Over the centuries, the use of wood in housing construction has accumulated vast experience in working with lumber. But today the material is very different from what it used to be. Products can be different not only by the type of wood, but also by its grade and processing method.
Methods for joining a beam in length
The standard length of a beam is 6 m. In the construction of walls exceeding this indicator, it is required to build it up, which is carried out by the ligation method, which excludes the location of joints on the same line. To do this, in the rows of bars, the connections are made alternately: either on one side of the house they will lay the missing segment, then on the other.
The crowns are built up using the “key groove” method, otherwise it is called “half-tree”. This is the easiest way to connect a beam and it is done by deepening one end into the thickness of the second. To do this, the corresponding sides of these elements are cut to ½ thickness. For greater certainty, the joints are fixed with studs or other fasteners.
More complex double-sided lock. It is a joining of lumber using the "groove to groove" method. To do this, cuts are made perpendicular to the cut plane at the ends of the joined bars. Each of the fastened elements must have its own groove and its own spike, but they must be located so that when the ends are connected, the protrusion of one enters the recess of the other, and vice versa. In this method of lengthening, it is very important to maintain the dimensions of the cuts, otherwise the strength of the joint will be doubtful.
Another way to connect lumber is a “deaf frying pan”. It is more often used in corner joints, but is also good for building in length. In order to fasten lumber with this method, a spike in the form of a triangle with a horizontally truncated top is cut out at one end of the timber, and a groove of a similar shape is cut at the second. Docking is done by applying a spike from above and driving it into the groove.
What is the most effective way to build a beam in length?
The most reliable connection is considered a four-sided groove. But it is very difficult to perform gashes, so it is rarely used in practice. It requires maximum accuracy in calculations, measurements, sawing. Therefore, such work is entrusted only to professionals. Previously, craftsmen could make these complex cuts with a single axe. Today, developers are armed with modern powerful tools, but not everyone succeeds in making this complex “lock”: a skill in such work is still necessary.
Today, when choosing a material for the construction of private houses, developers are increasingly choosing wood. This choice is due to a number of positive qualities this building material. Wooden house First of all, it is an environmentally friendly house. A wooden house can fit into any landscape, giving it a unique personality and a special atmosphere. To this it is worth adding affordable prices for wood and the relative ease of construction wooden house. And if we take into account the savings in time and money during its construction, then the choice of wood as a building material will be fully justified.
A house made of timber is environmentally friendly and harmoniously fits into any natural landscape, to which we should add the availability of material and the relative simplicity of construction.
Our ancestors over the centuries have accumulated vast experience in construction wooden houses. But today, more and more often, instead of a traditional log, wooden beam. And although the technique of connecting the elements of a log and a beam has much in common, it is still somewhat different. Therefore, when building a house from a bar, you need to know how to join the bar, if the need arises.
The need for docking
Marking and calculations of some types of joints of beam corners.
Although the houses being built may differ in the type of wood and the way it is processed, the question of how to properly lay the timber and securely fasten it between the crowns will always be relevant. It is from these two factors that the life of the built house depends. After all, improper installation will lead to the fact that the house will gradually tilt to one side. And with a loose connection of the crowns, the walls will certainly freeze through in winter.
The need for joining the ends can arise in only two cases: when cutting a corner and when the wall length is more than 6 m (the standard size of the beam length). You can also add a notch to them internal walls in external walls house under construction, but in this case we are talking about only one end.
Since these are three completely different operations and they perform different tasks, the joining of the ends in each case is performed differently, although it has similar elements.
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Types of fastening the beam at the corners
Two types of fastening of the beams in the corners: a log house "in the paw" and a log house "in the oblo".
The stability of the whole house depends on the reliability of fixing the corners. There are two ways to join a beam at the corners - with the remainder, i.e. with protruding ends, and without residue. The main type of connection with the remainder is a type of docking "in oblo".
