Wooden structures device rafters. Types of roof truss systems - their device and design

Rafters serve as the basis of the entire roof structure, and their installation is one of the most important tasks in building a house. The frame of the future roof can be made and installed independently, observing the technological features of roofs of different configurations. We will give the basic rules for the development, calculation and selection of the truss system, and also describe in stages the process of installing the "skeleton" of the roof.

Rafter system: rules for calculation and development

The rafter system is a supporting structure that can resist gusts of wind, take on all external loads and evenly distribute them to the internal supports of the house.

When calculating the rafter structure, the following factors are taken into account:

1. Roof pitch:
   • 2.5-10% - flat roof;
   • more than 10% - pitched roof.
2. Roof loads:
   • constants - the total weight of all elements of the "roofing pie";
   • temporary - wind pressure, snow weight, weight of people who carry out repair work on the roof;
   • force majeure, for example, seismic.

The magnitude of snow loads is calculated based on the characteristics of the climate of the region according to the formula: S=Sg*m, where Sg- snow weight per 1 m2, m- calculation coefficient (depends on the slope of the roof). The determination of the wind load is based on the following indicators: type of terrain, wind load standards of the region, building height.

Coefficients, necessary standards and calculation formulas are contained in engineering and construction reference books

When developing a truss system, it is necessary to calculate the parameters of all components of the structure.

Roof structure elements

The truss system includes many components that perform a specific function:

Materials for the manufacture of rafters

Rafters are most often made from coniferous trees (spruce, larch or pine). For the arrangement of the roof, well-dried wood with a moisture level of up to 25% is used.

The wooden structure has one significant drawback - over time, the rafters can be deformed, so metal elements are added to the supporting system.

On the one hand, the metal adds rigidity to the truss structure, but on the other hand, it reduces the life of the wooden parts. Condensation settles on metal platforms and supports, which leads to decay and damage to the wood.

Advice. When installing a truss system made of metal and wood, care must be taken that the materials do not come into contact with each other. You can use moisture barriers or apply film insulation

In industrial construction, metal rafters made of rolled steel (I-beam, brand, corners, channel, etc.) are used. This design is more compact than wood, but retains heat worse, and therefore requires additional thermal insulation.

The choice of truss system: hanging and hinged structures

There are two types of roof structures: hanging (spacer) and layered. The choice of system is determined by the type of roof, floor material and natural conditions of the region.

hanging rafters rely solely on the outer walls of the house, intermediate supports are not involved. Hanging type rafter legs perform work on compression and bending. The design creates a horizontal bursting force that is transmitted to the walls. With the help of wooden and metal puffs, this load can be reduced. Puffs are mounted at the base of the rafters.

A hanging truss system is often used to create an attic or in situations where roof spans are 8-12 m, and additional supports are not provided.

Rafters mounted in houses with an intermediate column support or an additional load-bearing wall. The lower edges of the rafters are fixed on the outer walls, and their middle parts are fixed on the inner wall or bearing pillar.

Installation of a single roofing system over several spans should include expansion and layered roof trusses. In places with intermediate supports, layered rafters are mounted, and where they are not, hanging ones.

Features of the arrangement of rafters on different roofs

Gable roof

The gable roof, according to building codes, has an angle of inclination up to 90 °. The choice of slope is largely determined by the weather conditions of the area. In areas where heavy rainfall prevails, it is better to install steep slopes, and where strong winds prevail - gentle roofs in order to minimize pressure on the structure.

A common version of a gable roof is a design with an angle of inclination of 35-45 °. Experts call such parameters the "golden mean" of the consumption of building materials and the distribution of the load along the perimeter of the building. However, in this case, the attic will be cold and it will not be possible to equip the living room here.

For a gable roof, a layered and hanging truss system is used.

hipped roof

All roof slopes have the same area and the same angle of inclination. There is no ridge run here, and the rafters are connected at one point, so the installation of such a structure is quite complicated.

It is advisable to install a hipped roof when two conditions are met:

• the base of the building is square;
• in the center of the structure there is a bearing support or wall on which it will be possible to fix a rack supporting the junction of the rafter legs.

It is possible to create a hipped roof without a rack, but at the same time, the structure must be strengthened with additional modules - rack puffs.

hip roof

The traditional design of the hip roof involves the presence of slanting rafters (diagonal) directed to the corners of the building. The angle of inclination of the slope of such a roof does not exceed 40 °. Diagonal runs are usually done with reinforcement, since they account for a significant part of the load. Such elements are made from a double board and a durable beam.

