The most important and difficult stage is installation rafter system. The operation of the roof is associated with constant and periodic loads in the form of snow or gusts of wind.
To figure out how to make a rafter system with your own hands, you need to decide on its components. The rafter frame is used for any type of roof; it differs in the level of complexity during installation. Single-pitch and gable roofs are considered simple designs. Hip or hip roofs provide a reliable roof, but are difficult to calculate and install rafters.
When choosing the size of material for the frame, many factors must be taken into account. The cross-section of the rafters and load-bearing base must withstand the weight of the roof, climatic loads, and the weight of the devices installed on the roof (if any are installed).
The following elements are required for the frame of a gable roof:
Several types of rafter systems are used to construct the frame of a gable roof.
Layered - the choice of this design implies the presence of a support in the form of a wall in the center of the building. They receive three points of support and experience only bending load. Top part the rafter leg rests on the purlin, and the lower one on the mauerlat. This system allows the use of thinner lumber, lower costs and lighter weight construction.
Hanging - rafter legs rest only on the walls, so they experience a large load. To add strength, they are connected by tightening. Such rafters are usually assembled at the bottom and delivered directly for installation.
Complex roof shapes require non-standard solutions; for them, combinations of hanging and layered rafters are used.
When installing a hipped roof, the basis of the frame is the diagonal rafters connecting the ridge girder and the corners of the building. They are supported by rafts - short rafters, which, together with ordinary side rafters, form the basis of the roof slope.
The service life of the rafter structure depends on the quality of the lumber and its processing. For structural elements, it is necessary to select dry wood with a moisture level below 22%. It should be smooth and without knots. Before installation, all parts are treated with two layers of antiseptic and a fire retardant. When processing, you should use a brush rather than a spray, then the composition will be better absorbed. When choosing lumber, preference is given to coniferous wood.
The durability of the structure will be ensured by proper installation of the rafter system with your own hands. To connect the rafters, various types of fastening are used: staples, nails, shaped steel parts - corners and plates, which are screwed with self-tapping screws.
The dimensions of the timber used for rafters are influenced by:
The constant load is calculated from the total weight of the roofing material, insulation and waterproofing. As the distance between the rafters increases, material of a larger cross-section is required. The wind and snow load coefficient must be included when calculating the cross-section. Common rafter sizes are 50x150 mm and 60x200 mm.
Symmetrical base gable roof is an isosceles triangle. Knowing the height of the ridge, you can calculate the length of the rafter using the Pythagorean theorem. In this case, it is the hypotenuse, and half the width of the queen and the height of the roof are the legs.
The first step in installing a rafter system for any type of roof is laying and fastening the Mauerlat. Waterproofing in the form of roofing material must be laid underneath it. This beam requires drilling holes along the length into which studs embedded in the masonry are inserted and tightened with a nut.
Having created the basis for the frame, a template is made according to which all the rafter legs for the hanging system are assembled on the ground. To create a sample, take two thin boards equal in length to the rafters and fasten them with a nail at the ends. This blank is set to the width of the purlin, and the resulting angle is fixed with pieces of board.
A second template is used to mark the mounting cuts at the top and bottom of the rafters. Its base is plywood. When assembling the legs, you need to strictly follow the template so that you do not have to redo the structure. The upper part of the rafters is connected by a wooden or metal plate.
If the assembled roof trusses have significant weight, you will have to use equipment or devices for lifting.
The first pair of rafters is installed on opposite gables. It is fixed with temporary struts and leveled. A cord is stretched between the legs as a guide for installing the remaining trusses. The structure is connected by crossbars, struts and supports.
With a short span, the rafters are not fastened with a ridge girder. A roof with a width of more than five meters requires reinforcement of the structure with a ridge beam. This beam is attached both under the rafters and above them. The connection occurs with a gash and plates. For long rafters, support posts are installed to prevent sagging.
The completion of the installation of the rafter system will be the fastening of the sheathing.
