Bolted rafter connection drawing with dimensions. Description of options for splicing rafters along the length. Making a rafter connection in the ridge

When erecting a roof, you can encounter a variety of difficulties. Let's give a simple example: after calculating the length of the slopes, you realized that the purchased bars are too short. What to do in such a situation? How to build rafters? This structural element must withstand heavy loads and therefore be durable. So how can you connect the rafters to each other so that they do not break during operation? What methods do professional builders suggest using?

First, about the material for the rafters

Splicing rafters along the length can be done in several ways. And here the material from which the elements themselves are made plays a very important role. In rare cases, rafters are made of metal. In such a situation, the extension is carried out using welding or bolting.

Most often, rafters are made of wood. But there are some differences here too, namely:

Elements can be made from beams or logs. The first option is the most common. In this case, the rafters are joined by cutting;
Single boards can also be used for these purposes. In this case, it is better to splice the rafters end-to-end or end-to-end. The overlap method is also used;
Another option for rafters is boards sewn in pairs. Here you can use the overlapping or splicing method when placing the joining line in a staggered direction.

There are quite a few methods for connecting rafters to each other. Some of them do not require special skills, others require additional accessories. But in any case, lengthening is not the most the best option. You can increase the length of the rafters, but solid elements will still be stronger. Therefore, before purchasing them, you need to carefully calculate everything.

Cutting method

Increasing the length of rafters is done in different ways, but some of them are the most popular. This is due not only to their proven reliability, but also to their ease of implementation. One of these popular methods of splicing rafters is the method of oblique cutting. It can be used both in the case of beams and when using single boards.

When making such a connection of rafters, the following rules should be observed:

From the side of the mating parts of the beams or boards, an oblique cutting or sawing is made. Its length is equal to twice the cross-section of the rafters;
The cut or cutting is done with a protrusion or ends. Their height should be 0.15 from the cross-section of the rafters;
To make the connection strong and reliable, you need to carefully make the cut. It is not allowed to fill the gaps between the rafters at the junction with wood chips, pieces of plywood or in any other way. The cuts must fit each other perfectly in configuration.

The junction of the rafters should be further strengthened. In what way - it depends on the material from which the element is made. For rafters made of timber, a bolted connection is used. In this case, a hole is drilled in the middle of the connection. To prevent the bolt from crushing the wood, you should use a nut. If the rafters are extended from a single board, then the fastening is strengthened using a clamp, twisting or nails.

Studs can act as a “strengthening” element. In this case, just as in the case of bolts, a solid hole is made into which a wooden pin is inserted. Another connection option is protrusions inside the cut. But not everyone can do such work, even with good carpentry experience. This option for building rafters requires increased precision.

We use the overlap method

For houses or buildings with a small roof area, rafters made of boards are often used. This option is considered cheap, but quite reliable, of course, provided that the material is selected of the required quality and with the required cross-section. In such a situation, the rafters can be overlapped.

For this splicing method, do the following:

Two boards are laid with an overlap, which should be at least one meter. In this case, the place where the rafters are spliced should be located directly above the support;
The connection is made using nails. They are driven in in a checkerboard pattern at a distance in a row of at least 50 centimeters;
Additionally, such composite rafters can be strengthened with clamps or twists;
Before connecting both ends, you should check the evenness of the boards relative to each other. Distortions must not be allowed.

The overlap method is used if it is no more than six and a half meters. If the span is larger, the load will be too large for this type of connection.

You can splice using this method not only along the length. Paired rafters are also made using this method. Two boards are placed on top of each other and “stitched” with nails. As a result, you can get rafters of the desired section for your roof structure.

Video on the topic:

Making a butt connection

Splicing rafters along the length can be done by connecting their ends. This method, called butt jointing, can be used for both boards and beams. How to properly lengthen the rafters in this way? To do this you need to do the following:

First of all, we prepare the ends. They must be carefully aligned so that there are no gaps or scars;
Next, the ends are joined and spliced using overlays. Then they are secured with nails;
In order for the connection of the rafters to be reliable, it is important to choose the correct length of the overlays. Everything will depend on the material. If boards are used for rafters, then the length of the overlays at the splice point should be at least three times greater than the width of the board. In the case of using wooden beams, their cross-section should be taken as a basis;
The length of the splice overlay also depends on the number of nails used. They are driven in in a checkerboard pattern. It should be remembered that they can split the thin lining.

If you need to lengthen the rafters from the beams, then for fastening you can use a bolted connection instead of nails. In this case, take a suitable overlay, preferably made of metal, and drill through holes. After this, the bolt is inserted and the nut is tightened on the other side. It is imperative to use a washer. This method of splicing completely eliminates the risk of deformation of the rafter connection.

Often during the construction of roof frames of complex configurations, there is a need to use elements custom size. 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 of technological nuances, it is quite difficult to make truly bending-stiff 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 the minimum load is placed on the system.

Options for splicing rafters

In addition to accurately determining the location 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 extended 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 section is found using the formula 0.15 × L, valid for all types of rafter frames, in which the value of 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 implement than the previous method, but in order not to waste hardware and not weaken the wood with unnecessary holes, you should accurately calculate the number of fastener 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, can simply be hammered into wooden parts.

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 the 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 are a 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 to the lateral 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

There is another very interesting way to connect and increase the length of the rafters: 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 installation 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 of sloping 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 techniques for merging structural elements of a rafter system:

A video with a step-by-step description of the process of connecting rafter parts:

Video example of one of the methods of joining lumber:

Compliance with the technological requirements according to which the rafters are spliced along the length guarantees trouble-free operation of the structure. Extension methods can reduce roof construction costs. You should not forget about preliminary calculations and preparation for making connections so that the result of your efforts becomes ideal.

Rafters are the most essential part of the roofing skeleton. The legs of the rafters transmit the thrust to the mauerlat and load-bearing walls of the house. What does the quality of the entire rafter system and the roof as a whole depend on? Experts remind that the reliability of any roofing structure will depend, first of all, on the quality of fastening the rafters to the Mauerlat. What principles and features of this process should every novice builder know and how to attach the rafters to the Mauerlat with your own hands, you will learn right now.

Attaching the rafters to the mauerlat: a little “materiel”

To begin with, we suggest looking at an illustration that shows two types of rafter systems:

The place where the rafter leg is attached to the base is called the support node. There are many such units in the system, but we will touch in detail on the lower fastenings of the frame with the rafters. The mauerlat and rafter legs are almost always made of wood, less often - of metal. It is more profitable and convenient to use wood, since this material is light in weight, easy to install and durable. correct installation and operation.

Types of support units by level of rigidity

Support nodes are the places where the rafters are attached to the roof elements:

In the case of iron connections, the nodes are fixed and rigid (welded or bolted). Wood is a softer and more dynamic material that can swell, dry out and deform. In this regard, experts recommend performing support units adjusted for possible changes wood shapes. Such nodes can have different degrees of mobility:

Zero mobility node- rigid fastening with corners on both sides, in which the fastening of the rafters to the mauerlat remains motionless.
Connection of the first degree of freedom– the beam can rotate in a circle.
Connection of the second degree of freedom– circular rotation with displacement, provision is made for the installation of special sliders or slides.
Third degree movable joint– possibility of horizontal, vertical and circular movement.

For any node, whether it is movable or not, at least two types of fixation should be used. For example, notched planks are additionally fixed from the inside using a support beam, and dynamic connections are strengthened with bolts and special steel angles.

About the types of fastening of rafters to the base

Let's talk about modern fasteners. For the strength and durability of the support units, a variety of metal fasteners are used: beam holders, equilateral, fastening, anchor, reinforced corners, plates, supports, profiles, connectors, anchors, etc. All these parts are made of high-quality metal. For dynamic units (types 1, 2 and 3), sliders, angles and perforated plates are used. For rigid fastening, stationary connectors, anchors and corners are used.

Such fasteners for the rafter system are most often used:

For self-assembly, perforated fasteners are more suitable than others, since they have many holes for self-tapping screws and bolts.

Rigid or flexible connections: what to choose

So, we noted that the support nodes connecting the Mauerlat to the boards can have different degrees of mobility: from “0” to “3”. Zero degree - these are rigid fastenings that exclude any changes in the position of the beams.

Rigid connections: when they are needed

The Mauerlat is installed when it is necessary to transfer the thrust load from the rafters to the load-bearing walls. This is done mainly in houses made of bricks, panels and blocks. In this case, they try to eliminate deformation and shrinkage of the roof in order to prevent changes in the load on the supporting walls. This is where the need arises for a fixed connection of the rafter system with the Mauerlat.