The joints of the elements are necessarily supported by a rack, which increases the reliability of the structure. The support is located at a distance of ¼ of the length of the large rafters from the ridge. In place of the gable roof gables, shortened rafters are installed.

The truss structure of a hipped roof may include very long diagonal elements (more than 7 m). In this case, a vertical rack must be mounted under the rafters, which will rest on the floor beam. Sprengel can be used as a support - the beam is located in the corner of the roof and is fixed on adjacent walls. The sprengel farm is reinforced with struts.

broken roof

Sloping roofs are usually created to equip a larger attic. The installation of rafters with this version of the roof can be divided into three stages:

1. Installation of a U-shaped structure - supports for purlins that hold the rafter legs. The base of the structure is floor beams.
2. At least 3 runs are installed: two elements pass through the corners of the U-shaped frame, and one (ridge run) is mounted in the center of the attic floor.
3. Installation of rafter legs.

Gable roof: do-it-yourself installation of rafters

Calculation of the angle of inclination and loads

The calculation of a gable roof, of course, can be done independently, but it is still better to entrust it to professionals in order to eliminate errors and be sure of the reliability of the structure.

When choosing the angle of inclination, it is necessary to take into account that:

• an angle of 5-15 ° is not suitable for all roofing materials, so first choose the type of coating, and then make the calculation of the truss system;
• at an angle of inclination over 45 ° - material costs for the purchase of the components of the "roofing pie" increase.

Snow load limits range from 80 to 320 kg/m2. The design coefficient for roofs with a slope of less than 25° is 1, for a roof with a slope of 25° to 60° - 0.7. This means that if 140 kg of snow cover falls on 1 m2, then the load on the roof with a slope at an angle of 40 ° will be: 140 * 0.7 = 98 kg / m2.

To calculate the wind load, the coefficient of aerodynamic influence and wind pressure fluctuations are taken. The value of the constant load is determined by summing the weight of all components of the "roofing cake" per m2 (on average - 40-50 kg/m2).

Based on the results obtained, we find out the total load on the roof and determine the number of rafter legs, their size and cross section.

Installation of Mauerlat and rafters

Do-it-yourself installation of rafters begins with the installation of a Mauerlat, which is fixed with anchor bolts to the longitudinal walls.

Further construction of the structure is carried out in the following sequence:

Installation of rafters: video

Ways to connect the elements of the truss structure: video

The gable roof, thanks to its simple, reliable and presentable design, has been popular for many years. Depending on the slope of the slopes, it is used in regions with different amounts of precipitation. The truss system of the gable roof provides natural rainfall.

1. Symmetrical - both slopes have the same length and are mounted at the same angle. Such a roof is an isosceles triangle with an obtuse or acute angle.
2. A sloping roof is created to accommodate an attic room, its truss system implies a complex, two-level structure.
3. Different angles of the slopes are an original design that emphasizes the unusual architecture of the house.

Tilt angle value

The angle of inclination is selected after analyzing several indicators: the type of roofing, rainfall, wind load. For regions with heavy rainfall, a small slope angle is recommended, but not less than 5 degrees. Snow masses do not linger on a steep surface. Sloping roofs with an obtuse angle of slopes are suitable for windy climates.

The gable roof truss system must comply with accepted safety standards and be built according to standards.

Rafter systems

Bearing elements and rafters take on the load from external forces and redistribute it to the walls of the building. The strength of the entire roof depends on their reliability. When constructing a structure, two rafter systems are used:

• Hanging - rafter legs have two points of support on the walls of the building. They are subjected to compressive and flexural loads. For span distances exceeding 8 meters, a headstock with struts is required. To reduce the impact of the rafters on the walls of the building, they are connected with a puff.
• Layered - these bars are supported by an inner wall or a special design.

If it is impossible to use one of the systems in its pure form, they resort to a hybrid design that allows you to alternate between hanging and layered rafters.

The device of the gable roof truss system allows you to carry out calculations yourself, based on knowledge of geometry. To calculate the area of ​​\u200b\u200bthe structure, you need to set the length of the slope. The amount of material needed depends on the angle of inclination. An acute angle allows you to save money, but at the same time minimizes attic space.

We calculate the height of the ridge, the length of the rafters and the area of ​​​​the roof using geometric formulas. Suitable for visualization scheme Houses. Example - let's take the slope angle of 45 degrees, the width of the house (the base of the isosceles triangle) is 6 m, the length is 10 m.

