Roof truss units. Fastening the rafters to the Mauerlat: consider the attachment points for the rafters to the Mauerlat

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 the walls, which 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 get acquainted with them in order to understand the purpose of each of them and not to 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 draw.
	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.

1. 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.
2. 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:

• 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.

Is it possible to single out some main detail in the roof? It is unlikely that this will work, since here each element performs its function. For example, a rafter is a part of a roof that has slopes, which can be called a frame. It is on them that the roofing material will be laid, other elements will be attached. It is on how the truss system is assembled and installed that the final shape of the roof will also depend. But if the work on creating the roof is done independently, then how to fix the rafters? In fact, this is a rather complicated stage of work, on which strength, reliability, and even the geometric correctness of the roof will depend.

The rafter system is a roof frame with slopes, assembled from the rafter legs themselves, as well as a Mauerlat and a ridge beam. Mauerlat is a support beam, which is located along the perimeter of the upper part of the walls of the house, and the ridge beam is installed directly in the upper part of the roof at the place where two opposite rafter legs are connected at an angle.

Designing a truss system is an important task, during which you have to correctly calculate the wind and snow loads that will fall on the roof, as well as take into account other parameters. The first indicators will depend on the climatic region in which the facility under construction will be located. Further, based on the data obtained, the thickness of the walls of the house (bearing) is directly calculated, and the quality and type of material for the roof itself is selected, the angle of inclination of its slopes and other points are calculated.

Attention! Shortcomings and errors made during the design can adversely affect the quality of the roof. In some cases, they can lead to rapid collapse or destruction of the roof.

The design of the rafter system may include the rafters themselves, the ties that will be located between them, runs, additional supports - the so-called rafter legs - and other elements. The assembled truss system usually relies on the same Mauerlat or on floor beams. Mauerlat helps to evenly distribute the load around the entire perimeter of the walls. This is the main difference between this method of attachment. If you fasten the truss system to the floor beams, that is, without installing a Mauerlat, then the main load will fall on the attachment points, and not be distributed evenly over all walls.

On a note! The latter case is not an option if the walls are made of brick, which will begin to collapse over time in places experiencing maximum load. But for a wooden frame, this method is quite suitable.

Table. The dependence of the cross section of the rafter legs on their length and pitch.

Pitch, cm / Length, cm	300	350	400	450	500	550	600
60	4x15	4x17.5	5x15	5x15	5x17.5	5x20	5x20
90	5x15	5x17.5	5x20	7.5x17.5	7.5x17.5	7.5x20	7.5x20
110	7.5x12.5	7.5x15	7.5x17.5	7.5x17.5	7.5x20	7.5x20	10x20
140	7.5x15	7.5x17.5	7.5x20	7.5x20	7.5x20	10x20	10x20
175	10x15	7.5x20	7.5x20	10x20	10x20	10x25	10x25
215	10x15	10x17.5	10x20	10x20	10x25	10x25	-

In any building, the main elements on which the maximum load falls are the foundation, walls and roof. The quality of the installation of the roof largely depends on whether the truss system is installed correctly or not. If the attachment points of the truss system do not meet certain requirements, then such a roof will not last even a minimum operational period without repair work.

Requirements for the truss system

The truss system of any roof must meet such important requirements as:

• Maximum rigidity. Any frame node must withstand loads without being subjected to deformation or displacement. The triangle obtained during the arrangement of the truss system must ensure the rigidity of the structure and its maximum stability;
• Optimal weight. Depending on the roofing material, the material used for the rafters is selected. Usually a wooden beam is chosen, but metal can also be used for heavy roofs.

  Important! To prevent damage to the rafters, their rotting and the formation of fungus on wood, it is treated with an antiseptic, and metal structures with anti-corrosion compounds.

• The high quality of the materials used. The wood used as rafter legs should not have cracks and chips.

Varieties of truss systems

The roof can be equipped with one of the types of truss system, of which there are only two:

• Hanging rafters;
• Overhead rafters.

Hanging truss system

Such a system is optimal in the case of a gable roof, when the span between the walls is no more than 6 meters, but when installing additional elements, it is also applicable for wider openings. The Mauerlat serves as the lower basis for the support, while the upper part of the structure abuts against each other. This design also contains a puff - necessary to relieve the load from the walls, by reducing the expansion of the rafters. Beam puffs are installed below the rafter legs and can serve as floor beams.

Attention! The role of the puff may not necessarily be played by a wooden beam, it can also be reinforced concrete flooring, which in some houses is equipped with an upper floor.

