Constructive knot of a roof truss ridge. Types of gable roof truss system: for small and large houses
The roof system is the outside part of the roof structure that is supported by the load-bearing structure. It includes a crate and a truss system. The triangle underlying this system should be a rigid and most economical structural element that contains the attachment points for the roof rafters.
The main characteristics of the nodes of the truss system
The main attachment points of the roof truss system are shown in fig. 1. They imply the presence of a rafter leg (Mauerlat - 1), a rafter leg (ridge run - 2), a rack (puffs - 3). The design of the truss system is the main load-bearing element of the roof.
All roof fasteners must be of sufficient strength to eliminate a significant degree of risk associated with roof collapse. The consequences of a mistake made when connecting elements can be the most unpredictable.
Figure 1. The main attachment points of the roof truss system: 1 - mauerlat, 2 - ridge run, 3 - puffs.
First, the rafters are installed on the Mauerlat if the building has brick walls. Similar nodes are provided for concrete blocks, then it is necessary to create a reinforced concrete stiffening belt, and it is necessary to insert studs into its design. Their location should be at a distance of 1 to 1.5 m from each other, and their diameter should be more than 14 mm. The top of the studs must be equipped with a special thread.
Mauerlat is drilled, making holes that are necessary for attaching elements to it. Each of the holes should be the same size as the diameter of the stud, and its pitch should correspond to the distance between the studs. A nut is put on each protruding end of the stud and tightened, which ensures the strength of the connection between the Mauerlat and the wall. The rafters should be connected to the Mauerlat in such a way that their bearing capacity is not weakened.
Description of the main fasteners for mounting the truss system
If during the construction of the house a rounded log or timber was used, then it is not necessary to create an armored belt. produced on the upper beam or on the log of the wall. For this purpose, connecting the Mauerlat with the rafters uses different methods of cutting (tie-ins).
What fasteners fasten metal rafters:
- Plates.
- Fasteners LK.
- corners.
- Brackets WW.
- Self-tapping screws.
- Varieties of the corner of the KR.
- Wire ties.
- Mounting tape perforated TM.
- Bolts with nuts.
- Brackets WW.
If brackets are used when connecting the rafters to the Mauerlat, then they are not cut into the rafters, which helps to strengthen the bearing capacity. Metal brackets are usually produced, and the metal is galvanized and has a thickness of 0.2 cm. The brackets are strengthened with nails, anchor bolts or screws.
You can use the LK fastener by creating attachment points not only for rafters with a Mauerlat, but also for various other elements that make up the roof structure. The LK fastener is fixed to the wood, as are the brackets, with the exception of the use of anchor types of bolts.
Mounting perforated tape allows you to strengthen the connecting nodes in the construction of roofing systems. It is used not only to create stronger nodes, but also to strengthen elements for additional use in order to give rigidity or strength to the system as a whole. They fix the perforated mounting tape with screws or nails, so it is used to strengthen the structure of the rafter system of any roof, the integrity of which will not be violated.
With the use of KR corners and their various modifications, the attachment points are reinforced so that they can effectively participate in the connection of the Mauerlat and rafters. Ensuring appropriate strength to the roof units is permissible when using corners, which improves the load-bearing characteristics of the roof structure.
The use of connecting elements made of metal is not associated with inserting corners into the roof system. This will not cause a decrease in the bearing capacity of the roofing system. You can use corners for connection using screws or nails, the protrusions of which resemble a ruff.
How are the knots connected in the ridge part?
There are three main types of fastening in the ridge parts of the roofing system:
- Butt connection.
- Mounting on the basis of a ridge run.
- Ridge joint overlap.
For the purpose of fastening, in the first way, the ridge part is cut off from the upper edge at an angle that is the same as the angle of the roof slope. Then it rests on the necessary rafter, which should also be cut at an angle, but on the opposite side of the roof. A special template is sometimes used to trim corners.
Nails for connecting the rafters under the ridge should be 150 mm or more in size, two of them will be needed. Each nail is driven into the rafters at the top of the rafters at the appropriate angle. The sharp end of the nail usually enters the cut of the rafter from opposite sides. Strengthening the ridge joint can be achieved by applying a metal plate to it on the side or a wooden lining so that it is enough to pull it with bolts or nails.