First, we divide the triangle in half with the height lowered from the top corner. It turns out two right-angled triangles, and one of their legs is the desired roof height. The height divides the isosceles triangle in half, which means that one leg is 3 m. The second is calculated by the formula:

3 × tg 45 0 \u003d 3 m.

Knowing the legs, using the Pythagorean theorem, we calculate the hypotenuse, which is the rafter:

3 2 + 3 2 = X 2 .

The length of the rafter will equal the square root of 18, approximately 4.25

The number of rafters is calculated by dividing the total length by a step (0.6 m):

10: 0.6 \u003d 16.6 - this value must be doubled.

We calculate the area by multiplying the length of the slope and the house and multiplying the value by 2:

4.25 × 10 × 2 \u003d 85 m 2.

The supporting base for the roof is a Mauerlat - a durable bar with a section of 150 × 150 mm made of treated coniferous wood. Its fastening is carried out on anchors walled up in the upper row of masonry. They should rise 2-3 cm above the timber to provide room for tightening the nut. A layer of roofing material is laid under the Mauerlat to protect it from moisture. A transverse beam is laid between the walls, fastening the Mauerlat and protecting it from longitudinal loads. To maintain the ridge, a special beam is laid along the slope - a bed, with a cross section equal to the Mauerlat. With a significant width of the building, the installation of runs is necessary.

The cross section of the rafters is determined by the pitch and length of the rafter element, usually these are boards 50 × 150 mm. Rafter trusses are easier to assemble on the ground and ready to be fed to the roof. For the template, two boards are taken, equal in length to the rafters, and connected with a nail. The free ends are laid on supports, the resulting angle is fixed with a crossbar. The places and shape of the cuts are marked with a second template made of plywood. The beams are fastened at the right angle with bolts, cuts are made on them, and after the truss they are lifted up for installation.

The rafters on the gables are installed first. They are attached to the Mauerlat with the help of corners or brackets. The first farms are set strictly according to the level. A cord is stretched between them, which is a guide for installing the remaining elements.

To give sufficient rigidity to the entire structure, struts and crossbars are attached to the rafter leg. The ridge run is bolted to each roof truss. This connecting element must be made of durable timber.

With a significant width of the building, it is necessary to install runs, this is a horizontal beam measuring 50 × 150 mm supporting the rafters. For its installation, vertical racks are installed, based on a bed. These elements will form the basis of the frame for the attic space.

To avoid water flowing onto the walls, it is necessary to provide for an overhang; for this, the rafters are made hanging by 30 cm or additional “filly” boards are attached.

A crate is stuffed onto the finished rafters, the required pitch is selected for each roofing material, and a continuous flooring is made for bituminous tiles. Roof insulation is an important part of construction. You can reduce heat loss to a minimum by correctly laying the insulation. For this, basalt wool is taken, the width of the material is equal to the step between the rafters, which allows you to quickly and reliably perform insulation. Laying waterproofing will help to ensure reliable protection of the roof from moisture.

The symmetrical gable roof model is the easiest to build and most reliable option in operation. The load in the truss system is distributed evenly, which allows you to extend the life of the structure. Visual video lessons will help to master the intricacies of work.

Video

This video explains how to build a gable roof truss system:

In this video you can see the truss system using one gable roof as an example:

The truss system of any object is equivalent to the value of the load-bearing structural elements of the house. The roof plays the role of a node under which the stiffening ribs of the building are assembled. Accordingly, when installing the roof with your own hands, it is required to give the maximum value to all structural units, even when using a simple option - gable.

Advantages of gable roofs

There are a lot of options for pitched truss systems. Among them, simple symmetrical is especially popular. Why? Here are her virtues:

• On the basis of a gable roof, variations are created to reflect the special architecture of the building.
• Simple calculations, easy to understand.
• The one-piece design creates favorable conditions for the dryness of the internal space and the unhindered flow of water, snow and ice.
• The maintainability, strength and durability of a gable roof are much higher than other options.

Depending on the size, homeowners always have the opportunity to equip the under-roof space, make it a full-fledged floor or attic. In a word, a gable roof is the right and profitable solution for any object, whether it is a residential building, a summer house or a bathhouse.

