Rafters without struts. Types of gable roof truss system: for small and large houses Due to the increased length, it is possible to

Rafter system Is a structure that provides the strength of the roof and serves as the basis for laying the roofing material. She is shown in the photo.

The roof is a load-bearing structure that performs the following functions:

• gives the structure a beautiful appearance;
• takes on external loads;
• protects the attic from the outside world;
• transfers the load from the battens and the material on it to the walls of the building and internal supports.

The main elements of the roof include lathing, rafters and Mauerlat. also in supporting structure includes additional fasteners - crossbars, racks, rafter struts, struts, etc. The reliability and strength of the roof is most influenced by the rafter system. The rafters are the main load-bearing part of the roof. The rafter system has weight not only roofing but also snow cover, wind pressure. It must withstand all these influences, therefore, the calculation is made taking into account the type of roofing material and the climatic characteristics of the region.

The structure of the rafter system

Connecting the rafters to each other stiffens the roof frame, and the result is a strong rafter structure. The load on the rafters can be quite significant, for example, during strong wind, therefore, the frame is firmly tied to the frame of the building.

In the construction of private houses and cottages, wooden truss systems are usually used, which are easy to manufacture and install. If mistakes were made during the construction of the walls, these products can be easily processed: shorten, build up, hang, etc.

During installation, fasteners of the rafter system are used: bolts, screws, clamps, nails, staples. They are also used to reinforce the load-bearing roof structure. The interconnected roof elements create a truss truss, which is based on triangles, which are the most rigid geometric figure.

When choosing a material for making a system from rafters, it is necessary to take into account the structural and architectural nuances of the project. Do not forget about antiseptic and fireproof impregnation for them, as this affects the durability of the roof.

The system consists of rafter legs... Install the rafters at an angle of inclination of the roof slopes. The lower sections of the rafter legs are supported on the outer walls with the help of a Mauerlat, which contributes to an even distribution of the load. The upper ends of the rafters are supported on a bar under the ridge or on intermediate fittings. The strut system transfers the load to the load-bearing internal walls.

Types of rafters

Hanging rafters consist of the following elements: rafter leg, attic overlap, crossbar. These rafters only have two extreme anchor points. They rest directly on the walls of the house. Rafter legs respond to both compression and bending. These rafters are without braces. See also: "Supporting the rafters on the floor beams."

The design of the hanging rafters transfers a significant horizontal expansion force to the walls. In order to reduce the load, a stretch is used, with the help of which the rafter legs are connected. They do it either at the base of the rafters, or at a higher height. The stretch at the base of the rafters is at the same time the floor beam - this is important when creating mansard roofs. With an increase in the height of the brace location, it is necessary to increase its power and make sure that it is securely attached to the rafters.

Part layered rafters includes: rafter leg, mauerlat, headstock, brace, tightening. This type of rafter is installed in buildings in which there is a middle load-bearing wall or intermediate supports in the form of pillars. Elements of this design work only for bending, performing the function of attendants. The slab rafter system is lighter and requires less materials and is therefore less expensive than a hanging system.

Installation of a layered system is done if the supports are no more than 6.5 meters apart from each other. If there is an additional support, the rafters sometimes overlap the width of 12 meters, and if there are two supports, up to 15 meters.

Rafter legs are most often based not on the walls of the building, but on a special beam - the Mauerlat. This element can be located along the entire length of the house or be placed only under the rafter legs. If the structures are wooden, a log or timber is taken for the Mauerlat, which is the upper crown of the log house.

When masonry walls, the Mauerlat is a bar installed flush with the inner surface of the walls, fenced off from the outside by a projection of the masonry. A layer of waterproofing is laid between this element and the brick - for example, roofing material can be put in two layers.

If the width of the rafters is small, they can sag over time. To prevent this from happening, use a lattice consisting of a rack, a crossbar and struts. At the top of the structure, a girder is laid, which connects the rafters or trusses. This is done regardless of the type of roof. Subsequently, on this run, the roof ridge is made. In places where there are no load-bearing walls, the heels of the rafters rest against the side girders - longitudinal beams of significant power. The dimensions of these parts depend on the expected load.

In the construction of private houses, log rafters are used - they are lighter. To create roofs on multi-storey residential buildings and industrial buildings, metal rafters are used.

Installation of roof systems

The slope angles of the slopes are selected based on the type of building and the purpose of the attic space. The amount of slope is also influenced by the material chosen to create the roofing.

If roll products are to be stacked, the angle of inclination should be 8-18 degrees. For tiles, the required angle is 30-60 degrees, for roofing steel or asbestos-cement sheets - 14-60 degrees.

The installation of the rafter system begins after the erection of the load-bearing walls of the house (for more details: "Installation of the rafter system"). Wooden rafters construction log house significantly differs from systems for houses made of aerated concrete, brick, timber frame or panel houses... The differences are significant even with the same shape, type and type of roof. As for how to treat the rafter system, it is necessary to use antiseptic and fire-fighting agents so that the roof will last for a long time.

The main elements of the supporting structure are roof trusses and lathing. The roof is the outer part of the roof, which is laid on a supporting structure consisting of battens and rafters.

For the production of rafters, material of a certain size is taken. So, the thickness of the rafters (section) is most often 150x50 and 200x50 millimeters. For the lathing, they usually take beams and boards measuring 50x50 and 150x25 millimeters. The distance between the rafter legs is on average 90 centimeters. If the slope of the roof is more than 45 degrees, this step is increased to 100-130 centimeters, and if a huge amount of snow falls in the region, then it is reduced to 60-80 centimeters.

To make more accurate calculations regarding the gap between the construction legs, you need to take into account their cross section, the step between the supports (struts, ridge run, uprights), and the type of roofing material.

The floating rafter system is attached using special brackets that allow the rafters to "sit down" together with the shrinkage of the gables and not hang over the ridge log.

Installation of the rafter system, see the video:

If the rigidity is provided by the trusses, the rafters are reinforced with diagonal ties (for more details: "How to make the rafters reinforced - options for strengthening the rafter system"). For them, boards with a thickness of 3-4 centimeters can be used, nailed at the base of the extreme rafter leg and in the middle part of the adjacent one. Rafter legs are the main element of the system, so they account for most of the roof load. For this reason, the system must be correctly calculated and installed in order for the roof to be reliable (see also: "How to put rafters on a house").

The installation of the rafter system must be carried out, strictly observing all the requirements. If you do not have experience in construction, it is better to entrust the construction of the roof to specialists, since this is not an easy task, and the slightest mistakes can lead to its collapse.

Source: kryshadoma.com

Rafters, supported on two supports without any additional stops, are used for single-pitched roofs with a span of 4.5 m or gable roofs with a span of up to 9 m (Fig. 30). The rafter system can be used with the transmission of the spacer to the Mauerlat (walls) and without the transmission of the spacer.

Rice. 30. Inclined rafters without struts

Expansionless layered rafters

A bending rafter that does not transmit the thrust to the walls must have one support fixed, but freely rotating, the other freely rotating and movable.

These conditions are met by three options for fastening the rafters:

1. The bottom of the rafter leg is hemmed with a support bar or a cut (cut) is made on it with a tooth and rests on the Mauerlat, and an enlarged horizontal cut (cut) with a bevel is made at the top of the rafter (Fig. 31). The depth of the cut (cut) in the upper part of the rafter should not exceed a = 0.25h... The length of the trim (support area) is made no more than the height of the rafter section (h)... It is recommended to cut the trim so that it does not interfere with the bending of the rafter, otherwise the cut with its side cheek will rest against the girder and we will get a spacer rafter system. The length of the beveled undercut is made at least two depths a... If it is impossible to trim the top of the rafter leg, it is hemmed with a rafter trim with double-sided mounting with mounting plates or wooden beads. The upper ends of the rafter legs fit freely on the girder. V gable roofs ah, they are attached to the girder as a sliding support, but they are not fastened to each other. A gable roof, in this case, is considered as two gable roofs, adjoined to each other by a high side. Pay attention to an extremely important condition: the upper support cut or hemming of the top of the rafters are made horizontally... One has only to change the support scheme for the girder, as the rafter immediately shows the thrust. This calculation scheme for installing rafters due to the rigidity of the conditions for manufacturing the upper unit (any inaccuracy in the design of the unit immediately turns the non-thrust scheme into a spacer) is practically not used for gable roofs, therefore it is more often used in pitched roofs. In addition, in gable roofs, for the lack of space on the Mauerlat when the rafters bend under the action of a load, you have to pay by opening the ridge node of the roof.

