Inspecting the roofs of houses, first of all, you can determine the type of roofing and the configuration of the slopes. But this information will not be enough to draw up a complete picture of the characteristics, pluses and minuses of this part of the structure. The greatest influence on such qualities as durability, reliability and stability of the roof is exerted by the type of rafter system used in the supporting structure.
Rafter device
If the main frame of the house is based on the foundation, then the “roofing cake”, we can say, rests on the rafter system. This is a kind of "skeleton" of the roof, providing power support to all its functional and protective parts. You should immediately consider the main types of rafter systems and a description of their device:
- Simple designs. Such systems are held on two rafter legs , which are emphasized in a horizontal beam - a Mauerlat mounted on the walls.
- Sophisticated designs. In addition to rafters and Mauerlat, such systems include beds, runs, struts and racks. These components may have different sizes and configurations, but in general they have one task and it is to support the loads that go from the roof itself and external influences.
Regardless of the type of construction, all rafter systems provide for rigid fastening. Mauerlati have already been mentioned, which are fixed directly to the walls by means of a screed or lock connection, but also truss elements are rarely dispensed with only groove joints. According to the type of fastening and ligament methods used, the following types of rafter systems can be distinguished:
- Cohesive. The transverse ligament is performed.
- Spliced or stackable.
- Nodal structures.
As the elements of the connection, metal plates, veneer, coupling bolts, anchor hardware, nails, screws, etc. can be used. Again, the methods of the so-called non-rigid or nailless connection of system components retain a certain distribution. In this case, roofers completely exclude the introduction of foreign solid fixatives into the design and are limited to the use of adhesive compositions with groove cut-outs (lock fasteners).
Design of rafter systems
Roof parameters largely depend on the characteristics of the main frame. In particular, loads, structural solutions, functionality of the elements, etc. are determined. By the time the rafter system is directly constructed, the initial design may undergo several changes. At a minimum, it should be audited. In Russian conditions, most often design inclined types of roof systems for a gable roof - a design that allows you to effectively drain melt and rainwater, equip attic rooms and attics.
The main task of the developers of the technical solution is to correctly calculate the area of the roof being erected, which will also project the parameters for the rafters. Among the initial data, broken elements of complex configuration are also taken and an adjustment is made for the shape of the roof itself. For convenience, the calculation of the entire area is usually divided into zones, after which the individual values are summed. The calculations made in the future will help to make an estimate. To avoid gross errors, one should take into account a number of design features of the rafter system. Types of sloping roofs intended for use in private housing construction require compliance with the following nuances:
- When laying roll and tile materials, the length of the ramps can be reduced by 70 cm.
- The lower parts of the ridge and the extreme part of the cornice can be considered as base and fixed points that determine the length of the ramp.
- When calculating the optimum angle of inclination, keep within the range of 15 ° to 45 °. The lower range up to 20 ° is rarely used due to technical and operational imperfections - this solution is ineffective in terms of counteracting precipitation, but it costs less. The optimal angle is in the range from 30 ° to 45 °, but the cost of such a roof will be more expensive.
Wooden rafters
The main material in the manufacture of rafters is wood. This choice is determined by the ease of procurement, environmental friendliness and affordability. From the point of view of the homeowner himself, lumber is also beneficial because of its easy handling. In such a system, it is not difficult to replace a damaged element with a new one. Private housebuilding mainly uses coniferous timber and a board.
Of course, wood has many serious drawbacks that complicate its use in such critical structures. Today, wooden types of rafter systems that have undergone special processing are popular. As an impregnation, flame retardants (from fire), antibacterial agents (from biological damage) and complex compounds that also protect the material from moisture and mechanical damage are used. As a result, unpleasant operational effects inherent in a tree are minimized.
Metal rafters
It would seem that rigid steel sheets are the optimal material for the manufacture of a bearing "skeleton" of the roof, thanks to which it is possible to lay any roofing without restrictions. But, heavy weight excludes metal from most projects designed for individual construction. There remains, however, a considerable segment of multi-storey and industrial facilities, which just require durable and resistant to load rafter roof systems. The types of structures in this group are also diverse. In addition to the steel frame, a compromise solution in the form of anodized aluminum can be used. This material is lighter than steel alloys and is not subject to corrosion damage, but is also more likely to be related to the same wood in its strength properties.
In principle, it is advisable to choose metal structures for a country house due to fire resistance. Beams and supporting elements do not support the spread of fire, preserving some time and integrity of communications (for example, ventilation ducts for chimney exhaust), but the most important thing is to prevent the collapse of the roof. Wood, even taking into account the use of modern refractory impregnations, has a not so high limit of containment of thermal effects. And here it is worth emphasizing the plus of metal systems in the form of the absence of the need for regular protective treatment. Coating with certain paints and varnishes can be carried out as part of the general maintenance of the roof, but there is no talk of specialized processing.
