The usual rigid system of attaching rafter legs to the mauerlat or the upper crown of a wooden frame using staples, nails or corners does not always justify itself. In many cases rafter beam must be able to move relative to the walls. To ensure this displacement, a sliding support for the rafters is used.
The design of the support unit, in which the rafter beam has free movement at the point of its support on the wall, is used mainly in construction wooden houses. The walls of a log house made of solid wood after assembly and during operation are subject to significant deformations and change their geometric characteristics. Not only wood with natural moisture, but also laminated timber shrinks to one degree or another. An ordinary log house can become 15% lower after being placed under a roof and the first snowy winter. Moreover, the walls can settle by significantly different amounts, resulting in a distortion at the top, in the roof area.
The roof rafters are attached to the upper crown of the log house made of rounded logs through sliding supports
During operation, slight deformations also occur. If the house has a central wall, it settles to a greater extent than the outer ones when the house begins to heat. This is explained by a decrease in the volume of wood due to a decrease in its moisture content. There are also seasonal deformations. During the rainy season, the walls of the house become a little higher, and in winter, when air humidity is minimal, they “shrink out.” Moreover, the southern wall dries out faster after rains, that is, the amplitude of changes in the height of the walls is not the same, the house “walks.” Temperature and humidity deformations occur in solid wood buildings throughout the entire life of the house.
Estimated value of change in the length of the rafter beam due to greater shrinkage of the central wall wooden house
A four-wall log house (there is no central wall) may have another problem. Logs that are constantly subject to stress can gradually bend. The rafter system, if it is not assembled rigidly and does not have closed loop according to the principle of a truss, it exerts not only vertical, but also horizontal pressure on the walls. The rafters can bend the central parts of the walls outward, and the log house will acquire a “barrel-shaped” outline in plan. And the roof will sag at the ridge. The presence of a cut with reliable locks located across the ridge (five-walled) will eliminate this problem or reduce it.
In addition, the wooden rafters themselves, if they have not been subjected to technical drying, will lose moisture and become shorter.
If you attach the rafters rigidly at the point of support to the wall, the deformations of the structure will be transferred to the roof. As a result, a roof that looked perfect during installation may, after some time, sag in the center, the planes will become crooked, bumps and depressions will appear, and the end and wind planes will lose their evenness.
To prevent the deformations of the walls from being transferred to the roof, the rafter system at the points of interface with the walls must be able to move while maintaining its shape. This task is provided by the sliding support for the rafters. Maximum effect benefits from the use of such supports are achieved when constructing houses made of solid wood with central walls parallel to the ridge of the roof.
Main design characteristics
The function of the sliding support is to clearly fix the rafter beam to the wall and the mauerlat in vertical plane and the possibility of its displacement along its own axis.
The sliding support consists of two elements. One is a guide (bar), which is attached to the rafter beam. The second is a corner with a support platform, fixed to the upper crown of the log house or mauerlat. The angle is equipped with a loop that engages with the guide, but does not prevent it from moving within certain limits.
The sliding support consists of two elements
The amount of deformation may vary. The support guide element limits possible movement. There are supports on sale with the ability to move to varying degrees.
The possible sliding amplitude of the rafter leg depends on the length of the free section of the support guide bar. These three options allow for an offset of 90 to 160 mm
The supports are made of steel at least 2 mm thick. The height of the angle is usually 90 mm, the width of the plates is 40 mm. Factory products have a galvanic anti-corrosion coating. Fasteners made of ordinary steel must be protected from rust by painting oil paint.
Application of sliding supports
The support platform must be mounted on the upper crown strictly perpendicular to the axis of the rafter beam, in the sliding direction. It is recommended to initially install the angle loop at the bottom of the sliding bar.
The rafter beam will sit down, so when installing the plank and corner are positioned in this way. The drawing indicates “shrinkage reserve”.
Metal elements are fastened only with screws with anti-corrosion coating.
Incorrect installation. The platform should be located on the upper crown at an angle, perpendicular to the axis of displacement of the rafter beam. IN in this case the plate will jam or the corner will tear off from the crown.
In addition to the described advantages, the use of sliding supports makes it possible to simplify the device rafter system. There is no need to make complex cuts to the rafter beams and the top crown to provide support. If the house is built of timber or logs manual cutting, it is enough to plan a platform at the crown for attaching the support under the right angle. In a structure made of rounded logs, this is even simpler: a square is used to measure the perpendicular on the roof element, and at the point of intersection of the log and the beam, a place for attaching the support is obtained.