If the puff is located above the bottom of the truss system, then it is called a crossbar. Important points in the arrangement of this type of truss system include:

• The roof overhang should not be allowed to rest on the lower part of the rafter legs, which extend beyond the wall. In such a situation, it is best to use a filly (the width of the overhang is set within one meter). With this arrangement, the rafter will be based on the Mauerlat. The cross section of the beam for the filly is chosen smaller than for the rafters;
• To give the roof additional rigidity, and prevent it from swaying and being destroyed by strong gusts of wind, a wind board is nailed on the slope, to the Mauerlat from the ridge;
• If the moisture content of the material used to equip the truss system is more than 18%, unsteadiness should be foreseen, which will cause gradual drying of the wood. That is why fastening should be done with bolts or screws, not nails.

Layered truss system

This arrangement is applicable for roofs with distances between walls from 10 meters (maximum 16 meters). The slope can be made at any angle, and inside the building there are load-bearing walls or supporting columns. From above, for the rafters, the ridge run serves as the main support, and from below this function is performed by the Mauerlat. The inner purlin is supported either by the inner wall or by the studs. Due to the presence of only vertical type of loads, there is no need to install the tightening.

With a 16-meter span, the replacement of the ridge run is carried out by two side structures, the support for which will be the racks.

Important! The absence of bends in the rafter legs is ensured by such nodes as struts and crossbars.

Particular attention to the arrangement of the roof using a layered truss system should be paid to such nuances:

Features of calculations of the gable roof truss system are shown in the video:

The main nodes of the truss systems

The main nodes of the roof truss system include:

• Rafter. They perform the function of a skeleton, supporting the internal and external elements of the roof, and also serve as the basis for laying communications;
• Mauerlat. This is a kind of roofing foundation, which is a beam on which the entire structure is installed. It performs an important function - uniform distribution of the load of the entire structure;
• Run. Designed for fastening rafter legs together and can be located both on top and on the side;
• Puff. Serves for fixing the rafters in the lower part of the structure;
• Struts and racks. Provide the most stable location of the rafter beams;
• Skate. The junction of the roof slopes;
• Filly. These are continuations of the rafter legs, which are sometimes equipped;
• Rigel. It is necessary for high-quality and reliable support of load-bearing elements;
• Sill. Cross bar necessary to distribute the load.

In addition to the listed elements, the design includes attachment points for the roof truss system. When performing them, it is necessary to follow certain rules.

Important! It is absolutely not worth performing a simple fastening of the base to the crossbar, as this can lead to the complete destruction of the truss system.

The following types of fasteners should be used:

• With emphasis on the end of the crossbar;
• Teeth point-blank;
• Teeth in a spike.

The number of teeth should be chosen depending on the slope of the slope, and additional structural reliability can be created using metal corners.

Description of the main fasteners for mounting the truss system

If during the construction of the house a rounded log or timber was used, then it is not necessary to create an armored belt. produced on the upper beam or on the log of the wall. For this purpose, connecting the Mauerlat with the rafters uses different methods of cutting (tie-ins).

What fasteners fasten metal rafters:

1. Plates.
2. Fasteners LK.
3. corners.
4. Brackets WW.
5. Self-tapping screws.
6. Varieties of the corner of the KR.
7. Wire ties.
8. Mounting tape perforated TM.
9. Bolts with nuts.
10. Brackets WW.

If brackets are used when connecting the rafters to the Mauerlat, then they are not cut into the rafters, which helps to strengthen the bearing capacity. Metal brackets are usually produced, and the metal is galvanized and has a thickness of 0.2 cm. The brackets are strengthened with nails, anchor bolts or screws.

You can use the LK fastener by creating attachment points not only for rafters with a Mauerlat, but also for various other elements that make up the roof structure. The LK fastener is fixed to the wood, as are the brackets, with the exception of the use of anchor types of bolts.

Mounting perforated tape allows you to strengthen the connecting nodes in the construction of roofing systems. It is used not only to create stronger nodes, but also to strengthen elements for additional use in order to give rigidity or strength to the system as a whole. They fix the perforated mounting tape with screws or nails, so it is used to strengthen the structure of the rafter system of any roof, the integrity of which will not be violated.

With the use of KR corners and their various modifications, the attachment points are reinforced so that they can effectively participate in the connection of the Mauerlat and rafters. Ensuring appropriate strength of the roof units is permissible when using corners, which improves the load-bearing characteristics of the roof structure.

The use of connecting elements made of metal is not associated with the insertion of corners into the roof system. This will not cause a decrease in the bearing capacity of the roofing system. You can use corners for connection using screws or nails, the protrusions of which resemble a ruff.

