The choice of the type of truss system. Rafter system: types and installation for different forms of pitched roofs. Determination of the reliability of the truss system

A good foundation does not mean that the house will stand "faithfully and truly" for many years. Another extremely important component is a reliable and high-quality roof truss system. Let's see how it works in the case of a pitched roof, what types it is and what elements it consists of.

Roof truss systems

What should be the rafters for roofs

Here are some types of rafters that are most often used in modern construction:

metal is difficult to change, but this material is durable;
wooden ones are easy to use and change, but require additional processing;
wooden I-beams (made of timber and OSB) are even with a maximum length of up to 12 meters, but the cost is higher than a conventional wooden system;
reinforced concrete are not amenable to change at all, but they are distinguished by a long service life;
mixed or combined systems.

Each of them has its pros and cons, which include strength, price, ease of installation, the possibility of small changes associated, for example, with inappropriate dimensions, interaction with the environment. In this material we will talk about the most popular material for the manufacture of rafters - wood. Let us highlight the main tasks that are set for structures of this type.

First, and most importantly - strength each element. The roof must not warp or move. The basis of the construction of the rafters is a triangle. It is in the form of a triangle that trusses (frames) are made that are attached in parallel. Fixed and rigid, they "lead" the entire structure.

Small mass. A heavy roof is extremely bad. Therefore, most elements are made from wood. If the weight of the roofing system is large, then it is reinforced with a metal frame. A basis - coniferous breeds of a tree of small humidity.

How requirements the tree should answer:

1-3 varieties. No chips, knots or cracks.
Wooden elements should not be less than 5 cm in thickness, and with an area of up to 45 square meters. cm.
The maximum length of a beam made of coniferous wood should not exceed 5-6 m.
Mauerlat and purlins are made exclusively from hardwood.

The main structural elements of the rafters

Any owner planning the construction of a truss system must be aware of what it consists of.

Mauerlat. The basis of the whole structure. With the help of this element, the correct load is established on all load-bearing elements of the house.
rafter leg. The slope of the slope is touched, gives the roof an attractive appearance, securely fixes the structural parts of the system.
puff. Does not allow the legs to "disperse". Holds them firmly at the bottom.
Run. Fastens the rafter legs at the top of the system (ridge run) and on the sides (side run).
crate. Mounted strictly perpendicular to the beams. It is made from cut timber or boards.
Racks / struts. "Add" to the legs even more durability.
Overhang. Protects the main structures of the building from various natural precipitation.
Skate. The place where the slopes are fixed.
Filly. Create an overhang. Necessary in the case when the rafters do not have the required length.

Details of truss systems on the example of a gable roof that can be used for various roof structures

Let's deal with such constituent elements of the truss system as a farm. It is made flat, and, in addition to stretching, it includes braces and the beams themselves. All these parts are fixed in such a way that the load on the main structures is vertical.

In the case when the span is quite large, the farm is made of several components. The lower part of the truss is the attic ceiling. The exact number of farms is determined after serious calculations at each specific facility.

Types of truss systems of different types of roofs

All design options are determined by two main types of truss systems: hanging and layered.

hanging

Ideal for gable roof types, with small spans - up to 5 m, without internal partitions. The lower support is Mauerlat. In such a system, tightening is used, which reduces the thrust of the structure on the main supports of the building.

Hanging roof structure

Hanging rafter beams are located below - they also play the role of floor beams. In the case when the floors were made of reinforced concrete structures, they can also be puffs of the system.

Important extras:

You should not use the legs as the main supporting element for the roof overhang. A more optimal option is a filly (provided that the overhang has a width of no more than 1 m.). The leg, with this solution, transfers the load over its entire plane to the Mauerlat.
When the wood has a moisture content of more than 20%, it is worth preparing in advance for the fact that after drying the system will begin to “walk”. The solution is to use bolts as fasteners, which can always be tightened. But, even more "advanced" option - "powerful" mounting screws.
At the top of the roof, it is imperative to fix the wind board (should go from the Mauerlat itself to the top of the ridge). The corner is organized from the attic. This is necessary to create the most durable roof, resistant to wind loads.

