Attachment of the truss truss to the Mauerlat. Strut truss system
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 bar 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 on the bottom 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 reliability of the roof structure directly depends on how correctly its entire supporting system will be mounted. And its main elements are rafters. The whole system consists of rafter legs that support and expand additional elements, such as struts, puffs, crossbars, side runs, support posts and extensions. The rafter legs are connected on the ridge beam from above, and their lower edges very often rest on, fixed on the side load-bearing walls of the building.
Since the biggest load falls on the Mauerlat, it is made from a powerful beam. Its cross section is determined by the massiveness of the entire truss system, but basically the size is from 150 × 150 to 200 × 200 mm. This load-bearing element is designed to evenly distribute the load from the entire structure of the roof and roof onto the load-bearing walls of the building. The fastening of the rafters to the Mauerlat is carried out in various ways. They are selected locally depending on the type of truss system (which can be layered or hanging), its complexity and massiveness, on the magnitude of the total loads to which the entire roof structure will be subjected.
Varieties of connecting nodes "rafters - Mauerlat"
First of all, there are sliding and rigid fastenings of rafters to the Mauerlat.
1. Sliding mounts consist of two separate elements, one of which has the ability to move relative to the other.
These mounts can be of different designs - closed and removable.
- The closed mount consists of a corner, which is attached on one side to the Mauerlat, and on the other side has a special slotted eye. A metal loop with holes for fastening to the rafters is installed in it. Thanks to the free, not fixed vertical side of the corner, the fastening allows the rafters to move slightly if necessary, without deforming the walls of the building.
- The open mount is arranged according to the same principle, and differs only in that the metal loop is not inserted into the eye, but simply the upper part of the vertical shelf of the corner is bent down after installation, thereby fixing the connection.
Video: an example of installing a movable mount on a rafter leg and Mauerlat
2. There are many more types of rigid fasteners. They are selected depending on the massiveness of the wooden structural elements and the method of installation on the Mauerlat.
These include metal corners of different sizes, LK fasteners, which securely fix the rafters, installed with the help of washed down, without damaging it with fixing screws or nails.
- LK fasteners are produced in several sizes, so they can be matched to any bar or board thickness. The thickness of the metal from which these fasteners are made is 2 mm, no matter what size they are. Depending on the size, fasteners have a different designation.
| Designation | Size in mm |
|---|---|
| LK-1L | 40×170 |
| LK-2P | 40×170 |
| LK-3L | 40×210 |
| LK-4P | 40×210 |
| LK-5L | 40×250 |
| LK-6P | 40×250 |
It should be noted that these fasteners are suitable not only for connecting rafters on the Mauerlat - they are also used to fix the nodes of the "floor beam - Mauerlat".
The main advantage of this fastener is the maximum rigidity and reliability of the connection of wooden elements.
- The fastening of the rafters with a gash on the Mauerlat with the help of corners is carried out on both sides, which provides the required rigidity.
There are corners designed for attaching rafters without cuts. They have higher shelves and are screwed with a large number of self-tapping screws. They are made from metal with a thickness of 2; 2.5 or 3 mm.
| Designation | The size (length height width, metal thickness) in mm | Designation | The size (length height width, metal thickness) in mm |
|---|---|---|---|
| reinforced corner | 105×105×90×2 | Reinforced corner KP5 | 140×140×65×2.5 |
| reinforced corner | 130×130×100×2 | Reinforced corner KP6 | 105×172×90×3.0 |
| reinforced corner | 105×105×90×2 | Reinforced corner KP7 | 145×145×90×2.5 |
| reinforced corner | 50×50×35×2 | Reinforced corner KP8 | 145×70×90×2.5 |
| reinforced corner | 70×70×55×2 | Reinforced corner KPL1 | 90×90×65×2 |
| reinforced corner | 90×90×40×2 | Reinforced corner KPL11 | 90×90×65×2 |
| Reinforced corner KP1 | 90×90×65×2.5 | Reinforced corner KPL2 | 105×105×90×2 |
| Reinforced corner KP11 | 90×90×65×2.5 | Reinforced corner KPL21 | 105×105×90×2 |
| Reinforced corner KP2 | 105×105×90×2.5 | Reinforced corner KPL3 | 90×50×55×2 |
| Reinforced corner KP21 | 105×105×90×2.5 | Reinforced corner KPL4 | 70×70×55×2 |
| Reinforced corner KP3 | 90×50×55×2.5 | Reinforced corner KPL5 | 50×50×35×2 |
| Reinforced corner KP4 | 70×70×55×2.5 | Reinforced corner KPL6 | 60×60×45×2 |
A few additional words need to be said about some of the corners shown in the table, since their description requires clarification:
— KR 11 and КР21 are improved corners, often marked as To P1 and KR2. These elements have an oval-shaped anchoring hole, which reduces the risk of bolt breakage in the event of structure shrinkage.
