Ridged roof truss knot. How are the roof nodes connected to each other?
The attachment points of the rafters must provide the necessary strength of the roof frame. It is important to choose the right technology for mounting the elements of the truss system among themselves and attaching them to the supporting contour so that the finished roof is able to withstand the design loads.
Features of roof structures
The task of layered and hanging roof truss systems is the most uniform transfer of the load of the sub-rafter structure, which, in turn, distributes the load on the load-bearing walls and the foundation of the building. The under-rafter structure is usually a mauerlat (beam laid lengthwise on each load-bearing wall). It can also be floor supports (laid across the wall) or the upper crown of a log house made of timber or logs.
The choice of the method of attaching the rafters to the Mauerlat depends on their type. The layered design makes the Mauerlat work in shear, while the hanging trusses work in compression, the direction of which coincides with the orientation of the load-bearing walls.
Puff setting
Installation of a gable roof requires the installation of a rafter system of a layered or hanging type. In order to mount a rigid hanging truss truss that does not transfer spacer loads to the walls, it is necessary to correctly perform the fastening points of horizontal jumpers - puffs and crossbars.
Depending on which roof structure was chosen, the puff can be mounted at the base of the rafters and serve as a floor beam. The truss truss, which is attached to the Mauerlat, is equipped with a crossbar to stiffen it - a jumper located closer to the ridge. In mansard roofs, the crossbars serve as the basis for the ceiling sheathing.
The connection node when installing the puff is recommended to be performed by the method of "cutting into the rafter with a half-pan" using a fixing screw. This mounting method requires precise fitting of the elements, since with large gaps, at the interface points, the attachment point under load may collapse.
An easier way is overlap installation. In this case, the jumper is made of a board or two boards installed on both sides of the rafter leg. Nails are used as fasteners. The knot can also be a bolted connection, but this will reduce the bearing capacity of the rafters by 20%.
Another option is to install the crossbar by surprise. Installation of this type of assembly became possible after the invention of nail plates. The design is able to withstand high loads - reliability is ensured due to the tight fit of parts and strong fixation on both sides due to the large number of teeth on the plate.
The cross section of a beam or board for the manufacture of an expansion crossbar must match the cross section of the rafter.
Mauerlat: attachment points for rafter legs
The support of wooden rafters on the Mauerlat can be performed using two technologies:
- rigid attachment to the Mauerlat;
- sliding fastening to Mauerlat.
With rigid fastening, any kind of displacement of the rafter leg, which rests against the Mauerlat (bends, shifts, torsion), is completely excluded. To this end, when installing the roof rafter system, the installation of rafters can be carried out using a hemmed bar, which prevents the rafter leg from slipping at the point of support. Lateral shifts with this connection method are excluded due to the installation of metal corners.
In the second variant of the rigid attachment of the rafter leg to the Mauerlat, it is necessary to make a gash (saddle) at the bottom of the rafter or board. The plane of support must be horizontal; for this, the cut in the rafters is made at an angle corresponding to the slope of the slope. To fix the knot on both sides, the rafters are driven at an angle along the nail (they must be crossed inside the Mauerlat), the third nail is driven vertically through the rafter into the Mauerlat.
A sliding mount is usually used when building a truss system on a house from a bar or log. The basis for supporting the rafter legs in this case is not the Mauerlat, but the upper crown of the log house. To avoid deformation of the roof during shrinkage of the house, it is necessary to perform a node with a certain degree of freedom for the rafter leg. Often, for this purpose, a special fastener made of metal is used - a sliding support ("sled"). Its upper part is a loop, which is displaced along the guide, fixed on the rafter leg, when the log geometry changes.
Other methods of mounting the sliding knot are also used. A cut is made in the rafter leg, the beam is installed with a cut on the upper crown, after which it is fixed in one of the following ways:
- by means of one vertically hammered nail;
- with the help of nails hammered from both sides, crossing in the Mauerlat;
- by means of a bracket;
- by performing a single fixation with steel fixing plates.
This method of fastening leaves the possibility for the elements of the system to move relative to each other when the geometry of building structures changes.
Ridge connections
The device of the roof truss system with two slopes implies the presence of a horizontal rib in the upper part of the roof, formed as a result of the junction of the slopes - the ridge. The ridge knot can be performed in several ways, the choice depends on the type of truss system and the features of the building itself.
The layered design involves attaching the rafter legs to the ridge run - a horizontal beam located on racks parallel to the long walls of the house. The upper ends of the rafter legs should be cut at an angle corresponding to the angle of inclination of the slopes. The junction of the cut ends of the rafters to the ridge should be as tight as possible. Nails are used as fasteners. Slanted rafters are used if it is possible to install racks on the inner wall or columnar supports for attaching a ridge run. In addition, the walls must be equipped with a power plate to support the rafters.
Assembling a hanging type truss requires joining the upper ends of a pair of rafter legs. To do this, the end of each of the rafters is cut at an angle equal to the angle of inclination of the roof, the beams are connected by cut planes - it is required to ensure their tightness. They are fixed with two nails hammered at an angle into the upper planes of the rafters. Then, on each side, a wooden overlay or metal plate is nailed, which close the junction.
