One of the most important elements of the house is its roof, which protects the house from various atmospheric phenomena of nature and keeps it warm. Therefore, the roof of the house must be reliable and durable. The basis of a solid roof is its frame -. From well-designed and correctly assembled structure roof frame depends on the strength of the roof, and ultimately the durability of the building itself.
The device of the truss frame depends on the type roofing and roof loads. Loads on the rafters are permanent and temporary.
Permanent loads are:
During the design of the frame, its type is first determined (depends on). Rafters can be hanging, layered or combined. The number of rafters, the distance between them and their cross section, depends on the type of attic. It can be attic or non-residential.
Wood is usually used to make rafters. conifers. The moisture content of the material should not exceed 20%. Lumber used for the construction of the truss system should not have rot and blue.
The material of the rafters, battens and counter battens is treated with an antiseptic and flame retardants.
Creating a roof begins with choosing the type of roof and roofing material. In individual housing construction, metal roofing is the most popular. This type of roof is light, durable, strong, has an attractive appearance quite easy to install and inexpensive. Metal roofing is much lighter ceramic tiles(1 sq.m of ceramics is approximately 35 kg heavier than metal tiles).
Calculation example: let the length of the slope be 18 meters, and the step size will be 0.8. This means that 18: 0.8 + 1 = 23.5 = 24 rafters is required for the construction of the roof frame.
Rafter systems for different types of roofs have slight differences. They mainly depend on the weight and dimensions of the coating sheets. To install the truss system, you will need the following tools and materials:
Having produced necessary calculations, having prepared the required material and tools, proceed to the assembly of the rafter system for the metal tile. The order of work is as follows:
This completes the process of mounting the roof frame, then it needs to be prepared for laying the roof.
truss system, on which the metal tile is laid, is prepared as follows:
The installation of the truss system is prepared for laying the roofing of metal tiles.
With certain building skills and two assistants, a solid roof frame can be made independently.
A roof made of metal tiles is the coating that is most often found in the construction of not only country houses but also urban cottages. Metal tile is called a fake clay tile, it is very popular and has its advantages over the original. Most importantly, the weight of a metal tile is much less than the weight of a clay tile. The difference in weight is very significant, it will be about 30 kg for just 1 square. m. Due to the lightness of the roofing, the parameters of the truss system can be reduced, for example, the step of the rafters under the metal tile.
Since the metal tile is sufficient lightweight material compared to the original (clay tiles), the pitch of the rafters can be reduced.
In addition, the installation of sheet metal tiles is much easier in terms of technology, which, of course, shortens the work period and saves not only time, but also money. In addition, it will simplify and facilitate the lifting of the tiles onto the roof, which, of course, is important, since it requires some effort.
The basis of any well-done and high-quality work is careful calculations made in advance.
In such an important matter as the roof covering system, you should not make mistakes, and you need to approach it responsibly.
A mistake, one wrong step or calculation threatens you with a violation of the entire coating, collapse of the base or a change in the shape of the rafter legs. The more accurate your calculations are, the more reliable the frame will be, and the calmer and more confident you will feel in the house with your own roof.
Therefore, carefully study all the nuances that you should pay attention to when calculating.
In order to measure the step distance, you need to take into account all the loads that will act on the roof. For example, in Russia (its middle lane) wind and snow load on the roof is approximately 200 kg per 1 sq. m.
In the north and in the areas closest to it, this number can increase almost three times. Naturally, the step of the rafter leg will change from these calculations in order to ensure the reliability of the entire structure.
Under the material in question, it should be up to 950 mm long with an estimated load of 200 kg, this is with a normal section of 150 * 50 mm. When increasing the thickness of the insulation, do not forget to increase the cross section of the rafters. At the same time, experts clarify that with a crate of 50 * 30 cm, you should not increase the step.
Roof truss calculation system
- With the greatest accuracy, measure the length of the slope along the eaves of the roof.
- The length of the slope is divided by the length of the selected step (the gap between the rafter legs).
- One is added to the result, and the resulting value is rounded up. thus, it turns out the number of rafters that will be needed only for one side of the roof slope under the metal tile.
- Then it's taken total length slope and is divided by the number of rafters, which was found out using previous calculations. The number that you get will be the value of the gap between the rafters. It is this figure, or rather the distance, that is called the pitch of the rafters.
rafter element length rafter installation step 3.0 (m) 4.0 (m) 5.0 (m) 6.0 (m) 60 (cm) 40x150 50x150 50x175 50x200 90 (cm) 50x150 50x200 75x175 75x200 110 (cm) 75x125 75x175 75x200 100x200 140 (cm) 75x150 75x200 75x200 100x200 175 (cm) 75x150 75x200 100x200 100x250 215 (cm) 100x150 100x200 100x250 100x250
Note. The sections of the rafters are indicated in millimeters.
Length roof slope- 25.5 m.
Length rafter pitch- 1m.
28.5/1 = 28.5+1 = 29.5, now rounding up: 29.5 = 30.
