Fastening points of the puff to the rafter leg. Types and diagrams of truss systems: an overview and recommendations for installing a roof truss system

Rafters are the most essential part of the roofing skeleton. The legs of the rafters transmit thrust to the Mauerlat and the load-bearing walls of the house. What determines the quality of the entire rafter system and the roof as a whole? Experts remind that the reliability of any roof structure will depend, first of all, on the quality of fastening the rafters to the Mauerlat. What principles and features of this process every novice builder should know and how to fix the rafters to the Mauerlat with your own hands, you will learn right now.

Fastening rafters to the Mauerlat: a little "materiel"

To begin with, we propose to consider an illustration that shows two types of truss systems:

The place of attachment of the rafter leg with the base is called the support node. There are many such nodes in the system, but we will touch in detail on the lower fasteners of the frame with rafters. Mauerlat and rafter legs are almost always made of wood, less often of metal. It is more profitable and convenient to use wood, as this material is light in weight, easy to install and durable with proper installation and operation.

Types of support nodes according to the level of rigidity

Support nodes - places where the rafters are attached to the roof elements:

In the case of iron joints, the nodes are fixed, rigid (welds or bolts). Wood is a softer and more dynamic material that can swell, dry out and deform. In this regard, experts recommend performing support nodes, adjusted for possible changes in the shape of the wood. Such nodes can have different degrees of mobility:

• Zero Mobility Node- rigid fastening with corners on both sides, in which the fastening of the rafters to the Mauerlat remains motionless.
• Connection of the first degree of mobility- the beam can rotate in a circle.
• Connection of the second degree of mobility- circular rotation with offset, the installation of special sliders or sleds is provided.
• Movable connection of the third degree– the possibility of horizontal, vertical and circular movement.

For any node, whether it is movable or not, at least two types of fixation should be used. For example, notched planks are additionally fixed from the inside with a support beam, while dynamic connections are strengthened with bolts and special steel angles.

About the types of fasteners for rafters to the base

Let's talk about modern fasteners. For the strength and durability of the support units, a variety of metal fasteners are used: beam holders, equilateral, fastening, anchor, reinforced corners, plates, supports, profiles, connectors, anchors, etc. All these spare parts are made of high-quality metal. For dynamic nodes (types 1, 2 and 3), sliders, corners and perforated plates are used. For rigid fastening, stationary connectors, anchors and corners are used.

Such fasteners for the truss system are most often used:

For self-assembly, more than others, perforated mounts are suitable, as they have many holes for self-tapping screws and bolts.

Rigid or movable connections: what to choose

So, we noted that the support nodes connecting the Mauerlat with the boards can be of varying degrees of mobility: from "0" to "3". Zero degree - these are rigid fasteners that exclude any changes in the position of the beams.

Rigid connections: when you need them

Mauerlat is installed when it is necessary to transfer the spacer load from the rafters to the load-bearing walls. This is done mainly in houses made of bricks, panels and blocks. In this case, they try to exclude deformation and shrinkage of the roof in order to prevent changes in the load on the supporting walls. This is where the need for a fixed connection of the truss system with the Mauerlat appears.

Fixed knots fixed with gash

Many experts recommend making appropriate cuts at the point where the rafters are attached to the floor beams for greater strength and immobility of the connecting nodes. These cuts should fit snugly with the Mauerlat. Additionally, such nodes are strengthened with bolts, anchors and metal plates:

Or long screws:

And one more important point: the size of the washed down bar should not exceed 1/3 of its section. Otherwise, the rafter system may lose its bearing capacity:

Rigid knots without notching rafters

The fastening method using a hemmed bar is used in layered truss systems. The rafter is cut according to the template and beveled (to give the roof the desired slope) at the point of contact with the Mauerlat. From the inside, such rafters are reinforced with supporting bars and reinforced with corners on both sides to the base frame:

Another option for a non-butt joint is a rigid fastening of the rafters, reinforced with overlay bars on both sides. Two boards at least a meter long border each rafter leg. One end of such supports is cut at an angle that corresponds to the slope of the roof slope (including rafters). The boards are fastened with a cut to the Mauerlat using long bolts and reinforced steel corners. The bars are attached to pre-marked places, first one at a time. Then, close to the overlays on one side, the rafters themselves are mounted, which are immediately reinforced with the same overlay on the other side. There is an option to install two overlay bars at once, and after that, rafters, but this method is used less often, since it requires more accurate calculations.

