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Constructive solutions for wooden rafters. Types of gable roof truss system: for small and large houses. Determining the number of trusses

The rafter system is the basis of the roof; the reliability and strength of the roof, its ability to withstand precipitation and wind depend on it. The design of the rafter system is determined by the shape of the roof and the layout of the house, as well as the materials used. A do-it-yourself rafter system is usually made of wood, but other materials can also be used, for example, a metal profile.

Types of rafters and their application

Choosing a rafter system is a crucial step that requires knowledge of the design of each type of roof. Rafters can be:

1. Layered rafters supported by a ridge girder and a mauerlat. They are used in the construction of a single-pitch roof, a simple gable roof, and also as one of the elements of a hip and sloping roof. mansard roof.
2. Sliding rafters are a type of layered rafters used for wooden buildings, giving greater shrinkage. Their difference is the sliding fastening of the rafters to the Mauerlat, which makes it possible to compensate for the shrinkage of the walls without deforming the roof.
3. Hanging rafters - a system of rafters tied together with crossbars or tie rods, usually used in the construction of a simple gable roof, as well as as the top rafters of an attic roof. In a hanging rafter system, there is no ridge purlin, and in the upper part the symmetrical rafter legs rest directly on each other.
4. Sloping rafters, otherwise called corner or diagonal. They are used to make three-pitched or hipped roofs, as well as for roofs with complex geometry.

Elements of the rafter system

Any rafters are designed to distribute and transfer the roof load to the walls of the house. The main elements on which the rafters rest are:

• Mauerlat is a beam fixed to the upper plane of the walls along the perimeter of the entire house;
• Bedding - support beams laid on internal load-bearing partitions or columns;
• Floor beams of the upper floor;
• Racks and supports;
• Purlins are horizontal supporting elements laid along the axis of the roof on racks.

The roof truss consists of the following elements:

• Rafter legs - boards or timber that form the contour of the roof and are laid at a certain pitch;
• Tightenings or crossbars are horizontal elements that tighten paired rafter legs together;
• Struts - supports placed at an angle and supporting the rafter legs;
• Rabs are boards attached to the lower end of the rafters and forming roof overhangs;

Rafts are short rafters resting on diagonal rafters in a hip roof.

All these elements in private construction are usually made of wood - timber or boards coniferous species, dried naturally. The wood is impregnated with an antiseptic, which extends its service life. The thickness and cross-section of the elements is determined by calculation.

Technology for making layered rafters

1. Before construction begins, it is necessary to sketch the roof and calculate its dimensions. The cross-section and pitch of the rafters, as well as the need to install additional supports and struts, are also determined by calculation.
2. Supporting elements are laid and positioned: mauerlat, floor beams and beams, racks, ridge and intermediate purlins. These operations are described in detail in articles dedicated to various types roofs:
3. Make a rafter template. To do this, take a board with a width corresponding to the estimated length of the rafters, with the same width, but with less thickness - it is lighter and easier to precisely adjust to the location. The board is applied to the installation site of the outer rafter with one end to the ridge girder and the other to the mauerlat.
4. At the top of the template, mark the top notch. The shape of the cut should be such that the board rests on the ridge girder and at the same time fits tightly to the opposite rafter. The depth of the cut should be no more than 1/3 of the width of the board.
5. After cutting out the top cut, the template is once again applied in place and the bottom cut is marked - it should rest on the Mauerlat without leaving large gaps. The end of the template is filed at an angle so that the cut is in vertical plane.

   

6. The resulting template is applied at the installation site of all rafter legs, checking whether adjustment will be needed in place. If the template fits perfectly (which rarely happens), you can immediately make required amount rafter legs. If you need to adjust the bottom cut, then only cut out the templates top part each rafter, and the bottom cut is done in place each time.
7. The rafters are installed at the calculated step. Typically it ranges from 50 to 120 cm and depends on the type roofing, namely on its severity, and on the expected snow load. The heaviest coverings are slate and ceramic tiles, but they are rarely used nowadays. More often, the choice is made in favor of more modern, lightweight and reliable materials: metal tiles, ondulin, soft roof. For them, the rafter pitch can be chosen to be about 100 cm without performing complex calculations.
8. First, install the rafters on the gable side. The rafter leg is supported on the ridge purlin and the Mauerlat and secured to two nails 100-150 mm in each fastening point. Having installed the rafter pair, they additionally fasten it: in the upper part with the help of metal plates and screws on one side and corners with a stiffener on the other, in the lower part with staples or also with corners.