How are the knots connected in the ridge part?

There are three main types of fastening in the ridge parts of the roofing system:

1. Butt connection.
2. Mounting on the basis of a ridge run.
3. Ridge joint overlap.

For the purpose of fastening, in the first way, the ridge part is cut from the upper edge at an angle that is the same as the angle of the roof slope. Then it rests on the necessary rafter, which should also be cut at an angle, but on the opposite side of the roof. A special template is sometimes used to trim corners.

Nails for connecting the rafters under the ridge should be 150 mm or more in size, two of them will be needed. Each nail is driven into the rafters at the top of the rafters at the appropriate angle. The sharp end of the nail usually enters the cut of the rafter from opposite sides. Strengthening the ridge joint can be achieved by applying a metal plate to it on the side or a wooden lining so that it is enough to pull it with bolts or nails.

The connection in the second way, that is, through the ridge run, is associated with the strengthening of the rafters on the ridge beam. The run is one of the additional support beams or beams, which is a support for the rafters. It is located parallel to the ridge or Mauerlat. The method differs from the previous one in that a ridge beam is laid between the rafters, which are sawn at an angle, which is a laborious process, so this method is used less frequently.

A more common method is similar to the first, but it differs in that the fastening is overlapped, and the joint method is not used. The rafters should be in contact with the ends, and not the side surfaces. The rafters should be pulled together with a bolt or hairpin, nails. This connection is used by many masters in practice.

In general, it is possible to install rafters on a Mauerlat by creating structures for roof truss systems that are expansion or non-expansion. This determines the choice of the appropriate method of connecting the power plate and rafters, which can be similarly strengthened to the ridge.

The main shortcomings in the installation of attachment points for the truss system

The problem of choosing the method of attaching the truss system to the structure of the building is very important when creating attachment points. Often, when creating nodes, the Mauerlat serves as a support for the rafters. The fastening of the Mauerlat beam is carried out “tightly” with the help of anchor bolts to the reinforced stiffening belt.

A possible drawback is an unanchored stiffening belt, which can lead to the overturning of the Mauerlat beam and the stability of the roof truss system. There is a loosening of the roof, and the roof is sliding down. Due to erroneous placement of anchor bolts or incorrectly made holes, the fastening is no longer effective.

If the nuts are screwed onto the bolts with an overtightening, then the fastening assembly becomes fragile and is subject to rapid destruction. In this case, wire twisting is sometimes used to create an attachment point.

During the construction of the truss system, the safety of the joints should be observed.

For example, if the truss structure is combined with the floor without taking into account the bearing capacity of the attic floor, then this is the most dangerous moment that can lead to the destruction of the building.

If the tightening is changed to a precast concrete floor beam intended for bending, then the use of precast concrete beams should be effective due to their rigid fixation in the reinforced floor stiffener, which is arranged using a reinforcing cage. Its axis must go in the same direction as the acting forces.

At the same time, the presence of shortcomings in the process of creating a truss system, which is a load-bearing wooden floor structure, often arises due to a misunderstanding of the functions performed by the puff and crossbar in the entire roofing system. The puff differs from the crossbar in that it is a longitudinal, and the crossbar is a transverse beam.

The construction of the truss system is associated with the creation of a spacer system that works on the principle of divergence at the bottom of the planes, which occurs under the influence of not only their own weight, but also the load that falls on the line of intersection of the planes, which should be prevented by the transverse beam, that is, tightening.

Getting to the roof device, you should find out all the points associated with the assumption of certain errors that occur when performing work on the installation of the truss system. The device of the roof of the house is associated with possible difficulties and shortcomings that do not allow achieving the goal.

Mauerlat is one of the main elements of the roof structure. Rafters are attached to it. The operational period of the entire roof depends on the quality creation of the truss structure.

The main ways of supporting rafters

There are several technologies for supporting rafters on the Mauerlat. It is possible to carry out a rigid fixation of the structure. It does not allow any displacement of the rafter leg. To do this, use a hemmed beam, which prevents the rafters from slipping at the point of support, and metal corners that eliminate any lateral shift of the structure.

The sliding connection of the rafter leg is used in wooden houses. Moreover, the main element for its emphasis is the upper crown, and not the Mauerlat. To prevent damage to the roof, the rafter support assembly is made as free as possible. To do this, use a sliding support, which, when the frame shrinks, is displaced along the guide fixed on the leg.

