For the constructed building to serve for more than one year, it needs both a solid foundation and a strong roofing system that withstands the vicissitudes of the weather. The roof must withstand heavy loads with dignity: heavy snowfalls, sharp gusts of wind, heavy rainfall. The roof rafter system is best suited for this.
Roof trusses and its types
The rafter system is the basis of the roof, which focuses on the supporting elements of the structure and also serves as a frame for various types of materials for the roof: insulation, waterproofing, various coatings.
The dimensions and design of the rafters depend on:
- purchased material;
- the size of the building;
- dimensions of the house;
- building material for rafters;
- individual preferences of the customer;
- roof loads relevant for a certain region.
The rafter system has:
- crate - beams that fit in the perpendicular direction on the rafter legs;
- screeds that absorb tensile forces;
- upright wooden racks;
- Mauerlat - a bar, the installation of which is carried out along the wall, the rafters are emphasized on it;
- rafter legs are a kind of wooden beams that take on 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 optimal for a particular situation.
When it comes to low-rise buildings, wood structures are the most common. In many cases, three types of trusses are used: hanging rafters, layered rafters and a mixed rafter system.
Characteristic of hanging rafters
Hanging rafters are the most elementary type of rafter systems, their characteristics are:
If the roof of the house is of a complex structure, the types of rafters can be alternated. For example, if there are supports or an average main wall, layered rafters are installed, and in the absence of such elements, hanging rafters.
Features of layered rafters
For a layered rafter system, the house must be additionally equipped with a load-bearing wall located in the middle. Distinguish layered rafters on the following grounds:
The design of the combined system is the most complex, since it includes parts of two other types of rafters - hanging and layered. It is used for mansard roofing. The walls of the rooms, which are located on the second floor, are formed by vertical supports, these supports are also intermediate posts for 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 tightening.
At the same time, the horizontal bars perform the following functions: for the upper slopes - the Mauerlat, for the side ones - the ridge bar. To increase the strength of the roof, struts are mounted that connect the side slopes and vertical posts.
The combined sling system to manufacture is the most complex and time-consuming, but these disadvantages 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 bridge significant spans in the building.
You can increase the load-bearing qualities of the roof using a mixed rafter system. Roof trusses for different types of roof
During the construction of a certain building, rafter systems of one type or another are necessarily used, and the type of roof will completely depend on the project of the future structure.
Gable roof truss
A gable roof is a common roof construction for residential buildings that are no more than three stories high. Preference is given to just such a design due to the technical characteristics of the inclined shape of the rafter system, and also due to the fact that installation work is carried out easily and easily.
The gable roof truss system includes two rectangular inclined planes. The upper part of the building looks like a triangle from the front side. The main components of the gable roof are the Mauerlat and the rafter legs. In order to properly distribute the load on the rafters and walls, struts, crossbars and racks are mounted, thanks to which you can create a durable, rigid, elementary and easy installation scheme for a structure for a gable roof.
A gable roof is considered the simplest roof system; it is used for residential buildings of no more than three floors. On top of the rafters, you can mount a sparse or solid lathing, and then attach a bituminous coating, tiles or some other type of material to it. The rafters and the sheathing itself are usually made of beams or planks, which are fastened with nails, bolts or metal fittings. Metal profiles can be used as rafters, thereby overlapping significant spans. In this case, you do not need to use extra stands and struts.
The device of the rafter system for a gable roof allows you to evenly distribute all the 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 Hip roof rafter system
When arranging a system for a hip roof, you will need to install different types of rafters:
- wives (shortened);
- lateral;
- hip main;
- oblique (diagonal elements that form a ramp in the shape of a triangle).
The rafter legs located on the side are made of planks, and they are mounted identically to the details of a traditional pitched roof with a layered or suspended structure. Hip main rafters are layered parts. Planks or bars are used for the handicraftsmen, which are attached not only to the Mauerlat, but also to the diagonal beams.
To install this type of structure, the angle of inclination is accurately calculated, as well as the cross-section of the support beams. The dimensions of the parts also depend on the length of the span.
To prevent the hip roof from deforming under heavy load, the angle of inclination of the diagonal beams for the rafters should be accurately calculated Observe symmetry when installing diagonal rafter beams, otherwise the roof will deform from a significant load.
Sloped roof rafter system
A sloping roof is a structure with rafters, which consist of several separate elements. Moreover, they should be located at different angles relative to the horizon. And since the lower rafter part is almost vertical, the attic room of the building receives additional space, so that it can be used as a living room. The device of this type of roof is carried out during the construction of a four- or gable structure of rafters.
Professionals need to calculate the gable rafter system, but the gable sloped roof can be made independently, since its installation is very simple. To do this, it is necessary to install a support frame, which should consist of purlins, as well as racks. The horizontal parts are secured with hanging rafters. But the supports of the broken roof are fixed to the Mauerlat with the shortened legs of the rafters.
The assembly of rafters for a broken gable roof can also be performed by non-professionals, since the installation of such a roof is very simple "Cuckoo" in the truss farm
The so-called cuckoo on the roof is a small ledge that is located on the attic floor. A window is located here for better illumination of the attic room. Installation of the "cuckoo" is carried out carefully, while controlling the parameters of the entire structure: the depth of the cut, the angle of inclination and other factors. However, before that, the necessary measurements are made.
The first stage of work begins with the installation of the Mauerlat (a beam with a section of 10x10 cm, which is needed to support the slings). The rafter system acts as a skeleton for the roofing material. To give the structure rigidity, spacers are used, which are mounted between the two legs of the rafters.
After the installation of the truss is completed, the crate is laid, the type of which depends on the purchased roof covering. Installation of the lathing is done solid or with a certain step. For it, boards, OSB and plywood sheets are usually used. In addition, the installation of the roofing material must be identical throughout the roof.
The main difficulty in installing such a rafter system is the location of the inner corners. Snow can accumulate in these places, which means that the load will increase, which is why a continuous crate is made.
A "cuckoo" on the roof is a small ledge on the attic floor, under which there is an additional window Chalet roof truss roof truss
The peculiarity of the device of this design is the removal of visors, as well as overhangs outside the house. In addition, there should be roof rafters and beams extending up to three meters along the sides of the building. Each of these elements is fixed with a bracket to the building wall at the bottom. Next, the edges of the beams are tied. They serve as a support for covering the roof of the building.
But creating large overhangs, it is necessary to install the reinforced belt in parallel with the installation of the Mauerlat studs. It is necessary to make anchors to help secure the consoles. In this case, the rafters are perfectly secured with anchors and, moreover, with tie-ins.
To take out the side cornices, a ridge bar is made, after which beams are brought out at the level of the Mauerlat, which should be identical to the length of the ridge. The truss is based on these structural details, and in the future - the building material for the roof.
When designing a building, the angle of the roof-chalet is calculated based on the characteristics of the local climate and other factors. At a slope angle of about 45 °, the load from the snow is not taken into account, since with this option it will not linger on the roof. At the same time, the sloping roof will withstand the load from the snow, however, it is necessary to install a reinforced truss truss. Before installing the roof-chalet, a building project is being prepared, because the originality of the roof itself, as well as long cornices and its overhangs, oblige this.
