Knots for connecting truss structures. Assembling a wooden skeleton: methods for attaching rafters
December 12, 2017Specialization: facade finishing, interior finishing, construction of dachas, garages. The experience of an amateur gardener and horticulturist. He also has experience repairing cars and motorcycles. Hobbies: playing the guitar and much more, for which there is not enough time :)
Any roof is subjected to various loads every day, as it is affected by wind, precipitation, and it also holds the roofing. In order for the roof to cope with all these loads for many decades, it must be properly designed. Therefore, for everyone who wants to do construction on their own, I recommend to figure out what parts and nodes of the truss system exist, and what function they perform.
Frame elements
All details of truss systems can be conditionally divided into two types:
- Basic. These parts form the roof frame, called the truss system. Not a single roof can do without them;
- Additional. This group includes elements that may be present in some types of roofs, while others do without them. The task of additional elements is to increase the rigidity and strength of the frame.
Main knots
So, the following elements belong to the main nodes and details of the truss system:
- Mauerlat. This, one might say, is the basis of all roofing systems, since rafter legs rest on the Mauerlat. Its design is extremely simple, in fact, it is an ordinary bar (a log in log houses), laid along the perimeter of the walls. Its task is to evenly distribute the load from the roof to the walls of the building.
I must say that at a gable roof, the Mauerlat can be located not along the perimeter, but only on the side walls, since there are pediments on the end walls, which are a continuation of the wall;
- Rafter legs (hereinafter CH), or simply rafters. These parts are the supporting element that forms the slope and its angle of inclination. They take on the wind and snow load, as well as the weight of the roofing material, and transfer it to the walls through the Mauerlat and other elements.
Rafters are lateral (main), diagonal (installed at the junction of hip roof slopes) and shortened (diagonal rafters rely on Mauerlat);
- Rafter farms. They are formed by paired (reciprocal) rafter legs. It must be said that truss trusses are present on all pitched roofs except for shed roofs, since they do not have reciprocal rafters;
- Skate knot. It is the top of the roof truss, i.e. formed by the junction of two CHs. The ridge knot, like the trusses themselves, is absent only from shed roofs.
That's all the main knots of wooden roof structures that form them.
Additional
Additional details include:
- Run. This is a horizontal beam that connects all CHs within one slope;
- Skate run. It is the same horizontal beam as a regular run, but which runs in a ridge knot, i.e. connects two legs of each truss at the same time.
I must say that the ridge run can be installed in several ways - above the junction of the rafters, in the center of the junction, i.e. legs rest on the run, or under the rafters;
- Puff (bolt, fight). It is a beam that connects two reciprocal legs, preventing them from moving apart. We can say that the tightening removes the spacer load from the bearing walls;
- Supports. Can support rafters, all types of runs or puffs. Supports transfer the load to the internal walls of the building, columns or ceilings;
- Struts (rafter legs). They are inclined supports, which have the same function as the vertical racks. The only thing is that they support only the legs, i.e. are one of the elements of wooden trusses. Rafter legs transfer the load to the load-bearing elements of the building, or to the ceiling;
- Filly. These elements form the overhang of the slope in the event that the CHs do not go beyond the walls. In fact, they lengthen CH, i.e. are their continuation.
That's all the elements that make up the frames of pitched roofs.
A few words about the types of systems
So, we figured out the nodes, now let's look at the main types of truss structures. There are several of them:
- Shed. As I said, these structures do not have trusses. The angle of the slope is formed due to the different heights of the walls on which the CHs are laid, or due to the run, which is laid on racks installed on one of the walls;
- Gablesloping. Rafters are called rafters, which are supported by racks or struts that transfer the load to the internal load-bearing elements of the building. The frame of such structures is formed only by trusses, i.e. they do not have diagonal legs.
- gable hanging. Hanging rafters differ from layered rafters in that they transfer the entire load from the roof only to the outer walls;
- Hip. Unlike gables, at the ends instead of vertical gables they have inclined hips, i.e. end slopes. As I said, the hips form diagonal and short legs;
- broken lines. They are a gable structure, each CH of which is divided into two parts and is located at a different angle. Skating, i.e. the upper legs form a gentle slope, and the lower legs are steep. This design allows you to increase the attic space, as a result of which it can be used as an additional floor.
