Knots for connecting truss structures. Types and diagrams of truss systems: an overview and recommendations for installing a roof 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 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 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 bar. 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 between these structural elements, the possibility of any influences (shifts, turns, bends, torsion) is completely excluded. 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 template. 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 truss system is the skeleton of the roof. It is she who is responsible for the strength of the roof, its reliability and resistance to stress. When building a house on your own, you need to know how to properly make the attachment points of the truss system so that the roof is reliable and safe.
The device of the truss system
The truss system consists of many elements, each of which performs its task.
- Mauerlats are responsible for distributing loads on the walls. These beams take on the weight of the entire roof and lie on the walls.
- rafter legs- these are inclined beams, which create the necessary angle of inclination of the roof.
- Runs are horizontal beams that hold the legs together. There is a ridge run, located at the top, and side ones, located with slopes.
- The puffs are located horizontally and do not allow the rafter legs to part, forming rigid triangles with them.
- Racks and struts(rafter legs) - additional elements on which the rafter legs rest. They rest on the beds.
- Lying - a horizontal beam located under the ridge; racks and struts rest on it. The task of the bed is to redistribute the point load from the racks.
- The ridge is the junction of the roof slopes.
- Sheathing - bars or boards that are stuffed perpendicular to the rafters. Roofing material is laid on it. The task of the crate is to distribute its weight.
- Overhang - an elongated edge of the slope that protects the walls from precipitation. If the length of the rafter legs is not enough to create an overhang, additional elements are used - filly.
The device of the truss system is shown in the figure.
Also, truss trusses are distinguished in the roof device. This is a solid knot consisting of rafter legs, stretch marks, racks and struts (braces, braces). The farm can be not only triangular, but also trapezoidal, segmental or polygonal. Which type of farm to choose depends on the size of the house. If the distance between the walls is 9-18 m, then a triangular truss will do. For houses with a width of 12 to 24 m, trapezoidal or segmental trusses are used. If the width of the building is greater (up to 36 m), then polygonal trusses are used.
The main attachment points for the roof truss system are beam, ridge and Mauerlat.
Types of truss systems
Rafters can be hanging and layered.
Hanging lean on the walls and create a spacer. To reduce it, puffs are made at the base of the rafters, which connect the rafters and form triangles with them. Hanging systems of various types are used for houses with a width of no more than 17 m. Depending on the width of the building, they arrange them differently.
If the width of the house is not more than 9 m, then the rafters are supported by a vertical bar - the so-called headstock. She is under the skate.
If the width of the house is from 9 to 13 m, struts are additionally installed, which at one end rest against the rafter legs, and at the other end against the headstock.
With a house width of 13-17 m, two vertical posts are used, connected at the top with a crossbar (fitted), as in the figure.
Sloped rafters rest on a load-bearing wall or columns inside a building. With this method, the rafter has three or more support points. The layered type of truss system creates less load on the walls of the building and is more durable; it is used for buildings of greater width. Such roofs can be arranged in different ways, depending on the location of the internal walls, they can be symmetrical or asymmetrical.
How to connect the parts of the truss system
To connect wooden elements to each other, nails, bolts, studs, as well as metal plates and corners are used to strengthen the knots. Additionally, wooden bars or plates are used.
Mounting Methods:
- teeth into a thorn
- point-blank teeth
- stop at the end of the crossbar.
The use of metal fasteners does not reduce the bearing capacity, since they do not need to be tapped, in contrast to fastening, for example, by the method of teeth into a tenon.
Rafters can be not only wooden, but also metal. For fixing metal rafters, various corners, brackets, mounting perforated tape, plates, bolts with nuts or self-tapping screws are used.
Mauerlat mount
If the wall is concrete, then a reinforced stiffening belt is made in its upper part, in which studs are provided. Mauerlat will be attached to them.
Rafters to the Mauerlat can be attached in two ways: rigid and sliding.
The first way is more popular. For fastening, special corners with a support bar are used. There are several ways to attach the rafter to the Mauerlat.
- Each rafter is nailed with three nails: two of them must be crossed, and the third is located vertically.
- Fastening with a bracket: one end of it is hammered approximately into the middle of the support beam, and the other is turned 90 degrees and hammered into the rafter.
- Fastening with wire rod: a clamp is made from a wire folded in 4 rows, with which the rafter is screwed to the timber. Instead of wire, a special perforated tape is also used. Sometimes this method is used in addition to other fastening methods.
- With the help of corners: the corner is screwed with screws to the Mauerlat and the rafter leg. It is better to use corners with two rows of holes and a stiffener.
The disadvantage of the hard method is that when the building settles, damage to the walls is possible. Therefore, rigid fastening is used in brick buildings.
The sliding method implies that the rafters are connected to the Mauerlat with such fasteners that do not prevent their movement within certain limits. This method is used in wooden buildings that can settle. With the help of special fastening methods, it is possible to achieve that the rafter will have one, two or three degrees of freedom. In the latter case, a special hinge is used.