- КР5 and КР6 are corners used for fastening elements on which a large bearing load falls. corner To P6 is also equipped with an oval hole, and it is recommended to use it when creating a rafter system on a new house, which will still shrink. These models are in demand for the installation of structures that have a lot of weight.
— Corner To M is made of perforated steel and is used for fastening rafters with a large section. It is especially well suited for wooden buildings. This corner fixes the structural elements very securely, and when using it, it is not necessary to cut the rafters into the Mauerlat - it is enough to cut the correct angle at the first.
- The KMRP corner is used to fasten parts of the truss system at right angles, including rafters with Mauerlat. It also differs from conventional angles in that it has an elongated hole, which allows displacement during shrinkage without damaging the fixing bolt. It can be used in a design where it is impossible to cut one element to another.
KMRP corners are produced from 2 mm thick steel. Three varieties are produced:
| Corner designation | Dimensions in mm | ||
|---|---|---|---|
| a | b | c | |
| KMRP1 | 60 | 60 | 60 |
| KMRP2 | 80 | 80 | 80 |
| KMRP3 | 100 | 100 | 100 |
- Another option for fixing the rafters on the Mauerlat is to install them between two boards, sawn at a certain angle, and additionally fixed at the bottom with metal corners or LK mounts.
Such fastening gives good rigidity and reliability. This method is well suited in cases where the rafter needs to be fixed at the right angle, lifting it above the horizontal plane of the Mauerlat, but fixing it to the vertical outer side.
- A method of attaching rafters to a Mauerlat made from a beam of not too large a section. It is carried out by reinforcing the bar with the help of wooden linings having the required thickness.
Fastening with reinforcing lining Pieces of boards are attached to the Mauerlat with nails or self-tapping screws, in those places where the rafter legs will be installed.
In this case, cutouts of the desired configuration and depth are made in the rafters. The rafter legs are securely fixed to the wall with the help of steel wire, which is fixed to a driven steel crutch.
- In addition to the above methods of fastening, the rafters are nailed to the Mauerlat using brackets. It should be noted that this method is quite common and has been used for a very long time. With proper fixing of these elements, the truss system will last for many years.
Fastening "the old fashioned way" - brackets Staples can have different sizes, driven in at different junction points.
- Another fastener that is used as an auxiliary is TM perforated tape. It is used to strengthen the fastening unit if necessary, its additional fixation.
In some cases, this element can be indispensable, so it also cannot be excluded when installing rafter legs on the Mauerlat.
Features of truss systems
It is selected depending on the location of the load-bearing walls of the building. Each of the systems has its own additional retaining or tightening elements.
Rafters
The system with layered rafters is characterized in that it has one or more reference points, in addition to the load-bearing walls. Due with this, with side walls remove a significant part of the load.
In the form of additional retaining elements, side racks and "grandheads" are used, supporting and fixed to the floor beams. And the beams themselves, in turn, simultaneously serve as puffs for the structure, and also lighten the load from the truss system on the load-bearing walls.
Laminated rafters are most often attached to the Mauerlat with sliding joints that can move when the walls shrink or deform, leaving the roof structure intact. This is especially important to take into account in new buildings, since any newly built building necessarily shrinks under the influence of temperature fluctuations and ground movements.
hanging rafters
Hanging rafters are called due to the fact that they do not have other supports, in addition to the two side load-bearing walls. It turns out that they seem to hang over the internal space of the building. In this case, the entire load from the roof frame structure falls on the Mauerlat.
For fastening hanging rafters to the Mauerlat, rigid fasteners are used with no degree of freedom of movement, since the frame structure has only two points of support.
The hanging rafter system is spacer, so it puts a lot of pressure on the walls.