To know how to properly perform a truss structure, you can watch a video describing the stages of work.
The basis of beautiful and reliable roof is the robust design of the rafter system. It is important to install it so that it serves for many years, especially in difficult places adjacent to the walls of the building, chimneys and pipes of the ventilation system. Depending on the weight of the snow, the wind load and the severity of the roof, it is necessary to select the correct rafter pitch and the design of the joints individual elements rafter group. We will consider options for attaching parts of the structure to floor beams and ridges, ways to increase the load capacity of rafter legs and step by step installation trusses and a complex roof in general.
The construction of the roof is the final stage of the construction of the house; it determines the degree of protection of the building from atmospheric influences and the appearance of the entire structure as a whole. The roof frame on which the roofing and insulation is mounted is called the rafter system. The structure of the rafter group depends on the type of roof and its complexity, on climatic conditions and from destination attic space. It is mounted on a Mauerlat fixed to the perimeter walls of the house and consists of the following elements:
Depending on the type and size of the roof, rafter systems can be layered, suspended or combined, but their main elements are largely repeated
Diagonal rafters hip roof fastened with rivets and trusses to ensure uniform load distribution
More complex species roofs are formed from a combination of pitched, hip and hip types; their rafter system is also assembled from the described elements.
The basis of any rafter and truss system is a rigid triangular connection, which gives strength to the roof structure and allows it to withstand the weight of snow and wind exposure.
A rafter system of any type is designed to create inclined pitched surfaces from which precipitation flows down without accumulating on the roof. In addition, the inclined surface better withstands multidirectional wind loads. When constructing a rafter system, the following types of rafters can be used:
These types of rafters are assembled different types roofs Let's look at the most popular device options pitched systems various configurations.
Shed roofs are used in the construction of country houses, garages, bathhouses and utility rooms. Such roofs are made using the simplest rafter system, which can become more complex as the length of the slope increases. If the distance between the walls of the building is more than 4.5 m, then the rafter legs are reinforced with struts. For spans of more than 6 m, it is necessary to use two rafter legs on each side or install an additional vertical post with symmetrical slopes.
The choice of design for a single-pitch rafter system depends on the length of the slope, while the use of composite beams is allowed
As the length of the slope increases, the design of the rafter system becomes more complicated with rigid triangular elements and contractions, which gives it additional strength.
Based on the experience of the author of this article, for soft roofing materials with small angles of inclination of the slopes, it is necessary to use a continuous sheathing of plywood with a thickness of 12 mm or more. When to use sheet roofing material, you should reduce the sheathing pitch to 10 cm, increase the overlap to 15 cm and additionally seal the joints of the sheets.
The gable roof type, traditional throughout our country, remains popular today. This is facilitated by the simplicity and reliability of the rafter system, as well as the ability to equip a cold or habitable attic. As a rule, a gable roof with an attic is formed by hanging rafters without a middle support, and its rigidity is ensured by crossbars and side posts, which serve as the walls and ceiling of the attic space.
Gable and sloping mansard roofs are very popular in suburban construction due to the possibility of equipping additional living space under the roof
Sloping gable roofs have the largest volume of built-in attic, frame system here it is represented by a combination of hanging and layered rafters with different angles of inclination of the slopes.
Gable rafter systems are distinguished by their simplicity of design, high strength and minimal consumption of building materials; such roofs are often used in budget dacha construction.
Four-slope roofs are formed by two trapezoidal and two triangular slopes and have a complex structure of a rafter system with a supporting frame on which row and diagonal beams are mounted. The space between the rafter joists is filled with trusses, and additional support for the diagonal legs is provided by trusses resting on the corner lintels.
Four-slope rafter systems are typical for hip and half-hip roofs, under which you can place a spacious attic space
Hip-slope roofs are perfectly protected from multidirectional gusts of wind and give the building a special chic, but their disadvantage is the expensive and difficult to install rafter system.