To provide the ridge with the necessary strength, cutting into half a tree can be performed: in this case, instead of the mating plane of the butt joint, the rafters are connected by a ledge. Next, a through hole is drilled for a stud or bolt with a diameter of 12 or 14 mm, nuts with wide washers are used for fastening.
If you have to install sliding supports on the wall of the log house or create adjunctions (rafter junctions with the Mauerlat) with a certain degree of freedom, special attention should be paid to the ridge. It is recommended to make a movable connection unit so that the roof does not deform during uneven shrinkage of the structure. To this end, the ends of the rafters are connected by a metal plate hinge.
The nodes of the hip roof truss system
A feature of the hip roof is the shape of its slopes: long slopes are trapezoidal, end slopes (hips) are triangular. The installation of such a rafter system requires the installation of diagonal (sloping) rafter legs, which form triangular slopes. The principle of fastening the diagonal rafters in the upper part depends on the design features of the main part of the roof. It can be formed from hanging trusses, or it can be a frame with a ridge run and layered rafters attached to the Mauerlat.
If the layered rafter legs of the trapezoidal slopes rest on the ridge beam (run), then the rafters must be supported on the console of the ridge run. Console outlets for the sub-rafter frame should be 100-150 mm. The lower part of the diagonal rafter legs are attached to the Mauerlat or a beam mounted on the wall.
If the rafters need to be supported on the extreme hanging truss, then the principle of creating the attachment point depends on the section of the side rafter legs. Sprengel with a stand is mounted if the rafter legs are made of a board. Diagonal rafters rest on the sprengel. In a situation where a beam was used to make the rafter legs, the rafters can be attached to the surf - a board with a thickness of 5 mm or more, fixed to the truss truss.
On the sloping rafters, washed down at an angle corresponding to the angle of inclination of the hip slope to ensure a tight connection with the truss or surf. For the strength of the nail connection, clamps and wire twists can be additionally used.
The shortened rafter legs (spreaders) are supported by the upper part on the rafter, the lower part is attached to the Mauerlat on the wall. The attachment point to the diagonal beam can be performed:
- washed down with a nail fastening method;
- via socket connection;
- by fastening bars with a section of 50x50 mm on both sides and along the entire length of the diagonal rafters and splints.
Auxiliary elements
To enhance the rigidity and reliability of roof structures, it is often necessary to install a strut, an additional run or support posts. Rafter purlins provide the rafter leg with an additional point of support. The run is a horizontal beam, fixed on vertical posts, parallel to the ridge. The attachment point is made using metal corner plates or an internal metal rod and an external straight bracket.
Wooden rafter braces allow to reduce the span of rafter legs (including rafters). The angle of inclination of the brace to the horizontal plane must be at least 45°. If the rafter is made of a log or timber, the strut is cut with the installation of a steel dowel at an angle of 90 ° to the junction, or the joint is closed from the outside with a plate.
If it is necessary to strengthen the roof frame, it is necessary to install a strut under each rack on which the layered rafter rests. In this case, all the struts of one slope rest against a common bed. Staples are used for fastening.
The struts of the extreme spans, which are subject to the maximum snow and wind load, require special attention. Attachment points when mounting the strut to the rack or run are made using pads and bolts.
When designing any residential building, architects pay special attention to the roof, as it performs not one, but several functions at once, depending on its design features. It must be said that not all future homeowners are satisfied with the usual gable roof, although it can be called the most reliable, since it has only two pitched planes and one joint between them. Many are attracted to more complex designs that add a special appeal and originality to the structure. Other, more practical homeowners prefer attic structures that can simultaneously serve as a roof and a second floor.
The basis of any roof is an individual truss system, which has its own design features. Making the choice of the desired roof frame will be much easier if you figure out in advance which ones types and schemes of truss systems used in building practice. After receiving such information, it will become more clear how complex such structures are in installation. This is especially important to know if the roof frame is supposed to be built independently.
The main functional tasks of truss systems
When arranging pitched roof structures, the truss system is a frame for covering and for holding materials of the "roofing pie". With proper installation of the frame structure, the necessary conditions will be created for the correct and non-insulated types of roofs that protect the walls and the interior of the house from various atmospheric influences.
The roof structure is also always the final architectural element of the exterior design of the building, supporting its stylistic direction with its appearance. Nevertheless, the design features of the truss systems must first of all meet the requirements of strength and reliability that the roof must meet, and only then - aesthetic criteria.
The frame of the truss system forms the configuration and angle of inclination of the roof. These parameters largely depend on the natural factors characteristic of a particular region, as well as on the desire and capabilities of the homeowner:
- The amount of precipitation in different periods of the year.
- Direction and average wind speed in the area where the building will be erected.
- Plans for the use of space under the roof - the arrangement of residential or non-residential premises in it, or using it only as an air gap for thermal insulation of the premises below.
- Variety of planned roofing material.
- Financial capacity of the homeowner.
Atmospheric precipitation and the strength of wind currents give a very sensitive load on the structure of the roof. For example, in regions with heavy snowfalls, you should not choose a truss system with a small angle of inclination of the slopes, as snow masses will linger on their surface, which can lead to deformation of the frame or roofing or leaks.
If the area where the construction will be carried out is famous for its winds, then it is better to choose a structure with a slight slope of the slope so that the sharp gusts that occur do not rip off individual elements of the roof and roof.
