The pitched roof of a house consists of a large number of parts, each of which is connected to the others in a special way. This connection is called a roof joint. In this article we will talk specifically about connection nodes, how they are carried out, what technologies are used, what fasteners are used.
Main parts of the roof structure
Before moving directly to the analysis of the topic of the article, it is necessary to indicate what elements (parts) the roof structure consists of. Let's list all the main parts 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 coming from the rafter 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. The rafters are the basis of the roof; they form the slopes and bear all the loads acting on the roof structure.
Ridge run. This is the most top beam, installed horizontally. Its purpose is to support the upper ends rafter legs. It is this that 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 we cannot say that others are less important. It’s just that these three elements form the structure itself. The only thing that needs to be added is that some roof structures do not have a ridge girder. The rafters simply rest against each other with their upper ends. This type of rafters is called hanging, and with a ridge girder, layered.
So that the roof structure is as reliable as possible, it is necessary that the roof components are correctly connected. In this case, the strength of the acting loads and their direction must be taken into account.
How to connect roofing elements
More recently connection of nodes wooden roof carried out using cuts. 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 parts do not reduce their strength characteristics, as well as load-bearing capacity, they were selected with a sufficiently large cross-section. And this is not economical. That is, the larger the cross-section of lumber, the more expensive it is.
Today, technologies for fastening components and parts of roofing structures have changed dramatically. To do this, use bolts, dowels or perforated metal profiles. The latter are made of galvanized steel, which makes it possible to use 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 unit. The photo below shows some of these fasteners.
It should be noted that perforated profiles gradually replaced all other types of fasteners due to their strength, reliability and ease of fastening operations. After all, to do this you just need to install the profile in the required place and attach it to various details wood screws or ruff nails.
Let's now look at how to fasten parts roofing structure with each other. In principle, there are two types of connections: Mauerlat-rafters, rafters-ridge girder. The remaining parts are connected parallel to these joints. He will also talk about them.
Connection of the Mauerlat and rafters
Mounting options actually great amount, starting with ordinary nails, ending with 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, into which a wire with a diameter of 6 mm is inserted. A hole is also made 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 to the Mauerlat. The connection is actually strong and reliable, but the process is labor intensive.
Instead of wire you can use metal tape 3 mm thick. It is simply wrapped around the two elements being connected and secured to them through the strip with self-tapping screws, 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. Most convenient option, but as reliable as possible. To do this, the corner is simply installed so that with its mounting shelves it is pressed tightly against the plane of the Mauerlat and the rafter leg. Fastening is carried out with self-tapping screws or nails.
Attach 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 for them, which increases the time required for this type of work. But in this case, quality comes first. 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 rafters.
And another mounting option - on the slider. This special type fastening element 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 was done specifically so that the rafters could move relative to the Mauerlat during 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 ridge girder
Second main node wooden roof – joint between rafter leg and ridge beam. Actually a ridge knot rafter roof it is very complex, because it is where two rafter legs and a beam are joined. In this case, all elements are located in different planes, meaning rafters and beams. This means that to connect them you will have to use more than one fastening element.
To connect rafters to each other, 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 on 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 the different type of fastening. Only corners are used here. This option is used if ridge beam install a board 50 mm thick.
Another interesting option fastening the rafter legs to the ridge span, for which special perforated profiles of complex shapes. Essentially, these are brackets into which the rafter leg is inserted. The bracket not only holds the parts together, it supports the rafter, reducing the load on its end.
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Pay attention to all of the above options for connecting the 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 fastening lock consisting of several plates that are connected with bolts. 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 girder. That is, the rafter legs in the upper part (ridge) rest against each other. To prevent them from moving apart in different directions, the rafters are connected to each other by a horizontal tie. The latter is a board located at any distance in height: above, below or in the middle.
It should be noted that hanging rafters They are not assembled separately on the roof. Trusses are assembled from them on the ground, which are installed in finished form on the roof of the house. In this case, all elements of the truss are connected to each other by perforated plates.
Video description
In the video, the master explains how to assemble a roof truss using perforated plates and nails:
Other types of knots
As mentioned above, there are many details in a roof structure. Therefore, we will tell and show a few more important connection points.