The connection in the second way, that is, through the ridge run, is associated with the strengthening of the rafters on the ridge beam. The run is one of the additional support beams or beams, which is a support for the rafters. It is located parallel to the ridge or Mauerlat. The method differs from the previous one in that a ridge beam is laid between the rafters, which are sawn at an angle, which is a laborious process, so this method is used less frequently.
A more common method is similar to the first, but it differs in that the fastening is overlapped, and the joint method is not used. The rafters should be in contact with the ends, and not the side surfaces. The rafters should be pulled together with a bolt or hairpin, nails. This connection is used by many masters in practice.
In general, it is possible to install rafters on a Mauerlat by creating structures for roof truss systems that are expansion or non-expansion. This determines the choice of the appropriate method of connecting the power plate and rafters, which can be similarly strengthened to the ridge.
The main shortcomings in the installation of attachment points for the truss system
The problem of choosing the method of attaching the truss system to the structure of the building is very important when creating attachment points. Often, when creating nodes, the Mauerlat serves as a support for the rafters. The fastening of the Mauerlat beam is carried out “tightly” with the help of anchor bolts to the reinforced stiffening belt.
A possible drawback is an unanchored stiffening belt, which can lead to the overturning of the Mauerlat beam and the violation of the stability of the roof truss system. There is a loosening of the roof, and the roof is sliding down. Due to erroneous placement of anchor bolts or incorrectly made holes, the fastening is no longer effective.
If the nuts are screwed onto the bolts with an overtightening, then the fastening assembly becomes fragile and is subject to rapid destruction. In this case, wire twisting is sometimes used to create an attachment point.
During the construction of the truss system, the safety of the joints should be observed.
For example, if the truss structure is combined with the floor without taking into account the bearing capacity of the attic floor, then this is the most dangerous moment that can lead to the destruction of the building.
If the tightening is changed to a precast concrete floor beam intended for bending, then the use of precast concrete beams should be effective due to their rigid fixation in the reinforced floor stiffener, which is arranged using a reinforcing cage. Its axis must go in the same direction as the acting forces.
At the same time, the presence of shortcomings in the process of creating a truss system, which is a load-bearing wooden floor structure, often arises due to a misunderstanding of the functions performed by the puff and crossbar in the entire roofing system. The puff differs from the crossbar in that it is a longitudinal, and the crossbar is a transverse beam.
The construction of the truss system is associated with the creation of a spacer system that works on the principle of divergence at the bottom of the planes, which occurs under the influence of not only their own weight, but also the load that falls on the line of intersection of the planes, which should be prevented by the transverse beam, that is, tightening.
Getting to the roof device, you should find out all the points associated with the assumption of certain errors that occur when performing work on the installation of the truss system. The device of the roof of the house is associated with possible difficulties and shortcomings that do not allow achieving the goal.
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 staggering 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.
When designing any residential building, architects pay special attention to the roof, as it performs not one, but several functions at once, depending on its design features. It must be said that not all future homeowners are satisfied with the usual gable roof, although it can be called the most reliable, since it has only two pitched planes and one joint between them. Many are attracted to more complex designs that add a special appeal and originality to the structure. Other, more practical homeowners prefer attic structures that can simultaneously serve as a roof and a second floor.
The basis of any roof is an individual truss system, which has its own design features. Making the choice of the desired roof frame will be much easier if you figure out in advance which ones types and schemes of truss systems used in building practice. After receiving such information, it will become more clear how complex such structures are in installation. This is especially important to know if the roof frame is supposed to be built independently.
The main functional tasks of truss systems
When arranging pitched roof structures, the truss system is a frame for covering and for holding materials of the "roofing pie". With proper installation of the frame structure, the necessary conditions will be created for the correct and non-insulated types of roofs that protect the walls and the interior of the house from various atmospheric influences.
The roof structure is also always the final architectural element of the exterior design of the building, supporting its stylistic direction with its appearance. Nevertheless, the design features of the truss systems must first of all meet the requirements of strength and reliability that the roof must meet, and only then - aesthetic criteria.