Chalet-style roofs are characterized by canopies extended several meters outside the house. Roof truss designed for a soft roof
A soft roof is made in various ways, however, there are general characteristics in the technological methods of its construction. Initially, you need to prepare. When equipping a roof for a house made of foam concrete or other material, a Mauerlat is first installed, then a cut is made in the upper crowns of the building under the ceiling beams in increments of one meter. The distance between the boards is calculated based on the type of rafter structure.
- Separate parts of the rafter system are mounted. To completely eliminate the risk, the boards of the rafter legs are attached to the ground with screws. After creating a truss, it is lifted to the top of the building.
- All elements of the rafters are fixed with ceiling overlap, internal boards, jibs, as well as crossbars. Further, this base for the roof will become a single whole structure.
- The next stage is the crate, which is installed under the soft roof with little or no gaps. Gaps of no more than 1 cm are allowed. Quite often, leveling plywood is installed on top of the boards. Its sheets are laid using the brickwork method. The resulting joints are not aligned with the gaps between the plywood and the board.
If the length of the crate boards is not enough, then the joints of the parts must be placed in different places. In this way, you can correctly distribute the areas that have been weakened.
Self-made rafter system
Before the installation of the rafter system is started, the Mauerlat must be fixed to the longitudinal walls with anchors. Next, you need to decide on the desired section of the legs 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 the rafter elements in order to reduce the amount of insulation scraps.
Installation of the rafter system must be done in the following order:
- A template is made according to which the farm is assembled. 2 boards are taken, corresponding to the length of the rafters, and connected to each other from one edge only with a nail.
A rafter template called "scissors" will help you quickly assemble the entire roof truss system - The result is a structure called "scissors". Its free edges are placed on supports at the contact points of the rafter legs. As a result, the final angle should be obtained, that is, the angle at which the roof slope will be inclined. It is fixed with several long nails and transverse planks.
- A second template is made, thanks to which the cuts are installed on the rafters. It is made of plywood.
- On the rafters, special assembly cuts are cut out (a prepared template is used for this purpose) and they are connected at an angle of inclination of the slope. You should get a triangle going up the stairs to the roof. Next, it must be attached to the Mauerlat.
- Initially, two side gable rafters are mounted. Their correct installation in the vertical and horizontal plane is due to temporary struts attached to the rafters.
For the correct installation of the entire rafter system, the first pair of rafters is installed on the roof - A cord is pulled between these tops of the rafters. It will indicate the future ridge and the level of other rafters located in the gap.
- Raise and mount the remaining rafters at the initially calculated distance, which should be at least 60 cm from each other.
- If a bulky rafter structure is provided, then it is additionally reinforced with struts, supports, and so on.
The bulky structure of the rafters is additionally reinforced with struts and supports - A ridge bar is installed on special supports, to which not only short, but also diagonal and intermediate rafter elements are attached.
Correct fastening of the ridge bar ensures the reliability of the entire rafter system
Typical nodes of a standard rafter system
The strength of the rafter structure depends on the perfectly matched 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 the established rules.
The main typical nodes in the rafter system:
- support node of the rafters on the Mauerlat;
- ridge;
- unit for combining the upper puffs and the entire rafter system;
- fastening the brace, 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 all the nodes are highlighted. In each structure, they are made in different ways, since it depends on different nuances: the type of roof, its size, the angle of inclination.
Rafters from a profile pipe are a metal structure that is assembled using lattice rods. The very production of such farms is a very time-consuming process, but also more economical. For the manufacture of rafters, paired material is used, and kerchiefs are connecting elements. The structure of the rafters from shaped pipes is assembled on the ground, while riveting or welding is used.
Thanks to such systems, any spans are covered, but the correct calculation must be made. Provided that all the welding work is done with high quality, in the future it remains only to transfer the structural elements to the top of the building and assemble them. Bearing rafters from a profile pipe have many advantages, such as:
Crossbar in the rafter system
The crossbar is a fairly broad concept, but in the case of roofs, it has a certain meaning. The crossbar is a horizontal bar that connects the rafters. Such an element does not allow the roof to "expand". It is made of wood, reinforced concrete, as well as metal - it all depends on the type of structure. And the crossbar serves to distribute the load that the rafter system has.
It can be fixed in various places between the legs of the sling. There is a direct pattern here - if the crossbar is fixed higher, then the timber for its installation must be selected with a large section.
There are many ways to fix the crossbar to the rafter system:
- bolts;
- nuts;
- pins with washers;
- special fasteners;
- nails;
- mixed fasteners, when different types of fasteners are used in parallel.
The mount exists with a cut-in or overhead. In general, the deadbolt is a design unit, as well as the entire roof slings system.
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, it is necessary to first figure out how they are fastened to the supporting roof and ridge. If fastening is made to prevent deformation of the roof during shrinkage of the house, then on top of the rafters are fixed with a hinge plate or 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 apply:
- overhead metal or wooden plates;
- cutting method;
- connection with long nails.
In the layered system, the rafter legs are not interconnected, since they are attached to the ridge run.
The rafters are fastened to the Mauerlat by the cutting method, which is done in the rafter leg. Thanks to this method of fastening, the roof support will not weaken. Cutting is also done when installing the rafters on the floor joists. In this case, an incision is made in the support beam.
Video: how to make rafters with your own hands
Thus, a perfectly matched rafter system and their design characteristics will help create the foundation for a reliable roof for your home.
The simplest gable roof is at the same time the most reliable. The availability of do-it-yourself execution does not give rise to self-confidence - before starting work, you need to thoroughly familiarize yourself with the design features in order to make decisions and execute them in a qualified manner.
Diagram and features of the gable roof device
A gable roof is called a roof formed by the intersection of two rectangular slopes at a certain angle. Such a device is the most reliable and simplest, therefore, even a person with average carpentry skills can independently mount a gable roof.
The base of the roof is a rafter system that acts as a support for the roofing cake and topcoat. The service life of the roof and the comfort of living in the house depend on its strength and reliability. The rafter system, subject to regular wind and snow loads, must be securely attached to the building body. This task is solved with the help of a Mauerlat, which is firmly fixed to the upper plane of the walls of the house. Thus, an almost monolithic system is created that reliably protects the internal space of the house from any manifestations of the external environment.
Photo gallery: how you can use the space under a gable roof
A residential attic can be arranged under a gable roof 
A gable roof with a Danish half-hip improves the exterior of the building and allows you to increase the size of the attic 
The attic above the garage can be used to store spare parts, set up a break room or equip a warehouse for household equipment 
The area of the attic under a gable roof depends on the height of the ridge and the angle of inclination of the slopes
The structure of the gable roof truss system
A roof with two opposite slopes is the most common construction used in individual housing construction. The intersection line forms a ridge, and the side openings of the extreme rafter legs serve for the device of gables - vertically located walls that create a closed under-roof space. To obtain a strong and durable structure, many retaining and reinforcing elements are used, giving additional rigidity to the entire structure. The gable structure is based on a triangle - the most rigid geometric figure. The rafter system consists of the following main elements:
- Mauerlat is a wooden beam that acts as a connecting element between the frame of the house and its rafter system. It is attached to the walls with threaded rods, anchor screws or wire harnesses. The size of the cross-section of the timber is from 100x100 to 150x150 mm and depends on the size of the building, its number of storeys and the shape of the roof.