The sliding support unit can also be made using a different technology. A notch is made in the rafters, which should adjoin the upper crown of the log house. To fix the beams, it is permissible to use any fasteners: staples, nails or steel plates.

Fasteners for installation work

To qualitatively connect the nodes of the rafters with the Mauerlat, you will need materials and tools such as:

• dry timber;
• boards;
• axe;
• hacksaw;
• hammer;
• roulette;
• plumb;
• level;
• screwdriver;
• drill;
• Bulgarian.

Particular attention should be paid to the presence of all fasteners. Beam consoles are fixed using galvanized steel beam brackets, which do not reduce the bearing capacity of the structure. Brackets do not need to be cut into the beams.

You also need to buy perforated mounting tape, which will strengthen the Mauerlat nodes. With its help, a strong connection of all structural elements is made. The tape also does not crash into the beams. For its reliable fixation, nails and self-tapping screws are used.

In addition to brackets and perforated tape, in order to securely support the rafters to the Mauerlat, you should purchase:

• universal bar connectors;
• fasteners for rafters;
• mortgage supports;
• wire rod;
• steel corners;
• rack mount;
• self-tapping screws;
• nails;
• staples;
• plates;
• galvanized nails;
• studs with washers and nuts;
• anchor bolts.

Creating a ridge and installing the bottom of the rafters

Installation work begins with the ridge part of the roof structure. You can install the rafters in one of three ways:

• butt;
• for the run;
• overlap.

Butt-joining the structure involves cutting the upper part of the rafter leg. This is done at an angle that is equal to the slope of the roof slope. On the skate, a pair of legs joins. To obtain the same support node for the Mauerlat elements, you should use a ready-made template.

A feature of fixing the rafters on the run is the presence of a ridge beam. This option for arranging the Mauerlat is characterized by increased reliability. But often such a rafter support system provides for the installation of additional supporting structures, which will lead to a decrease in the functionality of the attic. Naturally, this method is not suitable for small roofs.

The technology for installing overlapping rafters is in many ways similar to installing them on a ridge run. The main difference is that the connection of the upper part of the legs overlaps. This leads to a strong connection of the structure, since the studs hold two elements at once.

The connection of the lower ends of the rafters is carried out depending on the material of the walls. In the presence of wooden housing construction, the upper wall trim can act as a supporting element. If foam blocks (or aerated concrete) were used during the construction of the house, then the rafters are supported on the Mauerlat.

The device of a reinforced concrete belt is the optimal solution in the case of the use of masonry building materials. This technology does not provide for the creation of any methods of fixing the truss system. Vertically located anchor bolts act as fasteners for the timber. The main thing is that when pouring the concrete solution, the studs are located in a strictly vertical position.

Connection of rafters with beams and Mauerlat

After fixing the upper and lower parts of the rafters, they should be fixed to the beams. It is clear that you can connect the rafters to the beam with just nails. But this is not the best solution. Such a mount will not be as reliable as possible. To prevent slipping of all elements, the truss structure is fixed to the beams by using “thorn” and “tooth” connections.

In the presence of a steep roof slope (more than 35º), cutting technology is used with a single tooth. A tooth with a spike is made at the bottom of the rafter. Nests created in the beam should be at least 30% of the beam thickness deep. The device of rafter connections is carried out at a distance of 0.3-0.4 m from the extreme part of the beam. This prevents the splitting of the beams resulting from the high load from the pressure of the legs.

When arranging a roof with a slope of up to 35º, the installation of rafters is carried out by expanding the mating area of ​​\u200b\u200bthe main structural elements. Usually the rafter leg is covered with a beam. For this purpose, holes are cut in the rafter leg for two teeth:

• spike with emphasis;
• one more emphasis.

The depth of the cut when fixing the rafters to the beam is within 30% of the thickness of the beam.

Better connections can be obtained by using bolts or clamps. This technology involves the use of wire loops, with the help of which the assembly is fixed to the anchor bolts located in the wall of the building.

Relying on the Mauerlat is the most common option for fixing the lower part of the rafters. A cutout of such a size is made in the rafter leg so that it can be put on the Mauerlat without any problems. Otherwise, during the operation of the roof, a displacement of the bar may occur.

In some cases, the Mauerlat must be “equipped” with a reverse notch. It depends on the type of wood from which the beam is made. If hardwood was used for its production, then a slot is made, which, in combination with the recess of the rafters, will create a lock element. When making a beam from coniferous wood, a cutout is not required, as it will lead to a weakening of the structure.

The most acceptable option for the Mauerlat is the rigid connection of the truss system.