Layered

They are used for roofs with spans of 9-15 m. At the top, such rafters are mounted on a ridge run, at the bottom - on a Mauerlat.

Layered truss system

If the span is more than 15 m, then instead of the ridge run, two side ones are mounted, which are additionally attached to the racks. In the case when an attic will be created, a wall is used as a support for the layered beams.

Peculiarities:

Any structural part of such a system should not be thicker than 5 cm.
The surfaces of the elements should be as smooth and machined as possible.
Very carefully you need to consider the calculation of the loads on each structural element.
Mauerlat must be located strictly in a horizontal position relative to the vertical supports.
Symmetry must also be adhered to when mounting struts with racks.
High-quality ventilation is a guarantee that your rafter system will not rot in the future.
At the junction points of elements with stone or brick, good waterproofing is needed.

Depending on the shape of the roof chosen by the developer, its frame will also be different. We offer to explore various options for the most popular upper house designs.

Shed roofs

They are made at an angle of 13-25 degrees, such roofs have the simplest (in terms of manufacturing and installation) rafters. In the case of a small building with spans up to 5 m, a layered system is used. In the case when spans are more than 5 m, trusses are additionally used.

gable

It's also a pretty simple option. Especially when an attic or attic floor is equipped under such a roof. Tilt angles - 15-63 degrees. If the capital partitions are located at a distance of up to 6 m (relative to each other), hanging rafters are mounted. For running house sizes of 6x6 or 9x9 meters, we recommend using the following roof arrangement schemes.

Recommended scheme for mounting a hanging truss system for a gable roof

Increasing the size of the house, it is necessary to modify (strengthen) the structure. In such cases, it is necessary to use layered technology.

Gable roof options for spans over 10 meters: using a layered truss system

Hip or four-slope

Rules for the construction of a hip roof truss system

With angles of inclination of 20-60 degrees, and spans of no more than 13 m. A prerequisite is internal reinforcing elements. For roofs of this type, trusses are used, or rafters are mounted for roofs of a layered type.

broken roof

Installation of sloping roof rafters

In its lower part it can have a slope of up to 60 degrees, in the upper part it is gentle. In view of this feature, the attic area becomes somewhat larger. The same types of rafters are used as in the version with hipped roofs. But, it is recommended to use farms.

Additional elements

To create the most durable roof, each component of the structure must be very firmly connected to the frame and other elements. In this case, it is extremely important to take into account the force of the wind and the direction of possible mechanical loads.

Moreover, it is worth paying attention also to wood. It may crack due to drying out. Therefore, it is important to create a design in which each element will "work" as smoothly as possible.

Previously, all structural elements of the rafters were fixed with notches. But, it was not too "cheap and economical pleasure", since it is necessary to take wooden elements of a large section.

Methods for attaching rafters to the Mauerlat and ridge run

So, today, not cuttings are used for fasteners, but special bolts and dowels:

Metal overlays with an anti-corrosion coating are another option for fasteners. They are mounted on the elements of the system using toothed plates or nails. The advantages of such mounts are as follows:

Small consumption per unit of wood.
Ease of installation.
High fastening speed.

Perforated fasteners: corners, plates, timber support

Features of the installation of the truss system and Mauerlat gable roofs

The installation scheme of the truss system in the case of a gable roof

I - Mauerlat, II - rafter leg, III - ceiling.

Using narrow rafter legs is a "direct path" to system sagging in the future. To prevent this, you need to use a special lattice - reinforcement, which includes struts, racks and crossbars. To create it, you need to take wood with a thickness of 2.2 and a width of 15 cm, or use plates of wood with a minimum diameter of 13 cm.