To remove part of the load from the walls of the building, additional elements such as struts, “headstocks” and puffs-crossbars are used, which pull the system to the ridge bar and evenly distribute the load on all walls. Crossbars are installed parallel to the floor beams and pull the rafters together. Without these additional details, the design may become unreliable.
Calculation of the installation of rafters
In order for the rafter system to be reliable and durable, in addition to the optimal connection method, you need to choose the correct step for the location of the rafter legs. This parameter is selected depending on the size of the rafters (and the length between the support points), as well as on the roof structure.
In this table, you can get information about the necessary parameters for the installation of a reliable truss system.
| Step of installation of rafter legs in mm | Length of rafter legs in mm | ||||||
|---|---|---|---|---|---|---|---|
| 3000 | 3500 | 4000 | 4500 | 5000 | 5500 | 6000 | |
| 600 | 40×150 | 40×175 | 50×150 | 50×150 | 50×175 | 50×200 | 50×200 |
| 900 | 50×150 | 50×175 | 50×200 | 75×175 | 75×175 | 75×200 | 75×200 |
| 1100 | 75×125 | 75×150 | 75×175 | 75×175 | 75×200 | 75×200 | 100×200 |
| 1400 | 75×150 | 75×175 | 75×200 | 75×200 | 75×200 | 100×200 | 100×200 |
| 1750 | 100×150 | 75×200 | 75×200 | 100×200 | 100×200 | 100×250 | 100×250 |
| 2150 | 100×150 | 100×175 | 100×200 | 100×200 | 100×250 | 100×250 | - |
Use, in the article on our portal.
Prices for various types of fasteners for rafters
Fasteners for rafters
A few rules for attaching rafters to the Mauerlat
In order for the fasteners to be reliable, it is necessary to follow a number of rules that are provided for this process:
- If metal connecting parts are used for fastening, then they must be fixed to wooden connecting elements with the utmost care - high-quality self-tapping screws of the required length.
- If the rafters will fit into the cuts in the Mauerlat, then the dimensions must be precisely verified. This will ensure a tight, reliable installation of the rafters in the prepared gash, which should have a depth of ⅓ Mauerlat. However, it should be remembered that such a rule will be valid only if the Mauerlat is made of a powerful bar with a cross-sectional size of at least 150 × 150 mm.
- In order not to weaken the Mauerlat, most often the cuts are made in the rafter leg itself at the desired angle, and in addition the knot is then fixed with corners. Washed down should not in this case exceed ¼ of the thickness of the rafters. This mount is rigid and can be used in a hanging rafter system.
- When using bolts to fasten rafters with slopes, puffs and other wooden elements, it is imperative to install a washer or a metal plate on the bolt in order to avoid flooding the nut into the wood and, accordingly, weakening the structure.
- Fastening the rafters to the Mauerlat only with nails or self-tapping screws is considered unreliable. therefore, it is imperative to use corners or other metal fasteners of various configurations.
- When installing rafters on wooden walls, whether it is a hanging or layered system, it is recommended to attach them to the Mauerlat with a sliding fastener, especially if the roofing material is heavy enough.
Video: a few examples of attaching rafters to the Mauerlat
The roof structure will turn out to be durable and will last a long time, without being deformed by a variety of external influences, if the calculations of all elements are made correctly, correctly select and properly mount all fasteners.
In any building, the main elements on which the maximum load falls are the foundation, walls and roof. The quality of the roof installation largely depends on whether the truss system is installed correctly or not. If the attachment points of the truss system do not meet certain requirements, then such a roof will not last even a minimum operational period without repair work.
Requirements for the truss system
The truss system of any roof must meet such important requirements as:
- Maximum rigidity. Any frame node must withstand loads without being subjected to deformation or displacement. The triangle obtained during the arrangement of the truss system must ensure the rigidity of the structure and its maximum stability;
- Optimal weight. Depending on the roofing material, the material used for the rafters is selected. Usually a wooden beam is chosen, but metal can also be used for heavy roofs.
Important! To prevent damage to the rafters, their rotting and the formation of fungus on wood, it is treated with an antiseptic, and metal structures with anti-corrosion compounds.
- The high quality of the materials used. The wood used as rafter legs should not have cracks and chips.
Varieties of truss systems
The roof can be equipped with one of the types of truss system, of which there are only two:
- Hanging rafters;
- Overhead rafters.