Typical broken (mansard) systems have racks on which the upper and lower CHs rest. The reciprocal racks are interconnected by puffs (attic floor beams).
There are also semi-mansard structures, which, in fact, are the usual hanging gable roof systems. The only thing is that their fastening with a Mauerlat is usually made sliding (movable), which allows you to increase the CH deflection, and thereby reduce the spacer load on the walls.
Despite the fact that the designs of all of the above systems are different, they consist of the same parts that we have already familiarized ourselves with.
One last thing about fasteners
Finally, I propose to consider how the connections of the main nodes are made, such as:
- Rafter / Mauerlat;
- Skate knot.
The rest of the details do not deserve special attention, since their docking most often occurs by washing down the interface (to increase the area of \u200b\u200bfitting the parts) and lining the steel plastic / corners, which are fixed with screws. Sometimes fasteners are not even used, i.e. parts are fastened to each other with screws without any overlays.
Connection of rafters and Mauerlat
The leg and Mauerlat mount can be made in several ways:
- With grooves. In this case, grooves are cut out under the Mauerlat, into which CH is inserted. Then it is additionally attached to the Mauerlat on both sides with a steel corner;
- Tooth and thorn. This method is usually used to attach the CH to the puff. Its principle is based on the fact that a spike is selected at the end of the sawed CH, and a groove is selected in the puff. In addition, the leg itself rests against the so-called tooth, i.e. protrusion in the puff, which takes on the expansion load.
It must be said that in recent times, fasteners such as a tooth with a spike are rarely used, since it is much easier to use special fasteners, the same corners and plates;
- By washing down. In this case, the CH is sawn so that a right angle is formed at the junction with the Mauerlat, as a result of which the rafter not only rests on the beam, but also rests against its side surface, thus transferring the spacer load. I must say that instead of washing down, you can fix the bar, as shown in the diagram below.
Connection of rafters and ridge run
The connection of CH and run can be done as follows:
- With a groove. In CH, two reciprocal cuts are made, as a result of which, after the junction of the rafters, a groove is formed for the ridge run;
- Hard pinching. The principle is based on the fact that puffs are installed under the run and above it;
- Got drunk on the way. This is the simplest and most common method, the principle of which is based on sawing CH for maximum fit to the beam. In this case, fixation is carried out with a steel corner.
Here, perhaps, are all the main nuances of assembling truss systems.
Output
We have found out what parts the truss systems consist of, what types they are and how their main elements are connected. If I missed some points or something is not clear to you - write comments, and I will be happy to answer your questions.
December 12, 2017If you want to express gratitude, add a clarification or objection, ask the author something - add a comment or say thanks!
The reliability of the roof structure directly depends on how correctly its entire supporting system will be mounted. And its main elements are rafters. The whole system consists of rafter legs that support and expand additional elements, such as struts, puffs, crossbars, side runs, support posts and extensions. The rafter legs are connected on the ridge beam from above, and their lower edges very often rest on, fixed on the side load-bearing walls of the building.
Since the biggest load falls on the Mauerlat, it is made from a powerful beam. Its cross section is determined by the massiveness of the entire truss system, but basically the size is from 150 × 150 to 200 × 200 mm. This load-bearing element is designed to evenly distribute the load from the entire structure of the roof and roof onto the load-bearing walls of the building. The fastening of the rafters to the Mauerlat is carried out in various ways. They are selected locally depending on the type of truss system (which can be layered or hanging), its complexity and massiveness, on the magnitude of the total loads to which the entire roof structure will be subjected.
Varieties of connecting nodes "rafters - Mauerlat"
First of all, there are sliding and rigid fastenings of rafters to the Mauerlat.
1. Sliding mounts consist of two separate elements, one of which has the ability to move relative to the other.
These mounts can be of different designs - closed and removable.
- The closed mount consists of a corner, which is attached on one side to the Mauerlat, and on the other side has a special slotted eye. A metal loop with holes for fastening to the rafters is installed in it. Thanks to the free, not fixed vertical side of the corner, the fastening allows the rafters to move slightly if necessary, without deforming the walls of the building.