   

9. After installing the rafters from both gables of the roof, string is pulled between them and the remaining rafters are aligned along it. The rafters are fastened in the same way.

   

10. Install struts if the calculation results require it. The struts are made of the same material as the rafters. Attach a board suitable length at the desired angle to the rafters and mark the bottom cut. It is important to consider what the strut will rest on: the floor beam or the beam; the shape of the bottom cut depends on this. After completing the bottom cut, the strut is placed in place and the cutting line along the rafters is marked. The prepared strut is placed between the beams and rafters and secured with metal plates or corners.

Installation of roof struts

Technology for making hip diagonal rafters

1. Since the rafters are for hip roof installed diagonally, the usual methods of fastening them are not suitable. In addition, the load on diagonal rafters is much higher than on layered or hanging ones, so the material for their implementation must have a larger cross-section. You can use timber with a thickness of 100 mm or more, but practice shows that it is more convenient to make these rafters from two folded and fastened boards of standard thickness.
2. The upper end of the diagonal rafters rests on the racks, and the lower end on the mauerlat bars converging at right angles. They are marked in place, and their main feature is that the cuts are made not perpendicular to the plane of the board, but at an angle of 45 degrees. When making rafters from spliced ​​boards, first one side is made with oblique cuts, then the second, in a mirror image.
3. The boards are pulled together using screws, nails or studs. Fasten hip rafters using pads and screws.

The video will help you better understand the basic techniques for constructing a rafter system with your own hands.

When making any rafter system with your own hands, it is important to carefully secure all components and connections and remember that the roof is the main protection of your home from bad weather. Therefore, it is important not only to make a high-quality frame, but also to choose a suitable one, for example, corrugated board, and lay it correctly.

For the manufacture of rafters in individual construction, wooden materials are usually used: boards, timber, logs. Despite their relative cheapness, wooden roof rafters are strong enough to withstand all roofing loads and serve faithfully for many years.

Other possible materials for rafter systems– metal and reinforced concrete – it is not practical to use for private construction due to their heavy weight, complex installation and high cost.

The rafter system must be strong, but not heavy. Of course, for the load-bearing base of the roof of large industrial buildings and high-rise buildings, you have to use metal or reinforced concrete. But for ordinary private houses this is an unnecessary excess. In this case, the rafters are made of wood - from boards, timber (regular or glued), logs.

Logs are rarely used, exclusively for log houses. This material is too heavy, requiring high professionalism from the carpenter and the ability to make complex cuts in the fastening areas.

Timber is the best option from which you can mount strong and durable rafters. The only drawback of the timber is the high price.

Cheaper boards with a minimum thickness of 40-60 mm are often used as a replacement for timber. The list of their advantages also includes low weight, ease of installation and a high margin of safety.

The following requirements apply to the selected lumber:

• The minimum acceptable types of wood are 1-3. The presence of knots is allowed in small quantities (it is better to do without them at all!), no more than three knots, up to 3 cm high, per 3 m.p. Cracks are also acceptable, but they should not penetrate right through the wood, and their length cannot exceed half the length of the material.
• It is allowed to use dried wood with a moisture content of up to 18-22%. If these indicators are higher, the rafters, as they dry, may crack or bend and lose their shape.
• The load-bearing parts of the rafter system are made of material with a thickness of 5 cm and a width of 10-15 cm.
• The length of elements made from coniferous trees is up to 6.5 m, and from hard deciduous trees – up to 4.5 m.
• All wooden parts of the rafters must be treated before use. protective compounds, preventing their rotting, fire and damage by wood-boring insects.

Main parts of a wooden rafter system

The main component unit of a wooden rafter system is a truss - a flat triangular structure. The sides of the “triangle” form rafter legs connected at the top at an angle. To connect the rafters horizontally, tie-rods, crossbars, and clamps are used.

The rafter system is made up of several trusses placed on the mauerlat and fastened together by purlins.

To better understand the specifics of the farm, let’s define its elements. Their composition and quantity in one structure depends on the type of roof, its dimensions and the type of rafters used.