If the span of the house is more than 6 m, then a stand is installed under each rafter, which itself should rest against either concrete base, or into the floor beam. In this case, the connection of the rack with the rafter leg is carried out using ordinary boards, as shown in the photo below. Although you can use perforated metal plates.
They are also installed under the ridge beam vertical support posts, which are fastened together with perforated plates. But some roofing structures use a completely different approach to solving the installation of a ridge girder. Under the beam, jibs made of bars are mounted, which are secured 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. This is not difficult to do, and craftsmen use several technologies where they use various additional fasteners.
Video description
The video shows one of the options for lengthening the rafters:
Roofing structures come in 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 hip roof . Its distinctive feature is that the rafters are connected by their upper edges to one point, which is called a 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 only considered most of connecting nodes for fastening the roof truss system. But even with their example, the variety of parts and components becomes clear. That is, the roof structure is a complex system, consisting of a large number different elements and parts that are connected to each other in different ways.
Each roof is based on a large number of beams, rafters, posts and purlins, which are collectively called the rafter system. Behind centuries-old history Many types and methods of its organization have accumulated, and each has its own characteristics in the construction of nodes and cuts. Let's talk in more detail about what the rafter system of a gable roof can be and how the rafters and other elements of the system should be attached.
Design of a gable roof truss system
In the context gable roof is a triangle. It consists of two rectangular inclined planes. These two planes meet at the highest point at unified system ridge beam (purlin).
Now about the components of the system and their purpose:
- Mauerlat is a beam that connects the roof and walls of a building, serves as a support for rafter legs and other elements of the system.
- Rafter legs - they form the inclined planes of the roof and provide support for the sheathing under the roofing material.
- Ridge purlin (bead or ridge) - combines two roof planes.
- A tie is a transverse part that connects opposite rafter legs. Serves to increase structural rigidity and compensate for thrust loads.
- Lezhny - bars located along the mauerlat. Redistribute the load from the roof.
- Side purlins - support the rafter legs.
- Racks - transfer the load from the purlins to the beams.
There may still be fillies in the system. These are boards that extend the rafter legs to form an overhang. The fact is that to protect the walls and foundation of the house from precipitation, it is desirable that the roof ends as far from the walls as possible. To do this, you can take long rafter legs. But the standard length of lumber of 6 meters is often not enough for this. Ordering non-standard is very expensive. Therefore, the rafters are simply extended, and the boards with which this is done are called “fillies”.
There are quite a lot of designs of rafter 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 external walls without intermediate supports (load-bearing walls). For two pitched roofs the maximum span is 9 meters. When installing a vertical support and a strut system, it can be increased to 14 meters.
The good thing about the hanging type of gable roof rafter system is that in most cases there is no need to install a mauerlat, and this makes the installation of rafter legs easier: there is no need to make cuts, just bevel the boards. To connect the walls and rafters, a lining is used - a wide board, which is attached to studs, nails, bolts, crossbars. With this structure, most of the thrust loads are compensated, the impact on the walls is directed vertically downwards.
Types of rafter systems with hanging rafters for different spans between load-bearing walls
Gable roof rafter system for small houses
Exists cheap option rafter system when it is a triangle (photo below). Such a structure is possible if the distance between the external walls is no more than 6 meters. For such a rafter system, you can not make calculations based on the angle of inclination: the ridge must be raised above the tie 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, either rafters of a larger cross-section are taken or the ridge part is cut in such a way as to partially neutralize them. To give greater rigidity, wooden or metal plates are nailed on both sides at the top, which securely fasten the top of the triangle (also see the picture).
The photo also shows how to extend rafter legs to create a roof overhang. A notch is made, which should extend beyond the line drawn from interior wall up. This is necessary to shift the location of the cut and reduce the likelihood of the 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 installing a crossbar - used when. In this case, it serves as the basis for lining the ceiling of the room below. For reliable operation of a system of this type, the crossbar cut must be hingeless (rigid). The best option- half frying pan (see picture below). Otherwise, the roof will become unstable to loads.