At first glance, this scheme is generally paradoxical. We clearly see an emphasis on the Mauerlat in the lower part of the rafter leg, and the system seems to have to exert a horizontal force on it. However, she does not show strife. If someone wants to know why, then read the proof in the course of lectures of Professor V. G. Zalessky on pages 414–415.

rice. 31. Supporting the bottom of the rafter with a cut in the Mauerlat, and the top of the rafter on the run with a horizontal cut, with a beveled cheek, does not push against the walls

2. The most common way of installing rafters is related to gable roofs. The bottom of the rafter leg is made on a slider, and the top is fixed (Fig. 32): they are tied with a nail strike or a bolt, or abut against each other and tied with wooden beads or metal toothed plates (MZP).

rice. 32. Supporting the bottom of the rafters without cutting into the mauerlat with the top of the rafters secured, does not give space to the walls

What you need to pay special attention to is the fastening of the rafter leg to the Mauerlat.It comes down only to fixing the rafters in the design position, which ensures the step of their installation. To do this, it is enough to drive one nail diagonally from both sides into lateral surface rafters or one long nail on top, or put a flexible steel plate. If fashionable mounting angles are used, then one nail will be enough to secure the bottom of the rafter, or you need to press the rafter with corners on both sides without nails at all. Do not drive as many screws or nails into the corners as there are holes in the corner. Otherwise, you will turn the slider into an imperfect hinge and get a spacer on the Mauerlat. Flexible wire strands are held against the wind-driven overturning of the roof; it is not necessary to transfer this function to the corners, or the rafter system should be calculated as a spacer.

3. Does not give space and rigid pinching of the ridge knot when the bottom of the rafter leg is made on the slider, and the top is rigidly fixed (Fig. 33). However, a bending moment appears in the ridge knot, tending to destroy it. The maximum bending moment in such a structure occurs on the ridge support, and the rafter legs themselves receive less deflection. It is quite difficult to calculate such a node, and then accurately manufacture it on a construction site, therefore it is better to accept formulas for calculating the bending moment and deflection as for ordinary single-span beams.

rice. 33. Supporting the bottom of the rafters without cutting into the Mauerlat with pinching of the ridge knot, does not give space to the walls

In all three options, the rule is observed: one end of the rafter leg is made on a sliding support that allows rotation, the other on a hinge that allows only rotation. The fastening of rafters on sliders and fixed hinges is made by the most different designs... Now they are often performed on mounting plates. You can also fasten in the old fashioned way: with staples, nail strikes or using short bars and boards. You just need to choose the right type of fastener so that it allows or prevents the rafters from sliding in the support.

When calculating the rafter system, an "idealized" design scheme is adopted. It is believed that a uniformly distributed load presses on the roof, i.e. the same and even force acting evenly on all planes of the slopes. In fact, there is almost never a uniformly distributed load on roof slopes. The wind sweeping snow bags on one of the slopes and blowing snow off the other, the sun melting snow on the southern slopes, snow sliding in the spring - make the load on the slopes uneven. Under the action of an uneven load, all three of the above options of rafter systems are statically stable, but only if the ridge girder is rigidly fixed. Which ends are inserted into the gables of the walls or propped up with hip roof rafters. That is, the rafter system will be stable only if the ridge girder on which the top of the rafters rests is securely fixed against horizontal displacement.

In the manufacture of gable roofs and the support of the girder only on the racks (without resting their ends on the walls of the gables), the situation changes for the worse (Fig. 34). In the second and third variants, with a significant decrease in the load on one of the slopes, against the calculated one on the other slope, the roof will try to "leave" towards a higher load. The first option, in which the bottom of the rafter leg is made with a notch with a tooth or with a filing of a support bar, and the top with a horizontal notch is laid on the girder, holds an uneven load well, but only under the condition of the absolute verticality of the racks that hold the ridge girder.

rice. 34. Loss of stability by the rafter system

To give the rafter system stability, a horizontal grapple is introduced into it (Fig. 35). It increases the stability of the system, but only slightly. Therefore, in all places where the fight intersects with the posts supporting the ridge run, it is attached to the posts with a nail fight. There is a persistent misconception that the contraction always works in tension, it is not. The grapple is a multifunctional element: in non-expansion rafter structures, it does not work at all in the absence of snow on the roof, or it works in compression when an insignificant uniform load appears on the slopes. In tension, it works only in a pre-emergency situation when the ridge girder sags or deflects from the action of maximum loads. In fact, the scrum is an emergency element of the rafter system, which comes into operation when the roof is covered with the maximum possible amount of snow and the ridge girder bends over the entire calculated value, or when unexpected and uneven subsidence of the foundations occurs and, as a result, uneven settlement of the walls and ridge girder. The lower the contractions are set, the better. Usually they are installed at a height of at least 1.8–2 m from the floor surface, so that they do not interfere with a person passing through the attic.

If, in the second and third versions, the lower unit for supporting the rafter leg (slider) is replaced with a slider of a slightly different design (Fig. 35, c) - with the end of the rafters out of the wall, then this will further strengthen the entire system, making it a statically stable structure for any combination of loads.

rice. 35. The scrum between the rafters increases the stability of the rafter system

Another measure to increase the stability of the entire system is rigid (which is not always possible) securing the bottom of the racks supporting the run. They are cut into the bed and attached to the ceilings by any possible way, converting the lower support unit of the rack from a hinged one (in the plane of the rafters) into a unit with rigid pinching (Fig. 36).

rice. 36. An example of fastening the strut support unit

Due to the development of low stresses in them, the section of contractions is not calculated, they are taken constructively. In order to reduce the size of the parts used in the construction of the rafter system, the cross-section of the fight is used the same size as the rafters, but thinner boards can also be used. Fasteners are installed on one or both sides of the rafters and are attached to them with a nail and / or bolts (fig. 37). When calculating the cross-section of rafters, contractions are not considered additional supports, i.e. the rafter system is calculated as if there are no fights in it at all. However, if the scrapes are bolted to the rafters, then the load-bearing capacity of the wood due to weakening by the bolt holes is reduced by using a factor of 0.8. In other words, if holes are drilled in the rafter for the installation of the bolts of the contractions, then its design resistance is applied equal to 0.8R. When fastening the fight to the rafters only with a nail fight, the weakening of the calculated resistance of the wood of the rafter leg does not occur, but it is necessary to calculate the number of nails driven. The calculation is made for the cut (bend) of the nails. For the calculated shear force, a thrust is taken, which can occur in an emergency condition of the rafter system. In general, a spacer is introduced into the calculation of the nail connection of the scrum with the rafter (H), which does not exist, for normal work rafters.

rice. 37. Scrum attachment unit

Once again, we recall that the static instability of a non-thrust rafter system is manifested only in roofs where it is not possible to fix the ridge girder from horizontal displacement. In houses with hip roofs and in houses with brick and stone gables, the rafter-free systems are quite stable and there is no need for stability measures. However, "anti-emergency" designs are fights, it is still necessary to install.

When a thrust is introduced into the calculation of the rafter system (even if it is not there), the calculation of the compressive force S changes. Now it is calculated by dividing the resultant distributed load by the sine of the rafter tilt angle S = (qL / 2) / sinα. Without going into the details of the expansion of the force vectors, let us explain this with a small example. Suppose we have a rafter system with a steep slope of the slopes. When a load acts on it in an emergency state, for example, when a subsidence, a deviation from the vertical, or the destruction of a ridge run, tensile stresses will appear in the fight, neutralizing the so-called thrust. With a constant external load, the smaller the angle of inclination of the slopes, the more the spacer will grow and the more the rafter legs will be compressed. Conversely, if the rafter legs are not tied by contractions, then they work like ordinary beams laid in an inclined position. In this case, a decrease in the angle of inclination, with a constant load, reduces the compressive stresses in the rafter and increases the normal (perpendicular) force directed to the bending of the beam. Therefore, the compressive force in rafter systems without contractions is considered as S = (qL / 2) × sinα and with contractions S = (qL / 2) / sinα. Since double-slope rafter systems are almost never built without fights, and the calculation is always carried out for the worst working conditions, then on all schemes the compressive stresses will be written as S = (qL / 2) / sinα, regardless of whether there will be a thrust in these schemes or no.