This technology can be done in one of two ways:

• with the help of hemmed bars and corners made of metal;
• by arranging saddles on rafters.

The first option is that a support beam is used to place the rafters on the Mauerlat. Rigid support of the rafter leg is made. Reliable fixation of the structure is carried out by metal corners. This prevents lateral movement of the structure.

The second option is more popular. For fasteners, nails are used that are directed towards each other and hammered at an angle. Two hammered nails cross. Then another nail is driven in. The third nail should be in a vertical position. The fastening unit made will be characterized by maximum rigidity if additional fastening is carried out using wire rod.

At the beginning of the attic roof layout, a rafter system is selected that acts as a supporting structure. The required type of truss system is determined based on the type of roof.

Depending on the system chosen, these can be wooden beams, used as a roof frame, holding back the composite building materials of the entire structure, or specific elements that create supports called rafters. Before starting work, the wooden components are impregnated with special compounds that protect the roof from fire and decay. The durability of the roof directly depends on the quality of this procedure.

Varieties of truss systems and the arrangement of their nodes

The truss system is divided into two main types: layered and. Since the joints in each system have different characteristics, the specific type of rafter is selected based on the properties of the preferred roof, including its architectural features.

The main factors in choosing the right type of system:

• overall functionality of the roof;
• pressure force of roofing building materials on the structure;
• the prevalence and frequency of precipitation in the area where the house is located.

The hanging type of rafters does not have supports located in the gaps. For this reason, an increased thrust occurs, which is transmitted horizontally to the walls of the building. To reduce this figure, a protracted element made of wood or metal is introduced into the support assembly, designed to combine the rafter legs. Thus, the nodes of the hanging rafters take the form of a triangle. The tightening element is located at the base of the legs, it performs the function of a crossbar (most often used in gable roof structures) and works on bending and compression. The strength of the connection with the base of the supports depends on the height of the tightening element.

The layered type of rafters is often equipped in buildings where there is a central supporting column or load-bearing wall. The rafters rest with their limbs on the sides of the building, and the central part rests on a column or other support inside the house. Such a structural assembly is designed for flexural functioning. Layered supports create less load on the component parts of the building, so their installation is not as laborious as in the case of hanging rafters. In addition, it does not require large material costs.

There are also options for arranging the roof, combining both types of rafters. In this case, each type alternates, that is, zones without load-bearing walls are equipped with hanging rafters, and areas with the necessary supports are layered.

Competent arrangement of the truss system

The main factor in the high strength of the roof in the future construction is the competent arrangement of all nodes and reference points.

In the case of rafters for a mansard roof, at least 3 strong points are assumed. This value may change if the span exceeds standard limits. For example, if the span is not more than 10 m, only one additional support will be required.

The hanger assembly is assembled based on span dimensions. On small spans, the protracted element is most often replaced by a crossbar. With large spans, the lingering elements sag, and the supports bend.

Thus, dangling nodes can have the following differences regarding the span size:

Figure 1. Diagram of the Mauerat device.

1. 9 m. Supports must be restrained with a wooden block, which is installed perpendicular to the attic floor. In the base area, it is reinforced with staples, and the protracted elements are fastened with special clamps.
2. 13 m. Fastening is carried out with the help of struts, which abut against the base with the top, and with the lower part against the perpendicular beam. The interval between the supports should not be more than 5.5 m.
3. 17 m. The base must be strengthened with special devices. A trussed structure is used for the top: the protracted elements are attached to two wooden bars, and a crossbar is mounted between them.

Knot attachment methods

Regardless of whether it is required to replace the existing rafter system or build it from scratch, it is necessary to follow a certain set of rules when attaching its nodes.

First of all, the simplest fastening of the crossbeam and the base of the support should be avoided, as this can have a devastating effect on the entire roofing system.

Figure 2. Fastening the rafter leg to the Mauerlat.

In other words, from the load created by building materials or precipitation, the ends of the supports slide off, and the rafter system is damaged. This leads to its complete collapse. To prevent this outcome, it is necessary to increase the reliability of these nodes. This is achieved using the following types of fastening:

• teeth into a tenon;
• point-blank teeth;
• emphasis on the end of the crossbar.

One or two teeth can be used depending on the slope. To increase the reliability of the connection, you can create additional fasteners using metal corners.

Roof framing attachment points

The main attachment points of the truss system are:

• beam;
• Mauerlat;
• ridge.

Beam mount

Figure 3. Scheme of the ridge connection of the truss system.