So, the components could be like this:

• Rafter leg- these are the rafters themselves, on which the sheathing is stuffed and laid roofing material. The truss consists of two rafters (beams) connected at the top at the ridge in the form of a triangle. Their angle of inclination equal to angle slope of roof slopes.
• Puff– a crossbar that fastens the rafter legs horizontally and prevents them from moving in different directions under load. Used in a hanging rafter system.
• Rigel- a beam similar to a puff, but working on a different principle. In the system it is compressed, not stretched. Fastens the rafter beams in their upper part.
• Fight– also a horizontal crossbar that connects the rafter beams and increases the stability of the truss. Used in a layered rafter system.
• Rack– a horizontal beam that serves as an additional support for fixing the rafter legs.
• Strut- an element mounted at an angle to the horizontal, giving the rafters additional stability.
• fillies– used to lengthen rafter legs when it is necessary to create overhangs.

Also, the rafter system can include parts that are not directly related to the trusses, but are used for their installation and assembly. They are:

• Run- a beam running along the slopes, connecting the rafter legs of the trusses. A special case is a ridge purlin, which is installed along the roof slopes at its highest point (ridge).
• Lathing- consists of beams or boards placed on the rafters from above along the roof slopes. Roofing material is mounted on the sheathing.
• Mauerlat– timber or boards laid along the perimeter of the external (main) walls of the building. The presence of a Mauerlat is provided for securing the lower ends of the rafters to it.
• Sill- an element similar to a Mauerlat, but laid along the inner wall of the building. Vertical posts are fixed to the bed.

Types of rafter systems

From wood you can assemble many options for trusses and, accordingly, rafter systems. But all of them can be divided into two types: hanging and layered.

Hanging rafter systems

Used for rooms without internal walls. Trusses made up of rafters rest solely on the outer walls; there is no need for additional support. That is hanging rafters cover one span, 6-14 m wide.

An obligatory part of hanging trusses, in addition to the rafter legs connected at the top at an angle, is a tie - a horizontal beam connecting the rafters. The tie becomes the basis of the “triangle” of the truss. In most cases, it is located at the bottom of the structure, connecting the lower ends of paired rafters. But raised-pull designs are also used. And also with its modified version - a crossbar, which looks like a raised tightening, but works on compression, and not on tension, like a true tightening.

The need to use a Mauerlat depends on the presence of the tie and its location in the farm. If the tightening is located at the base of the rafter legs, then the Mauerlat is not needed. During installation, the truss is supported on the external walls through the existing tie, which at the same time becomes a floor beam. If the tie is raised upward or a crossbar is used instead, then the Mauerlat must be included in the diagram as the basis for attaching the rafters to the upper edges of the walls.

Headstocks and struts are used as additional elements in the hanging system. They serve to strengthen the truss when covering wide spans.

Grandma looks like vertical stand, running from the center of the tightening to the top point of the truss (ridge part). In fact, the headstock is a suspension, the function of which is to support a pull that is too long (more than 6 m) and prevent it from sagging.

In tandem with the headstock, with an even greater increase in the tightening length, struts are used - diagonal beams. They are rested with one end against the rafter leg, and the other against the headstock. In one farm, two struts are used, on both sides of the headstock.

In country houses and small private houses, hanging rafters made of wood are good because they allow you to create spacious attic rooms no partitions inside. Of course, we are talking about schemes where there are no struts and headstocks. Their presence imposes on the developer the need to divide the attic into at least two rooms.

Layered rafter systems

Layered design wooden rafters used for rooms with internal capital walls, which serve as additional support for the system. In this case, the distance between the external walls (total overlapped span) can be within 6-15 m.

Rafter trusses necessarily consist of rafter legs supported on the outer walls and a vertical drain supported on the inner wall. If there are two internal walls, two studs can be used in the scheme.

Unlike a hanging system, a layered system must have a Mauerlat to which the rafter legs are attached. The racks crash into a kind of mauerlat - a bench. This is a timber laid on top of an internal supporting wall.

For a span of 6 m or less, the simplest layered truss is used, consisting of two paired rafter legs and a stand. The construction of wooden rafters with an increase in span requires the addition of additional details to the diagram, such as contractions and struts (rafter legs).

Contractions are like puffs in hanging systems, but they are always located above the base of the rafter legs. The main purpose of scrum is to increase the stability of the system.

For stability, struts, also called rafter legs, are also provided. The strut supports the rafter leg, that is, in fact, it becomes an additional (third in a row, after the Mauerlat and ridge girder) support for it.

Layered wooden rafters are the most common for private residential buildings and cottages. As a rule, such buildings have one or more internal main partition walls, which can become a support and additional support for a strong rafter system.

