Rafter system nodes - how to make a reliable roof? Metal rafters for the roof

At the stage of building a house, special attention should be paid to the roof. The reliability of the entire structure will largely depend on how reliably, correctly and efficiently it will be done. One of the important parts of the roof is the truss system, which holds the finishing material, insulation, waterproofing and other elements. For gable roofs of houses, hanging rafters are often used, the design and components of which, as well as installation, are described in this material.

Rafters are the main load-bearing element of a pitched roof, which takes on the main load experienced by this structure. The rafter system is of two types - hanging or layered. You have to choose between them, based on whether there are internal walls in the structure under construction, which can serve as a support for parts of the roof. The hanging rafter system is used if there are no such walls, and here only the outer walls of the building will serve as a support. That is, these rafters do not have a central support as such and rest on the wall on one side, and on the opposite rafter on the other. The fastening of individual elements is carried out using slotted spikes, nails, anchors or metal plates.

Hanging rafters are usually used to cover spans with a width of 7-10 m. The scope of application may be different - such a system is used for the construction of roofs in warehouses, industrial buildings, residential buildings.

On a note! The maximum distance between walls that allows the use of a hanging rafter system is 14 m.

Despite the fact that such rafters are installed at a slope, they do not act on the walls like spacers - they transfer only vertical loads. This can be achieved through the use of stretch marks made of timber, located at the base of the roof.

On a note! The tightening between the legs of the rafters is located the higher, the greater the load it experiences.

Rafter elements are made of timber, boards or logs, metal. Without fail, before starting installation work, the material must be treated with special protective compounds that will provide the tree with a long service life. They will protect it from fungus, mold. If the material is treated with fire-fighting compounds, then the house will gain additional protection against fires.

What does the hanging rafter system consist of?

A system of this type has several components. And it is necessary to familiarize yourself with them in order to understand the purpose of each of them and not get confused in concepts.

Table. The constituent elements of the system.

Element	Description
	This is the basis of the system. It is thanks to them that it turns out to form the shape of the roof, slopes. They are created from a bar (or board) with a section of 50x150, 100x150 mm and are placed in increments of about 60-120 cm. The dimensions and pitch chosen will directly depend on the parameters of the roof, its design features, and the calculated load.
	The place where two roof slopes are connected. Usually there is an additional ridge beam.
	With the help of these elements, representing beams horizontally located between the rafters, the rafter legs are tightened and strengthened. Due to the puffs, the load experienced by the rafter legs is compensated.
	A kind of puff, which is located near the roof ridge. It is made of a very durable timber, as it experiences a colossal level of load.
	A beam, which is installed on the upper part of the load-bearing walls, rafters rest on it. It helps to distribute the weight of the entire roof along the perimeter of the building, which makes it possible for the foundation and walls to experience the load evenly. For manufacturing, a bar with a section of 100x100 or 150x150 mm is used. Interestingly, it may not always be used - some types of roofs are equipped without it.
	An element that is installed under the roof ridge and is designed to support a long tightening.
	These structural details are used for buildings that have too large spans between load-bearing walls. They are necessary to support the rafters, providing them with a minimum bending load, that is, they will not allow them to bend and sag.

Bar prices

Types of structures

There are five main types of roof structures of this type that can be used in construction, which can be obtained on the basis of hanging rafters. They differ in the presence of some structural elements, configuration, etc.

The simplest option is triangular articulated arch. Its shape is triangular, the puff here is under tensile load, and the rafters are under bending. Such a scheme is used only if the height of the ridge is at least 1/6 of the entire span between the walls, otherwise it will not function correctly. Quite often used in the construction of attics. In this case, two rafters are joined and connected to each other in the ridge part. At the bottom, the triangle can be connected with a long puff. The system can only be used if the span between the walls is no more than 6 m.