In the rafter leg, teeth are created into a spike, and a nest is cut out in the crossbar, which corresponds to the cut teeth. In this case, the nest should occupy no more than 30% of the entire thickness of the crossbar.

If lightweight materials were used in the construction of the roof, and its slope is less than 35 °, the bases of the supports are placed so that their area of ​​support is much larger than the beam. This can be achieved by using a mortise with two teeth in 2 studs, a stop (with or without a stud), and two studs in the lock.

The nodes of the system are fastened either with hardware with metal corners, or with wooden bars, overlays and spikes.

Mauerlat mount

There are 2 technologies for Mauerlat fastening of supports: rigid and sliding (Fig. 1).

In the first case, a strong connection is established between the rafter and the Mauerlat without the possibility of slipping, deflecting and popping out. This is achieved by placing special corners with a support bar. The formed knot must be fastened with a reliable wire using hardware. Nails are hammered under a certain slope from the side so that they are in the Mauerlat in a crossed state. The last nail is nailed vertically. This method is the most popular.

In the second case, fastening is carried out using a special mechanism that allows a certain element (in this case, the rafter) to move in the right direction (Fig. 2).

To create such a connection, you will need to make a tie-in on the supports, and then lay them on the Mauerlat. As in the previous case, both parts of the knot are fixed with two crossed nails and one vertical one on top. The boards are fixed to the Mauerlat with metal brackets. After that, the support base is extended beyond the wall and fastened with plates and sleds. Thus, the emphasis is on the Mauerlat, but all components of the truss system can move within acceptable limits.

This method is most often used in the construction of the roofing system of wooden buildings (logs, log cabins), which are prone to subsidence. It is worth remembering that with rigid fastening there is a possibility of damage to the walls of the building.

Ridge mount

Such a knot can be created in two ways: butt and overlap (Fig. 3).

The first method involves cutting the top of the supports at the same slope as the corner of the roof. They rest against opposite supports, which also need to be cut. The fastening is created using two nails (150 mm) hammered from above at a certain angle so that they are proportionately located inside each rafter. To increase reliability, the seams between the supports are fastened with wooden plates or metal plates.

The second method is the most popular. It is distinguished from the first method by the overlapping method. In this case, the supports are connected not by the ends, but by the side parts, after which they are fixed to the bolts.

Layered truss system - a structure used in the construction of roofs of buildings with intermediate load-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. A gable structure with one intermediate support is used for spans up to 9 m. Installing struts increases the maximum span length to 10 m. And the combination of struts with a scrum (a 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 spread 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 this type of layered rafters are performed as follows: 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 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, the same fastening options discussed above for non-thrust systems are used. 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 ridge run is still used in them, but it no longer plays a 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.

The installation of racks under the rafters 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.

The reliability of the roof structure directly depends on how correctly its entire supporting system will be mounted. And its main elements are rafters. The whole system consists of rafter legs that support and expand additional elements, such as struts, puffs, crossbars, side runs, support posts and extensions. The rafter legs are connected on the ridge beam from above, and their lower edges very often rest on, fixed on the side load-bearing walls of the building.

Since the biggest load falls on the Mauerlat, it is made from a powerful beam. Its cross section is determined by the massiveness of the entire truss system, but basically the size is from 150 × 150 to 200 × 200 mm. This load-bearing element is designed to evenly distribute the load from the entire structure of the roof and roof onto the load-bearing walls of the building. The fastening of the rafters to the Mauerlat is carried out in various ways. They are selected locally depending on the type of truss system (which can be layered or hanging), its complexity and massiveness, on the magnitude of the total loads to which the entire roof structure will be subjected.

Varieties of connecting nodes "rafters - Mauerlat"

First of all, there are sliding and rigid fastenings of rafters to the Mauerlat.

1. Sliding mounts consist of two separate elements, one of which has the ability to move relative to the other.

These mounts can be of different designs - closed and removable.

• The closed mount consists of a corner, which is attached on one side to the Mauerlat, and on the other side has a special slotted eye. A metal loop with holes for fastening to the rafters is installed in it. Thanks to the free, not fixed vertical side of the corner, the fastening allows the rafters to move slightly if necessary, without deforming the walls of the building.

• The open mount is arranged according to the same principle, and differs only in that the metal loop is not inserted into the eye, but simply the upper part of the vertical shelf of the corner is bent down after installation, thereby fixing the connection.

Video: an example of installing a movable mount on a rafter leg and Mauerlat

2. There are many more types of rigid fasteners. They are selected depending on the massiveness of the wooden structural elements and the method of installation on the Mauerlat.