Elements of the truss system

Depending on the type of roof, structural elements vary. Without knowledge of the appointments of each, it is impossible to arrange a reliable coverage at home. Let's analyze in detail:

Mauerlat

The basis of the truss system. It is a beam with a section of at least 150 mm, or an I-beam channel, if the roof structure is metal. It is located on the bearing walls of the object. Its purpose is to distribute the load of the system evenly throughout the structure of the house.

Rafter leg

Structural basic unit of the system. Together with others, it forms a truss system - strengthening the strength of the entire roof. It is made of a wooden beam, which is not inferior in cross section to Mauerlat or profile pipes.

Rafter rack

Vertical bar or pipes. Depending on the variant of the gable roof, the pillars can be located in the center and / or on the sides. They take part of the weight of the entire truss system, which is why the cross section is 150 mm.

Rafter girders

Horizontal beams laid on racks and under the ridge to support the rafter legs. They provide structural rigidity and relieve stress on trusses.

Puffs and braces

Connecting beam for rafters. The action is similar - relieving the stress of a beam or metal and making the structure rigid.

lying down

Mounting support for racks and struts. To securely connect these two elements, you need a large cross-section beam - 150 mm or a thick-walled pipe of impressive diameter.

Lathing beam

Elements laid perpendicular to the rafters. Serve to install the selected roofing and create a multilayer protective cake. The cross section is small - 40–50 mm.

If the conceived roof structure is made of wooden beams, you should carefully consider the quality of the wood upon purchase - the beam should not have interspersed knots, be made of soft woods.

Also, wood must have natural moisture, otherwise it will begin to dry right in the system structure, cracking, deforming the roof model, depriving it of reliability and safety.

Calculation of the truss system

A gable roof is a complex structure. The project takes into account many factors - natural nuances, wind, constant and variable loads. It is extremely difficult to make calculations on your own, without special knowledge about the climate of the area, the characteristics of the material for the manufacture of the system, and the nuances of pressure distribution.

Ideally, the calculations are at the mercy of professionals, you can independently choose only the material for coating - the following parameter depends on its type:

Tilt angle

The minimum angle of inclination of the roof relative to the parallel of the earth is 5 degrees. However, its dependence comes from the chosen roofing material. In this capacity, traditional slate, profiled sheet, flexible and metal tiles are used.

They are guided by the following rule: the steeper the slope, the more textured the roof can be.
From 5 degrees for laying rolled protective insulation of the roof. The number of layers matters - up to 15 degrees three-layer coatings, above - two- and single-layer coatings.

• From 6 - ondulin.
• From 11 - slate.
• From 12 - corrugated board.
• From 14 to 20 - metal tiles.
• From 15 to 45 - soft roof.

Thus, the resulting precipitation - snow, water - will not linger on the surface, although complete cleaning requires one's own efforts or the involvement of specialists for the installation of the Anti-Ice system.

Determining the parameters of the rafters - step, length, section

The rarer the step, the more impressive the cross-section of the beam or the diameter of the pipes should be. As a rule, for load-bearing structures, this parameter is at least 150 mm, 100 mm - for country houses and related construction - gazebos, bathhouses, outbuildings.

Next, you need to set the number of rafters per slope: its length is divided by the installation step, which is from 60 to 100 cm + 1 extreme leg. Multiplying the result by 2 gives the total. Depending on the section of the beam, the amount of rafter legs and the installation step vary.

The length of the rafters is simply calculated if the school knowledge about the right triangle is left in the luggage. The rafter leg is equal to the hypotenuse of the resulting figure. The calculation is as follows: A² + B² = C², where - A is the height of the roof, B is half the length of the pediment, C is the length of the rafter leg. To the resulting value is always added from 30 to 70 cm for cornice overhangs.

Types of truss systems

Before getting down to work, it is important to choose a truss system option for a gable roof. There are few of them, each has its own advantages and disadvantages:

hanging

Suitable only for a standard roof width of 6 m, respectively, this is the length of the rafter leg. Fastening occurs by fixing the ends to the ridge run and the bearing wall. Be sure to install a puff that levels the stress and pressure of the structure.

In addition, they will play the role of load-bearing beams. Without them, the structure will disperse under weight. The advantages of the option are in the absolute dryness of the roof surface during the off-season, and in less deformation at the time of shrinkage.