- Rafter leg - a wooden beam measuring 50x150 or 100x150 mm, connected at the top of the roof with the ridge and resting on the opposite end on the Mauerlat. Rafters are the main bearing element of the roofing system, which perceives all types of external loads: wind, snow, rain and the dead weight of the structure.
Roof trusses form the load-bearing frame of the roof and determine its geometric shape
- Lezhen - timber made of wood, laid horizontally with support on the internal load-bearing wall. The size of the bed, as a rule, is equal to the size of the Mauerlat. Supports roof racks.
- Tightening is an element used in hanging rafter systems. Its purpose is to compensate for the tensile forces that occur at the lower ends of the rafter legs.
- Racks - square beams that transfer part of the load from the rafters to the beds.
- Struts are structural elements that transfer part of the load from the rafter legs to the tightening. Thus, a farm with increased strength characteristics is formed.
- Counter lattice - wooden bars ranging in size from 25x50 to 50x50 mm, stuffed onto the upper edge of the rafters. The purpose of the counter-lattice is to form a ventilation gap between the lathing and the waterproofing film. This element is required when constructing a roofing pie in the attic.
- Sheathing is a support base for installing a finishing roof covering. The sheathing can be solid or sparse and can be made of 25 mm thick boards, waterproof plywood, OSB sheets and other similar materials. The choice of lathing design depends on the characteristics of the topcoat.
- A ridge is a horizontally located beam along which opposite slopes intersect.
- Roof overhang - is a continuation of the rafters at a distance of up to 40 cm from the walls of the building. Protects walls from getting wet, and also serves to place spotlights, which are an integral part of the ventilation system of the under-roof space. With insufficient rafter length, the overhang is formed by additional parts for their lengthening - filly.
The rafter system of a gable roof consists of triangular trusses, supported by a Mauerlat and a ridge, lathing and several auxiliary elements that reinforce the structure
Calculation of the load on the rafter system of a gable roof
The rafter system experiences certain loads, which can be divided into two types.
- Constant loads acting independently of any other factors. Their size is determined by the design of the roofing pie and consists of the weight of waterproofing and vapor barrier films, insulation, additional elements, fasteners and any other elements of the roofing covering, including the finishing one. In practice, the average weight of all components of the roof of a house is about 40–45 kg / m 2. More precisely, this value can be calculated by summing the specific load values of each material used, which can be taken from the look-up tables. When calculating the weight of the roof, it is recommended to lay a safety margin of 10%.
When calculating the load, the weight of each element of the roofing cake is taken into account
- Variable loads. These include the effects of wind and snow, depending on their intensity. In fact, the roof of the house is a sail that takes up the load from the wind. The force of direct impact on the roof along the normal depends on the angle of inclination of the slope - the smaller it is, the lower the load. At the same time, eddies arise on the leeward slope, and a load on the roof appears with an inverse impact vector. With hurricane winds, the separation force can reach 630 kg / m 2. Snow influences also belong to variable loads. It should be noted that they also have clearly defined regional indicators.
Wind loads are a risk factor for roofs as they create large tearing and overturning forces.
Obviously, careful calculation of snow and wind loads, taking into account local climatic conditions, is vital when choosing a roof structure and materials. These loads can be determined from the map drawn up on the basis of SNiP 2.01.07–85.
The map can be used to determine the value of wind and snow load in the construction region.
The values of snow and wind loads marked on the maps for each region are called normative. In order to obtain the calculated snow load, the standard value must be multiplied by a special coefficient that takes into account the angle of inclination of the roof. This coefficient is equal to:
- 1 with a slope of less than 25 o;
- 0.7 at an angle of inclination from 25 to 60 o;
- 0 for steeper slopes.
The calculated wind load is determined by multiplying the standard value by a factor that takes into account the height of the building and the type of terrain in which the construction is being carried out.
Table: Correction factor for calculating wind load (taking into account building height and type of terrain)
The specific load of the most popular roofing materials can be taken from the following table.
Table: Weights of some roof materials
It is possible to take into account the features of the impact of different types of loads only in aggregate, therefore, calculations of this nature should be entrusted to an experienced specialist.
Video: calculation of the rafter system
Types of gable roof truss systems
According to the principle of the device, rafter systems are of two types:
- Hanging.
- Forced.
Hanging rafters are used for buildings in which the bearing supports are located at a distance of up to 10 meters in the absence of an intermediate wall inside the building box. For other cases, it is necessary to use a layered rafter system.
Features of the device of the hanging rafter system
The hanging rafters are supported by the outer walls. Since the arch has a joint at the upper point, when vertical loads are applied to it, expanding loads are created on the lower supports. To compensate for them, puffs are used - horizontal ligaments between the lower ends of the rafter leg. The result is a rigid force triangle. When arranging an attic room, floor beams are used as a tightening. Various constructive solutions for the hanging rafter system are possible:
- Simple three-articulated arch. It is a triangle-shaped structure. In this case, the tightening works only in tension and is not a supporting one. Therefore, it can be replaced with a conventional metal beam. In this case, the connection of the cornice joint is performed with a simple orthogonal cut using wooden plates or metal plates.
The three-pivot arch is the simplest truss structure for a gable roof
- Reinforced three-articulated arch. This scheme was used earlier in the construction of industrial buildings, when the span exceeded 6 meters. In this case, the tightening is suspended on a wood headstock. The assemblies are connected using metal parts and equipped with devices for adjusting the tension. The main load in such a system falls on the ridge of the roof. In individual housing construction, such truss systems are not used.
A three-articulated arch with reinforcement differs from a simple one by the presence of a vertical stiffener (headstock) and the ability to adjust the tension at the joints
- Hinged arch with a raised latch. In this version, the rafter leg is partially unloaded through the roof ridge by the suspension to the raised puff. It rises to a height of at least 2.2 m from the attic floor level. Such a system is ideal for the construction of an attic room in the under-roof space. The connection of the tightening with the rafters is made by a tie-in, as a result of which the connection in the unit becomes fixed.
A hinged arch with a raised latch is ideal for installing an attic under-roof space
- A three-pivot arch with a deadbolt is used to strengthen the rafter system by creating an additional power triangle. The system is used for significant bursting loads. The connection of the crossbar to the rafter must be fixed, otherwise the entire system will not have the required rigidity.
An additional horizontal element (transom) gives the system greater resistance to bursting loads
The crossbar, in contrast to the lower tightening, operates in compression, not tension.
In addition to those listed, other elements are also used to strengthen the roofing skeleton. Very popular are struts and struts located in the system at the places where the rafters are most loaded.
In the most loaded places, roof trusses can be reinforced with struts and struts
Video: rafter system step by step
Roof systems of the layered type
Reinforced rafters are used for buildings with a width of more than 10 meters. They are characterized by the presence of a load-bearing wall inside the building, which is an additional support for the rafter system. Nesting structures are of several types:
In non-expansion layered systems, the main load from the roof frame is transferred to the Mauerlat
Determination of the pitch of the rafters of a gable roof
The task of ensuring sufficient strength of the rafter system is solved by selecting the material for the manufacture of its elements and calculating the parameters of their installation. The pitch of the rafters is one of these elements and is selected depending on the weight of the roofing cake. The distance between the support beams is usually set in the range of 0.6-1.5 m. The actual pitch between the rafters depends on the geometry of the roof and is calculated as follows:
- The number of rafter legs is determined. To do this, you need to use the ratio n = L / d 1 + 1, where n is the number of rafter legs, L is the length of the roof along the ridge, d 1 is the desired distance between the rafters.
