The service life of a construction site depends on many factors. It is necessary to use high-quality materials, do everything in accordance with SNIPs and apply suitable engineering designs.
Attention ! When it comes to the use of a sliding support for rafters, it becomes clear to every experienced builder that further we will talk about installing a frame for the roof.
The roof plays one of the most important roles in a building. It protects the interior from precipitation and cold. But in order for this design to serve faithfully for many years, it is necessary to use sliding supports for rafters.
Rafters play an important role in supporting the structure pitched roof, more precisely, the main one. Therefore, builders devote a lot of time to their selection and correct installation... It is at the installation stage that the use of sliding supports is required. The main task of these structural elements is extremely simple. They prevent the roof from collapsing during the shrinkage of the house.
Each new house over time, it gives a slight shrinkage. Perhaps you more than once had to communicate with neighbors whose roof began to leak a few years after the construction of the house. This is not surprising, because they, most likely, did not use sliding supports for rafters when installing. The use of these elements would minimize the damage from shrinkage and preserve the integrity of the roof.
Of course, the cause of the leak may lie in something else. But it is impossible not to take into account such a factor as breaking apart walls. The supports connect the rafters and the main structure to each other. But their main difference from standard mounts is mobility. They have some backlash, which takes into account shrinkage.
Attention ! The use of sliding rafter supports ensures that the correct geometry of the roof is maintained, provided that all others construction works done well.
Sliding bearings properties
Application features
In most cases, the use of sliding supports for rafters is justified when erecting log buildings. The fact is that structures made of wood give the greatest shrinkage. In general, this is somewhere around eight percent of the total.
Important ! The process of building shrinkage is strongly influenced by humidity and the building materials used.
In the worst case, uneven shrinkage of the object is observed. After all, it is not the use of sliding supports for the rafters that greatly harms the fixing elements, causing irreparable damage to them. As a result, the rafters lose their performance. The tightness is broken and the risk of collapse increases.
In the most unfavorable development of circumstances, it is necessary to completely change the cover. It is much cheaper and more practical to use sliding rafter supports from the outset. it perfect option for log cabins and other houses, the main materials for the construction of which are logs.
Design features
The main feature of sliding supports for rafters, the circumstance that justifies their use in modern construction- this is the absence of a rigid fixation. A similar effect is achieved thanks to the metal elements, which can be moved if necessary.
Sliding supports are installed on the upper logs, which must be load-bearing. Otherwise, the meaning of using these structural elements is lost.
If we compare conventional fixing structures with sliding supports for rafters, then in the second case, specific constructs are used. Unlike bolts, brackets and self-tapping screws, they provide the mobility required for the structure.
The sliding elements of the rafters are made of metal strips. In this case, one part is attached to the rafters, and the second to the logs. However, stripes are not static objects. They have a moving connection.
Attention ! For installation, special self-tapping screws are used.
The fact is that ordinary self-tapping screws are not able to cope with the load that will be exerted on the moving elements of the roof. Another advantage of using sliding supports for rafters is the relatively low price, moreover, they can be purchased at any hardware store.
Sliding elements are made of galvanized steel. In addition, they have ready-made mounting holes. Therefore, you do not have to drill or finish anything. This technology allows the rafters to easily change their position. Thanks to this, the tightness of the entire roof is maintained.
Mounting
To install sliding supports for rafters, the use of special structural elements... It's all about moving parts that require special handling.
To prevent the rafters from falling under their own weight, special roofing techniques are used to ensure sufficient strength of the entire structure and minimum load where possible.
First you need to make a special semicircular saw at the installation site. It is on it that the installation will be done in the future. Then, between the log and the rafter leg, you need to install two or one spike. The amount depends on the slope of the roof. It is they who will minimize the load by transferring part of the weight to the logs.
Important ! The use of thorns allows the entire structure to be secured against longitudinal shear.
It is also possible to use special cuts. They are made in a load-bearing log. However, this option is only possible if the slope angle is relatively small. Moreover, intermediate supports must be available.
The insertion into the body of the supporting log should be carried out by no more than three quarters of the total diameter. Otherwise, there is a risk of weakening of the structure. If you do the installation in this way, then the friction that occurs will hold all the elements during installation.