Methods of fastening rafters to the Mauerlat

The attachment point of the rafters to the mauerlat is one of the most important; the functionality of the rafter system and its ability to absorb loads depend on its correct execution.

There are two types of such fastenings: rigid and sliding. The choice of one of them depends on the design of the truss structure. Replacing a rigid fastening with a sliding one or vice versa, as well as insufficient provision of the required degree of shift of the rafter leg, will lead to the fact that the circuit will “break” and will not work.

The rigid fastening ensures a strong, motionless connection between the rafter and the mauerlat. Shift is not allowed, but the rafter can be rotated at the hinge. Such fastening is organized in two main ways:

• by cutting the rafter beam into the mauerlat and further fixing the assembly with corners, staples, nails;
• using metal corners and a support bar.

A sliding fastening (or, as roofers call it, a “sliding fastener”) is of a slightly different type and functionality. It allows rafter leg move relative to the support. Of course, this shift will not be noticeable to the eye, but will allow the rafter system not to deform during the natural shrinkage of the walls of the house. Sliding fastening is especially necessary in the construction of wooden log houses. It is also implemented in the construction of houses of any other type, if required by the design and calculations of wooden rafters.

To provide the rafter leg with a small range of movement relative to the Mauerlat, special fastening elements are used - sliders. Structurally, they consist of two metal elements, the first of which is static, and the second is capable of moving relative to the first. There are two types of sliding mounts: open and closed types.

Crawler open type is a prefabricated structure consisting of two separate parts: a static guide bar and an angle with a bend at the top. The guide is threaded into the bend of the corner and fixed on the rafter leg, the corner is attached to the mauerlat. When changing the geometric dimensions of the building, the guide can move relative to the rigidly fixed corner by 60-160 mm.

Sliding mount closed type its properties are exactly the same. The design changes a little; it is no longer collapsible, but solid. The corner, which is attached to the Mauerlat, has a loop in the central part. A guide is inserted into it, which, in turn, is attached to the rafter leg.

What both fastening options are (sliding and rigid) is shown in the video:

Another the most important node rafter truss - rafter attachment point in the ridge part. In private housing construction, the following fastening options are most often used for these purposes:

• overlap;
• end-to-end;
• using a half-tree cut.

Overlapping fastening is considered the simplest option. The upper edges of paired rafters are simply placed on top of each other. Then a hole is made at both ends and the connection is secured with a pin or bolt and nut.

To make a butt connection, the upper ends of the rafter legs are cut off at an angle to make it possible to align the sawn surfaces. Fastening is carried out using nails, which are driven into the end of the ridge part through both rafter legs. To further secure the nail joint, use wooden horizontal plates or metal plates that are placed over the joint on both sides of the truss.

A half-tree connection involves preliminary cutting out notches at the upper ends of the rafters to half the thickness of the beam. This allows you to combine the rafters in the ridge, like parts of a construction set, without increasing the thickness ridge knot(as happens with an overlap joint). After combining the parts, they are fixed with nails, bolts or dowels.

In addition to the methods described, there are other, less common ones. For example, a tongue-and-groove connection. It is not popular, as it requires great professionalism from the carpenter. The essence of the fastening is that a groove is made in one rafter, and a tenon is cut out on the other. The tenon and groove are combined and fastened with a nail or dowel.

One of the possible connections of the rafters in the ridge (end-to-end, through the ridge purlin) is discussed in the video:

Advantages and disadvantages of wooden rafters

However, working with wood and installing wooden rafters does not present any particular difficulties. In addition, there are other advantages of using wood as a material for rafters:

• low cost of wood;
• universal availability;
• relatively light weight, simplifying installation;
• there is no need to use heavy construction equipment;
• versatility, the ability to be used on buildings made of any material, regardless of the bearing capacity of the foundation.

The disadvantages of choosing wooden rafters are minor, but they also need to be known in person before starting construction:

• need for processing protective equipment, preventing fire and rotting of wood, as well as reducing its “attractiveness” to various insect pests;
• the use of wooden rafters is possible only on spans up to 14-17 m; for wider spans it is recommended to use metal or reinforced concrete;
• slightly reduced service life compared to metal or reinforced concrete trusses.

Thus, all shortcomings are more likely to be features than real ones negative aspects. This explains such a widespread use of wooden rafters in private housing construction.

As a rule, softwood lumber is used.