When do you need to make mobile connections?

So we come to dynamic reference nodes - connections that can change their position. What is it for? We recall the physical properties of materials - many of them shrink or swell. First of all, this applies to buildings made of pure wood - timber, log house, etc. Natural wood necessarily shrinks, due to which your roof can not only be deformed, but also completely destroyed. To avoid such fatal consequences, the masters recommend performing sliding fastenings of the rafter legs with a Mauerlat (or the upper crown of the log house).

A prerequisite for the installation of sliding nodes is the support of the truss frame on a strong ridge beam. Since the supporting lower nodes are dynamic, the maximum rigidity must be achieved at the roof ridge. The upper edges of the rafters are sawn for a tight connection between themselves and the ridge beam, connected and reinforced with crossbars, metal tapes, plates and corners. It is better to connect a truss element already fixed in the ridge with the crown of the log house.

What is a sliding mount?

The movable connection is carried out by establishing sliding fasteners, called "sleds" or "sliders". Such a node provides for a certain freedom of the rafter legs, which helps prevent the deformation of the roofing system after the natural shrinkage of wooden structures:

Here are the types of sliding supports:

Do I wash down on the rafters if the house is made of timber: an alternative expert opinion

I propose to still file down, but not the rafters, but the upper crown. Firstly, in this case, the risk of curvature of the rafters is reduced, secondly, the “cold bridge” decreases, thirdly, the tangential pressure on the Mauerlat (the upper beam of the log house) decreases, and fourthly, roof insulation is simplified in the future. The disadvantage of this method is that when the upper crown of the beam is cut down, the height of the ridge decreases, therefore, if in the future it is planned to raise the height of the ceiling, one more crown should be provided. But! Such schemes are only suitable for wooden houses, since in brick and concrete buildings the mauerlat must be intact in order to maintain load-bearing qualities.

How to fix the rafters to the beams?

In simple houses, mostly frame houses, the Mauerlat can be abolished. In this case, the rafters are attached to the floor beams. The most reliable option for assembling such a system is the preparation of roof trusses. Each truss consists of two rafter legs, a connecting crossbar and a lower puff. For strength, the trusses are reinforced with central beams and struts:

Floor beams are laid in such a direction that the roof trusses cross them perpendicularly in different planes. The puff performs the main load-bearing functions, is attached to the floor beams with anchors, through bolts, studs and is reinforced with plates and metal corners.

It is possible to attach the rafter legs directly to the beam, which will additionally perform the functions of tightening. To create high-quality support nodes in such a system, two methods of fastening are recommended:

1. The connection of the rafters with the beam with a double tooth - the cuts are made on the beam and the bevel of the rafter leg (two butt notches on each).
2. Bolt and clamp fastening. Through fastening may be provided, but if the boards have a large cross section, cuts are made and the parts are connected with long bolts.

Fastening the rafter to the Mauerlat: a step-by-step description

For example, we will describe the process of rigidly attaching rafter joints to the Mauerlat on a simple gable roof.

I. Preparation of the Mauerlat and rafters for work

At this stage, it is necessary to cut out the rafter legs of a given length and mark their step on the basis. The optimal step length of the rafter legs is 60-200 cm. You should also accurately determine the angle of inclination of the rafters.

Mauerlat installation master class:

II. Creating a gash

We carry out washed down on each rafter leg for a tight connection with the base. To enhance strength, you can provide an additional notch on the frame or rafter and install a thrust beam under each rafter leg.

III. Installation of rafters on the Mauerlat

It is necessary to impose rafters carefully so as not to damage other elements of the building (windows, walls, etc.). We start the boards with a cut on the beams and rest them on the ridge beam. First, we install the extreme rafter legs, between which you need to stretch the thread to align all the other rafters.

IV. Fastening each rafter to the Mauerlat

Now that all the trusses are in place, you need to firmly fix the support nodes. We use several of the mounts proposed above for this:

• Nails+ steel corners on the left and right side of the joints between the board and the base.
• Through bolts or studs+ support bar for cutting the rafters.
• Anchors or bolts+ corners or steel plates, etc.