Fixed units secured with a notch

Many experts recommend making appropriate cuts at the point where the rafters are attached to the floor beams for greater strength and immobility of the connecting nodes. These cuts should fit tightly with the Mauerlat. Additionally, such units are strengthened with bolts, anchors and metal plates:

Or with long screws:

And one more important point: the size of the cut of the bar should not exceed 1/3 of its cross-section. Otherwise, the rafter system may lose its load-bearing capabilities:

Hard knots without notching rafters

The fastening method using a hemming block is used in layered rafter systems. The rafters are cut according to a template and beveled (to give the roof the desired slope) at the point of contact with the mauerlat. From the inside, such rafters are reinforced with support bars and reinforced with corners on both sides to the base frame:

Another option for a non-joint joint is a rigid fastening of the rafters, reinforced with overlay beams on both sides. Two boards at least a meter long border each rafter leg. One end of such supports is cut at an angle that corresponds to the slope of the roof slope (including rafters). The boards are fastened with a cut to the Mauerlat using long bolts and reinforced steel corners. The bars are attached to pre-marked places, first one at a time. Then the rafters themselves are mounted close to the overlays on one side, which are immediately reinforced with the same overlay on the other side. There is an option to install two beams at once, and then rafters, but this method is used less often, since it requires more accurate calculations.

When do you need to make moving connections?

Here we come to dynamic support nodes - connections that can change their position. What is it for? Let's remember physical properties materials - many of them shrink or swell. First of all, this applies to buildings made of pure wood - timber, logs, etc. Natural wood necessarily shrinks, due to which your roof can not only be deformed, but also completely collapse. To avoid such fatal consequences, craftsmen recommend sliding fastenings of rafter legs with a mauerlat (or the upper crown of a log house).

A prerequisite when installing sliding units is to support the rafter frame on a strong ridge beam. Since the supporting lower nodes are dynamic, maximum rigidity should be achieved at the roof ridge. The upper edges of the rafters are sawed down for a tight connection between themselves and the ridge beam, connected and reinforced with crossbars, metal strips, plates and corners. It is better to connect the rafter element already fixed in the ridge to the crown of the log house.

What is a sliding mount?

The movable connection is made by installing sliding fasteners called “slides” or “sliders”. Such a unit provides a certain freedom for the rafter legs, which helps prevent deformation of the roofing system after the natural shrinkage of wooden buildings:

Here are the types of sliding supports:

Should I make a gash on the rafters if the house is made of timber: an alternative expert opinion

I still suggest cutting down, but not the rafters, but the top crown. Firstly, in this case, the risk of rafter bending is reduced, secondly, the “cold bridge” is reduced, thirdly, the tangential pressure on the mauerlat (top beam of the log house) is reduced, and fourthly, the insulation of the roof in the future is simplified. The disadvantage of this method is that when cutting down the upper crown of the beam, the height of the ridge decreases, therefore, if in the future it is planned to raise the height of the ceiling, one more crown should be provided. But! Such schemes are only suitable for houses made of wood, since in brick and concrete buildings the mauerlat must be intact in order to maintain its load-bearing qualities.

How to properly attach rafters to beams?

In simple houses, mostly frame ones, the Mauerlat can be abolished. In this case, the rafters are attached to the floor beams. Most reliable option assembling such a system - preparing roof trusses. Each truss consists of two rafter legs, a connecting crossbar and a bottom tie. For strength, the trusses are reinforced with central beams and struts:

The floor beams are laid in such a direction that the rafter trusses intersect them perpendicularly in different planes. The tie performs the main load-bearing functions, is attached to the floor beams with anchors, through bolts, studs and reinforced with plates and metal corners.

It is possible to attach the rafter legs directly to the beam, which will additionally serve as a tightening. To create high-quality support units in such a system, two fastening methods are recommended:

Connecting the rafters to the beam with a double tooth - cuts are made on the beam and the bevel of the rafter leg (two butt notches on each).
Fastening with bolt and clamp. Through fastening may be provided, but if the boards have a large cross-section, notches are made and the parts are connected with long bolts.

Attaching the rafters to the mauerlat: step-by-step description

As an example, we will describe the process of rigidly attaching rafter connections to the Mauerlat on a simple gable roof.

I. Preparing the mauerlat and rafters for work

At this stage, it is necessary to cut out the rafter legs of a given length and mark their step on the base. The optimal step length of the rafter legs is 60-200 cm. You should also accurately determine the angle of inclination of the rafters.