Roof rafters - the supporting structure of the slopes. It consists of elements that can be interconnected with crossbars, spacers, racks, etc. The material for the support beams, in addition to the most common - wood, can be any - metal, reinforced concrete, or mixed.

Table for calculating the rafter system, depending on the distance between them and the length

Wood (bar) should have a cross section of 40 by 150 to 100 by 250 mm. This figure depends on the distance of the legs from one another, and the number of sediment loads for a particular area (the calculation is carried out separately).

The board should not have more than 5 cm in cross section. The width is directly proportional to the length. For example, if your board is 5 m long, then its width should not be less than 13 cm. The main material of the roof sheathing is also important. When choosing it, you should pay attention to the presence of knots, chips and cracks. If you cannot find the most even wood blocks, then the maximum length of the knots should not be more than 1/3 of the thickness of the wood.

The last step in the installation of roof rafters is to securely fasten each element. Staples and metal corners are the most optimal elements for these purposes. But, in modern construction, bolts are increasingly used.

In order for the constructed building to serve for more than one year, it needs both a reliable foundation and a strong roof system that resists the vicissitudes of the weather. The roof must withstand heavy loads with dignity: heavy snowfalls, sharp gusts of wind, torrential downpours. The roof truss system is best suited for this.

Roof trusses and its types

The truss system is the basis of the roof, which focuses on the load-bearing elements of the structure and also serves as a frame for various types of roofing materials: insulation, waterproofing, various coatings.

The dimensions and design of the rafters depend on:

purchased material;
the size of the building;
dimensions of the house;
building material for rafters;
individual preferences of the customer;
roof loads relevant for a particular region.

The rafter system has:

crate - bars, in a perpendicular direction, fit on the rafter legs;
screeds that perceive tensile forces;
wooden racks, located in a vertical position;
mauerlat - a bar, the installation of which is carried out along the wall, the rafters focus on it;
rafter legs are a kind of wooden beams that take on the main load of the roof.

Each of these factors is very important, because it is necessary to understand what type of truss system will be best suited for a particular situation.

When it comes to low-rise buildings, wooden structures are the most common. In many cases, three types of truss trusses are used: hanging rafters, layered rafters and a mixed rafter system.

Characteristics of hanging rafters

Hanging rafters are the most elementary type of truss systems, their characteristics:

If the roof of the house is of complex construction, the types of rafters can be alternated. For example, in the presence of supports or the middle main wall, they install layered rafters, and in the absence of such elements, hanging rafters.

Features of layered rafters

For a layered rafter system, the house must be additionally equipped with a load-bearing wall located in the middle. There are layered rafters according to the following features:

The design of the combined system is the most complex, since it includes parts of two other types of rafters - hanging and layered. It is used for mansard roofing. The walls of the rooms, which are located on the second floor, form vertical supports, these supports are also intermediate racks for truss beams.

Part of the rafters that connect one end of the uprights functions as a crossbar for the slopes located on the side, and for the upper part of the structure they are a puff.

At the same time, the horizontal bars perform the following functions: for the upper slopes - a Mauerlat, for the side ones - a ridge beam. To increase the strength of the roof, struts are mounted that connect the side slopes and vertical racks.

The combined sling system is the most complex and time-consuming to manufacture, but these shortcomings are fully compensated by an increase in the bearing qualities of the roof in the absence of extra supports, especially when there is a need to cover significant spans in the building.

You can increase the bearing qualities of the roof using a mixed truss system

Rafter trusses for various types of roofs

During the construction of a certain building, truss systems of one kind or another are necessarily used, and the type of roof will completely depend on the design of the future structure.

Rafter truss for a gable roof

A gable roof is a common roof construction for residential buildings that have no more than three floors. Preference is given to just such a design because of the technical characteristics of the inclined shape of the truss system, and also due to the fact that installation work is carried out easily and simply.