The basis for the rafter system of a half-hip roof is the walls of the building, on which the mauerlat, purlins and longitudinal trusses are located
The rafter group of a half-hip roof, as a rule, rests on the side and front walls of the building and has a slightly different design from others with truncated triangular slopes.
The rafters of hipped roofs in the upper part converge at one point and form a multifaceted pyramid. To increase the strength of the connection of the rafter legs, special joining elements, sheathing beams and additional extensions are used.
Rafters tent system they converge at the top at one point and are fastened together with ties; in the lower part they are fixed with the help of cuts
Hip roofs give the building a unique look, but are characterized by increased consumption roofing and lumber. Most often they are used on outbuildings, gazebos, and in a truncated version - as roofs for bay windows.
Multi-gable roofs are pitched fragments cut at right angles to each other and forming at the junction internal corners or valleys. The rafters of such a roof have different lengths, and the assembly of this structure requires professional skills, since the size and angle of inclination of the slopes may differ from each other.
The multi-gable roof rafter system forms eight triangular slopes, at the junction of which valleys are located
Roofs of this type are designed to provide daylight under-roof space and have a very attractive appearance, but they are quite difficult to install and insulate.
The passage of ventilation and chimney pipes through the roof sometimes requires displacement of the rafter legs in violation of the selected step between them. But if there are pipes of sufficiently large dimensions combined into one block, this is not enough. It is necessary to cut the rafters at the place where the pipes pass and connect the cut sections with other rafters with bars secured at the corners. Distance between pipe and wooden elements must correspond to a fire clearance of 130–150 mm.
The rafter system around the chimney is built taking into account the fire gap, and the cutout is strengthened with additional racks
Next, the cut rafters are fastened using vertical posts to the tie rods or floor beams. Thus, a box is created around the pipe, which does not come into contact with its hot surface and, if necessary, is filled with non-flammable heat-insulating material.
During service, the roofing covering is subject to natural wear and tear. If there is no deformation of the old rafter system and you are convinced that it will last for a long time, then repairs can be carried out quickly and efficiently. When there is no time for dismantling old roof, you can lay a new covering directly on top of the old roof. To do this, you need to know exactly where the rafter beams with counter-lattice and sheathing boards go.
Personal opinion based on practical experience, for a new roofing it is better to choose corrugated sheeting, metal tiles or ondulin, which will not create a large load on the structure of the old roof.
When installing the roof, the rafters are installed at a certain distance from each other. This distance is called a step. Recommendations for choosing the pitch of the rafter system are set out in SNiP II-26–76 * “Roofs”. The decision must be made taking into account the following parameters:
The pitch and number of rafters can be selected based on recommendations and adjusted taking into account the characteristics of a particular roof. For simple gable roofs with cold attics, the calculation can be made based on the following table.
For mansard and complex roofs, a more durable rafter system is required with a more frequent arrangement of trusses and with a change in pitch at the joint areas with different types of slopes. On such roofs, the rafters are timber with a cross section of 50X150 and 100X200 mm, and the pitch is selected in the range from 60 to 120 cm.
When constructing roofs with a habitable attic space, timber of a larger cross-section is selected, and rafters are installed more often to increase the strength of the truss
According to the observations of the author of this article, the size of the insulation material has an indirect influence on the choice of step. For example, standard width insulation is 60 cm, and the permissible pitch of rafters with a section of 50X150 mm on a pitched roof is in the range from 60 to 120 cm. Thrifty owners choose a pitch that is a multiple of 59 cm in order to mount insulating mats tightly and without gaps between the rafters.
Complex roofs include multi-level architectural solutions, which are often distinguished by a mixture of styles, for example, a pitched roof with a bay window or a combination of a hip structure with a hipped element. Even an ordinary multi-gable roof with gables at different levels often has a very complex rafter system. The design of such systems is carried out in accordance with the requirements of SP 64.13330.2011 “ Wooden structures" and SP 17.13330.2011 "Roofs". Professional specialists should be involved in design work, since even a small mistake can lead to defects and loss of expensive materials.