The frame of the truss system forms the configuration and angle of inclination of the roof. These parameters largely depend on the natural factors characteristic of a particular region, as well as on the desire and capabilities of the homeowner:
- The amount of precipitation in different periods of the year.
- Direction and average wind speed in the area where the building will be erected.
- Plans for the use of the space under the roof - arranging residential or non-residential premises in it, or using it only as an air gap for thermal insulation of the premises below.
- Variety of planned roofing material.
- Financial capacity of the homeowner.
Atmospheric precipitation and the strength of wind currents give a very sensitive load on the structure of the roof. For example, in regions with heavy snowfalls, you should not choose a truss system with a small angle of inclination of the slopes, as snow masses will linger on their surface, which can lead to deformation of the frame or roofing or leaks.
If the area where the construction will be carried out is famous for its winds, then it is better to choose a structure with a slight slope of the slope so that the sharp gusts that occur do not rip off individual elements of the roof and roof.
The main elements of the roof structure
Details and nodes of truss systems
Depending on the chosen type of truss system, the structural elements used can vary significantly, however, there are details that are present in both simple and complex roof systems.
The main elements of the pitched roof truss system include:
- Rafter legs forming roof slopes.
- - a wooden bar fixed on the walls of the house and serving to fix the lower part of the rafter legs on it.
- The ridge is the junction of the frames of two slopes. It is usually the highest horizontal roof line and serves as a support on which the rafters are fixed. The ridge can be formed by rafters fastened together at a certain angle or fixed on a ridge board (run).
- Lathing - these are slats or beams mounted on rafters with a certain pitch and serving as the basis for the flooring of the selected roofing material.
- Retaining elements, where you can take beds, girders, racks, struts, ties and other parts, serve to increase the rigidity of the rafter legs, support the ridge, link individual parts into a common structure.
In addition to the structural details mentioned above, other elements can be included in it, the functions of which are aimed at strengthening the system and optimal distribution of roof loads on the walls of the building.
The truss system is divided into several categories depending on the different features of its design.
attic space
Before proceeding to the consideration of different types of roofs, it is worthwhile to figure out what an attic space can be, since many owners successfully use it as utility and full-fledged living quarters.
The design of pitched roofs can be divided into non-attic and attic. The first option is called just that because the space under the roof has a small height and is used only as an air layer that insulates the building from above. Such systems usually include or have several slopes, but located at a very slight angle.
The attic structure, which has a sufficiently large ridge height, can be used in different ways, be insulated and not insulated. These options include attic or gable version. If a roof with a high ridge is chosen, then it is imperative to take into account wind loads in the region where the house is built.
Slope slope
To determine the optimal slope of the roof slopes of the future residential building, first of all, you need to look at the already built low-rise neighboring houses. If they have been standing for more than one year and steadfastly withstand wind loads, then their design can be safely taken as a basis. In the same case, when the owners set the goal of creating an exclusive original project, unlike the buildings standing nearby, it is necessary to familiarize yourself with the design and operational features of various truss systems and make appropriate calculations.
It should be borne in mind that the change in the tangent and normal values of the wind force depends on how large the slope of the roof slopes is - the steeper the angle of inclination, the greater the importance of the normal forces and the smaller the tangents. If the roof is sloping, then the structure is more affected by the tangential wind load, since the lifting force increases on the leeward side and decreases on the windward side.
Winter snow load should also be taken into account when designing the roof. Usually this factor is considered in combination with the wind load, since the snow load on the windward side will be much lower than on the leeward slope. In addition, there are places on the slopes where snow will definitely collect, giving a big load on this area, so it should be strengthened with additional rafters.
Roof slopes can vary from 10 to 60 degrees and must be selected not only with regard to the consolidated external load, but also depending on the roofing that is planned to be used. This factor is taken into account because roofing materials differ in their mass, their fixing requires a different number of elements of the truss system, which means that the load on the walls of the house will also vary, and how large it will be, also depends on the angle of the roof slope. Equally important are the features of each coating in terms of resistance to moisture penetration - in any case, many roofing materials need one or another slope to ensure the free flow of storm water or melting snow. In addition, when choosing a roof slope, you need to think in advance how the process of cleaning and repair work on the roof will be carried out.