When installing structures of this type, the use of small groups of workers is allowed. The most important advantage of this technique is that even with a small number, all the work can be done quite quickly.
What conditions must be observed during installation
There are a number of conditions, the application of which to a large extent guarantees the construction of a strong and reliable roof that will last for many years, these include:
- Jumpers when connecting the Mauerlat or the upper crown of the log house with the rafter legs should be sliding supports for the rafters. At the same time, when creating them, it is necessary to use steel with a thickness of 2 mm. The length of each piece depends on the expected leg offset.
- The guide fence should be parallel to the rafter leg. In this case, the corner is mounted perpendicularly. The use of this design feature will ensure sliding even at maximum shrinkage.
- When making rafters, you need to use boards with a cross section of 200 by 50 mm.
- Before installation, each structural element must be treated with special compounds. This guarantees fire resistance as well as protection against rot, mildew and insects.
Compliance with these conditions will guarantee a long service life of the roof, even in the most extreme conditions. Particular attention should be paid to the selection of biosecurity drugs.
In order for the use of sliding supports for rafters to be justified and make it possible to strengthen the entire structure, it is necessary to follow certain recommendations:
- The objects on which the systems will be installed must have the correct proportions.
- All truss systems are manufactured according to a previously created template. This avoids fitting and at the same time maintains all the proportions of the structure.
- Moving elements can also be used to create a ridge connection. Bolts and studs are suitable for fasteners. Alternatively, hinges can be used. But they need to be additionally strengthened with self-tapping screws.
- Quite often, when creating a roof with sliding supports, the technology of building boards is used. This technique allows you to work even with long spans. When connecting elements, use of long bolts is necessary. Build-up should be done with an overlap. The mounting holes should be about 10 cm apart.
Outcomes
The use of sliding supports for rafters in timber houses is justified by shrinkage, which reaches eight percent in the first few years. These structural elements allow maintaining the tightness and geometric proportions of the roof.
Gone are the days when mansions were raised without a single nail. The architects of wooden architecture did not use fasteners in the form of those elements that are relevant in modern construction. However, the study of the foundations and principles of the ancient architectural heritage led to the invention of reliable connecting elements for roofing wooden or brick house, log house. These include in particular the sliding supports for the rafters.
Effective fasteners for wooden roofs
The invention of an effective support for fixing the rafters to the supporting element of the structure, the Mauerlat, the ridge, greatly facilitated the work of roofers. The roof frame consists of many elements of different functional purposes, interconnected. Wooden frame changes under the influence of natural conditions, may become 15% lower due to shrinkage, may swell from rain, dry out in frosts. The geometry of the walls of the house also changes, unevenly and in all seasons. The heating season, the rainy season, and the summer drought will undoubtedly affect the condition of the wood, especially if the house is five-walled.
Sliding rafter support fastener preventing deformation of the roof, preserving its original reliability and strength. Monolithic stiffness rafter system, which occurs when fastening is used with staples, nails, self-tapping screws, under the influence of vertical and horizontal loads leads either to sagging or to a curvature of the roof, deformation that cannot be eliminated simple repair... Fastening with a sliding support provides play for moving the rafter relative to the beam or Mauerlat. That is, sliding rafters, as they are popularly called, provide compensation for roof distortions from changes in its geometry during drying, swelling and other processes.
Benefits of using a crawling design
Sliding supports used for fastening the rafters ensure, above all, a reliable connection between the base of the structure and the roof. Provide the ability to move wooden roof structures, while maintaining the strength and tightness of the structure. Other advantages that are characteristic of supports for rafters of this type:
- simplicity of the device;
- reliability of fasteners;
- ease of use, installation;
- durability;
- low cost.
A log house with a rafter structure assembled using sliding supports, the surface of which is treated with an anti-corrosion compound, in any area with any climatic conditions, winds, frosts and high temperatures can stand for at least a hundred years without losing strength and habitability.