The truss system of a gable roof includes two rectangular inclined planes. The upper part of the building from the front side resembles a triangle. The main components of a gable roof are the Mauerlat and rafter legs. In order to properly distribute the load on the rafters and walls, struts, crossbars and racks are mounted, thanks to which you can create a durable, rigid, elementary and easy installation scheme for a gable roof structure.

A gable roof is considered the simplest roof system; it is used for residential buildings no more than three floors.

On top of the rafters, you can mount a sparse crate or a solid one, and then attach a bituminous coating, tiles or some other type of material to it. The rafters and sheathing itself are usually made of beams or boards, which are fastened with nails, bolts or metal fittings. Metal profiles can be used as rafters, due to which significant spans overlap. There is no need to use extra racks and struts.

The device of the truss system for a gable roof allows you to evenly distribute all the existing load along the perimeter of the building. The lower ends of the system focus on the Mauerlat. They are fixed with metal fasteners or staples. By the angle of inclination of the bars for the rafters, you can determine at what angle the roof slopes will be inclined.

The truss system for a gable roof allows you to evenly distribute the load from the roof along the perimeter of the building

Rafter system for a hip roof

When arranging a system for a hip roof, you will need to install different types of rafters:

conjurers (shortened);
side;
hip main;
sloping (diagonal elements that form a slope in the shape of a triangle).

The rafter legs located on the side are made of board, and they are mounted identically to the details of a traditional pitched roof with a layered or hanging structure. Hip main rafters are layered parts. For sprigs, boards or bars are used, which are attached not only to the Mauerlat, but also to the diagonal beams.

To install this type of construction, the angle of inclination is accurately calculated, as well as the cross section of the sloping beams. The dimensions of the parts also depend on the length of the span.

So that the hip roof does not deform from a heavy load, you should accurately calculate the angle of inclination of the diagonal beams for the rafters

Observe symmetry when installing diagonal beams for rafters, otherwise the roof is deformed from a significant load.

Rafter system for sloping roofs

A broken roof is a construction with rafters, which consist of several separate elements. Moreover, they should be located at different angles relative to the horizon. And since the lower rafter part is almost vertical, the attic of the building receives additional space, so that it can be used as a living space. The device of this type of roof is carried out during the construction of a four- or gable rafter structure.

Professionals need to calculate a four-pitched rafter system, but a gable broken roof can be made independently, since its installation is very simple. To do this, it is necessary to install a support frame, which should consist of runs, as well as racks. Horizontal parts are fixed with hanging rafters. But to the Mauerlat, the supports of the sloping roof are fixed with shortened legs of the rafters.

The assembly of rafters for a broken gable roof can also be performed by non-professionals, since the installation of such a roof is very simple.

"Cuckoo" in the roof truss

The so-called cuckoo on the roof is a small ledge that is located on the attic floor. Here is a window for better illumination of the attic room. The installation of the "cuckoo" is carried out carefully, while controlling the parameters of the entire structure: the depth of the cut, the angle of inclination and other factors. However, before that, the necessary measurements are made.

The first stage of work begins with the installation of a power plate (a beam with a section of 10x10 cm, which is needed to support the lines). The truss system acts as a skeleton for the roofing material. To stiffen the structure, spacers are used, which are mounted between the two legs of the rafters.

After the installation of the truss truss is completed, a sheathing is laid, the type of which depends on the roof covering purchased. The installation of the crate is done continuously or with a certain step. Boards, OSB and plywood sheets are usually used for it. In addition, the installation of roofing material must be identical throughout the entire roof.

The main difficulty in installing such a rafter system is the location of the internal corners. In these places, snow can accumulate, which means that the load will increase, which is why a continuous crate is made.

"Cuckoo" on the roof is called a small ledge on the attic floor, under which there is an additional window

Chalet roof truss truss

A feature of a device of this design is the removal of visors, as well as overhangs outside the house. In addition, there must be rafters and beams for the roof, which extend up to three meters on the sides of the building. Each of these elements is fixed with a bracket to the wall of the building in the lower part. Next, tie the edges of the beams. They serve as a support for covering the roof of the building.