- The calculated distance between the rafters is calculated, for which the length of the roof along the ridge is divided by the amount obtained in the previous paragraph: d = L / n.
For example, consider an option with a roof length of 13 m with a preferred distance between rafters of 750 mm (option for a roof with ceramic tiles).
- The number of rafter legs n = 13000/750 +1 = 18.33. Since the number of rafters must be sold in whole, round this value to 19.
- The rafter pitch d = 13000: 19 = 684 (mm).
Thus, on the roof we have chosen, the rafters must be installed with a pitch of 68.4 mm.
It should be remembered that the result obtained is the distance between the axes of the rafters.
Gable roof truss system units
We have already discussed the main types of joints in the nodes of the roof supporting structure above. But it makes sense to dwell in more detail on the auxiliary materials that make the rafter system more reliable and durable.
You can strengthen the fastening of parts when installing the rafter system using metal plates and corners of various shapes
Such products are made of galvanized steel up to 1.5 mm thick. They have various configurations and can be installed on any kind of connection.
Photo gallery: types of connections in the nodes of the rafter system of a gable roof
In the ridge part, the rafter legs are usually connected by flat bolted plates 
To strengthen the structure of the rafter system, it is necessary to select metal plates that correspond to the configuration of the fastening unit 
Sliding knot mates relieve the rafter structure 
Junction points in the rafter system can be additionally reinforced with metal inserts 
Depending on the type of rafter system used, there are different ways of attaching the ridge knot 
On flat joints operating under heavy loads, it is convenient to use nail plates
All docking nodes of the rafter system have the function of strengthening the rafters by redistributing the loads and strengthening the bearing elements. So, in the lower part, the rafter is supported on the Mauerlat at a right angle, for which the corresponding inserts are made.
To strengthen the rafter system, they try to use connections with the maximum bearing capacity, for example, cutting the rafters into the Mauerlat at a right angle
In addition, metal mounting plates are used for additional reinforcement in the docking points. The same principle is used when installing struts to the rafters. In any case, the mating parts must work "on the stop" and not move during operation.
Any parts must be loaded along their axis
There are three main types of nodes in the rafter system:
- Ridge connections. This is the joining of two rafter legs at a given angle along the line of intersection of the slopes. They can be hinged or blind. The first ones are used when installing a rafter system on log or log houses, which tend to sag and rise, depending on the season, during almost the entire period of operation. Blind joints are used in the truss systems of houses made of building stone. In such structures, a reinforced belt is installed on top of the wall, which takes on the lateral loads.
- Fastening the lower ends of the rafter legs to the Mauerlat. Since they are at an angle to the support bar, a sliding vector is created that is directed outward from the structure. To compensate for it, a tie-in is made in the Mauerlat, and a heel is made on the rafter. The rafter is inserted into the groove with an emphasis on it and is fastened with a nail through the edge of the beam into the Mauerlat. Additional support parts made of bars are also used. In cases where the rafter has to move (on wooden log cabins), sliding fasteners are used. They make it possible to compensate for seasonal changes in the height of the walls.
- Other nodes. All other parts of the rafter systems are essentially stubborn elements working in compression, rarely in tension. They are installed by cutting into the mating parts to prevent them from displacement under load. Such details include crossbars, struts, struts, stops and other similar parts.
For a stronger connection, the additional elements mentioned above are used.
Installation of a gable rafter system
Currently, the construction market offers services for the manufacture of individual roof trusses for specific buildings. It should be noted that this service has a number of advantages:
- Guaranteed product quality, ensured by the use of special equipment and assembly technologies.
- Fire safety, since all truss parts are flame retardant.
- Longer service life, which is achieved by antibacterial treatment of products with special compounds.
- Easy to install ready-made trusses.
The only drawback of this method of installing a rafter system is the relatively high cost of products.
For self-erecting a gable roof, you can use ready-made roof trusses ordered from professional manufacturers
Assembling roof trusses on the ground
The assembly of rafters on the ground is used in cases where there is a flat area of sufficient size right next to the house for the manufacture of trusses. In this case, not complete trusses are mounted, but rigid structures of three or four parts, which can be lifted to the installation site by the efforts of two or three people. Lifting is carried out with the help of ropes along the slopes. The advantage of this assembly method is the possibility of using a single template, which ensures high precision in the manufacture of each structural element. A possible option for partial installation of trusses below is as follows:
- Make a slipway for assembling trusses. It consists of three platforms, the distance between which corresponds to the length of the mating parts. They can be assembled from several boards or beams located in one horizontal plane.
For the convenience of assembling the rafter frame on the ground, you need a free area of a certain size and auxiliary elements on which you can place structural details
- To assemble the first truss, you need to take two rafter legs and a tightening - lower or upper.
- Having laid out the parts on the slipway, place them in accordance with the truss drawing and fasten them with nails. Check the truss blank for compliance with the dimensions specified in the technical documentation. Correct the location of the components if necessary.
- Carry out the final fixation of the parts in the truss nodes using additional fixing plates. The nail plates can be installed using a power clamp, using additional heavy plate shims under its jaws.
The power clamp allows you to pre-tighten the nail plates, and then fix them in any convenient way
- Lay the details of the second truss on top of the first and fix with clamps, exactly following the contours of the lower truss, which acts as a template. After assembling the second truss, move it to the side.
- Make the required number of trusses by repeating the operations from the previous paragraph. This ensures full compliance of all manufactured trusses.
When making trusses according to one template, they will exactly repeat the size and shape of each other.
Installation of the rafter system at the installation site is as follows:
- The first two trusses rise to the roof. To do this, you can use an inclined deck of several beams and fairly strong ropes.
- The first to install gable trusses at the ends of the roof. They need to be set strictly vertically and fixed to the Mauerlat with temporary jibs.
Gable trusses need to be installed first
- A construction cord is stretched between the gable trusses perpendicular to the location of the rafter legs.
- Each subsequent truss is installed in compliance with the previously calculated rafter pitch.
In order for all trusses to be installed evenly, twine is pulled between the extreme structures
- After the installation of the last truss, the entire structure of the rafter system is reinforced with girders, after which the temporary fasteners are dismantled.
- Further, the rest of the structural elements are mounted - jibs, ridge beams, beds, racks, etc., provided for in the project of the rafter system.
The lathing, which is stuffed last, gives additional strength to the roof.
Assembling the rafter legs directly at the installation site
On-site rafter assembly is used on small roofs. At the same time, billets are fed upward, from which the necessary parts are cut. Installation is carried out from the bottom up, starting with the installation of the rafter legs. The horizontal level of the rafter system is controlled by stretched cords, and the verticality of the truss assembly is controlled by a construction plumb line. The installation procedure is the same: first, gable trusses are mounted, then the rest in any convenient order.
The assembly of the rafter system directly on the roof begins with the installation of racks and a ridge girder on which the rafters are laid
Accurately following the requirements of the drawings, you can mount the rafter system yourself. It is almost impossible to do this alone, so the participation of one or two assistants is mandatory.
Video: installing rafters with your own hands
When assembling a rafter frame for a gable roof, it is important to adhere to certain rules:
- All wood used for the installation of the truss system must be treated with antiseptic and fire-fighting compounds.