The main elements of the roof structure
Details and nodes of truss systems
Depending on the type of truss system chosen, the structural elements used can vary significantly, however, there are details that are present in both simple and complex roof systems.
The main elements of the pitched roof truss system include:
- Rafter legs forming roof slopes.
- - a wooden bar fixed on the walls of the house and serving to fix the lower part of the rafter legs on it.
- The ridge is the junction of the frames of two slopes. It is usually the highest horizontal roof line and serves as a support on which the rafters are fixed. The ridge can be formed by rafters fastened together at a certain angle or fixed on a ridge board (run).
- Sheathing is slats or beams mounted on rafters with a certain pitch and serving as the basis for laying the selected roofing material.
- Retaining elements, where you can take beds, girders, racks, struts, ties and other parts, serve to increase the rigidity of the rafter legs, support the ridge, link individual parts into a common structure.
In addition to the above structural details, other elements can be included in it, the functions of which are aimed at strengthening the system and optimal distribution of roof loads on the walls of the building.
The truss system is divided into several categories depending on the different features of its design.
attic space
Before proceeding to the consideration of different types of roofs, it is worthwhile to figure out what an attic space can be, since many owners successfully use it as utility and full-fledged living quarters.
The design of pitched roofs can be divided into non-attic and attic. The first option is called just that because the space under the roof has a small height and is used only as an air layer that insulates the building from above. Such systems usually include or have several slopes, but located at a very slight angle.
The attic structure, which has a sufficiently large ridge height, can be used in different ways, be insulated and not insulated. These options include attic or gable option. If a roof with a high ridge is chosen, then it is imperative to take into account wind loads in the region where the house is built.
Slope slope
To determine the optimal slope of the roof slopes of the future residential building, first of all, you need to look at the already built low-rise neighboring houses. If they have been standing for more than one year and steadfastly withstand wind loads, then their design can be safely taken as a basis. In the same case, when the owners set the goal of creating an exclusive original project, unlike the buildings standing nearby, it is necessary to familiarize yourself with the design and operational features of various truss systems and make appropriate calculations.
It should be borne in mind that the change in the tangent and normal values of the wind force depends on how large the slope of the roof slopes is - the steeper the angle of inclination, the greater the importance of the normal forces and the smaller the tangents. If the roof is sloping, then the structure is more affected by the tangential wind load, since the lifting force increases on the leeward side and decreases on the windward side.
Winter snow load should also be taken into account when designing the roof. Usually this factor is considered in conjunction with the wind load, since the snow load on the windward side will be much lower than on the leeward slope. In addition, there are places on the slopes where snow will definitely collect, giving a big load on this area, so it should be strengthened with additional rafters.
Roof slopes can vary from 10 to 60 degrees and must be selected not only with regard to the consolidated external load, but also depending on the roofing that is planned to be used. This factor is taken into account because roofing materials differ in their mass, their fixing requires a different number of elements of the truss system, which means that the load on the walls of the house will also vary, and how large it will be, also depends on the angle of the roof slope. Equally important are the features of each coating in terms of resistance to moisture penetration - in any case, many roofing materials need one or another slope to ensure the free flow of storm water or melting snow. In addition, when choosing a roof slope, you need to think in advance how the process of cleaning and repair work on the roof will be carried out.
When planning this or that angle of the roof slopes, you need to know that the fewer joints between the sheets of the coating, and the tighter they are, the less you can make the slope of the slope, of course, if it is not supposed to arrange a residential or utility room in the attic space.
If a material consisting of small elements, for example, ceramic tiles, is used to cover the roof, then the slope of the slopes must be made steep enough so that water never lingers on the surface.
Given the weight of the roofing material, you need to know - the heavier the coating, the greater the angle of the slopes should be, since in this case the load will be correctly distributed to the rafter system and load-bearing walls.
The following materials can be used to cover the roof: either a profile sheet, galvanized steel, corrugated asbestos-concrete and bitumen-fiber sheets, cement and ceramic tiles, roofing felt, soft roofing and other roofing materials. The illustration below shows the allowable slope angles for various types of roofing.
Basic structures of truss systems
First of all, it is worth considering the basic types of truss systems regarding the location of the walls of the house, which are used in all roof structures. The basic options are divided into layered, hanging, and also combined, that is, including elements of both the first and second types of systems in their design.
fasteners for rafters
Layered system
In buildings where internal load-bearing walls are provided, a layered truss system is often installed. It is much easier to install than a hanging one, since the internal load-bearing walls provide reliable support for its elements, and in addition, fewer materials will be required for this design.
For rafters in this system, the defining reference point is the ridge board, on which they are fixed. The non-thrust type of the layered system can be equipped in three versions:
- In the first version, the upper side of the rafters is fixed on a ridge support, called a sliding one, and their lower side is fixed by cutting to the Mauerlat. Additionally, the rafters in the lower part are fixed to the wall with wire or staples.
- In the second case, the rafters in the upper part are cut at a certain angle and interconnected using special metal plates.
The lower edge of the rafter legs is attached to the Mauerlat with movable fasteners.
- In the third version, the rafters are rigidly fastened in the upper part with bars or processed boards located horizontally, parallel to each other on both sides of the rafters connected at an angle, and a ridge run is pinched between them.
In the lower part, sliding fasteners are used to fix the rafters, just as in the previous case.