Two overhead boards on both sides of the rafter leg, installed on pre-marked places of the Mauerlat, will help to strengthen the fastening. You can also use wire fastening as a reinforcement of the strength of the connections. To do this, you need to prepare a steel wire twist of 2-3 wires. Its length should be enough to wrap around the rafter leg at the junction with the Mauerlat and fix the ends of the twist on a metal crutch. As a crutch, you can take a long steel bolt, which is mounted into the wall 30-40 cm below the Mauerlat, strictly under the support node.

We will also consider one of the old-fashioned ways - fastening with brackets:

And finally, we invite you to watch the video:

What is the secret of the quality of the truss system: the three main rules of the master

• High-quality lumber is half the battle on the way to successful construction. Mauerlat and rafters should not have cracks, wormholes and knots.
• The accuracy of measurements, cuts and the uniformity of the position of the fasteners is no less important. If all rafter legs are of the same length and section, then it is better to prepare a template for making cuts and notches.
• Washed down on the Mauerlat - loss of the supporting functions of the base by 50% or more. The percentage of strength reduction depends on the depth of the notches.

When the rafter system is ready, it is the turn of the installation of the crate, insulation and flooring of the roofing material. But this is another interesting topic, which we will definitely cover in the next article. In the meantime, we wish you good materials, easy work and good helpers!

• The main obstacle for novice developers, even if we are talking about a simple roof, may be a lack of knowledge about what the nodes of the truss system are. How to fulfill them in order to get a strong, reliable and stable roof?

  The beginning of the design of a pitched roof is the choice of a truss system, which should perform the functions of a supporting structure. The type of structures is determined based on the type of roof.

  In one case, rafters are beams or boards that act as the "skeleton" of the roof, which holds the weight of the insulation and roofing material. In another, they can be composite, and are assembled from separate elements, known as rafter legs.

  The board and bars must undergo a special impregnation - fire-fighting and antiseptic. The better it is done, the longer it will last..

  Composite frames are divided into two types: layered and hanging. The choice of a particular system, in addition to the architectural preferences of the owners, depends on some parameters of the roof:

  • its functionality
  • the number of loads tested, including those related to the climatic features of the region.

  Hanging rafters do not have intermediate supports, therefore they create a significant bursting force, which is transmitted to the walls in the horizontal plane. To reduce it, a puff (wooden or metal) is used, which, connecting the legs, completes the triangular structure. The legs in it work on bending and compression. The puff can be located at the base, and in this case serves as a floor beam (this option is more common when installing attics), or higher.

  The higher the location of the puff, the more powerful it is, on the one hand, and more securely connected to the rafters, on the other.

  Layered views are arranged in houses with an average load-bearing wall or columnar intermediate supports. They rest with their ends on the outer walls, the middle part - on the supports or the inner wall. As a result, the elements work on the principle of beams - only for bending. The weight of the truss system in the case of layered ones with the same width of the house is less: it requires less lumber, and therefore, cash costs.

  If a single roof structure is installed over several spans, hanging and layered trusses can alternate: for sections without intermediate supports - hanging ones are installed, where there are - layered ones.

  How to properly install the truss system

  One of the conditions for the reliability of the future structure is the correct arrangement of the attachment points of the truss system.

  

  Pitched roof rafters usually have at least three points of support. Their number may vary depending on the size of the span. With a span width of up to 10 m, one additional support is required; for large values, their number increases.
  The design of the hanging also depends on the width of the span. If it is small, the puff is usually replaced with a crossbar. With an increase in span, the puff begins to sag, and the legs begin to sag.

  

  With a span
  up to 9 m, hanging rafters are supported by a headstock - a special vertical bar. The ends of the legs are attached to its upper end with the help of staples or clamps, the headstock with a puff - with a clamp.
  up to 13 m - strengthening is carried out with the help of struts. With their upper ends they rest on the leg, and its length between the supports should not be more than 5.5 m, and on the lower ends - in the headstock.
  up to 17 m, the legs in the lower part are reinforced with help, for the upper part they use a trussed system: the puff is attached to two grandmothers and a crossbar is installed between them.

  How to properly fix the rafters

  Whether the truss system is being replaced or it is being installed in a new house, certain rules should be followed.

  A simple fastening of the leg and the beam can even be destructive - when pressure is applied to the rafter, its end begins to slide along the beam, which leads to the destruction of the roof .