When installing studs or bolts for fastening scrapes, pay special attention to the diameter of the hole for them. It should be equal to the diameter of the studs (bolts) or even less than it by 1 mm. In an emergency, the scrum will not work until it chooses a gap between the pin and the wall of the hole at this time, the bottom of the rafter legs "erodes" a few millimeters or centimeters (depending on the height of the scrum installation), which can move or unscrew the Mauerlat and destroy the cornice of the walls, and in the spacer rafter systems, where the Mauerlat is rigidly fixed, "push apart" the light walls.

Spacer rafters

A bending rafter that transfers the spacer to the walls must have two fixed supports.

We take the same versions of rafter schemes and replace the lower supports with two degrees of freedom (sliders) with supports with one degree of freedom (hinges). Simply, where they are not, we nail the support bars to the bottom of the rafter leg. Typically, a bar about a meter long and a cross-section of 50 × 50 (60) mm is used with the calculation of a nail connection. Or we support the Mauerlat in the form of a tooth. In the first version of the design scheme, in the ridge where the rafters are horizontally supported on the girder, we sew the upper ends of the rafter legs with a nail fight or fasten them with a bolt and thus obtain a hinge support.

rice. 38. Rafters rested with both ends in the Mauerlat and in each other show the strut

The design schemes of rafter systems change slightly (Fig. 38), all internal compressive and bending stresses remain the same, but an equal distance appears in the lower supports of the rafters H = (qL / 2) × ctg α, (kg). In the upper nodes, the spacer in one rafter leg is destroyed by the oppositely directed spacer from the end of the other rafter leg, so here it does not bring much trouble. However, the ends of the rafter legs resting directly against each other or through a purlin can be tested for wood crushing, although this is not required in most cases.

In fact, spacer rafters are a transitional scheme between non-spaced layered and hanging rafters. They already show the scheme of the hanging rafters, but the rudiment in the form of a ridge run still remains. When the rafters are resting on the bottom against the walls, and on horseback against each other, then the run here is like the fifth wheel in a cart. On the one hand, it doesn't seem to hurt, but on the other, you can do without it. The rafter system shows the duality of its work, which depends on the tightness of the top of the rafters to the girder and to each other. The force vector pressing on the ridge knot is distributed both to the rafter legs and to the girder. In case of subsidence, as a result of wall shrinkage or deflection from its own weight, the girder goes out of work and the force vectors are completely distributed along the rafters, and the rafters themselves turn into hanging ones.

In spacer rafter systems, the purpose of the scrum is somewhat different - it works in compression in emergency situations. Getting into work, she lowers the spacer on the walls of the bottom of the rafter legs, but does not completely remove it. She will be able to remove it completely if it is located at the very bottom, fixed between the ends of the rafter legs, but this is already another constructive scheme and the fight in it is called a tightening.

What changes when a fight is included in the scheme? We will not burden you with the layout of the force vectors, just imagine a pre-emergency situation when maximum loads are acting on the roof. Where there are no racks under the ridge girder, the girder deflects and the layered rafters, tightened by a fight, instantly turn into a hanging rafter pattern with a compressed crossbar, and the bottom of the rafter legs receives a strut according to the corresponding design scheme. Where there are racks under the ridge girder or a rigid girder, the fight also works for compression and the bottom of the rafter legs also transfers the thrust, but weaker in the same way as the top of the rafters holds the ridge girder. However, the calculation is based on the worst-case scenario.

The use of spacer rafter systems requires taking into account the effect of the spacer on the walls. You can reduce the spacer by installing rigid ridge girders. For these rafter schemes, it will be better if the calculated deflection of the ridge run turns out to be much less than the normalized SNiP. Try to increase the rigidity of the purlin by installing struts, struts or cantilever beams (changing the section height) or doing a building lift on it. This is especially true for houses made of lightweight concrete, lumber and chopped from a log. Massive brick, concrete and panel houses easier to transfer the spacer to the walls.

It should be noted that the thrust is understood as the horizontal force arising from the compressive stress S rolling down the rafter leg. In other words, thrust is a horizontal vector of forces arising from the action of a vertical load... Do not confuse it with rafter deflection. In the design scheme, the rafters are considered to be bar elements that have no height, therefore, the deflection strut is not taken into account. This is what the standardization of the deflection in building structures is aimed at. SNiP, introducing normalized deflection values, brings idealized design schemes closer to real ones. In other words, if the deflection of the building structure does not exceed the standardized, then you should not think about the pressure from the deflection, it seems to be not there. Although in fact it is also in the spacer scheme, it manifests itself in to a greater extent than in non-thrust. You need to pay attention to the deflection strut when building the walls of a house from aerated concrete. These blocks absolutely do not hold the bend and can be destroyed by expansion even from the deflection of the rafters. Do not use rafters on these walls. In other cases, the deflection spacing does not do much harm, for example, in brick walls it is perceived by the elasticity of the Mauerlat and steel fasteners.

The rafter system, made according to the spacer option, is a statically stable system for any combination of loads and requires rigid fixing of the Mauerlat on the wall. To hold the gap, the walls must be massive enough or equipped with an unbreakable monolithic reinforced concrete belt along the entire perimeter, like a hoop on wooden barrel... In emergency situations, in contrast to non-thrust systems, in a thrust system, a compression scrum does not save the situation; it only partially reduces the thrust transmitted to the walls (Fig. 38.1). So that emergency situations do not occur, we collect to the maximum, the loads acting on the roof.

rice. 38.1. Compression scrum partly removes the spacer from the walls

The calculation of the rafter system with a compressed scrum introduced into it is done according to two combinations of loads. The cross-section of the rafter leg is selected according to the maximum bending moment and deflection without taking into account the work of the compressed fight. Imagine that an uneven load is acting on the roof: snow lies on one side of the slope, and on the other it has melted or slipped. The bending rafter leg will simply push the compressed grapple and will work like a regular single span beam. The selection of the section of the compressed fight and the determination of the thrust on the walls, on the contrary, will be carried out for a uniformly distributed load on both slopes. In this case, the fight will be compressed on both sides and will receive the maximum compression stress, the bottom of the rafter leg will give a reduced thrust to the wall, and the rafter leg itself will turn into a continuous beam on three supports.

At the heart of each roof is a large number of beams, rafters, uprights and purlins, which are collectively referred to as the rafter system. Over the centuries-old history of species and methods of its organization, a lot has accumulated, and each has its own characteristics in the construction of nodes and cuts. We will talk in more detail about what the rafter system of a gable roof can be and how the rafters and other elements of the system should be attached in this case.

The structure of the gable roof truss system

In section, the 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 by a ridge bar (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 sheathing under the roofing material.
• Ridge girder (bead or ridge) - unites two roof planes.
• Tightening is a transverse piece that connects opposing rafter legs. Serves to increase the rigidity of the structure and compensate for bursting loads.
• Beds are bars located along the Mauerlat. Redistribute the load from the roof.
• Side Girders - Supports the rafter legs.
• Racks - transfer the load from the girders to the benches.

Filly may still be present in the system. These are boards that lengthen the rafter legs to form an overhang. The fact is that to protect the walls and foundations 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 length of lumber of 6 meters is often not enough for this. Ordering a non-standard is very expensive. Therefore, the rafters are simply grown, and the boards with which they do it are called "filly".

There are quite a few constructions 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 (load-bearing walls). For gable roofs, the maximum span is 9 meters. When installing a vertical support and a system of struts, it can be increased up to 14 meters.

The hanging type of the gable roof rafter system is good because in most cases there is no need to install a Mauerlat, and this makes the installation of rafter legs easier: you do not need to make cuts, it is enough to 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 downward.

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

Gable roof rafter system for small houses

There is a cheap version of the rafter system when it is a triangle (photo below). Such a structure is possible if the distance between the outer walls is no more than 6 meters. For such a rafter system, you can not 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, either rafters of a larger section are taken or the cut of the ridge part is made so as to partially neutralize them. To give greater rigidity in the upper part, wooden or metal strips are nailed on both sides, which securely fasten the top of the triangle (also see not the picture).

