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Metal rafter knots. Mounting points of the truss system. Prices for metal corners

The structure of the rafters is the skeleton of the roof, which is obliged to take on and evenly distribute the weight of the roofing materials. If you correctly assemble the wooden skeleton for insulation, waterproofing film and top coat, you will be able to achieve a noticeable increase in the load capacity of the truss system.

The main elements of the truss system

The wooden frame of the roof is assembled from parts such as:

• mauerlat - a kind of base for roofing elements, attached around the entire perimeter of the building to the upper edge of the outer walls in order to disperse the pressure of the roofing pie;

  Mauerlat serves as the basis for the roof frame

• rafter legs - irreplaceable details of the wooden skeleton of the roof, which determine the angle of inclination of the slopes and the view of the upper part of the house;
• ridge run- bar fixed in horizontal position and, like a spine, connecting all the rafters of the roof frame in their upper part;

  The ridge run is located exactly in the middle of the building

• side run - a horizontal beam, which differs from a ridge run in that it is fixed in the middle of the rafter legs of each roof slope;
• puff - a spacer that unites two opposite rafters so that they do not move apart;

  Tightening and struts are necessary to properly distribute the load on the Mauerlat

• racks - vertical frame elements placed under the ridge and side runs to support the rafters and the ridge beam, and also, if necessary, substituted under the middle part of the rafter legs;
  

  Racks can support not only the ridge of the roof, but also the rafters

• struts - parts that rest against the bed, due to which the rafter legs become more stable;
• bed - a bar placed on the upper edge of the inner wall of the building parallel to the ridge and serving as a platform for attaching racks and struts;

  The bed is located on the inner wall parallel to the mauerlat beam

• roof ridge - the area of ​​​​combination of two slopes, along which a continuous crate is installed, necessary to strengthen the described part of the roof;

  The ridge is formed in the highest zone of the truss system

• filly - elements used in the arrangement of the overhang, when the rafter legs are not long enough;
  

  Fillies lengthen rafter legs

• roof overhang - a wooden frame area that protects the walls of the house from contact with big amount atmospheric precipitation;

  The cornice overhang is constructed to protect the walls from rain.

• lathing - bars or boards nailed perpendicular to the rafters and serving as a platform for attaching roofing materials.

  Sheathing boards are laid out perpendicular to the rafters

Main connecting nodes

The main nodes of the truss system are:

• roof truss - connection of a rafter pair, stretch marks, as well as racks and braces;
• ridge knot - combination of two opposite rafters;
• a link from a Mauerlat and a rafter resting on it;
• a module that includes a run, a rack and a bed;
• connection of the rafters with a strut and a rack.

The most complex link of the roof frame, according to the author, is a truss truss, which is distinguished by the fact that:

The ridge knot also has several features:

Rafters and Mauerlat become a single link, which is characterized by the following:

A module from a run, a rack and a bed is formed by driving building brackets, steel dowels or linings from steel strips into their joints.

A node of a bed, a rack and a run allows you to share the load between the external and internal walls of the building

Struts, racks and rafters are assembled into a single module, creating cuttings. To ensure that their connection is not weak, construction brackets are used.

A knot of struts, racks and rafters allows you to soften the pressure on the inner wall of the house

Ways of fastening rafters

In the lower part, the rafters can be connected both to the Mauerlat and to the floor beams. Sometimes, for example, during frame construction, they are fixed directly on the wall. And in the upper part, the rafter legs are combined with the ridge. Each labeled node can be created in several ways.

Mauerlat connection

The rigid fastening of the rafters on the Mauerlat guarantees the absence of any displacement of the assembly elements. It is performed by cutting in a certain sequence:

1. To speed up work, a template is made from a piece of board or thick cardboard. A line is drawn on the workpiece, stepping back from the side edge a distance equal to 1/3 of the width of the rafter, and then the point of contact with the Mauerlat beam is marked, along which a second line is drawn perpendicular to the first.

   If the width of the rafter is more than 200 mm, then washed down is done at a depth of 70 mm

2. At an angle of inclination of the roof slope, the template is substituted to the edge of the Mauerlat, making sure that the point marked on the piece of wood is strictly opposite the corner of the beam. Two lines are drawn from it with a pencil - vertical and horizontal, as a result of which a triangle is obtained on the workpiece, which is carefully cut out.
3. The made template is assessed for correctness by putting it on the Mauerlat in several places. If the groove made turned out to be smaller or larger than necessary, then the pattern is made anew, correcting the mistake made.
4. The template is placed on a horizontally located rafter. The triangle in the pattern is circled with a pencil. The same is done with other rafter legs. At the same time, make sure that the horizontal line of the groove in the pattern is always in the same place on the rafter. Otherwise, notches will be created on different distances from a skate.
5. The triangles drawn on the rafters are cut out hand saw. The tool is operated slowly so as not to accidentally increase the depth of the groove in the rafter leg. Possessing the skills of working with an electric saw, recesses can be made with this device. True, it must be borne in mind that a tool powered by the mains is much worse at listening to the hand and is able to go to the side.