  To avoid slipping and ensure reliability, the following types of connections are used:

  • spiked tooth,
  • pointed tooth,
  • stop at the end of the beam.

  It is possible to use two teeth - it depends on the angle of inclination. For fastening, in addition to this connection, metal corners are also used.

  The main nodes of the roof frame

  Attachment to the beam

  

  • A tooth with a spike is made in the heel of the rafter, and an emphasis is cut out in the beam with a corresponding socket for the spike.
  • The nest depth is about 25–30% of the beam thickness.
  • The cut is performed at a distance of 0.25–0.4 m, starting from the edge of the beam, which hangs down.
  • A single tooth is performed, as a rule, together with a spike, which does not allow shifting to the side. Therefore, such a connection is called a "tooth with a spike and an emphasis."

  

  In the case of a hollow roof, the angle of inclination of which is less than 35 °, the rafter legs are installed so that the bearing area per beam increases. To do this, use a cut with two teeth:

  • in two spikes;
  • emphasis with and without a spike;
  • two spikes to the castle.

  All connections in the structure are made using fasteners:

  • metal - screws, nails, bolts with washers, various corners;
  • wooden - bars, triangular overlays (kerchiefs), spikes.

  To Mauerlat:

  There are two technologies according to which .

  Rigid - in this option between these structural elements, the possibility of any influences (shifts, turns, bends, torsion) is completely excluded. To achieve a similar result:

  • when fastening, corners with a hemmed support bar are used;
  • a saddle (washed down) on the leg is performed, the resulting connection is additionally fixed with wire, nails and staples. The nails are nailed from the sides, towards each other at an angle (they cross inside the Mauerlat), then the third nail is hammered in a vertical position. This is the more common mounting method.

  Sliding (articulated)- such a pairing, which has two levels of freedom, is achieved through the use of special fasteners, which allows one of the mating elements to move freely (within specified limits).

  The following options for sliding fastening of rafters and Mauerlat can be distinguished:

  • washed down, after which the rafters are washed down on the Mauerlat:
  • the elements are connected obliquely with two nails towards each other;
  • they are connected with one nail, which is nailed vertically from top to bottom into the body of the base beam through the leg;
  • an alternative to nails can be steel plates with holes for nails;
  • fasten the boards to the Mauerlat with a bracket;
  • release the rafter leg behind the wall and perform a single fixation with fixing plates;
  • use special steel fasteners - "sleds".

  In all these cases, the foot rests on the Mauerlat, but when moving, the elements of the system have the ability to move relative to each other.

  Such a pairing is especially important for wooden houses erected from timber or logs, which shrink over time. Using a hard mate can cause damage to the integrity of the walls.

  The truss system can be "floating" or rigidly fixed. The floating one is mounted on special brackets that allow the wooden frame to “sit down” simultaneously with the shrinkage of the gables and prevent them from hanging over the ridge log.

  Ridge knot

  There are three ways to connect in the ridge part.

  butt
  The upper edge of the rafters is cut at the same angle as the angle of the roof, rest against the desired rafter located on the opposite side, it should be cut in the same way. Corner trimming is usually done according to a template. For fixing under the ridge, two nails (150″) or more are used. One nail at an angle is hammered into the upper plane of the first and second rafters, while they must enter the cut of the opposite. The ridge joint is additionally strengthened by placing a wooden lining or a metal plate on the side of it, which is attracted with bolts or nails.

When designing any residential building, architects pay special attention to the roof, as it performs not one, but several functions at once, depending on its design features. It must be said that not all future homeowners are satisfied with the usual gable roof, although it can be called the most reliable, since it has only two pitched planes and one joint between them. Many are attracted to more complex designs that add a special appeal and originality to the structure. Other, more practical homeowners prefer attic structures that can simultaneously serve as a roof and a second floor.

The basis of any roof is an individual truss system, which has its own design features. Making the choice of the desired roof frame will be much easier if you figure out in advance which ones types and schemes of truss systems used in building practice. After receiving such information, it will become more clear how complex such structures are in installation. This is especially important to know if the roof frame is supposed to be built independently.