For various elements and parts of the wooden rafter system, wood of a certain type and grade is used. When using lumber in a rafter-beam system, the following properties and indicators of wood must be taken into account: bending strength, compression, chipping, wood density and moisture content.

Wooden rafter structures must necessarily comply with the special degree of fire resistance of the room. They must be treated with special fire retardants and...

There is a huge variety of options and elements for wooden construction. truss structures. Exist the following types rafter structures: layered or hanging rafters, combined, with ties, etc. The most popular rafter structures are layered and hanging.

To avoid sagging of the entire structure, a horizontal tie is attached to the lower end of the beam using strip steel clamps to support the entire beams attic floor. If the span is up to 12 m, then struts are introduced into the rafter structure, which reduce the estimated length of all rafter legs.

Hanging wooden rafters work in both compression and bending.

Below we consider the types of rafter structures:

1. ordinary hanging rafters
2. double hanging rafters

Not uncommon to increase the entire area attic space in the system of wooden hanging rafters, tie-downs are not used, but struts are used.

Roof Mauerlat

In this case, the rafter legs are cut into the Mauerlat itself. The lower plane should lie on the wall, and in the upper one you need to make certain cuts for proper connection with the rafter legs.

All struts rest against the end of the wooden one. In this case, the loads that would be compensated by the tightening are directly transferred to all walls. As a result, this solution for a wooden rafter system is only possible if there is a special massive construction.

Hanging rafters are parts and elements of rafter structures that are located in the same vertical plane and are connected to each other using notches, bolts, nails, clamps and staples.

There is a combined rafter system - this is the installation of both a layered and a hanging rafter structure, which alternate in turns. Where there are no intermediate supports, hanging rafter systems are used, and where they are present, layered rafter systems are used.

Rafters with tie

Used for spans up to 15 m. Spans of this length require certain intermediate struts, i.e. in special puffs. They are mounted at the height of the building between two rafters and tied together. And longitudinal struts will prevent lateral bending.

Tightening the roof rafters

All structures with retaining wooden beams must be assembled in the form of rafter structures reinforced with special supports that will rest on cross beams and that's all load-bearing walls, as well as in the form of truss systems. The concept of sprengel is structural element according to the type of open triangular rod system, which is attached to the main truss load-bearing structures.

The structural rigidity of this roof is provided by a longitudinal strut or strut. The use of struts reduces the overall load on the entire structure. Vertical struts are usually attached to either racks using notches, trunnions, or steel plates.

Truss hanging timber trusses systems

Sprengel

The entire load from the rafter legs goes to the racks, which transfer it further to the load-bearing main ones. With this design, the load will be distributed between all load-bearing walls. The racks are mounted at the ends of the main load-bearing walls. The lower ends of all racks are secured using hanging pins.

Truss beams are made from solid solid wood or laminated boards. Usually they are small in height. Good and high-quality load-bearing capacity of truss beams is achieved using truss system and wooden beams supporting it.

Shrengel beams can cover huge spans. Sometimes they are equipped with steel belts.

Complex rafter system designs

Available by type roof trusses. Lattice trusses are divided into types according to the shape of their openings: triangular, trapezoidal or parallel belts. Typically, lattice trusses are made symmetrical, but other options are possible, for example,. A common lattice truss includes top and bottom chords, posts and braces.

Reliable and high-quality connection of carriers wooden structures with central supports in one common system called a frame. The racks and beams connected into the frame are necessarily fastened or included in each other. Today there are two main types of frames - double-hinge and three-hinge. Double-hinged frames are equipped with a crossbar that runs across the entire width of the finished frame. Frame data the best way suitable for structures with a small angle of inclination. Tri-hinged frames consist of two equal halves that support each other at the ridge of the roof. Triple-hinged frames are used where more significant angle tilt

Trust the calculations of rafter structures and the final selection of their elements and parts to specialists. Huge loads are applied. In addition to its own weight, it is affected by wind loads, heavy rains, hail, snow and ice. The roof quite often undergoes various

The roof is one of the most important enclosing elements of the house, which must reliably protect the floors from external influences. Service life of the house and its appearance depend on how well the roof is built. Let's look at how you can make your own rafters from boards and other materials.

When making rafter systems, it is extremely important to avoid mistakes, and for this you should listen to the advice given by experienced builders.

The roof is one of the main elements of any structure. This design simultaneously performs several important functions. It is the roof that protects inner space houses from the penetration of wind and precipitation, so it must be reliable and durable.