Complex roofs should be erected only according to ready-made design solutions, which contain all the necessary information for selecting materials and describe the sequence of installation work
The rafter system of complex roofs can be divided into simpler components, and valleys, vertical posts and horizontal ridge-type beams can be installed at the points where they are connected.
When installing complex rafter systems, it is important to ensure that there is a gap on all slopes for under-roof ventilation, otherwise condensation will lead to damage to the rafters, sheathing and insulating layer.
The nodes connecting the elements of the rafter group perform the function of providing rigid and durable fastening of the parts. Increased demands are placed on the quality of assembly of units, since in these connections there is a uniform distribution of load with load-bearing elements for tie rods, floor beams and mauerlat. The main types of connections that are used when installing rafters include the following components:
There are also particularly complex connections, for example, the junction of the diagonal rafters of a hip roof to the purlin and Mauerlat, or the sloping roof junction, where five parts of the rafter system are connected.
When assembling a sloping roof Special attention should be given to the transition of hanging rafters to layered rafters, since they connect five load-bearing elements at once
Let's look at the attachment point for rafters, racks, purlins and tie-downs using the example of a broken line mansard roof. In it, a vertical post is connected using a tie-in to a horizontal purlin and a tie; then a lower rafter leg is mounted to them, which rests on the tie using a tie-in and a metal bracket. Then the upper truss is fastened with ridge ties and is also cut into the tie and fixed to the bracket. In other components of the rafter system, which are used on various types of roofs, the same principles of connecting parts are used. Nails, self-tapping screws, bolts, perforated metal strips and corners of various designs are used as fastening elements.
Before starting the construction of the rafter system, it is necessary to carry out preparatory measures to ensure effective and quick assembly. Need to create safe conditions to carry out work, prepare a place for cutting and making templates, and also ensure the availability of lumber and fasteners. During the installation process, working drawings and the following tools will be required:
Before assembly, it is necessary to make templates of the same type of elements of the rafter system and make sure that they are well connected and fit well at the installation site.
Rafter trusses must be made according to a single template, and this can be done both on the ground and directly at the work site
The final stage preparatory work involves cutting lumber to size, impregnating the elements with fire-retardant and antiseptic compounds and allowing natural drying for at least 24 hours.
In the absence of design documentation for the roof, it is important to select in advance methods for attaching the rafter legs in the ridge and eaves parts, as well as Constructive decisions for connecting parts in various docking and other units.
The rafters are fastened to the floor beams or tightened in the lower part different ways depending on the complexity of the truss and the length, and therefore the weight, of the rafter legs. Rafters with a length of less than 4 m and a cross-section of 50X100 mm are sufficient to be fastened to the beams with a plank assembly or with the help of metal plates, cutting the beam at the required angle and using nails.
The choice of method of attaching the rafter legs to the mauerlat or floor beams depends on the angle of inclination of the slopes, the weight and length of the rafters, as well as on the expected external load
For large lengths and weights of rafter legs and expected snow and wind loads, the connection must be made with a frontal notch, single or double tooth. In this case, sub-beam pads are used to ensure a tight fit of the threaded rods. Before installation, it is necessary to create templates that will ensure correct cutting of materials at the cutting unit and perfect fit of the elements. To avoid chipping at the edges of the floor beam, it is necessary to cut to a depth of at least 2 cm and at a distance of 1.5 h from the edge of the beam (where h is the height of the beam).
It is important that the holes for the threaded rods are located at an angle of 90° to the upper plane of the rafters, as this will ensure a tight fit and reliable fastening of the parts to each other without displacement or distortion.
During the assembly of the rafter system, it is necessary to join elements with different angles of inclination. To mark cuts, notches and corner joints, construction levels and goniometer tools are used, and in the mass production of similar parts, templates are made. Cuts on the rafters can be made in next sequence.