The main functional tasks of truss systems

When arranging pitched roof structures, the truss system is a frame for covering and for holding materials of the "roofing pie". With proper installation of the frame structure, the necessary conditions will be created for the correct and non-insulated types of roofs that protect the walls and the interior of the house from various atmospheric influences.

The roof structure is also always the final architectural element of the exterior design of the building, supporting its stylistic direction with its appearance. Nevertheless, the design features of the truss systems must first of all meet the requirements of strength and reliability that the roof must meet, and only then - aesthetic criteria.

The frame of the truss system forms the configuration and angle of inclination of the roof. These parameters largely depend on the natural factors characteristic of a particular region, as well as on the desire and capabilities of the homeowner:

• The amount of precipitation in different periods of the year.
• Direction and average wind speed in the area where the building will be erected.
• Plans for the use of the space under the roof - arranging residential or non-residential premises in it, or using it only as an air gap for thermal insulation of the premises below.
• Variety of planned roofing material.
• Financial capacity of the homeowner.

Atmospheric precipitation and the strength of wind currents give a very sensitive load on the structure of the roof. For example, in regions with heavy snowfalls, you should not choose a truss system with a small angle of inclination of the slopes, as snow masses will linger on their surface, which can lead to deformation of the frame or roofing or leaks.

If the area where the construction will be carried out is famous for its winds, then it is better to choose a structure with a slight slope of the slope so that the sharp gusts that occur do not rip off individual elements of the roof and roof.

The main elements of the roof structure

Details and nodes of truss systems

Depending on the chosen type of truss system, the structural elements used can vary significantly, however, there are details that are present in both simple and complex roof systems.

The main elements of the pitched roof truss system include:

• Rafter legs forming roof slopes.
• - a wooden bar fixed on the walls of the house and serving to fix the lower part of the rafter legs on it.

• The ridge is the junction of the frames of two slopes. It is usually the highest horizontal roof line and serves as a support on which the rafters are fixed. The ridge can be formed by rafters fastened together at a certain angle or fixed on a ridge board (run).
• Lathing - these are slats or beams mounted on rafters with a certain pitch and serving as the basis for the flooring of the selected roofing material.
• Retaining elements, where you can take beds, girders, racks, struts, ties and other parts, serve to increase the rigidity of the rafter legs, support the ridge, link individual parts into a common structure.

In addition to the structural details mentioned above, other elements can be included in it, the functions of which are aimed at strengthening the system and optimal distribution of roof loads on the walls of the building.

The truss system is divided into several categories depending on the different features of its design.

attic space

Before proceeding to the consideration of different types of roofs, it is worthwhile to figure out what an attic space can be, since many owners successfully use it as utility and full-fledged living quarters.

The design of pitched roofs can be divided into non-attic and attic. The first option is called just that because the space under the roof has a small height and is used only as an air layer that insulates the building from above. Such systems usually include or have several slopes, but located at a very slight angle.

The attic structure, which has a sufficiently large ridge height, can be used in different ways, be insulated and not insulated. These options include attic or gable option. If a roof with a high ridge is chosen, then it is imperative to take into account wind loads in the region where the house is built.

Slope slope

To determine the optimal slope of the roof slopes of the future residential building, first of all, you need to look at the already built low-rise neighboring houses. If they have been standing for more than one year and steadfastly withstand wind loads, then their design can be safely taken as a basis. In the same case, when the owners set the goal of creating an exclusive original project, unlike the buildings standing nearby, it is necessary to familiarize yourself with the design and operational features of various truss systems and make appropriate calculations.

It should be borne in mind that the change in the tangent and normal values ​​​​of the wind force depends on how large the slope of the roof slopes is - the steeper the angle of inclination, the greater the importance of the normal forces and the smaller the tangents. If the roof is sloping, then the structure is more affected by the tangential wind load, since the lifting force increases on the leeward side and decreases on the windward side.

Winter snow load should also be taken into account when designing the roof. Usually this factor is considered in combination with the wind load, since the snow load on the windward side will be much lower than on the leeward slope. In addition, there are places on the slopes where snow will definitely collect, giving a big load on this area, so it should be strengthened with additional rafters.