It is necessary to explain why sliding fasteners are often used to fix the rafters on the Mauerlat. The fact is that they are able to save the load-bearing walls from excessive stress, since the rafters are not rigidly fixed, and when the structure shrinks, they have the ability to move without deforming the overall structure of the roofing system.
This type of fastening is used only in layered systems, which also distinguishes them from the hanging version.
However, in some cases, a spacer system is used for layered rafters, in which the lower end of the rafters is rigidly fixed to the Mauerlat, and in order to remove the load from the walls, puffs and struts are built into the structure. This option is called complex, as it includes elements of a layered and hanging system.
At the heart of each roof is a large number of beams, rafters, racks and runs, which are collectively called the truss system. Over the centuries-old history of types and methods of its organization, a lot has accumulated, and each has its own characteristics in the construction of knots and cuts. We will talk in more detail about what the gable roof truss system can be and how the rafters and other elements of the system should be attached in more detail.
The design of the gable roof truss system
In the context of a gable roof is a triangle. It consists of two rectangular inclined planes. These two planes are connected at the highest point into a single system with a ridge beam (run).
Now about the components of the system and their purpose:
- Mauerlat - a beam that connects the roof and walls of the building, serves as a support for the rafter legs and other elements of the system.
- Rafter legs - they form the inclined planes of the roof and are the support for the crate under the roofing material.
- Ridge run (bead or ridge) - combines two roof planes.
- A puff is a transverse part that connects opposite rafter legs. Serves to increase the rigidity of the structure and compensate for bursting loads.
- Beds - bars located along the Mauerlat. Redistribute the load from the roof.
- Side runs - support the rafter legs.
- Racks - transfer the load from the runs to the beds.
Filly may still be present in the system. These are boards that extend the rafter legs to form an overhang. The fact is that in order to protect the walls and foundation of the house from precipitation, it is desirable that the roof ends as far as possible from the walls. To do this, you can take long rafter legs. But the standard lumber length of 6 meters is often not enough for this. Ordering non-standard is very expensive. Therefore, the rafters are simply grown, and the boards with which this is done are called “fillies”.
There are quite a few designs of truss systems. First of all, they are divided into two groups - with layered and hanging rafters.
With hanging rafters
These are systems in which the rafter legs rest only on the outer walls without intermediate supports (bearing walls). For gable roofs, the maximum span is 9 meters. When installing a vertical support and a strut system, it can be increased up to 14 meters.
The hanging type of gable roof truss system is good because in most cases there is no need to install a Mauerlat, and this makes the installation of rafter legs easier: no need to make cuts, just mow the boards. To connect the walls and rafters, a lining is used - a wide board, which is attached to studs, nails, bolts, crossbars. With such a structure, most of the bursting loads are compensated, the impact on the walls is directed vertically downwards.
Types of truss systems with hanging rafters for different spans between load-bearing walls
Gable roof truss system for small houses
There is a cheap version of the truss system when it is a triangle (photo below). Such a structure is possible if the distance between the outer walls is not more than 6 meters. For such a rafter system, it is possible not to calculate the angle of inclination: the ridge must be raised above the puff to a height of at least 1/6 of the span length.
But with this construction, the rafters experience significant bending loads. To compensate for them, they either take rafters of a larger section or cut the ridge part in such a way as to partially neutralize them. To give greater rigidity in the upper part, wooden or metal plates are nailed on both sides, which securely fasten the top of the triangle (also see not the picture).
The photo also shows how to grow rafter legs to create a roof overhang. A notch is made, which should go beyond the line drawn from the inner wall upwards. This is necessary to move the incision site and reduce the likelihood of a rafter breaking.
Ridge knot and fastening of rafter legs to the backing board with a simple version of the system
For mansard roofs
Option with the installation of a crossbar - used when. In this case, it is the basis for filing the ceiling of the room below. For reliable operation of this type of system, the crossbar notch must be hingeless (rigid). The best option is semi-pan (see the picture below). Otherwise, the roof will become unstable to loads.
Please note that in this scheme there is a Mauerlat, and the rafter legs should extend beyond the walls to increase the stability of the structure. To secure them and dock with the Mauerlat, a cut is made in the form of a triangle. In this case, with an uneven load on the slopes, the roof will be more stable.
With such a scheme, almost the entire load falls on the rafters, therefore they must be taken with a larger section. Sometimes the raised puff is reinforced with a suspension. This is necessary to prevent it from sagging if it serves as a support for ceiling sheathing materials. If the puff is short, it can be secured in the center on both sides with boards nailed to the nails. With a significant load and length, there may be several such insurances. In this case, boards and nails are also enough.
For big houses
With a significant distance between the two outer walls, a headstock and struts are installed. This design has high rigidity, since the loads are compensated.
With such a long span (up to 14 meters), it is difficult and expensive to make a one-piece puff, because it is made from two beams. It is connected by a straight or oblique cut (picture below).
For reliable docking, the junction is reinforced with a steel plate mounted on bolts. Its dimensions should be larger than the dimensions of the cut - the extreme bolts are screwed into solid wood at a distance of at least 5 cm from the edge of the cut.
In order for the circuit to work properly, it is necessary to correctly make the struts. They transmit and distribute part of the load from the rafter legs to the puff and provide structural rigidity. Metal strips are used to reinforce the connections.