Please note that in this scheme there is a Mauerlat, and the rafter legs must extend beyond the walls to increase the stability of the structure. To secure them and dock them with the Mauerlat, a notch 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 this scheme, almost the entire load falls on the rafters, so they need to be taken with a larger cross-section. Sometimes the raised puff is reinforced with a pendant. This is necessary to prevent it from sagging if it serves as a support for ceiling cladding materials. If the tie 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 belays. In this case, too, boards and nails are enough.
For large houses
If there is 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 the tie in one piece, so it is made from two beams. It is connected by a straight or oblique cut (picture below).
For reliable docking the connection point is reinforced with a steel plate mounted on bolts. Its dimensions must be larger than the dimensions of the notch - the outer bolts are screwed into solid wood at a distance of at least 5 cm from the edge of the notch.
In order for the circuit to work properly, it is necessary to make the struts correctly. They transfer and distribute part of the load from the rafter legs to the tie and provide structural rigidity. Metal pads are used to strengthen 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 bears a greater load.
With layered 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 push through the walls, some don't. In any case, the presence of a Mauerlat is mandatory.
Non-thrust schemes and notch units
Houses made of logs or timber do not respond well to thrust loads. For them they are critical: the wall may fall apart. For wooden houses, the rafter system of a gable roof must be non-thrust. Let's talk about the types of such systems in more detail.
The simplest non-thrust rafter system diagram is shown in the photo below. In it, the rafter leg rests on the mauerlat. In this version, it bends without pushing the wall.
Pay attention to the options for attaching the rafter legs to the Mauerlat. In the first, the support area is usually beveled, its length being no more than the 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. The structure turns out to be two pitched roofs, which in the upper part are adjacent (but not connected) to one another.
The option with rafter legs fastened at the ridge part is much easier to assemble. They almost never push against the walls.
To operate this scheme, the rafter legs at the bottom are attached using a movable connection. To secure the rafter leg to the mauerlat, one nail is driven from above or a flexible steel plate is placed from below. See the photo for options for attaching rafter legs to the ridge girder.
If you plan to use heavy roofing material, you need to increase bearing capacity. This is achieved by increasing the cross-section of the rafter system elements and strengthening the ridge assembly. It is shown in the photo below.
Reinforcing the ridge assembly for heavy roofing material or for significant snow loads
All of the above gable roof schemes are stable in the presence of uniform loads. But in practice this practically never happens. There are two ways to prevent the roof from sliding towards a higher load: by installing a screed at a height of about 2 meters or by struts.
Options for rafter systems with contractions
Installing contractions increases the reliability of the structure. In order for it to work properly, it needs to be secured to them with nails at the places where it intersects with the drains. The cross-section of the timber for the scrum is 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. See the figure below for attaching the screed to the rafters and ridge girder.
In order for the system to be rigid and not “creep” even under emergency loads, it is enough in this option to ensure rigid fastening of the ridge beam. In the absence of the possibility of its horizontal displacement, the roof will withstand even significant loads.
Layered rafter systems with struts
In these options, for greater rigidity, rafter legs, also called struts, are added. They are installed at an angle of 45° relative 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 brace is simply placed at the required angle to the beams and nailed on the sides and bottom. Important Requirement: the strut must be cut accurately and fit tightly to the posts and rafter leg, eliminating the possibility of it bending.
Systems with rafter legs. The top is a spacer system, the bottom is a non-spacer system. The correct cutting nodes for each are located nearby. Below are possible strut mounting schemes
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°.
Systems with struts are necessary if significant uneven shrinkage of the foundation or walls is possible. Walls can settle differently depending on wooden houses, and the foundations are on layered or heaving soils. In all these cases, consider installing rafter systems of this type.
System for houses with two internal load-bearing walls
If the house has two load-bearing walls, install two rafter beams, which are located above each of the walls. The beams are laid on the intermediate load-bearing walls, the load from the rafter beams is transferred to the beams through the racks.
In these systems, a ridge run is not installed: it provides 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-thrust system, the pushing force is neutralized by the tightening. Please note that the tightening is placed under the purlin. Then it works effectively (top diagram in the figure). Stability can be provided by racks, or joints - beams installed diagonally. In the spacer system (in the picture it is below) the crossbar is a crossbar. It is installed above the purlin.
There is a version of the system with racks, but without rafter beams. Then a stand is nailed to each rafter leg, the other end of which rests on the intermediate load-bearing wall.