- When working with a hand-held power tool, the safety requirements specified in the instructions must be observed.
- Installation of nail plates cannot be done by hammering in, this leads to their deformation. A clamping tool must be used during installation.
- A waterproofing layer must be laid under the Mauerlat. Roofing material is traditionally used for this.
- When installing the rafter system, you must use fasteners with a protective coating.
- Installation of the rafter system should be done in dry, calm weather.
Video: gable roof for metal tiles
Like any roofing system, a gable roof requires careful and responsible attitude. Mistakes in the construction of such roofs are usually costly. Not only a careful selection of materials is important, but also their competent use. Nevertheless, the main part of the work can be done independently. I wish you success!
The gable roof is very popular, as its construction is considered a relatively simple and quick step in building a house. Different types of gable roofs allow you to choose the appropriate option for a specific building. It will not be difficult to install such a roofing structure, if there is even a little experience in construction, but, of course, you cannot cope alone. All work is carried out in stages, taking into account the characteristics of such a roof.
Peculiarities
When erecting a gable roof, a rafter system and the main parts of the roofing structure are installed. This includes the frame (in the form of rafters with struts), Mauerlat. They are made of high-quality wood - these are bars of 150x150 mm and boards with a section of 50x150 mm. Symmetrical gable roofs with straight slopes (gable roof) are considered traditional. The angle of inclination of the slopes of such a roof reaches 45 degrees, which avoids stress on the structure (for example, during snowfall and wind).
Other types of gable roofs, for example, with broken slopes, allow you to equip an attic under the roof. In this case, the slopes on top of the roof are more gentle slopes, and below - with a sharp slope. A sloping gable roof should be erected on a more complex and durable structure. When constructing an asymmetrical roof, the ridge of the roof is performed with an offset from the center. This is done taking into account the structural features of the building.
Views
The frame structure of a gable roof can be:
- layered;
- hanging.
It is characteristic that in most buildings a layered rafter system is used, inside which there are load-bearing walls. The frame thus serves as an intermediate support. With a roof width of no more than 10 m, one support is usually used. The roof is more than 10 m wide and has several proportionally positioned supports. A frame in the form of a hanging rafter system is possible in the case when the structure can do with one support without having internal load-bearing walls. Such a roof is built from two belts - the upper (two rafters), the lower (rigidly connected puffs). The rafters rest on the Mauerlat, and the ends of the rafters go out onto the outer walls.
The gable sloped roof can be reinforced in the form of support frames that prevent the sloped roof from sagging. In this way, a more robust structure can be obtained. The hanging sloping roof has additional support frames to which the attic walls are installed. The support frame, which is located inside the load-bearing wall, takes on some of the load, which makes the roof structure slightly lighter.
Device
The structure of the gable roof is characterized by the presence of inclined surfaces on both sides. The base area of the roof has a rectangular surface. The slopes prevent snow and melt water from gathering on the roof. The roof is naturally cleaned. The roof consists of structural units: Mauerlat, rafter system, ridge and filly, roof overhangs, struts, braces, battens and racks. It is worth figuring out what is characteristic of all the structural elements of a gable roof.
Mauerlat is necessary for the correct distribution of the load on the load-bearing walls from the rafters. For this purpose, a solid wood is usually chosen - a bar (it can be oak, larch, pine). The choice of cross-sectional timber is determined by the type of wood (solid or glued). For example, 100 by 100 mm or 150 by 150 mm. It is worth noting that when choosing a metal rafter system, the Mauerlat should also be made of metal.
The main element of the gable roof system is the rafter leg. These elements are made from durable timber and logs. When the rafter leg is connected from above, a truss is formed with a different type of intermediate support. An important role here is played by the parameters of the rafters and structural units.
Tightening is necessary to connect the rafter system (rafter leg) and to give strength and the necessary rigidity to the structure.
A run can be of two types: a ridge run, in which the installation is carried out at the junction of the rafters (in this place the roof ridge is then installed), and a side run, which provides the roofing elements (truss) with additional rigidity (the size and number of such runs will depend on the load on the structure ).
The rafter posts in the form of a vertical bar also take up a significant part of the load from the roof. The gable roof rafters are usually centered. If the width of the span is greater than usual, then also on the sides. When erecting an asymmetrical roof, the racks are placed depending on the length of the rafters. For a sloping roof, the installation of racks is carried out on the sides, while leaving free space. If you plan to have two rooms under the roof, then the rafters are placed in the center and on the sides.
The struts are the supports for the stanchions. When braced at an angle of more than 45 degrees, the roof is better protected from deformation (snow, wind). Depending on the climatic zone, both longitudinal and diagonal struts can be installed with a rafter pair on the same plane.
The bed serves as a reliable support for the racks. This is the place where the brace is attached.
The lathing is necessary to fix the materials and structural elements of the roof. The lathing is installed perpendicular to the rafter legs. One of the important purposes of the lathing is to redistribute the load from the roof to the rafter system.
Requirements for building materials
The choice of materials for the rafter system is an important step in preparing for the arrangement of the roof structure. When calculating the material for a gable roof, one must proceed from the fact that it must be high-quality wood, the material has no knots, damage or wormholes, is well processed and impregnated with special compounds (for safety and reliability during operation). For the reliability of the structure, there must be a stable connection of the elements of the entire rafter system. The roof must be a solid structure made of modern high-quality materials.
Wood species such as larch, cedar, spruce or pine are easily processed, so they are most often used in the rafter system. The rafters are made of timber with a width of 10 to 15 cm and a thickness of 5 cm. In this case, a mature timber is usually used, which will no longer change shape after arranging the roof. This is necessary to increase the stability of the structure. In addition to timber, boards are taken for rafters, especially when it comes to cocking the roof of a private house.
In multi-storey construction, metal rafters are used. The downside of a metal truss system for private housing is that such a structure is not able to retain heat. In this regard, wood has more advantages - the material is distinguished by a high degree of thermal insulation and energy saving. The wood is sorted by grade. Top-notch material is used to create hanging rafters and puffs. Racks and struts are made of material of both the first and second grade.
Projects and drawings
In the process of planning a gable roof, a drawing is prepared. This is a diagram of the future design, where there are ramps, a pediment, a ridge. In fact, the plan is a drawing with elaborated elements in different projections, showing the ways of tying rafters. Drawing up a drawing of a gable roof is carried out taking into account all stages of work.
The scheme of its construction includes:
- bars for the lathing;
- beams and rafters;
- installation scheme for heat and waterproofing;
- roofing layout;
- installation diagram of additional fasteners;
- ventilation system installation drawing, chimney.
A competently drafted roofing plan will reduce the expense item for the purchase of building materials. To create a project of any type, one or another type of materials is used, based on calculations and taking into account the reliability of the coating. The size of the roof covering is also taken into account. In the drawing, a part of the rafter system is necessarily prescribed, which makes it possible to understand how much the maximum load on the roof can be.
The plan also includes:
- storm drain plan (storm sewers of a certain length);
- elements of connection of rays;
- construction area;
- diagram of the roof junction (clamping profile).
The type of roof must be clearly displayed in the structure diagram. Detailed details on the diagram will allow you to get the job done faster and better.
Drawing up a diagram
Depending on the characteristics of the roof (one- or two-pitch, shape, etc.), project documentation is drawn up.