Roof slopes can vary from 10 to 60 degrees and must be selected not only with regard to the consolidated external load, but also depending on the roofing that is planned to be used. This factor is taken into account because roofing materials differ in their mass, their fixing requires a different number of elements of the truss system, which means that the load on the walls of the house will also vary, and how large it will be, also depends on the angle of the roof slope. Equally important are the features of each coating in terms of resistance to moisture penetration - in any case, many roofing materials need one or another slope to ensure the free flow of storm water or melting snow. In addition, when choosing a roof slope, you need to think in advance how the process of cleaning and repair work on the roof will be carried out.

When planning a particular angle of the roof slopes, you need to know that the fewer joints between the sheets of the coating, and the tighter they are, the less you can make the slope of the slope, of course, if it is not supposed to arrange a residential or utility room in the attic space.

If a material consisting of small elements, for example, ceramic tiles, is used to cover the roof, then the slope of the slopes must be made steep enough so that water never lingers on the surface.

Given the weight of the roofing material, you need to know - the heavier the coating, the greater the angle of the slopes should be, since in this case the load will be correctly distributed to the rafter system and load-bearing walls.

The following materials can be used to cover the roof: either a profile sheet, galvanized steel, corrugated asbestos-concrete and bitumen-fiber sheets, cement and ceramic tiles, roofing felt, soft roofing and other roofing materials. The illustration below shows the allowable slope angles for various types of roofing.

Basic structures of truss systems

First of all, it is worth considering the basic types of truss systems regarding the location of the walls of the house, which are used in all roof structures. The basic options are divided into layered, hanging, and also combined, that is, including elements of both the first and second types of systems in their design.

fasteners for rafters

Layered system

In buildings where internal load-bearing walls are provided, a layered truss system is often installed. It is much easier to install than a hanging one, since the internal load-bearing walls provide reliable support for its elements, and in addition, fewer materials will be required for this design.

For rafters in this system, the defining reference point is the ridge board, on which they are fixed. The non-thrust type of the layered system can be equipped in three versions:

• In the first version, the upper side of the rafters is fixed on a ridge support, called a sliding one, and their lower side is fixed by cutting to the Mauerlat. Additionally, the rafters in the lower part are fixed to the wall with wire or staples.

• In the second case, the rafters in the upper part are cut at a certain angle and interconnected using special metal plates.

The lower edge of the rafter legs is attached to the Mauerlat with movable fasteners.

• In the third version, the rafters are rigidly fastened in the upper part with bars or processed boards located horizontally, parallel to each other on both sides of the rafters connected at an angle, and a ridge run is pinched between them.

In the lower part, sliding fasteners are used to fix the rafters, just as in the previous case.

It is necessary to explain why sliding fasteners are often used to fix the rafters on the Mauerlat. The fact is that they are able to save the load-bearing walls from excessive stress, since the rafters are not rigidly fixed, and when the structure shrinks, they have the ability to move without deforming the overall structure of the roofing system.

This type of fastening is used only in layered systems, which also distinguishes them from the hanging version.

However, in some cases, a spacer system is used for layered rafters, in which the lower end of the rafters is rigidly fixed to the Mauerlat, and in order to remove the load from the walls, puffs and struts are built into the structure. This option is called complex, as it includes elements of a layered and hanging system.

Specify the requested values ​​and click the button "Calculate the excess Lbc"

Base length (horizontal projection of the slope)

Planned roof slope angle α (degrees)

Rafter Length Calculator

The calculation is based on the values ​​of the horizontal projection (Lsd) and the height of the rafter triangle, previously determined (Lbc).

If desired, you can include in the calculation the width of the cornice overhang, if it is created by protruding rafters.

Enter the requested values ​​and click the "Calculate rafter length" button

Excess value Lbc (meters)

The length of the horizontal projection of the rafter Lsd (meters)

Calculation conditions:

Required eaves width (meters)

Number of overhangs:

Gable truss system

Gable truss systems are the most popular for one-story private houses. They look neat, fit well into any style of construction, are reliable and can be used, depending on the angle of their slope, to equip the attic for living rooms, utility rooms, or simply to create an air gap that retains heat in the building.

wood screws

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 tightening may not necessarily be performed by a wooden beam, it can also be a ceiling made of reinforced concrete structures, 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 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.

The main attachment points of the truss structure include:

• Beam knot;
• Mauerlat knot;
• Skate knot.

beam knot

With such a node for connecting elements, an insertion of teeth into a spike is made into the rafter, and a recess corresponding to the teeth is made in the transverse section of the crossbar. Such a recess or nest should not exceed 30% of the timber thickness.