The photo also shows how to extend the rafter legs to create a roof overhang. A cut is made, which should go beyond the line drawn from the inner wall upwards. This is necessary in order to displace the cut and reduce the likelihood of breaking the rafter.

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

For mansard roofs

The version with the installation of the crossbar is used for. In this case, it is the basis for filing the ceiling of the room below. For reliable work systems of this type, the crossbar cut must be non-hinged (rigid). The best option is semi-rotten (see the picture below). Otherwise, the roof will become unstable to loads.

Please note that a Mauerlat is present in this scheme, and the rafter legs should extend beyond the walls to increase the stability of the structure. To fix 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 this scheme, almost all the load falls on the rafters, therefore they must be taken of a larger section. Sometimes the raised tie is reinforced with a suspension bracket. This is to prevent it from bending if it supports the ceiling sheathing materials. If the tightening is short, it can be secured in the center on both sides with boards nailed to the nails. With a significant load and length of such insurance, there may be several. In this case, too, planks and nails are enough.

For large 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 an integral tightening, therefore it is made of two beams. It is connected with a straight or oblique cut (figure below).

For a secure fit, the joint is reinforced with a bolted steel plate. 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 make the braces correctly. They transmit and distribute part of the load from the rafter legs to the tightening and provide the rigidity of the structure. Metal pads 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 large load.

With layered rafters

In gable roofs with layered rafters, their ends rest on the walls, and in the middle part they rest on load-bearing walls or columns. Some schemes burst the walls, some don't. In any case, the presence of a Mauerlat is required.

Spreader-free schemes and cutting units

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

The simplest spreader-free diagram of the rafter system is shown in the photo below. In it, the rafter leg rests on the Mauerlat. In this version, it works for bending without bursting the wall.

Pay attention to the options for attaching the rafter legs to the Mauerlat. In the first, the support area 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. The structure turns out to be two pitched roofs, which in the upper part adjoin (but do not connect) one with the other.

The version with the rafter legs fastened in the ridge part is much easier to assemble. They almost never give space to the walls.

For this scheme to work, the rafter legs at the bottom are attached using a movable joint. To secure 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 the options for attaching the rafter legs to the ridge girder.

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

Reinforcement of the ridge knot 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 practically does not happen. There are two ways to prevent the roof from sliding towards a higher load: by installing a scrum at a height of about 2 meters or with struts.

Variants of rafter systems with scrapes

Installation of scrapes increases the reliability of the structure. In order for it to work normally, at the points of its intersection with the drains, you need to fasten it to them with nails. The cross-section of the timber for the fight is used the same as for the rafters.

Attached to the rafter legs with bots or nails. Can be installed on one or two sides. See the figure below for attaching the scrum to the rafters and ridge girder.

In order for the system to be rigid and not "crawl" even under emergency loads, it is sufficient in this version to provide a rigid fastening of the ridge bar. In the absence of the possibility of its displacement horizontally, the roof will withstand even significant loads.

Systems of layered rafters with struts

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

The brace is simply placed 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 tightly to the uprights and rafter leg, excluding the possibility of its deflection.

Systems with rafter legs. Above the spacer system, from the bottom - non-spacer. The nodes of the correct felling for each are located next to each other. Below - possible schemes for attaching the strut

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

Strut systems are necessary if significant uneven shrinkage of the foundation or walls is possible. Walls can sit in different ways on wooden houses, and foundations - on layered or heaving soils. In all these cases, consider the device of this type of rafter system.

System for houses with two internal load-bearing walls

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

In these systems, the ridge girder is not installed: it provides thrust forces. The rafters in the upper part are connected to one another (they are cut and docked without gaps), the joints are reinforced with steel or wooden strips, which are nailed.

In the upper non-thrust system, the tightening force is neutralized by the tightening. Please note that the tightening is placed under the purlin. Then it works effectively (top diagram in the figure). Stability can be provided by uprights, or joists - beams installed obliquely. In the spacer system (in the picture it is below), the cross member is the crossbar. It is installed over the purlin.

There is a variant of the system with racks, but without the rafter beams. Then a stand 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 girder

For fastening the racks, 150 mm nails and 12 mm bolts are used. Dimensions and distances in the figure are in millimeters.

The frame format stands out among a number of types of roofing. It can be performed in a rather different way, but in any case, you will need to calculate the rafters and install them according to all the rules. With proper knowledge of the problem, you can solve it on your own without contacting specialists.

Features and shapes of the roof

A frame roof can only be installed with spans no longer than 1220 cm, while the gap from one truss to another is a maximum of 0.6 m. The dimensions of the frame fragments are determined by the span distances and the calculated snow load. The rafters can be either freely installed or take the load from the attic elements. In the case of a broken roof, it is possible to provide a ceiling height sufficient for a residential attic, and it will look best on a square structure.

The multi-gable roof is considered the most difficult and hardly affordable variation for amateur builders. The balanced rafter system effectively withstands even very high loads, while having an excellent "appearance". Since the slope is steep, the risk of snow retention will be minimal. But at the same time, you will have to very carefully calculate all the structural elements, and in the process of work there will be a lot of waste. In addition, the valley will have to survive the impact of a significant amount of snow.

Purpose and types of systems

In the most different systems rafters can be used Mauerlat. The mass of the roof of a house differs depending on the area occupied by the slopes and on the materials used. But in any case, the created load is very solid. When there is a ridge on the structures, a rafter frame must be provided, with its feet resting on the walls. The force is applied in several directions at once, and in the cold season, the accumulation of snow only exacerbates the problem.

Mauerlat aims to eliminate this deficiency and prevent the destruction of the walls. This word means a beam of significant section, which can be both wood and steel. In most cases, they take the same material that was used to form the rafters, but they necessarily achieve the continuity of the strapping or create strong and especially stable joints. They refuse to use the Mauerlat only in log houses or in buildings built using frame technology - and even there they have their own parts that perform a similar task. When it is not possible to make a continuous block, all fragments must be strictly the same length.

The T-shaped roof is characterized by the inset of two wings at a certain angle. Because of this, it is necessary to form a valley. The outer rafters will abut against the support boards. In addition to them, there will also be basic parts directly attached to the wall. To make everything in the valley correspond to the task being solved, wooden elements with a thickness of 3.8 cm are used.The lathing is supposed to be made monolithic, the coating is attached to it with clamps every 50 cm.A typical Mauerlat is three times less thick than the load-bearing wall, and if it is made made of steel, you can slightly reduce this figure.

A reinforcing belt is often equipped under the Mauerlat. This is especially important if you plan to insulate the roof and provide reliable waterproofing. Such a belt is formed from the same mixture that is used to build the foundation. Completely the entire formwork is poured with concrete at one step, the slightest separate layers are unacceptable. In the aerated concrete wall, intermediate jumpers are cut down at the upper line of the blocks - and a practical chute immediately appears. The attachment of the Mauerlat is done either with a knitting wire, or with reinforcing bolts (but they will not help in any way without a reinforcing belt), or with construction pins.

Having dealt with the support for the rafters, you need to find out what they can be, and what is more correct to use to support the roof. Hanging rafters are used if there is no main wall inside the building, their support points are located exclusively on the outer contours.

Such props were in demand during the construction:

• residential buildings with one span;
• production facilities;
• various pavilions;
• attics.

This option should not be underestimated, thanks to engineering developments, suspended rafters are able not to bend, blocking spans of 15-17 m. But it is important to understand that they acquire all their capabilities only in close interaction with other details. You will have to use puffs, and headstock, and crossbars. The simplest truss is made of two beams connected in the upper position, according to the configuration, such a device is close to a triangle. The horizontal connection of the frame parts is provided by tightening (a beam made of wood or metal profile).

Due to the tightening, the transfer of the thrust to the walls is excluded, while the force applied in the horizontal plane is suppressed. The outer walls survive the action of only those forces whose vector is oriented vertically. Builders do not always place a puff at the very bottom, often it is exhibited at the very ridge. When preparing for the construction of an attic, this element is most often placed higher than the base of the rafter legs. Then it will be possible to make a floor, against the ceiling of which you will not have to bang your head for any careless movement.