   The triangular cut allows the rafter to rest against the Mauerlat

6. The correctness of the size of the grooves made is checked with a pattern. If discrepancies are found, the notch is corrected with a hacksaw.
7. Two extreme rafter legs are placed on top of the house. They are inserted into the Mauerlat with grooves, fixed on the sides with metal corners or brackets.
8. On the bottom edge between two established elements stretch the rope. Then the remaining rafter legs are attached to the Mauerlat one by one.

The technology of attaching the rafter legs to the Mauerlat with a patch of a thrust bar can be taken into account by builders without experience. With this method of creating a node, as the author of the article noted, it is possible to change the position of the rafters until it becomes completely correct.

To connect the main elements of the roof frame with the Mauerlat with a stripe of a thrust bar, do the following:

During the construction of the roof frame for wooden frame, which always shrinks, they prefer to use the sliding method of attaching the rafters to the Mauerlat. Thanks to it, it is possible to avoid deformation of the truss structure and deterioration in the stability of the upper row of logs, which replaces the Mauerlat.

The choice of sliding rafters is justified only when a ridge beam is provided for the main elements of the roof frame, against which they could abut with their upper part.

When the rafters are fixed on the Mauerlat using the sliding method, certain steps are taken:

The layered method of attaching rafters to the Mauerlat is adopted when the purchased lumber turned out to be shorter than necessary. Also, this method of fixing the main elements of the rafter system is used during the repair of a roof of complex configuration.

When fixing the rafters on the Mauerlat using the layered method, only 3 tasks are performed:

Video: installing rafters

Combination with floor beams

It is possible to fasten the rafters to the floor beams only being sure that the walls of the building will withstand the pressure of the roof frame. Still, in the absence of a Mauerlat, the load on the house is not uniform, but point.

Without fear and doubt, the rafters are attached to the floor beams if they are building a light mansard roof. At the same time, as ceiling beams use boards with a section of 5x15 cm.

The rafters are not connected to the Mauerlat, but to the beams of the attic, if they know for sure that they will withstand the pressure exerted

To firmly fix the rafter legs on the floor beams, perform the following tasks:

wall mount

If for some reason the rafters have to be fixed directly on the walls, then they will definitely need to be connected with a puff. She, as the author of the article personally made sure, who helped build the roof of the utility room, will remove part of the stress transmitted by the rafters from the house.

Rafters should never be directly connected to the outer walls of the building if they are built from foam or gas blocks. These materials freely transfer their moisture to the wood and are unable to retain fasteners.

On the wall, the rafters can be fixed using a sliding method, but this is not the most reasonable solution.

To securely fix the rafter legs on the walls, it is necessary to take certain measures:

1. At the right angle, make on the rafters washed down with one tooth.
2. Install the rafters on the walls with the butt end and drive a nail 10-12 cm long into them.
3. If necessary, attach to the sides of the rafters metal corners.

Since the roof ridge is under serious pressure from the entire truss system, roofers with extensive experience create a ridge knot in five ways: butt, on a beam, overlap, in a groove, in half a tree.

To create a ridge knot by connecting opposite rafters end-to-end, do the following:

When attaching rafters to a beam, or rather, to a special ridge run, they act in a special way:

When the rafters are connected to the beam, the ridge is not pointed, but flat.

If the ridge knot is made by fastening the rafters with an overlap, then you will need to perform a few simple tasks:

To connect the rafter legs into a ridge knot using a groove, several skillful carpentry actions are performed:

Having chosen the method of connecting the rafters to half a tree, do the following:

Video: building a roof frame with connecting rafters with a ridge run

The construction of the rafter system should not be started until it is possible to understand the features of attaching the rafters to other elements. load-bearing structure roofs. By the way, among the various ways of fixing the rafter legs, there are options not only for experienced builders.

In order for the constructed building to serve for more than one year, it needs both a reliable foundation and a strong roof system that resists the vicissitudes of the weather. The roof must withstand heavy loads with dignity: heavy snowfalls, sharp gusts of wind, torrential downpours. The roof truss system is best suited for this.

Roof trusses and its types

The truss system is the basis of the roof, which focuses on the supporting elements of the structure and also serves as a frame for various types of roofing materials: insulation, waterproofing, various coatings.

The dimensions and design of the rafters depend on:

• purchased material;
• the size of the building;
• dimensions of the house;
• building material for rafters;
• individual preferences of the customer;
• roof loads relevant for a particular region.

The rafter system has:

• crate - bars, in a perpendicular direction, fit on the rafter legs;
• screeds that perceive tensile forces;
• wooden racks, located in a vertical position;
• mauerlat - a bar, the installation of which is carried out along the wall, the rafters focus on it;
• rafter legs are a kind of wooden beams that take on the main load of the roof.