Features of fastening rafters in a wooden house
Rigid or beamed supports when erecting a roof structure is especially not desirable in a timber structure. The inevitability of a change in the geometry of the rafter under the influence of moisture requires the creation of an opportunity for displacement of the rafter along the support. Sliding rafters in a wooden house provide reliable fastening and free play of the rafter at the junction with the support.
Wooden houses are subject to shrinkage to one degree or another. The degree of shrinkage is determined by the material from which they are built wooden houses:
- timber;
- glued laminated timber;
- simple chopped log;
- round log.
The highest degree of shrinkage is characteristic of houses made of solid wood, glued beams are least susceptible to deformation. The collection or loss of moisture by wood leads to a change in the geometry of the rafter system, and this process is characterized by unevenness and multidirectionality. Special fastening design at connection points rafter legs with a support using a device that allows the roof to move, while maintaining its geometry, ensures the integrity and reliability of the roof.
Varieties of sliding supports
The movable, sliding fastening of the rafters to the base is the only possible way prevent roof deformation. All such crawling supports have the same design principle. They consist of a fixed base, which serves as a guide and a movable element in the form of an angle, crawling along this base under the influence of a longitudinal or lateral load.
Support for rafters is:
- Open type;
- Closed type.
It is believed that an open-type support, a collapsible fastening device consisting of a stationary rail that is mounted to the rafter leg and a crawling corner, with attachment to the Mauerlat, is much more convenient in installation. Its use will not cause difficulties even for a novice roofer. It has varieties in terms of the number of mounting holes and the amount of travel from 60 mm to 160 mm. The maximum value of this parameter is more effective, since it provides better mobility of the rafters.
The support for rafters of a closed type differs in that it is non-separable. The monolithic one-piece structure of the device is mounted assembled in the same way as the open-type support described above. The corner is attached to the Mauerlat, it is equipped with a loop through which a guide is threaded, fixed to the rafter. Obviously, the utmost accuracy is required when installing a closed support, exact dimensions and calculations are required. On the other hand, anchorage with a closed support ensures the most efficient operation of the roofing system.
Separately, it is worth highlighting the popularity of such a name for the roof fastener as a sliding support for kucis rafters. Depending on the model, it has a stroke length of:
- 60 mm;
- 120 mm;
- 160 mm.
Kucis is made of 08PS low-carbon steel in accordance with GOST 14918-80 for perforated elements. The sliding support has high strength characteristics and is capable of withstanding serious loads. Its standard sizes are: - at least 2 mm thick;
- in width - 40 mm;
- in height - 90 mm.
Length dimensions provide a range of rafter travel 60 mm - 160 mm.
Floating or sliding rafter system technology
The development of modern architecture, the creation of extraordinary striking examples of individual housing construction has led to the birth of new technologies. The construction of a roof, a protective dome of a house from the vagaries of nature is an important stage of construction that determines the comfort of life. Therefore, to create complex systems roofs where floating rafters are used, or as they are also called sliding rafters, require accurate calculations. Calculations should reflect the angle of inclination, the volume of roofing material, and other components of a particular type of roof.
Sliding (layered) rafters are used for the following types of roofs:
- attic;
- tent;
- hip and half hip;
- multi-plated complex;
- steeple;
- domed.
That is, complex types of structures that need to be calculated. This is a job for specialists, amateurs have nothing to do in these matters, here even online calculator will not help in determining the elementary volumes of roofing material.
The sliding support of the rafters is connected to the Mauerlat, and at the top it rests on the ridge girder. Sliding rafters are connected by a knot, the angle of which can change depending on subsidence under load, so they do not slide off the roof, but slide a certain distance under load, keeping the entire roof structure intact.
The content of the articleThe erection of truss structures is a very responsible event, since the safety and durability of the object as a whole depends on their geometric accuracy and reliability of fastening. Some additional difficulties arise when installing rafters on buildings made of natural wood (log cabins, etc.).
In this situation, the sliding rafters will optimal solution to ensure the geometry of the roof.
Features of using sliding rafters
The technology of using sliding rafters is necessary for objects erected from logs, since these structures, unlike other materials, give a rather strong shrinkage during operation. Shrinkage of logs continues for several years and amounts to 5 - 8% of the volume of wood (depending on the moisture content of the materials used in the construction). The greatest danger is not the shrinkage of the structure itself, but the unevenness of this process.