Slightly different from the above system - articulated arch with headstock. In this case, the design has a support in the form of a headstock installed under the ridge. Due to the tightening, it works in tension. The headstock can be made of either metal or wood. The system is used if the spans between the walls are 6 meters or more. The headstock will not allow the puff to sag - it acts as a kind of suspension and allows you to adjust the degree of deflection of the horizontal part.

Articulated arch with puff that is raised, is usually used when planning the construction of attics and spacious attic spaces - that is, where the ceiling height is important. In this case, puffs will be installed at the top of the rafters. And the higher the puff is located, the greater the tensile force it perceives.

If the support is a fixed hinge element, then the structure will be called arch with crossbar. Here the roof is attached to the Mauerlat by forming a tooth on the rafters. The bolt itself resembles a small puff, but in this case it works not in tension, but in compression. Rafter legs are fixed quite rigidly.

Arch with struts and headstock resembles an arch system with a suspension. Here, during the installation of the rafters, struts are used, which ensure that the structure is relieved of excess stress. The option is suitable for closing spans with a width of 9-14 m.

On a note! Any scheme for the design of hanging rafters involves accurate calculations that will clarify all external and internal loads.

The rafter system is quite difficult to install, sometimes its parts are assembled directly on the ground, and then rise to the roof. But also rafters can be mounted right on the spot. In general, a roof with hanging rafters is the simplest option, therefore it is often made by novice builders or on their own.

Perforated plates used for attaching rafters

Prices for various types of fasteners for rafters

Fasteners for rafters

Ways of fastening rafters

These structural details can be fixed in two ways.

Bolt and clamp, where in this case the end part of the rafter is cut off, and she herself is placed on the beam in the place where the notch is made. The fastening of individual elements is carried out with the help of bolts. They are connected so that the attachment point is perpendicular to the upper part of the rafter. Sometimes clamp systems are used for connection.
double tooth. The method is applicable if the slope of the roof slope relative to the horizontal is less than or equal to 35 degrees. In this case, two stops are made on the beam, a special hole is made in the rafter leg, and a spike is cut out at the place of the extreme stop on the beam. In size, these elements must correspond to each other.

System design

To correctly create a system layout, it is important to consider:

rafter installation step;
load on the structure and structure;
section of rafters;
material that will be used to create the roof;
construction type;
roof pitch angles
the dimensions of the building as a whole;
climatic conditions of the region.

The more accurately the calculation is made and the more correctly the rafter system is designed, the stronger and more reliable the whole structure will turn out. For convenience, you can use the existing online calculators, which is important for those who are not friends with the exact sciences, or for beginners.

Video - Roof truss system, what you need to know for proper design

Installation rules

Installation of hanging rafters must be carried out in compliance with certain rules. Only in this case it will be possible to make a correct and stable design. The work rules are as follows:

Installation of hanging rafters

For the construction of the truss system, certain tools and materials may be required. The list below is quite approximate, but can be used as a basis during preparation for the start of work.

Tools for creating a rafter system:

a hammer;
axe;
jigsaw or hacksaw;
building level, twine, tape measure;
thread with a load (plumb line);
pencil, ruler.

Prices for popular models of jigsaws

As necessary materials, you can directly list the beams and boards for rafters, self-tapping screws and nails, anchor bolts, waterproofing material, antiseptic compounds for wood processing.

Sigma-Extra - outdoor work, antiseptic for wood

Consider the installation process of the truss system step by step.

Step 1. All wood material is treated with antiseptic agents that prevent the development of decay processes, the occurrence of fungus and mold. Prior to installation, the material is well dried.

Step 2 Building material is delivered to the top of the building.

Step 3 A mauerlat is nailed along the perimeter of the load-bearing wall, consisting of two boards of such a width that they can cover the entire upper part of the wall with themselves. Between the Mauerlat and the wall, it is recommended to lay a layer of waterproofing material (for example, roofing material). This will seal the joint, protect the material from moisture and reduce drafts in the future.