Each of these factors is very important, because it is necessary to understand what type of truss system will be best suited for a particular situation.

When it comes to low-rise buildings, wooden structures are the most common. In many cases, three types of truss trusses are used: hanging rafters, layered rafters and a mixed rafter system.

Characteristics of hanging rafters

Hanging rafters are the most elementary type of truss systems, their characteristics:

If the roof of the house complex design, types of rafters can be alternated. For example, in the presence of supports or the middle main wall, they install layered rafters, and in the absence of such elements, hanging rafters.

Features of layered rafters

For a layered rafter system, the house must be additionally equipped bearing wall located in the middle. There are layered rafters according to the following features:

Design combined system the most complex, since it includes parts of two other types of rafters - hanging and layered. It is applied for mansard roof. The walls of the rooms, which are located on the second floor, form vertical supports, these supports are also intermediate racks for truss beams.

Part of the rafters that connect one end of the uprights functions as a crossbar for the slopes located on the side, and for the upper part of the structure they are a puff.

At the same time, the horizontal bars perform the following functions: for the upper slopes - a Mauerlat, for the side ones - a ridge beam. To increase the strength of the roof, struts are mounted that connect the side slopes and vertical racks.

The combined sling system is the most complex and time-consuming to manufacture, but these shortcomings are fully compensated by an increase in the bearing qualities of the roof in the absence of extra supports, especially when there is a need to block significant spans in the building.

You can increase the bearing qualities of the roof using a mixed truss system

Rafter trusses for various types of roofs

During the construction of a certain building, roof systems of one kind or another are necessarily used, and the type of roof will completely depend on the design of the future structure.

Rafter truss for a gable roof

A gable roof is a common roof construction for residential buildings that have no more than three floors. Preference is given to this design because specifications inclined form of the truss system, and also due to the fact that installation work carried out easily and simply.

As part of the truss system gable roof includes two rectangular inclined planes. The upper part of the building from the front side resembles a triangle. The main components of the two pitched roof- this is a Mauerlat and rafter legs. In order to properly distribute the load on the rafters and walls, struts, crossbars and racks are mounted, thanks to which you can create a durable, rigid, elementary and easy installation scheme for a gable roof structure.

A gable roof is considered the simplest roof system; it is used for residential buildings no more than three floors.

On top of the rafters, you can mount a sparse crate or a solid one, and then attach a bituminous coating, tiles or some other type of material to it. The rafters and sheathing itself are usually made of beams or boards, which are fastened with nails, bolts or metal fittings. metal profiles can be used as rafters, due to which significant spans overlap. There is no need to use extra racks and struts.

The device of the truss system for a gable roof allows you to evenly distribute all the existing load along the perimeter of the building. The lower ends of the system focus on the Mauerlat. They are fixed with metal fasteners or staples. By the angle of inclination of the bars for the rafters, you can determine at what angle the roof slopes will be inclined.

The truss system for a gable roof allows you to evenly distribute the load from the roof along the perimeter of the building

Rafter system for a hip roof

When arranging a system for a hip roof, installation will be required different types rafters:

• conjurers (shortened);
• side;
• hip main;
• sloping (diagonal elements that form a slope in the shape of a triangle).

The rafter legs, located on the side, are made of board, and they are mounted identically to the details of a traditional pitched roof with a sloping or hanging structure. Hip main rafters are layered parts. For sprigs, boards or bars are used, which are attached not only to the Mauerlat, but also to the diagonal beams.

To install this type of construction, the angle of inclination is accurately calculated, as well as the cross section of the sloping beams. The dimensions of the parts also depend on the length of the span.

So that the hip roof does not deform from a heavy load, you should accurately calculate the angle of inclination of the diagonal beams for the rafters

Observe symmetry when installing diagonal beams for rafters, otherwise the roof is deformed from a significant load.

Rafter system for sloping roofs

A broken roof is a construction with rafters, which consist of several separate elements. However, they should be located under different angles relative to the horizon. And since the bottom rafter part is located almost vertically, the attic of the building receives additional space, so that it can be used as a living space. The device of this type of roof is carried out during the construction of a four- or gable rafter structure.

count four-slope system rafters are needed by professionals, but a gable broken roof can be made independently, since its installation is very simple. To do this, it is necessary to install a support frame, which should consist of runs, as well as racks. Horizontal parts are fixed with hanging rafters. But to the Mauerlat, the supports of the sloping roof are fixed with shortened legs of the rafters.

The assembly of rafters for a broken gable roof can also be performed by non-professionals, since the installation of such a roof is very simple.

"Cuckoo" in the roof truss

The so-called cuckoo on the roof is a small ledge that is located on attic floor. Here is the window for better lighting attic room. The installation of the "cuckoo" is carried out carefully, while controlling the parameters of the entire structure: the depth of the cut, the angle of inclination and other factors. However, before that, the necessary measurements are made.