- The open mount is arranged according to the same principle, and differs only in that the metal loop is not inserted into the eye, but simply the upper part of the vertical shelf of the corner is bent down after installation, thereby fixing the connection.
Video: an example of installing a movable mount on a rafter leg and Mauerlat
2. There are many more types of rigid fasteners. They are selected depending on the massiveness of the wooden structural elements and the method of installation on the Mauerlat.
These include metal corners of different sizes, LK fasteners, which securely fix the rafters, installed with the help of washed down, without damaging it with fixing screws or nails.
- LK fasteners are produced in several sizes, so they can be matched to any bar or board thickness. The thickness of the metal from which these fasteners are made is 2 mm, no matter what size they are. Depending on the size, fasteners have a different designation.
| Designation | Size in mm |
|---|---|
| LK-1L | 40×170 |
| LK-2P | 40×170 |
| LK-3L | 40×210 |
| LK-4P | 40×210 |
| LK-5L | 40×250 |
| LK-6P | 40×250 |
It should be noted that these fasteners are suitable not only for connecting rafters on the Mauerlat - they are also used to fix the nodes of the "floor beam - Mauerlat".
The main advantage of this fastener is the maximum rigidity and reliability of the connection of wooden elements.
- The fastening of the rafters with a gash on the Mauerlat with the help of corners is carried out on both sides, which provides the required rigidity.
There are corners designed for attaching rafters without cuts. They have higher shelves and are screwed with a large number of self-tapping screws. They are made from metal with a thickness of 2; 2.5 or 3 mm.
| Designation | Size (length height width, metal thickness) in mm | Designation | Size (length height width, metal thickness) in mm |
|---|---|---|---|
| reinforced corner | 105×105×90×2 | Reinforced corner KP5 | 140×140×65×2.5 |
| reinforced corner | 130×130×100×2 | Reinforced corner KP6 | 105×172×90×3.0 |
| reinforced corner | 105×105×90×2 | Reinforced corner KP7 | 145×145×90×2.5 |
| reinforced corner | 50×50×35×2 | Reinforced corner KP8 | 145×70×90×2.5 |
| reinforced corner | 70×70×55×2 | Reinforced corner KPL1 | 90×90×65×2 |
| reinforced corner | 90×90×40×2 | Reinforced corner KPL11 | 90×90×65×2 |
| Reinforced corner KP1 | 90×90×65×2.5 | Reinforced corner KPL2 | 105×105×90×2 |
| Reinforced corner KP11 | 90×90×65×2.5 | Reinforced corner KPL21 | 105×105×90×2 |
| Reinforced corner KP2 | 105×105×90×2.5 | Reinforced corner KPL3 | 90×50×55×2 |
| Reinforced corner KP21 | 105×105×90×2.5 | Reinforced corner KPL4 | 70×70×55×2 |
| Reinforced corner KP3 | 90×50×55×2.5 | Reinforced corner KPL5 | 50×50×35×2 |
| Reinforced corner KP4 | 70×70×55×2.5 | Reinforced corner KPL6 | 60×60×45×2 |
A few additional words need to be said about some of the corners shown in the table, since their description requires clarification:
— KR 11 and КР21 are improved corners, often marked as TO P1 and KR2. These elements have an oval-shaped anchoring hole, which reduces the risk of bolt breakage in the event of structure shrinkage.
- КР5 and КР6 are corners used for fastening elements on which a large bearing load falls. corner TO P6 is also equipped with an oval hole, and it is recommended to use it when creating a rafter system on a new house, which will still shrink. These models are in demand for the installation of structures that have a lot of weight.
— Corner TO M is made of perforated steel and is used for fastening rafters with a large section. It is especially well suited for wooden buildings. This corner fixes the structural elements very securely, and when using it, it is not necessary to cut the rafters into the Mauerlat - it is enough to cut the correct angle at the first.
- The KMRP corner is used to fasten parts of the truss system at right angles, including rafters with Mauerlat. It also differs from conventional angles in that it has an elongated hole, which allows displacement during shrinkage without damaging the fixing bolt. It can be used in a design where it is impossible to cut one element to another.