The main types of connection without residue: in the paw, with a key groove of the "in the oblo" type and T-shaped connections - a straight or key groove and a trapezoidal tenon, rectangular or symmetrical.
The main advantage of the joint without residue is the saving of material. But on the other hand, a house where the ends in the corners are connected to the rest is more stable. In addition, it resists wind and rain better, it will be less swept up with snow in winter. And all taken together contributes to a more comfortable atmosphere inside the house. It is easier for a non-professional to make such a joint, therefore, if you do not have sufficient experience in building wooden houses, then it is better to choose this method for corner joints.
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Ways to connect corners with the remainder
Most often, for joining corners with the remainder, the “in oblo” type (into the bowl) is used. With this method, the bars are interconnected using locking grooves. Such grooves can be made single-line, double-sided and four-sided.
For the device of a single-line lock, a transverse notch is made at the junction at the end. The width of such a notch must exactly correspond to the cross section of the end. This method of corner connection is mainly used for profiled timber.
To make a double-sided lock, perpendicular cuts are made at the end on both sides for a quarter of its thickness. When assembling, the groove cuts join the groove. It is very important that the grooves match each other as closely as possible. A large mismatch in size will adversely affect the reliability of the connection as a whole. In addition, additional sealing of cracks is required.
If you need to join the beam at the corners as reliably as possible, use a four-sided lock. With it, cuts are made not from two, but from all four sides of the butt. If the grooves are made correctly, then the corner will be complex, like a designer. But you need to have a very high qualification to make them as accurate as possible.
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Ways to connect corners without residue
The simplest corner connection of this type is a butt joint. With this method, no cuts are needed - the bars are joined at the ends. The connection is fixed with metal plates using nails or staples. However, this method cannot guarantee sufficient tightness of the corners of the house, even with perfectly flat ends. Therefore, in the construction of residential buildings, it is practically not used.
Use for connecting the ends of special dowels made of hard rock tree allows you to make such connections much better. Special grooves are made in the end: in one beam, longitudinal at the very end, in the other, transverse not far from the end. When connecting, these grooves must match so that a key can be inserted into them. Without sufficient experience, it is better to stop at a perpendicular-parallel groove. For greater reliability, such grooves are made oblique by professionals.
Fastening with a root tenon is the most common type of corner assembly using a beam. A groove is made at the end of one of the bars, and the end of the other is sawn off, leaving a spike of the same size. When connecting, the spike enters the groove, thus fixing the connection. To make it even more reliable, not one, but several grooves and spikes are made at the ends.
The most reliable fastening of this type is the “dovetail”, when the spike at the end is made not rectangular, but trapezoidal. Accordingly, a groove is made under this form at the end of the beam to be joined.
There are very important point which should not be forgotten. When using a tongue-to-groove fastening, in order to compensate for future shrinkage of the log house, it is necessary to leave vertical gaps between the groove and the tongue.
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Longitudinal beam connection
Longitudinal connection of the beam: a, c. half a tree; b, d. oblique cut. 1. Nagel. 2. Nest.
Since the standard length of the beam is 6 m, when building walls of greater length, it becomes necessary to join the beam along the length. When choosing docking methods, it is necessary to take into account what kind of force and type of deformation the docking site will be subjected to in the future. Without taking into account these factors, it is impossible to properly join the timber.
The most common methods of this type of connection are half a tree, a longitudinal tenon on a key, a longitudinal root tenon, and an oblique lock.
If a compression force acts on the docking site, a half-tree docking is used. To join the beam along the length in this way, a rectangular groove is made on each beam for half its thickness. The length of the groove should be 2 or 3 times the width of the beam.
Then the grooves overlap each other. Such a connection is very unstable, so it must be fastened with nails and additionally reinforced with dowels - rods made of hard wood. the main task pins - exclude the possibility of displacement of the connected ends. Holes are drilled in the beams with a diameter corresponding to the thickness of the dowels, into which they are then inserted.