These include metal corners of different sizes, LK fasteners, which securely fix the rafters, installed with the help of washed down, without damaging it with fixing screws or nails.

• LK fasteners are produced in several sizes, so they can be matched to any bar or board thickness. The thickness of the metal from which these fasteners are made is 2 mm, no matter what size they are. Depending on the size, fasteners have a different designation.

Designation	Size in mm
LK-1L	40×170
LK-2P	40×170
LK-3L	40×210
LK-4P	40×210
LK-5L	40×250
LK-6P	40×250

It should be noted that these fasteners are suitable not only for connecting rafters on the Mauerlat - they are also used to fix the "floor beam - Mauerlat" nodes.

The main advantage of this fastener is the maximum rigidity and reliability of the connection of wooden elements.

• The fastening of the rafters with a gash on the Mauerlat with the help of corners is carried out on both sides, which provides the required rigidity.

There are corners designed for attaching rafters without cuts. They have higher shelves and are screwed with a large number of self-tapping screws. They are made from metal with a thickness of 2; 2.5 or 3 mm.

Designation	Size (length height width, metal thickness) in mm	Designation	Size (length height width, metal thickness) in mm
reinforced corner	105×105×90×2	Reinforced corner KP5	140×140×65×2.5
reinforced corner	130×130×100×2	Reinforced corner KP6	105×172×90×3.0
reinforced corner	105×105×90×2	Reinforced corner KP7	145×145×90×2.5
reinforced corner	50×50×35×2	Reinforced corner KP8	145×70×90×2.5
reinforced corner	70×70×55×2	Reinforced corner KPL1	90×90×65×2
reinforced corner	90×90×40×2	Reinforced corner KPL11	90×90×65×2
Reinforced corner KP1	90×90×65×2.5	Reinforced corner KPL2	105×105×90×2
Reinforced corner KP11	90×90×65×2.5	Reinforced corner KPL21	105×105×90×2
Reinforced corner KP2	105×105×90×2.5	Reinforced corner KPL3	90×50×55×2
Reinforced corner KP21	105×105×90×2.5	Reinforced corner KPL4	70×70×55×2
Reinforced corner KP3	90×50×55×2.5	Reinforced corner KPL5	50×50×35×2
Reinforced corner KP4	70×70×55×2.5	Reinforced corner KPL6	60×60×45×2

A few additional words need to be said about some of the corners shown in the table, since their description requires clarification:

— KR 11 and КР21 are improved corners, often marked as TO P1 and KR2. These elements have an oval-shaped anchoring hole, which reduces the risk of bolt breakage in the event of structure shrinkage.

- КР5 and КР6 are corners used for fastening elements on which a large bearing load falls. corner TO P6 is also equipped with an oval hole, and it is recommended to use it when creating a rafter system on a new house, which will still shrink. These models are in demand for the installation of structures that have a lot of weight.

— Corner TO M is made of perforated steel and is used for fastening rafters with a large section. It is especially well suited for wooden buildings. This corner fixes the structural elements very securely, and when using it, it is not necessary to cut the rafters into the Mauerlat - it is enough to cut the correct angle at the first.

- The KMRP corner is used to fasten parts of the truss system at right angles, including rafters with Mauerlat. It also differs from conventional angles in that it has an elongated hole, which allows displacement during shrinkage without damaging the fixing bolt. It can be used in a design where it is impossible to cut one element to another.

KMRP corners are produced from 2 mm thick steel. Three varieties are produced:

Corner designation	Dimensions in mm
	a	b	c
KMRP1	60	60	60
KMRP2	80	80	80
KMRP3	100	100	100

• Another option for fixing the rafters on the Mauerlat is to install them between two boards, sawn at a certain angle, and additionally fixed at the bottom with metal corners or LK mounts.

Such fastening gives good rigidity and reliability. This method is well suited in cases where the rafter needs to be fixed at the right angle, lifting it above the horizontal plane of the Mauerlat, but fixing it to the vertical outer side.

• A method of attaching rafters to a Mauerlat made from a beam of not too large a section. It is carried out by reinforcing the bar with wooden linings having the required thickness.

Fastening with reinforcing lining

Pieces of boards are attached to the Mauerlat with nails or self-tapping screws, in those places where the rafter legs will be installed.

In this case, cutouts of the desired configuration and depth are made in the rafters. The rafter legs are securely fixed to the wall with the help of steel wire, which is fixed to a driven steel crutch.

• In addition to the above methods of fastening, the rafters are nailed to the Mauerlat using brackets. It should be noted that this method is quite common and has been used for a very long time. With proper fixing of these elements, the truss system will last for many years.

