Knot of fastening of a rafter leg. Mounting points for the roof truss system

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

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

Varieties of connecting nodes "rafters - Mauerlat"

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Features of truss systems

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

Rafters

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

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

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

hanging rafters

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

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

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

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

Calculation of the installation of rafters

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

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

Use, in the article on our portal.

Prices for various types of fasteners for rafters

Fasteners for rafters

A few rules for attaching rafters to the Mauerlat

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

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

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

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

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

Video: a few examples of attaching rafters to the Mauerlat

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

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

The main elements of the truss system

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

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

  Mauerlat serves as the basis for the roof frame

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

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

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

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

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

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

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

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

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

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

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

  Fillies lengthen rafter legs

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

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

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

  Sheathing boards are laid out perpendicular to the rafters

Main connecting nodes

The main nodes of the truss system are:

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

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

The ridge knot also has several features:

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

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

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

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

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

Ways of fastening rafters

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

Mauerlat connection

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

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

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

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

   The triangular cut allows the rafter to rest against the Mauerlat

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

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

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

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

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

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

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

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

Video: installing rafters

Combination with floor beams

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

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

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

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

wall mount

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

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

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

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

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

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

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

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

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

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

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

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

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

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

At the heart of each roof is a large number of beams, rafters, racks and girders, which are collectively called the truss system. Over the centuries-old history of types and methods of its organization, a lot has accumulated, and each has its own characteristics in the construction of knots and cuts. We will talk in more detail about what the gable roof truss system can be and how the rafters and other elements of the system should be attached in more detail.

The design of the gable roof truss system

In the context of a gable roof is a triangle. It consists of two rectangular inclined planes. These two planes are connected at the highest point into a single system with a ridge beam (run).

Now about the components of the system and their purpose:

• Mauerlat - a beam that connects the roof and walls of the building, serves as a support for the rafter legs and other elements of the system.
• Rafter legs - they form the inclined planes of the roof and are the support for the crate under the roofing material.
• Ridge run (bead or ridge) - combines two roof planes.
• A puff is a transverse part that connects opposite rafter legs. Serves to increase the rigidity of the structure and compensate for bursting loads.
• Beds - bars located along the Mauerlat. Redistribute the load from the roof.
• Side runs - support the rafter legs.
• Racks - transfer the load from the runs to the beds.

Filly may still be present in the system. These are boards that extend the rafter legs to form an overhang. The fact is that in order to protect the walls and foundation of the house from precipitation, it is desirable that the roof ends as far as possible from the walls. To do this, you can take long rafter legs. But the standard lumber length of 6 meters is often not enough for this. Ordering non-standard is very expensive. Therefore, the rafters are simply grown, and the boards with which this is done are called “fillies”.

There are quite a few designs of truss systems. First of all, they are divided into two groups - with layered and hanging rafters.

With hanging rafters

These are systems in which the rafter legs rest only on the outer walls without intermediate supports (bearing walls). For gable roofs, the maximum span is 9 meters. When installing a vertical support and a strut system, it can be increased up to 14 meters.

The hanging type of gable roof truss system is good because in most cases there is no need to install a Mauerlat, and this makes the installation of rafter legs easier: no need to make cuts, just mow the boards. To connect the walls and rafters, a lining is used - a wide board, which is attached to studs, nails, bolts, crossbars. With such a structure, most of the bursting loads are compensated, the impact on the walls is directed vertically downwards.

Types of truss systems with hanging rafters for different spans between load-bearing walls

Gable roof truss system for small houses

There is a cheap version of the truss system when it is a triangle (photo below). Such a structure is possible if the distance between the outer walls is not more than 6 meters. For such a rafter system, it is possible not to calculate the angle of inclination: the ridge must be raised above the puff to a height of at least 1/6 of the span length.

But with this construction, the rafters experience significant bending loads. To compensate for them, they either take rafters of a larger section or cut the ridge part in such a way as to partially neutralize them. To give greater rigidity in the upper part, wooden or metal plates are nailed on both sides, which securely fasten the top of the triangle (also see not the picture).

The photo also shows how to grow rafter legs to create a roof overhang. A notch is made, which should go beyond the line drawn from the inner wall upwards. This is necessary to move the incision site and reduce the likelihood of a rafter breaking.

Ridge knot and fastening of rafter legs to the backing board with a simple version of the system

For mansard roofs

Option with the installation of a crossbar - used when. In this case, it is the basis for filing the ceiling of the room below. For reliable operation of this type of system, the crossbar notch must be hingeless (rigid). The best option is semi-pan (see the picture below). Otherwise, the roof will become unstable to loads.

Please note that in this scheme there is a Mauerlat, and the rafter legs should extend beyond the walls to increase the stability of the structure. To secure them and dock with the Mauerlat, a cut is made in the form of a triangle. In this case, with an uneven load on the slopes, the roof will be more stable.

With such a scheme, almost the entire load falls on the rafters, therefore they must be taken with a larger section. Sometimes the raised puff is reinforced with a suspension. This is necessary to prevent it from sagging if it serves as a support for ceiling sheathing materials. If the puff is short, it can be secured in the center on both sides with boards nailed to the nails. With a significant load and length, there may be several such insurances. In this case, boards and nails are also enough.

For big houses

With a significant distance between the two outer walls, a headstock and struts are installed. This design has high rigidity, since the loads are compensated.

With such a long span (up to 14 meters), it is difficult and expensive to make a one-piece puff, because it is made from two beams. It is connected by a straight or oblique cut (picture below).