One degree of freedom means that the rafter can turn in a circle. In this case, they are fastened with one nail or screw. The two degrees of freedom are circular rotation and horizontal displacement. For this, the rafters are attached to the Mauerlat with metal brackets. Special corner-sleds are also used.
With a sliding connection in small buildings with a not very heavy roof, the fastening is done without cuts. If the building is large, it is recommended to do this knot with a gash on the rafter leg.
Important! Washed down is cut out on the rafters, and not on the Mauerlat, so as not to damage or weaken the beam.
In this case, the fixation can be either rigid (with emphasis on the beam) or movable (with a tooth on the outside). Sometimes, instead of sawing out a tooth, an additional bar is used.
Ridge connection
After the rafter leg is fixed on the Mauerlat, they move on to the ridge attachment point. This connection can be made in three ways: butt, to the ridge run and overlap.
For butt fastening, the rafters are sawn in the upper part at an angle equal to the slope of the roof, and connected with nails (150 mm), driving them into the upper planes of the rafters, so that the nails enter the end of the opposite rafter. For strength, a metal plate or wooden plate is attached, which is also nailed or attached with bolts.
When attaching to a ridge run, a ridge beam (run) is additionally laid between the rafters, this method is more laborious.
When fastening with an overlap, the rafters located on opposite sides overlap each other and touch the side surfaces. They are connected with bolts, nails or studs.
beam knot
The rafters are attached to the beams as follows. The main task of fastening is to prevent the rafters from sliding along the beam, so various techniques are used.
- In the heel of the rafter, it is necessary to cut a tooth and a spike, and an emphasis of the appropriate size is cut out in the beam.
- From the hanging edge of the beam, the attachment point should be 25-40 cm away.
- The mounting socket should be 1/4 - 1/3 of the beam thickness deep.
- Together with the tooth, a spike is cut out, which prevents the rafter from moving sideways. Such a connection is called a "tooth with a spike and an emphasis."
If the roof is flatter (its angle of inclination is less than 35 degrees), then the rafters are fixed in such a way that the area of their contact with the beam increases. Then use the following methods:
When creating a truss system for a roof, it is important to remember the following.
- All wooden elements are treated with an antiseptic and a refractory compound before installation.
- The thickness of any wooden part should not be less than 5 cm.
- Rafters without racks and struts are not made longer than 4.5 m.
- Mauerlat should be located strictly horizontally.
- Racks and struts are recommended to be done as symmetrically as possible.
- You can not add elements to the calculated truss system - this can lead to the appearance of loads where they are not needed.
- At the junction of wood with stone (brick) masonry, waterproofing is needed.
Properly made truss system is the key to the reliability of the roof. It is the rafters that take on the entire weight of the roofing materials and resist wind loads. Therefore, it is very important to build a truss system in compliance with the technology.
At the heart of each roof is a large number of beams, rafters, racks and runs, 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.
In addition to correctly made calculations and drawings, fasteners for rafters and all its elements are of no small importance in the stability of the structure.
In addition to the load of atmospheric precipitation, the rafters must withstand the weight of the crate and the total weight of the roofing pie, which must be taken into account when choosing a fastener.
The truss system is a spatial structure consisting of the following elements:
- Mauerlat;
- rafter legs;
- valleys;
- ridge beams;
- runs;
- crate.
In order to understand how all parts of the truss system are attached to each other, you need to figure out what nodes it consists of, what fasteners are used in each case and what they are. When assembling the supporting structure of the roof, fasteners, both steel and wooden, are used.
The main nodes of the connection of the truss system
Before connecting the Mauerlat and the rafter leg to each other, the first one will need to be firmly connected to the wall. Mauerlat is a thick beam (15x15), laid along the axis of the wall and parallel to the ridge of the beam, on which the rafter legs rest. The functions assigned to this element of the supporting structure are to distribute the load from the rafters, the weight of the roofing pie and atmospheric precipitation throughout the wall, including internal supports. In other words, the Mauerlat is the foundation for the entire roof. It is laid on the axis of the wall and fixed to it. In this case, there are several connection methods.
Method one. When constructing a roof of a large area along the entire length of the wall, an armored belt is poured, where metal pins are immediately embedded under the M12 thread every 2 m. In this method, the Mauerlat fasteners with the wall will be studs that pass through the beam and are attracted to the wall with a nut and pucks. With a small area of \u200b\u200bthe roof, where there is no large load on the wall, they do without a Mauerlat and the rafters are attached directly to the studs embedded in the masonry process.
Method two. Another quite affordable way to make the truss system stable is to attach the Mauerlat to the wall with a wire. To do this, you need to lay the middle of the wire between the rows of bricks 3 rows before the end of the masonry. Its length should be sufficient to tie and pull the Mauerlat to the wall. You can also do without the Mauerlat and fix the rafter with wire directly to the wall. But such a connection will give a point load on the wall, which may affect its integrity.
The scheme for attaching the rafter leg to the Mauerlat can be rigid and sliding. The type of connection depends on the shape of the roof and the type of rafters, which can be hanging or layered.