Fastening "the old fashioned way" - staples

Staples can have different sizes, driven in at different junction points.

• Another fastener that is used as an auxiliary is TM perforated tape. It is used to strengthen the fastening unit if necessary, its additional fixation.

In some cases, this element can be indispensable, so it also cannot be excluded when installing rafter legs on the Mauerlat.

Features of truss systems

It is selected depending on the location of the load-bearing walls of the building. Each of the systems has its own additional retaining or tightening elements.

Rafters

The system with layered rafters is characterized in that it has one or more reference points, in addition to the load-bearing walls. Due with this, with side walls remove a significant part of the load.

In the form of additional retaining elements, side racks and "grandheads" are used, which support and are fixed to the floor beams. And the beams themselves, in turn, simultaneously serve as puffs for the structure, and also lighten the load from the truss system on the load-bearing walls.

Laminated rafters are most often attached to the Mauerlat with sliding joints that can move when the walls shrink or deform, leaving the roof structure intact. This is especially important to take into account in new buildings, since any newly built building necessarily shrinks under the influence of temperature fluctuations and ground movements.

hanging rafters

Hanging rafters are called due to the fact that they do not have other supports, in addition to the two side load-bearing walls. It turns out that they seem to hang over the internal space of the building. In this case, the entire load from the roof frame structure falls on the Mauerlat.

For fastening hanging rafters to the Mauerlat, rigid fasteners are used with no degree of freedom of movement, since the frame structure has only two points of support.

The hanging rafter system is spacer, so it puts a lot of pressure on the walls.

To remove part of the load from the walls of the building, additional elements such as struts, “headstocks” and puffs-crossbars are used, which pull the system to the ridge bar and evenly distribute the load on all walls. Crossbars are installed parallel to the floor beams and pull the rafters together. Without these additional details, the design may become unreliable.

Calculation of the installation of rafters

In order for the rafter system to be reliable and durable, in addition to the optimal connection method, you need to choose the correct step for the location of the rafter legs. This parameter is selected depending on the size of the rafters (and the length between the support points), as well as on the roof structure.

In this table, you can get information about the necessary parameters for the installation of a reliable truss system.

Step of installation of rafter legs in mm	Length of rafter legs in mm
	3000	3500	4000	4500	5000	5500	6000
600	40×150	40×175	50×150	50×150	50×175	50×200	50×200
900	50×150	50×175	50×200	75×175	75×175	75×200	75×200
1100	75×125	75×150	75×175	75×175	75×200	75×200	100×200
1400	75×150	75×175	75×200	75×200	75×200	100×200	100×200
1750	100×150	75×200	75×200	100×200	100×200	100×250	100×250
2150	100×150	100×175	100×200	100×200	100×250	100×250	-

Use, in the article on our portal.

Prices for various types of fasteners for rafters

Fasteners for rafters

A few rules for attaching rafters to the Mauerlat

In order for the fasteners to be reliable, it is necessary to follow a number of rules that are provided for this process:

• If metal connecting parts are used for fastening, then they must be fixed to wooden connecting elements with the utmost care - high-quality self-tapping screws of the required length.
• If the rafters will fit into the cuts in the Mauerlat, then the dimensions must be precisely verified. This will ensure a tight, reliable installation of the rafters in the prepared gash, which should have a depth of ⅓ Mauerlat. However, it should be remembered that such a rule will be valid only if the Mauerlat is made of a powerful bar with a cross-sectional size of at least 150 × 150 mm.

• In order not to weaken the Mauerlat, most often the cuts are made in the rafter leg itself at the desired angle, and in addition the knot is then fixed with corners. Washed down should not in this case exceed ¼ of the thickness of the rafters. This mount is rigid and can be used in a hanging rafter system.

• When using bolts to fasten rafters with slopes, puffs and other wooden elements, it is imperative to install a washer or a metal plate on the bolt in order to avoid flooding the nut into the wood and, accordingly, weakening the structure.
• Fastening the rafters to the Mauerlat only with nails or self-tapping screws is considered unreliable. therefore, it is imperative to use corners or other metal fasteners of various configurations.

• When installing rafters on wooden walls, whether it is a hanging or layered system, it is recommended to attach them to the Mauerlat with a sliding fastener, especially if the roofing material is heavy enough.

Video: a few examples of attaching rafters to the Mauerlat

The roof structure will turn out to be durable and will last a long time, without being deformed by a variety of external influences, if the calculations of all elements are made correctly, correctly select and properly mount all fasteners.