Fastening the rack and tightening in the rafter system without a rafter purlin
To fasten the racks, 150 mm long nails and 12 mm bolts are used. Dimensions and distances in the figure are indicated in millimeters.
In order for a constructed building to last for more than one year, it needs both a reliable foundation and strong system roofs that can withstand the vicissitudes of the weather. The roof must withstand heavy loads with dignity: heavy snowfalls, sharp gusts of wind, heavy downpours. The roof truss system is best suited for this.
Roof trusses and its types
The rafter system is the basis of the roof, which focuses on load-bearing elements structure and also serves as a frame for various types roofing materials: insulation, waterproofing, various coatings.
The dimensions and design of the rafters depend on:
- purchased material;
- size of the building;
- house dimensions;
- building materials for rafters;
- individual customer preferences;
- roof loads relevant for a particular region.
The rafter system has:
- sheathing - beams laid perpendicularly on the rafter legs;
- ties that absorb tensile forces;
- wooden racks located in a vertical position;
- mauerlat - a beam, the installation of which is carried out along the wall, the rafters rest on it;
- rafter legs are a kind of wooden beams that bear the main load of the roof.
Each of the above factors is very important, since it is necessary to understand what type of rafter system will be optimally suited for a particular situation.
When it comes to low-rise buildings, wood structures are the most common. In many cases, three types of rafter trusses are used: hanging rafters, layered rafters and a mixed rafter system.
Characteristics of hanging rafters
Hanging rafters are the most elementary type of rafter systems, their characteristics:
If the roof of the house has a complex structure, the types of rafters can be alternated. For example, if there are supports or a middle main wall, layered rafters are installed, and if there are no such elements, hanging rafters are installed.
Features of layered rafters
For a layered rafter system, the house must be additionally equipped load-bearing wall, located in the middle. Layered rafters are distinguished according to the following characteristics:
Design combined system the most complex, since it includes parts of two other types of rafters - hanging and layered. It is used for mansard roof. The walls of the rooms located on the second floor form vertical supports, these supports are also intermediate supports for the rafter beams.
The part of the rafters that connect one end of the racks functions as a crossbar for the slopes located on the side, and for the upper part of the structure they are a tie.
At the same time, the horizontal beams perform the following functions: for the upper slopes - the Mauerlat, for the side slopes - the ridge beam. To increase the strength of the roof, struts are installed that connect the side slopes and vertical posts.
The combined sling system is the most complex and time-consuming to manufacture, but these shortcomings are fully compensated by the increase in the load-bearing qualities of the roof in the absence of unnecessary supports, especially when there is a need to cover significant spans in the building.
You can increase the load-bearing qualities of the roof using a mixed rafter system
Roof trusses for various roof types
When constructing a certain building, rafter systems of one type or another are necessarily used, and the type of roof will completely depend on the design of the future structure.
Rafter truss for gable roof
Gable roofing is a common roof construction for residential buildings that have no more than three floors. Preference is given to this particular design due to the technical characteristics of the inclined shape of the rafter system, and also due to the fact that installation work carried out easily and simply.
The rafter system of a gable roof includes two rectangular inclined planes. The upper part of the building from the end side resembles a triangle. The main components of a gable roof are the mauerlat and rafter legs. In order to properly distribute the load across the rafters and walls, struts, crossbars and racks are installed, thanks to which you can create a durable, rigid, elementary and lightweight structure for installing a structure for a gable roof.
A gable roof is considered the simplest roofing system; it is used for residential buildings of no more than three floors
You can install sparse or solid sheathing on top of the rafters, and then attach bitumen coating, tiles or some other type of material to it. The rafters and the sheathing itself are usually made of beams or boards, which are fastened with nails, bolts or metal fasteners. Metal profiles can be used as rafters, thereby covering significant spans. There is no need to use extra racks and struts.
The installation of a rafter system for a gable roof allows you to evenly distribute the entire existing load along the perimeter of the building.
The lower ends of the system focus on the Mauerlat. They are fixed with fasteners or metal brackets. By the angle of inclination of the rafter bars, you can determine at what angle the roof slopes will be inclined.
The rafter system for a gable roof allows you to evenly distribute the load from the roof along the perimeter of the building
Rafter system for hip roof
- When arranging a system for a hip roof, you will need to install different types of rafters:
- narozhniki (short);
- lateral;
- hip main;
obliques (diagonal elements that form a slope in the shape of a triangle). The rafter legs, located on the side, are made of boards, and they are mounted identically to the parts of a traditional pitched roof with a pitched or hanging structure
. Hip main rafters are layered parts. For sprigs, boards or bars are used, attached not only to the Mauerlat, but also to the diagonal beams.
To install this type of structure, the angle of inclination, as well as the cross-section of the slanting beams, are accurately calculated. The dimensions of the parts also depend on the span length.
To prevent the hip roof from deforming from heavy loads, you should accurately calculate the angle of inclination of the diagonal beams for the rafters
Rafter system for a sloping roof
A broken roof is a structure with rafters that consist of several individual elements. Moreover, they should be located at different angles relative to the horizon. And since the lower rafter part is almost vertical, attic room The building receives additional space, thanks to which it can be used as a residential building. The installation of this type of roof is carried out during the construction of a four- or gable rafter structure.
Calculate four-slope system rafters are needed by professionals, but you can make a gable sloping roof yourself, since its installation is very simple. To do this, it is necessary to install a support frame, which should consist of purlins and racks. Horizontal parts are fixed with hanging rafters. But the supports of the sloping roof are secured to the mauerlat with the shortened legs of the rafters.
The assembly of rafters for a sloping gable roof can also be carried out by non-professionals, since the installation of such a roof is very simple
"Cuckoo" in a roof truss
The so-called cuckoo on the roof is a small protrusion that is located on attic floor. There is a window here for better lighting attic room. The installation of the “cuckoo” is carried out carefully, while monitoring the parameters of the entire structure: depth of cut, angle of inclination and other factors. However, before this, the necessary measurements are made.
The first stage of work begins with the installation of the Mauerlat (beam with a cross-section of 10x10 cm, which is needed to support the slings). The rafter system acts as a skeleton for the roofing material. To impart rigidity to the structure, spacers are used, which are mounted between the two legs of the rafters.
After installation is complete roof truss lay the sheathing, the type of which depends on the roof covering purchased. Installation of the sheathing is done continuously or with a certain step. For it, boards, OSB and plywood sheets. In addition, the installation of roofing material must be identical throughout the entire roof.
The main difficulty when installing such a rafter system is the location of the internal corners. Snow can accumulate in these places, which means the load will increase, which is why a continuous sheathing is made.
A “cuckoo” on the roof is a small protrusion on the attic floor, under which there is an additional window.
Chalet roof rafter truss
The peculiarity of this design is that the canopies and overhangs are moved outside the house. In addition, there must be rafters and roof beams extending up to three meters on the sides of the building. Each of these elements is secured with a bracket to the wall of the building in the lower part. Next, tie the edges of the beams. They serve as a support for covering the roof of the building.
But when creating large overhangs, it is necessary to install reinforced belt in parallel with the installation of studs for the Mauerlat. It is necessary to make anchors that help secure the consoles. In this case, the rafters will be perfectly fixed with anchors and, in addition, with mortises.
To carry out the side cornices, a ridge beam is made, after which beams are placed at the level of the mauerlat, which must be identical to the length of the ridge. The truss, and subsequently the building materials for the roof, rest on these structural details.
When designing a building, the angle of the chalet roof is calculated based on the characteristics of the local climate and other factors.
With a slope angle of about 45°, the load from snow is not taken into account, since with this option it will not linger on the roof. At the same time, the flat roof will withstand the load from snow, but it is necessary to install a reinforced roof truss. Before installing the chalet roof, a building design is prepared, because the originality of the roof itself, as well as the long eaves and overhangs, oblige this.
A chalet-style roof is characterized by canopies placed several meters outside the house
Rafter truss designed for soft roofing Soft roofing is done different ways , however, they exist in the technological methods of its construction General characteristics
- . Initially, you need to prepare. When arranging a roof for a house made of foam concrete or other material, a mauerlat is first installed, then in the upper crowns of the building a cut is made for the ceiling beams in increments of up to one meter. The distance between the boards is calculated based on the type of rafter structure.