Step 4 Next, beams are created from the timber, which will be attached to each pair of rafters in the lower part. They are attached to the Mauerlat and connect two load-bearing walls together. You can temporarily move along them during the work, and boards that are used to create rafters are also folded on them.

Step 5 To form the top of the roof, a ridge beam is cut out. It should have a length from one part of the future roof to another and be parallel to the long load-bearing walls.

Step 6 The required roof height is determined - the level at which the ridge beam will be attached. The angle of inclination of the slope is recommended to be done within 25-45 degrees. You can find out the angle of the roof and the length of the rafters using the Pythagorean theorem. To do this, you need to measure the distance from the ridge, the height of the roof and the distance to the outer wall.

Step 7 The ridge board is installed at the place of the future docking of two rafter legs.

Step 8 From the prepared lumber, future rafters of the desired length are measured and cut. They will be attached with the selected pitch to the ridge board and Mauerlat.

Step 9 To make it possible to attach the rafters to other elements, special triangular cutouts are made. To do this, the board is installed so that one side lies on the ridge board, and the other on the Mauerlat. The cut mark is applied. Next, the marked sections are cut.

Step 10 The second rafter is prepared in the same way. Now they should be docked with each other. To do this, the boards are moved as close as possible to each other, markings are applied indicating the place of the cut. The cut is made and the boards can be joined.

Step 11 The rafters are attached to the Mauerlat using metal corners and self-tapping screws. With the help of them, the boards are also fixed on the roof ridge.

Step 12 Two rafters are interconnected using metal plates and self-tapping screws. Thus, the first two structures are installed, which will be located at the edges of the roof.

Step 13 In order to make it easier to evenly install other rafters, a rope is stretched strictly horizontally between the extreme structures.

The process of installing rafters

Step 15 If necessary, the rafters can be reinforced with puffs that are attached to two joining rafters.

Video - Installation of the truss system

Video - Installation of rafters

Video - Using a crossbar (screed) for rafters as an interior element

Hanging rafters are considered a fairly simple design compared to other types of truss systems. But there should be no rush during their installation. It is important to remember that at the slightest skew, all work will go down the drain, so you need to work carefully and carefully.

The rafter system is the frame of the roof of the house, which bears and evenly distributes the weight of the roofing pie, sometimes reaching up to 500 kg / m2. The reliability of this kind of skeleton depends on three factors: the accuracy of the calculation, on the basis of which the number and cross section of the supporting elements are selected, the material from which it is made, and also on the correct fastening technology. Knowing how to properly fix the rafters, you can significantly increase the bearing capacity of the frame, making it more durable and reliable. Installation errors, on the contrary, lead to noticeable strength losses and roof deformations. In this article we will talk about the main types and methods of fastening, with which you can install the rafters with your own hands.

The truss frame of the roof of the house is a system of interconnected supporting elements made of wood or metal, which give the structure a shape, slope, and evenly distribute its weight between the bearing walls. Its main component is the rafter legs, which are angled beams that are connected in pairs along the slope, forming a ridge at the top of their connection. There are two main types of rafters:

Layered. Rafters are called supporting elements, which in the roof structure have two points of support - on the ridge run and the Mauerlat. This type of rafter system is used in structures that have one or more load-bearing walls inside, on which the rafters can be “leaned”. This fastening of the rafters allows you to unload them through the use of additional vertical supports.
Hanging. Hanging elements are called elements that have only one point of support, located where the rafters are attached to the wall or Mauerlat. The hanging type truss system experiences a load not only in bending, but also in bursting, therefore it is reinforced by horizontal compensating elements (crossbars, puffs, contractions).

Note! In most of the most popular truss systems, the rafters are attached to the Mauerlat. Mauerlat is a massive bar or beam with a section of 150x150 mm or 200x200 mm, laid along the load-bearing walls of the structure, on which the rafter legs will subsequently rest. It softens the pressure on the walls of the house, and also evenly distributes the weight of the roofing cake. You can attach the Mauerlat to the upper belt of the walls using anchor bolts or embedded metal studs.