If a tearing force acts on the wall, it is necessary to join the timber along the length with the help of locks. For this, grooves are also made at a right angle, but in a different way. Such a groove is 2 times the width of the beam, while from the end the groove is made 1/4 of its thickness, and then deepens to 1/2. The resulting ledges interlock with each other. For greater reliability, they also need to be additionally strengthened with nails and dowels or used for fastening bolts.
Longitudinal connection of the beam: a, c. direct padlock; b, d. oblique overhead lock.
If the wall of the house will experience a strong “bending” force, then increased strength will be needed for the connection. Here, for reliable fixation, “oblique locks” are needed. This is the most difficult longitudinal connection in terms of execution, but it significantly surpasses all other types in terms of reliability.
The execution technique is the same as with the device of conventional interlock connections, only the cuts are made not even, but oblique. When using this connection, it is extremely important to accurately observe the proportions of the fasteners, since the quality of the joints depends on their accuracy. If possible, the place of such a connection is additionally strengthened with 2 construction staples by stuffing them crosswise.
Despite this variety of species, there are general rule to be performed. To rainwater did not accumulate in the connecting grooves, on the outside of the wall the beam must be rounded off.
Also, regardless of the chosen docking method, it is desirable to treat the docking site with a special compound, a mixture of an epoxy wall and sand or sawdust. Joints treated in this way are more airtight, moreover, the resin glues the joined surfaces, giving them additional strength.
All these types of connections are described in detail in GOST 30974-2002. But this is not a dogma, but only recommendations. In the process of building a house from a bar, each developer must decide for himself which type of connection is suitable for his house in each case.
Good luck to you! Strong walls to your home!
In private construction when creating truss system lumber is commonly used. Reinforced concrete or metal constructions are less common. Creating a roof frame design involves performing a number of different calculations to select the best parameters for each individual element rafter system. During the operation of the roof, the rafters take on the main percentage external load, therefore, increased requirements are imposed on their strength. It will often be very useful to know how to build rafters - this will help solve many complex construction problems.
To calculate the required length rafter leg you need to decide on the slope of the roof and calculate the height of the roof, taking into account the width of the house. Hanging or layered rafters with small sizes buildings can be made of solid board or timber. If the available lumber is not long enough, splicing must be done to fit the rafter leg to the specified dimensions.
The length of the rafter depends on the size of the span between the top of the wall and the ridge. The cross section of the rafter leg is selected according to the calculated load and the distance between the legs. When in a role roofing it is supposed to use asbestos-cement slate or ceramic tiles, it is recommended to make the roof frame from sawn timber of increased section. Which roof structure to choose and how to splice - it is worth understanding individually.
Not all builders know how to properly splice rafters for a particular roof structure, so anyone who is going to build a roof should learn more about this issue. The rafters are built up by connecting short elements from a bar or board. The docking unit, in most extension methods, is a fairly plastic hinge. However, the rafter must have the necessary rigidity along its entire length, so the joint should be located in a place where there is practically no bending moment. So the joint (plastic hinge) must be made at a distance from the support, which is 15% of the length of the overlapped span.
It should be borne in mind that the distance from the intermediate rafter support to the Mauerlat differs from the distance between this support and the ridge. Therefore, it is necessary to use an equal strength scheme - it is necessary to ensure the same strength along the entire length, while creating an equal deflection is not required.
Important! Special requirements in terms of strength are imposed on diagonal (sloping) rafters of hip and semi-hip type roofs. They are longer than the rafters of the side slopes and act as a support for the sprigs - shortened rafter legs.
Rafter splicing options
Splicing of rafters, if necessary, to increase their length, is performed in several ways:
- Method "oblique prirub";
- Butt connection of boards;
- Overlap splicing.
The use of a miter box allows you to cut the ends of the boards clearly at a given angle, which ensures the necessary tightness of the joints.