In addition, the appearance of the entire house greatly depends on the type of roof, that is, this structure simultaneously acts as a decorative element.

There are quite a large number of types of roofs.

Among those that occur most often:

• Single-pitch. This is the simplest option, the construction of which can be completed even by an inexperienced builder. However, such a roof looks too simple, so this type is usually used in the construction of various outbuildings– garages, bathhouses, outbuildings, etc.
• Gable. This option is often used in the construction of private houses and summer cottages. One of the options gable roof is broken or attic. Both of these structures are quite complex, but with a competent design plan, you can cope with the construction of such roofs yourself.
• hip. This design, as well as its variety - hipped roof, are quite complex, therefore, as a rule, their construction is entrusted to professionals. But this roof option is one of the most reliable, able to withstand strong wind loads.
• Cross, hipped, domed roofs have complex design, therefore they are less often used in private construction.

Any roof structure consists of two main elements: the roof and, which, in turn, includes rafters and floor beams. The rafter system is the load-bearing part of the structure, and the roof is the enclosing part.

Materials for making rafters

As already mentioned, they are load-bearing, that is, they must be able to withstand the design loads. Therefore, the material for the rafters must have high performance strength and be durable.

In private construction, wood is most often used to make rafters. At the same time, special requirements are imposed on the material. So, the rafters must be made of first-grade coniferous wood, not have a large number of knots, cracks and be well dried.

Logs of appropriate thickness can be used to construct rafter systems. However, this material is heavy, so roofers do not recommend using it. It is much more convenient to use boards or rafter beams. These materials are easy to install because they are quite lightweight. And this is especially important if you plan to do the work yourself, without the help of professional roofers.

Less commonly used in private construction are rafter systems made of metal. In this case, the structures are more reliable and durable than when using wood. Metal rafters are chosen if it is necessary to increase the rigidity of the roof, as well as in cases where the roof has long spans.

Advice!
If the length of the roof span exceeds 10 meters, then it is recommended to use not only metal rafters, but also replace the Mauerlat beam with a metal channel.
Fastening the rafter legs in this case can be done using welding and metal corners.

However, metal roof trusses are not used so often in private construction, since their installation is quite complicated.

• made of metal are distinguished by their impressive weight, that is, to lift the trusses to the required height and install them, it is necessary to use construction equipment.
• A metal rafter system is more expensive than a similar structure, for the manufacture of which a rafter board was used.

Types of rafters and their sizes

The main types of rafters used in the construction of roofs are hanging and inclined rafters.

Hanging rafters

Hanging rafters are usually called a structure consisting of two rafter legs and a tightening beam that connects them at the bottom. To give the structure the necessary rigidity, additional elements– crossbars, or provide additional supports for each pair of rafter legs.

Another option to add rigidity to the structure is to install struts located at an angle of 45 degrees to the post and resting with the other end on the rafter legs.

Sloping rafters

This design consists of two rafter legs, which rest their ends on the mauerlat. The opposite ends of the rafter legs are laid on a girder beam, which is mounted on racks supported on the internal wall of the house. In some cases, inclined rafters are installed without an internal girder (this is possible if the width of the house is less than 7 meters). In this case, each pair of rafter legs is connected to each other using a crossbar.

Size and section of rafters

To correctly determine the size of the rafters, the following factors must be taken into account:

• Estimated load. Here you should take into account the weight of the future roof, the amount of snow in winter period, wind force.
• Dimensions of spans in the house.
• The slope of the roof, that is, the angle of installation of the rafters.
• Rafter spacing.

Advice!
As a rule, for climatic conditions middle zone, it is recommended to build gable roofs with a slope of at least 30 degrees with a rafter spacing of at least 120 cm.

What relationship exists between the installation step of the rafter leg and its cross-section?

• If you plan to install rafters in increments of up to 300 cm, then it is allowed to use rafter boards with a cross-section of 8×14 or 6×14 cm. You can also take timber measuring 10×12 cm.
• If the step is 400 cm, then material with a cross-section of 8×18 or 6×20 cm is required. When using timber, its size should be 10×16 cm.
• With a pitch of 500 mm, boards 8x22 or beams 10x20 cm are required.

Advice!
If it is necessary to use a material with a smaller cross-section, you need to use additional elements in the design - struts.

Methods for connecting rafters

The choice of method of fastening the rafters depends on what material the house is built from, as well as on the design of the roof.