Layered

The option is suitable for any roof width. Reliability and stability is ensured by fixing the bed to the Mauerlat. Thus, the pressure is leveled by the rack, which reduces the tension in the rafter legs. The advantage of the system is simplicity, but the design requires large investments - additional lumber is required to equip the beds.

hybrid

These systems are typical for multi-pitched roofs, where transitions are accompanied by numerous reinforcements, beams, posts, beds, slopes and other elements for the stability of the entire structure. The device is expensive and complicated, so only a professional should deal with the project and construction. At least curate it.

Do-it-yourself installation of a gable roof

So, when the option of the truss system is selected, lumber is purchased, a roof project is drawn up, you can get to work. You cannot deviate from the sequence of steps. This threatens to delay installation and loss of structural reliability.

Mauerlat mount

If the length of the beam for installing the Mauerlat is insufficient, an extension is made. Using the half-tree cutting method, the ends are connected. Additional fasteners are anchor bolts. Do not use self-tapping screws, dowels or nails - they are unreliable. Mounting to the wall is as follows:

• There must be a margin of at least 5 cm from the edge.
• Holes are drilled along the wall for inserting fasteners. Similar actions are carried out with a bar.
• Mauerlat is attached to the edge with steel studs. The fastening step is more often 2 times than the distance between the rafter legs. Subsequently, before installing the main units, they are guided by metal marks.

Important - before laying the Mauerlat, the edge of the wall is protected with waterproofing. Spread one layer even if the house is made of wood.

Making and fixing rafters

Roof trusses are convenient in that they can be assembled on the ground into a finished structure and moved to the roof. This will reduce installation time, however, the model is heavy and lifting equipment will be required, which, of course, will increase the cost of the project.

For budget construction, another method is suitable:

• At the bottom and top of the rafter legs, a gash is made to attach to the Mauerlat and the ridge run. This must be done separately with each unit, after lifting the wood up.
• Places for fixing are marked on the Mauerlat and a ridge run is installed: racks are installed along the gables, on which a beam is placed. If the length is not enough, it is increased, but in a different way, unlike the Mauerlat - a board is screwed to the junction from both sides.
• Depending on the chosen model of the truss system - layered, hanging - they make cuts in the ridge beam, Mauerlat or drill holes in them for fasteners.
• Next, begin the installation of rafter legs from opposite ends of the roof, gradually moving towards the middle. Between the corners of the extreme trusses, it is not bad to stretch the cord to exactly match the entire horizontal part.
• Between themselves, the rafter legs are connected by puffs and struts. Under the ridge part, at the angle formed by the rafters, wooden linings are stuffed, and the ends themselves are tightened with bolts.

More recently, professional builders have begun to use sliding fasteners for roof installation. Metal plates securely hold the bearing elements and at the same time move due to shrinkage. This cancels out its effects.

The work of fixing the rafters is hard and long. You should calculate the time in advance - you can not leave the roof unfinished during the rainy season, otherwise the rigidity of the structure will be lost in the future due to absorbed moisture.

Gables and framing

The side parts of the roof - gables, are made in the form of ready-made shields from boards and are completely installed at the top. Difficulties should not arise - it is only important to carefully file them at the required angle. It is necessary to fasten the crate only after the final appearance of the roofing is known. For example:

• Under the corrugated board, the step of the crate beam will be 440 mm.
• The metal tile is fastened to the crate in increments of 350 mm.
• A soft roof needs a solid plywood coating.

It is important to note the places for the passage of the chimney - the crate should not come into contact with a brick or metal surface. The distance to the hot unit is at least 15 cm. Before installing the lathing, the finished roof is covered with waterproofing with allowances extending beyond the edges of the walls. Then the beam is mounted.

If it is decided to make an insulation cake from above, then first the vapor barrier is strengthened from the inside, then the selected material is put into the boxes formed by the rafter legs. Next, waterproofing and wind protection.

Then it is required to re-mark the contours of the rafter legs with a bar 20 * 20 and then fill a new layer of the crate, along which the laying of the roofing material will take place - the formation of ventilation ducts. This method will save the capacity of the under-roof space if the owners are going to use it for a specific purpose.

Roofing material flooring

Regardless of the type of roofing raw material, installation starts from the edges of the roof and leads it up, overlaying one unit on another. Thus, rain moisture will not get under the material.

The method of fastening depends on the type of material - soft tiles or tiles with a bitumen or polymer base are fused. Solid profiled sheets - ondulin, metal tiles - are fixed in pre-drilled holes to the crate, using rubber pads to seal and preserve the anti-corrosion layer.