When planning this or that angle of the roof slopes, you need to know that the fewer joints between the sheets of the coating, and the tighter they are, the less you can make the slope of the slope, of course, if it is not supposed to arrange a residential or utility room in the attic space.
If a material consisting of small elements, for example, ceramic tiles, is used to cover the roof, then the slope of the slopes must be made steep enough so that water never lingers on the surface.
Given the weight of the roofing material, you need to know - the heavier the coating, the greater the angle of the slopes should be, since in this case the load will be correctly distributed to the rafter system and load-bearing walls.
The following materials can be used to cover the roof: either a profile sheet, galvanized steel, corrugated asbestos-concrete and bitumen-fiber sheets, cement and ceramic tiles, roofing felt, soft roofing and other roofing materials. The illustration below shows the allowable slope angles for various types of roofing.
Basic structures of truss systems
First of all, it is worth considering the basic types of truss systems regarding the location of the walls of the house, which are used in all roof structures. The basic options are divided into layered, hanging, and also combined, that is, including elements of both the first and second types of systems in their design.
fasteners for rafters
Layered system
In buildings where internal load-bearing walls are provided, a layered truss system is often installed. It is much easier to install than a hanging one, since the internal load-bearing walls provide reliable support for its elements, and in addition, fewer materials will be required for this design.
For rafters in this system, the defining reference point is the ridge board, on which they are fixed. The non-thrust type of the layered system can be equipped in three versions:
- In the first version, the upper side of the rafters is fixed on a ridge support, called a sliding one, and their lower side is fixed by cutting to the Mauerlat. Additionally, the rafters in the lower part are fixed to the wall with wire or staples.
- In the second case, the rafters in the upper part are cut at a certain angle and interconnected using special metal plates.
The lower edge of the rafter legs is attached to the Mauerlat with movable fasteners.
- In the third version, the rafters are rigidly fastened in the upper part with bars or processed boards located horizontally, parallel to each other on both sides of the rafters connected at an angle, and a ridge run is pinched between them.
In the lower part, sliding fasteners are used to fix the rafters, just as in the previous case.
It is necessary to explain why sliding fasteners are often used to fix the rafters on the Mauerlat. The fact is that they are able to save the load-bearing walls from excessive stress, since the rafters are not rigidly fixed, and when the structure shrinks, they have the ability to move without deforming the overall structure of the roofing system.
This type of fastening is used only in layered systems, which also distinguishes them from the hanging version.
However, in some cases, a spacer system is used for layered rafters, in which the lower end of the rafters is rigidly fixed to the Mauerlat, and in order to remove the load from the walls, puffs and struts are built into the structure. This option is called complex, as it includes elements of a layered and hanging system.
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 cut in, 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 stage of building a house, special attention should be paid to the roof. The reliability of the entire structure will largely depend on how reliably, correctly and efficiently it will be done. One of the important parts of the roof is the truss system, which holds the finishing material, insulation, waterproofing and other elements. For gable roofs of houses, hanging rafters are often used, the design and components of which, as well as installation, are described in this material.
Rafters are the main load-bearing element of a pitched roof, which takes on the main load experienced by this structure. The rafter system is of two types - hanging or layered. You have to choose between them, based on whether there are internal walls in the structure under construction, which can serve as a support for parts of the roof. The hanging rafter system is used if there are no such walls, and here only the outer walls of the building will serve as a support. That is, these rafters do not have a central support as such and rest on the wall on one side, and on the opposite rafter on the other. The fastening of individual elements is carried out using slotted spikes, nails, anchors or metal plates.
Hanging rafters are usually used to cover spans with a width of 7-10 m. The scope of application may be different - such a system is used for the construction of roofs in warehouses, industrial buildings, residential buildings.
On a note! The maximum distance between the walls, which allows the use of a hanging rafter system, is 14 m.
Despite the fact that such rafters are installed at a slope, they do not act on the walls like spacers - they transfer only vertical loads. This can be achieved through the use of stretch marks made of timber, located at the base of the roof.
On a note! The tightening between the legs of the rafters is located the higher, the greater the load it experiences.
Rafter elements are made of timber, boards or logs, metal. Without fail, before starting installation work, the material must be treated with special protective compounds that will provide the tree with a long service life. They will protect it from fungus, mold. If the material is treated with fire-fighting compounds, then the house will gain additional protection against fires.