Places for cuts are marked in several stages using a construction pencil and a goniometer tool.
Diagonal rafters or rafters come to the joint at different angles in two planes; in this case, using a level, the vertical angle of the joint is marked, and then the desired angle of abutment is fixed with a small tool and transferred to the part.
According to the author of the article, cutting material according to a single sample is not an unnecessary operation, since the time lost on making templates is more than compensated for in the installation process, which is significantly faster and becomes more rational and of higher quality. You need to pay attention to the good condition of the goniometer tool and use only proven specimens.
Many owners, in order to save money, install the roof of their house themselves. If you have some construction experience, this decision is completely justified, since even complex roofs can be assembled with your own hands, having project documentation. In the absence of a project, you need to make a drawing of the future structure yourself with the main parameters and dimensions of the elements of the rafter system.
Blanks for roof trusses can be collected on the ground or directly on the roof. Usually a triangle is made from two side beams and a bottom tie; all other elements are mounted after installing the truss in a vertical position. Each structure must be made according to a template made in advance and tested at the installation site. If the structural elements are significant in length and weight, assembly is carried out in stages.
Installation is carried out in the following sequence.
In houses made of concrete or building blocks, the Mauerlat is installed on studs embedded in an armored belt, in wooden buildings its role is usually played by the last crown of the wall
Roof trusses on the gables are installed first
Guide cords are stretched between the trusses installed on the gables to control the correct position of the intermediate elements
After installing all trusses, horizontal purlins and additional reinforcing elements are installed
Installation of a waterproofing film, counter-batten and sheathing completes the assembly of the rafter system
Experience shows that when the length of rafters is more than 6 m, they need to be built up at the joints using a tenon, double-sided overlays and using threaded rods or bolts installed in increments of 15 to 20 cm. The joint must be reinforced with additional posts or struts. In 2010, using the specified technology, the author installed a roof with a length of rafter legs of more than eight meters; to date, no deflections or other changes in shape have been found on the slopes.
Complex roofs are installed starting from the main supporting structures on which the rafter system is based. Then ordinary and diagonal rafter legs, extensions and auxiliary elements are installed. In conclusion, different types of fragments are joined together into a single structure.
According to the author of this article, who installed three roofs of varying complexity with his own hands, the installation of the rafter system can and should be done by yourself. The first roof was cut and assembled according to the drawing in four days, and on the fifth and sixth days the waterproofing, sheathing, fascia boards and roofing material were installed. The second roof took three and a half days, and the third was erected in two days. With increasing skill and with proper planning of work, the installation of the rafter system is significantly accelerated. If you have construction experience, then installing a roof with the proper quality is not difficult at all. If difficulties arise, it is necessary to involve design engineers or professional builders for consultation who will help in a difficult situation.
We considered options for assembling the rafter system at the junction with pipes, on top of old roofs, at the points adjacent to the Mauerlat, as well as in the case of complex rafter structures. Along the way, we studied some ways to connect elements of trusses and slopes. You can assemble the roof with your own hands, it is important to strictly follow step by step instructions and strictly follow safety precautions, then success will be ensured.
Installing rafters, like creating the entire roof, is a very responsible process. Taking into account that the base of the roof can be fixed to the wall using available means for lifting, subsequent work on its creation, which includes the installation of rafters, will be impossible without the installation of scaffolding, which also includes mobile structures. Scaffolding is used to lift the desired height materials; in addition, they can be used as a working platform for humans and a place for laying building materials.
Construction of the rafter system.
Installing rafters with your own hands may seem very labor-intensive, but if you follow all the tips and do them correctly, the process will be fun. If you are building a house, then you must use at least 3 scaffolds, in any case their number should not be less than 2. For work, it is better to make mobile scaffolding, as they are very convenient. The installation of rafters should begin only after all safety issues have been resolved; in no case should this be neglected, since health is more important than the speed of construction.