That is, exactly 30 rafters you will need for a roof slope.
28.5 / 30 \u003d 0.95, that is, 95 cm is the step distance.
All calculations must be made taking into account the shape of the roof, design features frame, as well as an individual microclimate for each region. Calculation roof truss produced at the design stage.
Also, experts advise to improve ventilation, when installation is carried out, drill holes with a diameter of 10 mm in the rafters near the upper edge.
Mandatory Precautions
To ensure durability and reliability, the truss structure under the metal tile must be treated with a special solution, it is better to do this in advance in order to process all the places, since some of them will be inaccessible after fixing.
To prevent grinder beetles from starting in the rafters, which over time can wear out the entire wooden part of the roof, it is necessary to carry out mandatory treatment with an antiseptic. The timeliness of processing will save you not only from insects, but also from mold and fungus, which can destroy the rafters even faster than grinder beetles.
The need for processing rafters by special means as protection against fire is not in doubt. By choosing any impregnation suitable for its properties and processing the rafters, you can be sure that you will greatly increase their resistance to fire.
Types of existing structures
For the structural rigidity of the truss structure, it must certainly consist of triangles that are conjugated with each other and do not have freedom. Rafter structures are divided into two types:
- hanging;
- oblique.
The hanging truss structure is a rafter leg in the amount of two pieces, which are connected at the very bottom with a puff. It is the tightening that does not give grounds to increase the distance, that is, to part.
If the spans exceed 8 m in size, then to reduce the deflection, a rack (headstock) with struts is installed. For spans less than 8 m long, an additional puff is placed, which cuts between the top of the rafters and the bottom puff.
For it you need to use a log or horizontal bar, which is attached to the base of the rafter legs, which reduces the bursting horizontal forces acting on the walls of the building.
"Fire" - this is the name of the continuation of the rafter leg, fastened with nails to the rafter leg. It can be made from a board, which will be half the size of the leg itself.
The rafter structure is supported by the middle part and ends on the supports or walls of the building and is installed only in cases where the spans do not exceed 6 m.
Adding a beam that cuts horizontally below the ridge between two rafters allows you to increase the distance between the supports up to 8 m.
If there is an additional support, then the width can be increased to 12 m, and if there are two supports, up to 16 m. In cobbled buildings or in chopped wooden rafter legs rest on the upper crowns.
- In stone buildings - on a supporting beam, in wooden frame buildings - on top harness. The dimensions of the building and the presence of internal supports (walls, columns) in it dictate what the location of the rafters will be.
Some Features
Between roof structure for metal tiles and other structures there are no fundamental differences. The main difference between them is that the upper support is installed on top of the ridge run, and not on ridge beam.
For a metal surface, air circulation is important, which is formed in the form free zone between joined wooden parts. This reduces the risk of condensation forming under the roof deck.
If the installation of the house involves replacing the Mauerlat on the top log crown, then it is necessary to make a calculation that finds out the step of the rafters as carefully as possible and double-check.
Since after that it will be impossible to make even the slightest changes, since notches are made in the crown, which increase the reliability of fastening.
Rafters for metal tiles (their installation) are carried out using special corners, which are used to fix structural elements.
The use of such corners for fastening will provide high bearing capacity and, in addition, will give you the opportunity to work without special tools. In this case, it will be possible to use ordinary nails and screws to fasten the corners.
Knowing the features of the calculations, the distance and the required step, you can easily understand the intricacies of this construction process. Good luck!
The rafter system is the basis of any roof and the reliability of the entire roof directly depends on its design. The calculation of rafters for metal tiles has some features, this is due to the fact that the material is quite light. Installing a metal tile is quite simple, it saves not only time for the construction of the roof, but also money.
Before installing the truss system, it is necessary to carefully carry out all the calculations. Special attention should be given to the calculation of the load, which includes the following parameters:
Mistakes made in the calculations can lead to a number of negative consequences:
The calculation of the roof structure primarily requires correct calculation the distance between the rafters - the so-called step of the rafters. The calculation method presented below will allow you to do this with high accuracy.
The procedure for correctly calculating the required step between the rafters is as follows:
Most often, to complete the truss system, they take a step of 60-95 cm at a cross section wooden beam 150 by 50 mm, subject to the use of metal tiles as a roofing material.
This thickness of the beam allows you to place inside the roof a layer of insulation sufficient for good thermal insulation thickness. Some methods recommend using rafters with a thickness of 200 mm, which will significantly improve the thermal insulation properties of the roof.
To ensure the necessary ventilation of the insulation layer, 10 mm holes are usually drilled in the upper edges of the rafters. The rafters under are installed not on the side of the ridge beam, but on top, which allows you to get a free gap between them.
This zone serves as an additional ventilation duct and reduces the formation of condensate, which is very important when organizing a metal roof.
Installation of rafters is usually carried out on special metal corners with holes that allow the use of a minimum of tools during installation, for fasteners you only need a screwdriver with self-tapping screws or a hammer with nails.