Rigid and sliding connection of the lower part of the rafters with Mauerlat
Connection nodes in this case will be made of wood and can have several types:
- A tooth that has only an emphasis.
- A tooth with a spike and an emphasis.
- Emphasis directly on the beam.
A single tooth notch is used for a roof with a large angle of inclination, where the angle between the mauerlat and the rafter leg is more than 35º. To do this, you will need to cut a tooth with a spike in the rafter leg, and create a nest under it in the Mauerlat. The use of a spike avoids lateral displacement of the rafters. The double tooth notch is used when installing more gently sloping roofs. The latter method is used extremely rarely.
Recently, more and more often, a wooden mount for rafters has been replaced by a metal one, since it allows not only to get a more reliable one, but also to significantly reduce the installation work. Therefore, metal rafter bolts, brackets, plates, clamps, hinges and various corners are used as additional fasteners.
The most used method of rigid connection is driving nails from the sides at an angle into the mauerlat. Thus, internal crossing takes place within it. Further, for the final fixation of the connection, the third nail is driven vertically. Another way to prevent transverse displacement of the rafter leg is to fix it on the sides with metal corners.
The scheme for movable fastening of the rafters in the lower part is used for houses built from logs or timber. Since during operation the truss system is in motion due to a change in its physical properties, i.e., the building shrinks.
The rigid fastening scheme in this case is unacceptable, since such movements can lead to the destruction of the wall. This means that the attachment points need to provide mobility. In such cases, special swivel joints are used, which are called skids or corners with an oblong hole for fasteners. The sliding interface in this fastener achieves two levels of freedom through the free movement of one of the fastener elements.
Nodal ridge connection
The ridge connection of the truss system can be obtained in three ways: butt, overlap and on the ridge beam.
Butt. The upper part of the rafter leg must be cut at an angle equal to the slope of the roof. The opposite leg is also adjusted to the appropriate angle, but with an inclination to the other side. Further, they are interconnected at the top point with the help of a nail, which must be driven into the end of the rafters with the capture of the opposite end. In addition to nails, special plates are used for a more durable connection of joints. Both a 30 mm wooden board and a double-sided metal fixing plate can act as such fasteners. For its installation, bolts or nails are used.
The next two methods will be similar to the first, but have a slight difference. When fastening with an overlap, the upper parts of the rafter leg will be interconnected by their sides. The latter option is carried out by connecting each rafter directly to the ridge beam. In this case, threaded studs with washers and bolts are used as fasteners.
If trusses are used to stiffen the truss system, then to ensure good resistance to wind loads, it will be necessary to install the required number of diagonal ligaments. The presence of a brace and a brace (rafter leg) in the supporting structure helps the gables of the house to be more stable. The brace is installed by resting the upper part in, and with the lower part it rests against the main floor beam. The strut helps to reduce the load on the rafters in the center. Its installation is carried out at an angle of 45º. Diagonal connections are fixed using clamps, corners, plates.
Types and features of metal fasteners for rafters
If earlier craftsmen used wooden elements as such fasteners (bars, slips, dowels, metal staples, wooden pins, wedges), now such methods are inferior to more modern types. The construction market has a large range of metal fasteners, which are now much stronger and make the process much easier. The manufacturing technology of these elements uses metal, the thickness of which varies from 1.5 ... 3.0 mm, which allows the product to be more resistant to loads compared to any other material. In addition, rafter fasteners are available in any size and allow you to carry out the technological process with great accuracy.
The metal fasteners of the rafters, which can be perforated and nailed, include:
- perforated mounting tape;
- corners;
- plates;
- beam support;
- beam support;
- wire tie;
- self-tapping screws;
- bolts with nuts;
- corners of the KR;
- brackets WB;
- fasteners LK.
The use of perforated products allows strong enough with all parts of the system and provide good rigidity and strength at any angle. They are characterized by the presence of many holes for bolts, screws and self-tapping screws, with the help of which the attachment to the tree is carried out. The size of the product is adjusted by trimming to the desired length and width.
Also fasteners can be nailed. However, the use of this type is possible only in the factory by cutting, which bends the cone-shaped part. This operation is carried out by special machines under pressure.
KR corners have a large number of modified types, which reduce the risk of bolted joint breakage during natural settlement of the structure. Fastening is carried out without the use of special equipment using screws and nails.
Brackets WB are used for fastening the console of the supporting beam when installing wooden floors in houses made of logs or timber. At the same time, the tie-in on the rafter leg is not made, which does not weaken its bearing capacity. The connection is carried out using anchor bolts, nails or screws.
LK rafter fasteners are applicable where it is required to connect rafters and beams. It has the same advantages as WB fasteners, but the process is carried out only with screws or nails. Used in the construction of wooden houses.
Fasteners in the rafter system play a huge role. It depends on him the strength and duration of operation of the entire roofing pie. Therefore, the choice of type and method of attachment should be treated with great attention.