KMRP corners are produced from 2 mm thick steel. Three varieties are produced:
| Corner designation | Dimensions in mm | ||
|---|---|---|---|
| a | b | c | |
| KMRP1 | 60 | 60 | 60 |
| KMRP2 | 80 | 80 | 80 |
| KMRP3 | 100 | 100 | 100 |
- Another option for fixing the rafters on the Mauerlat is to install them between two boards, sawn at a certain angle, and additionally fixed at the bottom with metal corners or LK mounts.
Such fastening gives good rigidity and reliability. This method is well suited in cases where the rafter needs to be fixed at the right angle, lifting it above the horizontal plane of the Mauerlat, but fixing it to the vertical outer side.
- A method of attaching rafters to a Mauerlat made from a beam of not too large a section. It is carried out by reinforcing the bar with wooden linings having the required thickness.
Fastening with reinforcing lining Pieces of boards are attached to the Mauerlat with nails or self-tapping screws, in those places where the rafter legs will be installed.
In this case, cutouts of the desired configuration and depth are made in the rafters. The rafter legs are securely fixed to the wall with the help of steel wire, which is fixed to a driven steel crutch.
- In addition to the above methods of fastening, the rafters are nailed to the Mauerlat using brackets. It should be noted that this method is quite common and has been used for a very long time. With proper fixing of these elements, the truss system will last for many years.
Fastening "the old fashioned way" - staples Staples can have different sizes, driven in at different junction points.
- Another fastener that is used as an auxiliary is TM perforated tape. It is used to strengthen the fastening unit if necessary, its additional fixation.
In some cases, this element can be indispensable, so it also cannot be excluded when installing rafter legs on the Mauerlat.
Features of truss systems
It is selected depending on the location of the load-bearing walls of the building. Each of the systems has its own additional retaining or tightening elements.
Rafters
The system with layered rafters is characterized in that it has one or more reference points, in addition to the load-bearing walls. Due with this, with side walls remove a significant part of the load.
In the form of additional retaining elements, side racks and "grandheads" are used, which support and are fixed to the floor beams. And the beams themselves, in turn, simultaneously serve as puffs for the structure, and also lighten the load from the truss system on the load-bearing walls.
Laminated rafters are most often attached to the Mauerlat with sliding joints that can move when the walls shrink or deform, leaving the roof structure intact. This is especially important to take into account in new buildings, since any newly built building necessarily shrinks under the influence of temperature fluctuations and ground movements.
hanging rafters
Hanging rafters are called due to the fact that they do not have other supports, in addition to the two side load-bearing walls. It turns out that they seem to hang over the internal space of the building. In this case, the entire load from the roof frame structure falls on the Mauerlat.
For fastening hanging rafters to the Mauerlat, rigid fasteners are used with no degree of freedom of movement, since the frame structure has only two points of support.
The hanging rafter system is spacer, so it puts a lot of pressure on the walls.
To remove part of the load from the walls of the building, additional elements such as struts, “headstocks” and puffs-crossbars are used, which pull the system to the ridge bar and evenly distribute the load on all walls. Crossbars are installed parallel to the floor beams and pull the rafters together. Without these additional details, the design may become unreliable.
Calculation of the installation of rafters
In order for the rafter system to be reliable and durable, in addition to the optimal connection method, you need to choose the correct step for the location of the rafter legs. This parameter is selected depending on the size of the rafters (and the length between the support points), as well as on the roof structure.
In this table, you can get information about the necessary parameters for the installation of a reliable truss system.
| Step of installation of rafter legs in mm | Length of rafter legs in mm | ||||||
|---|---|---|---|---|---|---|---|
| 3000 | 3500 | 4000 | 4500 | 5000 | 5500 | 6000 | |
| 600 | 40×150 | 40×175 | 50×150 | 50×150 | 50×175 | 50×200 | 50×200 |
| 900 | 50×150 | 50×175 | 50×200 | 75×175 | 75×175 | 75×200 | 75×200 |
| 1100 | 75×125 | 75×150 | 75×175 | 75×175 | 75×200 | 75×200 | 100×200 |
| 1400 | 75×150 | 75×175 | 75×200 | 75×200 | 75×200 | 100×200 | 100×200 |
| 1750 | 100×150 | 75×200 | 75×200 | 100×200 | 100×200 | 100×250 | 100×250 |
| 2150 | 100×150 | 100×175 | 100×200 | 100×200 | 100×250 | 100×250 | - |
Use, in the article on our portal.