Fastening is carried out with special hardware with metal corners, or wooden beams, spikes and overlays.

Attention! If the roof is made of materials with low weight, and the slope of its slope does not exceed 35º, then the bases of the supports should be placed so that they rest against an area larger than the beam itself.

Mauerlat knot

Such fastening can be performed both by rigid technology and by sliding technology. Rigid technology involves the installation of a strong connection between the Mauerlat and the rafters, preventing the possibility of slipping, deflecting or popping out. For this, special support corners with bars are used. The resulting knot is fastened with wire using hardware. At the same time, nails should be hammered obliquely so that they enter the wood crosswise. The last nail must be driven in vertically.

In the case of a sliding fastening, alignment is performed using a special mechanism that allows you to move the rafter leg in the required direction. To do this, a tie-in is made on the supports, on which the Mauerlat is then laid. The structure is fixed, as in the previous case, with crossed nails. This method of arranging the connection nodes allows all nodes of the truss structure to move within certain limits.

Attention! Rigid fastening with inexperience of builders can lead to damage to the walls of the building.

ridge knot

In this case, the fastening can also be made in two types - butt and overlap. With a butt joint, the top of the supports is cut with a bevel, as is the angle of the roof. They rest on the same undercut opposite supports. Fastening is carried out using nails, in the amount of two pieces. They are hammered from above at a certain angle. The seams that form between the supports are connected with metal plates or plates. In the second case, fastening is carried out by overlapping, not by end parts, but by lateral sections and fixed with bolts.

Conclusion

When performing work on the installation of the roof, the arrangement of the truss system should be given careful attention, avoiding disruption of technological processes. This will provide the structure with strength, durability and reliability.

December 12, 2017
Specialization: facade finishing, interior finishing, construction of dachas, garages. The experience of an amateur gardener and horticulturist. He also has experience repairing cars and motorcycles. Hobbies: playing the guitar and much more, for which there is not enough time :)

Any roof is subjected to various loads every day, as it is affected by wind, precipitation, and it also holds the roofing. In order for the roof to cope with all these loads for many decades, it must be properly designed. Therefore, for everyone who wants to do construction on their own, I recommend to figure out what parts and nodes of the truss system exist, and what function they perform.

Frame elements

All details of truss systems can be conditionally divided into two types:

• Basic. These parts form the roof frame, called the truss system. Not a single roof can do without them;
• Additional. This group includes elements that may be present in some types of roofs, while others do without them. The task of additional elements is to increase the rigidity and strength of the frame.

Main knots

So, the following elements belong to the main nodes and details of the truss system:

• Mauerlat. This, one might say, is the basis of all roofing systems, since rafter legs rest on the Mauerlat. Its design is extremely simple, in fact, it is an ordinary bar (a log in log houses), laid along the perimeter of the walls. Its task is to evenly distribute the load from the roof to the walls of the building.

It must be said that at a gable roof, the Mauerlat can be located not along the perimeter, but only on the side walls, since pediments are located on the end walls, which are a continuation of the wall;

• Rafter legs (hereinafter CH), or simply rafters. These parts are the supporting element that forms the slope and its angle of inclination. They take on the wind and snow load, as well as the weight of the roofing material, and transfer it to the walls through the Mauerlat and other elements.

Rafters are lateral (main), diagonal (installed at the junction of hip roof slopes) and shortened (diagonal rafters rely on Mauerlat);

• Rafter farms. They are formed by paired (reciprocal) rafter legs. It must be said that truss trusses are present on all pitched roofs except for shed roofs, since they do not have reciprocal rafters;
• Skate knot. It is the top of the roof truss, i.e. formed by the junction of two CHs. The ridge knot, like the trusses themselves, is absent only from shed roofs.

That's all the main knots of wooden roof structures that form them.

Additional

Additional details include:

• Run. This is a horizontal beam that connects all CHs within one slope;
• Skate run. It is the same horizontal beam as a regular run, but which runs in a ridge knot, i.e. connects two legs of each truss at the same time.