The first stage of work begins with the installation of a power plate (a beam with a section of 10x10 cm, which is needed to support the lines). The rafter system acts as a skeleton for roofing material. To stiffen the structure, spacers are used, which are mounted between the two legs of the rafters.

After the installation of the truss truss is completed, a sheathing is laid, the type of which depends on the roof covering purchased. The installation of the crate is done continuously or with a certain step. Boards, OSB and plywood sheets are usually used for it. In addition, the installation of roofing material must be identical throughout the entire roof.

The main difficulty in installing such a rafter system is the location of the internal corners. In these places, snow can accumulate, which means that the load will increase, which is why a continuous crate is made.

"Cuckoo" on the roof is called a small ledge on the attic floor, under which there is an additional window

Chalet roof truss truss

A feature of a device of this design is the removal of visors, as well as overhangs outside the house. In addition, there must be rafters and beams for the roof, which extend up to three meters on the sides of the building. Each of these elements is fixed with a bracket to the wall of the building in the lower part. Next, tie the edges of the beams. They serve as a support for covering the roof of the building.

But when creating large overhangs, it is necessary to install the reinforced belt in parallel with the installation of the Mauerlat studs. It is necessary to make anchors that help fix the consoles. In this case, the rafters will be perfectly fixed with anchors and, in addition, tie-ins.

To carry out the side cornices, a ridge beam is made, after which beams are taken out at the Mauerlat level, which must be identical to the length of the ridge. The truss is based on these structural details, and in the future - building material for the roof.

When designing a building, the angle of the roof-chalet is calculated based on the characteristics of the local climate and other factors. With a slope angle of about 45 °, the load from snow is not taken into account, since with this option it will not linger on the roof. At the same time, the sloping roof will withstand the load from the snow, but it is necessary to install a reinforced roof truss. Before installing the roof-chalet, a building project is prepared, because the originality of the roof itself, as well as long cornices and its overhangs, oblige this.

The roof in the style of a chalet is characterized by visors, taken out several meters outside the house.

Roof truss designed for soft roofing

Soft roof is being done different ways, however, exist in the technological methods of its construction General characteristics. Initially, you need to prepare. When equipping a roof for a house made of foam concrete or other material, a Mauerlat is first installed, then a cut is made under the ceiling beams in increments of up to one meter in the upper crowns of the building. The distance between the boards is calculated based on the type of rafter structure.

1. Mount individual parts of the rafter system. To completely eliminate the risk, the boards of the rafter legs on the ground are attached with screws. After creating a truss truss, it is raised to the top of the building.
2. They fix all the elements of the rafters with ceiling overlap, internal boards, jibs, as well as crossbars. Further, this basis for the roof will become a single whole structure.
3. The next stage is the crate, which is under soft roof installed with little or no gaps. Gaps of no more than 1 cm are allowed. Quite often, leveling plywood is installed on top of the boards. Her sheets are laid according to the method brickwork. The resulting joints do not align with the gaps between the plywood and the board.

If the length of the boards of the crates is not enough, then the joints of the parts must be located in different places. In this way, areas that have been weakened can be correctly distributed.

Self-manufacturing of the truss system

Before the installation of the truss system begins, the Mauerlat must be fixed to the longitudinal walls with anchors. Next, you need to decide on the desired section of the legs for the rafters, depending on the distance and their length. If there is a need to increase the length of the rafters, then connect them with various fasteners.

When using different insulation, you need to choose the ideal distance between the elements of the rafters in order to reduce the number of thermal insulation scraps.

Installation of the truss system must be carried out in the following order:

1. A template is made according to which the farm is assembled. 2 boards are taken, corresponding to the length of the rafters, and connected to each other from only one edge with a nail.

   A rafter template called "scissors" will help you quickly assemble the entire roof truss system

2. You get a design called "scissors". Its free edges are placed on supports at the points of contact of the rafter legs. The result should be the final angle, that is, the angle at which the roof slope will be tilted. It is fixed with several long nails and transverse boards.
3. A second template is made, thanks to which the cuts on the rafters are installed. It is made from plywood.
4. Special mounting cuts are cut out on the rafters (a prepared template is used for this purpose) and connected at an angle of inclination of the slope. You should get a triangle that rises to the roof along the stairs. Next, it must be attached to the Mauerlat.
5. Initially, two side gable rafters are mounted. Their correct installation in the vertical and horizontal plane occurs due to temporary struts attached to the rafters.

   For the correct installation of the entire rafter system, the first pair of rafters is installed on the roof

6. A cord is stretched between these tops of the rafters. It will indicate the future skate and the level of other rafters located in the gap.
7. Raise and mount the remaining rafters at the initially calculated distance, which should be at least 60 cm from each other.
8. If a bulky construction of rafters is provided, then it is additionally strengthened with struts, supports, and so on.

   The bulky construction of the rafters is additionally reinforced with struts and supports.