Uneven shrinkage of load-bearing walls can damage rigidly connected truss structures, disrupting their geometry. After that, the rafters cannot serve as a reliable base for roofing materials, which breaks the tightness of the entire structure, significantly increasing the danger of operation. Therefore, the sliding rafter system is the optimal way out when erecting log cabins and other objects from logs.
Design features of sliding rafter systems
Sliding rafter systems are not rigidly fixed structures as they are mounted using movable metal elements. As with traditional installation, the rafter systems are installed on the upper load-bearing log of the log house, but instead of rigid fixing with brackets, bolts or self-tapping screws, so-called “sliders” are used for the rafters.
These elements are metal strip structures, one part of which is fixed to the log, and the other to the rafters.
... In this case, the structural elements can move relative to each other, creating a movable connection.
The installation of these structures is carried out using special self-tapping screws, since ordinary self-tapping screws cannot always cope with the required load. Assembled sliders are sold in many hardware stores and are relatively cheap. They are manufactured from galvanized steel with pre-assembled mounting holes. The use of these elements makes it possible for the roof systems to move the required distance during the shrinkage of the load-bearing walls, without violating the integrity of the structure.
- Sliding truss systems should be installed on objects that have the correct geometric shape... Otherwise, it is very difficult to carry out the correct roofing, since there are moving elements in the systems. Before starting the installation of rafters, it is necessary to carefully check the perimeter of the object and ensure it meets the recommended tolerances.
- The manufacture of rafter systems is carried out according to a pre-made template. This approach makes it possible to create the same structures for all roof elements.
- The ridge connection in rafter systems of this type is also performed using movable elements. Bolts and studs, which are a connecting axle, or movable hinges, reinforced with self-tapping screws, can be used as mounting elements.
- With a significant length of overlapped spans, it is often necessary to resort to building up the boards from which the rafter structures are made. If it is necessary to carry out this operation, the boards are connected with long bolts or special brackets. The boards are built up with an overlap along the pre-drilled mounting holes. When drilling, the mounting holes must be located at a distance (at least 10 cm) from each edge of the board. Hole drilling should be random to prevent the board from splitting through the holes.
- Each support for sliding rafters must be installed strictly parallel to the previous one and perpendicular to the supporting log of the structure. Deviation from this rule can lead to jamming of moving structural elements and their destruction when the task shrinks.
- Installation of "slides" is carried out on special cuts at an angle of 90 0 to the rafter support, which ensures free movement of the structure ... During installation, these elements must be brought to the extreme position, ensuring the maximum possible movement of the rafter structure when the building shrinks.
Installation of sliding rafters
Sliding rafters cannot be installed on support logs without the use of some structural elements, since they contain moving parts and will simply fall under their own weight, destroying the entire structure.
To prevent this situation, the sliding fastening of the rafter legs is carried out using special techniques.
On the rafter support at the installation site, a special semicircular gash is made, along which the installation is carried out. One or two spikes are installed between the load-bearing log and the rafter leg (depending on the angle of inclination of the roof), which remove the load from the rafter system, transferring it to the support log and protecting it from longitudinal shift.
It is also possible to install rafter structures in special cuts made in a load-bearing log (mauerlat). This method of fastening is applicable with a small angle of the roof slope and in the presence of additional intermediate supports.
The insert into the body of the Mauerlat is carried out no more than 3/4 of its diameter, in order to avoid weakening the structure. A similar way installation creates additional friction over a larger area, reliably holding structural parts during installation.
The basis of the wooden roof of the house is a frame that supports the roof covering. He contains a large number of elements, each of which is necessary and intended for a specific function. One of them is a sliding support for rafters, which serves to prevent deformation of the roof during shrinkage of a wooden house when its geometry changes.