As a result: the description of the installation of the truss system and the roof is easy only on the screen or paper. In reality, the process is complex and multifaceted. Therefore, if knowledge is not enough, it is better to invite professionals to work - their work is always guaranteed.

Almost any modern roof of a low-rise building is built on a frame truss system. In theory, the roof device can be made in the form of a flat ceiling. But the simple manufacture of the construction of such a roof is leveled by a mass of shortcomings, a thorough increase in the heat-insulating layer and the provision of forced removal of snow and rain-melt water will be required. Even in the construction of garages or outbuildings, such a roof device is resorted to in extreme cases, preferring a more complex truss option.

Why truss systems are so popular

The truss system appeared as a result of natural selection among many different options for building a frame. The modern device of the roof truss system is based on several basic structural elements:

• Rafter frame, which is a set of beams of the same length, forming the plane of the roof slope. The rafters are laid symmetrically with a “hut”, with the upper edge on the highest horizontal part of the frame - the ridge run, and rest on the Mauerlat - a thick board sewn onto the upper horizontal plane of the brick box of the building;
• The base or fastening system on which the truss frame rests consists of a mauerlat, beams and ceiling beams on the upper part of the walls of the building. Thanks to this device, the load from the weight of the roof and rafters is redistributed, leveled and transferred to the internal and external walls of the house;
• Roofing lathing, together with additional power elements - struts, spacers, crossbars, serves to give additional rigidity to the rafter beams.

Note! In addition, the basis for laying the roofing is formed from the boards of the crate.

Pine logs and beams are traditionally used to construct the roof truss system of a low-rise building. This makes it possible to provide a light and at the same time rigid roof structure. Attempts to replace a wooden beam with a steel profile lead to a weight and cost of the rafter system at least two to three times heavier, and due to numerous cold bridges, an additional layer of thermal insulation will need to be laid.

One of the most popular truss systems is a device in the form of a two or four-pitched roof with a pair of rafters. In this case, the frame of symmetrical power elements perfectly perceives the load in the vertical and transverse directions in relation to the ridge run.

If the predominant direction of the winds in a given area is approximately the same, then the longitudinal force on the roof device arising from the air flow is most often compensated by folding the pediments of brick. With a strong and changeable wind, it is more rational to use a four-slope hip design.

The device and features of the truss system

It is clear that the use of truss technology is aimed at forming roof slopes with the most rational slope angle for a given area. The steeper the angle of inclination, the faster and easier it is to remove rainwater and snow.

To assess the load, you can use the information of the meteorological service on the thickness and maximum pressure of a layer of snow per square meter of a flat roof for various regions of the country.

For the rafter system, the load on the elements of the truss system is reduced, based on the angle of inclination of the roof slope:

1. For options with a slope angle of up to 10-20 o, the decrease in the pressure of the mass of snow is extremely insignificant, on average, a force of 80-90% of the value for a flat surface falls on a low roof;
2. For roof slopes installed at a slope of 25 °, the load will be 70% of the “flat” value, while for an angle of 65 °, the snow pressure will decrease by 70-80%;
3. On steeper slopes, pressure is not taken into account at all; in this case, the strength of the truss system is calculated based on the wind load.

Important! Even a small one-story house, with a roof slope of 45o, located in central Russia, with a high level of precipitation receives an additional load from snow, reaching 5 tons.

Therefore, even in small cottages and houses, a log or timber with a cross section of at least 100-150 mm is used as a material for the construction of the truss system.

Types of truss systems

The design of the rafter system of the roof frame is most often carried out according to the scheme with hanging or layered rafters. The use of a particular scheme is determined by many factors, among which the size of the house and the ceiling, the presence of internal walls or partitions, the nature of the use of the attic space play a decisive role.

The main differences between layered and hanging rafters are as follows:

In the case of a free landing of the end of the rafter on the ridge run, each pair of gable roof beams is not fastened together, but cuts in a sliding pattern. In the lower part, the rafter legs are attached to the Mauerlat in the form of a rigidly fixed hinge, using a bolted connection or nails. Under load, such a device works like a non-thrust rafter system, due to the fact that any vertical or lateral force on the truss system does not lead to the appearance of horizontal bursting forces at the reference points on the Mauerlat.

Important! An important feature of such a frame device is the minimal bursting effect on the walls of the house, which is extremely important for wooden houses made of timber or logs. But the practical assembly of such a design requires the most accurate and careful observance of the dimensions and accuracy of the installation of elements.

