The issue of the strength of the roofing system is always given the closest attention, because much will depend on this stage of construction. For example: protection of the home from the environment and adverse weather conditions. And mistakes made in the organization of such an important factor as attaching rafters to floor beams threaten various troubles, from unplanned repairs to dismantling the roof with the construction of an alternative frame. Rafters and floor beams are irreplaceable segments of the roof system structure. Wood is usually used in their manufacture. And they are also attached in various ways, which we will talk about in today’s article.
Roof rafter system: one of the possible options
But first, just a few words about the features of rafter systems - they are also different, and this directly determines how to attach the rafters to the beams. When designing a structure, they usually choose the most suitable option for a particular case. Rafters available:
- hanging,
- layered.
The first type of segments is taken for the construction of light roofs with a fairly large area. They will be supported by the walls of the building. The system with the second type of rafters is more complicated, in which the rafter legs rest on additional points.
- When constructing rafters, the entire structure can be based on a Mauerlat. This method is most popular and effective when constructing the roof of brick and block dwellings.
- If at the top of the walls there is, for example, a monolith - a concrete beam, or the walls of the building are made of beams (logs), the roof usually rests not on the Mauerlat, but on horizontal floor beams that overlap the box of the building across.
- Roof structures supported by beams are the simplest variation of the construction of an attic, lighter roof. The main thing in the project is to correctly calculate the thickness of both the floor beams and the rafter legs, taking into account the possible loads on the entire roof structure. And during installation, you need to correctly support the rafters into the floor beams. Roofs with rafter system supports on overlapping beams (without the participation of a Mauerlat) can be mounted on the condition that the walls of the building will be able to withstand fairly large loads at the points of application.
It is worth additionally noting that the correct choice of rafter installation option, as well as maximum adherence to architectural technologies, will optimally guarantee that there is no risk of damage to all attachment points of rafters to beams in particular, and to the roof in general.
Fastening method
In current conditions, several variations of fastening rafters to the walls of buildings are practiced.
- Using Mauerlats.
- To the beams (floor).
- Drawstring design.
- Fastening to the crown at the top during the construction of log houses from beams.
- Upper strapping system for a building erected using frame technologies.
Fastening parts
Wooden and metal parts are used for the installation of rafter systems. The first include: block, triangle and dowel, etc. Metal in fastener parts is quite widely represented: nails, angles, bolts and screws, clamps and brackets. As well as special devices for installing rafters, which are called “sleds”.
Fastenings of this kind are used during installation work on load-bearing floor beams during the construction of wooden buildings. Their main advantages: no cutting into the beams themselves is required, and fastening is carried out using bolts with screws of large nails.
Mauerlat
A popular method of securing rafter systems at the bottom is considered to be connection to the Mauerlat. But, despite the spread, in order to do this work efficiently, you need to know some nuances. After all, if something goes wrong, it can affect the reliability and service life of the entire roof.
- Before fastening the rafters to the mauerlat, special inserts must be made at the bottom of the rafter legs. It is not recommended to install the structure without them, since under load the edge of the block will slide off the smooth coating of the beam.
- As for the recesses in the Mauerlat itself (whether it’s worth making them or not), it may depend on the materials from which it is made.
- In the case of using hardwood, experienced craftsmen advise making a cut in the Mauerlat beam - this, together with the cut made in the rafter leg, will reliably create a “point-blank” lock. And when you use a softwood Mauerlat, it is not advisable to make a cut - it will lead to a possible weakening of the entire arrangement.
- The reliability of the roof under different weather conditions may depend on the method of fastening the rafters to the Mauerlat.
How to fasten with a Mauerlat
Connection: rafter leg + beam
Any roof, under the influence of various types of loads, tends to “float” to the sides and downwards. To prevent this from happening, various methods can be used to prevent displacement of rafter system segments.
Support diagram
One of the time-tested and experience-tested methods of masters is cutting out connectors in the rafter legs, which can be done by connecting using a tooth with a stop, with a tenon, or supporting the rafters on a beam floor.
The notch in the first option is used if the roof has a large sloping angle. This means that the rafters are attached at an angle of more than 35 degrees. A tooth with a stop and a tenon is made in the rafter leg, and a corresponding socket is made in the body of the beam for the tenon (the insert is deepened to one third of the thickness of the beam itself, otherwise the structure will be weakened). The cut is made at a distance of no more than 40 cm from the edge; in this case, it is usually possible to avoid chipping. And in order to prevent the joints from sliding sideways, a single tooth is created together with a tenon.