Shrinkage of a wooden house
In one year, a log house can be reduced by 15%. The average shrinkage is 8%. Moreover, it can occur unevenly, which negatively affects the state of the rafter system. The resizing of the wooden structure occurs all year round... In the rainy summer season, the wood swells, and in the winter the material dries out. In addition, the walls gain and lose moisture in different ways, depending on the light and the wind rose. If there is a support on the central bearing wall, the deformations of it and the outer walls differ significantly, which also affects the uneven changes in the geometric dimensions of the house. During the heating season, the walls, especially the central one, decrease in size from drying out.
In the absence of a central wall, even bigger problems can arise. If the rafter system is not assembled as a truss, its rigidity is much lower. As a result, not only vertical but also horizontal loads act on the walls. Under the influence of pressure, they can bend outward, and the house will take the shape of a barrel in plan. In this case, the roof deforms and sags in the ridge. "Five-wall" allows you to get rid of this problem or significantly reduce it.
Application of screw jacks
To compensate for the processes of precipitation and seasonal movements of the house, screw jacks can be installed. They should be located on all vertical supports in the house. By twisting the jacks with the help, the movement of the log structures is compensated.
Purpose of using sliding bearings
It is not always advisable to rigidly fasten to the Mauerlat or to nails, staples, etc. If the box of the house can shrink, it is necessary to create an opportunity for the rafters to move relative to the supports. Previously, this was done using forged wire, which created a connection with a certain degree of freedom of parts of the structure.
Since then, the technology has changed, and more advanced devices have been used, such as a sliding support for rafters. It is attached to the walls as follows:
- to the upper crown of the log house;
- to the upper trim of the frame structure;
- to floor beams;
- to the Mauerlat.
Why are the supports made sliding?
The sliding support makes it possible to compensate for the distortions of the roof frame during its operation. When the wood dries out, the geometric dimensions of the structures change. At the same time, the width of the house decreases, but due to sliding along the floor beam, sagging or expansion of the roof, leading to subsequent leaks, does not occur. The reason for the ingress of precipitation inside may be different, but in no case should the effect of deformations from shrinkage be underestimated.
The advantages of sliding bearings
- Creation of a reliable connection between the base and the roof.
- Ensuring the mutual movement of wooden structures during the shrinkage of the base, which preserves the strength and tightness of the roof.
- Simplicity of the device, reliability and durability.
- Low cost and the ability to do it yourself from scrap materials. In this case, steel plates must be at least 2 mm thick and protected from above with an anti-corrosion coating.
Design features of rafters
Pair of rafters gable roof made according to one sample. The joint in the ridge is made end-to-end, with a gap or overlap. The rafters are connected to each other by a metal plate with bolts and nuts. The main design feature is the creation of sliding mountings in the lower supports. The rafters are placed on top of the Mauerlat or with a tie-in to fix the structure in the vertical plane.
The sliding support for the rafters, which serves as a fastening element, is made of two parts:
- a bar fixed on the rafter leg;
- corner with a loop, attached to the supporting beam (Mauerlat or support beam).
There is an even simpler option for how a sliding support for rafters can be made (photo below). For this, a corner with a slot is used. It is attached to the rafter along its axis, and in the slot with a gap is the head of the bolt screwed into the body of the Mauerlat.
This support for rafters (sliding - Kucis 120x40x40) costs only about 25 rubles apiece and is easier than others in installation.
The devices are made of galvanized steel plates. They are attached to one or both sides of the rafters. The double-sided version is preferable for roofs with high wind and snow loads and low weight roof structure... The fasteners are coated against corrosion so as not to spoil the wood. Stroke length depends on expected displacements and ranges from 6 to 16 cm.
Open and closed supports
Sliding supports for rafters ("slides") of the open type, consisting of two parts, can be made by hand, but you should use a template. All parts must be sized to fit. An open joint consists of a curved plate (fastening strip) and a corner with fastening holes (at least five).
When closed, the bar is inserted into the angle holder with the ability to move, but cannot be removed from it and is non-separable. Assembled construction allows for better installation. If there is an effort to detach the rafters from the Mauerlat under the action of wind loads, the loop can unbend, and the closed sliding support of the rafters is more durable.