Main connecting nodes

The rafter frame is called a system because all its elements are closely interconnected and fixed, as a result of which the roof structure acquires a stable shape, rigidity and high bearing capacity. Each connecting node between its parts is a weak point that can easily be deformed under load, so all fastenings must be carried out strictly according to the technology. Experienced craftsmen distinguish types of connections in the roof structure:

Fastening rafters to the ridge beam. This connecting node is typical only for layered truss systems, in which the upper part of the rafter leg rests on a ridge run, mounted on vertical posts. The rafters can be fastened to it with the help of metal plates, nails or sliding sliders.
Fastening rafters to the Mauerlat. The most important fastening unit of the rafter frame is the junction of the Mauerlat beam with the rafter legs. You can fix the rafters on it with nails, metal corners or wooden bars.
The connection of the rafters to each other. To lengthen the rafter legs, if the length of the slope exceeds the standard length of lumber, they are assembled from several elements interconnected with nails, glue or metal linings.
Connection of rafter legs with auxiliary supporting elements. In the design of the truss frame, the rafters can be connected to a puff, crossbar or struts to increase rigidity, strength and bearing capacity.

Please note that any cuts made to attach the rafters to beams, mauerlat or other structural elements of the frame lead to a decrease in their strength, so experienced craftsmen recommend connecting them together using corners and overlays.

Fixation methods

When deciding how to attach the rafters to the Mauerlat or ridge run, it is necessary to choose the right mounting hardware. The modern construction market has a huge assortment of fasteners of various designs and sizes. The main criteria for choosing fasteners are the material used to make the rafters, their cross section, as well as the type of load to which they are subjected. There are the following ways of fastening rafters:

Experienced craftsmen believe that the most reliable way to fix the rafters is to use metal corners that firmly connect the wooden elements to each other, rigidly fixing the angle between them. The corner that overlaps the joint between the rafter leg and the ridge beam or Mauerlat serves as a kind of spacer between them.

Varieties of fasteners

Wood is a natural material that, in the process of leveling moisture and drying, shrinks significantly, due to which the linear dimensions of the structure change. That is why experienced craftsmen recommend building a roof for timber and log houses, a year after construction, when the shrinkage process passes from an active to a passive phase. If you fix the wooden elements of the frame rigidly, then after drying the roof of the house may be deformed. Therefore, the following types of fasteners are used to connect the rafters:

Interestingly, there are several options for combinations of movable and fixed connecting nodes. The most common are truss systems with one rigid and two sliding fasteners, which provide sufficient mobility with high strength and rigidity of the structure.

Types of fasteners

Among experienced roofers, disputes do not subside, the more efficient it is to fasten rafters to floor beams and Mauerlat. However, in most cases, the catch is that in these conditions it is more practical to use nails or self-tapping screws. Both of these fasteners have their own advantages and disadvantages:

Nails are good because only a hammer is needed to drive them, which is in every household. However, some masters complain that scoring them by hand is too long. It is worth recalling that special serrated nails are used to fix the rafters, which securely adhere to the wood.
To assemble the rafter frame, galvanized self-tapping screws are used, which are not afraid of corrosion. Due to the thread, they are firmly screwed into the thickness of the wood, securely fixing the elements together. Screw them quickly and conveniently with a portable screwdriver. The disadvantage of this type of fastener is that during dismantling, removing self-tapping screws from wood is long and dreary.

Most experienced roofers agree that it is better to use galvanized ruff nails to fix the rafter legs, the length of which is 5-3 mm longer than the thickness of the lumber. Properly selected fasteners are the key to high-quality and long-term fixation of the roof frame, which will not be afraid of either mechanical stress or wind load.

Video instruction

In addition to correctly made calculations and drawings, fasteners for rafters and all its elements are of no small importance in the stability of the structure.