When assembling a gable roof with hanging rafters, the cross-section of lumber is always larger than in systems with layered rafters: there are fewer load transfer points, therefore, each element has a greater load.
With rafters
In gable roofs with layered rafters, their ends rest on the walls, and the middle part rests on load-bearing walls or columns. Some schemes burst walls, some do not. In any case, the presence of a Mauerlat is mandatory.
Bezporny schemes and knots of cuts
Houses made of logs or timber do not respond well to spacer loads. For them, they are critical: the wall can fall apart. For wooden houses, the gable roof truss system must be non-expansion. Let's talk about the types of such systems in more detail.
The simplest non-spacer scheme of the truss system is shown in the photo below. In it, the rafter leg rests on the Mauerlat. In this embodiment, it works on a bend, without bursting the wall.
Pay attention to the options for attaching the rafter legs to the Mauerlat. In the first, the support platform is usually beveled, while its length is no more than the cross section of the beam. The depth of the cut is no more than 0.25 of its height.
The top of the rafter legs is laid on the ridge beam without fastening it to the opposite rafter. Two shed roofs are obtained according to the structure, which adjoin (but do not connect) one with the other in the upper part.
It is much easier to assemble the option with rafter legs fastened in the ridge part. They almost never give a thrust on the walls.
For this scheme to work, the rafter legs below are attached using a movable joint. To fix the rafter leg to the Mauerlat, one nail is hammered from above or a flexible steel plate is placed from below. See the photo for options for attaching rafter legs to a ridge run.
If the roofing material is planned to be heavy, it is necessary to increase the bearing capacity. This is achieved by increasing the cross section of the elements of the truss system and strengthening the ridge assembly. It is shown in the photo below.
Strengthening the ridge assembly for heavy roofing material or with significant snow loads
All of the above gable roof schemes are stable in the presence of uniform loads. But in practice, this almost never happens. There are two ways to prevent the roof from sliding in the direction of greater load: by installing a brace at a height of about 2 meters or by struts.
Options for truss systems with contractions
The installation of contractions increases the reliability of the structure. In order for it to work normally, at the places where it intersects with drains, you need to attach nails to them. The cross section of the beam for the scrum is used the same as for the rafters.
They are attached to the rafter legs with bots or nails. Can be installed on one or both sides. The knot for attaching the bout to the rafters and the ridge run, see the figure below.
In order for the system to be rigid and not “crawl” even under emergency loads, it is enough in this embodiment to provide a rigid fastening of the ridge beam. In the absence of the possibility of its displacement in the horizontal, the roof will withstand even significant loads.
Rafter systems with braces
In these options, rafter legs, which are also called struts, are added for greater rigidity. They are installed at an angle of 45° with respect to the horizon. Their installation allows you to increase the span length (up to 14 meters) or reduce the cross section of beams (rafters).
The strut is simply substituted at the required angle to the beams and nailed from the sides and bottom. An important requirement: the brace must be cut accurately and fit snugly against the uprights and the rafter leg, excluding the possibility of its deflection.
Systems with rafter legs. Above is a spacer system, below is a non-spacer system. The nodes of the correct felling for each are located nearby. Below - possible schemes for attaching the strut
But not in all houses, the average load-bearing wall is located in the middle. In this case, it is possible to install struts with an angle of inclination relative to the horizon of 45-53 °.
Bracing systems are necessary if significant uneven shrinkage of the foundation or walls is possible. Walls can sit differently on wooden houses, and foundations on layered or heaving soils. In all these cases, consider the installation of truss systems of this type.
System for houses with two internal load-bearing walls
If the house has two load-bearing walls, two rafters are installed, which are located above each of the walls. Beds are laid on the intermediate load-bearing walls, the load from the rafter beams is transferred to the beds through the racks.
In these systems, a ridge run is not installed: it gives expansion forces. The rafters in the upper part are connected to one another (cut and joined without gaps), the joints are reinforced with steel or wooden plates, which are nailed.
In the upper non-expansion system, the expanding force is neutralized by tightening. Please note that the puff is placed under the run. Then it works efficiently (the top diagram in the figure). Stability can be provided by racks, or jointing - beams installed obliquely. In the spacer system (in the picture it is below), the cross member is a crossbar. It is installed above the run.
There is a variant of the system with racks, but without rafters. Then a rack is nailed to each rafter leg, which rests on the intermediate load-bearing wall with the second end.
Fastening the rack and tightening in the rafter system without a rafter run
To fasten the racks, nails for 150 mm and bolts 12 mm are used. Dimensions and distances in the figure are in millimeters.
The pitched roof of the house consists of a large number of parts, each of which is connected to others in a special way. Such a connection is called a roof node. In this article, we will talk specifically about the connection nodes, how it is carried out, what technologies are used, what fasteners are used.
The main parts of the roof structure
Before proceeding directly to the analysis of the topic of the article, it is necessary to indicate what elements (details) the roof structure consists of. We list all the main details and indicate their purpose.
Mauerlat. This is a beam that is laid on the walls of the house, located along the perimeter of the building. The purpose of the Mauerlat is to evenly distribute the loads emanating from the truss system. After all, if there is no Mauerlat, then each rafter will put pressure on the wall pointwise. And it is in this place that the destruction of the wall structure will occur.
rafter legs. They are made either from boards with a thickness of at least 50 mm, or from timber. Rafters are the basis of the roof, it is they who form the slopes and bear all the loads acting on the roof structure.