Hinged ridge design
To prevent the rafter legs from moving apart, the rafter beam must have one or more support points in the middle, on the ridge or next to it. When the walls are deformed, the angle of articulation of the rafters in the ridge may also change. To prevent the roof plane from bending, a sliding (hinge) connection is also used in the ridge.
The ideal “sliding” rafter system. The ridge rests on the central wall. Hinge from metal plates, connected by a tie, is much more reliable than a regular bolt.
Other uses of sliding supports
The sliding support can be used wherever it is necessary to ensure the movement of elements wooden structures. In particular, when installing partitions and linings in wooden houses. For example, in the bathroom of a wooden house it is planned to finish part of the wall ceramic tiles. To do this you need to sheathe the wall sheet material(GVL, gypsum board, OSB), having previously made a frame. Moreover, the frame must be “floating”, because the walls can settle over time and be subject to seasonal deformation. If the lining is not extended to the ceiling, and the frame posts are secured to the wall on sliding supports, the problem is solved.
How to avoid wasting time on shrinking the frame and move straight to finishing work? First, you should read a short introduction, we hope that this will make the problem that we will solve today more clear to many. So that's it wooden log houses shrink construction technologies We strongly recommend that developers give time for their shrinkage. As a rule, the house should stand under the roof for about a year, during which time the timber will take on its natural moisture, its plane will level out, the insulation will shrink, etc. Note that complete shrinkage of the house is considered one of the essential conditions High Quality finishing works. Let time be lost in the form of “downtime”, but time is saved on performing finishing work on external and interior walls, the cladding is of higher quality, more reliable and durable.
But life can dictate its own conditions, which do not always meet the requirements of SNiPs, so you have to sheathe the walls even before the walls shrink; this issue can be solved in two ways.
Using floating devices
Now they are produced by several companies, but from an engineering point of view there are no differences between them. The principle of operation is very simple - those elements that are attached to the walls have slots that ensure the mobility of the sheathing installed for fastening facing materials. The thickness of floating hardware for internal walls is slightly less than the thickness of hardware for external walls. This difference is explained by the weight finishing materials, some are much heavier than others. Before we talk in detail about the technology of sliding finishing, we consider it necessary to warn you once again. Firstly, you must keep in mind that finishing a house without natural shrinkage is not the best The best decision. Secondly, in most cases you will still have to do some work after the walls have completely settled. The fact is that no one can calculate the shrinkage of walls down to the centimeter: it depends on too many factors. This means that you will then have to seal the gaps between the flow and the walls inside the buildings and between the walls and the roof of the roof outside the buildings. How to make a floating sheathing?
- Make markings on an interior or exterior wall. Determine the distance between the guides, a planed block will do, taking into account the size of the finishing materials and methods of their fastening, draw vertical lines in these places using a plumb line.
- Using a special self-tapping screw with a large head and a washer, secure the metal square to the wall. Before doing this, you need to check the condition of the wall surface. To do this, use a level or ropes stretched in the corners. Large bulges will have to be trimmed. Do not try to fine-tune the position metal corners, more precise installation can be executed already during direct commit wooden slats to metal plates.
- Under the rope, begin fastening to the slats plates, carefully ensure that the crowns of the house can move as they shrink from top to bottom; for this, the self-tapping screw must be at the upper edge of the slot.
- Check the fastening of each rail; it must be able to move in a vertical direction. Choose the position of the slats taking into account the method of upholstering the walls; it can be vertical or horizontal. The slats should move with little effort, do not allow them to wobble.
- Start upholstering the walls from the bottom up, depending on the height of the wall and the material of the frame, the gap between the flow and the unupholstered wall should be approximately ten to twelve centimeters. At the same height, vertical slats should not reach the ceiling.
- The baguette needs to be nailed to the ceilings; it is not possible to know exactly the optimal gap, even theoretically. This means that after the house shrinks, you will have to install a new baguette. This is unpleasant, but better than causing the entire wall paneling to deform.
The technology for cladding external walls is carried out according to the same algorithm; differences can only be in the strength characteristics of metal devices. They are made from high-quality carbon structural steels, the surface must be hot-dip galvanized, the thickness of the zinc coating cannot be less than 40 microns.