Important! It is advisable to produce a rafter system with the ability to slide relative to the base only for a symmetrical gable roof. This is its advantage as it increases reliability at low cost. Supports can also be used for pitched roofs.
for rafters: dimensions
The support includes two components - a guide plate and a corner. The size of the permissible movement of the rafter leg depends on the size of the product.
The popular Kucis open and closed rafter sliding support has a plate width of 40 mm, a support height of 90 mm, and a length of up to 160 mm. The metal for the plates is taken with a thickness of 2-2.5 mm. They are cold formed from low carbon steel with good ductility. Hot-applied zinc coating serves as corrosion protection. When purchasing uncoated products, they should be painted with paint so that the material does not rust.
The corner is attached to the support bar. If its surface is round, a flat area is prepared for installation, grinding wood on a log to the size of the L-shaped part of the part. The photo below shows a similar closed rafter sliding support (Paz). Both types of products are stamped and inexpensive.
The rails are attached to the rafters in the extreme position to ensure maximum movement. Since when the roof shrinks, the angle of inclination changes relative to the ridge, it is necessary to make a hinge in the upper part of the rafters. Here, special perforated plates can be used.
Mounting
The sliding support for the rafters is used for the installation of the roof frame as follows.
- The rafters are made of boards 150-200 mm wide and 50 mm thick. If the length is insufficient, the rafter leg is lengthened, building up an overlap with a chaotic arrangement of fastening elements to prevent cracking.
- A girder is installed on top - a bearing bar located horizontally and perpendicular to the sliding rafters.
- In the lower part, the rafter legs are fixed on the saws made in the Mauerlat. In this case, their jamming is not allowed. But at the same time, the cuts should keep the boards from lateral distortions. The presence of a Mauerlat evenly distributes the loads across the entire building. In its absence, the local pressure on the walls from the rafters becomes greater.
- Fasteners of suitable sizes are selected based on the rafter offset range.
- A platform is being prepared for a corner on a support log.
- The corner is attached perpendicular to the log to allow free movement of the plate.
- The guide is inserted into the corner loop and attached to the rafter along its axis. Installation is done in the extreme lower position, since the bottom of the wall will shrink and decrease in size. In this case, the rafter leg will go down.
- The rafter boards are connected from above in a hinged manner.
Conditions that guarantee the strength, reliability and durability of the roof
- Compliance with the required mechanical properties and dimensions of the sliding supports for the rafters.
- The location of the guide support is parallel to the axis of the rafter, and the angle is perpendicular to ensure reliable sliding.
- The cross-section of the boards for the rafters should not be less than 150x50 mm.
- The roof frame must be treated with an antiseptic and fire-resistant compound.
- Compliance correct proportions roof frame.
- Manufacturing of the entire rafter system according to the template.
- Creation of an articulated ridge connection.
- The build-up should be done alternately in the lower and upper parts.
Sliding rafter support: other applications
Timber shrinkage compensation is applied not only to roof frames. It is used wherever it is necessary to create the ability to move parts of wooden structures, for example, when erecting partitions in wooden houses. If you need to finish the wall in the bathroom ceramic tiles, you cannot simply sheathe it with sheet material.
It is necessary to install a "floating" frame, fixed from above on sliding supports, and then attach the drywall to it, on which the tiles will be glued. Moreover, the stitching is not done up to the ceiling itself. When the walls are deformed, the frame will remain motionless, and the cladding will not collapse.
Conclusion
Sliding supports for rafters in wooden houses are necessary to prevent deformation of the roof during shrinkage of the house. It occurs especially actively in the first years after construction (about 8%). Correct installation rafters will ensure the permanent tightness and strength of the roof.
Despite the abundance of modern building materials characterized by a long service life and affordable cost, natural wood for centuries it has not lost its leading position in private housing construction, thanks to environmental safety and exceptional energy efficiency. However, when building timber or log houses, one problem arises - a strong shrinkage of the structure, which does not allow it to be blocked immediately after the end of construction. Due to this feature of the material, it is impossible to immediately start interior decoration and move to a new home. To avoid deformation of the roof during shrinkage, a special device will help - sliding rafters, the device of which we will describe in our article.