Skate run. This is the uppermost beam, installed horizontally. Its purpose is to support the upper ends of the rafter legs. It is he who forms the ridge of the roof.
These are the three main elements of the roof, which will be discussed further. Of course, these are not all the details of the roof, and it cannot be said that others are less important. It's just that these three elements form the structure itself. The only thing to add is that in some roof structures there is no ridge run. It's just that the upper ends of the rafters rest against each other. This type of rafters is called hanging, and with a ridge run layered.
In order for the roof structure to be the most reliable, it is necessary that the roof nodes are correctly connected. In this case, the force of the acting loads and their direction must be taken into account.
How to connect the elements of the roof structure
More recently joining timber roofing carried out with the help of notches. That is, they cut the elements of the roof structure in order to connect them along one fairly wide plane. Therefore, so that the roof details do not reduce their strength characteristics, as well as their bearing capacity, they were selected with a sufficiently large cross section. And it's not economical. That is, the larger the cross-section of lumber, the more expensive it is.
Today, the technology of fastening nodes and parts of the roof structure has changed dramatically. To do this, use bolts, dowels or metal perforated profiles. The latter are made of galvanized steel, which makes it possible to operate fasteners for a long time without losing their quality. At the same time, manufacturers offer a fairly wide range of them for each type of node. The photo below shows some of these fasteners.
It should be noted that perforated profiles gradually replaced all other types of fasteners due to the strength, reliability and ease of fastening operations. After all, for this you just need to install the profile at the required place and fix it to various parts with wood screws or ruff nails.
Let's now look at how fasten parts roof structure to each other. In principle, there are two types of connection: Mauerlat-rafter, rafter-ridge run. The remaining parts are connected parallel to these joints. They will also be talked about.
Mauerlat and rafters connection
There are actually a huge number of fastening options, from ordinary nails to perforated profiles. For example, the photo below shows an option where ordinary wire is used as fasteners. That is, a through hole is made in the rafter itself, where a wire with a diameter of 6 mm is inserted. They also make a hole in the Mauerlat or in the floor beam.
Then the ends of the wire are pushed into this hole and twisted, pressing the rafter leg against the Mauerlat. The connection is actually strong and reliable, but the process is laborious.
Can be used instead of wire metal tape 3 mm thick. She simply wraps two connected elements and through the strip is attached to them with self-tapping screws, more often with nails. In the latter case, there is no need to drill through holes in the metal. note that in the lower photo, the fastening is carried out to the reinforced belt with an anchor, which increases the strength and reliability of the connection.
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The next type of fastening is a perforated corner made of galvanized steel. The most convenient option, but the most reliable. To do this, the corner is simply installed so that it is tightly pressed against the plane of the Mauerlat and the rafter leg with its mounting shelves. Fastening is carried out with screws or nails.
Fasten the corners it is possible not only with self-tapping screws or ruff nails. There is another more reliable option where bolts are used. True, holes will have to be made under them, which increases the costly time for carrying out this type of work. But in this case, the quality is above all. The photo below shows just such a mounting option. Please note that the corner is attached to the Mauerlat with self-tapping screws, and to the rafter leg with a bolt. In this case, one bolt is used to connect two corners located at opposite ends of the rafter.
And another mounting option - on the slider. This is a special type of fastener, consisting of two parts. One is attached to the Mauerlat, the second to the rafter leg. In this case, both parts are not tightly connected to each other. This is done specifically so that the rafters can move relative to the Mauerlat during the thermal expansion of the lumber. This means that there will be no loads that act on the junction of two roof parts. The photo below shows this connection option.
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Connection of rafters with a ridge run
The second main node of the wooden roof - joint between rafter leg and ridge beam. In fact, the ridge roof truss assembly is very complicated, because two rafter legs and a beam are joined on it. In this case, all the elements are located in different planes, meaning the rafters and timber. This means that more than one fastener will have to be used to connect them.
To connect the rafters to each other, they use perforated plate. There are two of them, installed on different sides of the rafter legs to increase strength and reliability.
Perforated corners connecting the rafters to the Mauerlat. There are four of them, two for each rafter leg, installed from different sides.
It should be noted that fastenings can be carried out not only with self-tapping screws or nails. Often masters use bolts for connection paired fasteners.
Pay attention to a different type of fastening. Only corners are used here. This option is used if a board with a thickness of 50 mm is installed as a ridge beam.
Another interesting option for attaching rafter legs to a ridge span, for which special perforated complex shape profiles. In fact, these are brackets into which the rafter leg is inserted. The bracket not only fastens the parts together, it supports the rafters, reducing the load on its end.
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Pay attention to all of the above options for connecting rafters to each other. They clearly show that the ends of the rafter legs are joined tightly to each other, for which they have to be filed at a certain angle. You can do without filing if you use a complex mounting lock, consisting of several plates that are bolted together. In the photo below, this connection option is clearly visible.
Connection of hanging rafters
The rafter system of this type differs from the layered one in that it does not have ridge run. That is, the rafter legs in the upper part (ridge) rest against each other. In order for them not to disperse in different directions, the rafters are connected to each other by a horizontal tightening. The latter is a board located at any distance in height: from above, below or in the middle.
