Attachment points for rafter legs. The nodes of the truss system or what the wooden frame of pitched roofs consists of

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 washed 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, the possibility of any influences (shifts, turns, bends, torsion) is completely excluded between these structural elements. 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 pattern. 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 its side, which is attracted with bolts or nails.

Experienced builders are well aware that during the construction of the truss system there are no nodes that would not play an important role in ensuring the strength of the structure. This, among other things, also applies to the methods of attaching the rafter leg to the Mauerlat. We will not dwell on the characteristics of the Mauerlat itself, the methods of its construction and the methods of its fastening. The initial data for all options for attaching rafters to Mauerlats are standard - they must all be made in accordance with the requirements of existing building codes and regulations.

It is necessary to briefly clarify one more question - it is not always possible to attach rafters to Mauerlats.

When and why it is impossible to use this method of fastening the truss system?

We figured out this issue, now we should consider a few general recommendations regarding the fastening of rafters.

And we figured out this topic, now we can already consider the most common ways of attaching rafter legs to the Mauerlat. We will talk about three: sawing with an emphasis (hard), sliding and layering methods.

Rigid fastening of rafters

The most reliable, most time-consuming and most versatile method can be performed by cutting or by sewing retaining bars onto the rafters. First, consider the option of cutting the rafters.

Do not worry if, as a result of cutting out your leg, the slope of the slope changes slightly. The main thing is that all the rafters lie on the same line. Before washing down the rafter leg, you need to take the dimensions of the place where it fits to the Mauerlat, and this is quite difficult. We will not perform various mathematical calculations, it is long and useless, and in practice no one bothers with such a head.

Step 1. We offer two options: make one universal template for all legs at once or make cuts for each separately.

If everything is fine with the position of the Mauerlat, then it is better to make a template, if there are problems, then you will have to prepare each rafter separately.

The template can be made from cutting boards, a piece of fiberboard, or thick cardboard. Draw a line on it at the bottom edge at a distance of no more than 1/3 of the width of the rafter leg. On all rafter legs, draw the same parallel line, mark the places where the rafters fit the Mauerlat, and draw a line perpendicular to it.

Now you need to trace the angle of the vertical and horizontal planes of the notch for one fit to the Mauerlat over the entire surface. Let's say right away that it will not be possible to achieve the ideal option, but the loose fit of the planes of a few millimeters does not play a critical role. Attach the template to the end of the Mauerlat beam at an angle of slope. The point of intersection of the vertical and horizontal lines must be exactly opposite its corner. Draw the resulting triangle, cut out the drawn part.

Step 2 Check the correctness of the template in several parts of the Mauerlat, walk along both sides of the building. If necessary, slightly change the angle of the sawn part, you need to achieve the most accurate fit of the notch around the entire perimeter.

Step 3 Attach the template to the rafter, the point of the angle of the upper stop should be on all rafters at the same distance from their ridge part.

Step 4 With an electric saw or a hand saw, cut the cut across the fibers of the rafter leg.

Sawing very carefully, do not reduce the width of the remaining intact rafter with a cut. With insufficient experience with electric tools, it is better to use hand saws. Let it take more time and effort, but the likelihood of marriage is significantly reduced. And if you take into account the time for rework, then the loss of labor productivity from a hand tool will not be so large.

Step 5 At an angle, select the second slice.

Attention: this is the most difficult job. Sawing such a surface with an electric saw is undesirable, the risks of intercession are high. You need to work with an ax, the ax must be very sharp. Working with an ax will require not only skill, but also physical strength. By the way, the ability to work with an ax (and not at the professional level) will always come in handy when building a wooden bath.

Step 6 Check the template made seat, if necessary, correct it. You can prepare seats for the entire set of rafter legs at once, or you can perform work in turn. It all depends on your skill and accuracy of installing the Mauerlat.

Step 7 Put the rafter leg in place, fix its position. For fixing, you can use homemade staples, metal corners or other durable devices.

Thus, you need to put the two extreme rafters, pull the rope between them in the lower part and put the next ones in turn. Be prepared that for some rafters you will have to adjust the heel sizes several times. The more practical experience you have, the less often you will have to remove / put the rafter leg to fit. During the installation of the truss system, each pair of legs should be temporarily fixed with various wooden braces or struts. Temporary fastening is removed only after stuffing the crate under the roof finish.