Master class on installing the Mauerlat:

II. Creating a gash

We make a gash on each rafter leg for a tight connection with the base. To increase strength, you can provide an additional notch on the frame or rafter and install a thrust beam under each rafter leg.

III. Installing rafters on the mauerlat

The rafters must be laid carefully so as not to damage other elements of the building (windows, walls, etc.). We place the boards with a cut on the beams and rest them on the ridge beam. First, we install the outer rafter legs, between which you need to stretch a thread to align all the other rafters.

IV. Fastening each rafter to the mauerlat

Now that all the trusses are in place, you need to firmly secure the support units. For this we use several of the mounts suggested above:

Nails+ steel corners on the left and right sides of the joints between the board and the base.
Through bolts or studs+ support beam for rafter bevel.
Anchors or bolts+ angles or steel plates, etc.

Two overhead boards on both sides of the rafter leg, installed on pre-marked places on the mauerlat, will help to strengthen the fastening. You can also use wire fastening as a strength enhancer for connections. To do this, you need to prepare a steel wire twist of 2-3 wires. Its length should be enough to wrap around the rafter leg at the junction with the Mauerlat and secure the ends of the twist to a metal crutch. As a crutch, you can take a long steel bolt, which is mounted into the wall 30-40 cm below the Mauerlat, strictly under the support unit.

We will also consider one of the old-fashioned methods - fastening with staples:

And finally, we suggest you watch the video:

What is the secret of the quality of the rafter system: three main rules of the master

High-quality lumber is half the battle on the path to successful construction. The mauerlat and rafters should not have cracks, wormholes or knots.
The accuracy of measurements, cuts and uniformity of the position of the fasteners is an equally important point. If all the rafter legs are the same length and cross-section, then it is better to prepare a template for making cuts and notches.
Gaps on the Mauerlat – loss of the load-bearing functions of the base by 50% or more. The percentage of strength reduction depends on the depth of the notches.

When the rafter system is ready, it’s time to install the sheathing, insulation and roofing material. But this is another interesting topic, which we will definitely talk about in the next article. In the meantime, we wish you good materials, easy work and good helpers!

The connection of the rafters is necessary when building up elements, joining with the Mauerlat, in the ridge, with additional elements of the system (racks, tie-downs). Methods of fastening wooden structures are selected depending on the design of the rafter system, the preferences of the craftsman, and the characteristics of the lumber. In this case, planed timber or boards joined across the width are usually used.

There are layered, hanging rafters that transfer the load from the roof's load-bearing frame to the walls unequally.

Additional elements are:

ridge runs;
racks;
struts;
crossbars;
fillies.

They give the spatial structure the necessary rigidity, increase the operational life and safety of use. For any type of connection, fasteners are used.

Extension of rafters

If the building is large, the standard length of lumber is not enough, so the timber has to be increased. The rafters are connected along the length using several technologies:

overlap - no need to trim the ends of the parts, the overlap is at least 0.7-1.2 m, staggered arrangement of hardware;
end-to-end - the elements are fixed with toothed plates or wooden plates, the screws are located offset;
for a run - the knot is strengthened by resting on a longitudinal beam or board;
oblique cut - angled cut of lumber, fixation into a through hole with studs/bolts (10-14 mm) with wide washers;
“three boards” - double overlap, excessive increase in the weight of the rafter system, maximum rigidity, structural strength.

The last method of connecting rafters is used in the manufacture of complex mansard and hip-type roofs. Empty spaces after the joint are filled with scraps of lumber. using boards of equal thickness.

Connecting the rafters with support on the purlin allows you to increase the pace of work - all blanks of one slope have the same size and are sawn off according to a template. When using half-timbered construction technology, metal parts for fixation are traditionally replaced by cutting all the elements into each other. This ensures maximum rigidity. The oblique cutting method is more often used for hanging rafters, butt jointing is used for layered rafters.

Upper ridge knot

The rafters at the junction of the ridge slopes rest on each other or on the ridge girder. In the first option, the template method is used:

triangular structures are prepared in advance;
the outer triangles are mounted in place;
a cord is pulled along them in a horizontal manner;
middle structures are installed.

Connecting the rafters at the ridge with a purlin does not require horizontal control with a cord; the reference point is the purlin itself. No preliminary assembly of roof trusses is required; the roof is assembled from locally supplied lumber.