Butt joint
This method makes it possible to increase the rafter leg using a special lining. To properly connect the rafters to each other, it is required to cut the joined ends of the timber or boards at an angle of 90 degrees. This is done to prevent the formation of deflection at the junction of the ends of the rafters under load. The cut ends are fixed with metal fasteners or using overlays from board scraps, which are installed on both sides of the joint. Overlays must be nailed. Butt joint is more suitable for splicing board rafters.
Method of "oblique cutting"
The "oblique cut" method is optimally suited for increasing the rafter legs from a large-section beam. This technology is so named in connection with the principle of trimming components. The adjacent ends of the boards are cut at a certain angle. The elements made of timber are tightly joined by planes. A through vertical hole for a bolt or stud must be made at the junction. The diameter of this hole must exactly match the diameter of the fastener or be less than 1 mm. In this way, the fastener will be firmly seated in the wood without the possibility of play creating an unwanted bending load.
Important! When installing bolts or studs, wide metal washers should be used so that the fasteners do not damage the wood over time.
Lap joint
Splicing of rafters along the length can also be done with an overlap - this creates a rigid connection. This extension of the rafters is relatively simple: two boards are stacked on top of each other and connected with nails. This option fasteners - the most easy way rafter connections. It does not require compliance with the accuracy of trimming elements. In addition to nails, nuts and studs with washers can be used as fasteners.
Paired and composite rafters from boards
As elongated rafter legs, structures made of boards are also used - composite and paired. Paired boards are made from two boards or more, connected by wide sides. They are sewn together with nails arranged in a checkerboard pattern. To increase the length of the rafter leg, boards connected in pairs are fastened end-to-end and overlap with another paired system. This creates an equal-strength structure that can withstand increased loads. Rafters from twin boards are almost as good as conventional products from solid timber; they are used in the construction of rafters for various types roofs
Important! When extending the rafter leg, the bonded boards must be offset by at least one meter. It is necessary to connect them in a checkerboard pattern, so each joint is closed with a solid board.
A composite rafter is created from three boards. Two boards are taken as the basis, which have the same length. The third board is laid between them, in width it should correspond to the main ones. Its length provides right size rafter board. The remaining free gap between the main boards is filled with plank trimmings, which correspond in width to the insert board. This design stitched with nails. Between the main boards, the additional one should go no less than a meter in length. It is also fastened with nails arranged in a checkerboard pattern. In terms of reliability, composite rafters are significantly inferior to paired structures. Systems with composite rafters are successfully used to create pitched roofs, however, they cannot be used as rafters for hip roofs.
For correct installation elongated beams, the location of the joints of the resulting structure should be taken into account. They should be located near the support, so they will be minimally subject to bending loads. From an economic point of view, splicing rafters is a rather profitable step, because it allows the use of unified materials to obtain structures of the required length.
Fasteners
For greater reliability, the docking nodes are connected with various fastening elements such as bolts, metal corners, plates, brackets, and so on. The dimensions of the fasteners are determined based on the thickness of the rafters. Steel parts with pre-drilled holes are fastened with screws or self-tapping screws. It is not worth saving on these products - it is always better to buy high-quality hardware with guaranteed strength. Also, do not forget that nails have their own plasticity, they can bend and stretch, and self-tapping screws most often just break under pressure. To date, ruffed nails are especially popular in the rafter business.
How to lengthen the rafters depends on the loads and the degree of expected deformation of each particular roof structure. This issue should be approached with great responsibility and in case of difficulty it is better to use the services of professionals.
Timber joints in the corners and straight walls of the house require strength and tightness. For tightness log house Humidity has a huge effect on building materials. If you build a house from a bar natural humidity, during shrinkage and shrinkage, the log house will experience significant internal stresses, which can lead to its deformations.
By using lumber that has been dried to 20%, you can kill several problems at once in the bud - cracks, cracks, heavy draft, etc. Ideally, use profiled or glued beams from kiln-dried lamellas for a log house. The shrinkage of such a log house will be minimal.
The second method to avoid blowing corners is to make these corners with special, complex forms of connections.