- Install individual parts of the rafter system. To completely eliminate the risk, the rafter boards are attached to the ground with screws. After the roof truss is created, it is raised to the top of the building.
- The next stage is the sheathing, which is installed under the soft roof with small gaps or no gaps at all. Gaps of no more than 1 cm are allowed. Quite often, leveling plywood is installed on top of the boards. Its sheets are laid according to the method brickwork. The resulting joints are not aligned with the gaps between the plywood and the board.
If the length of the sheathing boards is not enough, then the joints of the parts must be placed in various places. In this way, you can correctly distribute areas that have been weakened.
Self-production of the rafter system
Before the installation of the rafter system begins, the mauerlat must be secured to the longitudinal walls with anchors. Next you need to decide on the required leg section for the rafters, depending on the distance and their length. If there is a need to increase the length of the rafters, then connect them with various fasteners.
When using different insulation, you need to choose the ideal distance between rafter elements in order to reduce the number of thermal insulation scraps.
Installation of the rafter system must be done in the following order:
- A template is made according to which the truss is assembled. Take 2 boards corresponding to the length of the rafters and connect them together at just one edge with a nail.
A template for rafters called “scissors” will help you quickly assemble the entire roof rafter system
- The result is a design called “scissors”. Its free edges are placed on supports at the points of contact between the rafter legs. The result should be the final angle, that is, the angle at which the roof slope will be inclined. It is fixed with several long nails and transverse boards.
- A second template is made, thanks to which the cuts are installed on the rafters. It is made from plywood.
- Special mounting cuts are cut on the rafters (a prepared template is used for these purposes) and connected at an angle of inclination of the slope. You should end up with a triangle going up the stairs to the roof. Next, it must be attached to the Mauerlat.
- Initially, two side gable rafters are installed. Their correct installation in the vertical and horizontal planes occurs due to temporary struts attached to the rafters.
For proper installation of the entire rafter system, the first pair of rafters is installed on the roof
- A cord is stretched between these tops of the rafters. It will indicate the future ridge and the level of other rafters located in the gap.
- Raise and install the remaining rafters at the initially calculated distance, which should be at least 60 cm from each other.
- If a bulky rafter structure is envisaged, then it is additionally strengthened with struts, supports, and so on.
The bulky structure of the rafters is additionally strengthened with struts and supports
- A ridge beam is installed on special supports, to which not only short, but also diagonal and intermediate elements of the rafters are attached.
Proper fastening of the ridge beam ensures the reliability of the entire rafter system
Typical components of a standard rafter system
The strength of the rafter structure depends on the ideally selected section of the boards, as well as on the high quality of the rafter assemblies. The connection of parts for the roof structure is done according to established rules.
The main typical units in the rafter system:
- rafter support assembly on the mauerlat;
- ridge;
- unit for combining the top ties and the entire rafter system;
- securing the strut, rack, as well as rafters and beams.
After the design of the rafter system has been chosen, it is necessary to draw up a plan in which to highlight all the nodes. They are made differently in each design as it depends on different nuances: type of roof, its size, angle of inclination.
Rafters from profile pipe is a metal structure that is assembled using lattice rods. The production of such farms itself is a very labor-intensive process, but also more economical. For the manufacture of rafters, paired material is used, and gussets are connecting elements. The structure of the rafters from profile pipes is assembled on the ground, using riveting or welding.
Thanks to such systems, any spans are blocked, but the correct calculation must be made. Provided that all welding work is done efficiently, in the future all that remains is to transfer the structural elements to the top of the building and assemble them. Load-bearing rafters made from profile pipes have many advantages, such as:
Crossbar in the rafter system
Crossbar is a fairly broad concept, but in the case of roofs it has a certain meaning. The crossbar represents horizontal beam, which connects the rafters. This element prevents the roof from “expanding”. It is made of wood, reinforced concrete, and also metal - it all depends on the type of structure. And the crossbar serves to distribute the load exerted by the rafter system.
It can be fixed in various places between the legs of the slings. There is a direct pattern here - if the crossbar is fixed higher, then the timber for its installation must be selected with a large cross-section.