Prices for various types of fasteners for rafters
Fasteners for rafters
A few rules for attaching rafters to the Mauerlat
In order for the fasteners to be reliable, it is necessary to follow a number of rules that are provided for this process:
- If metal connecting parts are used for fastening, then they must be fixed to wooden connecting elements with the utmost care - high-quality self-tapping screws of the required length.
- If the rafters will fit into the cuts in the Mauerlat, then the dimensions must be precisely verified. This will ensure a tight, reliable installation of the rafters in the prepared gash, which should have a depth of ⅓ Mauerlat. However, it should be remembered that such a rule will be valid only if the Mauerlat is made of a powerful bar with a cross-sectional size of at least 150 × 150 mm.
- In order not to weaken the Mauerlat, most often the cuts are made in the rafter leg itself at the desired angle, and in addition the knot is then fixed with corners. Washed down should not in this case exceed ¼ of the thickness of the rafters. This mount is rigid and can be used in a hanging rafter system.
- When using bolts to fasten rafters with slopes, puffs and other wooden elements, it is imperative to install a washer or a metal plate on the bolt in order to avoid flooding the nut into the wood and, accordingly, weakening the structure.
- Fastening the rafters to the Mauerlat only with nails or self-tapping screws is considered unreliable. therefore, it is imperative to use corners or other metal fasteners of various configurations.
- When installing rafters on wooden walls, whether it is a hanging or layered system, it is recommended to attach them to the Mauerlat with a sliding fastener, especially if the roofing material is heavy enough.
Video: a few examples of attaching rafters to the Mauerlat
The roof structure will turn out to be durable and will last a long time, without being deformed by a variety of external influences, if the calculations of all elements are made correctly, correctly select and properly mount all fasteners.
Rafters and lathing - the roof frame, which bears the brunt of the roofing pie, thermal insulation, snow load, so they must have a high bearing capacity, strength. The idea of using metal rafters to make the roof structure more rigid is not new, but in the past it was mainly used to cover industrial or utility structures. Now the rafter frame and the metal profile crate are considered a real alternative to wooden roof elements if the slope length exceeds 10 meters.
The design of the roof truss frame consists of many interconnected elements that form trusses. The step, the size of the section between the rafters and other supports determines the calculation of the loads to which they are subjected during operation. The roof frame performs the following functions:
- Load distribution. Interconnected nodes, reinforced with corners, evenly distribute the weight of the roof, which can reach up to 500-600 kg, taking into account the snow load. The larger the cross section of the rafters and the smaller the pitch between them, the greater the bearing capacity of the structure.
- Giving slope and shape. The rafters, located at an angle to the base of the roof, form an inclined plane of the slopes, so that snow and water do not accumulate on the roof surface.
- Formation of the base for fixing the roofing material. The top coat of the roofing pie is fastened to the roof frame. The crate acts as a basis for fixing the coating, distributing its weight evenly over the rafters.
Note! What should be all the nodes, rafters and lathing of the roof structure determines the engineering calculation. To determine the required bearing capacity of the frame, it is necessary to calculate the total load to which it will be subjected. To do this, add up the weight of the roofing material, insulation, waterproofing, the maximum snow load with the weight of the truss system.
Types of truss systems
The most common material from which the crate and rafters of the roof frame are made is wood. However, if the weight of the roofing material is large enough, and the length of the slope is more than 6 meters, then the structure is too massive. Builders have to reduce the step between the rafter legs, increase their cross section, which is why the roof units acquire a lot of weight, increasing the load on the foundation. You can unload the load-bearing walls and the base of the building using stronger, but lighter metal rafters. According to the type of material used, the following types of truss systems are distinguished:
- Wooden. Rafters and lathing made of wood are used for the construction of roofs, the slope length of which does not exceed 7-10 meters. The fastening of the frame elements to each other occurs with the help of self-tapping screws, nails or movable metal elements. The step between the legs is usually in the range of 50-80 cm.