Hanging rafters for spans longer than 6 m must be reinforced with hangers and braces. In this case, the monolithic tightening is replaced by one assembled from a pair of connected beams. V classic pattern(triangular articulated) lower bases abut against horizontal details. For the system to function properly, the ridge height must be at least 15% of the span of the trusses. The rafters act on the bend, but the tightening does not allow them to move to the sides. To make the beams bend less, the ridge nodes are cut in with the expectation of eccentricity (the occurrence of a bending force opposite in the vector).

Mansard attics are built mostly with triangular arches on three hinges, and the puffs are assigned the function of floor beams. The components of the tightening are bolted by means of an oblique or direct cut. The raised fastening can also be used in the construction of rafters under the attic. The higher it rises, the more the ceiling can be raised. But it is important to remember that at the same time the loads on all elements grow. The transfer of forces is made to the Mauerlat using a movable mount that dampens changes in dimensions from changes in humidity and temperature.

The rafters can be subject to uneven loading as they are higher on one side. This leads to a shift in the same direction for the entire system. You can eliminate such an unpleasant effect if you take out the rafters outside the contour of the walls. Tightening at such a decision ceases to be a support, it transfers either tensile forces (if an attic is arranged), or stretched-bending (when an attic is being built). Hinged arches with the inclusion of a deadbolt differ from the previous version by replacing the sliding support with a rigid support that is identical in function. Due to the change in the type of supports, the type of stresses generated also becomes different, the rafter system turns into a spacer.

The tightening is formed in the upper lobe of the arch. Its purpose is not to endure stretching, but compressive force. An additional tightening, reinforcing the deadbolt, is needed with a significant load. Arches with hangers and struts complement the system of arches with "headstock". Such a system is needed for significant spans (from 6 to 14 m). The braces that correct the resulting bend must be resting against the headstock. Regardless of the specific type of rafter system, it is necessary to carry out all the details and their connections with each other as clearly as possible.

Not always hinged rafters can fulfill the task. Then the nipple elements come to the rescue. This type of rafters is used under hip roofs and under roofs equipped with valleys. Their length is longer than usual. In addition, they become supports for the shortened rafters of the slopes. That is why the overhead rafters have a load of about 50% more than in other structures.

Due to the increased length, it is possible to:

• resist significant impacts;
• form beams without cuts;
• bring parts to a uniform size by pairing boards.

To build hip roof with many spans, the diagonal legs are provided with supports. Such supports are made in the form of standard struts or racks from a bar, or a pair of connected boards. Support through wood lining and waterproofing layer is made directly on reinforced concrete floor... The braces are placed at an angle of no less than 45 and no more than 53 degrees, at the bottom such a part rests on the beds. The angle of installation is less important than the ability to fix parts of the rafters at a point experiencing the strongest stress.

Slant rafters placed in openings up to 750 cm should be supported by struts only in the upper lobe. With a length of 750 to 900 cm, a truss truss or rack is additionally mounted below. And if the total length of the span exceeds 9 m, then for maximum reliability you need to put a stand in the middle, no other support will work. If the selected floor is unable to withstand the load, you will have to reinforce it with a beam. The type of support in the ridge is determined by how many intermediate supports are used, what they are, how the key layered rafters are made.

In addition to the type of rafters, you need to clearly understand their material. Both wooden and metal constructions can be good, but only each in its place. Even the high strength of the metal does not allow us to push aside the usual wood. The tree has confidently proven its advantages over the millennia, and now it is even growing in popularity due to its excellent environmental characteristics. Boards and timber can be bought at an affordable price, and if something was not taken into account, it is always easy to cut off the desired fragment or build up a part right on the construction site.

Sometimes there are problems associated with the operation of the created structures. Wooden rafters will have to be carefully treated with antiseptics, as well as agents that block the development of mold colonies, eating by insects. The combustibility of wood is suppressed due to regular processing, and in addition, it is too difficult to find the necessary components for slopes longer than 7 m. Before installation, the walls are laid with a Mauerlat made from a log frame or based on a block of timber. The thickness of the structures is at least 180 mm, this is the only condition for a uniform distribution of loads.

Metal rafters are inevitably heavier than wooden ones with an identical cross section. Therefore, the walls need to be strengthened, the work on their construction becomes more expensive and longer. It will not be possible to assemble metal blocks manually; lifting cranes will be required. It is impossible or very difficult to adjust the dimensions and geometry of the rafters, therefore, you will immediately have to construct the walls as accurately as possible and eliminate errors in their construction. The slightest mistake can make an expensive block almost useless in practice.

Metal rafters are connected by welding, and welded joints are inevitably weakened, since corrosion develops there accelerated. The cost of the work is very high, and when performing them, it is necessary to comply with the requirements of fire and electrical safety. But there is such undeniable advantage, as an opportunity to support the roof slope from 700 cm and longer. If you use a special anti-corrosion paint, the durability of metal structures is fully ensured. All these advantages make it possible to quickly and comfortably build industrial buildings with significant heights and span lengths.

How to choose: what to consider?

The rafter system should be chosen as correctly and clearly as possible.

When looking for a suitable solution, you need to pay attention to the following points:

• strength;
• the ability to support the slopes and the roof as a whole of a certain size and geometry;
• creating a positive aesthetic image of the building as a whole.

The technical parameters take precedence. Even the most beautiful designs that follow the design principles will not show their positive qualities if they last too little. Experienced builders they always analyze the average annual and seasonal temperatures, the financial capabilities of developers, the maximum possible wind rate and the severity of the overlying roof. The future use of the roof space and the scale required for it are also taken into account. Wind, snow and rain cannot be underestimated, since these factors can have a very strong effect on the roof, and through it on the rafters.

If it is reliably known that a particular area is characterized by heavy snowfall, the minimum slope angle is impractical. This point is even more relevant when using flat roofs. Under the pressure of the accumulating sediments, the frame can rapidly deform or water will pour inward. Another thing is when a certain region is often subject to the arrival of cyclones and the strong winds they bring. Here, the ramp should be made smaller, then the situation with the breakdown of single structural elements will be practically excluded.

You can avoid mistakes if you look at houses that have already been built nearby and have been in use for a long time. By accurately reproducing the structure of their roof and the rafter system interconnected with it, you can the best way take into account local specifics. But not everyone follows this path, sometimes the task is to develop exclusively original project... Then you will have to carefully collect the initial data, carry out scrupulous calculations. In the absence of special knowledge, it is better to attract qualified performers to help.

After analyzing the total load created by wind and snow, you can sometimes find that certain parts of the rafter complex need selective reinforcement. When assessing the required angle of inclination of the roof, attention is also paid to the type of coating used. Heavy metal tile or corrugated board with a very large slope can spontaneously slide down, you have to additionally fix them, complicating your work and increasing the cost of installation. In addition, certain materials have a tendency to retain water or soak in it, which can only be dealt with by making the slope steeper. Creating a good roof and rafter system that meets such conflicting requirements is not always available to the layman.

What does it consist of?

The device of the rafter system, as it is easy to see, is rather complicated and even contradictory. Each part of this structure has a strictly defined role. So, Mauerlat is a long blocks of coniferous wood, and strictly resinous wood is used for work. Such elements are laid out along the external load-bearing walls, attaching to the base with anchors or rods of a special design (threaded). This part transfers the load from the roof to the wall.

This is followed by such a device as a rafter leg. Under this name, a wooden beam appears, used to erect the contour of the slopes. The shape of the structure is always triangular, because it best helps the roof to withstand the destructive effects of winds, snow and other atmospheric processes. Rafter legs are placed at even distances along the entire roof, the step cannot exceed 120 cm.

The bed is of a certain importance for the support of the roof - it is wooden block replacing the Mauerlat in some cases. The beds are placed on the inner support walls. They become the base of the roofing triangle. Thanks to them, the slopes do not creep under their own weight. And it is also worth mentioning about the racks - these are vertical bars with a square section. They perceive the pressure that the ridge knot exerts downward and transmit it mechanically to the inner bearing plane. Sometimes the racks end up under the rafter legs.