Types of rafter systems.
If the house does not have an internal load-bearing wall, that is, there is no additional support, and the construction legs rest only on the outer walls of the house, in this case it is necessary to use hanging rafters.
What are rafters? Translated from Old Russian, this is a structure for supporting a gable roof. And the rafter legs are inclined, with the help of which the roof slope is formed. Rafter legs are usually connected by “headstocks” or “fillies”, which are made vertically. The tie is a horizontal beam, with its help the rafter legs are connected.
Roof structures usually contain the following components:
Schemes of layered rafters and their application.
A triangle is the optimal shape of a roof truss. This design has the greatest rigidity.
Despite the many possible roof shapes, two types of rafters are usually used:
Figure 1. Installation of rafters.
The first case is used subject to the presence of internal load-bearing elements in the building structure. At the same time, the rafter legs have an emphasis not only on external walls, but also on internal columns or supports. Racks are used to transfer the load. Figure 1 shows rafter installation diagrams.
The hanging structure has support only on the outer walls, and at the ridge the rafters rest on each other. Hanging rafters are used in the absence of intermediate supports; the span width is less than 12 m. A design feature is a high thrust load; special tie-downs are used to reduce it. The legs of such a rafter system should be strengthened with the help of struts, which will also reduce the pressure on the load-bearing walls.
Walls made of brick or stone require the installation of a Mauerlat. Mauerlat is a wooden beam, which usually has a cross-section of 150x150 mm and is secured with special pins. These studs must be embedded in the wall in advance. A waterproofing layer must be laid under the Mauerlat.
For work you will need the following tools:
Diagram and installation of hanging rafters.
To install the rafters, you need to take a beam, the length of which will be 6 m and the cross-section 50x200 mm. It should be noted that if suddenly the cross-section is small, then after some time such a structure may sag. Based on the case described above, the roof slope, namely its angle, should be equal to 33 º. The next step in installing the rafters is that, using scaffolding, you need to lift 2 beams and connect them at the top.
Knots of layered rafters.
Installation of a gable roof.
In the case under consideration, due to the large distance between the load-bearing walls, where the width of the house itself is about 11 m, the tie will consist not of one beam, but of several boards interconnected. Such a tightening, made of several boards, will help solve several problems at once:
For the required length, 4 and 6 m boards were cut, after which they were fastened with nails, twisted with nuts and studs with rafter legs.
You need to keep the distance between the puffs under constant control. It should be the same as that between the rafter legs.
To do this, you need to use narrow boards, as in the case of adjusting the distance of the rafter pairs at the ridge, which are marked and correspond to the markings on the mauerlat. You must always keep your distance under control!
In addition to all this, the tie and the ridge were connected by another board. Considering the fact that there is no retaining wall, the tie will simply bend, unable to withstand its own weight. To avoid such troubles, the tie together with the ridge of the rafter pair is connected by a “headstock”. All the above actions must be done with each rafter pair.
For a good roof, it is very important that every step in its creation goes perfectly. The basis of the entire roof structure is the rafter system, the configuration of which determines the type of upper part of the building. There are different types of such systems, among which you need to choose the most suitable one for yourself, because the functionality and quality of the entire roof depends on the correctness of your choice.
The construction of the roof during the construction of a building is of significant importance. And in order for the roof to be strong enough, special attention is paid to load-bearing systems, which are divided into:
The roof is a rather complex structure consisting of various parts. The main requirement for a roof is - this is the ability to protect a structure from all kinds of weather conditions and withstand different loads.
The main loads of the roof fall on the rafter system, so it is very important to select the right materials, calculate everything correctly and carry out installation in accordance with the technology.
Hanging rafters are intended for buildings in which there are no permanent partitions inside, and the distance between the common load-bearing and side walls is no more than 10 meters. The roof structure in this embodiment rests on the main walls of the building, but because of this it is exposed to high loads. To make the tension a little weaker, additional parts (tightenings or crossbars) are used that fasten the truss in a horizontal position.