But when creating large overhangs, it is necessary to install the reinforced belt in parallel with the installation of the Mauerlat studs. It is necessary to make anchors that help fix the consoles. In this case, the rafters will be perfectly fixed with anchors and, in addition, tie-ins.

To carry out the side cornices, a ridge beam is made, after which beams are taken out at the Mauerlat level, which must be identical to the length of the ridge. The truss is based on these structural details, and in the future - building material for the roof.

When designing a building, the angle of the roof-chalet is calculated based on the characteristics of the local climate and other factors. With a slope angle of about 45 °, the load from snow is not taken into account, since with this option it will not linger on the roof. At the same time, the sloping roof will withstand the load from the snow, but it is necessary to install a reinforced roof truss. Before installing the roof-chalet, a building project is prepared, because the originality of the roof itself, as well as long cornices and its overhangs, oblige this.

The roof in the style of a chalet is characterized by visors, taken out several meters outside the house.

Roof truss designed for soft roofing

Soft roofing is done in various ways, but there are common characteristics in the technological methods of its construction. Initially, you need to prepare. When equipping a roof for a house made of foam concrete or other material, a Mauerlat is first installed, then a cut is made under the ceiling beams in increments of up to one meter in the upper crowns of the building. The distance between the boards is calculated based on the type of rafter structure.

Mount individual parts of the rafter system. To completely eliminate the risk, the boards of the rafter legs on the ground are attached with screws. After creating a truss truss, it is raised to the top of the building.
All elements of the rafters are fixed with ceiling overlap, internal boards, jibs, and also crossbars. Further, this basis for the roof will become a single whole structure.
The next stage is a crate, which is installed under a soft roof with small gaps or no gaps at all. Gaps of no more than 1 cm are allowed. Quite often, leveling plywood is installed on top of the boards. Its sheets are laid according to the brickwork method. The resulting joints do not align with the gaps between the plywood and the board.

If the length of the boards of the crates is not enough, then the joints of the parts must be located in different places. In this way, areas that have been weakened can be correctly distributed.

Self-manufacturing of the truss system

Before the installation of the truss system begins, the Mauerlat must be fixed to the longitudinal walls with anchors. Next, you need to decide on the desired section of the legs for the rafters, depending on the distance and their length. If there is a need to increase the length of the rafters, then connect them with various fasteners.

When using different insulation, you need to choose the ideal distance between the elements of the rafters in order to reduce the number of thermal insulation scraps.

Installation of the truss system must be carried out in the following order:

A template is made according to which the farm is assembled. 2 boards are taken, corresponding to the length of the rafters, and connected to each other from only one edge with a nail.

A rafter template called "scissors" will help you quickly assemble the entire roof truss system
You get a design called "scissors". Its free edges are placed on supports at the points of contact of the rafter legs. The result should be the final angle, that is, the angle at which the roof slope will be tilted. It is fixed with several long nails and transverse boards.
A second template is made, thanks to which the cuts on the rafters are installed. It is made from plywood.
Special mounting cuts are cut out on the rafters (a prepared template is used for this purpose) and connected at an angle of inclination of the slope. You should get a triangle that rises to the roof along the stairs. Next, it must be attached to the Mauerlat.
Initially, two side gable rafters are mounted. Their correct installation in the vertical and horizontal plane occurs due to temporary struts attached to the rafters.

For the correct installation of the entire rafter system, the first pair of rafters is installed on the roof
A cord is stretched between these tops of the rafters. It will indicate the future skate and the level of other rafters located in the gap.
Raise and mount the remaining rafters at the initially calculated distance, which should be at least 60 cm from each other.
If a bulky construction of rafters is provided, then it is additionally strengthened with struts, supports, and so on.

The bulky construction of the rafters is additionally reinforced with struts and supports.
On special supports, a ridge beam is installed, to which not only short, but also diagonal and intermediate elements of the rafters are attached.