For reliable docking, the junction is reinforced with a steel plate mounted on bolts. Its dimensions should be larger than the dimensions of the cut - the extreme bolts are screwed into solid wood at a distance of at least 5 cm from the edge of the cut.

In order for the circuit to work properly, it is necessary to correctly make the struts. They transmit and distribute part of the load from the rafter legs to the puff and provide structural rigidity. Metal strips are used to reinforce the connections.

When assembling a gable roof with hanging rafters, the cross-section of lumber is always larger than in systems with layered rafters: there are fewer load transfer points, therefore, each element has a greater load.

With rafters

In gable roofs with layered rafters, their ends rest on the walls, and the middle part rests on load-bearing walls or columns. Some schemes burst walls, some do not. In any case, the presence of a Mauerlat is mandatory.

Bezporny schemes and knots of cuts

Houses made of logs or timber do not respond well to spacer loads. For them, they are critical: the wall can fall apart. For wooden houses, the gable roof truss system must be non-expansion. Let's talk about the types of such systems in more detail.

The simplest non-spacer scheme of the truss system is shown in the photo below. In it, the rafter leg rests on the Mauerlat. In this embodiment, it works on a bend, without bursting the wall.

Pay attention to the options for attaching the rafter legs to the Mauerlat. In the first, the support platform is usually beveled, while its length is no more than the cross section of the beam. The depth of the cut is no more than 0.25 of its height.

The top of the rafter legs is laid on the ridge beam without fastening it to the opposite rafter. Two shed roofs are obtained according to the structure, which adjoin (but do not connect) one with the other in the upper part.

It is much easier to assemble the option with rafter legs fastened in the ridge part. They almost never give a thrust on the walls.

For this scheme to work, the rafter legs below are attached using a movable joint. To fix the rafter leg to the Mauerlat, one nail is hammered from above or a flexible steel plate is placed from below. See the photo for options for attaching rafter legs to a ridge run.

If the roofing material is planned to be heavy, it is necessary to increase the bearing capacity. This is achieved by increasing the cross section of the elements of the truss system and strengthening the ridge assembly. It is shown in the photo below.

Strengthening the ridge assembly for heavy roofing material or with significant snow loads

All of the above gable roof schemes are stable in the presence of uniform loads. But in practice, this almost never happens. There are two ways to prevent the roof from sliding in the direction of greater load: by installing a brace at a height of about 2 meters or by struts.

Options for truss systems with contractions

The installation of contractions increases the reliability of the structure. In order for it to work normally, at the places where it intersects with drains, you need to attach nails to them. The cross section of the beam for the scrum is used the same as for the rafters.

They are attached to the rafter legs with bots or nails. Can be installed on one or both sides. The knot for attaching the bout to the rafters and the ridge run, see the figure below.

In order for the system to be rigid and not “crawl” even under emergency loads, it is enough in this embodiment to provide a rigid fastening of the ridge beam. In the absence of the possibility of its displacement in the horizontal, the roof will withstand even significant loads.

Rafter systems with braces

In these options, rafter legs, which are also called struts, are added for greater rigidity. They are installed at an angle of 45° with respect to the horizon. Their installation allows you to increase the span length (up to 14 meters) or reduce the cross section of beams (rafters).

The strut is simply substituted at the required angle to the beams and nailed from the sides and bottom. An important requirement: the brace must be cut accurately and fit snugly against the uprights and the rafter leg, excluding the possibility of its deflection.

Systems with rafter legs. Above is a spacer system, below is a non-spacer system. The nodes of the correct felling for each are located nearby. Below - possible schemes for attaching the strut

But not in all houses, the average load-bearing wall is located in the middle. In this case, it is possible to install struts with an angle of inclination relative to the horizon of 45-53°.

Bracing systems are necessary if significant uneven shrinkage of the foundation or walls is possible. Walls can sit differently on wooden houses, and foundations on layered or heaving soils. In all these cases, consider the installation of truss systems of this type.

System for houses with two internal load-bearing walls

If the house has two load-bearing walls, two rafters are installed, which are located above each of the walls. Beds are laid on the intermediate load-bearing walls, the load from the rafter beams is transferred to the beds through the racks.

In these systems, a ridge run is not installed: it gives expansion forces. The rafters in the upper part are connected to one another (cut and joined without gaps), the joints are reinforced with steel or wooden plates, which are nailed.

In the upper non-expansion system, the expanding force is neutralized by tightening. Please note that the puff is placed under the run. Then it works efficiently (the top diagram in the figure). Stability can be provided by racks, or jointing - beams installed obliquely. In the spacer system (in the picture it is below), the cross member is a crossbar. It is installed above the run.

There is a variant of the system with racks, but without rafters. Then a rack is nailed to each rafter leg, which rests on the intermediate load-bearing wall with the second end.

Fastening the rack and tightening in the rafter system without a rafter run

To fasten the racks, nails for 150 mm and bolts 12 mm are used. Dimensions and distances in the figure are in millimeters.

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

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

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

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

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

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

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

Consider the basic designs of layered rafters.

Bezrasporny rafters without struts

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

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

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

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

Options for fixing rafter legs

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

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

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

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

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

The most common scheme for private houses.

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

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

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

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

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

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

Ways to increase the stability of non-thrust systems

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

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

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

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

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

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

Spacer rafters without struts

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

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

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

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

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

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

Rafters with struts

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

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

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

Laying system with rafter beams

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

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

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

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

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

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

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

Key points for installing layered rafters

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

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

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

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

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

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

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

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

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

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

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

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

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

Main connecting nodes

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

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

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

Fixation methods

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

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

Varieties of fasteners

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

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

Types of fasteners

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

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

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

Video instruction