Edged board prices

edged boards

Fastening the rafter legs with a stripe of a thrust bar

For small baths, we recommend using this method - much easier and faster. As for the mechanical stability of the structure, it depends on the conscientiousness of the performance of all work. Even very inexperienced builders can use this method of fastening the rafters, it makes it possible to move the rafter legs in any position until they occupy the correct position and fix the knot in place.

Step 1. Install the gable rafters in place, temporarily fix their position.

Step 2 From a wide board, cut a piece at least 40 cm long. Determine the angle of inclination of the butt end in the Mauerlat. The upper horizontal notch on the board can be omitted, it does not carry any load. The rafters will hold the vertical load. In order to increase the area of ​​\u200b\u200btheir emphasis in the Mauerlat, it is necessary to saw through the seats in them to the width of the rafters.

There were no pieces of durable boards - nail two thin rafters on both sides. We only recommend planting them on one through hardware (optimally long bolt), you should not loosen the rafters with a large number of nails or self-tapping screws.

Step 3 If you have boards on both sides of the rafter, then you can not use additional methods of fixing the element from side overturning. If the board is on one side, then you will need to fix them with metal corners or staples.

It should be said that each truss system on any building is carried out by craftsmen with individual differences. It all depends on their experience and preferences. And you may not follow our recommendations exactly, make original decisions on the spot, taking into account the characteristics of the bath and the availability of building materials.

Work on fastening the rafters should always be done with a rope, the ridge and lower legs should be controlled. If there are height problems, then put wooden stops on the Mauerlat, to prevent slipping, nail them with small cloves or self-tapping screws.

Prices for a set of hardware

set of hardware

According to this method, a truss system is built in wooden log cabins.

The fact is that the log house must stand under the roof, during which time it shrinks. Shrinkage, as a result, slightly changes the position of the truss system, in the case of rigid fastening of the rafter legs, either deformation of the truss system will certainly appear, or the stability of the upper row of the log house will be disturbed. It is this row that plays the role of the Mauerlat. In order to increase the area of ​​\u200b\u200bsupport for the rafters and Mauerlat, you need to remove the sharp edge of the latter. Otherwise, heavy loads will cause the beam to be pressed into the corner of the Mauerlat, and the truss system will begin to change its position. This will be done unevenly along the perimeter of the log house - the rafters can significantly disrupt their original position, the roofing will become wavy. And this can violate its tightness, as a result, leaks will appear with all very negative consequences.

Sliding rafters can only be installed when the rafter system has an emphasis in the upper part on the ridge beam and vertical stops; to enhance the stability of the structure, it is desirable to additionally install braces or stocks. A specific decision should be made taking into account the size of the bath, the material of construction and the architectural characteristics of the roof.

Very important: if you intend to fix the rafter legs using a sliding method, then the fixation assembly of the upper ridge parts should be done on a hinge. In the upper part, the rafter legs should oscillate in the axial direction, which makes it possible for them, depending on the shrinkage of the bath, to change the angle of inclination of the truss system. Thus, possible vertical loads are extinguished.

Step 1. Install the ridge beam in size. It should be located exactly in the middle of the bath, otherwise the angle of inclination of the slopes will not be the same. What difficulties are caused by the unequal angle of inclination of the slopes during the construction of cornice overhangs, we have already described in the article above.

Step 2 Start the installation with the installation of the extreme gable rafters.

For sliding fastening, you need to buy special clamps, you need to install them on both sides of each rafter.

Sliding support for rafters - dimensions

Step 3 Take the dimensions of the rafters along the length, determine the specific places for their installation.

Step 4 To increase the plane of contact between the rafter leg and the Mauerlat, remove the corner of the beam. You can shoot the corner around the entire perimeter (difficult and long) or only in the places where the rafter legs rest. To do this, make two cuts in the Mauerlat at a distance slightly greater than the width of the rafter board.

With a chisel, carefully remove the wood in the cut, trim its surface. We advise you not to neglect this advice, such a simple installation method will make it possible to significantly increase the stability of the entire truss system. In addition, it will not be necessary to apply other methods for the stability of the system to longitudinal wind loads.