I must say that the ridge run can be installed in several ways - above the junction of the rafters, in the center of the junction, i.e. legs rest on the run, or under the rafters;

• Puff (bolt, fight). It is a beam that connects two reciprocal legs, preventing them from moving apart. We can say that the tightening removes the spacer load from the bearing walls;

• Supports. Can support rafters, all types of runs or puffs. Supports transfer the load to the internal walls of the building, columns or ceilings;
• Struts (rafter legs). They are inclined supports, which have the same function as the vertical racks. The only thing is that they support only the legs, i.e. are one of the elements of wooden trusses. Rafter legs transfer the load to the load-bearing elements of the building, or to the ceiling;
• Filly. These elements form the overhang of the slope in the event that the CHs do not go beyond the walls. In fact, they lengthen CH, i.e. are their continuation.

That's all the elements that make up the frames of pitched roofs.

A few words about the types of systems

So, we figured out the nodes, now let's look at the main types of truss structures. There are several of them:

• Shed. As I said, these structures do not have trusses. The angle of the slope is formed due to the different heights of the walls on which the CHs are laid, or due to the run, which is laid on racks installed on one of the walls;

• Gablesloping. Rafters are called rafters, which are supported by racks or struts that transfer the load to the internal load-bearing elements of the building. The frame of such structures is formed only by trusses, i.e. they do not have diagonal legs.

• gable hanging. Hanging rafters differ from layered rafters in that they transfer the entire load from the roof only to the outer walls;

• Hip. Unlike gables, at the ends instead of vertical gables they have inclined hips, i.e. end slopes. As I said, the hips form diagonal and short legs;

• broken lines. They are a gable structure, each CH of which is divided into two parts and is located at a different angle. Skating, i.e. the upper legs form a gentle slope, and the lower legs are steep. This design allows you to increase the attic space, as a result of which it can be used as an additional floor.

Typical broken (mansard) systems have racks on which the upper and lower CHs rest. The reciprocal racks are interconnected by puffs (attic floor beams).

There are also semi-mansard structures, which, in fact, are ordinary hanging gable roof systems. The only thing is that their fastening with a Mauerlat is usually made sliding (movable), which allows you to increase the CH deflection, and thereby reduce the spacer load on the walls.

Despite the fact that the designs of all the above systems are different, they consist of the same parts that we have already familiarized ourselves with.

One last thing about fasteners

Finally, I propose to consider how the connections of the main nodes are made, such as:

• Rafter / Mauerlat;
• Skate knot.

The rest of the details do not deserve special attention, since their docking most often occurs by washing down the interface (to increase the area of ​​\u200b\u200bfitting the parts) and lining the steel plastic / corners, which are fixed with screws. Sometimes fasteners are not even used, i.e. parts are fastened to each other with screws without any overlays.

Connection of rafters and Mauerlat

The leg and Mauerlat mount can be made in several ways:

• With grooves. In this case, grooves are cut out under the Mauerlat, into which CH is inserted. Then it is additionally attached to the Mauerlat on both sides with a steel corner;

• Tooth and thorn. This method is usually used to attach the CH to the puff. Its principle is based on the fact that a spike is selected at the end of the sawed CH, and a groove is selected in the puff. In addition, the leg itself rests against the so-called tooth, i.e. protrusion in the puff, which takes on the expansion load.

It must be said that in recent times, fasteners such as a tooth with a spike are rarely used, since it is much easier to use special fasteners, the same corners and plates;

• By washing down. In this case, the CH is sawn so that a right angle is formed at the junction with the Mauerlat, as a result of which the rafter not only rests on the beam, but also rests against its side surface, thus transferring the spacer load. I must say that instead of washing down, you can fix the bar, as shown in the diagram below.

Connection of rafters and ridge run

The connection of CH and run can be done as follows:

• With a groove. In CH, two reciprocal cuts are made, as a result of which, after the junction of the rafters, a groove is formed for the ridge run;
• Hard pinching. The principle is based on the fact that puffs are installed under the run and above it;

• Got drunk on the way. This is the simplest and most common method, the principle of which is based on sawing CH for maximum fit to the beam. In this case, fixation is carried out with a steel corner.

Here, perhaps, are all the main nuances of assembling truss systems.

Conclusion

We have found out what parts the truss systems consist of, what types they are and how their main elements are connected. If I missed some points or something is not clear to you - write comments, and I will be happy to answer your questions.

December 12, 2017

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