The corners must be strong. The log house is affected by forces from possible ground movements, from its own weight and the weight of the roof, roof and snow, as well as pressure from the force of the wind. The corners must withstand all loads, and in addition, withstand deformations from fluctuations in linear dimensions due to rain, snow and changes in the heat and humidity regime.
Corner connection with remainder
Very important advantages of this type of felling:
- Blowing from the street is minimal, even with strong wind and frost;
- High reliability. Even not fixed with dowels, the beams, connected at the corners by one of the types of cutting with the remainder, do not move even with moderate movements of the base soils under the action of heaving or seismic. The lower crowns hold the weight of the upper ones and the tight connection of the corners.
The main types of felling with residue
Cutting method with a one-sided locking groove
This method is equally good for both square timber and profiled. One side of the timber is sawn to form a groove perpendicular to the axis of the timber. The thickness of the groove is equal to half the thickness of the beam, the width and length of the groove are the same. The lock is obtained when this groove accommodates ½ of the timber located perpendicular to it. Such a crown is tightly fixed in relation to the underlying crown in one direction. Additional fixation with dowels gives the corner sufficient strength.
Cutting with a double-sided lock groove
This type of felling is a little more complicated - you will have to choose the grooves from both the upper edge of the beam and the bottom. The grooves in this case have the same width as in the one-sided groove method and a depth equal to ¼ of the thickness. Double-sided sampling of grooves takes twice as much time and requires greater accuracy, but it gives an undeniable advantage - the rigid fixation of each pair of bars not in one, but in two directions. That is, there is already spatial rigidity. Now, with any temperature and humidity fluctuations, the shift of bars and crowns relative to each other is practically impossible.
Cutting with a four-sided lock groove
A very complex cutting, the grooves can be both symmetrical and asymmetric, and it is extremely laborious to select such a complex groove manually. Typically, such complex grooves with ideal geometry are made on equipment that produces house kits. Then, at the construction site, these sets are assembled from numbered bars, like Lego constructors.
Complicated and expensive processing, but no practical improvement in the tightness of the corner is observed, although in theory such an angle should become completely ideal.
The main types of felling without residue
An angle without residue saves on lumber. The bar is entirely in the plane of the wall, the ends do not protrude outward. But the overall savings are not observed, since these angles require additional insulation and caulks. In terms of strength, reliability and protection against blowing, these types of felling are also inferior to corners felled with the remainder. Only a warm corner, which is also a root spike, can compete.
Cutting without residue allows you to make the facade of the house more strict geometrically, it is easier to perform exterior finish. The issue of aesthetics is debatable, and more related to style.
Without a trace, corners are cut both from a square bar and from a profiled one.
Butt cutting without residue
The simplest and fast way for the construction of a farm building. No additional processing is required, just lay the bars desired lengths chess. So that the bars in the crowns and the crowns themselves do not move relative to each other, with this cutting method, fasteners are necessarily used - galvanized steel overhead plates, steel brackets or wooden dowels.
Labor costs in this case are minimal, carpentry experience may be completely absent. If you make a log house in this way from dried timber, you can get an acceptable result. From raw lumber, as carpenters say, with any effort, the corner will walk after shrinkage. The corner is deformed, and fluctuations in humidity will contribute to linear fluctuations, as a result, blown gaps will appear.
Butt cutting on dowels
The key can be of different shapes. For a straight key, you will need to choose straight grooves along the ends and side surfaces of adjacent bars. Under the dovetail key, it is required to choose a rather complex groove, with broadenings from the middle. The key also has a complex shape.
The connection with a straight key will prevent the crown bars from moving in the horizontal plane, but not in the vertical one. Vertically, the crowns will be held only by their own weight and the weight of the overlying structures. dowel shaped dovetail securely fix the angle and prevent the bars from moving in both directions. This method of cutting without residue gives a practically windproof corner.