The structural rigidity of the truss system under the metal tile should be quite high. Reach good result It is possible by using structures in the form of triangles rigidly fixed to each other. There are 2 types of truss systems:
Such a rafter system consists of 2 legs, which are connected at the bottom with a puff. Thanks to this tightening, the legs do not move apart. If there are spans of more than 8 m, the deflection of the rafters is eliminated by installing a special rack with struts, called the "headstock".
On spans up to 8 m, it is possible to install an additional puff, mounted in the gap between the middle and top of the rafters. Such a tightening is usually performed from a log or timber, placed horizontally. This tightening reduces the effect of bursting horizontal forces on the walls of the room.
This design involves supporting the rafters with the middle part and their ends on the walls of the building or support. It is usually used with a span of no more than 6 m. In case of strengthening the structure by adding a beam mounted horizontally between two rafters, it is possible to increase the distance between the supports up to 8 m.
If there is an additional support, the width distance can be increased to 12 m, and if there are two supports, the distance can be increased to 16 m.
Given the fact that most often the rafter system for metal tiles is made of wood, it is necessary to thoroughly approach the issue of protecting wood from the following factors:
The rafter system must provide a solid foundation for the installation of the battens, insulation layers and roofing. Compliance with the instructions for performing calculations and installation will allow you to get excellent results and confidence in the reliability and durability of the roof.
The truss system for metal tiles is one of the most economical designs. modern roofs. This is due to the light weight of steel profile sheets coating, the absence of solid bases such as OSB or plywood. Process correct installation a lot of literature and instructions, videos are devoted to roofing elements. The process of choosing a truss system for an individual developer is less clear. This article attempts to inform the general reader how to choose the right rafters for metal roofing.
The structural solution of the truss system depends on the shape of the roof, the shape and size of the building. There are two main structural schemes of truss systems: Laminated rafters - a simple and reliable non-expansive rafter system in which roof beams rest (lean) at the top and bottom on walls or beam elements. This rafter system is most popular in individual construction. The layered system consists of rafter legs resting on the Mauerlat below and on the run at the top, racks resting on beds and linings, as well as struts, struts and trusses. 
Hanging rafters - a more complex system, used in the absence internal walls, as a rule, when long distances between supports. This design is spacer, in which the spacer force is extinguished by puffs. The structural elements of the system are various types of roof trusses. The advantage of this system is that all elements can be manufactured and assembled both on site and in the factory. In the latter case, it remains only to perform pre-assembly and installation. The use of such a system is justified for facilities with short construction periods. 
Another advantage is that finished elements, as a rule, are subjected to fire-retardant impregnation in the factory. In addition, businesses have big choice ready design decisions For different types roofs 
For the manufacture of load-bearing roof structures, wood with a moisture content of not more than 25% should be used. Elements can be from logs, timber and edged boards.The total massiveness of the elements roof truss depends on the distance between bearing walls building, climatic region of construction and roof slope. The larger the span, the amount of snow and the heavier the roof structure, the more massive the supporting frame of the roof.
So, among the known values are the length of the roof, the span of the building (the distance between the supports C), the height of the roof, and, at a minimum, general idea O snow load. Among the unknowns there is a rafter pitch (B), a rafter section (a × b). Getting rid of the unknown, we will assign a step of rafters under the metal tile. The rational distance varies between 0.6 and 1.2 m. If the roof is with log rafters, then the rafter spacing can be increased to 1.8 m. In a situation with metal tiles, this is not necessary, since you will have to carry out a thickened crate. 
Rafter spacing from 0.6 to 0.9 m is mainly used for cold attic roofs and single rafters. It should be noted that the minimum step is rarely used, and the installation is carried out in steps of at least 0.7 m. If no attic floor is foreseen, any rafter step can be taken for a cold attic. Sections of rafter legs for simple roofs under normal conditions in the climatic zone of central Russia can be preliminarily determined from the following table. Roof slope, hail | Step of rafter legs, m | Board section |
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Distance between supports, m |
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| 20 - 30 | 3,0 | 3,5 | 4,0 | 4,5 | |
| 0,7 | 50×120 | 50×150 | 50×175 | 50×175 | |
| 0,9 | 50×150 | 50×175 | 50×175 | 50×200 | |
| 1,2 | 50×175 | 50×200 | 2×50×150 | 2×50×200 | |
table 2
Roof slope, hail | Step of rafter legs, m | Section of the rafter leg |
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Distance between supports, m |
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| 3,0 | 3,5 | 4,0 | 4,5 | 5,0 | ||
| 20 - 25 | 1,2 | 2×50×150 | 2×50×175 | 2×50×175 | 2×50×200 | 2×50×200 |
It is necessary to connect two boards through gaskets with a step of no more than 1 meter. A rafter system made of paired boards is more reliable than a single system.. And in order to sleep completely calmly under the new roof, you need to contact the designers for the calculation of the roof elements. I recommend watching the following video:
