Over many centuries of using wood in housing construction, vast experience has been accumulated in working with lumber. But today the material is largely different from what it was before. Products can differ not only in the type of wood, but also in its grade and processing method.
Methods for connecting timber in length
The standard length of the beam is 6 m. In the construction of walls exceeding this figure, it is required to build it up, which is done using the ligation method, which eliminates the location of the joints on the same line. To do this, the connections in the rows of beams are made alternately: first the missing section will be laid on one side of the house, then on the other.
The crowns are built up using the “key groove” method, otherwise it is called “half-tree”. This is the simplest way to connect a beam and is done by deepening one end into the thickness of the second. To do this, the corresponding sides of these elements are cut down to ½ thickness. For greater confidence, the joints are fixed using pins or other fasteners.
The double-sided lock is more complex. It is a joining of lumber using the “groove to groove” method. To do this, cuts are made at the ends of the joined beams perpendicular to the cut plane. Each of the fastened elements must have its own groove and its own tenon, but they must be positioned so that when the ends are connected, the protrusion of one fits into 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 questionable.
Another way to join lumber is “blind frying pan”. It is more often used in corner joints, but is also good for extending lengthwise. To fasten lumber using this method, a tenon in the form of a triangle with a horizontally truncated apex is cut out at one end of the beam, and a groove of a similar shape is cut at the second. Docking is done by placing a tenon on top and driving it into the groove.
What is the most effective way to lengthen timber?
The most reliable connection is considered to be a four-sided groove. But it is very difficult to make cuts, so it is rarely used in practice. This requires maximum accuracy in calculations, measurements, and cutting. Therefore, such work is trusted 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 is able to make this complex “lock”: skill in such work is still necessary.
Today, when choosing materials 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 is first and foremost an environmentally friendly home. 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 on wood and relative ease of construction wooden house. And if we take into account the saving of time and money during its construction, then the choice of wood as a building material will be completely justified.
A house made of timber is environmentally friendly and fits harmoniously into any natural landscape; to this we should add the availability of the material and the relative ease of construction.
Our ancestors have accumulated vast experience in construction over the centuries. wooden houses. But today, more and more often, instead of traditional logs, wooden beam. And although the technique of connecting the elements of logs and beams has much in common, it is still somewhat different. Therefore, when building a house from timber, you need to know how to join the timber if such a need arises.
Necessity of docking
Marking and calculations of some types of beam corner connections.
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. The service life of a built house depends on these two factors. After all, improper installation will lead to the house gradually tilting to one side. And if the connections between the crowns are not tight, the walls will probably freeze in the winter.
The need to join the ends may arise in only two cases: when cutting a corner and when the length of the wall is more than 6 m (the standard length of timber). You can also add a notch to them interior 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 is performed differently in each case, although it has similar elements.
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Types of timber fastening at corners
There are two types of fastening of beams in the corners: a log house “in the paw” and a log house “in the claw”.
The stability of the entire house depends on the reliability of the corners. There are two ways to join the timber 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 joining “in the area”.
The main types of connections without residue: in the paw, with a key groove of the “in the head” type and T-shaped connections - straight or key groove and trapezoidal tenon, rectangular or symmetrical.
The main advantage of a joint without a residue is considered to be material savings. 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, and will be less likely to be covered in snow in winter. And everything taken together contributes to a more comfortable atmosphere inside the house. Such a joint is easier for a non-professional to make, so 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 remainder
Most often, for joining corners with the remainder, the “into the bowl” type is used. With this method, the beams are connected to each other using key grooves. Such grooves can be made single-line, double-sided or four-sided.
To install a one-line lock, a transverse notch is made at the end at the junction. 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 of a quarter of its thickness. During assembly, the cuts are joined groove to groove. It is very important that the grooves coincide with each other as accurately as possible. A large discrepancy in size will negatively affect the reliability of the connection as a whole. In addition, additional sealing of cracks will be required.
If you need to join the timber at the corners as securely as possible, use a four-sided lock. With it, cuts are made not from two, but from all four sides of the end. If the grooves are made correctly, the corner will be folded like a construction set. But you need to have very high qualifications to make them as accurate as possible.