Fastening can be done:

• Using a Mauerlat.
• By installing rafter bars and tightening.
• Through the beams that make up the floor.
• If the rafters are attached to the log house, then the rafter legs can be attached to the upper crown of the log wall.
• During construction frame houses, fastening to the upper frame of the structure is used.

• To prevent the end of the rafter leg from sliding off the beam and chipping it, a “tooth” connection is used, and the notch should be made at a distance of 25-30 cm from the edge.

Advice!
To correctly carry out the groove-tooth connection, proceed as follows.
They retreat from the edge of the tightening by an amount equal to a quarter of the height of the tightening and draw a line parallel to the edge.
The resulting angle should be divided into two equal parts, and a line should be drawn from the top of the angle to the intersection with the first marked line.
The intersection point of the lines is connected to the underside of the rafter leg, resulting in the outline of a tooth. Now you need to cut out a “nest” in the beam, and a “tooth” in the rafter leg.

• To increase the area of ​​support of the rafter leg on the beam, use a “double tooth” connection. In this case, for the first tooth in the beam, a stop and a tenon are made, and for the second - only a stop.

Advice!
As a rule, the height of the first “tooth” is a fifth of the thickness of the puff, and the second is a third of this value. But some craftsmen prefer to make the “teeth” the same size.

• To give the connection strength, use bolts or brackets for rafters. Since the use of bolts can slightly weaken the cross-section of the rafter leg, the second option is preferable.
• When connecting the strut to the headstock, a nest is made in the latter, and a “tooth” is cut out in the strut.
• If the span is more than 4.5 meters, then the rafters are fastened to the ridge by installing a ridge beam. The beam can be fixed to the top of the rafters; for this purpose, the corresponding corners are cut out in it. An option with lower fastening of the timber is possible, for which small cutouts are made in the rafter legs themselves.
• When constructing a roof with a light roof and small spans, ridge beams may not be installed. In this case, the ends of the rafter legs are overlapped together. Can be used to attach rafter plates.
• To give greater rigidity to a structure that does not include a ridge beam, it is recommended to additionally secure a crossbar between the rafters, under which to place a stand.
• In order to protect the walls and foundation of the building from moisture, the roof is equipped with an overhang. Yes, y wooden houses and log buildings, the overhang size should be no less than 55 cm. This circumstance must be taken into account when assembling the rafters.
  

• If the overhang is large and the beam is laid along the inner edge of the walls, a deflection in the roof may occur. To avoid such a risk, the Mauerlat is laid with some indentation from the inner edge of the walls, and the place of deflection in the structure is leveled by strengthening the board on the “edge”.

conclusions

Construction of a rafter system is an extremely responsible event that requires special knowledge and skills. If you plan to build a roof complex shape, then the preparation of projects and the execution of work should be entrusted to professionals.

Each roof is based on a large number of beams, rafters, posts and purlins, which are collectively called the rafter system. Over the centuries-old history, many types and methods of its organization have accumulated, and each has its own characteristics in the construction of nodes and cuts. Let's 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.

Design of a gable roof truss system

In cross-section, a gable roof is a triangle. It consists of two rectangular inclined planes. These two planes meet at the highest point at unified system ridge beam (purlin).

Now about the components of the system and their purpose:

• Mauerlat is a beam that connects the roof and walls of a building, serves as a support for rafter legs and other elements of the system.
• Rafter legs - they form inclined planes roofs and are a support for the sheathing under the roofing material.
• Ridge purlin (bead or ridge) - combines two roof planes.
• A tie is a transverse part that connects opposite rafter legs. Serves to increase structural rigidity and compensate for thrust loads.
• Lezhny - bars located along the mauerlat. Redistribute the load from the roof.
• Side purlins - support the rafter legs.
• Racks - transfer the load from the purlins to the beams.

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

There are quite a few designs of rafter 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 external walls without intermediate supports(load-bearing walls). For gable roofs the maximum span is 9 meters. When installing a vertical support and a strut system, it can be increased to 14 meters.

The good thing about the hanging type of gable roof rafter system is that in most cases there is no need to install a mauerlat, and this makes the installation of rafter legs easier: there is no need to make cuts, just bevel 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 bursting loads are compensated, the impact on the walls is directed vertically downwards.