The braces are designed to strengthen the entire roof structure, they tie the legs and the legs into one whole. This detail resembles a rhombus in shape. The community formed by the puff and braces is called the farm. In addition to them, you also need a crate, which is a thin board stuffed at right angles to the legs of the rafters. It helps to hold the rafter legs as a single system. Absolutely any roof covering is attached to the crate.

For soft materials, the crate should be made inseparable, and plywood is considered the best tool. At the very top is the ridge, which logically and physically completes the roofing triangle. The connection of a pair of opposed rafter legs is provided by a square wooden beams, which prevents the destruction of the roof as a whole. And at the very bottom of the pitched roof there is an overhang, which is displayed approximately 0.5 m from the perimeter. Thanks to him, the streams of rain leaving the roof do not flood the outer bearing planes and do not harm them.

Fillets are used only in a situation where the rafter legs cannot be performed along the length that would allow organizing the overhang. The connection with low-cut planks effectively solves this problem. For fastening wooden elements of rafters, it is most often recommended to use clamps, staples. It is undesirable to use nails, because the tree pierced by them becomes weak and fragile after a few years. Therefore, if professionals use connections made directly on the construction site, they use bolts.

But even a bolted bond weakens building structures, albeit relatively slightly. The connections are the strongest with the help of clamps or metal staples. Only their industrial production can maximize the quality of products, since only in strictly standardized and fully controlled conditions deviations from norms and deterioration of quality are excluded. It is possible to assemble a truss structure from completely finished trusses very quickly, there is no risk in using it. Another thing is that it is required to collect information about the required characteristics as accurately as possible and transfer it to the manufacturer without distortion.

In addition to the named elements, the rafter system borders on the valley. This is the name of a special compound geometrically complex roof at the points where its trajectory changes. The difference from the ridge is that in such places the roofing parts form a negative angle. The technical essence of the product lies in the fact that the chute helps to drain the liquid aside. The more complex the configuration, the more should be the number of such gutters.

The cornice beam serves to abut the spacers, the other end of which abuts against the frontal board, while the drip is not deformed and its configuration is not distorted. Wind ties are those elements of the rafter system that transfer the load generated by the wind from the roof to the foundation. They not only increase the overall stability of the structure, but also help to avoid its overturning when single parts are unstable. The roof will retain its spatial rigidity even in very strong winds.

Horizontal wind ties are elements such as:

• braces;
• parabolic tightening;
• complexes of conventional puffs;
• trusses complemented by a cross-shaped lattice.

Vertical retention of characteristics under strong air pressure is ensured by wind supports and beams. Sometimes a monolithic reinforcing core is used. Engineers have come up with many other design options for wind communication. It is provided with frames and semi-frames, clamped by supports. In small buildings, rigid (resisting compression) or stretched diagonals are used, some cover two spans at once. The location of each of the elements is accurately reflected in the design documentation.

Qualitative characteristics rafter systems and their composition is not so difficult to understand if you show care and diligence. But it is equally important to calculate the quantitative parameters of these systems. If you do not do this or carry out the calculations incorrectly, you can either spend too much money, or face leaks, even with the destruction of individual elements.

• roof bends;
• average annual snow mass;
• irregularities in its distribution along the slopes, depending on the steepness of the slope and the wind rose;
• wind transfer of already fallen snow;

• the descent of snow and ice masses, runoff liquid water way down;
• aerodynamic performance and windage of the structure;
• differences in the force of impact on individual points.

Calculating everything you need, moreover, simulating realistic situations and laying a reasonable margin of safety in the project is not so easy. Moreover, it is necessary to pay attention to the addition of various loads, to their combined effect. But still, any customer is quite capable of assessing the quality of the designers' work. The loads applied to the rafter systems are divided into three key groups: main, additional and extreme.

The main category includes:

• stable factors - the severity of the roof and rafter structures, additional elements installed on top of them;
• long-term effects - snow, temperature;
• periodically changing factors - complete calculations of snow and temperature effects, taking into account all the subtleties.

An additional group is the pressure exerted by the wind, builders and repairmen, ice and rain. The extreme category includes all natural and man-made emergencies that may occur in a particular place. Their level is forecasted with a margin to guarantee exclusion unpleasant consequences... When calculating the frame roof and the structures under it, the ultimate load is taken into account, in the case of which the entire structure crumbles. Additionally, an indicator or a group of indicators is given, upon reaching which various deformations inevitably appear.

Snow drift rate reflects how much more snow will be deposited on the leeward side and in front of objects (parts) that trap the flow of air. V problem areas you will have to bring the rafters as close as possible and thoroughly calculate the required thickness of the front material. The most accurate assessment of all parameters can be given only by multiplying any obtained figures by the reliability factors. As for the wind, the force it develops is aimed at dropping steep roofs and lifting from the leeward section of a flat roof. We must not forget that the air flow acts simultaneously on facades and roof slopes.

When it hits the facade, the air splits into two waves: one goes down and is no longer of interest, and the other presses tangentially on the roof overhang, trying to raise it. The action on the slope occurs at a right angle, this area is pressed inward. At the same time, a vortex is formed, which tangentially affects the windward sector of the slope. This vortex bypasses the ridge and begins to create lift when applied to the leeward segment. For your information: when calculating the mass of the roof, you need to take into account the severity of the rafters, insulation, waterproofing and vapor barrier.

Standard load for 1 square meter the roof is up to 50 kg, regardless of its size and other significant circumstances. By changing the distance from some rafter legs to others, you can set the actual distribution of loads on them. According to most experts, acceptable values ​​will be from 60 to 120 cm. But on an insulated roof, it is worth choosing such distances that are equal to one sheet or roll of insulation materials. At the same time, it should be borne in mind that among several suitable options for placing the rafters, the one that gives the optimal effect with the minimum consumption of the materials used is preferable.

When calculating the loads carried by the rafters, they always look to ensure that they do not exceed the maximum endurance of the roofing material. After all, there is no point in such an excess. If, with the planned impact, the roof still begins to sag, it is impossible to talk about a solid result. In the calculations, the payload from the structures connected to the trusses of the rafters is calculated according to the area of ​​contact that is plotted on the drawing. Such structures include ventilation chambers, attic and first floor ceilings, water tanks installed on the roofs. In addition to the magnitude of the pressure on the rafter system, the sharpness of the roof slope is also calculated.

Tilt angle: value

On the forums, with the advice of specialists and in professional literature, you can find references to three units of slope measurement at once. In addition to the usual and expected degrees, there will be both percentages and ratios between the parties. Often they get along together even within the same publication or instructions from the manufacturer of roofing materials. But in fact, there is nothing mysterious about this, any consumer can understand the essence. Experts understand the angle of inclination of the roof as the angle that occurs at the intersection of the horizontal with the roof slope.

Obtuse angles in this case it cannot be in principle. Moreover, you can find a slope steeper than 50 degrees only in decorative elements, all kinds of turrets. The only exceptions to the general rule are the ramps on the lower rows of rafters. mansard roof... In all other cases, the angles range from 0 to 45 degrees. The relative aspect ratios are calculated as the ratio between the height of the ramp and its projection onto the horizontal. This figure is equal to half the span for a uniformly constructed roof with a pair of slopes.

On shed roof the proportion is equal to one, and in more complex configurations, you still have to carry out all calculations and estimates yourself, without starting from ready-made values. The draft angle is usually expressed as a fraction, the numerator and denominator are separated by a colon. But when the resulting figures cannot be rounded to whole numbers, it is recommended to use percentages: they simply divide one by the other and increase by a hundred times. Flat roofs are those that have a slope of no more than 5 degrees; a slope of 6-30 degrees is recognized as small, and all other roofs are considered to be steep. Flat design radically increases the usable area and is quite wind-resistant, but you will need to clean it of snow by hand and strengthen the waterproofing to the limit. The slope must be consistent with the specific material, and the required values ​​can be found in the instructions from the manufacturer. To calculate even the most complex and bizarre roof configurations, they are mentally broken into triangles and the angle in each is calculated separately.

Step, length and section of rafters

When it became clear how long the slopes were, what the angles formed by these slopes with a horizontal plane, it was time to start actually calculating the rafters. If the roof frame is made of 5x15 cm timber under the metal tile, the installation step fluctuates from 0.6 to 0.8 m. As the slope increases, the gap also increases. If the roof is tilted at 45 degrees, rafters are required every 800 mm, and for slopes of 75 degrees, another 200 mm can be added.