This work takes place in several stages:
- a sketch of the future roof is drawn up (at this stage, the drawing should have a ready-made view of the roof with the elaboration of the style of the structure);
- the main roofing elements are being worked out (the degree of load and the amount of materials are displayed on the drawing);
- the diagram shows the construction of the roof.
It is worth considering that the differences in pitched structures are associated with the type of rafters(hanging or layered), with uneven inclination angles, with the dimensions of the eaves overhang. It is also worth considering design errors. One of the most common of them is considered to be an error in calculating the consumption of materials for the entire complex. It is best to entrust the process of drawing up drawing diagrams to specialists. The roof structure is erected in accordance with the accepted building codes. In addition, it is important to minimize possible errors and defects. So, if the choice of the type of roof and the installation method are chosen incorrectly, this will cause the roof structure to collapse. With an incorrectly drawn slope and its construction, there is a risk of increasing the load on the roof. Although mistakes are made in the design of ventilation elements. The drawing itself should not be complicated, however, the rules for installing all roofing elements should be observed, respectively, they should be spelled out. A professionally executed roof plan increases the safety of the structure.
Payment
The importance of calculating the gable roof truss system cannot be underestimated. In the design process, it is necessary to calculate the useful area and, based on the data obtained, decide how high the vertical posts will be. In this case, several factors matter.
When erecting a roof structure, it is important to calculate the maximum load on the roof of the house, on all rafters and beams. Strengthening of the rafters may be needed, then adjustments are made to the project. For example, it may be necessary to use additional pads or a beam with a larger section than planned. The weight of the entire rafter system is also important. In this case, the calculation is carried out taking into account not only the section of sawn timber, but also the density and moisture content of the wood, the distance of the step between the rafters is determined.
Today there is a special classification of loads on the roofing system:
- The main load concerns the weight of the truss structure, load temperature, snow and other weather factors.
- An additional burden concerns the calculations of the effect of wind and ice.
- Force majeure loads are associated with man-made circumstances (a modern roof must withstand everything).
The limiting calculations of the rafter system, taking into account all the loads, are built according to two criteria (limits or states): the limit at which the structure can be destroyed, and the limit at which the probability of deformation and deflections is taken into account.
Slope
It is important to correctly calculate the angle of inclination of the slopes. With a standard house width of 6-8 m, the angle of the slopes is 45 degrees, but this is not enough for the space in the attic. At an angle of inclination of 60 degrees, the construction will cost more, but the entire roof will be more successful. At 45 degrees of inclination, you can choose any roofing materials. If the gable roof is initially planned to be asymmetric, then in the attic space you can safely equip a residential attic, but for this you need to calculate the usable area. Usually a standard gable roof is chosen. In doing so, it is important to take into account the load on the roof due to wind and snow. With an increase in the angle of inclination of the slopes, the consumption of materials will also increase. But the operational characteristics of such a roof will differ favorably. If you plan to build a gable roof with unequal slope angles, then all work can be done in the original design. However, when designing, it is better to build on the classic structure in the form of a symmetrical roof with an isosceles triangle at the base.
Step
The step of the rafters used when creating a roof is one of the fundamental in the construction of a structure. There is a dependence of the step of the rafter system on the roofing material. As the latter, corrugated board, slate, soft roofing or metal tiles are used.
Roof slate is used everywhere. This roofing material is distinguished by its relative strength, low cost and resistance to temperature extremes. However, the material has a certain weight, respectively, it is necessary to provide the roof with a powerful rafter system. It is worth considering that for a slate roof there must be at least three support points (in the center and at the edges).
In recent years, metal tiles have become quite widespread among roofing materials. The material is easy to install and has an attractive appearance. It is convenient to use metal sheets for roofing, as they are lightweight. In this regard, the distance between the rafters can be large (for example, 600-950 mm with a section bar of 150x50 mm).
The sheeting can be made of galvanized steel sheet with a special protective coating (from external weather influences). Modern corrugated board differs in color, corrugation width. Outwardly, such a coating differs in design. The step between the rafters under the corrugated board will depend on the type of profile, on the angles of inclination and the configuration of the roof. For the rafter system, in this case, a bar with a cross section of 50-75 mm is used. It can be a board 20-50 mm wide.
Instruments
When installing the rafter system, a set of tools is required. For this purpose, traditional tools are usually dispensed with - an electric saw (it can be a hacksaw), a hammer and screwdrivers. Sheathing of the roof with metal sheets is carried out with special metal shears. You can not cut the material with a polymer coating with a simple grinder, so as not to damage the top layer with the sheet protection. Otherwise, the skin will quickly rust. To cover the roof with roofing material, a barrel is needed in which the bitumen will be melted.
Undoubtedly, when performing installation and any construction work, you cannot do without a reliable ladder. It is also worth thinking about your own equipment. For example, when working, shoes with non-slip soles are required.
Mounting
It is better to do the installation of the gable roof truss system with your own hands with assistants, and many structural elements cannot be installed alone. The installation of the rafter system is carried out in several stages.
Let's consider them step by step:
- First you need to make a template. Roof trusses are assembled according to a template. So, you need to take two boards of the same length as the rafter leg. They are attached to each other from the edges with one nail. The result is a scissor design.
- This structure with other edges must be placed in those places where there are supports on the rafter legs. The angle obtained in this way (by the slope of the roof slope) is fixed with several nails. Fastening the corners must be done on an additional crossbar between the boards.
- Next, another template is being prepared. With its help, you can further assemble the structure. Installation of saw cuts on the rafters is in progress. The template itself is easier to make from plywood.
- The cuts are cut on the rafters using a template. The elements are connected at an angle of inclination of the ramp. The finished triangle is the rafter truss. It is lifted to the roof and attached to the Mauerlat (this will require logs, ladders).
- The fastening of the rafter system to the Mauerlat is done using nails, staples, corners. And wooden "shorties" help to fix the structure from displacement along the axis, they need to be exposed over the entire area.
- At the initial stage, two gable trusses are installed along the edges. Installation and correct fixation horizontally and vertically is carried out using temporary struts, to which the structure is attached.
- For reliability and convenience, a cord is pulled along the edges (between the tops of the trusses). You need to fix it in such a way as to mark the place for the future ridge. You will also need a cord when installing intermediate rafters.
- At the next stage, the remaining trusses are lifted and installed (at a certain distance (usually 0.6 m) from each other).
- In the presence of bulky structures, if there is a need to strengthen the structure, they are strengthened with crossbars, struts and supports.
- The run (ridge bar) is placed on special supports. Rafters of various types (short, intermediate or diagonal) are then attached to it.
The basis of the frame is the Mauerlat. Its manufacture and assembly forms the basis of the roof structure.
Mauerlat fasteners
The frame structure made of rafters is fixed to the floor beams. However, in this case, the load on the rafter structure is distributed at the points of attachment of the beams. This approach when installing a roof structure is possible for small and light buildings. Mauerlat is needed to evenly distribute the load of the roof in the upper part of the walls. Mauerlat is mounted parallel to the ridge of the future roof. This is how the main frame is drawn up. A wooden beam with a section of 150x150, 100x100 or 100x150 mm is used for the manufacture of a Mauerlat.