9. On special supports, a ridge beam is installed, to which not only short, but also diagonal and intermediate elements of the rafters are attached.

   Proper fastening of the ridge beam ensures the reliability of the entire rafter system

Typical nodes of a standard truss system

The structural strength of the rafters depends on the ideally selected section of the boards, as well as on High Quality truss knots. The connection of parts for the roof structure is done in accordance with established rules.

The main typical nodes in the truss system:

• supporting knot of rafters on the Mauerlat;
• ridge;
• a node for combining the upper puffs and the entire truss system;
• fixing the strut, rack, as well as rafters and beams.

After the design of the rafter system has been chosen, it is necessary to draw up a plan in which to select all the nodes. In each design, they are made differently, as it depends on different nuances: type of roof, its size, angle of inclination.

Rafter from profile pipe- this is a metal structure that is assembled using lattice rods. The very production of such farms is a very time-consuming process, but also more economical. Paired material is used for the manufacture of rafters, and scarves are connecting elements. The construction of rafters from profile pipes is assembled on the ground, while riveting or welding is used.

Thanks to such systems, any spans are blocked, but it is necessary to make the correct calculation. Provided that all welding work will be done with high quality, in the future it remains only to transfer the structural elements to the top of the building and assemble them. Bearing rafters from a profile pipe have many advantages, such as:

Crossbar in the truss system

Rigel is a fairly broad concept, but in the case of roofs it has a certain meaning. The crossbar is a horizontal bar that connects the rafters. Such an element does not allow the roof to "burst". It is made of wood, reinforced concrete, and also metal - it all depends on the type of structure. And the crossbar serves to distribute the load exerted by the truss system.

It can be fixed in various places between the legs of the lines. There is a direct pattern here - if the crossbar is fixed higher, then the timber for its installation must be selected with a large cross section.

There are many ways to fix the crossbar to the truss system:

• bolts;
• nuts;
• studs with washers;
• special fasteners;
• nails;
• mixed fasteners when applied in parallel different types fasteners.

Mounting exists with a tie-in or overhead. In general, the crossbar is a design unit, as, indeed, the entire roof sling system.

The crossbar in the truss system is designed to reinforce the roof structure

Rafter system fastening

To ensure the reliability of the rafter system, it is necessary to initially find out how they are fastened to the supporting roof and the ridge. If fastening is done to prevent deformation of the roof during shrinkage of the house, then the rafters are fixed on top with a hinged plate or a nut with a bolt, and from below - with a sliding support.

Hanging rafters need a tighter and more reliable fastening in the ridge, so in this case can be applied:

• overhead metal or wooden plates;
• cutting method;
• connection with long nails.

In the layered system, the rafter legs are not connected to each other, since they are attached to the ridge run.

The rafters are fastened to the Mauerlat by cutting down, which is done in the rafter leg. Thanks to this method of fastening, the support of the roof will not be weakened. Cutting is also done when installing rafters on floor beams. In this case, the cut is also made in the support beam.

Video: how to make rafters with your own hands

Thus, a perfectly matched system of rafters and their structural characteristics will help create the basis for a reliable roof for your home.

Rafters and lathing - the roof frame, which bears the brunt of the roofing cake, thermal insulation, snow load, so they must have a high bearing capacity, strength. The idea of ​​using metal rafters to make the roof structure more rigid is not new, but in the past it was mainly used to cover industrial or utility structures. Now the rafter frame and the metal profile crate are considered a real alternative to wooden roof elements if the slope length exceeds 10 meters.

The design of the roof truss frame consists of many interconnected elements that form trusses. The step, the size of the section between the rafters and other supports determines the calculation of the loads to which they are subjected during operation. The roof frame performs the following functions:

1. Load distribution. Interconnected nodes, reinforced with corners, evenly distribute the weight of the roof, which can reach up to 500-600 kg, taking into account the snow load. How larger section rafters and less step between them, the greater the bearing capacity of the structure.
2. Giving slope and shape. The rafters, located at an angle to the base of the roof, form an inclined plane of the slopes, so that snow and water do not accumulate on the roof surface.
3. Formation of the base for fixing the roofing material. The top coat of the roofing pie is fastened to the roof frame. The crate acts as a basis for fixing the coating, distributing its weight evenly over the rafters.

Note! What should be all the nodes, rafters and lathing of the roof structure determines the engineering calculation. To determine the required bearing capacity of the frame, it is necessary to calculate the total load to which it will be subjected. To do this, add up the weight of the roofing material, insulation, waterproofing, the maximum snow load with the weight of the truss system.