It should be noted that hanging rafters not assembled separately on the roof. Farms are assembled from them on the ground, which are installed ready-made on the roof of the house. In this case, all elements of the farm are interconnected by perforated plates.
Video description
In the video, the master tells how to assemble a roof truss using perforated plates and nails:
Other types of knots
As mentioned above, there are many details in the roof structure. Therefore, we will tell and show a few more important connection nodes.
If the span of the house is more than 6 m, then a rack is installed under each rafter, which itself must rest either on a concrete base or on a floor beam. In this case, the connection of the rack with the rafter leg is carried out with ordinary boards, as shown in the photo below. Although you can use perforated metal plates.
Under the ridge beam is also installed vertical support posts, which are attached to each other by perforated plates. But in some roof structures, a completely different approach is used to solve the installation of a ridge run. Under the beam, jibs are mounted from the bars, which are fixed to the ridge with special fasteners made of metal. The photo below shows one of the options for this type of fastener.
Very often, when constructing a rafter system, it becomes necessary to lengthen the rafters themselves. It is not difficult to do this, while the masters use several technologies, where they use various additional fasteners.
Video description
The video shows one of the options for lengthening the rafters:
Roof structures are several varieties of their forms. Almost all models have a large number of identical elements. But among them there is one design that differs significantly from the others. This hipped roof. Its distinctive feature is that the rafters are connected by their upper edges to one point, which is called the ridge knot.
So, in order to connect the rafter legs to each other, you need a support to which they are attached. There are several ways to ensure high node reliability. The photo below shows one of them, which uses U-shaped perforated metal mounting profiles.
Conclusion on the topic
In fact, we have considered only a small part of the connecting nodes for attaching the roof truss system. But even on their example, the variety of parts and assemblies becomes clear. That is, the roof structure is a complex system, consisting of a large number of different elements and parts that are interconnected in different ways.
The structure of the rafters is the skeleton of the roof, which is obliged to take on and evenly distribute the weight of the roofing materials. If you correctly assemble the wooden skeleton for insulation, waterproofing film and top coat, you will be able to achieve a noticeable increase in the load capacity of the truss system.
The main elements of the truss system
The wooden frame of the roof is assembled from parts such as:
- mauerlat - a kind of base for roofing elements, attached around the entire perimeter of the building to the upper edge of the outer walls in order to disperse the pressure of the roofing pie;
Mauerlat serves as the basis for the roof frame
- rafter legs - irreplaceable parts of the wooden skeleton of the roof, which determine the angle of inclination of the slopes and the view of the upper part of the house;
- ridge run - a bar fixed in a horizontal position and, like a spine, connecting all the rafters of the roof frame in their upper part;
The ridge run is located exactly in the middle of the building
- side run - a horizontal beam, which differs from a ridge run in that it is fixed in the middle of the rafter legs of each roof slope;
- puff - a spacer that unites two opposite rafters so that they do not move apart;
Tightening and struts are necessary to properly distribute the load on the Mauerlat
- racks - vertical frame elements placed under the ridge and side runs to support the rafters and the ridge beam, and also, if necessary, substituted under the middle part of the rafter legs;
Racks can support not only the ridge of the roof, but also the rafters
- struts - parts that rest against the bed, due to which the rafter legs become more stable;
- bed - a bar placed on the upper edge of the inner wall of the building parallel to the ridge and serving as a platform for attaching racks and struts;
The bed is located on the inner wall parallel to the mauerlat beam
- roof ridge - the area of combination of two slopes, along which a continuous crate is installed, necessary to strengthen the described part of the roof;
The ridge is formed in the highest zone of the truss system
- filly - elements used in the arrangement of the overhang, when the rafter legs are not long enough;
Fillies lengthen rafter legs
- roof overhang - a wooden frame area that protects the walls of the house from contact with a large amount of precipitation;
The cornice overhang is constructed to protect the walls from rain.
- crate - bars or boards nailed perpendicular to the rafters and serving as a platform for attaching roofing materials.
Sheathing boards are laid out perpendicular to the rafters
Main connecting nodes
The main nodes of the truss system are:
- roof truss - connection of a rafter pair, stretch marks, as well as racks and braces;
- ridge knot - combination of two opposite rafters;
- a link from a Mauerlat and a rafter resting on it;
- a module that includes a run, a rack and a bed;
- connection of the rafters with a strut and a rack.
The most complex link of the roof frame, according to the author, is a truss truss, which is distinguished by the fact that:
The ridge knot also has several features:
Rafters and Mauerlat become a single link, which is characterized by the following:
A module from a run, a rack and a bed is formed by driving building brackets, steel dowels or linings from steel strips into their joints.
A node of a bed, a rack and a run allows you to share the load between the external and internal walls of the building
Struts, racks and rafters are assembled into a single module, creating cuttings. To ensure that their connection is not weak, construction brackets are used.
A knot of struts, racks and rafters allows you to soften the pressure on the inner wall of the house
Ways of fastening rafters
In the lower part, the rafters can be connected both to the Mauerlat and to the floor beams. Sometimes, for example, during frame construction, they are fixed directly on the wall. And in the upper part, the rafter legs are combined with the ridge. Each labeled node can be created in several ways.