Notches with 2 “teeth” can be used for flat roofs, in cases where the angle between the connected elements is not more than 35 degrees. The process itself is implemented using one of the following methods:
- in 2 spikes;
- at stops - without the participation of spikes;
- into stops complemented by spikes;
- fastening the lock plan with 2 tenons (other variations are possible).
For 2 teeth, the entrance is usually the same in depth. However, in some variants, the first of the teeth supplemented with spikes is buried by a third of the thickness of the entire beam, and the second by half.
When arranging roof structures, a technique can also be used when they are connected to each other: a rafter leg plus a ceiling beam from the ceiling (used quite infrequently). In this case, a thrust tooth is constructed in the leg in such a way that the first of the planes fits onto a flat beam cut, and the second is fixed into a cutout, which is buried in a third of the thickness of the beam. For greater strength, in addition to notches, additional connections are often made using bolts and clamps.
Types with a puff
On a skate
When constructing roofs, modern craftsmen use several types of fastenings for the rafter system on the ridge:
- joint to joint;
- for a run;
- overlap onto the upper ridge run.
Butt-to-butt connection. At the top, the rafter segment is cut at an angle (which is equal to the planned roof slope). And then they rest on the opposite leg, where circumcision is performed in the same way, but only in an asymmetrical direction. It is better to do this using preliminary templates. In some cases, the cut is performed during installation, and the cut is made through 2 beams.
On the run
Installation for run similar to the above variation. The differences will be in the installation of the ridge beam itself. This design is highly reliable, but it cannot always be abused, since it will require additional installation of support beams. As a result: the attic is not very convenient for further use. This method will allow you to complete the installation of pairs of rafter legs on site, without any preliminary “curtsies” or templates. In this case, the upper segments of the legs rest against the ridge beam, and the lower segments rest against the mauerlat.
Overlap on the ridge run. Here, the installation is carried out in the same way as in the previous version, only the upper joints of the rafters are overlapped, touching from above not with their ends, but with their sides. In this case, the fasteners will be bolts (or studs as an option).
Calculation principle
At the preparatory stage for construction, it is necessary to calculate the rafters with floor beams in advance. When designing a roof frame, the climatic and other features of a particular region, as well as its characteristic snow and wind loads, are taken into account. Based on these data and SNiP, which determine the relative and permissible deflections, the section will be calculated for all elements of the system: roof beams, rafters, and other parts of the truss. It is also necessary to perform structural calculations that determine the laying step for the beams. And the distance between the beams, in turn, determines the step for placing the rafter legs.
As you can see, it is quite possible to build a roof rafter system with your own hands if you study the entire process step by step: from purchasing the material to determining the load the building structure can withstand and how to attach the rafters to the floor beams.
10.05.2016 0 Comments
Many owners of suburban land plots, in order to save money, prefer to build a house themselves. If you have certain skills, this allows you to significantly reduce the cost of paying employees. The final stage of self-construction of a building is erecting the roof with your own hands. This structure is an integral and one of the most important parts of the building, which protects it from atmospheric influences. It should be noted that you cannot do a roof with your own hands alone; in any case, you will need 2-3 assistants.
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Roof Element Definitions
First, you need to familiarize yourself with some terms and definitions:
- Roof is a building structure that covers the top floor. It provides thermal insulation and performs waterproofing functions.
- Roofing is a roof covering that provides protection from precipitation.
- Mauerlat is an element of the roofing system that transfers the load from the roof structures to the load-bearing walls. Usually it is a beam or log laid on the walls along the perimeter of the building, but in the case of installing a metal frame it can be made of rolled metal - a channel or an I-beam.
- Rafter - an inclined load-bearing element of the roof, most often in the form of a beam. The combination of rafters forms a rafter system that carries the roof deck and transfers the load to the mauerlat.
Roof construction process
The step-by-step instructions below for building a roof with your own hands will help you avoid mistakes and build the roof correctly. The technology of work production includes several stages.
Drawing up a roof structure drawing
Before starting work, it is necessary to draw up a detailed drawing of the future structure of the pitched roof, this will allow you to determine the required amount of building materials and prepare the necessary tools. Roofs can be single-pitched, sloped only in one direction, gable and more complex structures (four-pitched, hipped and spire-shaped). It is best to take as a basis standard drawings of roof structures developed by professionals and available in the public domain.