Cutting in half a tree
Also an easy cut. At the ends of the bars, cuts are made for ½ thickness, a spike is obtained that is the same in length and width. Without fixing with dowels, this connection will not be reliable. After shrinkage and settlement of the log house, the corner will most likely be blown through and will require additional insulation. The second caulk of log cabins after exposure and precipitation is always done.
As with butt cutting, you can modify this method by securing the corners with dowels. In this case, the bars will not move.
You can still improve the method of cutting into half a tree, if you join the ends into a paw. The paw has a more complex shape - the cuts are made oblique, wedge-shaped, exactly in size. The result is an increase in the strength of the frame, the beams are fixed relative to each other in the crowns, and the weight of the overlying crowns prevents the displacement of the underlying ones. The corner looks aesthetically pleasing from the inside and outside, the facade of the house is geometric, smooth.
Connection in a warm corner (in the root spike)
It is considered the warmest, windproof connection and at the same time guarantees the fixation of the crowns. The method is not the most difficult:
The ends are cut, leaving spikes, and the length and width of which should be exactly 1/3 of the beam section. A simpler spike has the shape of a rectangle, a more difficult one has a spike with one-sided widening. The grooves of the joined beams are selected according to the size of these spikes, but without an exact fit, since the grooves need to be caulked with moss, linen or jute fiber, hemp or felt. Bars with spikes are upset from above on bars with grooves. Fastening the crowns with dowels is mandatory for this cutting method.
Fastening the beams with dowels
- The classic wood for dowels is birch, free of defects, knots and slant, and also with a parallel arrangement of fibers relative to the longitudinal axis.
- The optimal length of the dowels is 0.8 of the sum of the heights of the two connected crowns. Sometimes not two, but three beams are connected with one dowel. Dowel diameters from 25 to 35 mm.
- Nagels are installed in the interval up to 1.5 m, and always on both sides of each corner. On the horizontal rows, the dowels are shifted in a checkerboard pattern.
Connections of bars along the length
Long, straight sections of walls can exceed the length of the lumber. The splicing of the timber along the length is done in one plane. The requirements for joints are the same as for corners - strength and tightness.
The easiest way to join a beam along the length is a connection on rectangular dowels. The crowns will be securely fixed in the transverse direction, such a joint will not be blown. The key is cut a little less than the groove to leave gaps for the caulk. The grooves for the dowel are sealed with moss, jute and linen fiber, and other material.
Harder and more efficient way joining the beams with a root spike. Direct splicing is technologically a bit simpler than angular splicing, but it also requires accuracy. The gaps between the groove and the spike should be several mm in order to pave them with a caulk.
The most complex, costly in terms of material and labor, and at the same time the best type of splicing in a straight line in terms of result is docking with an oblique lock. Dimensions must be accurate, fit close to perfect. The lock configuration is not easy. As a result, two beams have two completely overlapped sections in the joint, which gives strength to the joint, and the cunning shape of the oblique lock makes it impossible for a gap to appear even with significant shrinkage.
Often, during the construction of frames for roofs of complex configuration, there is a need to use elements of non-standard size. Typical examples include hip and half-hip structures, the diagonal ribs of which are significantly longer than ordinary rafter legs.
Similar situations arise in the construction of systems with valleys. So that the created connections do not become the cause of the weakening of the structures, you need to know how the rafters are spliced along the length, in what way their strength is ensured.
Splicing the rafter legs allows you to unify the lumber purchased for the construction of the roof. Knowledge of the intricacies of the process makes it possible to almost completely build a truss frame from a bar or board of one section. The construction of a system of materials of the same size has a positive effect on the total cost.
In addition, a board and a bar of increased length, as a rule, are produced with a larger cross section than that of the material standard sizes. Along with the cross section, the cost also increases. Such a margin of safety when constructing hip and valley ribs is most often not needed. But with proper splicing of the rafters, the elements of the system are provided with sufficient rigidity and reliability at the lowest cost.