Floating wall cladding
Sliding board
Now that you are familiar with how industrial metal floating cladding fixtures work, it will be easier to make your own. There are several options for making cladding, but we will consider only one of them, the simplest. The guides are made from ordinary boards; choose the thickness of the boards taking into account the weight of the cladding materials. For internal walls, boards 25 millimeters thick will be sufficient; for external walls, you need to choose thicker boards. In each board, at a distance of approximately one meter, vertical slots with a length of 10–15 centimeters must be milled; the length of the slots is selected in accordance with the expected maximum shrinkage of the wall.
Another important point It should be remembered that window and door openings will shrink, you need to leave a gap between the sheathing and the window sills, and nail the trim not to the wall, but to the sheathing. The size of the gaps is also unpredictable; it is better to make them with a clear margin. What's the result? We strongly advise you not to choose this method. finishing Houses. “Whoever is in a hurry will make people laugh.” Remember this proverb. And, besides, such a rush always leads, ultimately, to an increase in construction time and to an increase in the cost of construction work. You will have to do the final “finishing” of the cracks in the living quarters, and this is in all cases an unpleasant task.
The content of the articleThe construction of rafter structures is a very responsible undertaking, since they geometric accuracy and the reliability of fastening depends on the safety and durability of the object as a whole. Some additional difficulties arise when installing rafters on buildings made of natural wood (log cabins and 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 buildings built from logs, since these structures, unlike other materials, shrink quite strongly during use. Shrinkage of logs continues over several years and amounts to 5–8% of the volume of wood (depending on the moisture content of the materials used in construction). The greatest danger is not the shrinkage of the structure itself, but the unevenness of this process.
Uneven shrinkage load-bearing walls can damage rigidly connected rafter structures, violating their geometry. After this, the rafters cannot serve as a reliable base for roofing materials, which violates the tightness of the entire structure, significantly increasing the danger of operation. Therefore, a sliding rafter system is the optimal solution for the construction of log houses and other objects made of logs.
Design features of sliding rafter systems
Sliding rafter systems are not rigidly fixed structures, since they are mounted using movable metal elements. Same as during installation traditional way, rafter systems are installed on the top load-bearing log of the log house, but instead of rigidly fastening with staples, bolts or screws, so-called “slider” rafters are used.
These elements are structures made of a metal strip, one part of which is fixed to a log, and the second to the rafters
. In this case, the structural elements can move relative to each other, creating a movable connection.
Installation of these structures is carried out using special self-tapping screws, since ordinary self-tapping screws will not always be able to cope with the required load. "Slippery" assembled ones are sold in many construction stores and are relatively cheap. They are made of galvanized steel and are supplied with ready-made mounting holes. The use of these elements allows rafter systems to move the required distance when load-bearing walls shrink, without compromising the integrity of the structure.
- Sliding rafter systems should be installed on objects that have the correct geometric shape . Otherwise, it is very difficult to perform a correct roof, since the systems have moving elements. Before installing the rafters, it is necessary to carefully check the perimeter of the object and ensure that it complies with the recommended tolerances.
- The production of rafter systems is carried out according to a pre-made template. This approach makes it possible to create identical designs for all roof elements.
- The ridge connection in rafter systems of this type is also made using movable elements. As mounting elements Bolts and studs can be used to form a connecting axis, or movable hinges secured with self-tapping screws.
- 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 this operation is necessary, the boards are connected with long bolts or special brackets. The boards are built up overlapping along pre-drilled mounting holes. When drilling, the mounting holes must be located at a certain distance (at least 10 cm) from each edge of the board. Drilling holes must wear chaotic character to prevent the board from splitting along the holes.
- Each sliding rafter support must be installed strictly parallel to the previous one and perpendicular to the load-bearing log of the structure. Deviation from this rule can lead to jamming of moving structural elements and their destruction during shrinkage of the task.
- Installation of “sliding wheels” is carried out using special cuts at an angle of 90 0 to rafter support, which ensures free movement of the structure . When installing, these elements must be brought to their extreme position, ensuring the maximum possible stroke truss 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.
A special semicircular cut is made on the rafter support at the installation site, along which installation is carried out. One or two spikes are installed between the supporting log and the rafter leg (depending on the angle of inclination of the roof), which relieve the load from the rafter system, transferring it to the supporting log and protecting it from longitudinal shift.
You can also install rafter structures in special cuts made in a load-bearing log (mauerlat). This method of fastening is applicable for small roof slope angles and in the presence of additional intermediate supports.
Insertion into the body of the Mauerlat is carried out no more than 3/4 of its diameter, in order to avoid weakening of the structure. This installation method creates additional friction on larger area, securely holding the structural parts during installation.