- Metal. Metal roof frames are made of zinc-coated steel profile, which is not afraid of moisture. The rafters and the crate made of this material are light, durable, so the step between them can be increased to 1.5-2 meters. The fastening of the metal profile is carried out by welding or fasteners. Metal roof units are used with a slope length of 10 meters or more.
- Combined. The truss frame, combining metal and wooden knots, is called combined. The combination of wooden and galvanized steel support elements allows for a cheaper structure with a high load-bearing capacity by increasing the spacing between the rafters.
Please note that metal and wooden frame elements cannot be connected to each other without a gasket made of waterproofing material or treated with an antiseptic preparation. Since the metal has a high thermal conductivity, its proximity to the tree leads to the formation of condensation and rotting of the rafters.
Fastening methods
Metal rafters are assembled into triangular, trapezoidal or arched trusses. Internal stiffeners are attached to the frame beams, which form corners that significantly increase the load-bearing capacity of the frame. Such a system allows you to take a step between the rafters more, taking into account the support capabilities of each truss. The fastening of the metal elements of the roof frame is carried out by one of the following methods:
- Fastening by welding. If you weld the details of the truss system using a welding machine, you can get a rigid structure with high strength and bearing capacity. If you correctly calculate the roof, you can lighten the frame and reduce the load on the foundation of the structure. The disadvantage of this method is that only a professional with the help of special equipment can perform welding.
- Fastening with bolts. Fixing the rafters with fasteners allows for less rigid fastening. This method of assembling a truss frame based on a metal profile is used in private housing construction, where the length of the slopes does not exceed 10 meters. Rejection of welding allows you to speed up the installation of the roof.
Experienced craftsmen rely on the fact that the rafters can withstand more weight than wooden ones, so you can increase the step between them and reduce the thickness of the section of the elements. Moreover, ready-made roof trusses are sold in hardware stores, the fastening of which was carried out by welding, suitable for overlapping buildings of standard width.
Advantages
The metal truss frame is used for the construction of roofs of any shape, any slope with a slope of 1-2 degrees. As the material from which the rafters and lathing are made, steel corners, pipes of round and rectangular cross-section, and tauri are used. In order to correctly select the thickness of the frame elements and choose the step between them, the calculation of the roof structure is performed, taking into account the permanent and temporary loads that are transferred to the rafter beams during operation. The advantages of a truss system made of this material are:
- Fire safety. Unlike wooden beams, metal frame beams are not flammable, which increases the fire safety of the building.
- Ease of maintenance. Zinc galvanized coating, which covers the steel corners, protects the roof frame from corrosion during the entire service life. They, unlike wooden ones, do not require annual antiseptic treatment.
- Zero waste. Although metal structures are quite expensive, it is considered cost-effective, since the fastening is carried out by welding, and there is practically no waste left.
- Long service life. If you correctly calculate the loads, then the metal roof frame will last more than 100 years, which exceeds the life of even the most stable roofing.
Professional roofers believe that it is advisable to use welded metal structures for the manufacture of a roof truss frame with a slope length of 10-12 meters. In this case, the main task is to correctly calculate the loads, and then determine the step between the legs in accordance with the climatic characteristics and properties of the roofing material.
disadvantages
Despite the obvious advantages, metal truss systems are not the most popular design solution in private housing construction. Even a large step between the rafters and a sparse crate at a high cost of metal cannot make the structure cheaper than wood. The disadvantages of metal rafters are:
- High thermal conductivity. The metal has a high coefficient of thermal conductivity, so the rafters and form bridges are cold. From the point of view of energy efficiency, a metal profile frame is not the best solution.
- Difficulty in transportation and installation. When choosing a metal rafter system, take into account that transporting, lifting and securing long and heavy elements is more difficult than standard length lumber rafters.
- Difficulty of installation. To rise to a height and fix the trusses, special equipment is used, the rental or purchase of which is expensive.
- Deformation under high temperature. Although metal is considered a non-combustible material, during a fire it is highly deformed, which usually leads to the collapse of the roof.
To determine whether it makes sense to use more expensive metal profile truss elements, you need to calculate the roof frame. If the slope length exceeds 10 meters, and the load is more than 450-600 kg, then the installation of a metal frame is economically feasible.