Next important parameter Is the length of the rafters. It is closely related to the step: if the blocks are made long, they are brought together as close as possible, and when a single piece is shortened, they are pushed apart. When calculating the pitch of the lathing, they proceed from the view of the tiles laid on top and from the fact that an integer number of rows should be laid out on each slope. If you get a fraction, it is better to round, decrease or increase the indicator slightly. The rafter legs under the metal tile, the section of which is 15x5 cm, range from 65 to 95 cm.It is impossible to increase the step when the sheathing is 3x5 cm.

To make the insulation better ventilated, in the area of ​​the upper edge of the rafters, rows of holes with a diameter of 1-1.2 cm are prepared. Ordinary rafters under the corrugated board go every 0.6-0.9 m. with a significant cross section. The lathing under the corrugated board is assembled from boards with dimensions of 3x10 cm, which are placed at intervals of 0.5 m. The interval must be calculated according to the height and thickness of the materials.

With all the revealed shortcomings of slate, it remains widely in demand. Under slate roof rafters with a cross section of 5x10-15 cm are mounted, 60-80 cm apart from each other. Most often, an average distance of 0.7 m is recommended. The pauses between the parts of the sheathing are calculated in accordance with the steepness of the material. In relatively flat areas, the support of 4 pieces of wood pays off. If the roof is steeper, put 3 bars, separated by 63–65 cm.

We must not forget that due to the responsibility of the rafter system, it is better to leave a reserve of strength than to make an unreasonably weak type of rafters. For their manufacture, a bar is used, dried to a maximum of 15%. A substitute for a bar can not serve edged board the same dryness. Under the ceramic tiles, a lathing of a 5x5 cm bar is used. In the places designated according to the calculated distance, nails for slate or simple self-tapping screws are used.

Installation: technology

Roof construction involves the use of a standard range of carpentry tools and an electric drill. If metal structures are used, a grinder is required for precise cutting. Remember that it is impossible to process metal tiles or corrugated board with it, this can lead to damage to the material. Hipped roof without racks, it is done with puffs that strengthen the structure.

In the hip version, it is necessary to strengthen the diagonal runs. Paired boards and a particularly strong beam are taken away to them. The connection points always have a support (post), and main support placed about a quarter of the length that separates the large rafters from the ridge. Under the gables on a gable roof, rafters are always made of shorter length. But under the main part of the four-slope structure, extremely long parts can be placed, even more than 7 m. To keep them securely, they use either a stand that transfers the voltage to the floor, or a truss.

The first step in creating rafters under a sloping roof is the formation of a support complex in the form of the letter P. It rests on the floor beams and is held by the rafter legs. Next, they put three or more runs, two of them are brought out to the corners of the frame, and the rest are placed in the middle of the overlap. The final step in the rafter is to secure the legs. It is advisable to make rafter systems according to a pattern - to connect two boards, which coincide in length with the rafters, and nail to each other with a nail. The template is placed with its edges at the points of attachment of the rafter legs and fixed with a crossbar.

An additional template (this time plywood) will help you make a cutting saw. Farms are attached to the Mauerlat, starting with the extreme ones. In order not to get confused with the point of attachment of the skate, the tops of these trusses are tied with a straight rope. The massiveness of the puffs increases as you approach the ridge. If the rafters are bolted, washers or plates should be used. This will prevent the nuts from sinking into the wood.

How to install rafters with your own hands, see the video below.

Rafters perform a number of significant roofing functions. They set the configuration future roof, perceive atmospheric loads, hold the material. Among the rafter duties, the formation of flat planes for laying the coating and providing space for the components of the roofing pie.

In order for such a valuable part of the roof to flawlessly cope with the listed tasks, information is needed about the rules and principles of its construction. The information is useful both for those who construct the gable roof rafter system with their own hands, and for those who decide to resort to the services of a hired team of builders.

In the device of the rafter frame for pitched roofs, wooden and metal beams are used. Source material for the first option, a board, a log, a bar is used.

The second is built from rolled metal: channel, profile pipe, I-beam, angle. There are combined structures with the most loaded steel parts and timber elements in less critical areas.

In addition to the "iron" strength, the metal has a lot of disadvantages. These include heat engineering qualities that do not satisfy the owners of residential buildings. The need for welded joints is disappointing. Most often, industrial buildings are equipped with steel rafters, less often private cabins assembled from metal modules.

In the case of independent construction of truss structures for private houses, wood is a priority. It is not difficult to work with it, it is lighter, "warmer", more attractive in terms of environmental criteria. In addition, to make nodal connections, you do not need a welding machine and welder skills.

Rafters - a fundamental element

The main "player" of the frame for the construction of the roof is the rafter, among the roofers called the rafter leg. Beds, braces, headstock, purlins, tightenings, even a Mauerlat may or may not be used depending on the architectural complexity and dimensions of the roof.

The rafters used in the construction of the frame of gable roofs, according to technical characteristics and the method of laying, are divided into:

• Fortified rafter legs, both heels of which have reliable structural supports. The lower edge of the layered rafter rests against the Mauerlat or the ceiling crown of the log house. The support for the upper edge can be a mirror analogue of the adjacent rafters or a girder, which is a beam horizontally laid under the ridge. In the first case, the rafter system is called spacer, in the second it is non-spaced.
• Hanging rafters, the top of which rests against each other, and the bottom is based on an additional beam - a tightening. The latter connects the two lower heels of adjacent rafter legs, resulting in a triangular module called a rafter truss. The tightening dampens the stretching processes, due to which only the vertically directed load acts on the walls. The structure with hanging rafters, although it is a spacer, does not transfer the spacer itself to the walls.

In accordance with the technological specifics of rafter legs, structures constructed from them are divided into layered and hanging ones. For the stability of the structure, they are equipped with struts and additional struts.

For the device of the supports for the top of the layered rafters, beams and girders are mounted. In reality, the rafter structure is much more complex than the described elementary templates.

Note that the formation of a gable roof frame can generally be performed without truss structure... In such situations, the supposed planes of the slopes are formed by slugs - beams laid directly on the bearing gables.

However, we are now specifically interested in the device of the gable roof rafter system, and it can involve both hanging or layered rafters, or a combination of both types.

The subtleties of attaching the rafter legs

Fastening the rafter system to brick, foam concrete, aerated concrete walls produced through the Mauerlat, which in turn is fixed with anchors.

Between the Mauerlat, which is a wooden frame, and the walls made of these materials, a waterproofing layer of roofing material, waterproofing, etc. is necessarily laid.

The top of the brick walls is sometimes specially laid out so that something like a low parapet is obtained along the outer perimeter. So it is necessary that the Mauerlat placed inside the parapet and the walls do not burst the rafter legs.

The rafters of the roof frame of wooden houses rest on the upper crown or on the ceiling beams. The connection in all cases is made by cuts and duplicated with nails, bolts, metal or wooden plates.

How to do without furious calculations?

It is highly desirable that the cross-section and linear dimensions of wooden beams are determined by the project. The designer will give clear design justifications for the geometric parameters of the board or timber, taking into account the entire spectrum of loads and weather conditions. If the home master does not have design development at his disposal, his path lies on the construction site of a house with a similar roofing structure.

You can ignore the number of storeys of the building being erected. It is easier and more correct to find out the required dimensions from the foreman than to learn them from the owners of shaky unauthorized construction. Indeed, in the hands of the foreman, the documentation with a clear calculation of the loads on 1m² of the roof in a particular region.

The step of installing the rafters determines the type and weight of the roofing. The heavier it is, the less the distance between the rafter legs should be. For laying clay tiles, for example, the optimal distance between the rafters will be 0.6-0.7 m, and for the profiled sheet, 1.5-2.0 m is permissible.

However, even if the step required for the correct installation of the roof is exceeded, there is a way out. This is a reinforcing counter-grid device. True, it will increase both the weight of the roof and the construction budget. Therefore, it is better to understand the step of the rafters before the construction of the rafter system.

Craftsmen calculate the step of the rafters according to the design features of the building, corny dividing the length of the ramp into equal distances. For insulated roofs, the step between the rafters is selected based on the width of the insulation plates.

On our website you can find, which may also help you a lot during construction.