The service life of a construction project depends on many factors. Nessesary to use quality materials, do everything in accordance with SNIPs and use suitable engineering structures.
Attention ! When talking about the use of a sliding support for rafters, it becomes clear to every experienced builder that next we will talk about installing a frame for the roof.
The roof plays one of the most important roles in a building. She protects interior spaces from atmospheric precipitation and cold. But for this design to serve faithfully long years it is necessary to use sliding supports for the 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 as the house shrinks.
Every new house Over time it shrinks slightly. Perhaps, you have more than once had to communicate with neighbors whose roof began to leak a few years after the construction of their house. This is not surprising, because they most likely did not use sliding supports for the rafters when installing them. The use of these elements would minimize damage from shrinkage and maintain 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 moving walls. The supports connect the rafters and the main structure. But their main difference from standard mounts is their mobility. They have some play, which takes into account shrinkage.
Attention ! The use of sliding supports for rafters guarantees the preservation correct geometry roofs, provided that everyone else construction works made well.
Properties of sliding supports
Features of application
In most cases, the use of sliding supports for rafters is justified when constructing log objects. The fact is that structures made of wood give the greatest shrinkage. In general, this is somewhere around eight percent of the total volume.
Important ! The shrinkage process of a building is greatly influenced by humidity and the building materials used.
In the worst case, the object shrinks unevenly. After all, not using sliding supports for rafters greatly harms the fixing elements, causing them irreparable damage. As a result, the rafters lose their performance qualities. The tightness is broken and the risk of collapse increases.
In the worst case scenario, you have to completely replace the cover. It is much cheaper and more practical to use sliding supports for the rafters from the very beginning. This perfect option for log houses 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 rigid fixation. A similar effect can be achieved thanks to 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 structures are used. Unlike bolts, staples and self-tapping screws, they provide the mobility necessary for the structure.
The moving elements of the sliding supports for the rafters consist of metal strips. In this case, one part is attached to the rafters, and the second to the logs. But stripes are not static objects. They have a moving joint.
Attention ! Special screws are used for installation.
The point is that ordinary self-tapping screws are not able to cope with the load that will be placed on the moving elements of the roof. Another advantage of using sliding supports for rafters is their relatively low price, and they can be purchased at any hardware store.
The sliding elements are made of galvanized steel. In addition, they have ready-made mounting holes. So you don't have to drill or finish anything. This technology allows the rafters to easily change their position. This ensures that the entire roof is sealed.
Installation
To install sliding supports for rafters, it is necessary to use special structural elements. It's all about moving parts that require special handling.
To prevent the rafters from falling under their own weight, they are used special techniques roof construction, ensuring sufficient strength of the entire structure and minimal load where possible.
First you need to make a special semicircular cut at the installation site. It is on this that installation will be done in the future. Then you need to install two or one tenon between the log and the rafter leg. The quantity depends on the slope of the roof. They will minimize the load by transferring part of the weight to the logs.
Important ! The use of spikes allows you to protect the entire structure from longitudinal shift.
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, there must be intermediate supports available.
The insertion into the body of the supporting log should be carried out no more than three-quarters of the total diameter. Otherwise, there is a risk of weakening the structure. If you do the installation in this way, the resulting friction will allow you to 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 of people, 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 largely guarantees the construction of a durable and reliable roof, which will last for many years, these include:
- Sliding supports for the rafters should serve as jumpers when connecting the mauerlat or the upper crown of the frame with the rafter legs. At the same time, when creating them, it is necessary to use steel with a thickness of 2 mm. The length of each element depends on the expected displacement of the legs.
- The guide ruler must be installed parallel to the rafter leg. In this case, the corner is mounted perpendicularly. Application of such design feature will ensure sliding even with maximum shrinkage.
- When making rafters, you need to use boards whose cross-section is 200 by 50 mm.
- Before installation, each structural element must be processed special compounds. This guarantees fire resistance as well as protection against rot, mold and insects.
Compliance with these conditions will ensure long service roofs even in the most extreme conditions. Special attention You need to pay attention to the selection of bioprotection drugs.
In order for the use of sliding supports for rafters to be justified and 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 rafter systems are manufactured according to a previously created template. This avoids adjustment and at the same time maintains all the proportions of the structure.
- When creating a ridge connection, movable elements can also be used. Bolts and studs are suitable for fastenings. As an alternative, hinges can be used. But they need to be further strengthened with self-tapping screws.