In the second case, the layered beams on the ridge run are rigidly fastened with reinforcing plates made of metal or board, much like in the case of hanging rafters. The lower edge is mounted on a power plate with a cutout on the rafter of the supporting surface and side guides that prevent the board or beam from twisting.

Rafter system nodes

To ensure the necessary strength of the rafter device, especially for buildings with spans of more than 8-9 m, it is required to use logs and beams of considerable thickness, which makes the assembly of the roof frame very difficult and expensive. It is easier and more efficient to install additional power elements that compensate for the deflection or transfer the main part of the force to the less loaded parts of the frame.

For example, to compensate for the deflection of the rafter leg, two main elements are used - struts and vertical racks. Depending on the design of the truss system, power racks can be installed in the central part and support the ridge run, taking on part of the load from the weight of the frame. Elements can be combined with struts in the middle of the rafters, thereby transferring the load from the side girders to the tightening or laying - longitudinal beams resting on the ceiling or internal main walls. The struts do not cut into the body of the rafters, but are fastened with nails, bolts, self-tapping screws through steel plates or wooden lining.

The second most popular element for reinforcing hanging rafters is or a raised puff. This element allows you to reduce the horizontal bursting action of the rafter legs and the entire system, unlike the previous ones, it works in tension, so the device is attached to the side surface of the rafters using a tricky self-tightening knot called a semi-pan.

For layered rafters, a similar element is used, called a scrum. If the frame device, the length and thickness of the rafters do not provide the proper stability of the triangle, in this case it is necessary to install an additional horizontal strut - scrum. This method of reinforcing the system is effective in counteracting uneven asymmetric loads, such as heavy slanting downpour or sharp gusts of wind.

To obtain a long ceiling beam or puff, more than 8 m long, it is often necessary to splice two six-meter pieces according to the scheme shown in the figure.

One of the problems characteristic of hanging rafters with a long span can be a deflection in the center of tightening of the base of the ceiling. In this case, they resort to a suspension or headstock device. Despite the external similarity with the rack, this element works in tension, so its cross section can be much smaller. When installing the headstock, it is necessary to provide a tensioning device that allows you to select gaps and even out the tightening deflection.

The fastening of the elements of the truss system in nodes and joints, as a rule, is carried out using nails 150-200 mm, hammered at different angles and distances from the edge of the beam. On the reverse side, the nail is bent with a twist. Such a fastening device avoids the effect of "self-pulling" of the nail from landing in a log or beam. If a beam is used in the rafter system, it will be most convenient to connect using overhead steel profiled plates, corners and holders.

In some cases, the use of such devices allows you to perform a temporary or preliminary assembly of truss beams on self-tapping screws, accurately measure the dimensions and places of cuts, and only after that make capital fasteners.

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

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

In the device of the truss frame for pitched roofs, wooden and metal beams are used. The starting material for the first option is a board, log, beam.

The second is constructed from rolled metal: a channel, a profile pipe, an I-beam, a corner. There are combined structures with steel most loaded parts and wood elements in less critical areas.

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

In the case of self-construction of truss structures for private houses, wood is a priority. It is easy to work with it, it is lighter, “warmer”, more attractive in terms of environmental criteria. In addition, nodal connections do not require a welding machine and welder skills.

Rafters - a fundamental element

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

The rafters used in the construction of the gable roof frame are divided into:

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

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

For the arrangement of supports for the top of the layered rafters, beds and girders are mounted. In reality, the truss structure is much more complicated than the elementary patterns described.

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

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

Subtleties of fastening rafter legs

The rafter system is fastened to brick, foam concrete, aerated concrete walls through the mauerlat, which in turn is fixed with anchors.

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

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

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

How to do without furious calculations?

It is highly desirable that the cross section and linear dimensions of the wooden beams be determined by the project. The designer will give clear calculation justifications for the geometric parameters of the board or beam, taking into account the entire range of loads and weather conditions. If there is no home design development master at his disposal, his path lies on the construction site of a house with a similar roof structure.

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

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

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

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

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

Rafter structures of layered type

Rafter structures of the layered type are much simpler in execution than their hanging counterparts. A justified plus of the layered scheme is to provide full ventilation, which is directly related to the longevity of the service.

Distinctive design features:

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

The minus of the scheme is the presence of structural elements that affect the layout of the internal space of the operated attic.

If the attic is cold and the organization of useful premises is not supposed to be in it, then the layered construction of the truss system for the installation of a gable roof should be preferred.