Roof structures of layered type

The rafter structures of the layered type are much simpler in execution than their hanging counterparts. A reasonable plus of the layered scheme is to provide full ventilation, which is directly related to the long-term service.

Distinctive design features:

• Mandatory support under the ridge heel of the rafter leg. The role of support can be played by a run - wooden beam resting on racks or on inner wall structures, or the upper end of the adjacent rafters.
• The use of Mauerlat for the construction of a truss structure on walls made of brick or artificial stone.
• The use of additional girders and racks where the rafter legs, due to the large size of the roof, require additional support points.

The disadvantage of the scheme is the presence structural elements affecting the layout of the internal space of the exploited attic.

If the attic is cold and it is not supposed to organize useful premises in it, then the layered structure of the rafter system for the device of a gable roof should be preferred.

Typical work sequence for the construction of a layered rafter structure:

• First of all, we measure the height of the building, the diagonals and the horizontality of the upper cut of the frame. If vertical deviations of brick and concrete walls are detected, we eliminate them cement-sand screed... We reduce the excess of the heights of the log house. By placing wood chips under the Mauerlat, vertical flaws can be dealt with if their size is insignificant.
• The overlap surface for laying the bed must also be leveled. He, the Mauerlat and the girder should be clearly horizontal, but the location of the listed elements in the same plane is not necessary.
• We process everything wooden parts constructions before installation with fire retardants and antiseptic preparations.
• On concrete and brick walls, we lay waterproofing for the installation of the Mauerlat.
• We lay the Mauerlat timber on the walls, measure out its diagonals. If necessary, slightly move the bars and turn the corners, trying to achieve the perfect geometry. Align the frame horizontally if necessary.
• We mount the Mauerlat frame. The splicing of the beams into a single frame is carried out by means of oblique cuts, the joints are duplicated with bolts.
• We fix the position of the Mauerlat. Fastening is made either by staples to the ones laid in the wall ahead of time wooden plugs, or anchor bolts.
• We mark the position of the bed. Its axis should recede from the bars of the Mauerlat at equal distances on each side. If the girder rests only on racks without a bed, the marking procedure is carried out only for these posts.
• We install the bed on a two-layer waterproofing. We fasten it to the base with anchor bolts, and connect it to the inner wall with wire twists or staples.
• We mark the installation points of the rafter legs.
• We cut out the racks to the same size, because The bed is on the horizon. The height of the racks should take into account the dimensions of the cross-section of the purlin and the bed.
• We install racks. If provided by the project, we fasten them with spacers.
• We put the run on the racks. Check the geometry again, then install the brackets, metal plates, wooden fixing plates.
• We install a test rafter board, mark the cutting points on it. If the Mauerlat is set strictly to the horizon, there is no need to adjust the roof rafters in fact. The first board can be used as a template for making the rest.
• We mark the installation points of the rafters. For marking, folk craftsmen usually prepare a pair of rails, the length of which is equal to the gap between the rafters.
• According to the markings, we install the rafter legs and fasten them first at the bottom to the Mauerlat, then at the top to the girder to each other. Every second rafter is screwed to the Mauerlat with a wire bundle. In wooden houses, the rafters are screwed to the second crown from the top row.

If the rafter system is made flawlessly, the planks are mounted in random order.

If there is no confidence in the ideal structure, then the extreme pairs of rafters are first installed. A control twine or fishing line is pulled between them, according to which the position of the newly installed rafters is adjusted.

The installation of the rafter structure is completed by the installation of fillies, if the length of the rafter legs does not allow the formation of an overhang of the required length. By the way, for wooden buildings, the overhang should "go out" beyond the contour of the building by 50 cm. If the organization of the visor is planned, separate mini-rafters are installed under it.

Another useful video about building a gable rafter base with your own hands:

Hanging truss systems

The hanging type of rafter systems is a triangle. The two upper sides of the triangle are folded by a pair of rafters, and the tightening that connects the lower heels serves as the base.

The use of a tightening allows you to neutralize the action of the thrust, therefore, only the weight of the sheathing, the roof, plus the weight of precipitation, depending on the season, acts on the walls with hanging rafter structures.

The specifics of hanging truss systems

Characteristic features of hanging rafter structures:

• Mandatory presence of a puff, made most often from wood, less often from metal.
• Ability to refuse to use Mauerlat. The timber frame will be successfully replaced by a board laid on a two-layer waterproofing board.
• Installation on the walls of ready-made closed triangles - roof trusses.

The advantages of the hanging scheme include the space under the roof free of racks, which allows you to organize an attic without pillars and partitions. There are disadvantages.

The first of them is restrictions on the steepness of the slopes: the angle of their slope can be at least 1/6 of the span of a triangular truss, steeper roofs are strongly recommended. The second disadvantage is the need for thorough calculations for the competent device of the cornice nodes.

Among other things, the corner of the truss will have to be set with pinpoint accuracy, because the axes of the connected components of the hanging rafter system must intersect at a point, the projection of which must fall on the central axis of the Mauerlat or the lining board replacing it.

Subtleties of large-span hanging systems

The brace is the longest element of the hanging truss structure. Over time, as is typical for all sawn timber, it deforms and sags under the influence of its own weight.

Owners of houses with spans of 3-5 m are not too worried about this, but owners of buildings with spans of 6 or more meters should think about installing additional parts that exclude geometric changes in tightening.

There is a very significant component to prevent sagging in the rafter system installation scheme for a large-span gable roof. This is a pendant called a headstock.

Most often, it is a bar attached with wooden surfacing to the top of a truss. The headstock should not be confused with the racks, because its lower part should not come into contact with the puff at all. And the installation of racks as supports in hanging systems is not used.

The bottom line is that the headstock seems to hang on the ridge knot, and a tightening is already attached to it with the help of bolts or nailed wooden linings. Threaded or collet type clamps are used to correct slack.

Adjustment of the tightening position can be arranged in the area of ​​the ridge assembly, and the headstock is rigidly connected to it with a cut. Instead of a bar on non-residential attics for the manufacture of the described tightening element can be used reinforcement. It is recommended to arrange a headstock or suspension also where the tightening is assembled from two bars to support the connection section.

In an improved hanging system of this type, the headstock is supplemented by strut beams. The stress forces in the resulting rhombus are extinguished spontaneously due to the competent arrangement of the vector loads acting on the system.

As a result, the rafter system pleases with stability with minor and not too expensive modernization.

Hanging type for attics

In order to increase useful space the tightening of the truss triangles for the attic is moved closer to the ridge. A perfectly reasonable move has additional advantages: it allows puffs to be used as a basis for ceiling filing.

It is connected to the rafters by cutting it with a semi-rotary screw with a duplication of a bolt. It is protected from sagging by installing a short headstock.

A tangible disadvantage of the attic hanging structure is the need for accurate calculations. It is too difficult to calculate it yourself, it is better to use a ready-made project.

Which design is more cost effective?

Cost is an important argument for an independent builder. Naturally, the price of a structure for both types of rafter systems cannot be the same, because:

• In the construction of a layered structure for the manufacture of rafter legs, a board or a beam of a small section is used. Because layered rafters have two reliable supports under them, the requirements for their power are lower than in the hanging version.
• In the construction of a hanging structure, rafters are made of thick timber. For the manufacture of a puff, a material similar in cross-section is required. Even taking into account the abandonment of the Mauerlat, the consumption will be noticeably higher.

It will not work to save on the grade of the material. For the supporting elements of both systems: rafters, girders, bedsteads, Mauerlat, attendants, racks, 2nd grade sawn timber is needed.

For crossbars and tension rods, grade 1 is required. In the manufacture of less critical wooden linings, the 3rd grade can be used. Without counting, we can say that expensive material is used to a greater extent in the construction of hanging systems.

Hanging trusses are assembled in an open area next to the object, then transported assembled upstairs. To lift weighty triangular arches from a bar, you will need equipment, which you will have to pay for rent. And the project for complex nodes of the hanging version is also worth something.

Video instruction on the construction of the hanging category truss structure:

There are actually much more methods for constructing truss systems for roofs with two slopes.

We have described only the basic varieties, which in reality are applicable for small country houses and buildings without architectural undertakings. However, the information provided is sufficient to cope with the construction of a simple truss structure.