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

Gable roof rafter system for small houses

Exists cheap option rafter system when it is a triangle (photo below). Such a structure is possible if the distance between the external walls is no more than 6 meters. For such a rafter system, you can not make calculations based on the angle of inclination: the ridge must be raised above the tie 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 cross-section are taken or the ridge part is cut in such a way as to partially neutralize them. To give greater rigidity, wooden or metal plates are nailed on both sides at the top, which securely fasten the top of the triangle (also see the picture).

The photo also shows how to extend rafter legs to create a roof overhang. A notch is made, which should extend beyond the line drawn from the inner wall upward. This is necessary to shift the location of the cut and reduce the likelihood of the rafter breaking.

Ridge knot and fastening of rafter legs to the backing board when simple version systems

For mansard roofs

Option with installing a crossbar - used when. In this case, it serves as the basis for lining the ceiling of the room below. For reliable operation of a system of this type, the crossbar cut must be hingeless (rigid). The best option- half frying pan (see picture below). Otherwise, the roof will become unstable to loads.

Please note that in this scheme there is a Mauerlat, and the rafter legs must extend beyond the walls to increase the stability of the structure. To secure them and dock them with the Mauerlat, a notch 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 the entire load falls on the rafters, so they need to be taken with a larger cross-section. Sometimes the raised puff is reinforced with a pendant. This is necessary to prevent it from sagging if it serves as a support for ceiling cladding materials. If the tie 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 belays. In this case, too, boards and nails are enough.

For large houses

If there is 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 the tie in one piece, so it is made from two beams. It is connected by a straight or oblique cut (picture below).

For reliable joining, the connection point is reinforced with a steel plate mounted on bolts. Its dimensions should be more sizes notches - the outermost bolts are screwed into solid wood at a distance of at least 5 cm from the edge of the notch.

In order for the circuit to work properly, it is necessary to make the struts correctly. They transfer and distribute part of the load from the rafter legs to the tie and provide structural rigidity. Metal pads are used to strengthen 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 bears a greater load.

With layered rafters

In gable roofs with layered rafters, the ends rest on the walls, and the middle part rests on load-bearing walls or columns. Some schemes push through the walls, some don't. In any case, the presence of a Mauerlat is mandatory.

Non-thrust schemes and notch units

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

The simplest non-thrust rafter system diagram is shown in the photo below. In it, the rafter leg rests on the mauerlat. In this version, it bends without pushing the wall.

Pay attention to the options for attaching the rafter legs to the Mauerlat. In the first, the support area is usually beveled, its length being no more than the 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 are adjacent (but not connected) to one another.

The option with rafter legs fastened at the ridge part is much easier to assemble. They almost never push against the walls.

To operate this scheme, the rafter legs at the bottom are attached using a movable connection. To secure the rafter leg to the mauerlat, one nail is driven from above or a flexible steel plate is placed from below. See the photo for options for attaching rafter legs to the ridge girder.

If you plan to use heavy roofing material, you need to increase bearing capacity. This is achieved by increasing the cross-section of the rafter system elements and strengthening the ridge assembly. It is shown in the photo below.

Reinforcing the ridge assembly for heavy roofing material or for significant snow loads

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

Options for rafter systems with contractions

Installing contractions increases the reliability of the structure. In order for it to work properly, it needs to be secured to them with nails at the places where it intersects with the drains. The cross-section of the timber for the scrum is 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. See the figure below for attaching the screed to the rafters and ridge girder.

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

Layered rafter systems with struts

In these options, for greater rigidity, rafter legs, also called struts, are added. They are installed at an angle of 45° relative 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 brace is simply placed at the required angle to the beams and nailed on the sides and bottom. An important requirement: the strut must be cut accurately and fit tightly to the posts and rafter leg, eliminating the possibility of it bending.

Systems with rafter legs. The top is a spacer system, the bottom is a non-spacer system. The correct cutting nodes for each are located nearby. At the bottom - possible schemes strut fastenings

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°.

Systems with struts are necessary if significant uneven shrinkage of the foundation or walls is possible. Walls can settle differently depending on wooden houses, and the foundations are on layered or heaving soils. In all these cases, consider installing rafter systems of this type.

System for houses with two internal load-bearing walls

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

In these systems, a ridge run is not installed: it provides 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 overlays which are nailed down.

In the upper non-thrust system, the pushing 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 racks, or joints - beams installed diagonally. In the spacer system (in the picture it is below) the crossbar is a crossbar. It is installed above the purlin.

There is a version of the system with racks, but without rafter beams. Then a stand is nailed to each rafter leg, the other end of which rests on the intermediate load-bearing wall.

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

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