Mauerlat installation
Typically, the Mauerlat is made from timber with a cross-section of 150×100 (150) mm. It is laid along the inner edge of the wall on a waterproofing material, which can be a double layer of roofing felt or polyethylene. The Mauerlat is protected from external atmospheric influences if the house is made of stone - next to the brickwork, if it is wooden - with the same layer of waterproofing or facing materials. The Mauerlat bars around the perimeter are fastened together into a single structure, cutting out sections 100-150 mm long into half the thickness of the beam. and connecting them with bolts or nails. The Mauerlat is attached to wooden walls with metal brackets, to walls made of brick, foam and gas silicate blocks - using threaded rods with a diameter of about 12-16 mm, embedded in a reinforced concrete belt arranged along the top of the wall. The studs are placed around the perimeter at a distance of 1500-2000 mm, and holes are drilled for them in the timber of the structure.
This is the next stage of building a roof with your own hands. The layout of the rafters is determined based on the selected design features of the roof. The distance between structural elements and the cross-sectional size of the material depends on the length of the roof slope. Thus, with rafter lengths up to 4 meters, the rafter pitch varies from 1000 mm. (with a beam cross-section of 80×160 mm.) up to 1800 mm. (with a timber cross-section of 90×180 mm), with a roof slope length of up to 6 meters for a rafter pitch of 1000 (1400) mm. you will need a beam with a cross section of 80×200 (100×200) mm. However, these values are not mandatory; if the option of laying roll or slab thermal insulation is subsequently considered, then it would be most advisable to adjust the pitch of the rafters to the size of the insulation. Also, the pitch and cross-sectional size of the rafters is influenced by the type and, accordingly, the weight of the selected roof. For example, heavy ceramic tiles or slate require greater load-bearing capacity of roof structures than roofing made of ondulin or galvanized steel.
An important point is the choice of roof angle. The greater the angle to the horizontal, the less snow will be retained on the roof, which makes it possible to reduce the cross-section of the timber for making rafters. The optimal tilt angle is 45 degrees., it ensures the structure’s stability against strong gusts of wind and at the same time prevents significant snow masses from accumulating on the roof.
The rafters are attached to the Mauerlat using several methods; this can be a tie-in followed by fastening with nails or using metal brackets. When using brackets, labor-intensive insertion into the rafter leg is not required; the structures are connected using self-tapping screws or bolts. The metal thickness of the bracket is about 2 mm. and anti-corrosion coating ensure reliability and durability of fastening. Recently, in the construction of wooden houses, the fastening element “sled” has become popular, which provides a small degree of freedom of fastening to compensate for possible deformations during settlement of the building. In parallel with the fastening of the rafters to the mauerlat, the installation of ceiling joists is carried out - transverse beams that serve as the basis for the installation of the attic floor. The usual cross-section of the joists is 100×150 or 200×100 mm, depending on the span width of the building. When connecting ceiling joists to rafters, it is possible to provide additional strength to the rafter system.
When installing a roof with your own hands, the upper part of the rafters can also be connected using several methods:
- overlapping (in this case, a cut is made to half the section of the rafters and a hole is drilled for a bolted connection using wide washers)
- by cutting the ends of the rafters at an angle (the upper ends of the beam are cut to obtain a vertical joint; fastening plates or wooden plates are used to ensure the strength of the assembly)
To provide additional rigidity, at a distance from the top of the rafters approximately ¼ of the total height of the structure, horizontal ties with a cross-section of 100×50 mm are attached.
It is done along the roof directly to the rafters using small nails or a construction stapler. Work begins from the bottom of the rafters so that the top sheet overlaps the bottom by 5-10 cm. In this case, the film should sag, but not more than 2 cm. At the final stage of this work, counter battens with a cross section of 25x50 mm are nailed onto the rafters on top of the film.
The sheathing is used to attach roofing elements to the roof structure. Typically, boards with a cross section of 100×25 mm are used for its implementation. and a length sufficient to cover two steps of the rafter legs. Fastening to the rafters is done using nails no less than 
100 mm. The joint of the sheathing boards should be on supports and the distance between their ends should not exceed 5 mm. The boards forming the ridge (the top of the rafter system) should be as close to each other as possible. The type of sheathing is selected based on the type of roof being laid. For soft, tiled and rolled roofs, continuous flooring is required. Sometimes a two-layer flooring is required; in this case, the first layer of boards is located parallel to the ridge, the second - perpendicular, along the roof slope. For slate and metal roofs, sheathing with a pitch of boards commensurate with the dimensions of the material used is quite suitable.
