In any construction, the most important step is the creation of a roof. It accounts for mechanical snow pressure in winter, significant wind loads and the influence of precipitation. That is why the process of manufacturing a roof requires close attention and the execution of all work with special accuracy and accuracy.
Differences
Roof construction, like most of the other home-building work, is divided into several stages. The device of the hanging rafters is one of them. It is worth noting that rafter systems in their technological characteristics can differ markedly.
The main difference between the hanging version is the support of structural elements on the Mauerlat on top of each other and from below or on the upper ridge detail. That is, they are located without a vertical support, which can not be avoided when forming a layered system.
It is advisable to use this option in the absence of load-bearing internal walls in the building. It is also possible to use the attic space if necessary. As an example, the construction of the attic roof.
The design of the hanging rafters transfers bursting mechanical load to the walls of the building - this is an inevitable cost of the absence of vertical supports in the composition. Therefore, the arrangement of such a rafter system can not do without the so-called screed. It is a horizontally placed element that pulls the rafters, so the walls are subject to less bursting loads. It is worth noting that with a decrease in the level of installation of the screed, the effectiveness of the application increases.
Advantages
The rafter system, made with a hanging arrangement, has many operational positive characteristics. High-quality and competent execution will give sufficient strength to the roof and reduce the impact of the loads exerted on it. Compared with the layered system, it has a lower weight, which reduces the overall load on the wall structures and, accordingly, on the base of the house.
By using fewer parts, less material is required to create hanging rafters.
Raised and hanging rafters
If the house has a major internal wall, when erecting a roof as the supporting structure, the most commonly used layered system is used. It has the main difference, which consists in the presence of an internal additional element having emphasis on the column or internal bearing wall. Due to this, only the bending load is transferred. Among the advantages of this design, it is worth noting its relatively low weight and the need to use a small amount of material for the construction.
For certain cases, for example, when arranging a single roof over several spans, simultaneous use of both curtain systems and hanging systems is required. The rafters, nodes of the lay-on structure in this embodiment are used in that part of the house where there are internal supports, respectively, where they are not, another system is being arranged.
Stages of construction
After determining the type of rafters, you can take on the construction itself. First, a schematic drawing is performed. It is worth noting immediately that it is advisable to entrust it to professionals, since it requires special knowledge and experience in this field. Making calculations at the level of the layman is a rather dangerous undertaking, since errors can be made during the design, which can later lead to a change in the integrity of the roofing system or to its destruction.
After the drawing is created, the execution of further tasks begins, that is, the installation of the Mauerlat. A wooden beam with a cross section of 20x20 cm is used for this, it is placed around the perimeter of the walls and is strengthened. It is necessary to pay attention to the fact that a Mauerlat needs protection against moisture, therefore a special material is mounted under it, for example, roofing material.
When using blocks or bricks for building walls, a concrete leveling screed is required along their perimeter, only after that a Mauerlat can be installed.
As a material for rafters, it is best to use a wooden beam with a cross section of 20x5 cm. If necessary, it is sawed to a suitable length, special cuts are made from the underside to ensure their strong emphasis on the Mauerlat.
Hanging rafters can be installed using a ridge beam, which gives the structure additional rigidity. When organizing a roof without it, the connection of the rafters in the upper part should be made with emphasis, and not with an overlap.
There are two installation options: first, installation of the two extreme pairs of legs using a ridge beam, after which the remaining ones are placed, or in order. The first option is more preferable, since due to it you can get time savings, as well as a more reliable design that is resistant to many types of loads.
For the manufacture of puffs, the same material is used as for the rafter legs. The tightening is mounted in horizontal position. As noted earlier, the lower its location, the better its characteristics become. It is necessary to take into account this circumstance, which is of particular importance if the operation of the attic space is planned. In the absence of a suitable beam size, overlap trimming can be used to create a puff.
Hanging rafters: construction and components
When installing a hanging system, the way to connect the nodes is important. In addition to fastening with screws or nails, there must be a connection with the help of nuts and bolts, for this, holes are drilled in certain places.
Technological cuts are mandatory. For each connection point of the elements of the rafter system, at least two fastener elements must be made. An example of this is the fastening of a puff with two self-tapping screws or nails, followed by pulling with a threaded rod.
Cornice elements
When installing a system of hanging rafters, it is worth remembering the formation of eaves overhangs. It is desirable that initially their length was laid in the size of the rafter legs, but the cost of the structure increases because of this. For a more budgetary production of overhangs, a trim board is used, the parameters of which are 10x5 cm. “Filly” are formed from it, their length must be selected so that the overlap on the rafter legs in the upper part is at least 50 cm. The parts are fixed using threaded parts .
In the Mauerlat, cuts of the required size are performed for a denser connection. To give increased mechanical strength in the middle, the “filly” is also fixed with a small supporting block, which is fixed on the side of the overhang and on the upper part of the Mauerlat.
The rafters are lapped and butt. In the first version, the hanging rafters are fixed to each other using a bolted connection. In the second, the force is given to the nodes by overlays, which are metal plates or boards.
The cornice assembly connecting rafters and tightening is performed by a frontal orthogonal cut, having a single or double tooth, as well as plates or boards.
Articulated Triangular Arch
This version of the truss truss is the simplest. The arch is based on three elements: a horizontal beam (puff), which secures the hanging rafters in the center of the span or at the base, as well as two rafters inclined legs, united at the top point. A tightening formed from steel rods or a wooden beam takes up the supporting force, therefore only a vertical load is transferred to the external walls of the house. Due to this, it becomes much easier to mount the truss support on the wall structure: instead of the Mauerlat, a conventional board is mounted on it, which is used to redistribute the existing load.
In the place of the base of the rafters, a puff is placed if it is necessary to create an attic floor. It is used to support floors. In other situations, the puff is mounted at a higher level. This increases the tensile stress that falls on it, but at the same time in the span of the rafters bending forces are reduced.
Articulated hinged arch
This farm visually looks like a gable roof with hanging rafters, described above, in the form of a triangle. The main difference lies in the used wall support. In the crossbar arch, the base of the rafter legs is fixed in the grooves that are in the Mauerlat. On the walls, in addition to vertical efforts, there are also spacers. In the middle of the span, a puff is mounted (in this method it is called a deadbolt) and is used for compression. As a result, the attachment point of the rafter legs and the crossbar is simplified.
Pivot arch with suspension
If the roof with hanging rafters has a width of more than 6 m, it is quite difficult to equip a three-element simple truss. Firstly, it takes a lot of time to search for a beam to produce a puff of this size. Secondly, due to the large weight, a long puff sags in the center. Therefore, as a complement to the arch, a suspension is used - this is a part that combines the center of tightening and the upper part of the arch. The tightening element is made up of two parts using a bolted connection. A wooden pendant is often called a grandmother, while a metal pendant is called a heavy.
Articulated arch with struts
To reduce the deflection present in the rafters, struts are added to the arch with the suspension, which are inclined elements for supporting the rafter legs in the center of the span. At the same time, a suspension is used to emphasize the struts themselves.
Conclusion
In conclusion, it is worth noting that due to the competent execution of calculations and the total amount of work, hanging rafters in terms of performance will not be inferior to layered ones. In addition to stability and high strength, the use of this design will allow you to form an attic space suitable for use in household or other purposes. In the case of the attic roof, such a rafter system becomes an ideal option.