edge from resting on the girder, as there will be a chance of exerting pressure on the rafters, which will lead to a deflection.
Given that at the ends of the support the deflection tends to zero, it can still be cut, but with a small reservation. In all cases, the size of the undercut must be less than the size of the support section. If, due to certain circumstances, it is not possible to trim, it is customary to build with rafter trimming. They are fixed with construction plates from all sides.
During the installation, you will need to create the greatest degree of horizontal to cover the top notch. By changing the type of bearing support, there is the likelihood of the formation of an expansion nylon system.
In the 2nd case, the lower part of the support base is placed on the slider. This method is the most popular. The upper part is mounted on a bolted joint or nails. Fastening is also done by placing rafters into each other, they are connected using mounting plates or wood plates.
Scheme of the rafter attachment unit on the slider.
This method implies fixing the support to the power plate, taking into account the planned interval. The connection can be created by means of 2 nails, which are hammered under a certain inclination into the marginal covering, or with the help of the 1st one, nailed to the top. In addition, you can use any plate of the softened type.
In the 3rd case, a strong clamping of the ridge is created. If the upper part is fixed in this way, and the lower part is placed on the slider, it is possible to avoid the occurrence of expansion on the walls. This method involves the formation of increased pressure on the bend, but at the same time the support base is more protected from deflection. Strong clamping of the upper part of the rafters allows to provide backup reliability that increases the bearing capacity of the support.
The above methods for the construction of wall-mounted rafters have a unified construction principle: one side of the support is mounted on a hinge, and the other side is placed on a slide, which allows turning.
Diagram of options for attaching rafters to the wall.
Fastening on sliding supports is carried out in several ways:
All methods endow the structure with immobility when providing uneven pressure and with varying degrees of roof slope. To do this, it will be necessary to support the ridge girder with edges on wall gables. If the emphasis is placed on the rack, then the stillness is not guaranteed.
2 and 3 methods provide immobility by means of uniform pressure on 2 roof slopes, as well as identity of the degree of their slope. Practice shows that there is no absolutely uniform pressure on the roof slopes. This is due to atmospheric and weather phenomena, as melted snow and wind exert varying degrees of stress on each of the slopes.
The first method allows you to create varying degrees of slope roof slopes, perfectly coping with uneven pressure. But for this you will need to achieve the absolute verticality of the rafters that support the roof ridge.
Connection diagram of expansion flat rafters.
To obtain a spacer system in all 3 methods, it is necessary to change the double level of support to single. The first method involves firmly fastening the upper parts of the support base to the bolts or nails, forming a bearing on the basis of a hinge.
The connection nodes for the spacer system are almost the same as for the non-spacing one. Pressure on bending and pinching remains unchanged, forming a thrust that exerts pressure on the walls of a building. This system includes in its design and suspended, and trailing supports, so it is called hybrid.
The distance structure is static, resistant to all possible types of pressure, but for this it is necessary to fix the power plate well on the wall. Installing ridge girders also reduces thrust. Its reliability can be improved by increasing the number of supports and crossbars. This system is most suitable for buildings built on the basis of logs, timber and lightweight concrete. Buildings on a concrete, brick and panel basis cope much better with spreading.
Scheme of cross rafters.
To impart reliability to the structure, it is necessary to equip it with a side fight. This method slightly increases the stability in the nodes of the rafters. The fixing of the bout is made at the intersection points of the supports that keep the ridge girder. It is located at a distance of 2 m from the floor of the attic, so that people can move freely through it. If the edge of the rafter is placed outside the wall, the reliability of the nacelle system is ensured at any type of pressure.
While reinforcing the lateral contractions, it is necessary to drill holes that are identical with bolt diameters or 1 mm smaller. If an unexpected emergency occurs, the fight will work instantly.
Improving the reliability of glazed rafters is achieved by additionally strengthening the lower part of the supports supporting the ridge girder. However, this is not always feasible, since each attic has its own construction features.
If a strut is used, the rafters are supported by an additional post that creates a 2-span system. It is fixed at an inclination of 45 ° with a bar or overlays.
Competent selection of the system of wall-mounted rafters and its design features, taking into account all the details, will provide any roof with a high degree of strength.
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