Depending on the selected roofing material, the corresponding installation method is used. Roofs made of slate, ondulin and flexible bitumen tiles start from the bottom of the roof, ensuring sufficient overlap of the overlying row onto the underlying one. Slate and ondulin are attached to the sheathing with roofing nails, bitumen shingles - with galvanized nails with a wide head. Metal tiles are laid using the following method: the first sheet is aligned along the end of the roof and the eaves, the second is above the first, the third is on the side, the fourth is above the second. The sheets of metal tiles are fastened with galvanized self-tapping screws. Ceramic tiles are attached from bottom to top in rows from right to left. First, all the material is laid out evenly on the crate, in stacks of 5-6 tiles. Fastening to the sheathing is done with galvanized screws.
Laying thermal insulation
It is carried out from the inside of the roof into the space between the rafters. The insulation is cut to the required size so that the width of the sheet is 20-30 mm. greater than the inter-rafter distance. This will ensure that the material is fixed “by surprise”; to straighten the material after pushing it between the rafters, you need to press on the middle of the sheet. A vapor barrier film is attached on top of the insulation layer using a construction stapler. The film must be attached with an overlap of 5-7 cm.
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Roof design begins with the collection of loads. It is necessary to calculate the total weight of one square meter of the entire roof structure. To do this, you need to first draw roof drawings and calculate snow and wind loads according to the area where construction is taking place.
In order to correctly collect the load, you need to know the specific gravity of all materials that are used to build the roof, from the type of wood to the type of insulation and outer covering. This data is necessary for the correct selection of the pitch of the rafter legs. The greater the load, the smaller the distance should be between the rafters.
The maximum distance that is allowed between rafters should not exceed 1200 mm. A distance of one meter is considered optimal. Next, you should select the cross-section of the beam.
To calculate the roof structure, there is a special algorithm consisting of many formulas, but all of them are intended only for analyzing the construction of large industrial buildings. For private construction, the process of selecting a section can be simplified.
The height of the beam is calculated from the maximum length of the rafter leg. 1/20 of the length will be the optimal height of the beam. But 1/3 of the resulting height will be the required width of the beam. The result is a durable system that can withstand heavy loads.
In a wooden house, the top framing beam for a frame house will serve as a support for the rafters. In a brick house, along the upper edge of the masonry, you need to install a mauerlat - a horizontal powerful beam, which is attached to the wall with crutches.
You can build a roof with your own hands in a few days if you plan the whole process correctly. At the junction of two different materials, for example, brick and wood, it is always necessary to install waterproofing. Instructions for constructing a roof begin with the correct installation of load-bearing beams. Then inclined rafters are installed at the angle specified in the project.
To secure the rafters, bevels and strapping boards are installed as part of the sheathing. Fastening all the rafters into a single structure makes the wooden roof stable. At this stage, it is important to accurately align the position of the rafter legs; they must be in the same plane, strictly in the correct design position.
After securing the rafter legs, the sheathing is filled, which is a row of boards with a certain pitch; the final covering will then be attached to them. If the roof is made of soft materials, the sheathing is made of a continuous type from sheets of plywood. In all other cases, it is enough to nail the sheathing elements at a certain distance from each other.
Afterwards, protective materials are laid (insulation and vapor barrier) and the final roof covering is installed. In some cases, insulation is done inside the structure after installation of the roofing material. The rafter roof must be ventilated to ensure a normal microclimate for the structures and their durability.
Any work can be divided into stages. So, do it yourself roof step by step.
First step. Calculate the roof, collect the load, determine the cross-section of the beam and its length. Be sure to summarize all data in a material consumption specification.
Second step. Prepare all the necessary tools, purchase materials, prepare a place for storage. Consider a mechanism for feeding heavy structures onto the roof. On the day of work, you may need to hire a truck crane.
Third step. Prepare the surface for work. Start installing the mauerlat, strapping beam and rafter legs. Carefully check the design position of the rafters. At the end of the working day, make sure that the working structure is securely fastened.
Fourth step. Supply of sheathing boards. Fastening the sheathing and laying protective materials under the roof. At this stage you will have to do a lot of trimming work. Working with a hacksaw is difficult and takes a long time, so you need to rent a parquet saw or jigsaw.
Fifth step. Installation of roofing material, checking joints. Here, after completing the installation work, you can hem the box to eliminate wind pressure from the side of the wall under the covering structure.
A gable sloping roof significantly improves the functionality of the attic space. A conventional gable roof creates dead space with an inclined plane, in which you cannot stand at full height.
A gable sloping roof expands the space due to the special design of the inclined plane. Thus, you get a full-fledged interior space that can be equipped as a bedroom.