Hanging truss system
Such a system is optimal in the case of a gable roof, when the span between the walls is no more than 6 meters, but when installing additional elements, it is also applicable for wider openings. The Mauerlat serves as the lower basis for the support, while the upper part of the structure abuts against each other. This design also contains a puff - necessary to relieve the load from the walls, by reducing the expansion of the rafters. Beam puffs are installed below the rafter legs and can serve as floor beams.
Attention! The role of the puff may not necessarily be played by a wooden beam, it can also be the overlap of reinforced concrete structures, which in some houses is equipped with an upper floor.
If the puff is located above the bottom of the truss system, then it is called crossbar. Important points in the arrangement of this type of truss system include:
- The roof overhang should not be allowed to rest on the lower part of the rafter legs, which extend beyond the wall. In such a situation, it is best to use a filly (the width of the overhang is set within one meter). With this arrangement, the rafter will be based on the Mauerlat. The cross section of the beam for the filly is chosen smaller than for the rafters;
- To give the roof additional rigidity, and prevent it from swaying and being destroyed by strong gusts of wind, a wind board is nailed on the slope, to the Mauerlat from the ridge;
- If the moisture content of the material used to equip the truss system is more than 18%, unsteadiness should be foreseen, which will cause gradual drying of the wood. That is why fastening should be done with bolts or screws, not nails.
Layered truss system
This arrangement is applicable for roofs with distances between walls from 10 meters (maximum 16 meters). The slope can be made at any angle, and inside the building there are load-bearing walls or supporting columns. From above, for the rafters, the ridge run serves as the main support, and from below this function is performed by the Mauerlat. The inner purlin is supported either by the inner wall or by the studs. Due to the presence of only vertical type of loads, there is no need to install the tightening.
With a 16-meter span, the replacement of the ridge run is carried out by two side structures, the support for which will be the racks.
Important! The absence of bends in the rafter legs is ensured by such nodes as struts and crossbars.
Particular attention to the arrangement of the roof using a layered truss system should be paid to such nuances:
Features of calculations of the gable roof truss system are shown in the video:
The main nodes of the truss systems
The main nodes of the roof truss system include:
- Rafter. They perform the function of a skeleton, supporting the internal and external elements of the roof, and also serve as the basis for laying communications;
- Mauerlat. This is a kind of roofing foundation, which is a beam on which the entire structure is installed. It performs an important function - uniform distribution of the load of the entire structure;
- Run. Designed for fastening rafter legs together and can be located both on top and on the side;
- Puff. Serves for fixing the rafters in the lower part of the structure;
- Struts and racks. Provide the most stable location of the rafter beams;
- Skate. The junction of the roof slopes;
- Filly. These are continuations of the rafter legs, which are sometimes equipped;
- Rigel. It is necessary for high-quality and reliable support of load-bearing elements;
- Sill. Cross bar necessary to distribute the load.
In addition to the listed elements, the design includes attachment points for the roof truss system. When performing them, it is necessary to follow certain rules.
Important! It is absolutely not worth performing a simple fastening of the base to the crossbar, as this can lead to the complete destruction of the truss system.
The following types of fasteners should be used:
- With emphasis on the end of the crossbar;
- Teeth point-blank;
- Teeth in a spike.
The number of teeth should be chosen depending on the slope of the slope, and additional structural reliability can be created using metal corners.
The main attachment points of the truss structure include:
- Beam knot;
- Mauerlat knot;
- Skate knot.
beam knot
With such a node for connecting elements, an insertion of teeth into a spike is made into the rafter, and a recess corresponding to the teeth is made in the transverse section of the crossbar. Such a recess or nest should not exceed 30% of the timber thickness. Fastening is carried out with special hardware with metal corners, or wooden beams, spikes and overlays.
Attention! If the roof is made of materials with low weight, and the slope of its slope does not exceed 35º, then the bases of the supports should be placed so that they rest against an area larger than the beam itself.
Mauerlat knot
Such fastening can be performed both by rigid technology and by sliding technology. Rigid technology involves the installation of a strong connection between the Mauerlat and the rafters, preventing the possibility of slipping, deflecting or popping out. For this, special support corners with bars are used. The resulting knot is fastened with wire using hardware. At the same time, nails should be hammered obliquely so that they enter the wood crosswise. The last nail must be driven in vertically.