A typical sequence of work on the construction of a layered truss structure:

• First of all, we measure the height of the building, the diagonals and the horizontalness of the upper cut of the skeleton. When identifying vertical deviations of brick and concrete walls, we eliminate them with a cement-sand screed. Exceeding the heights of the log house we squeeze. By placing chips under the Mauerlat, vertical flaws can be dealt with if their magnitude is insignificant.
• The floor surface for laying the bed must also be leveled. He, the Mauerlat and the run must be clearly horizontal, but the location of the listed elements in the same plane is not necessary.
• We process all wooden parts of the structure before installation with fire retardants and antiseptic preparations.
• We lay waterproofing on concrete and brick walls for the installation of a Mauerlat.
• We lay the Mauerlat beam on the walls, measure its diagonals. If necessary, we slightly move the bars and turn the corners, trying to achieve the perfect geometry. Align the frame horizontally if necessary.
• We mount the Mauerlat frame. The splicing of the beams into a single frame is carried out by means of oblique cuts, the joints are duplicated with bolts.
• We fix the position of the Mauerlat. Fasteners are made either with brackets to wooden plugs laid in the wall ahead of time, or with anchor bolts.
• We mark the position of the bed. Its axis should recede from the Mauerlat bars at equal distances on each side. If the run will be based only on racks without lying down, the marking procedure is carried out only for these columns.
• We install the bed on a two-layer waterproofing. We fasten it to the base with anchor bolts, connect it to the inner wall with wire twists or staples.
• We mark the installation points of the rafter legs.
• We cut out racks according to uniform sizes, because our bed is set to the horizon. The height of the racks must take into account the dimensions of the section of the run and the bed.
• Installing racks. If provided by the project, we fix them with spacers.
• We lay the run on the racks. We check the geometry again, then install the brackets, metal plates, wooden mounting plates.
• We install a trial rafter board, mark the places of trimming on it. If the Mauerlat is set strictly to the horizon, there is no need to adjust the roof rafters in fact. The first board can be used as a template for making the rest.
• We mark the installation points of the rafters. Folk craftsmen for marking usually prepare a pair of slats, the length of which is equal to the gap between the rafters.
• According to the markup, we install the rafter legs and fasten them first at the bottom to the Mauerlat, then at the top to the run to each other. Every second rafter is screwed to the Mauerlat with a wire bundle. In wooden houses, the rafters are screwed to the second crown from the top row.

If the rafter system is done flawlessly, the layered boards are mounted in random order.

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

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

Another useful video about the construction of a gable truss base with your own hands:

Hanging truss systems

The hanging type of truss systems is a triangle. The two upper sides of the triangle are folded by a pair of rafters, and the puff connecting the lower heels serves as the base.

The use of tightening allows you to neutralize the effect of the spread, therefore, only the weight of the crate, the roof, plus, depending on the season, the weight of precipitation, acts on walls with hanging truss structures.

The specifics of hanging truss systems

Characteristic features of hanging type truss structures:

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

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

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

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

Subtleties of long-span hanging systems

Puff - the longest element of the hanging rafter structure. Over time, it, as is typical of all lumber, deforms and sags under the influence of its own weight.

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

To prevent sagging in the installation scheme of the truss system for a large-span gable roof, there is a very significant component. This is a pendant called a grandmother.

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

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

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

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

As a result, the truss system pleases with stability with a slight and not too expensive upgrade.

Hanging type for attics

In order to increase the usable space, the tightening of the rafter triangles for the attic is moved closer to the ridge. A perfectly reasonable move has additional advantages: it allows you to use puffs as the basis for filing the ceiling.

It is attached to the rafters by cutting with a semi-frying pan with a duplication of a bolt. It is protected from sagging by installing a short headstock.

A noticeable drawback of the attic hanging structure is the need for accurate calculations. It is too difficult to calculate it on your own, it is better to use a ready-made project.

Which design is more cost effective?

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

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

Saving on the grade of material will not work. For the bearing elements of both systems: rafters, purlins, beds, Mauerlat, attendants, racks, lumber of the 2nd grade is needed.

For crossbars and puffs working in tension, you will need the 1st grade. In the manufacture of less responsible wooden slips, the 3rd grade can be used. Without counting, we can say that in the construction of hanging systems, expensive material is used to a greater extent.

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

Video instruction on the installation of a truss structure of a hanging category:

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

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