Video instruction
The attachment points of the rafters must provide the necessary strength of the roof frame. It is important to choose the right technology for mounting the elements of the truss system among themselves and attaching them to the supporting contour so that the finished roof is able to withstand the design loads.
Features of roof structures
The task of layered and hanging roof truss systems is the most uniform transfer of the load of the sub-rafter structure, which, in turn, distributes the load on the load-bearing walls and the foundation of the building. The under-rafter structure is usually a mauerlat (a beam laid lengthwise on each load-bearing wall). It can also be floor supports (laid across the wall) or the upper crown of a log house made of timber or logs.
The choice of the method of attaching the rafters to the Mauerlat depends on their type. The layered design makes the Mauerlat work in shear, while the hanging trusses work in compression, the direction of which coincides with the orientation of the load-bearing walls.
Puff setting
Installation of a gable roof requires the installation of a rafter system of a layered or hanging type. In order to mount a rigid hanging truss truss that does not transfer spacer loads to the walls, it is necessary to correctly perform the fastening points of horizontal jumpers - puffs and crossbars.
Depending on which roof structure was chosen, the puff can be mounted at the base of the rafters and serve as a floor beam. The truss truss, which is attached to the Mauerlat, is equipped with a crossbar to stiffen it - a jumper located closer to the ridge. In mansard roofs, the crossbars serve as the basis for the ceiling sheathing.
The connection node when installing the puff is recommended to be performed by the method of "cutting into the rafter with a half-pan" using a fixing screw. This mounting method requires precise fitting of the elements, since with large gaps, at the interface points, the attachment point under load may collapse.
An easier way is overlap installation. In this case, the jumper is made of a board or two boards installed on both sides of the rafter leg. Nails are used as fasteners. The knot can also be a bolted connection, but this will reduce the bearing capacity of the rafters by 20%.
Another option is to install the crossbar by surprise. Installation of this type of assembly became possible after the invention of nail plates. The design is able to withstand high loads - reliability is ensured due to the tight fit of parts and strong fixation on both sides due to the large number of teeth on the plate.
The cross section of a beam or board for the manufacture of an expansion crossbar must match the cross section of the rafter.
Mauerlat: attachment points for rafter legs
The support of wooden rafters on the Mauerlat can be performed using two technologies:
- rigid attachment to the Mauerlat;
- sliding fastening to Mauerlat.
With rigid fastening, any kind of displacement of the rafter leg, which rests against the Mauerlat (bends, shifts, torsion), is completely excluded. To this end, when installing the roof rafter system, the installation of rafters can be carried out using a hemmed bar, which prevents the rafter leg from slipping at the point of support. Lateral shifts with this connection method are excluded due to the installation of metal corners.
In the second variant of the rigid attachment of the rafter leg to the Mauerlat, it is necessary to make a gash (saddle) at the bottom of the rafter or board. The plane of support must be horizontal; for this, the cut in the rafters is made at an angle corresponding to the slope of the slope. To fix the knot on both sides, the rafters are driven at an angle along the nail (they must be crossed inside the Mauerlat), the third nail is driven vertically through the rafter into the Mauerlat.
A sliding mount is usually used when building a truss system on a house from a bar or log. The basis for supporting the rafter legs in this case is not the Mauerlat, but the upper crown of the log house. To avoid deformation of the roof during shrinkage of the house, it is necessary to perform a node with a certain degree of freedom for the rafter leg. Often, for this purpose, a special fastener made of metal is used - a sliding support ("sled"). Its upper part is a loop, which is displaced along the guide, fixed on the rafter leg, when the log geometry changes.
Other methods of mounting the sliding knot are also used. A cut is made in the rafter leg, the beam is installed with a cut on the upper crown, after which it is fixed in one of the following ways:
- by means of one vertically hammered nail;
- with the help of nails hammered from both sides, crossing in the Mauerlat;
- by means of a bracket;
- by performing a single fixation with steel fixing plates.
This method of fastening leaves the possibility for the elements of the system to move relative to each other when the geometry of building structures changes.
Ridge connections
The device of the roof truss system with two slopes implies the presence of a horizontal rib in the upper part of the roof, formed as a result of the junction of the slopes - the ridge. The ridge knot can be performed in several ways, the choice depends on the type of truss system and the features of the building itself.