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Ways to connect corners without leaving any residue
The simplest corner connection This type is a butt joint. With this method, no cuts are needed - the beams are joined at the ends. The connections are fixed with metal plates using nails or staples. However, this method cannot guarantee sufficient tightness of the corners of the house even with perfectly straight ends. Therefore, it is practically not used in the construction of residential buildings.
Use for connecting the ends of special keys made of hard rock wood allows you to make such connections much better. Special grooves are made at the end: in one beam it is longitudinal at the very end, in the other it is transverse not far from the end. When connected, these grooves must coincide so that the key can be inserted into them. Without sufficient experience, it is better to stop at a perpendicular-parallel groove. For greater reliability, professionals make such grooves oblique.
Fastening with a root tenon is the most common type of corner assembly using timber. A groove is made at the end of one of the beams, and the end of the other is sawed off, leaving a tenon of the same size. When connecting, the tenon fits into the groove, thus securing the connection. To make it even more reliable, not one, but several grooves and tenons are made at the ends.
The most reliable fastening of this type is the “dovetail”, when the tenon at the end is made not rectangular, but trapezoidal. Accordingly, a groove is made in the end of the joined beam to fit this shape.
There are very important point, which should not be forgotten. When using a “tenon-to-groove” type fastening, in order to compensate for future shrinkage of the log house, it is imperative to leave vertical gaps between the groove and the tenon.
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Longitudinal beam connection
Longitudinal connection of the beam: a, c. half a tree; b, d. with an oblique cut. 1. Nagel. 2. Nest.
Since the standard length of the beam is 6 m, when building walls of longer length, it becomes necessary to join the beam along the length. When choosing joining methods, it is necessary to take into account what force and type of deformation the joint will be subjected to in the future. Without taking these factors into account, it is impossible to properly join the timber.
The most common methods of this type of connection are half-timber, longitudinal tenon on a key, longitudinal root tenon, oblique lock.
If a compression force is applied to the joint, use a half-tree joint. To join a beam along its 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.
The grooves are then overlapped. 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 dowels - eliminate 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 is applied to the wall, the timber must be joined along its length using locks. For this, grooves are also made at right angles, but in a different way. Such a groove is 2 times the width of the beam, while from the end the groove is made to 1/4 of its thickness, and then deepens to 1/2. The resulting ledges interlock the ends with each other. For greater reliability, they also need to be additionally reinforced with nails and dowels or use bolts for fastening.
Longitudinal connection of the beam: a, c. direct patch lock; b, d. with an oblique patch lock.
If the wall of the house experiences 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 complex longitudinal connection in execution, but in terms of reliability it is significantly superior to all other types.
The technique is the same as for conventional lock connections, only the cuts are made not straight, but oblique. When using this connection, it is extremely important to accurately observe the proportions of the fastening elements, since the quality of the joints depends on their accuracy. If possible, the place of such a connection is further strengthened with 2 construction staples, stuffing them crosswise.
Despite such a variety of species, there are general rule, which needs to be carried out. To rainwater does not accumulate in the connecting grooves; on the outside of the wall, the beam must be rounded.
Also, regardless of the chosen joining method, it is advisable to treat the joining area with a special compound, a mixture of epoxy wall and sand or sawdust. Joints treated in this way are more airtight, and the resin glues the joined surfaces together, giving them additional strength.
All these types of connections are described in detail in GOST 30974-2002. But this is not a dogma, but just recommendations. In the process of building a house from timber, each developer himself must decide which type of connection is suitable for his house in each specific case.
Good luck to you! Strong walls for your home!
In private construction when creating rafter system lumber is usually used. Reinforced concrete or metal constructions are less common. Creating a roof frame project involves performing a number of different calculations to determine 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 demands are placed 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 boards or timber. If the length of the available lumber is insufficient, it is necessary to perform a splice to match 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 section of the rafter leg is selected according to the calculated load and the distance between the legs. When in role roofing It is assumed that asbestos-cement slate or ceramic tiles will be used; the roof frame is recommended to be made of lumber with an increased cross-section. Which roof structure to choose and how to do the splicing is worth understanding individually.
Not all builders know how to properly splice rafters for a particular roof structure, so anyone who is planning to build a roof would do well to learn more about this issue. Rafter extensions are made by connecting short elements made of timber or boards. The connecting point, 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 that is 15% of the length of the span being overlapped.