The gable roof rafter system is considered one of the simplest in purely constructive terms. It contains only a few elements, the number of which decreases or increases due to the size of the roof itself. But despite the apparent simplicity, the process of erecting a gable roof itself requires knowledge of some nuances that affect the quality of the final result.
Gable roof rafter system
What is a gable roof
From the name it becomes clear that the roof structure is two slopes that have a rectangular shape in the plane. More often the slopes have the same dimensions, but there are so-called asymmetric structures in which the slopes differ in size from each other.
In this case, the slopes are set to each other at a certain angle, which is called an inclination. The line of contact is the ridge beam, which is part of the rafter system. In a simple way, it is called a ridge, and it is the highest point of the roof.
The side planes formed by the slopes are called gables. They are triangular in shape. After the construction of the roof, the sidewalls are revetted with sheet or panel materials: plywood, OSB, even boards, etc.
What is the gable roof truss system
The basis of the constructions of the slopes are rafter legs, they are also rafters. They are made either from lumber (beams, boards), or from a steel profile (corner, channel). In private housing, wood is used. It is easier to work with, plus lumber is cheaper.
The device of the gable roof rafter system is not only rafters. In addition to them, there are several more required elements. In the photo below, all the elements of the gable roof are shown. Let's designate them.
Each of the elements of the roof has its own purpose.
Elements of the gable roof truss system
Mauerlat... In fact, this is a beam on which the rafters rest. Its purpose is to evenly distribute the loads from the rafter legs on the walls of the house. If the Mauerlat is not used, then the rafters will press on the walls pointwise, that is, large stresses will arise at the installation sites, which will lead to cracking of the walls.
Rafters installed at an angle.
Ridge, he is a ridge bar or girder. Its task is to form the junction of the rafter legs. A ridge bar is an optional element of a gable roof. There are designs in which it is not installed. But more on that below.
Puffs... They are not always used, but only on hanging rafters or, if the rafter system is installed on a wide house.
Floor beams that form the ceiling in the room and the floor in the attic.
One of the floor beams, which is called lie... It additionally acts as a base for the support posts that support the rafters. Not always used.
Support posts, they are also the grandmas supporting the rafter legs. They are installed only if the length of the span of the house is at least 6 m.
Braces, they are also diagonal props. They are used only if the support posts cannot provide the overall reliability of the rafter system.
There is one more element that is clearly visible in the photo below. These are the support legs for the ridge run. They are installed if the structure of the rafter system is heavy. That is, the entire structure is assembled under heavy roofing material, for example, under ceramic tiles.
Rafter rafters with support legs under the ridge girder
You may be interested in this! A warm roof is an important detail when building an energy efficient home. From the article at the following link you can find out.
Types of rafters
The roof rafter system (gable) can be assembled from layered or hanging rafters.
Fortified
They got their name because they rest on the lower ends of the walls of the house, the upper ends on the ridge girder. In this case, the rafter elements are subjected to loads that bend them. The construction is reliable, durable, with a high load-bearing capacity.
The photo above just shows the layered rafter system. It is clearly seen that the legs rest in the upper part on the ridge. In this case, there are two types of fastening of the rafters themselves in the upper part:
fastening is made to the ridge:
fastening is made to each other with an emphasis on the ridge (photo above).
Hanging
It is necessary to immediately indicate that this type of rafter system can be used if the distance between the walls of the house does not exceed 12 m. Because the rafters rest against the lower ends of the walls, and the upper ends only between themselves (there is no ridge run in the structure). Hence the low bearing capacity with a large expansion.
Hanging roof rafters have one purely constructive drawback - a large supporting load on the walls of the house. To reduce it, tightens are installed between the legs to make a hard triangle. Often, the functions of the puffs are performed by load-bearing floor beams.
If necessary, strengthen the hanging rafters, install racks and struts under them.
Hanging gable roof rafters
Installation of the gable roof truss system
Two types of rafter system determine two types of technology for their assembly. Let's consider each separately.
Installation of layered rafters
There is a certain sequence for assembling layered rafters.
Two extreme support posts are installed under the ridge beam. They will not only support the timber, but also be the elements that form the gables of the building. Attach them at the bottom to the Mauerlat. In this case, they are strictly set vertically, and the upper ends are in the same horizontal plane. To do this, a strong thread is pulled between the racks, the level is checked for horizontalness. If there are deviations, then one of the supports (low) is raised using wooden supports.
Along a horizontally stretched thread, intermediate support posts are mounted with a step of 2-2.5 m. To prevent the beams of the posts from moving, they are propped up with temporary fasteners: props or puffs.
A ridge bar is laid on the racks, which is attached to them.
Produced in pairs installation of gable roof rafters... Installation can be started from either side. Fastening is immediately carried out to the Mauerlat and to the ridge. The main thing is to maintain the distance between the legs, which is determined depending on the severity and bearing capacity of the roofing material. Usually, this parameter is indicated in a house project.
If necessary, intermediate support posts and struts are mounted.
Installing rafters on a ridge along a stretched thread
Installation of hanging rafters
The technology for installing hanging rafters is different. For this, the entire structure, assembled from two rafters and tightening, is assembled on the ground. That is, roof trusses are prepared in the required quantity, which are then raised to the roof. Sometimes craftsmen assemble roof trusses. Collected one - installed, collect the next.
It should be noted that such farms have a significant mass. It is difficult and dangerous to lift them manually, therefore they use the services of a crane. And this increases the cost of the structure.
Suspended trusses assembled on the ground
The hardest part is setting up the farms. All of them are installed at the installation site with a planned step, where they are temporarily fixed with jibs and props. Then a thread is pulled between the extreme trusses. It must be positioned so that, firstly, it is stretched strictly along the horizon, and secondly, according to the structure, which is higher than the rest.
It remains only to raise the rafter structures, which were below the tensioned level. And the last is the installation of the lathing, which will fix all the trusses into one rafter system. Please note that at the bottom of the rafters will be fixed to the Mauerlat.
You may be interested in this! When the installation of the rafter system is completed, then the turn of the roofing work comes. From the article at the following link you can find out.
Calculation of rafters
the length of the rafter legs;
step of their installation;
section of the used lumber.
With the length, everything is simple, for this you have to use the Pythagorean theorem, which is based on the formula: c 2 = a 2 + b 2, where c is the hypotenuse of the triangle (these are the rafters), a and b are the legs. The latter are the height of the roof and half the width of the house. All parameters can be easily measured.
The length of the rafters is l 2 + H 2
It is more difficult with the installation step, because much will depend on the mass of the roofing material and the loads from natural precipitation. The larger both loads, the smaller the installation step. But, as practice shows, this parameter varies from 60 cm to 2 m. The latter indicator is used if corrugated board with large corrugation parameters is used as a roofing material, for example, H75.
As for the cross-section of the rafter legs, here, as in the case of the installation step, loads are taken into account, as well as the length of the legs and the step of their installation. Here the dependence is as follows: the greater the load, step and length, the larger the section.
Video description
In the video, the process of installing the rafter system:
And one moment. Rafters for a gable roof are laid at a certain angle (marked with the letter "a" in the photo). The slope is selected taking into account the choice of roofing material. That is, some coatings cannot be laid on roofs if the angle of inclination is less than required. Here are some ratios:
the minimum angle of inclination of the rafter system for slate is 22 °;
for corrugated board - 12 °;
for metal tiles - 14 °;
soft tiles - 15 °.