In the case of a sliding fastening, alignment is performed using a special mechanism that allows you to move the rafter leg in the required direction. To do this, a tie-in is made on the supports, on which the Mauerlat is then laid. The structure is fixed, as in the previous case, with crossed nails. This method of arranging the connection nodes allows all nodes of the truss structure to move within certain limits.
Attention! Rigid fastening with inexperience of builders can lead to damage to the walls of the building.
ridge knot
In this case, the fastening can also be made in two types - butt and overlap. With a butt joint, the top of the supports is cut with a bevel, as is the angle of the roof. They rest on the same undercut opposite supports. Fastening is carried out using nails, in the amount of two pieces. They are hammered from above at a certain angle. The seams that form between the supports are connected with metal plates or plates. In the second case, fastening is carried out by overlapping, not by end parts, but by lateral sections and fixed with bolts.
Conclusion
When performing work on the installation of the roof, the arrangement of the truss system should be given careful attention, avoiding disruption of technological processes. This will provide the structure with strength, durability and reliability.
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The main obstacle for novice developers, even if we are talking about a simple roof, may be a lack of knowledge about what the nodes of the truss system are. How to fulfill them in order to get a strong, reliable and stable roof?
The beginning of the design of a pitched roof is the choice of a truss system, which should perform the functions of a supporting structure. The type of structures is determined based on the type of roof.
In one case, rafters are beams or boards that act as the "skeleton" of the roof, which holds the weight of the insulation and roofing material. In another, they can be composite, and are assembled from separate elements, known as rafter legs.
The board and bars must undergo a special impregnation - fire-fighting and antiseptic. The better it is done, the longer it will last..
Composite frames are divided into two types: layered and hanging. The choice of a particular system, in addition to the architectural preferences of the owners, depends on some parameters of the roof:
- its functionality
- the number of loads tested, including those related to the climatic features of the region.
Hanging rafters do not have intermediate supports, therefore they create a significant bursting force, which is transmitted to the walls in the horizontal plane. To reduce it, a puff (wooden or metal) is used, which, connecting the legs, completes the triangular structure. The legs in it work on bending and compression. The puff can be located at the base, and in this case serves as a floor beam (this option is more common when installing attics), or higher.
The higher the location of the puff, the more powerful it is, on the one hand, and more securely connected to the rafters, on the other.
Layered views are arranged in houses with an average load-bearing wall or columnar intermediate supports. They rest with their ends on the outer walls, the middle part - on the supports or the inner wall. As a result, the elements work on the principle of beams - only for bending. The weight of the truss system in the case of layered ones with the same width of the house is less: it requires less lumber, and therefore, cash costs.
If a single roof structure is installed over several spans, hanging and layered trusses can alternate: for sections without intermediate supports - hanging ones are installed, where there are - layered ones.
How to properly install the truss system
One of the conditions for the reliability of the future structure is the correct arrangement of the attachment points of the truss system.
Pitched roof rafters usually have at least three points of support. Their number may vary depending on the size of the span. With a span width of up to 10 m, one additional support is required; for large values, their number increases.
The design of the hanging also depends on the width of the span. If it is small, the puff is usually replaced with a crossbar. With an increase in span, the puff begins to sag, and the legs begin to sag.
With a span
up to 9 m, hanging rafters are supported by a headstock - a special vertical beam. The ends of the legs are attached to its upper end with the help of staples or clamps, the headstock with a puff - with a clamp.
up to 13 m - strengthening is carried out with the help of struts. With their upper ends they rest on the leg, and its length between the supports should not be more than 5.5 m, and on the lower ends - in the headstock.
up to 17 m, the legs in the lower part are reinforced with help, for the upper part they use a trussed system: the puff is attached to two grandmothers and a crossbar is installed between them.How to properly fix the rafters
Whether the truss system is being replaced or it is being installed in a new house, certain rules should be followed.
A simple fastening of the leg and the beam can even be destructive - when pressure is applied to the rafter, its end begins to slide along the beam, which leads to the destruction of the roof .
To avoid slipping and ensure reliability, the following types of connections are used:
- spiked tooth,
- pointed tooth,
- stop at the end of the beam.
It is possible to use two teeth - it depends on the angle of inclination. For fastening, in addition to this connection, metal corners are also used.