What does the hanging rafter system consist of?
A system of this type has several components. And it is necessary to get acquainted with them in order to understand the purpose of each of them and not to get confused in concepts.
Table. The constituent elements of the system.
| Element | Description |
|---|---|
| This is the basis of the system. It is thanks to them that it turns out to form the shape of the roof, slopes. They are created from a bar (or board) with a section of 50x150, 100x150 mm and are placed in increments of about 60-120 cm. The dimensions and pitch chosen will directly depend on the parameters of the roof, its design features, and the calculated load. |
| The place where two roof slopes are connected. Usually there is an additional ridge beam. |
| With the help of these elements, representing beams horizontally located between the rafters, the rafter legs are tightened and strengthened. Due to the puffs, the load experienced by the rafter legs is compensated. |
| A kind of puff, which is located near the roof ridge. It is made of a very durable timber, as it experiences a colossal level of load. |
| A beam, which is installed on the upper part of the load-bearing walls, rafters rest on it. It helps to distribute the weight of the entire roof along the perimeter of the building, which makes it possible for the foundation and walls to experience the load evenly. For manufacturing, a bar with a section of 100x100 or 150x150 mm is used. Interestingly, it may not always be used - some types of roofs are equipped without it. |
| An element that is installed under the roof ridge and is designed to support a long draw. |
| These structural details are used for buildings that have too large spans between load-bearing walls. They are necessary to support the rafters, providing them with a minimum bending load, that is, they will not allow them to bend and sag. |
Bar prices
Types of structures
There are five main types of roof structures of this kind that can be obtained on the basis of hanging rafters and can be used in construction. They differ in the presence of some structural elements, configuration, etc.
The simplest option is triangular articulated arch. Its shape is triangular, the puff here is under tensile load, and the rafters are under bending. Such a scheme is used only if the height of the ridge is at least 1/6 of the entire span between the walls, otherwise it will not function correctly. Quite often used in the construction of attics. In this case, two rafters are joined and connected to each other in the ridge part. At the bottom, the triangle can be connected with a long puff. The system can only be used if the span between the walls is no more than 6 m.
Slightly different from the above system - articulated arch with headstock. In this case, the design has a support in the form of a headstock installed under the ridge. Due to the tightening, it works in tension. The headstock can be made of either metal or wood. The system is used if the spans between the walls are 6 meters or more. The headstock will not allow the puff to sag - it acts as a kind of suspension and allows you to adjust the degree of deflection of the horizontal part.
Articulated arch with puff that is raised, is usually used when planning the construction of attics and spacious attic spaces - that is, where the ceiling height is important. In this case, puffs will be installed at the top of the rafters. And the higher the puff is located, the greater the tensile force it perceives.
If the support is a fixed hinge element, then the structure will be called arch with crossbar. Here the roof is attached to the Mauerlat by forming a tooth on the rafters. The bolt itself resembles a small puff, but in this case it works not in tension, but in compression. Rafter legs are fixed quite rigidly.
Arch with struts and headstock resembles an arch system with a suspension. Here, during the installation of the rafters, struts are used, which ensure that the structure is relieved of excess stress. The option is suitable for closing spans with a width of 9-14 m.
On a note! Any scheme for the design of hanging rafters involves accurate calculations that will clarify all external and internal loads.
The rafter system is quite difficult to install, sometimes its parts are assembled directly on the ground, and then rise to the roof. But also rafters can be mounted right on the spot. In general, a roof with hanging rafters is the simplest option, therefore it is often made by novice builders or on their own.
Perforated plates used for attaching rafters
Prices for various types of fasteners for rafters
Fasteners for rafters
Ways of fastening rafters
These structural details can be fixed in two ways.
- Bolt and clamp, where in this case the end part of the rafter is cut off, and she herself is placed on the beam in the place where the notch is made. The fastening of individual elements is carried out with the help of bolts. They are connected so that the attachment point is perpendicular to the upper part of the rafter. Sometimes clamp systems are used for connection.