The layered design involves attaching the rafter legs to the ridge run - a horizontal beam located on racks parallel to the long walls of the house. The upper ends of the rafter legs should be cut at an angle corresponding to the angle of inclination of the slopes. The junction of the cut ends of the rafters to the ridge should be as tight as possible. Nails are used as fasteners. Slanted rafters are used if it is possible to install racks on the inner wall or columnar supports for attaching a ridge run. In addition, the walls must be equipped with a power plate to support the rafters.
Assembling a hanging type truss requires joining the upper ends of a pair of rafter legs. To do this, the end of each of the rafters is cut at an angle equal to the angle of the roof, the beams are connected by cut planes - it is required to ensure their tightness. They are fixed with two nails hammered at an angle into the upper planes of the rafters. Then, on each side, a wooden overlay or metal plate is nailed, which close the junction.
To provide the ridge with the necessary strength, cutting into half a tree can be performed: in this case, instead of the mating plane of the butt joint, the rafters are connected by a ledge. Next, a through hole is drilled for a stud or bolt with a diameter of 12 or 14 mm, nuts with wide washers are used for fastening.
If you have to install sliding supports on the wall of the log house or create adjunctions (rafter junctions with the Mauerlat) with a certain degree of freedom, special attention should be paid to the ridge. It is recommended to make a movable connection unit so that the roof does not deform during uneven shrinkage of the structure. To this end, the ends of the rafters are connected by a metal plate hinge.
The nodes of the hip roof truss system
A feature of the hip roof is the shape of its slopes: long slopes are trapezoidal, end slopes (hips) are triangular. The installation of such a rafter system requires the installation of diagonal (sloping) rafter legs, which form triangular slopes. The principle of fastening the diagonal rafters in the upper part depends on the design features of the main part of the roof. It can be formed from hanging trusses, or it can be a frame with a ridge run and layered rafters attached to the Mauerlat.
If the layered rafter legs of the trapezoidal slopes rest on the ridge beam (run), then the rafters must be supported on the console of the ridge run. Console outlets for the sub-rafter frame should be 100-150 mm. The lower part of the diagonal rafter legs are attached to the Mauerlat or a beam mounted on the wall.
If the rafters need to be supported on the extreme hanging truss, then the principle of creating the attachment point depends on the section of the side rafter legs. Sprengel with a stand is mounted if the rafter legs are made of a board. Diagonal rafters rest on the sprengel. In a situation where a beam was used to make the rafter legs, the rafters can be attached to the surf - a board with a thickness of 5 mm or more, fixed to the truss truss.
On the sloping rafters, washed down at an angle corresponding to the angle of inclination of the hip slope to ensure a tight connection with the truss or surf. For the strength of the nail connection, clamps and wire twists can be additionally used.
The shortened rafter legs (spreaders) are supported by the upper part on the rafter, the lower part is attached to the Mauerlat on the wall. The attachment point to the diagonal beam can be performed:
- washed down with a nail fastening method;
- via socket connection;
- by fastening bars with a section of 50x50 mm on both sides and along the entire length of the diagonal rafters and splints.
Auxiliary elements
To enhance the rigidity and reliability of roof structures, it is often necessary to install a strut, an additional run or support posts. Rafter purlins provide the rafter leg with an additional point of support. The run is a horizontal beam, fixed on vertical posts, parallel to the ridge. The attachment point is made using metal corner plates or an internal metal rod and an external straight bracket.
Wooden rafter braces allow to reduce the span of rafter legs (including rafters). The angle of inclination of the brace to the horizontal plane must be at least 45°. If the rafter is made of a log or timber, the strut is cut with the installation of a steel dowel at an angle of 90 ° to the junction, or the joint is closed from the outside with a plate.
If it is necessary to strengthen the roof frame, it is necessary to install a strut under each rack on which the layered rafter rests. In this case, all the struts of one slope rest against a common bed. Staples are used for fastening.
The struts of the extreme spans, which are subject to the maximum snow and wind load, require special attention. Attachment points when mounting the strut to the rack or run are made using pads and bolts.