In addition to the load of atmospheric precipitation, the rafters must withstand the weight of the lathing and the total weight of the roofing pie, which must be taken into account when selecting fasteners.
The truss system is a spatial structure consisting of the following elements:

Mauerlat;

rafter legs;

valleys;

ridge beams;

runs;

crate.

In order to understand how all parts of the truss system are attached to each other, you need to figure out what nodes it consists of, what fasteners are used in each case and what they are. When assembling the supporting structure of the roof, fasteners, both steel and wooden, are used.
The main nodes of the connection of the truss system

Before connecting the Mauerlat and the rafter leg to each other, the first one will need to be firmly connected to the wall. Mauerlat is a thick beam (15x15), laid along the axis of the wall and parallel to the ridge of the beam, on which the rafter legs rest. The functions assigned to this element of the supporting structure are to distribute the load from the rafters, the weight of the roofing pie and atmospheric precipitation throughout the wall, including internal supports. In other words, the Mauerlat is the foundation for the entire roof. It is laid on the axis of the wall and fixed to it. In this case, there are several connection methods.
Method one. When constructing a roof of a large area along the entire length of the wall, an armored belt is poured, where metal pins are immediately embedded under the M12 thread every 2 m. In this method, there will be studs that pass through the beam through the wall and are attracted to the wall with a nut and pucks. With a small area of \u200b\u200bthe roof, where there is no large load on the wall, they do without a Mauerlat and the rafters are attached directly to the studs embedded in the masonry process.

Method two. Another quite affordable way to make the truss system stable is to attach the Mauerlat to the wall with a wire. To do this, you need to lay the middle of the wire between the rows of bricks 3 rows before the end of the masonry. Its length should be sufficient to tie and pull the Mauerlat to the wall. You can also do without the Mauerlat and fix the rafter with wire directly to the wall. But such a connection will give a point load on the wall, which may affect its integrity.
The scheme for attaching the rafter leg to the Mauerlat can be rigid and sliding. The type of connection depends on the shape of the roof and the type of rafters, which can be hanging or layered.

Rigid and sliding connection of the lower part of the rafters with Mauerlat

Connection nodes in this case will be made of wood and can have several types:

A tooth that has only an emphasis.

A tooth with a spike and an emphasis.

Emphasis directly on the beam.

A single tooth notch is used for a roof with a large angle of inclination, where the angle between the mauerlat and the rafter leg is more than 35º. To do this, you will need to cut a tooth with a spike in the rafter leg, and create a nest under it in the Mauerlat. The use of a spike avoids lateral displacement of the rafters. The double tooth notch is used when installing more gently sloping roofs. The latter method is used extremely rarely.

Recently, more and more often, a wooden mount for rafters has been replaced by a metal one, since it allows not only to get a more reliable one, but also to significantly reduce the installation work. Therefore, metal rafter bolts, brackets, plates, clamps, hinges and various corners are used as additional fasteners.

The most used method of rigid connection is driving nails from the sides at an angle into the mauerlat. Thus, internal crossing takes place within it. Further, for the final fixation of the connection, the third nail is driven vertically. Another way to prevent transverse displacement of the rafter leg is to fix it on the sides with metal corners.

The scheme for movable fastening of the rafters in the lower part is used for houses built from logs or timber. Since during operation the truss system is in motion due to a change in its physical properties, i.e., the building shrinks.

The rigid fastening scheme in this case is unacceptable, since such movements can lead to the destruction of the wall. This means that the attachment points need to provide mobility. In such cases, special swivel joints are used, which are called skids or corners with an oblong hole for fasteners. The sliding interface in this fastener achieves two levels of freedom through the free movement of one of the fastener elements.

Nodal ridge connection

The ridge connection of the truss system can be obtained in three ways: butt, overlap and on the ridge beam.