It is worth considering 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 - equal strength should be ensured 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 half-hip roofs. They are longer than the rafters of the side slopes and act as a support for the rafters - shortened rafter legs.
Rafter splicing options
Splicing rafters, if it is necessary to increase their length, is carried out in several ways:
- Method "oblique cut";
- Butt joint of boards;
- Overlapping splicing.
Using a miter box allows you to cut the ends of the boards at a precise angle, thereby ensuring the required density of the joints.
Butt connection
This method makes it possible to extend the rafter leg using a special overlay. In order to correctly connect the rafters to each other, it is necessary to cut the joining ends of the beams 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 secured with metal fasteners or using overlays from scrap boards, which are installed on both sides of the connection. Overlays must be nailed in place. The butt joint is more suitable for splicing rafters from boards.
“Oblique cut” method
The “oblique cut” method is optimal for increasing rafter legs from large-section timber. This technology bears this name in connection with the principle of cutting components. The touching 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 connection point. The diameter of this hole must exactly match the diameter of the fastener or be 1 mm less. This way, the fastener will sit tightly in the wood without the possibility of play that could create unwanted bending stress.
Important! When installing bolts or studs, use wide metal washers to prevent the fasteners from damaging the wood over time.
Lap joint
Splicing rafters along the length can also be done with an overlap - this creates a rigid connection. This rafter extension is relatively simple: two boards are stacked on top of each other and connected with nails. This option fastenings - the most easy way rafter connections. It does not require precision trimming of elements. In addition to nails, nuts and studs with washers can be used as fasteners.
Paired and composite rafters from boards
Structures made from boards – composite and paired – are also used as elongated rafter legs. Paired ones are made of two or more boards 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 attached end-to-end and overlapping with another paired system. This creates an equally strong structure that can withstand increased loads. Rafters made from paired boards are almost as good as conventional products made from solid timber; they are used in the construction of slanted rafters for various types roofs
Important! When lengthening the rafter leg, the bonded boards must be positioned with a shift of at least one meter. They must be connected in a checkerboard pattern, so that each joint is covered with a solid board.
A composite rafter is created from three boards. The basis is taken of two boards that have the same length. The third board is laid between them; its width should correspond to the main ones. Its length provides right size rafter board. The remaining free space between the main boards is filled with board scraps, which correspond in width to the insert board. This design stitched with nails. Between the main boards, the additional one should extend at least a meter in length. It is also secured with staggered nails. 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 sloping 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 close to the support, so they will be minimally subject to bending loads. From an economic point of view, splicing rafters is a fairly profitable step, because it allows the use of standardized materials to obtain structures of the required length.
Fastening elements
For greater reliability, the docking units are connected with various fastening elements such as bolts, metal corners, plates, staples, and so on. The dimensions of the fasteners are determined based on the thickness of the rafters. Steel parts with ready-made holes are attached using screws or self-tapping screws. There is no need to save on these products - it is always better to buy high-quality hardware of guaranteed strength. Also, do not forget that nails have their own plasticity, they can bend and stretch, and self-tapping screws most often simply break under pressure. Today, ribbed nails are especially popular in rafters.
How to lengthen rafters depends on the loads and the degree of expected deformation of each particular truss structure. This issue should be approached with great responsibility and in case of difficulties it is better to use the services of professionals.
Beam connections in corners and straight walls of a house require strength and tightness. For tightness timber house The humidity of the building material has a huge impact. If you build a house from timber 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 in the bud at once - cracks, cracks, heavy settlement, etc. Ideally, use profiled or laminated timber from chamber-drying lamellas for the 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 joint shapes.
The corners must be strong. The frame is subject to forces from possible ground movements, from its own weight and the weight of the roof, roofing 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 heat and humidity conditions.
Corner connection with remainder
Very important advantages of this type of cutting:
- Blowing from the street is minimal, even in strong winds and frost;
- High reliability. Even if not fixed with dowels, the beams, connected in the corners by one of the types of felling with the remainder, do not move even with moderate movements of the foundation soil under the influence of heaving or seismicity. The lower crowns hold the weight of the upper ones and tightly connect the corners.