The ridge assembly is connected using one of three technologies:

overlapping - the ends of the rafters are cut off after fixing them to each other with nails, screws, transverse plates;
tongue and groove - the connection is similar to the previous one, however, each edge has a selection of half a tree;
trimming the ends - the joint of the rafters is made strictly vertically, the angle of the cut is marked in place, the elements rest against each other.

All connections must have one degree of freedom, the minimum. This is due to shrinkage of lumber in the first 1.5-2 years. Otherwise, the structure will weaken and collapse under its own weight. Therefore, fastening with bolts or studs into through holes is always preferable to nails or self-tapping screws.

Rafters can also be fixed with special hinged metal elements placed on the beam or attached to it with self-tapping screws.

This slightly increases the cost of construction, but dramatically increases the service life and maintainability of the roof. Connections with two degrees of freedom are used in complex structures.

Lower support unit

In the lower part (the connection between the roof slopes and the walls of the building), the rafters rest on a longitudinal beam called a mauerlat. It is fixed in the upper perimeter of the walls in such ways as:
wire binding;
putting on embedded studs;

embedding in concrete pouring, brickwork.

Depending on the layout of the rafters, the loads either push the walls of the building apart or compress them. The rigid connection of the rafters with the Mauerlat has two varieties:
support beam - the rafters are cut at an angle, resting on the mauerlat inside the perimeter of the building or outside it;

To connect the notch to the Mauerlat, three hardware is used: one passes through the entire thickness of the leg at an angle of 90 degrees, the other two are attached to the sides. When leaning on the Mauerlat in the first way, lateral shift is eliminated by fastening the support corners on both sides. There is an option of supporting it with a tie, when transverse beams extending beyond the perimeter of the walls are placed on the Mauerlat. The triangular truss rests on these beams; the beam is fixed in the same way as a notch with three self-tapping screws or nails.

The main purpose of the puffs is to compensate for the loads pushing the walls apart.

They perceive forces from the rafter legs, change their direction to vertical, which is beneficial for the resource of the building frame.

For wooden cottages prone to shrinkage, sliding metal fasteners are often used. It adds the necessary degree of freedom to the lumber in the longitudinal direction. This technology ensures maximum maintainability of the roof; all loads are compensated by the system itself.

Additional elements have their own fastening methods:

the board crossbar is sewn to the legs with an overlap;
the bar crossbar is cut into the saddles of both legs;
the racks are usually cut into the legs and connected with corners to the tie beams;
the ridge girder, due to its large length, is extended using the methods indicated above;
the rafters are cut into the ridge girder with saddles.

Template technology for manufacturing trusses is always preferable to on-site assembly. In this case, the slopes are guaranteed to have a rectangular rather than trapezoidal shape, which makes it easier to lay the roofing material and ensures maximum aesthetics.

When using cutting the bottom of the rafter legs into the mauerlat, the saddle can be cut out in any structural element, depending on the required amount of eaves overhang. In practice, the Mauerlat is cut less often than the timber from which the rafters are made.

In hip roofs, each rafter leg consists of two parts that are joined at an angle to each other. The methods for fixing timber and boards in this case do not differ from the above. The most commonly used method is three boards, filling the internal space with scraps of lumber of the same thickness.

The choice of sliding fastenings is justified only in the case of log, frame wall manufacturing technology. Panel and half-timbered structures do not shrink vertically, so the rafters can be rigidly attached to the mauerlat and tension beams.

In private construction, lumber is usually used to create a rafter system. Reinforced concrete or metal structures are less common. Creating a roof frame project involves performing a number of different calculations that allow you to select the best parameters for each individual element of the rafter system. During the operation of the roof, the rafters take on the main percentage of the external load, so 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 of the rafter leg, you need to determine the slope of the roof and calculate the height of the roof taking into account the width of the house. Hanging or layered rafters for small building sizes 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 asbestos-cement slate or ceramic tiles are intended to be used as a roofing covering, it is recommended to make the roof frame from lumber with an enlarged 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 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 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 abutting 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 fit tightly into 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 fastening option is the easiest way to connect rafters. 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 the required size of the 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 is 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. Composite rafter systems have been successfully used to create pitched roofs, but they cannot be used as sloping rafters for hip roofs.

For proper installation of 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 the rafters depends on the loads and the degree of expected deformation of each specific rafter structure. This issue should be approached with great responsibility and in case of difficulties it is better to use the services of professionals.

THE BELL