According to the drawings, such a house roof is built by installing strictly vertical posts and horizontal ties, and hanging and layered rafters are lined up on the sides of the improvised rectangle. To provide the structure with the necessary strength, struts are installed from the floor beam to the middle of the layered rafter.
All other work is carried out similarly to the scheme described above. The main difficulty in building a structure for a gable sloping roof is choosing the right section of timber and installing all the elements according to the drawing. In most cases, insulation and vapor barrier are added to the roofing pie. This significantly complicates the process of installing a rafter roof, but without these elements there is no point in making an attic room.
For a private house, it is preferable to choose a pitched roof with a slope of more than 2.5%. The simplest option is a pitched roof, but this is used only on utility-type buildings. The design is characterized by one flat sloping roof plane, which rests on the two side walls of the building.
A gable roof is considered universal, which rests on two external walls at the same level, and the inclined planes are brought together in the middle into one ridge unit. The end part of such a roof is called a pediment and is usually sealed with the same material from which the load-bearing part of the house is built.
A hip roof is a hip roof without a gable. On all sides of the building, the roof slopes upward from the top edge of the wall. This type of roof is better suited than others to withstand wind and snow loads, but is quite difficult to construct. All components of the roof frame must be built in compliance with the complex laws of statics of structures.
A hip roof looks something like a hip roof, but its main difference is that all four planes of the roof have a strictly triangular shape. As a result, from the center of the building, inclined planes diverge in four directions, forming a tent.
A broken or mansard roof is the creation of broken roof planes at an obtuse angle. The result is a fairly voluminous attic-type room that can be used as a living space.
All types of roofs have their advantages and disadvantages. Some look better, but require significant construction costs, others are simple to construct, but also unpresentable in appearance. The choice of roof is usually made after determining the snow and wind area. It is important to agree on the type of roof at the design stage.
In fact, building the roof of a frame house is no different from building a roof for other types of buildings. The only point concerns the fastening of the rafter legs to the supporting structures. Here, instead of a Mauerlat, a strapping beam is used.
The rest of the technique is similar. For ease of construction, before starting it is necessary to build a raised floor or install a full wooden floor. Installing rafters from scaffolding is inconvenient and labor-intensive.
For a frame house, it is recommended to choose the least massive roof structure, so that it does not create critical pressure on the load-bearing elements. You should not add additional elements to the roof, including dormer windows, unless they are provided for in advance in the project.
DIY roof. Design
Depending on the roof structure, you should select the amount of materials and the cross-section of the support beams. For a private house, especially a frame type, the most effective are gable and gable sloping roofs. All other structures are quite complex and require a large number of supporting elements, which significantly weigh down the entire roof.
For a frame house, it is better not to use natural ceramic tiles as a coating. In addition to the fact that it is very heavy, for installation you will need to pack the sheathing thickly. As a result, it will be necessary to further strengthen the supporting posts or reduce the pitch between them, which will lead to waste of materials.
The support beam serves to secure the rafters at the bottom. It is impractical to rest the rafters on the wall, so an additional beam is used, which takes up the inclined load and transfers it to the supporting structures strictly vertically.
A beam of sufficiently large cross-section should be used as a support beam. It must be firmly fixed to the wall. In the case when the roof, together with the supporting beam, simply lies on the wall, the roof can be undermined by the wind. Despite the heavy weight of the entire roof, it can fly away in heavy gusts of wind.
The strength of load-bearing roof systems must be given special attention, since the protection of the building from bad weather depends on it. Mistakes made when attaching rafters to beams can lead to big troubles, including repairing the roof or even dismantling it and creating a new frame. Rafter beams are an indispensable part of the entire roof structure. They are made of wood and metal; reinforced concrete rafter beams are also available for sale.
When developing a roofing project and when creating it, many factors that create loads on rafter structures are taken into account, among them:
- weight of the covering and other elements of the roofing “pie”;
- wind force;
- the greatest possible thickness of snow on the roof;
- the presence of equipment and other loads on the frame.
The main elements of the roof structure that bear the most loads include:
- rafter system or truss;
- composite beams.
Of course, the quality of the material from which the above materials are made is of great importance, but no less important is the strength and reliability of the connection of the roof elements to each other.
I-beams
I-beams of wood are a structural material that is used for the construction of buildings using frame technology, as well as for the construction of floors. They do not have the disadvantages inherent in wood, and due to the presence of an I-section, high strength characteristics are achieved. The joining of I-beams is done using carpentry tools.