The main nodes of the roof frame
Attachment to the beam
- A tooth with a spike is made in the heel of the rafter, and an emphasis is cut out in the beam with a corresponding socket for the spike.
- The nest depth is about 25–30% of the beam thickness.
- The cut is performed at a distance of 0.25–0.4 m, starting from the edge of the beam, which hangs down.
- A single tooth is performed, as a rule, together with a spike, which does not allow shifting to the side. Therefore, such a connection is called a "tooth with a spike and an emphasis."
In the case of a hollow roof, the angle of inclination of which is less than 35 °, the rafter legs are installed so that the bearing area per beam increases. To do this, use a cut with two teeth:
- in two spikes;
- emphasis with and without a spike;
- two spikes to the castle.
All connections in the structure are made using fasteners:
- metal - screws, nails, bolts with washers, various corners;
- wooden - bars, triangular overlays (kerchiefs), spikes.
To Mauerlat:
There are two technologies according to which .
Rigid - in this option, the possibility of any influences (shifts, turns, bends, torsion) is completely excluded between these structural elements. To achieve a similar result:
- when fastening, corners with a hemmed support bar are used;
- a saddle (washed down) on the leg is performed, the resulting connection is additionally fixed with wire, nails and staples. The nails are nailed from the sides, towards each other at an angle (they cross inside the Mauerlat), then the third nail is hammered in a vertical position. This is the more common mounting method.
Sliding (articulated)- such a pairing, which has two levels of freedom, is achieved through the use of special fasteners, which allows one of the mating elements to move freely (within specified limits).
The following options for sliding fastening of rafters and Mauerlat can be distinguished:
- washed down, after which the rafters are washed down on the Mauerlat:
- the elements are connected obliquely with two nails towards each other;
- they are connected with one nail, which is nailed vertically from top to bottom into the body of the base beam through the leg;
- an alternative to nails can be steel plates with holes for nails;
- fasten the boards to the Mauerlat with a bracket;
- release the rafter leg behind the wall and perform a single fixation with fixing plates;
- use special steel fasteners - "sleds".
In all these cases, the foot rests on the Mauerlat, but when moving, the elements of the system have the ability to move relative to each other.
Such a pairing is especially important for wooden houses erected from timber or logs, which shrink over time. Using a hard mate can cause damage to the integrity of the walls.
The truss system can be "floating" or rigidly fixed. The floating one is mounted on special brackets that allow the wooden frame to “sit down” simultaneously with the shrinkage of the gables and prevent them from hanging over the ridge log.
Ridge knot
There are three ways to connect in the ridge part.
butt
The upper edge of the rafters is cut at the same angle as the angle of the roof, rest against the desired rafter located on the opposite side, it should be cut in the same way. Corner trimming is usually done according to a pattern. For fixing under the ridge, two nails (150″) or more are used. One nail at an angle is hammered into the upper plane of the first and second rafters, while they must enter the cut of the opposite. The ridge joint is additionally strengthened by placing a wooden lining or a metal plate on the side of it, which is attracted with bolts or nails.
The rafter system is the frame of the roof of the house, which bears and evenly distributes the weight of the roofing pie, sometimes reaching up to 500 kg / m2. The reliability of this kind of skeleton depends on three factors: the accuracy of the calculation, on the basis of which the number and cross section of the supporting elements are selected, the material from which it is made, and also on the correct fastening technology. Knowing how to properly fix the rafters, you can significantly increase the bearing capacity of the frame, making it more durable and reliable. Installation errors, on the contrary, lead to noticeable strength losses and roof deformations. In this article we will talk about the main types and methods of fastening, with which you can install the rafters with your own hands.
The truss frame of the roof of the house is a system of interconnected supporting elements made of wood or metal, which give the structure a shape, slope, and also evenly distribute its weight between the bearing walls. Its main component is the rafter legs, which are angled beams that are connected in pairs along the slope, forming a ridge at the top of their connection. There are two main types of rafters:
- Layered. Rafters are called supporting elements, which in the roof structure have two points of support - on the ridge run and the Mauerlat. This type of rafter system is used in structures that have one or more load-bearing walls inside, on which the rafters can be “leaned”. This fastening of the rafters allows you to unload them through the use of additional vertical supports.