Types of truss systems

The most common material from which the crate and rafters of the roof frame are made is wood. However, if the weight of the roofing material is large enough, and the length of the slope is more than 6 meters, then the structure is too massive. Builders have to reduce the step between the rafter legs, increase their cross section, which is why the roof nodes become big weight, increasing the load on the foundation. You can unload the load-bearing walls and the base of the building using stronger, but lighter metal rafters. According to the type of material used the following types truss systems:

• Wooden. Rafters and lathing made of wood are used for the construction of roofs, the slope length of which does not exceed 7-10 meters. The fastening of the frame elements to each other occurs with the help of self-tapping screws, nails or movable metal elements. The step between the legs is usually in the range of 50-80 cm.
• Metal. Metal roof frames are made of zinc-coated steel profile, which is not afraid of moisture. The rafters and the crate made of this material are light, durable, so the step between them can be increased to 1.5-2 meters. The fastening of the metal profile is carried out by welding or fasteners. Metal roof units are used with a slope length of 10 meters or more.
• Combined. The truss frame, combining metal and wooden knots, is called combined. The combination of wooden and galvanized steel support elements allows for a cheaper structure with a high load-bearing capacity by increasing the spacing between the rafters.

Please note that metal and wooden elements frames cannot be interconnected without a gasket made of waterproofing material or treated with an antiseptic preparation. Since the metal has a high thermal conductivity, its proximity to the tree leads to the formation of condensation and rotting of the rafters.

Fastening methods

Metal rafters are assembled into triangular, trapezoidal or arched trusses. Internal stiffeners are attached to the frame beams, which form corners that significantly increase the load-bearing capacity of the frame. Such a system allows you to take a step between the rafters more, taking into account the support capabilities of each truss. The fastening of the metal elements of the roof frame is performed by one of the following methods:

1. Fastening by welding. If you weld the details of the truss system using a welding machine, you can get a rigid structure with high strength and bearing capacity. If you correctly calculate the roof, you can lighten the frame and reduce the load on the foundation of the structure. The disadvantage of this method is that only a professional with the help of special equipment can perform welding.
2. Fastening with bolts. Fixing the rafters with fasteners allows for less rigid fastening. This method of assembling a truss frame based on a metal profile is used in private housing construction, where the length of the slopes does not exceed 10 meters. Rejection of welding allows you to speed up the installation of the roof.

Experienced craftsmen rely on the fact that the rafters can withstand more weight than wooden ones, so you can increase the step between them and reduce the thickness of the section of the elements. Moreover, ready-made roof trusses are sold in hardware stores, the fastening of which was carried out by welding, suitable for overlapping buildings of standard width.

Advantages

The metal truss frame is used for the construction of roofs of any shape, any slope with a slope of 1-2 degrees. As the material from which the rafters and lathing are made, steel corners, pipes of round and rectangular cross-section, and tauri are used. In order to correctly select the thickness of the frame elements and choose the step between them, the calculation of the roof structure is performed, taking into account the permanent and temporary loads that are transferred to the rafters during operation. The advantages of a truss system made of this material are:

• Fire safety. Unlike wooden beams, metal frame beams are not flammable, which increases the fire safety of the building.
• Ease of maintenance. Zinc galvanized coating, which covers the steel corners, protects the roof frame from corrosion during the entire service life. They, unlike wooden ones, do not require annual antiseptic treatment.
• Zero waste. Although metal constructions are quite expensive, it is considered cost-effective, since the fastening is carried out by a welded method, and there is practically no waste left.
• Long service life. If you correctly calculate the loads, then roof frame from metal will last more than 100 years, which exceeds the life of even the most stable roofing.

Professional roofers believe that it is advisable to use welded metal structures for the manufacture of a roof truss frame with a slope length of 10-12 meters. In this case, the main task is to correctly calculate the loads, and then determine the step between the legs in accordance with the climatic characteristics and properties of the roofing material.

Flaws

Despite the obvious advantages, metal truss systems are not the most popular constructive solution in private housing. Even a large step between the rafters and a sparse crate at a high cost of metal cannot make the structure cheaper than wood. The disadvantages of metal rafters are:

1. High thermal conductivity. The metal has a high coefficient of thermal conductivity, so the rafters and form bridges are cold. From the point of view of energy efficiency, a metal profile frame is not the best solution.
2. Difficulty in transportation and installation. When choosing a metal rafter system, take into account that transporting, lifting and securing long and heavy elements is more difficult than standard length lumber rafters.
3. Difficulty of installation. For lifting to a height and fixing trusses, it is used special equipment which is expensive to rent or buy.
4. Deformation under action high temperature. Although metal is considered a non-combustible material, during a fire it is highly deformed, which usually leads to the collapse of the roof.

To determine whether it makes sense to use more expensive metal profile truss elements, you need to calculate the roof frame. If the slope length exceeds 10 meters, and the load is more than 450-600 kg, then the installation metal frame economically viable.

Video instruction

Layered truss system - a design used in the construction of roofs of buildings with intermediate bearing walls, supporting pillars or columns. It relies not only on the walls outside, but also on the inner central support (in some cases, two).

If we talk about use, then layered rafters are the most common for residential private houses, which, as a rule, have internal partition walls.