Proper fastening of the ridge beam ensures the reliability of the entire rafter system

Typical nodes of a standard truss system

The structural strength of the rafters depends on the ideally selected section of the boards, as well as on the high quality of the rafter units. The connection of parts for the roof structure is done in accordance with established rules.

The main typical nodes in the truss system:

supporting knot of rafters on the Mauerlat;
ridge;
a node for combining the upper puffs and the entire truss system;
fixing the strut, rack, as well as rafters and beams.

After the design of the rafter system has been chosen, it is necessary to draw up a plan in which to select all the nodes. In each design, they are made in different ways, since it depends on different nuances: the type of roof, its size, and the angle of inclination.

A rafter from a profile pipe is a metal structure that is assembled using lattice rods. The very production of such farms is a very time-consuming process, but also more economical. Paired material is used for the manufacture of rafters, and scarves are connecting elements. The construction of rafters from profile pipes is assembled on the ground, while riveting or welding is used.

Thanks to such systems, any spans are blocked, but it is necessary to make the correct calculation. Provided that all welding work will be done with high quality, in the future it remains only to transfer the structural elements to the top of the building and assemble them. Bearing rafters from a profile pipe have many advantages, such as:

Crossbar in the truss system

Rigel is a fairly broad concept, but in the case of roofs it has a certain meaning. The crossbar is a horizontal beam that connects the rafters. Such an element does not allow the roof to "burst". It is made of wood, reinforced concrete, and also metal - it all depends on the type of structure. And the crossbar serves to distribute the load exerted by the truss system.

It can be fixed in various places between the legs of the lines. There is a direct pattern here - if the crossbar is fixed higher, then the timber for its installation must be selected with a large cross section.

There are many ways to fix the crossbar to the truss system:

bolts;
nuts;
studs with washers;
special fasteners;
nails;
mixed fasteners, when different types of fasteners are used in parallel.

Mounting exists with a tie-in or overhead. In general, the crossbar is a design unit, as, indeed, the entire roof sling system.

The crossbar in the truss system is designed to reinforce the roof structure

Rafter system fastening

To ensure the reliability of the rafter system, it is necessary to initially find out how they are fastened to the supporting roof and the ridge. If fastening is done to prevent deformation of the roof during shrinkage of the house, then the rafters are fixed on top with a hinged plate or a nut with a bolt, and from below - with a sliding support.

Hanging rafters need a tighter and more reliable fastening in the ridge, so in this case you can apply:

overhead metal or wooden plates;
cutting method;
connection with long nails.

In the layered system, the rafter legs are not connected to each other, since they are attached to the ridge run.

The rafters are fastened to the Mauerlat by cutting down, which is done in the rafter leg. Thanks to this method of fastening, the support of the roof will not be weakened. Cutting is also done when installing rafters on floor beams. In this case, the cut is also made in the support beam.

Video: how to make rafters with your own hands

Thus, a perfectly matched system of rafters and their structural characteristics will help create the basis for a reliable roof for your home.

The gable roof truss system is considered one of the simplest in purely constructive terms. It consists of only a few elements, the number of which decreases or increases due to the size of the roof itself. But with seeming simplicity, the process of erecting a gable roof itself requires knowledge of some of the nuances that affect the quality of the final result.

Rafter system for a gable roof Source tues.ru

What is a gable roof

From the name it becomes clear that the roof structure is two slopes that have a rectangular shape in the plane. More often, the slopes have the same dimensions, but there are so-called asymmetric designs in which the slopes differ in size from each other.

In this case, the slopes are set to each other at a certain angle, which is called the slope. The line of contact is the ridge beam, which is part of the truss system. In a simple way, it is called a ridge, and it is the highest point of the roof.

The side planes formed by the slopes are called gables. They are triangular in shape. After the construction of the roof, the sidewalls are lined with sheet or panel materials: plywood, OSB, even boards, etc.