Main types of cutting with residue
Method of cutting with a one-sided locking groove
This method is equally good for both square and profiled timber. One side of the beam is cut to form a groove perpendicular to the axis of the beam. The thickness of the groove is equal to half the thickness of the timber, the width and length of the groove are the same. The lock is obtained when this groove accommodates ½ of a beam 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 double-sided locking groove
This type of cutting is a little more complicated - you will have to select grooves from both the top edge of the beam and the bottom. The grooves in this case have the same width as with the one-sided groove method and a depth equal to ¼ of the thickness. Double-sided cutting of grooves takes twice as long and requires greater precision, but provides an undeniable advantage - rigid fixation of each pair of beams not in one, but in two directions. That is, spatial rigidity is already evident. Now, with any temperature and humidity fluctuations, shifting the beams and crowns relative to each other is practically impossible.
Cutting with a four-sided locking groove
The cutting is very complex, the grooves can be either symmetrical or asymmetrical, and choosing such a complex groove manually is extremely labor-intensive. Typically, such complex grooves with ideal geometry are made on equipment that produces house kits. Then, at a construction site, these kits are assembled from numbered beams, like Lego constructors.
Complex and expensive processing, but no practical improvement in the tightness of the corner is observed, although in theory such a corner should become absolutely ideal.
Main types of cutting without residue
The angle without any residue saves on lumber. The beam is entirely in the plane of the wall, the ends do not protrude outward. But there is no overall saving, since these angles require additional insulation and caulking. In terms of strength, reliability and protection from blowing, these types of cuttings are also inferior to corners cut with the remainder. Competition can only come from a warm corner, also known as a root thorn.
Cutting without residue allows you to make the façade of the house more geometrically strict, making it easier to complete exterior finishing. The issue of aesthetics is controversial, and has more to do with style.
Corners from both square and profiled timber are cut without residue.
Butt cutting without residue
The simplest and fast way for the construction of outbuildings. No additional processing is required, simply lay the beams required lengths checkerboard To ensure that the beams in the crowns and the crowns themselves do not move relative to each other, with this method of felling it is necessary to use fasteners - galvanized steel overlay 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, no matter how hard you try, the corner will move after drying. The corner is deformed, and humidity fluctuations will contribute to linear fluctuations, resulting in blown gaps.
Butt cutting with dowels
The key can be of different shapes. For a straight key, you will need to select straight grooves along the ends and side surfaces of adjacent beams. Under the dovetail key, you need to choose a rather complex groove, with widening from the middle. The key also has a complex shape.
The connection with a straight key will prevent the crown beams from moving in the horizontal plane, but not in the vertical. Vertically, the crowns will be held only by their own weight and the weight of the overlying structures. Key in shape swallowtail will securely fix the angle and prevent the bars from moving in both directions. This method of cutting without residue gives an almost windproof corner.
Half-tree felling
Also an easy cut. At the ends of the beams, cuts are made to ½ thickness, resulting in a tenon that is the same in length and width. Without fixation with dowels, this connection will not be reliable. After the log house shrinks and settles, the corner will most likely be blown out and will require additional insulation. The second caulking of log houses after curing and settling 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 also improve the method of cutting half a tree if you join the ends into a paw. The paw has a more complex shape - the cuts are made inclined, wedge-shaped, exactly to size. The result is an increase in the strength of the log house, 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 façade of the house is geometric and smooth.
Connection to a warm corner (to a root tenon)
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 off, leaving tenons, the length and width of which should be exactly 1/3 of the section of the beam. A simpler tenon has the shape of a rectangle, while a more complex tenon has a one-sided widening. The grooves of the joined beams are selected according to the size of these tenons, but without an exact fit, since the grooves need to be caulked with moss, flax or jute fiber, hemp or felt. Bars with spikes are placed on top of bars with grooves. Fastening the crowns with dowels is mandatory with this cutting method.
Fastening beams with dowels
- The classic wood for dowels is birch, free of defects, knots and cross-layers, and 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. The diameters of the dowels are from 25 to 35 mm.
- Dowels are installed at intervals of up to 1.5 m, and always on both sides of each corner. Along horizontal rows, the dowels are shifted in a checkerboard pattern.