The constituent elements of the layered system: two rafter legs, the lower edges of which are supported and fixed on the outer walls (Mauerlat), and the upper ones - on a horizontal ridge run. The run, in turn, is held by vertical posts resting against an intermediate wall.

This is a classic layout of a layered system, suitable for a gable roof. With a shed roof, the same rules can be traced, but with a different implementation. The rafters included in the rafter system are laid with support on opposite load-bearing walls (it turns out that only on two supports). An internal partition is not needed here. In fact, its function is performed by a higher wall.

To increase the bearing capacity of the truss structure, struts are introduced into the system. Their presence allows you to increase the length of overlapped spans.

For shed roofs, it is possible to use layered rafters without the introduction of struts for spans up to 4.5 m. The presence of a strut increases this possible length to 6 m. A similar trend can be traced with gable roofs. double slope design with one intermediate support is used for spans up to 9 m. Installing struts increases maximum length span up to 10 m. And the combination of struts with a scrum (horizontal beam connecting a pair of rafter legs) - up to 14 m.

There are several options for the implementation of layered systems, among which there are non-thrust and spacer structures with additional supporting struts, scrambles, and rafter beams.

Consider the basic designs of layered rafters.

Bezrasporny rafters without struts

This type of layered rafters does not give a thrust on external walls. Leveling of bursting loads occurs due to a special combination of fasteners. One edge of the rafter is always fixed rigidly, and the second - on a sliding support. This gives the absence of thrust.

Rigid fastening can mean that the node is fixed, but the beam can be rotated in the hinge (one degree of freedom). There is also a rigid pinching of the rafter beam, in which any displacement is impossible (zero degree of freedom).

More freedom is given by a sliding mount, which allows the rafter leg not only to turn, but also to move horizontally (two degrees of freedom).

The non-thrust design is characterized by the fact that it always has both a rigid and a sliding fastening. Due to this, under the influence of the load, the rafters bend without transferring the thrust to the walls.

Options for fixing rafter legs

The bottom of the rafter is fixed rigidly, the top is loose (sliding support)

The lower edge of the rafter is fixed rigidly to the Mauerlat (one degree of freedom), by cutting with a tooth. In another case, apply washed down with fixation with a support bar.

At the upper end of the rafter, a horizontal cut is made with a bevel. If cutting is not possible, then the edge of the rafter leg is hemmed from below with a trim of the beam and fastened on both sides with mounting plates. The fastening of the upper edge of the rafter to the run is performed according to the type of sliding support. At the same time, opposite rafters are laid on the ridge one by one, without fastenings between them. Therefore, a gable roof made according to this scheme can be perceived as two shed roofs adjacent to each other.

The complexity of the scheme is that any error in the implementation of the ridge knot turns the non-thrust structure into a spacer. Therefore, this option is rarely used for gable roofs, more often for shed roofs.

The bottom of the rafter leg is fixed freely, the top is rigid

The most common scheme for private houses.

The lower edge of the rafter is fixed to the Mauerlat on a slider (metal bracket), so that it can move and bend under load. So that the rafter could not “leave” in the lateral direction, it is fixed on both sides with metal corners or bars.

The top of the rafter legs is fixed on a hinge with a rotation tolerance (one degree of freedom). At the same time, the ridge knots of the layered rafters of this type perform this: the edges of the rafters are whipped together and connected with a bolt or nails. Or, the ends pre-cut at an angle are joined, and then they are tied with metal or wooden linings.

The bottom of the rafter leg is fixed freely, the top is rigidly pinched

This scheme differs from the previous one in that the connection of the rafters in the ridge knot is carried out with a rigid pinch. The rafters are supported by beveled ends against each other, and then they are connected to each other and to the ridge run with two crossbars-puffs. It turns out a knot with pinching.

The bottom of the rafter legs is connected to the Mauerlat freely, on a slider.

This mounting option is characterized by increased bearing capacity, which allows it to be used in regions with an increased level of snowfall.

Ways to increase the stability of non-thrust systems

All three considered truss systems show themselves as stable under uneven loads only in the case of rigid fixation of the ridge run. That is, when its ends are brought out to the gables or supported with additional slanting rafters.

If the ridge run rests only on the racks, the roof may lose stability. In the second and third options considered (the bottom of the rafter leg is on the slider, the top is rigidly fixed), with an increase in the load on one of the slopes, the roof will shift towards the increased load. The first option will keep its shape, but only with perfectly vertical racks (under the run).

So that, despite the non-rigid fixation of the run and uneven loads, the layered rafter system remains stable, it is supplemented with a horizontal scrum. The scrum is a beam, usually with the same section as the rafters.

It is fastened to the rafters with nails or bolts. The intersection of fights and racks is fixed with a nail fight. The work of the fight can be described as emergency. In the event of an uneven heavy load on the slopes, the fight is included in the work and protects the system from skew.