The ratio of the slope of the roof to the type of roofing material
On our website you can find contacts of construction companies that offer turnkey roof design and repair services. You can communicate directly with representatives by visiting the Low-Rise Country exhibition of houses.
Generalization on the topic
Gable roofs are traditional designs. But from the article it becomes clear that there are two rafter systems that form the basis for the construction of roofs. The one that fits the size of the house is chosen. As a selection criterion, the loads that press on them are also taken into account. Therefore, it is important to correctly correlate everything, taking into account the nuances of construction processes.
In previous articles, which described the structure of the roof, we have already said that the hanging rafters rest on the Mauerlat with their lower end, and the upper ends of the adjacent rafters abut (either directly or through the ridge board) against each other. In the most simplified version, this is shown in Fig. 1:
Picture 1
I think it is obvious to everyone that with such a layout, there are bursting loads on the walls. To reduce them, puffs are added to the truss. But let's talk about everything in order.
As an example, let's take a house with a half-attic in the Volgograd region. The sum of snow and wind loads is 155 kg / m 2. The dimensions of the house are 8x10 meters. The thickness of the walls is 50 cm. The slope of the slopes is 40 ° (see Fig. 2):
Picture 2
STEP 1: Install. In this design, in addition to the usual loads, expanding forces will act on it, tending to move it off the wall. For more reliable fastening, you can add metal fastening plates to the anchor bolts (or studs) (see Fig. 3). The plates can be fixed to the wall, for example, with frame anchors, and to the Mauerlat it can be done with nails, self-tapping screws, and "wood grouses".
Figure 3
STEP 2: Determine the required cross-section of the rafters. The calculation is made in the "Arch" tab (see Fig. 4):
Figure 4
The cross-section of the rafters is taken 50x200 mm with a step of 60 cm.
A question may immediately arise here. Where do we take the distance from the ridge to the tightening (crossbar). We have it equal to 2 meters. Earlier on the site, we have already said that before proceeding with the construction of a roof, we need to make a drawing of it on paper, necessarily on a scale (in compliance with all proportions). If you can, you can draw on the computer. Further, according to this drawing, we determine all the dimensions and angles of interest to us.
Ties are installed between the hanging rafters to reduce the bursting loads on the walls. The lower the puff is, the more benefit it will get. Those. the less the bursting load falls on the walls. But since in our example the puffs still play the role of the ceiling beams of the attic floor, we also determine the height of their location based on the desired ceiling height. I took this height 2.5 meters (see fig 5):
Figure 5
STEP 3: We make a template for the bottom rafter saw. To do this, we take a piece of a board of the desired section with a length of about a meter, apply it to the Mauerlat at our angle of inclination of the ramps of 40 ° (navigate along the pediment) and make markings, as shown in Figure 6:
Figure 6
We draw the necessary vertical and horizontal lines (shown in blue) using a level. The depth washed down 5 cm.
So, let's make a template.
STEP 4: We install a ridge board, through which all the rafters will be connected to each other. First you need to outline the place of its installation.
We take the template made earlier and apply it to the Mauerlat. We are interested in the size shown in Figure 7 (here it is 18 cm):
Figure 7
The lower point on the Mauerlat is called point "A".
We transfer the resulting size to the top of the pediment, make the markup in accordance with Figure 8:
Figure 8
The lower right corner will be designated as point "B". Now we can measure the distance from the attic floor to point B (the length of the temporary posts).
We install temporary stands strictly vertically from a 50x200 board and put a ridge board of the same section on them. To fix them, you can put a board under the racks, fixed with simple dowels with nails to the floor slabs (see Fig. 9). It is not necessary to fasten it strongly, then we will remove it. The distance between the racks is no more than 3 meters.
Figure 9
We fasten the ridge board to the gables with metal brackets. The stability of the struts is ensured by jibs.
You may have seen somewhere how hanging rafters are installed without a ridge board (see the picture on the left). This method is very familiar to me, we did it before too.
But when we tried the skateboard version, we settled on it. Despite the fact that it takes some time to install racks and ridge boards, the subsequent installation of rafters is much more convenient and faster. As a result, you win in time. In addition, the design is more stable and more geometrically even.
STEP 5: We manufacture and install rafters.
We do the rafter like this: take a board of the required length, apply a template to one end, mark it out and make the bottom cut. Then measure the distance between points "A" and "B" with a tape measure (see Fig. 7-8). We transfer this size to our workpiece and make the upper cut. The angle we need for the top cut is on our template (see Figure 10). We have it equal to 90 ° + 40 ° = 130 °
Figure 10
Thus, we put all the rafters (see fig. 11)
Figure 11
The connection of the rafters with the Mauerlat here does not look the same as it was, for example, I think you have already understood that this is due to the presence of bursting loads, which were not in that version. However, in future articles you will see that this option is only one of the possible, and not the only correct one. We will use cuts that are more familiar to us. The main thing is to securely fasten the rafters to the Mauerlat.
At the top, the rafters will protrude beyond the ridge board. You can drive small bars between them, or you can leave it as it is. This, in principle, does not play any role (see Fig. 12):
Figure 12
We fasten the rafters to the ridge with nails or self-tapping screws. It is not necessary to install any additional fasteners here. In general, in this design, due to the lower cut, the rafters are obtained, as it were, sandwiched between the Mauerlat and the ridge board.
STEP 6: Installing the puffs.
We make them from boards of the same section as the rafters. It is not necessary to make any cuts and cuts here. We make the tightening overlapping on the rafters. We fasten them with several nails and tighten them with a threaded rod with a diameter of 12-14 mm (see Fig. 13):
Figure 13
Thus, we install all the puffs and remove our temporary stands, on which the ridge board was placed:
Figure 14
Now you can guess the purpose of the small windows in the upper part of the pediment. Through them, the ventilation of the insulation will be carried out, which will lie on the ceiling of the semi-attic floor (between puffs).
STEP 7: We attach the eaves filly to the lower ends of the rafters (see Fig. 15). We make them from boards with a section of 50x100 mm. We make the length of the filly so as to obtain the eaves overhang of the desired width (40-50 cm), and so that it overlaps the rafter by at least 50 cm. We fasten the filly with several nails and tighten it with 2 threaded rods. In the middle part, for additional emphasis on the wall, you can fix a small block with nails or self-tapping screws to the filly.
Figure 15
Please note that at the junction of the overhang filly with the Mauerlat, we do not wash it down on it, because this will reduce its already not large section. Here we preliminarily make a small cut in the Mauerlat itself (see Fig. 16):
Figure 16
Use a lace to keep the cornice straight. First, put the outer filly, then pull the lace between them and put all the others. In Figure 17 the lace is shown in blue.
Figure 17
Step 8: The following actions are already known to us from previous articles. We put the filly on the pediment and fasten the wind boards (see fig. 18):
Figure 18
STEP 9: Now we can leave the cornices as they are.
Let's see another version of the eaves overhangs (see Fig. 19):
Figure 19
Such "earrings" are made of 1-inch boards 10-15 cm wide. We fasten them with self-tapping screws.
Thus, now it remains for us to hem to the eaves from the bottom of the siding belt; fixing a protective film on the rafters, make a counter-lattice and crate; cover the roof with roofing material. We have covered these steps in previous articles. I think it makes no sense to repeat myself here and when considering other roof structures in the future.