There are many ways to fix the crossbar to the rafter system:
- bolts;
- nuts;
- studs with washers;
- special fasteners;
- nails;
- mixed fastenings, when different types of fastenings are used in parallel.
The fastening is available with a mortise or overhead. In general, the crossbar is a design unit, as is the entire system of roof slings.
The crossbar in the rafter system is designed to strengthen the roof structure
Fastening the rafter system
To ensure the reliability of the rafter system, you must first find out how they are attached to the supporting roof and ridge. If a fastening is made to prevent deformation of the roof when the house shrinks, then the rafters are secured on top with a hinge plate or a nut and bolt, and below with a sliding support.
Hanging rafters need a tighter and more reliable fastening in the ridge, so in this case you can use:
- overhead metal or wooden plates;
- cutting method;
- connection using long nails.
In the layered system, the rafter legs are not connected to each other, since they are attached to the ridge girder.
The rafters are attached to the mauerlat using the cutting method, which is made in the rafter leg. Thanks to this fastening method, the roof support will not weaken. Cutting is also done when installing rafters on floor beams. In this case, a cut is also made in the support beam.
Video: how to make rafters with your own hands
Thus, an ideally selected rafter system and their design characteristics will help create the basis for a reliable roof for your home.
When designing any residential building, architects Special attention pay attention to the roof, since 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 an ordinary gable roof, although it can be called the most reliable, since it has only two pitched planes and one joint between them. Many people are more attracted to complex designs, which add special attractiveness and originality to the building. Other, more practical homeowners prefer attic structures, which can simultaneously serve as a roof and a second floor.
The basis of any roof is an individual rafter system, which has its own design features. It will be much easier to choose the right roof frame if you figure out which ones in advance. types and diagrams of rafter systems used in construction practice. After receiving such information, it will become more clear how difficult such structures are to install. This is especially important to know if you plan to build the roof frame yourself.
Main functional tasks of rafter systems
When arranging pitched roof structures, the rafter system serves as a frame for covering and for holding materials “ roofing pie" With proper installation of the frame structure, the necessary conditions for correct and non-insulated types of roofs, protecting walls and inner space houses from various atmospheric influences.
Roof structure is also always final architectural element exterior design of the building, supporting it with its appearance stylistic direction. However, the design features of rafter systems must first of all meet the strength and reliability requirements that the roof must meet, and only then the aesthetic criteria.
The frame of the rafter system forms the configuration and angle of inclination of the roof. These parameters largely depend on natural factors, characteristic of a particular region, as well as the desires and capabilities of the homeowner:
- Amount of precipitation in different periods of the year.
- Direction and average speed winds in the area where the building will be erected.
- Plans for the use of space under the roof - arranging residential or non-residential premises in it, or using it only as air gap for thermal insulation of rooms below.
- Type of planned roofing material.
- Financial capabilities of the homeowner.
Atmospheric precipitation and the strength of wind currents place a very sensitive load on the roof structure. For example, in regions with heavy snowfall, you should not choose a rafter system with small angle slope of the slopes, since snow masses will linger on their surface, which can lead to deformation of the frame or roofing or to leaks.
If the area where the construction will take place is famous for its winds, then it is better to choose a structure with a slight slope of the slope so that sudden gusts that occur do not tear off individual elements of the roof and roofing.
Main elements of roof structure
Parts and components of rafter systems
Depending on the chosen type of rafter system, the structural elements used can vary significantly, however, there are parts that are present in both simple and complex systems roofs
The main elements of a pitched roof rafter system include:
- Rafter legs that form the roof slopes.
- - wooden beam, fixed to the walls of the house and used to fix the lower part of the rafter legs on it.
- A ridge is the junction of the frames of two slopes. It is usually the highest horizontal line of the roof and serves as the support to which the rafters are anchored. The ridge can be formed by rafters fastened together at a certain angle or fixed on a ridge board (purlin).
- Sheathing is slats or beams mounted on rafters at a certain pitch and serving as the basis for laying the selected roofing material.
- Supporting elements, which include beams, purlins, racks, struts, ties and other parts, serve to increase the rigidity of the rafter legs, support the ridge, and connect individual parts into an overall structure.
