Supporting the struts on the bed. Types of gable roof truss system: for small and large houses

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

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

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

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

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

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

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

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

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

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

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

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

Rigid fastening of rafters

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

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

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

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

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

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

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

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

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

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

Step 5 At an angle, select the second slice.

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

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

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

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

Edged board prices

edged boards

Fastening the rafter legs with a stripe of a thrust bar

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

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

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

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

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

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

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

Prices for a set of hardware

set of hardware

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

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

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

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

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

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

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

Sliding support for rafters - dimensions

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

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

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

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

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

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

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

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

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

Scheme - rafters with sliding support and cuts

sliding support prices

sliding support

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

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

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

Rafter rafters - schemes

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

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

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

Prices for metal corners

metal corners

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

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

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

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

Video - Fastening rafters to the Mauerlat, sliding support

Video - Installation of rafters

Video - Assembly of rafters

Video - Quick installation of the truss system

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 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 rigid 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 roof system is the outside part of the roof structure that is supported by the load-bearing structure. It includes a crate and a truss system. The triangle underlying this system should be a rigid and most economical structural element that contains the attachment points for the roof rafters.

The main characteristics of the nodes of the truss system

The main attachment points of the roof truss system are shown in fig. 1. They imply the presence of a rafter leg (Mauerlat - 1), a rafter leg (ridge run - 2), a rack (puffs - 3). The design of the truss system is the main load-bearing element of the roof.

All roof fasteners must be of sufficient strength to eliminate a significant degree of risk associated with roof collapse. The consequences of a mistake made when connecting elements can be the most unpredictable.

Figure 1. The main attachment points of the roof truss system: 1 - mauerlat, 2 - ridge run, 3 - puffs.

First, the rafters are installed on the Mauerlat if the building has brick walls. Similar nodes are provided for concrete blocks, then it is necessary to create a reinforced concrete stiffening belt, and it is necessary to insert studs into its design. Their location should be at a distance of 1 to 1.5 m from each other, and their diameter should be more than 14 mm. The top of the studs must be equipped with a special thread.

Mauerlat is drilled, making holes that are necessary for attaching elements to it. Each of the holes should be the same size as the diameter of the stud, and its pitch should correspond to the distance between the studs. A nut is put on each protruding end of the stud and tightened, which ensures the strength of the connection between the Mauerlat and the wall. The rafters should be connected to the Mauerlat in such a way that their bearing capacity is not weakened.

Description of the main fasteners for mounting the truss system

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

What fasteners fasten metal rafters:

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

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

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

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

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

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

How are the knots connected in the ridge part?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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