Mauerlat connection
The rigid fastening of the rafters on the Mauerlat guarantees the absence of any displacement of the assembly elements. It is performed by cutting in a certain sequence:
- To speed up work, a template is made from a piece of board or thick cardboard. A line is drawn on the workpiece, stepping back from the side edge a distance equal to 1/3 of the width of the rafter, and then the point of contact with the Mauerlat beam is marked, along which a second line is drawn perpendicular to the first.
If the width of the rafter is more than 200 mm, then washed down is done at a depth of 70 mm
- At an angle of inclination of the roof slope, the template is substituted to the edge of the Mauerlat, making sure that the point marked on the piece of wood is strictly opposite the corner of the beam. Two lines are drawn from it with a pencil - vertical and horizontal, as a result of which a triangle is obtained on the workpiece, which is carefully cut out.
- The made template is assessed for correctness by putting it on the Mauerlat in several places. If the groove made turned out to be smaller or larger than necessary, then the pattern is made anew, correcting the mistake made.
- The template is placed on a horizontally located rafter. The triangle in the pattern is circled with a pencil. The same is done with other rafter legs. At the same time, make sure that the horizontal line of the groove in the pattern is always in the same place on the rafter. Otherwise, notches will be created at different distances from the ridge.
- The triangles drawn on the rafters are cut out with a hand saw. The tool is operated slowly so as not to accidentally increase the depth of the groove in the rafter leg. Possessing the skills of working with an electric saw, recesses can be made with this device. True, it must be borne in mind that a tool powered by the mains is much worse at listening to the hand and is able to go to the side.
The triangular cut allows the rafter to rest against the Mauerlat
- The correctness of the size of the grooves made is checked with a pattern. If discrepancies are found, the notch is corrected with a hacksaw.
- Two extreme rafter legs are placed on top of the house. They are inserted into the Mauerlat with grooves, fixed on the sides with metal corners or brackets.
- A rope is pulled along the bottom edge between the two installed elements. Then the remaining rafter legs are attached to the Mauerlat one by one.
The technology of attaching the rafter legs to the Mauerlat with a patch of a thrust bar can be taken into account by builders without experience. With this method of creating a node, as the author of the article noted, it is possible to change the position of the rafters until it becomes completely correct.
To connect the main elements of the roof frame with the Mauerlat with a stripe of a thrust bar, do the following:
When building a roof frame for a wooden frame, which always shrinks, they prefer to use the sliding method of attaching rafters to the Mauerlat. Thanks to it, it is possible to avoid deformation of the truss structure and deterioration in the stability of the upper row of logs, which replaces the Mauerlat.
The choice of sliding rafters is justified only when a ridge beam is provided for the main elements of the roof frame, against which they could rest with their upper part.
When the rafters are fixed on the Mauerlat using the sliding method, certain steps are taken:
The layered method of attaching rafters to the Mauerlat is adopted when the purchased lumber turned out to be shorter than necessary. Also, this method of fixing the main elements of the rafter system is used during the repair of a roof of complex configuration.
When fixing the rafters on the Mauerlat using the layered method, only 3 tasks are performed:
Video: installing rafters
Combination with floor beams
It is possible to fasten the rafters to the floor beams only being sure that the walls of the building will withstand the pressure of the roof frame. Still, in the absence of a Mauerlat, the load on the house is not uniform, but point.
Without fear and doubt, the rafters are attached to the floor beams if they are building a light mansard roof. At the same time, boards with a section of 5x15 cm are used as ceiling beams.
The rafters are not connected to the Mauerlat, but to the beams of the attic, if they know for sure that they will withstand the pressure exerted
To firmly fix the rafter legs on the floor beams, perform the following tasks:
wall mount
If for some reason the rafters have to be fixed directly on the walls, then they will definitely need to be connected with a puff. She, as the author of the article personally made sure, who helped build the roof of the utility room, will remove part of the stress transmitted by the rafters from the house.
Rafters should never be directly connected to the outer walls of the building if they are built from foam or gas blocks. These materials freely transfer their moisture to the wood and are unable to retain fasteners.
On the wall, the rafters can be fixed using a sliding method, but this is not the most reasonable solution.
To securely fix the rafter legs on the walls, it is necessary to take certain measures:
- At the right angle, make on the rafters washed down with one tooth.
- Install the rafters on the walls with the butt end and drive a nail 10-12 cm long into them.
- If necessary, attach metal corners to the sides of the rafters.
Since the roof ridge is under serious pressure from the entire truss system, roofers with extensive experience create a ridge knot in five ways: butt, on a beam, overlap, in a groove, in half a tree.
To create a ridge knot by connecting opposite rafters end-to-end, do the following:
When attaching rafters to a beam, or rather, to a special ridge run, they act in a special way:
When the rafters are connected to the beam, the ridge is not pointed, but flat.
If the ridge knot is made by fastening the rafters with an overlap, then you will need to perform a few simple tasks:
To connect the rafter legs into a ridge knot using a groove, several skillful carpentry actions are performed:
Having chosen the method of connecting the rafters to half a tree, do the following:
Video: building a roof frame with connecting rafters with a ridge run
The construction of the rafter system should not be started until it is possible to understand the features of fastening the rafters to other elements of the roof supporting structure. By the way, among the various ways of fixing the rafter legs, there are options not only for experienced builders.