Connections of beams along the length
Long straight sections of walls can exceed the length of the lumber. The joining of timber along the length is done in one plane. The requirements for connections are the same as for corners - strength and tightness.
The easiest way to join a beam along its length is to join with rectangular dowels. The crowns will be securely fixed in the transverse direction; such a joint will not be blown through. The key is cut slightly smaller than the groove to leave gaps for the caulking. The grooves under the key are sealed with moss, jute and flax fiber and other materials.
More difficult and more efficient way joining beams with a root tenon. Direct splicing is technologically a little simpler than corner splicing, but also requires precision. There should be a few mm gaps between the groove and the tenon to be filled with caulk.
The most complex, costly in terms of material and labor, and at the same time the best in terms of results, type of straight splicing is joining with an oblique lock. The dimensions must be accurate, the fit close to ideal. The lock configuration is not simple. As a result, two beams have two completely overlapped sections in connection, which gives the joint strength, and the clever shape of the oblique lock makes it impossible for a gap to appear even with significant shrinkage.
Often during the construction of roof frames with complex configurations, the need arises to use elements of non-standard sizes. Typical examples include hip and half-hip structures, the diagonal ribs of which are significantly longer than ordinary rafter legs.
Similar situations arise when constructing systems with valleys. To ensure that the created connections do not cause weakening of structures, you need to know how rafters are spliced along the length and how their strength is ensured.
Splicing the rafter legs allows you to unify the lumber purchased for constructing the roof. Knowledge of the intricacies of the process makes it possible to almost completely construct a rafter frame from a bar or board of the same section. The design of the system from materials of the same size has a beneficial effect on the total cost.
In addition, boards and bars of increased length, as a rule, are produced with a cross-section larger than that of the material standard sizes. Along with the cross-section, the cost also increases. Such a safety factor when installing hip and valley ribs is most often not needed. But if the rafter splicing is carried out correctly, 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-rigid lumber joints. The connecting nodes of the rafters belong to the category of plastic hinges, which have only one degree of freedom - the ability to rotate in the connecting node when a vertical and compressive load along the length is applied.
In order to ensure uniform rigidity when bending force is applied along the entire length of the element, the junction of the two parts of the rafter leg is located in places with the lowest bending moment. In diagrams demonstrating 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 rafters, at which the bending moment approaches zero values.
Let us take into account that when constructing a rafter frame, it is necessary to ensure equal resistance to bending along the entire length of the element, and not equal opportunities to bend. Therefore, the interface points are located next to the supports.
Both the intermediate post installed in the span and the Mauerlat or truss truss itself are used as support. The ridge girder can also be assessed as a possible support, but the joining areas of the rafter legs are better located lower along the slope, i.e. where minimal load is placed on the system.
Options for splicing rafters
In addition to accurately determining the place for mating the two parts of the system element, you need to know how the rafters are extended correctly. The method of forming the connection depends on the lumber chosen for construction:
- Bars or log. They are built up with an oblique cut formed in the joint area. To strengthen and to prevent rotation, the edges of both parts of the rafters, cut at an angle, are fastened with a bolt.
- Boards sewn together in pairs. They are spliced with the arrangement of joining lines staggered. The connection of two overlapping parts 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 application of one or a pair of wooden or metal overlays. Less commonly, due to the insufficient thickness of the material, an oblique cut with fastening with metal clamps or traditional nailing is used.
Let us consider these methods in detail in order to understand in depth the process of increasing the length of the rafters.
Option 1: Oblique cut method
The method involves the formation of two inclined notches or cuts arranged on the side where the parts of the rafter leg meet. The planes of the notches to be joined must be perfectly aligned without the slightest gap, regardless of their size. The possibility of deformation must be excluded in the connection area.
It is prohibited to fill cracks and leaks with wood wedges, plywood or metal plates. It will not be possible to adjust 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 denotes 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 cutting are located is determined by the formula 2 × h.
The location for the joining area is found according to the current rules for all types rafter frames formula 0.15 × L, in which the value L reflects the size of the span covered by the rafters. The distance is measured from the center of the support.
Parts made of timber when making an oblique cut are additionally secured 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 mounting location, wide metal washers are placed under the nuts.