You can strengthen the system with a rigidly fixed top and a free bottom (second and third options) with the help of a slight transformation of the lower node. Rafter legs are taken out of the edge of the walls. At the same time, the fastening itself remains sliding, like a slider.

Another option for increasing stability is to rigidly mount the bottom of the racks on which the horizontal ridge run is held. To do this, they are cut into the bed and fixed to the floors, for example, using linings from boards or bars.

Spacer rafters without struts

In this case, the rafters rest on the load-bearing walls and transfer the thrust to them. Therefore, such systems cannot be used for houses whose walls are built of aerated concrete. Aerated concrete blocks do not resist bending at all and collapse under expansion loads. And other materials, such as brick or concrete panels, easily withstand such loads and do not deform.

The spacer rafter system requires a rigidly fixed Mauerlat. Moreover, in order to withstand the thrust, the strength of the walls must be high. Or an inextricable reinforced concrete belt should go along the top of the walls.

For spacer rafters use the same fastening options discussed above for non-thrust systems. But with one caveat: all existing sliding mounts (sliders) are replaced with hinged ones with the ability to rotate. To do this, a support beam is nailed to the bottom of the rafter or a cut is made with a tooth in the Mauerlat. Hinged fastening in the ridge knot is performed by laying the rafters on top of each other and fastening them with a nail or bolt.

The spacer structure is a cross between layered non-spacer and hanging systems. The skating run is still used in them, but it no longer plays significant role. After all, the rafters are rested with their lower edges against the walls, and with their upper edges against each other. When the walls subside or the ridge run sags under its own weight, the run stops working altogether. In essence, such rafters become hanging.

To increase the stability of the system, a contraction is included in it, which works in compression. It partially, albeit to a small extent, removes the pressure on the walls. In order for the fight to remove the thrust completely, it must connect the lower edges of the rafter legs. But then it will no longer be a fight, but a puff.

The installation of a rigidly fixed ridge run also reduces the thrust.

Rafters with struts

Such systems can be arranged both according to spacer and non-spacer schemes. Their difference from the options already considered is the presence of a third supporting part under the rafter leg - a strut (rafter leg).

The brace changes the system. The rafter from a single-span beam turns into a two-span continuous one. This allows you to increase the overlapped span, up to 14 m. And also - to reduce the cross section of the rafters.

The brace is connected to the rafter in such a way as to prevent its displacement. This is done as follows: the strut is brought under the rafter and fixed with wooden plates on the sides and bottom.

Laying system with rafter beams

This rafter design is suitable for buildings with two longitudinal load-bearing walls or intermediate transverse walls. Racks in this case are located not under the ridge, but under the rafters. There is no ridge run.

The rafter legs in the scheme are supported by two rafter beams (through girders), which, in turn, are laid along the roof slopes and rest on vertical racks. Racks are fixed to the bearing intermediate walls through the beds.

Through runs may not be included in the scheme. Then the racks will have to be brought directly under each rafter and secured with a puff with a nail fight.

From above, the rafter legs are joined together and connected with overlays made of metal or wood on both sides.

The absence of a ridge run automatically means that the rafter system forms a spacer. In order to neutralize it in the non-spacer version of the system, a puff is fixed below the through runs. Under load, it will stretch and eliminate unwanted thrust. To maintain stability in the system, a scrum is used, fixed at the bottom of the hasty legs. Also, the structure will be protected from folding by special jointing, which is fixed crosswise between the uprights.

In the spacer system, the scrum is set above the through runs. Then the contraction under load will shrink and, in fact, turn into a crossbar.

Installation of racks under rafter legs or through runs (and the absence of central racks!) makes it possible to use this type of layered rafters for arranging spacious attic spaces. Other schemes are only suitable for attics and attics with partitions.

Key points for installing layered rafters

Having on hand a calculated scheme of the device, you can proceed with the installation of the truss system. Installation is carried out in several stages, the main ones are:

1. A Mauerlat is laid on top of the outer walls - a board or timber. To prevent the Mauerlat from rotting, a waterproofing material is laid between it and the wall - roofing material, roofing felt, etc.

2. A bed is laid on top of the intermediate wall, which is necessary for attaching vertical racks.

3. Racks are fixed on the bed with a step of 3-6m.

4. From above, on the racks, install a ridge run.

5. Expose the rafters in increments of 0.6-1.2 m. From below, the rafter leg is attached to the Mauerlat in accordance with the selected mounting scheme (on a hinge or on a slider). From above, the rafter legs are either laid out separately on the ridge run, or they connect the upper edges to each other, resting on the ridge.

6. If the scheme provides, the rafter legs are connected by horizontal contractions.

7. Again, at the request of the scheme, struts, support elements are set.

When performing work on the installation of rafters, missteps should not be allowed. It should be remembered that the truss system is a roof frame that must withstand all possible loads. An incorrectly calculated or mounted system can easily lead to skew and even destruction of the entire roof.