Methods for attaching rafters to walls
Today, the main options for installing rafters and attaching them to the walls of houses are as follows:
Rafter Fasteners
Wooden elements and metal products are used to assemble the truss structure. Wooden fasteners include: bars; triangles; dowels, etc.
Metal fasteners include nails, bolts, angle iron, screws, studs, clamps, staples, special rafter devices called skids or sliders, and more.
Fastenings for WB beams are used when installing load-bearing beams for wooden structures in the construction of wooden houses. Its advantage is that it does not require cutting into the beam, and fastening is done using nails, screws or anchor bolts.
Methods for attaching rafters to the Mauerlat
The most common way of attaching rafters at the bottom is to connect them to the Mauerlat (read: ""). Despite its popularity, not every builder will be able to perform such work efficiently, and this cannot but affect the strength and reliability of the roof.
Before attaching the rafters to the mauerlat beams, a special cutout is made at the bottom of the rafter leg. It is impossible to install rafters without this, since at the slightest load the flat edge of the beam will slide off the surface of the beam. As for the notch in the Mauerlat, whether to make it or not depends on the material it is made of.
In the case of using hardwood, experts recommend making a cut in the beam - it, together with the slot made in the rafter leg, will create a persistent lock. When the Mauerlat is made of coniferous wood, it is not advisable to make slits, as they will lead to a weakening of the structure. The condition of the roof in different weather conditions depends on the way in which the beams are attached to the mauerlat (read also: " ").
Connection between beam and rafter leg
The roof of the house, under the influence of loads on it, tends to move apart and down. To prevent this, various design solutions are used to prevent the roof frame elements from moving.
This is how cutting out recesses in the rafter legs was invented, which can be done using connections such as:
- tooth with one stop;
- tooth with a spike and stop;
Attaching the rafters to the mauerlat, watch the video:
A notch with one tooth is used when the roof has a large slope angle. This means that the rafters are attached to the floor beams at an angle greater than 35 degrees. A tooth with a spike is cut out in the leg, and a nest is created in the beam for the spike to enter. In this case, the depth of the notch cannot be more than 1/3 or 1/4 of the beam thickness, otherwise the element will weaken. The cutting is carried out at a distance of 25 - 40 centimeters from the edge of the beam, then the possibility of chipping will be avoided. To prevent the connection from moving sideways, a single tooth must be created together with a tenon.
A notch with a double tooth is performed for flat roofs, when the angle between the connection elements does not exceed 35 degrees, it is performed in one of the following ways:
- two spikes;
- stop without tenon;
- emphasis complemented by a spike;
- connection like a lock with two spikes and other options.
The mortise depth is usually the same for both teeth. But in some cases, the first tooth supplemented with a tenon is cut into 1/3 of the thickness of the beam, and the second - 1/2.
When creating roofs, this method of arranging rafters is encountered when the rafter legs and wooden ceiling beams are connected, but it is rarely used. In this case, a stop tooth is cut in the leg so that one of its planes rests on the flat edge of the beam, and the other plane rests on a cut made with a depth of 1/3 of the thickness of the beam. For reliability, in addition to cutting, an additional connection is made using clamps, bolts, wire loops or strips of metal.
Connection of rafters at the roof ridge
Currently, in the construction industry, when creating a rafter system, 3 methods are used to connect rafters at the ridge:
- butt connection;
- installation on a ridge run;
- overlapping fastening to the ridge girder.
To understand which option is preferable, you need to understand how they are performed.
Butt connection . The upper part of the rafter leg is cut at an angle that is equal to the angle of inclination of the roof and rests it against another rafter leg, which is also trimmed only in the opposite direction. This work is carried out according to a pre-made template. In some cases, to ensure greater tension in the stop, trimming is performed during installation, with the cut being made through both bars, as a result of which the two planes fit tightly against one another. Then the rafters are connected to each other using long nails.
When this method is used, a metal or wooden plate is used for additional fastening - it is installed with bolts or nails are driven into the joint.
Installation on a ridge run . This method is in many ways similar to the previous method. The difference lies in the installation of the ridge beam. This type is reliable, but it cannot always be used, since it requires additional installation of support beams and then the attic is not very convenient to use.
This option allows you to carry out the installation of each pair of rafter legs directly on site without preliminary work or the use of templates. The upper edge of the leg in this case rests against the ridge beam, and the lower edge rests against the mauerlat.
Overlap fastening to ridge purlin . The work is carried out similarly to the previous option, only the upper joint of the rafters is overlapped. They touch at the top not with their ends, but with their sides. Fastening elements are bolts or studs.