If a board is connected using an oblique cut, then additional fixation is made using clamps or nails.
Option 2: Placing the boards together
When using bonding technology, the center of the connected area 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 of 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 to perform than the previous method, but in order not to waste hardware and weaken extra holes wood, you should accurately calculate the number of fastening points to be installed.
Nails with a stem cross-section up to 6 mm are installed without preliminary drilling of the corresponding holes. It is necessary to drill for fasteners larger than the specified size so as not to split the board along the fibers when connecting. The exception is hardware with a cross-section, which, regardless of size, wooden parts you can just score.
To ensure sufficient strength in the bonding zone, the following conditions must be met:
- Fasteners are placed every 50 cm along both edges of the boards being joined.
- Along end connections nails are placed in increments of 15 × d, where d is the diameter of the nail.
- Smooth round, screw and threaded nails are suitable for holding the board together at the joint. However, threaded and screw options priority because their pull-out strength is much higher.
Note that connecting rafters by welding is acceptable if an element is constructed from two sewn boards. As a result, both joints are covered with a solid section of lumber. The advantages of this method include the size of the overlapped span, which is impressive for private construction. In a similar way, you can extend the rafter legs if the distance from the top to the bottom support reaches 6.5 m.
Option 3: Frontal rest
The method of frontal extension of rafters consists in the end joining of the connected parts of the rafter leg with fixation of the section with nails, dowels or bolts through linings installed on both side planes.
To avoid play and deformation of the extended rafter leg, you must adhere to the following rules:
- The edges of the boards to be joined must be perfectly trimmed. Gaps of any size along the connection line must be eliminated.
- The length of the pads is determined by the formula l = 3 × h, i.e. they must be no less than three times the width of the board. Usually the length is calculated and selected based on the number of nails; the formula is given to determine the minimum length.
- The overlays are made of material whose thickness is at least 1/3 of the same size as the main board.
Nails are driven into the linings in two parallel rows with a staggered “dispersion” of fastening points. To avoid damaging the overlay, which is thin in relation to the main lumber, the number of attachment points is calculated based on the resistance of the nails shear 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 to calculate nailing to fix the linings. True, in this case the docked leg will begin to work as two separate beams both for deflection and compression, i.e. according to the normal scheme, you will have to calculate the load-bearing capacity for each of the component parts.
If steel rod bolts or rods without threads, dowels are used as fasteners when joining thick boards or timber, then the threat of deformation will be completely eliminated. In fact, even some gaps in the joining of the ends can be ignored, although it is still better to avoid such flaws.
When using screws or screws, pre-drill holes for their installation; the Ø of the holes is 2-3 mm less than the same size of the fastener leg.
When making frontal connections of rafters, it is necessary to strictly observe the design installation pitch, the number and diameter of fasteners. When the distances between fixation points are reduced, wood splitting may occur. If the holes for the fasteners are larger than the required dimensions, the rafters will be deformed, and if they are smaller, the lumber will split during the installation of the fasteners.
Extension with composite rafters
To connect and increase the length of the rafters there is still quite interesting way: extension using two boards. They are sewn to the side planes of the extended single element. Between the extended parts there remains a gap equal to the width of the top board.
The gap is filled with scraps of equal thickness, installed at intervals of no more than 7 × h, where h is the thickness of the board being extended. The length of spacer bars inserted into the lumen is at least 2 × h.
Extension using two extension boards is suitable for the following situations:
- The construction of a layered system along two side girders, which serve as a support for the location of the joining area of the main board with the attached elements.
- Installation of a diagonal rafter that defines the inclined edge of hip and half-hip structures.
- Construction broken roofs. The strapping of the lower tier of rafters is used as a support for the connection.
Calculation of fasteners, fixation of spacer bars and connection of boards is carried out by analogy with the methods described above. For the manufacture of spacer bars, trimmings from the main lumber are suitable. As a result of installing these liners, the strength of the prefabricated rafter significantly increases. Despite the significant savings in material, it works like a solid beam.
Video about ways to build rafters
Demonstration of basic splicing techniques structural elements rafter 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 the 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. We should not forget about preliminary calculations and about preparing to make connections so that the result of the efforts is perfect.