Step 5 Carefully place the rafters on the prepared seats, fix with floating metal mechanisms. They must be installed in such a position that most of the protruding node allows the rafters to go down, it is in this direction that shrinkage occurs.

Step 6 Between the extreme gable rafter legs, pull the ropes on the slope of the cornice overhangs, mount all the remaining rafters along the rope. If necessary, adjust the length of the structures. Simultaneously with the legs, fix the ridge parts of the rafter legs with a swivel joint.

Such a device of the truss system is considered the least stable. Despite the fact that the forces expanding the rafter legs are much less than the bending forces, the sliding legs are the weakest node of the entire structure.

Practical advice. At the slightest doubt about the stability of the constructed truss system, reinforce it. It does not matter in what way the system is strengthened, the main thing is that it always has a fairly large margin of safety and reliability. Remember that reinforcing a structure after a problem is discovered is much more difficult than doing all the work in a timely manner.

There is another kind of sliding method, it is more reliable in strength, but only suitable for baths made of rounded bursa or round whips - a sliding method with a gash in an arc.

Making it a little more difficult, each rafter at the point of contact with the upper crown of the log house must be cut in an arc. For sawing, it is better to use an electric jigsaw. The depth of cut is no more than 1/3 of the width of the rafter. The mark can be removed from the end of the timber, the rafters can be made all the same. Such a connection has an additional degree of freedom, but at the same time excludes axial movements - the reliability of the entire truss system increases.

Scheme - rafters with sliding support and cuts

sliding support prices

sliding support

It is used in the case during the production of repair work on roofs of complex construction or insufficient length of available lumber for the manufacture of rafters. Of course, the rafters can be connected and in this way increase the length. But builders do not advise doing these things; at the slightest opportunity to avoid the connections of the rafter legs, you need to use them. In addition to the fact that each connection requires a lot of time and labor, it always significantly reduces the strength of the rafters. We repeat once again - always the bearing characteristics of the connected rafters are much less than the whole ones.

It is better to use the layered method during the construction of the rafters, and with the help of ordinary fillies, make the roofing part of the eaves.

Step 1. Measure the exact length of each rafter until the end part stops in the Mauerlat. Determine the angle of inclination of the thrust plane.

Rafter rafters - schemes

Make a drink along the marked line. If the width of the rafter leg allows, then it is recommended to wash down with a tooth. The tooth will prevent the rafters from sliding on the Mauerlat. If this is not possible, then at the bottom of each rafter leg, stubborn boards about 40 centimeters long should be added. Boards are attached to the rafters with nails or screws.

Step 2 To prevent lateral vibrations and overall strengthening of the joint, the rafters are additionally fixed with metal corners or brackets. Driving large nails into the end is not recommended due to the high risk of cracking the wood.

Step 3 Next, you need to do fillies for cornices. For this, edged boards with a thickness of more than 30 millimeters are suitable. Cut them to length, taking into account the expected overhang of the eaves, and nail them firmly to the rafter legs. All work must be done only under a rope stretched between the extreme gable rafter legs.

Prices for metal corners

metal corners

For the rafter system, choose only the highest quality materials, this is not a design that you can save on. Many ordinary architectural elements have several additional components of load-bearing structures, they complement and insure each other. The rafters work "alone", in case of violation of stability, no other elements take on the load.

Try to make knots of rafters with Mauerlat in those places where there are no natural malformations of wood, including healthy knots. The hardness of the knots themselves is large, but swirls of wood fibers form around them, and they no longer have high rates of physical strength.

Do the markup, and especially the cropping, very carefully. To correct errors, you can use various linings, but this is highly undesirable.

And the last. You can find recommendations to install the truss system on your own without helpers. Some of the simplest types of truss systems can be done alone. The only question is, why is it needed? Why risk your health if there will be no savings in time and money in the long run. And the quality of the connection of all nodes will suffer significantly.

Video - Fastening rafters to the Mauerlat, sliding support

Video - Installation of rafters

Video - Assembly of rafters

Video - Quick installation of the truss system

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 above structural details, 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 version. 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 this or that 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.

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 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 staggering 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 to 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 inserting 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 off 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 violation of 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 point 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 the perpendicular beam with the bottom. 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 truss 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 crossbar 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 truss 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.