Without knowledge technological nuances it is quite difficult to make truly bending lumber joints. Rafter junctions belong to the category of plastic hinges that have only one degree of freedom - the ability to rotate in the connecting node when a vertical and compressive load is applied along the length.
In order to ensure uniform rigidity when a bending force is applied along the entire length of the element, the pairing of the two parts of the rafter leg is located in places with the smallest bending moment. On diagrams showing the magnitude of the bending moment, they are clearly visible. These are the points of intersection of the curve with the longitudinal axis of the rafter, at which the bending moment approaches zero values.
We take into account that during the construction of the truss frame, it is required to ensure that bending resistance is equal over the entire length of the element, and not the same opportunities to bend. Therefore, the junction points are arranged next to the supports.
As a support, both an intermediate rack installed in the span, and directly a Mauerlat or a trussed truss are taken. The ridge run can also be assessed as a possible support, but it is better to place the rafter legs joining areas lower along the slope, i.e. where the minimum load is placed on the system.
Splicing options for rafters
In addition to accurately determining the location for pairing the two parts of the system element, you need to know how the rafters are properly extended. The method of forming the connection depends on the lumber chosen for the construction:
- Bars or log. They are built up with an oblique cut formed in the connection zone. For reinforcement and to prevent rotation, the edges of both parts of the rafters cut at an angle are fastened with a bolt.
- Boards sewn in pairs. They are spliced with the location of the docking lines apart. The connection of two parts superimposed on each other is made with nails.
- Single board. The priority is splicing with a frontal stop - by joining the trimmed parts of the rafter leg with the imposition of one or a pair of wooden or metal linings. Less commonly, due to the insufficient thickness of the material, an oblique cut is used with fastening with metal clamps or a traditional nail fight.
Let us consider in detail these methods in order to understand in depth the process of increasing the length of the rafters.
Option 1: Bevel cut method
The method involves the formation of two inclined cuts or cuts, arranged from the side of the pairing of parts of the rafter leg. The cutting planes to be joined must be perfectly aligned without the slightest gaps, regardless of their size. In the connection area, the possibility of deformation must be excluded.
It is forbidden to fill cracks and leaks with wedges made of wood, plywood or metal plates. It will not work to fit and correct flaws. It is better to accurately measure and draw cutting lines in advance, according to the following standards:
- The depth is determined by the formula 0.15 × h, where h is the height of the beam. This is the size of the area perpendicular to the longitudinal axis of the beam.
- The interval within which the inclined sections of the cut are located is determined by the formula 2 × h.
The place for the docking site is found according to the current one for all types roof frames the formula 0.15 × L, in which the value L displays the size of the span covered by the rafters. The distance is measured from the center of the support.
Details from a bar, when making an oblique cut, are additionally fastened with a bolt passing through the center of the connection. The hole for its installation is drilled in advance, its Ø is equal to the Ø of the fastener rod. To prevent the wood from being crushed at the place where the fastener is installed, wide metal washers are placed under the nuts.
If a board is connected using an oblique cut, then additional fixation is carried out using clamps or nails.
Option 2: Rallying the boards
In the case of using rallying technology, the center of the connected section is located directly above the support. The joining lines of the trimmed boards are located on both sides of the center of the support at a calculated distance equal to 0.21 × L, where L denotes the length of the overlapped span. Fixation is carried out with nails installed in a checkerboard pattern.
Backlash and gaps are also unacceptable, but they are easier to avoid by carefully trimming the board. This method is much simpler than the previous method in execution, but in order not to waste hardware and not to weaken extra holes wood, it is necessary to accurately calculate the number of points of fasteners to be installed.
Nails with a stem section up to 6 mm are installed without pre-drilling the corresponding holes. For fasteners larger than the specified size, it is necessary to drill so that when connecting, the board does not split along the fibers. An exception are fasteners with a cruciform section, which, regardless of the size in wooden details you can just hit it.