- double tooth. The method is applicable if the slope of the roof slope relative to the horizontal is less than or equal to 35 degrees. In this case, two stops are made on the beam, a special hole is made in the rafter leg, and a spike is cut out at the place of the extreme stop on the beam. In size, these elements must correspond to each other.
System design
To correctly create a system layout, it is important to consider:
- rafter installation step;
- load on the structure and structure;
- section of rafters;
- material that will be used to create the roof;
- construction type;
- roof pitch angles
- the dimensions of the building as a whole;
- climatic conditions of the region.
The more accurately the calculation is made and the more correctly the rafter system is designed, the stronger and more reliable the whole structure will turn out. For convenience, you can use the existing online calculators, which is important for those who are not friends with the exact sciences, or for beginners.
Video - Roof truss system, what you need to know for proper design
Installation rules
Installation of hanging rafters must be carried out in compliance with certain rules. Only in this case it will be possible to make a correct and stable design. The work rules are as follows:
Installation of hanging rafters
For the construction of the truss system, certain tools and materials may be required. The list below is quite approximate, but can be used as a basis during preparation for the start of work.
Tools for creating a rafter system:
- a hammer;
- axe;
- jigsaw or hacksaw;
- building level, twine, tape measure;
- thread with a load (plumb line);
- pencil, ruler.
Prices for popular models of jigsaws
As necessary materials, you can directly list the beams and boards for rafters, self-tapping screws and nails, anchor bolts, waterproofing material, antiseptic compounds for wood processing.
Sigma-Extra - outdoor work, antiseptic for wood
Consider the installation process of the truss system step by step.
Step 1. All wood material is treated with antiseptic agents that prevent the development of decay processes, the occurrence of fungus and mold. Prior to installation, the material is well dried.
Step 2 Building material is delivered to the top of the building.
Step 3 A mauerlat is nailed along the perimeter of the load-bearing wall, consisting of two boards of such a width that they can cover the entire upper part of the wall with themselves. Between the Mauerlat and the wall, it is recommended to lay a layer of waterproofing material (for example, roofing material). This will seal the joint, protect the material from moisture and reduce drafts in the future.
Step 4 Next, beams are created from the beam, which will be attached to each pair of rafters in the lower part. They are attached to the Mauerlat and connect two load-bearing walls together. You can temporarily move along them during the work, and boards that are used to create rafters are also folded on them.
Step 5 To form the top of the roof, a ridge beam is cut out. It should have a length from one part of the future roof to another and be parallel to the long load-bearing walls.
Step 6 The required roof height is determined - the level at which the ridge beam will be attached. The angle of inclination of the slope is recommended to be done within 25-45 degrees. You can find out the angle of the roof and the length of the rafters using the Pythagorean theorem. To do this, you need to measure the distance from the ridge, the height of the roof and the distance to the outer wall.
Step 7 The ridge board is installed at the place of the future docking of two rafter legs.
Step 8 From the prepared lumber, future rafters of the desired length are measured and cut. They will be attached with the selected pitch to the ridge board and Mauerlat.
Step 9 To make it possible to attach the rafters to other elements, special triangular cutouts are made. To do this, the board is installed so that one side lies on the ridge board, and the other on the Mauerlat. The cut mark is applied. Next, the marked sections are cut.
Step 10 The second rafter is prepared in the same way. Now they should be docked with each other. To do this, the boards are moved as close as possible to each other, markings are applied indicating the place of the cut. The cut is made and the boards can be joined.
Step 11 The rafters are attached to the Mauerlat using metal corners and self-tapping screws. With the help of them, the boards are also fixed on the roof ridge.
Step 12 Two rafters are interconnected using metal plates and self-tapping screws. Thus, the first two structures are installed, which will be located at the edges of the roof.
Step 13 In order to make it easier to evenly install other rafters, a rope is stretched strictly horizontally between the extreme structures.
The process of installing rafters
Step 15 If necessary, the rafters can be reinforced with puffs, which are attached to two joining rafters.
Video - Installation of the truss system
Video - Installation of rafters
Video - Using a crossbar (screed) for rafters as an interior element
Hanging rafters are considered a fairly simple design compared to other types of truss systems. But there should be no rush during their installation. It is important to remember that at the slightest skew all the work will go down the drain, so you need to work carefully and carefully.