In addition to the mentioned design details, it may also include other elements, the functions of which are aimed at strengthening the system and optimally distributing roof loads on the walls of the building.
The rafter system is divided into several categories depending on different features of its design.
Attic space
Before we look at different types roofs, it is worth understanding what the attic space can be, since many owners successfully use it as utility and full-fledged residential premises.
The design of pitched roofs can be divided into attics and attics. The first option is called that way because the space under the roof has small height and is used only as an air layer insulating the top of the building. Such systems usually include or have several slopes, but located at a very slight angle.
An attic structure that has a sufficiently high ridge height can be used in different ways, be insulated and not insulated. Such options include an attic or gable option. If you choose a roof with a high ridge, then it is imperative to take into account the wind loads in the region where the house is built.
Slope slope
To determine optimal inclination roof slopes of a future residential building, first of all you need to take a closer look at the already built low-rise neighboring houses. If they have been standing for more than one year and can withstand wind loads, then their design can be safely taken as a basis. In the same case, when the owners set a goal to create an exclusive original project, unlike the neighboring buildings, it is necessary to familiarize themselves with the design and operational features of various rafter systems and make the appropriate calculations.
It should be taken into account 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 normal forces and the less tangent forces. If the roof is flat, 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 on the windward side the snow load will be much lower than on the leeward slope. In addition, there are places on the slopes where snow will certainly accumulate, putting a large load on this area, so it should be reinforced with additional rafters.
The slope of roof slopes can vary from 10 to 60 degrees, and it must be selected not only taking into account the consolidated external load, but also depending on the roofing covering that is planned to be used. This factor is taken into account because roofing materials differ in their weight; to secure them, a different number of elements of the rafter system is required, 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. The characteristics of each coating in terms of resistance to moisture penetration are also important - many roofing materials in any case require one or another slope to ensure free descent storm water or melting snow. In addition, when choosing a roof slope, you need to think in advance about how the process of cleaning and repair work on the roof will be carried out.
When planning a particular angle of the roof slopes, you need to know that the fewer joints between the sheets of roofing, and the more airtight they are, the less you can make the slope of the slope, of course, if it is not intended to be arranged in attic space residential or commercial premises.
If a material consisting of small elements is used to cover the roof, for example, ceramic tiles, then the slope of the slopes must be made steep enough so that water never lingers on the surface.
Considering the weight of the roofing material, you need to know that the heavier the covering, the larger the angle of the slopes should be, since in this case the load will be correctly distributed over the rafter system and load-bearing walls.
Can be used to cover the roof following materials: or profile sheet, galvanized steel, corrugated asbestos concrete and bitumen-fiber sheets, cement and ceramic tiles, roofing felt, soft roof and other roofing materials. The illustration below shows the permissible slope angles for various types roofing coverings.
Basic designs of rafter systems
First of all, it is worth considering the basic types of rafter systems relative to the location of the walls of the house, which are used in all roof structures. Basic options They are divided into layered, hanging, and also combined, that is, including elements of both the first and second types of systems in their design.
fastenings for rafters
Layered system
In buildings where internal load-bearing walls are provided, a layered rafter 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, this structure will require less materials.
For rafters in this system, the defining reference point is the ridge board, on which they are fixed. The non-thrust type of layered system can be arranged in three options:
- In the first option, 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 using wire or staples.
- In the second case, the rafters in the upper part are cut at a certain angle and connected to each other using special metal plates.
The lower edge of the rafter legs is attached to the Mauerlat with movable fasteners.
- In the third option, the rafters are rigidly fastened in the upper part with bars or treated boards located horizontally, parallel to each other on both sides of rafters connected at an angle, and a ridge girder is clamped between them.
In the lower part, sliding fasteners are used to secure the rafters, just as in the previous case.
It is necessary to explain why sliding fasteners are often used to secure rafters to the mauerlat. The fact is that they are able to relieve 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 general design roofing system.
This type of fastening is used only in layered systems, which also distinguishes them from the hanging version.
However, in some cases, for layered rafters, a spacer system is used, in which the lower end of the rafters is rigidly fixed to the Mauerlat, and to relieve the load from the walls, tie-downs and struts are built into the structure. This option is called complex, as it includes elements of a layered and hanging system.