- Quite often, when creating a roof with sliding supports, the technology of building up boards is used. This technique allows you to work even with long spans. When connecting elements, it is necessary to use long bolts. The extension should be done overlapping. Mounting holes should be about 10 cm apart from each other.
Results
The use of sliding supports for rafters in houses made of timber is justified by shrinkage, which in the first few years reaches eight percent. These structural elements help maintain the tightness and geometric proportions of the roof.
Wooden house construction has maintained its leading position for many years. However, wood as building material has some quality characteristics, among which the percentage of shrinkage is high, which inevitably provokes the development of deformation changes in the structure. It is for this reason that sliding rafter supports are used.
Purpose and scope
The sliding version of the supports allows the structure to easily adapt to configuration changes of various nature, including geometric changes during natural shrinkage.
The process of rigidly attaching a rafter structure to a mauerlat or to floor beams using fasteners is sometimes impractical.
If the frame of the structure is prone to shrinkage processes, it is recommended to allow the legs of the rafter system to move freely in relation to the support.
Previously, during construction, for this purpose, the strongest wire system was used, with which it was used with the upper part of the erected log house. In the conditions of modern house construction, such fastening is carried out with a special fastening element– a sliding support, which is easy to install, reliable and durable. It is worth considering that any movable support is characterized by the presence of fixed frames for performing movements.
Characteristics and dimensions of sliding supports
Sliding supports are perforated elements that highly effectively prevent freezing of roof structures and the process of expanding walls in wooden housing construction.
The result of shrinkage of a wooden truss structure is a significant weakening of the entire system and the occurrence of numerous distortions. The use of sliding supports for floating rafters minimizes Negative influence shrinkage. The components of such elements are represented by a metal bracket and an angle with a loop part.
Main parameters:
- height - 9 centimeters;
- width - 4 centimeters;
- thickness - 2 millimeters;
- length - 9 - 16 centimeters.
All elements are highly durable and reliable, and installation requires the use of a screwdriver.
Types of supports
Depending on the type of construction, several methods can be used to fasten the main elements. Most often, the material used for the manufacture of such fasteners is low-carbon steel that has undergone a hot-dip galvanization process.
Two types can be used as sliding joints:
- open sliding joint type
- closed sliding joint type
Full-fledged fastening for movable joints is carried out on the basis of calculations for uniform distribution of the created loads on the walls of the structure. In addition, it is necessary to take into account not only the weight of the rafter system, but also the entire roof being erected.
Open connection option
It is characterized by the presence of two open elements: a guide, which is attached to rafter leg and is a curved steel plate with holes and a fixed angle. The number of mounting holes on the guide may vary, and the stroke length is at least six centimeters and no more than sixteen centimeters. The corner has no more than five holes.
Closed connection option
Represents a single and monolithic structure and is installed already assembled. The corner of the fixed part has a special holder on its long side through which the fastening strip is removed. It is advisable to purchase rafter connections in finished form, which will allow for the highest quality installation.
Installation of a sliding rafter system
The basis of the sliding supports are two parts, represented by a guide and a bent plate. During operation, the guide performs sliding, the amplitude of which does not exceed the limits of the bent plate.
In addition to mobility, installation takes into account the reliability of the fastening, which does not allow the load-bearing log to come off under conditions of significant roofing loads.
Sliding joints are characterized by fastenings perpendicular to the rafters, which results in cutting at right angles.
The basics of installation consist of the following steps:
- making a semicircular cut on the supports of the rafter legs;
- installation of spikes to remove the load from the rafter structure.
Sometimes you can find fastening done in a different way, when special cuts are made at 75% in load-bearing logs. Creating little friction large area allows you to maintain the system in conditions of strong winds and heavy snowfalls. This method is used when there is a small angle roof slope or in the presence of intermediate supports. During the installation process, high-quality, galvanized self-tapping screws are used.
For more information on DIY installation, watch the video.
Let's sum it up
- Installation of sliding joints is possible only on roofs that have a correct and geometrically correct shape.
- Installation is carried out only after all parameters of the structure have been verified for compliance with dimensions, which will simplify installation work and minimize the need to “adjust” all elements.
- Movable connections can be used not only for fastening rafters and walls, but also for arranging ridge connections.
- To prevent jamming on moving systems, strictly parallel fastening of all the supports of the sliding rafters to each other and perpendicular to the mauerlat is possible.