What is a gable roof truss system

The basis of the structures of the slopes are rafter legs, they are also rafters. They are made either from lumber (beams, boards), or from a steel profile (corner, channel). In private housing construction, wood is used. It is easier to work with, plus lumber is cheaper.

The device of the gable roof truss system is not only rafters. In addition to them, there are several other mandatory elements. The photo below shows all the elements of a gable roof. Let's designate them.

Each of the elements of the roof has its own purpose. Source lestorg32.ru

Elements of the gable roof truss system

Mauerlat. In fact, this is a beam on which the rafters rest. Its purpose is to evenly distribute the load from the rafters on the walls of the house. If the Mauerlat is not used, then the rafters will put pressure on the walls pointwise, that is, large stresses will arise at the installation sites, which will lead to cracking of the walls.

rafters installed at an angle.

Skate, he is a ridge beam or run. Its task is to form a place for joining the rafter legs. A ridge beam is an optional element of a gable roof. There are designs in which it is not installed. But more on that below.

Puffs. They are not always used, but only on hanging rafters or if the rafter system is installed on a wide house.

floor beams that form the ceiling in the room and the floor in the attic.

One of the floor beams, which is called lying down. It additionally functions as a base for the support posts that support the rafters. Not always used.

Support legs, they are grandmas supporting the rafter legs. They are installed only if the span of the house is at least 6 m.

Struts, they are also diagonal props. They are used only if the support posts cannot ensure the overall reliability of the truss system.

There is another element that is clearly visible in the photo below. These are support posts for the ridge run. They are installed if the design of the truss system is heavy. That is, the entire structure is assembled under heavy roofing material, for example, under ceramic tiles.

Sloped rafters with support posts under the ridge run Source seaside-home.ru

You might be interested! A warm roof is an important detail in the construction of an energy-efficient home. From the article at the following link you can find out.

Types of rafters

The roof truss system (gable) can be assembled from layered or hanging rafters.

Layered

They got their name because the lower ends rest on the walls of the house, the upper ends on the ridge run. In this case, the truss elements are subjected to loads that bend them. The design is reliable, durable, with a large bearing capacity.

The photo above just shows the rafter system of a layered type. It is clearly seen that the legs rest in the upper part on the skate. In this case, there are two types of fastening of the rafters themselves in the upper part:

fastening is made to the ridge:

fastening is made between each other with an emphasis on the ridge (photo above).

hanging

It is necessary to immediately indicate that this type of truss system can be used if the distance between the walls of the house does not exceed 12 m. Because the rafters abut the lower ends against the walls, and the upper ends only between themselves (there is no ridge run in the structure). Hence the low bearing capacity with a large spread.

Hanging rafters for the roof have one purely design flaw - a large support load on the walls of the house. To reduce it, puffs are installed between the legs to form a rigid triangle. Often, the functions of the puffs are performed by the load-bearing floor beams.

If necessary, strengthen the hanging rafters, install racks and struts under them.

Hanging rafters of a gable roof Source postila.ru

Installation of a gable roof truss system

Two types of truss system determine two types of their assembly technology. Let's consider each separately.

Installation of layered rafters

There is a certain sequence for assembling layered rafters.

Two extreme support posts are installed under the ridge beam. They will not only support the beam, but also be the elements that form the gables of the building. Attach them at the bottom to the Mauerlat. At the same time, they are strictly set vertically, and the upper ends are in the same horizontal plane. To do this, a strong thread is pulled between the racks, the level is checked for horizontalness. If there are deviations, then one of the supports (low) is raised using wooden supports.

Intermediate support posts are mounted along a horizontally stretched thread in increments of 2-2.5 m. To prevent the beams of the racks from moving, they are supported with temporary fasteners: props or puffs.

A ridge beam is laid on the racks, which is attached to them.