Head rafters
According to the device of the supporting rafter structure, which distributes the loads from the roof with a roofing, it is possible to distinguish overhead and hanging systems. In the first case, three basic reference points are mounted - two Mauerlat beams that are placed on the walls of the house, as well as a central rack connecting the ridge and the attic floor. But even in this configuration, different schemes of the carrier base can be performed. So, in the group of layered frame models, the following types of rafter systems and their designs are distinguished:
- The classic version. The rafters are laid on the ridge beam, also providing fixation with a sliding support post. The lower parts of the slings are attached to the Mauerlat by means of a notch.
- Construction with hardware. In the ridge joint, the rafters are joined with metal brackets, nails or bolts. The fastening to the Mauerlat is carried out by a movable connecting system like mounting sliders.
- System with a rigid ridge fixation. In the upper joint of the sling, a common connecting node is realized, in which clamping bars and metal profiles are involved. This is the most reliable design, but it requires appropriate bearing capacity from the frame of the house.
The advantages of layered types of rafter systems include the possibility of a balanced load distribution, which reduces the destructive and bursting effects on the walls.
Hanging rafters
In this case, the mass from the roof and rafters is shifted to the two extreme racks. That is, intermediate supporting elements will be absent, which determines both the pros and cons of this system. The stability of the roof is provided with rafter legs, which "work" on bending and compression. For the same reason, the load on the walls also increases, since the number of reference points is reduced - the exclusion of the central rack increases the responsibility of the main frame of the building. Hanging types of rafter systems and their structural elements can be made of wood and metal, but a fundamentally important condition will be the inclusion of connecting braces and floor beams in the frame. These are some kind of insurance parts of the system that take on part of the load. A horizontal beam connecting two opposite rafter legs also eliminates the risks of deformation of load-bearing elements under the influence of dynamic loads.
Types of rafter systems of a hip roof
This is a four-pitched roof, characterized by a more complex supporting structure and giving more opportunities for organizing the internal attic space. For the same reason, hip systems are more often used to equip an attic with windows. Unlike gable structures, this type of roof is formed by a shorter ridge of the beam and a complicated arrangement of the rafters. In the usual system there are angular, central, intermediate and short rafters. They have different shapes, lengths and materials of manufacture, but most of these elements perform the same functions of supporting slopes in the direction of the ridge beam. The most common are oblique (diagonal) types of the rafter system, a photo with an example of which is presented below.
These are hip structures in which the supporting elements are mounted towards the corners of the walls of the main frame. Inside the system, layered or hanging rafter installation configurations can also be implemented. Since the four-pitched roof as such has more reference points with fixation to the Mauerlat, the installation of central racks with support for the ridge is not necessary. The hanging structure, with the correct calculation of the loads, will completely cope with the task of retaining a heavy roofing.
Types of roof truss system over the veranda
We can talk about any unheated glazed room of small area with its own external walls, and sometimes the foundation. Actually, the classification of roof systems for verandas is determined by the method of extension to the main building. The transition of the roofing through the mating zone will depend on this. In particular, according to the adjacency configuration, the following types of roof truss system above the veranda are distinguished:
- Separate design. Usually a steel supporting apron is used as a gable or gable system. It is performed from the front side of the building, while there is no direct coupling of the roof of the house and the veranda.
- Adjoining design. One common rafter system is implemented, in which the top of the slope of the main building passes from the attic zone to the roof frame of the veranda. The slope can be refracted due to certain structural conditions, but experts advise to do without technological joints, since they reduce the tightness and reliability of the entire system.
Classification of trusses
This is one of the components of the supporting roof structure, which is on a par with the crate, racks and braces. The rafter system can do without trusses, but if reinforcement and stiffening of the frame is required, then it is better to use this addition. The farm is a series of bars or profile components that are mounted on a specific section of the ramp for strengthening. Both hanging and layered types of roof systems for a gable roof can technologically contain farms made of timber, round timber or a regular board. Fundamentally, such elements differ in degree of rigidity. Most often, light or single-wall trusses containing one shaped sheet in the structure are used. Double-walled structures have several sheets and are mainly used in the roofs of large buildings - in warehouses, hangars, etc. In the system of a country house, the presence of pitched farms can be justified if it is planned to install massive engineering equipment in the roof structure. This can be air conditioning, ventilation shafts or chimneys.
Conclusion
The roof in any structure plays an important role, providing protection of the internal space from various external threats. In order for the roofing to properly perform its tasks, under it should be located an optimal supporting structure for the technical characteristics. Also, in the process of developing the project, the operational properties of this part of the house are taken into account. For example, modern types of roof systems for the attic fundamentally differ in the presence of a kink in the gable system, due to which the interior space of the room expands. Conversely, optimized single-pitch systems are performed with a minimum volume of load-bearing elements without additional beams and trusses. In each case, it is important to take into account the individual requirements for the operation of the roof, which will make the right choice of roof structure.