Sliding supports for rafters are called special devices that are necessary to connect the elements of the rafter frame to each other, but leave them a small power reserve, which prevents the structure from deforming during the shrinkage process. In everyday life, these fasteners are often called sliders or sleds. They consist of two parts, one of which is stationary, and the other is capable of sliding. Sliding bearings are made of durable, corrosion-resistant metal that can withstand significant loads. The advantages of this method of attaching the rafters are:
- The ability of the roof to change its geometry during the shrinkage process, so that the roof can be erected immediately after the completion of the construction of a wooden house, without waiting for the wood to dry completely.
- Facilitating the process of attaching the rafters. The use of special movable mounts reduces the manual labor when assembling the truss frame, it reduces the time spent on roofing work.
- Provides a secure fit. Factory-made sliding supports go through several stages of quality checks, so they are guaranteed to withstand the snow and wind loads that the rafters are subjected to during operation.
Please note that movable rafters are subject to intense loads during operation, so they are made only of high-strength, low-carbon steel with a thickness of at least 2 mm.
Functions
Shrinkage is the process of changing the size of wooden buildings due to a decrease in the moisture content of the wood, which lasts for 1-3 years from the date of construction. The most active shrinkage occurs in the first year, during which the house can become 1-2 times the width of 1-2 crowns lower. It is because of this property of the tree that it is not recommended to overlap the roof immediately after construction. The sliding rafter support solves this problem by performing the following functions in the rafter frame structure:
- Prevention of deformation of the rafters during the shrinkage of the wooden house. Thanks to such a movable system, the rafter legs adapt to the size and geometry of the structure, compensating for the bursting loads to which they are subjected load-bearing walls.
- Ensuring the mobility of the frame during operation. Wood is a natural material that, during operation, even after the end of the shrinkage process, can change its moisture content and dimensions. They say about wooden houses that they "breathe", so the roof truss frame must adapt to them, also changing dimensions when the humidity rises or falls.
Note! Many believe that if the rafters and the box of the house are made of the same material, then the rafter system will not deform during the shrinkage process. In fact, the shrinkage of different parts of the structure is uneven. In this case, the dimensions and geometry of the frame elements change in several planes at once.
Varieties
The use of movable fasteners to fix the rafter legs to the Mauerlat is the only way to prevent roof deformation during the shrinkage of wooden houses. As a rule, sliders have a fairly typical design, consisting of a static guide base and a corner with a loop that moves along it. There are the following types of movable mounts:
Professional roofing masters believe that movable fasteners for open rafters are much more convenient for installation, especially if the assembly of the rafter frame is carried out by the hands of an inexperienced worker. On the other hand, closed supports are more reliable in operation, and also withstand heavy loads.
Installation technology
The process of assembling the roof truss frame using movable fasteners is not much different from the standard procedure. However, it requires maximum dimensional accuracy in the manufacture of elements, as well as maintaining the same angle between the base of the roof and the end of the rafter leg when installing it. The rafter system is being installed in the following order:
- First, a Mauerlat is laid on the load-bearing walls of the house. This element of the roof truss frame performs supporting functions, evenly distributing the loads between the supports and transferring them to the foundation. In log cabins or log houses the functions of the Mauerlat can be performed by the upper crowns.
- A rafter leg template is made, which will become a model for the manufacture of all other rafters of the structure.
- At the end of each rafter leg, they make a wash under the Mauerlat. Experienced craftsmen note that in no case should cuts be made in the Mauerlat, as this reduces its strength and bearing capacity.
- First, the first and last rafter pair are installed, carefully checking the angle between the elements using a verified building level.
- A sliding support for rafters is attached to the lower end of the leg. To ensure a secure fit, it is necessary to secure the guide and slider with 2-3 fasteners.
- The upper ends of the rafter legs in the area of the ridge connection are fixed with nails or metal plates, connected with a hairpin, which ensures the mobility of the structure.
- A cord is pulled between the first and last rafter pair, and then the remaining structural elements are installed.
Remember that the choice of the length of the guide rail for the movable fastener depends on the possible amount of shrinkage of the house. The higher the moisture content of the wood used for construction, the larger the size of the sled should be.
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