Produced in pairs installation of gable roof rafters. Installation can be started from either side. Fastening is immediately carried out to the Mauerlat and to the ridge. The main thing is to maintain the distance between the legs, which is determined depending on the severity and bearing capacity of the roofing material. Usually this parameter is indicated in the project of the house.

If necessary, intermediate support posts and struts are mounted.

Installing rafters on a ridge along a stretched thread Source kbumb.ru

Installation of hanging rafters

The technology for installing hanging rafters is different. To do this, the entire structure, assembled from two rafters and puffs, is assembled on the ground. That is, roof trusses are prepared in the required quantity, which then rise to the roof. Sometimes craftsmen assemble trusses on the roof. Collected one - installed, collect the next.

It should be noted that such farms have a significant mass. Lifting them manually is difficult and dangerous, so they use the services of a crane. And this increases the cost of construction.

Hanging trusses assembled on the ground Source moydom-irk.ru

The most difficult thing is to set farms. All of them are installed at the installation site with a planned step, where they are temporarily fixed with jibs and props. Then a thread is pulled between the extreme farms. It must be set so that, firstly, it is stretched strictly along the horizon, and secondly, according to a design that is higher than the rest.

It remains only to raise the truss structures, which turned out to be below the stretched level. And the last - the installation of the crate, which will secure all the trusses into one truss system. Please note that at the bottom of the rafters will be fixed to the Mauerlat.

You may be interested! When the installation of the truss system is completed, the turn of roofing comes. From the article at the following link you can find out.

Rafter calculation

length of rafter legs;

the step of their installation;

section of the lumber used.

Everything is simple with the length, for this you will have to use the Pythagorean theorem, which is based on the formula: c 2 \u003d a 2 + b 2, where c is the hypotenuse of the triangle (this is the rafters), a and b are the legs. The latter are the height of the roof and half the width of the house. All parameters can be easily measured.

The length of the rafter is l 2 + H 2 Source remontik.org

It is more difficult with the installation step, because a lot will depend on the mass of the roofing material and the loads from natural precipitation. The larger both loads, the smaller the installation step. But, as practice shows, this parameter varies from 60 cm to 2 m. The latter indicator is used if corrugated board with large corrugation parameters, for example, H75, is used as a roofing material.

As for the section of the rafter legs, here, as in the case of the installation step, loads are taken into account, as well as the length of the legs and their installation step. Here the dependence is as follows: the greater the load, step and length, the larger the cross section.

Video description

In the video, the installation process of the truss system:

And one moment. Rafters for a gable roof are laid at a certain angle (indicated by the letter “a” in the photo). The slope is selected with the calculation of the choice of roofing material. That is, some coatings cannot be laid on roofs if the angle of inclination is less than required. Here are some ratios:

the minimum angle of inclination of the truss system for slate is 22 °;

for corrugated board - 12 °;

for metal tiles - 14 °;

soft tiles - 15 °.

The ratio of the roof slope to the type of roofing material Source arhplan.ru

On our website you can find contacts of construction companies that offer a turnkey roof design and repair service. You can directly communicate with representatives by visiting the exhibition of houses "Low-Rise Country".

Generalization on the topic

Gable roofs are traditional designs. But from the article it becomes clear that there are two truss systems that form the basis of the construction of roofs. The one that fits the size of the house is selected. As a selection criterion, the loads that put pressure on them are also taken into account. Therefore, it is important to correlate everything correctly, taking into account the nuances of construction processes.

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

The design of the gable roof truss system

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

Now about the components of the system and their purpose:

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

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

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

With hanging rafters

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

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

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

Gable roof truss system for small houses

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

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

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

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

For mansard roofs

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

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

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

For big houses

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

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

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

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

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

With rafters

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

Bezporny schemes and knots of cuts

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

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

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

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

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

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

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

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

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

Options for truss systems with contractions

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

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

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

Rafter systems with braces

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

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

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

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

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

System for houses with two internal load-bearing walls

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

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

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

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

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

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