Repair of truss structure
A private house can be used for decades, and a situation often arises when it is necessary to repair elements of the rafter structure. The condition of the roof frame and roofing must be constantly monitored, since their destruction leads to great trouble. If defects are detected, emergency measures must be taken.
Problem: the end of the rafter began to rot , resting on the mauerlat. In such a situation, a log is placed on the floor of the attic; it must rest on several beams (the installation of the floor beams must be reliable). Place struts under the rafter leg being repaired so that they rest against the log. The distance between the extreme strut and the place of decay should exceed 20 centimeters. After the damaged section is removed by sawing, a pre-prepared liner is installed in its place.
Problem: wood rot was found in the middle of the rafter . In order to strengthen the truss structure, wooden overlays made of boards 50-60 millimeters thick are nailed on both sides of the damaged element. Nails for fastening are driven along their edges into the undamaged part of the rafters.
Problem: the power plate is damaged . When this is a small area, experts advise installing struts with a rafter leg attached to them using staples. The struts are mounted with support on the undamaged part of the mauerlat. If the area of damage to the Mauerlat is significant, then an overlay of boards is nailed to the rafter leg, which in turn is attached to a new Mauerlat, which is installed slightly lower than the damaged one. An additional Mauerlat is mounted into the wall using pins, and is carried out in accordance with the project.
Problem: a crack has appeared in the rafter leg , as a result of which the roof deflected. To carry out the repair, you need to prepare 2 boards, one of them will become a squeezing rack, and the second will be a support for it. The support board is attached perpendicular to the load-bearing beams of the attic floor. The squeezing rack is installed on a previously fixed support and brought under the deflection of the leg. Between the end of the squeezing stand and the support board, 2 wedges are driven in, one towards the other. They continue to be driven in until the deflection is eliminated. At the place where the crack is located, two boards are placed, the length of which is at least a meter longer than the size of the damaged area. They are secured with bolts. Then the wedges are knocked out, the support board and temporary stand are removed.
Problem: reinforcement of the rafter system is required , since the new roofing material is heavier than the previous one. To do this, increase the main section of the rafters, building it up with boards. What amount needs to be increased (but not more than 5 centimeters) is determined using calculations (read also: " "). The gasket and rafter are connected using nails.
Rafters serve as the basis for the entire roofing structure, and their installation is one of the most important tasks when building a house. The frame of the future roof can be made and installed independently, observing the technological features of roofs of different configurations. We will present the basic rules for the development, calculation and selection of a rafter system, and also describe the step-by-step process of installing the “skeleton” of the roof.
Rafter system: rules for calculation and development
The rafter system is a supporting structure capable of resisting gusts of wind, taking on all external loads and evenly distributing them to the internal supports of the house.
When calculating the truss structure, the following factors are taken into account:
- Roof angle:
- 2.5-10% - flat roof;
- more than 10% - pitched roof.
- Roof loads:
- constant - the total weight of all elements of the “roofing pie”;
- temporary - wind pressure, the weight of snow, the weight of people carrying out repair work on the roof;
- force majeure, for example, seismic.
The amount of snow loads is calculated based on the climate characteristics of the region using the formula: S=Sg*m, Where Sg- weight of snow per 1 m2, m-calculation coefficient (depending on the slope of the roof). The determination of wind load is based on the following indicators: type of terrain, regional wind load standards, building height.
Coefficients, necessary standards and calculation formulas are contained in engineering and construction reference books
When developing a rafter system, it is necessary to calculate the parameters of all components of the structure.
Elements of the truss structure
The rafter system includes many components that perform a specific function:
Materials for making rafters
Rafters are most often made from coniferous trees (spruce, larch or pine). For roofing, well-dried wood with a humidity level of up to 25% is used.
A wooden structure has one significant drawback - over time, the rafters can become deformed, so metal elements are added to the supporting system.
On the one hand, metal adds rigidity to the rafter structure, but on the other hand, it reduces the service life of wooden parts. Condensation settles on metal platforms and supports, which leads to rotting and damage to the wood.
Advice. When installing a rafter system made of metal and wood, care must be taken to ensure that the materials do not come into contact with each other. You can use moisture-proofing agents or use film insulation
In industrial construction, metal rafters made of rolled steel (I-beams, T-beams, angles, channels, etc.) are used. This design is more compact than wood, but retains heat less well and therefore requires additional thermal insulation.
Choosing a rafter system: hanging and suspended structures
There are two types of rafter structures: hanging (spacer) and layered. The choice of system is determined by the type of roof, floor material and natural conditions of the region.