To ensure sufficient strength in the rally zone, the following conditions must be observed:
- Fasteners are placed every 50 cm along both edges of the boards to be joined.
- Along end connections nails are placed in increments of 15 × d, where d is the diameter of the nail.
- For rallying the board at the interface, smooth round, screw and threaded nails are suitable. However, threaded and screw options in priority, because they have a much higher pull-out strength.
Note that the connection of rafters by rallying is acceptable in the case of an element of two sewn boards. As a result, both joints are overlapped with a solid piece of lumber. The advantages of the method include the size of the overlapped span, which is impressive for private construction. Similarly, rafter legs can be increased if the distance from the top to the bottom support reaches 6.5 m.
Option 3: Frontal stop
The method of frontal extension of the rafters consists in the end joining of the connected parts of the rafter leg with the fixation of the section with nails, dowels or bolts through the lining installed on both side planes.
To exclude backlash and deformation of the extended rafter leg, the following rules must be followed:
- The edges of the board to be joined must be perfectly trimmed. Gaps of any size along the connection line must be excluded.
- The length of the overlays is determined by the formula l = 3 × h, i.e. they must be no less than three board widths. Usually the length is calculated and selected based on the number of nails, the formula is given to determine the minimum length.
- Overlays are made of material, the thickness of which is not less than 1/3 of the same size of the main board.
Nails are hammered into the overlays in two parallel rows with a checkerboard "scatter" of fixing points. In order not to damage the overlay thin in relation to the main lumber, the number of attachment points is calculated based on the resistance of nails transverse force acting on the legs of the hardware.
When the junction of the rafter parts is located directly above the support, there is no need for nailing calculations to fix the overlays. True, in this case, the docked leg will work as two separate beams for both deflection and compression, i.e. according to the normal scheme, it will be necessary to calculate the bearing capacity for each of the constituent parts.
If steel rod bolts or rods without thread, dowels are used as fasteners, when joining a thick board or beam, then the threat of deformation will be completely eliminated. In fact, even some gaps in the joining of the ends can be ignored, although such flaws are still best avoided.
When using screws or screws, holes are pre-drilled for their installation, the Ø of the holes is 2-3 mm less than the same size of the fastener leg.
In the production of frontal joints of rafters, it is necessary to strictly observe the estimated installation step, the number and diameter of fasteners. If the distance between fixing points is shortened, splitting of the wood may occur. If the holes for the fasteners are larger than the prescribed dimensions, the rafter will be deformed, and if less, the lumber will crack during the installation of the fasteners.
Extension with composite rafters
To connect and increase the length of the rafters, there is still a very interesting way: building with two boards. They are sewn to the side planes of the single element being extended. Between the extended parts there is a gap equal to the width of the top board.
The clearance is filled with trimmings of equal thickness, set at intervals of not more than 7 × h, where h is the thickness of the board being extended. The length of the distance bars inserted into the clearance is at least 2 × h.
Extension using two stackable boards is suitable for the following situations:
- The device of a layered system along two side runs, which serve as a support for the location of the docking area of the main board with the attached elements.
- Installation of a diagonal rafter that defines an inclined edge of hip and half-hip structures.
- Construction broken roofs. As a support for the connection, the strapping of the lower tier of rafters is used.
Calculation of fasteners, fixation of remote bars and connection of boards is carried out by analogy with the methods described above. For the manufacture of remote bars, trimming of the main lumber is suitable. As a result of the installation of these liners, the strength of the prefabricated rafters significantly increases. Despite significant material savings, it works like a solid beam.
Video about how to build rafters
Demonstration of basic splicing techniques structural elements truss system:
A video with a step-by-step process for connecting rafter parts:
Video example of one of the ways to connect lumber:
Compliance with technological requirements, according to which the rafters are spliced along the length, guarantees trouble-free operation of the structure. Elongation methods allow you to reduce the cost of building roofs. You should not forget about preliminary calculations and about preparing to make connections so that the result of the effort becomes perfect.