- Hanging. Hanging elements are called elements that have only one point of support, located where the rafters are attached to the wall or Mauerlat. The hanging type truss system experiences a load not only in bending, but also in bursting, therefore it is reinforced by horizontal compensating elements (crossbars, puffs, contractions).
Note! In most of the most popular truss systems, the rafters are attached to the Mauerlat. Mauerlat is a massive bar or beam with a section of 150x150 mm or 200x200 mm, laid along the load-bearing walls of the structure, on which the rafter legs will subsequently rest. It softens the pressure on the walls of the house, and also evenly distributes the weight of the roofing cake. You can attach the Mauerlat to the upper belt of the walls using anchor bolts or embedded metal studs.
Main connecting nodes
The rafter frame is called a system because all its elements are closely interconnected and fixed, as a result of which the roof structure acquires a stable shape, rigidity and high bearing capacity. Each connecting node between its parts is a weak point that can easily be deformed under load, so all fastenings must be carried out strictly according to the technology. Experienced craftsmen distinguish types of connections in the roof structure:
- Fastening rafters to the ridge beam. This connecting node is typical only for layered truss systems, in which the upper part of the rafter leg rests on a ridge run, mounted on vertical posts. The rafters can be fastened to it with the help of metal plates, nails or sliding sliders.
- Fastening rafters to the Mauerlat. The most important fastening unit of the rafter frame is the junction of the Mauerlat beam with the rafter legs. You can fix the rafters on it with nails, metal corners or wooden bars.
- The connection of the rafters to each other. To lengthen the rafter legs, if the length of the slope exceeds the standard length of lumber, they are assembled from several elements interconnected with nails, glue or metal linings.
- Connection of rafter legs with auxiliary supporting elements. In the design of the truss frame, the rafters can be connected to a puff, crossbar or struts to increase rigidity, strength and bearing capacity.
Please note that any cuts made to attach the rafters to beams, mauerlat or other structural elements of the frame lead to a decrease in their strength, so experienced craftsmen recommend connecting them together using corners and overlays.
Fixation methods
When deciding how to attach the rafters to the Mauerlat or ridge run, it is necessary to choose the right mounting hardware. The modern construction market has a huge assortment of fasteners of various designs and sizes. The main criteria for choosing fasteners are the material used to make the rafters, their cross section, as well as the type of load to which they are subjected. There are the following ways of fastening rafters:
Experienced craftsmen believe that the most reliable way to fix the rafters is to use metal corners that firmly connect the wooden elements to each other, rigidly fixing the angle between them. The corner that overlaps the joint between the rafter leg and the ridge beam or Mauerlat serves as a kind of spacer between them.
Varieties of fasteners
Wood is a natural material that, in the process of leveling moisture and drying, shrinks significantly, due to which the linear dimensions of the structure change. That is why experienced craftsmen recommend building a roof for timber and log houses, a year after construction, when the shrinkage process passes from an active to a passive phase. If you fix the wooden elements of the frame rigidly, then after drying the roof of the house may be deformed. Therefore, the following types of fasteners are used to connect the rafters:
Interestingly, there are several options for combinations of movable and fixed connecting nodes. The most common are truss systems with one rigid and two sliding fasteners, which provide sufficient mobility with high strength and rigidity of the structure.
Types of fasteners
Among experienced roofers, disputes do not subside, the more efficient it is to fasten rafters to floor beams and Mauerlat. However, in most cases, the catch is that in these conditions it is more practical to use nails or self-tapping screws. Both of these fasteners have their own advantages and disadvantages:
- Nails are good because only a hammer is needed to drive them, which is in every household. However, some masters complain that it takes too long to hammer them manually. It is worth recalling that special serrated nails are used to fix the rafters, which securely adhere to the wood.
- To assemble the rafter frame, galvanized self-tapping screws are used, which are not afraid of corrosion. Due to the thread, they are firmly screwed into the thickness of the wood, securely fixing the elements together. Screw them quickly and conveniently with a portable screwdriver. The disadvantage of this type of fastener is that during dismantling, removing self-tapping screws from wood is long and dreary.
Most experienced roofers agree that it is better to use galvanized ruff nails to fix the rafter legs, the length of which is 5-3 mm longer than the thickness of the lumber. Properly selected fasteners are the key to high-quality and long-term fixation of the roof frame, which will not be afraid of either mechanical stress or wind load.
Video instruction