Butt. The upper part of the rafter leg must be cut at an angle equal to the slope of the roof. The opposite leg is also adjusted to the appropriate angle, but with an inclination to the other side. Further, they are interconnected at the top point with the help of a nail, which must be driven into the end of the rafters with the capture of the opposite end. In addition to nails, special plates are used for a more durable connection of joints. Both a 30 mm wooden board and a double-sided metal fixing plate can act as such fasteners. For its installation, bolts or nails are used.

The next two methods will be similar to the first, but have a slight difference. When fastening with an overlap, the upper parts of the rafter leg will be interconnected by their sides. The latter option is carried out by connecting each rafter directly to the ridge beam. In this case, threaded studs with washers and bolts are used as fasteners.

If trusses are used to stiffen the rafter system, then to ensure good resistance to wind loads, it will be necessary to install the required number of diagonal ligaments. The presence of a brace and a brace (rafter leg) in the supporting structure helps the gables of the house to be more stable. The brace is installed by resting the upper part in, and with the lower part it rests against the main floor beam. The strut helps to reduce the load on the rafters in the center. Its installation is carried out at an angle of 45º. Diagonal connections are fixed using clamps, corners, plates.

Types and features of metal fasteners for rafters

If earlier craftsmen used wooden elements as such fasteners (bars, slips, dowels, metal staples, wooden pins, wedges), now such methods are inferior to more modern types. The construction market has a large range of metal fasteners, which are now much stronger and make the process much easier. The manufacturing technology of these elements uses metal, the thickness of which varies from 1.5 ... 3.0 mm, which allows the product to be more resistant to loads compared to any other material. In addition, rafter fasteners are available in any size and allow you to carry out the technological process with great accuracy.

The metal fasteners of the rafters, which can be perforated and nailed, include:

perforated mounting tape;

corners;

plates;

beam support;

beam support;

wire tie;

self-tapping screws;

bolts with nuts;

corners of the KR;

brackets WB;

fasteners LK.

The use of perforated products allows strong enough with all parts of the system and provide good rigidity and strength at any angle. They are characterized by the presence of many holes for bolts, screws and self-tapping screws, with the help of which the attachment to the tree is carried out. The size of the product is adjusted by trimming to the desired length and width.

Also fasteners can be nailed. However, the use of this type is possible only in the factory by cutting, which bends the cone-shaped part. This operation is carried out by special machines under pressure.

KR corners have a large number of modified types, which reduce the risk of bolted joint breakage during natural settlement of the structure. Fastening is carried out without the use of special equipment using screws and nails.

Brackets WB are used for fastening the console of the supporting beam when installing wooden floors in houses made of logs or timber. At the same time, the tie-in on the rafter leg is not made, which does not weaken its bearing capacity. The connection is carried out using anchor bolts, nails or screws.

LK rafter fasteners are applicable where it is required to connect rafters and beams. It has the same advantages as WB fasteners, but the process is carried out only with screws or nails. Used in the construction of wooden houses.

Fasteners in the rafter system play a huge role. It depends on him the strength and duration of operation of the entire roofing pie. Therefore, the choice of type and method of attachment should be treated with great attention.

Rafters and lathing - the roof frame, which bears the brunt of the roofing pie, 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:

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. The larger the cross section of the rafters and the smaller the pitch between them, the greater the bearing capacity of the structure.
Giving slope and shape. The rafters, located at an angle to the base of the roof, form an inclined plane of slopes, so that snow and water do not accumulate on the roof surface.
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 units acquire a lot of 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 of truss systems are distinguished:

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 frame elements cannot be connected to each other 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 carried out by one of the following methods:

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.
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 rafter beams 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 structures are quite expensive, it is considered cost-effective, since the fastening is carried out by welding, and there is practically no waste left.
Long service life. If you correctly calculate the loads, then the metal roof frame 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 design solution in private housing construction. 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:

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.
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.
Difficulty of installation. To rise to a height and fix the trusses, special equipment is used, the rental or purchase of which is expensive.
Deformation under 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 of a metal frame is economically feasible.