Hanging rafters rest solely on the external walls of the house, intermediate supports are not used. Hanging type rafter legs perform compression and bending work. The design creates a horizontal bursting force that is transmitted to the walls. Using wooden and metal ties you can reduce this load. The ties are mounted at the base of the rafters.
A hanging rafter system is often used to create an attic or in situations where roof spans are 8-12 m and additional supports are not provided.
Layered rafters are installed in houses with an intermediate columnar support or an additional load-bearing wall. The lower edges of the rafters are fixed on the external walls, and their middle parts are fixed on the internal pier or load-bearing pillar.
Installation of a single roofing system over several spans must include spacer and layered roof trusses. In places with intermediate supports, layered rafters are installed, and where there are none, hanging rafters are installed.
Features of arranging rafters on different roofs
Gable roof
A gable roof, according to building codes, has an inclination angle of up to 90°. The choice of slope is largely determined by the weather conditions of the area. In areas where heavy rainfall prevails, it is better to install steep slopes, and in areas where strong winds prevail, flat roofs are installed in order to minimize the pressure on the structure.
A common version of a gable roof is a design with a slope angle of 35-45°. Experts call such parameters the “golden mean” of consumption of building materials and load distribution along the perimeter of the building. However, in this case, the attic space will be cold and it will not be possible to arrange a living room here.
For a gable roof, a layered and hanging rafter system is used.
Hip roof
All roof slopes have the same area and the same angle of inclination. There is no ridge girder here, and the rafters are connected at one point, so the installation of such a structure is quite complicated.
It is advisable to install a hip roof if two conditions are met:
- the base of the building is square in shape;
- in the center of the structure there is a load-bearing support or wall on which it will be possible to fix a rack that supports the junction of the rafter legs.
It is possible to create a hip roof without a stand, but the structure must be strengthened with additional modules - tie-down stands.
Hip roof
The traditional design of a hip roof involves the presence of slanted rafters (diagonal) directed towards the corners of the building. The slope angle of such a roof does not exceed 40°. Diagonal runs are usually made with reinforcement, since they account for a significant part of the load. Such elements are made from double boards and durable timber.
The joining points of the elements must be supported by a stand, which increases the reliability of the structure. The support is located at a distance of ¼ of the length of the large rafters from the ridge. Shortened rafters are installed in place of the gable roof gables.
The rafter structure of a hipped roof can include very long diagonal elements (more than 7 m). In this case, a vertical post must be mounted under the rafters, which will rest on the floor beam. You can use a truss as a support - the beam is located in the corner of the roof and fixed to adjacent walls. The truss truss is reinforced with struts.
broken roof
Sloping roofs are usually created to accommodate a larger attic. The installation of rafters with this roofing option can be divided into three stages:
- Installation of a U-shaped structure - supports for purlins that hold the rafter legs. The base of the structure is floor beams.
- At least 3 purlins are installed: two elements run through the corners of the U-shaped frame, and one (ridge purlin) is mounted in the center of the attic floor.
- Installation of rafter legs.
Gable roof: do-it-yourself rafter installation
Calculation of inclination angle and loads
Of course, you can calculate a gable roof yourself, but it’s still better to entrust it to professionals in order to eliminate errors and be confident in the reliability of the structure.
When choosing the angle of inclination, it is necessary to take into account that:
- an angle of 5-15° is not suitable for all roofing materials, so first choose the type of coating, and then calculate the rafter system;
- at an angle of inclination over 45°, material costs for the purchase of components of the “roofing cake” increase.
Load limits from snow exposure range from 80 to 320 kg/m2. The design coefficient for roofs with a slope angle of less than 25° is 1, for roofs with a slope from 25° to 60° - 0.7. This means that if there are 140 kg of snow cover per 1 m2, then the load on a roof with a slope at an angle of 40° will be: 140 * 0.7 = 98 kg/m2.
To calculate the wind load, the aerodynamic influence coefficient and wind pressure fluctuations are taken. The value of the constant load is determined by summing the weight of all components of the “roofing cake” per m2 (on average 40-50 kg/m2).
Based on the results obtained, we find out the total load on the roof and determine the number of rafter legs, their size and cross-section.
Installation of Mauerlat and rafters
Do-it-yourself installation of rafters begins with the installation of a mauerlat, which is fixed with anchor bolts to the longitudinal walls.
Further construction of the structure is carried out in the following sequence:
Installation of rafters: video
Methods for connecting rafter structure elements: video