Depending on the span length, various reinforcing elements are used in the construction of hanging raftersThe bottom ties are connected at the base of the rafters and can be used as beams for attic floor, and they must be laid on the Mauerlat. To make hanging rafters, a board with a cross-section of 50x200 mm is usually taken, but each individual building needs its own specific calculations.
Sequence of actions for installing hanging rafters:
Layered rafters are mainly installed in those buildings where there are load-bearing partitions. They are much easier to install than a hanging system, since strong load-bearing walls located inside the house provide reliable support for the rafters. In addition, this system requires a minimum amount of building materials.
The ridge board in this case serves as a reference point. Such a roofing system is installed in one of the three options:
To secure the rafters at the bottom of the roof, it is necessary to use sliding fasteners, which relieve the load-bearing partitions from additional stress. In this case, the rafters are not fixed very tightly, so that when the building shrinks, they can move without overloading the roof structure.
But in some cases, you can use a spacer system that is tightly attached to the Mauerlat below. Struts and ties are installed in the structure to reduce the load on the walls. This method is called complex because it combines elements of two systems.
This roofing system is used mainly for the construction of private buildings, so it is worth mentioning the installation work, which is carried out in the following sequence:
Installation work Installation of a layered system should begin with laying boards on the floor beams. This device will help you carry out work comfortably and safely.
Combined rafters have in their design elements made of layered and hanging systems. They are used in the manufacture mansard roof. The walls of the rooms on the second floor are made up of vertical posts, which act as a fulcrum for the rafter beams.
Horizontal bars, which were installed on top of the racks, perform two functions: for the upper slopes they are the Mauerlat, and for the side ones - ridge beam. Some part of the rafter system, which is connected at the top of the ends of the racks, simultaneously becomes a tightening for the upper elements and a crossbar for the slopes located on the sides.
The combined roof uses fragments of layered and hanging rafter systems To increase the strength of the structure, it is necessary to install struts that secure the rafters and vertical roof posts. Making combined rafters is a little more difficult than other systems, but the labor intensity of the work is offset by an increase in the load-bearing characteristics of the roof and the presence of a full-fledged room under the roof.
In the design of a hip roof, layered rafters are used. For an envelope roof, a rafter system is erected, similar to an attic. In the construction of broken roofs, at the joints there are special rafters that support the valleys. Multi-gable roofs consist of several different rafter systems, combined into one. In the rafter system of an attic roof, one and the same element can be both a mauerlat and a ridge
The rafter system is made of coniferous wood. You can use boards or timber that are treated with antiseptic substances before installation. Fasteners can be as follows:
When starting to install the rafters, the level of the floors and load-bearing walls is raised, after which waterproofing is laid. The rafter structure is necessary to prevent deformation of the rafters. The supporting elements that give the rafter system stability can be:
Insulation of the roof is necessary, but for this you should choose a material for hydro-, heat- and vapor barrier. Installation is carried out layer by layer and only in the sequence in which it is necessary: initially steam-, then heat- and finally moisture-proofing material.
Before laying the roof covering, the necessary protective materials are installed in compliance with the established ventilation gaps To ensure long-term operation of the rafter system, the necessary air circulation is arranged by installing ventilation holes. To prevent leaks, “collars” are made near the holes to prevent water from penetrating under the roof.
The Mauerlat is the foundation of the roof, so you should treat it responsibly. Otherwise, roof repairs will be inevitable in the future. Sequence of work:
The Mauerlat is attached to the walls of the building along the entire perimeter, and the fastenings must be located in close proximity to the inside of the wall. Outside the house, the wooden part is protected by a slight projection of the wall. The mounting location is also initially determined.
The Mauerlat can be attached to the wall in the following ways:
All options for attaching the roof rafter system to the Mauerlat can be divided into the following types:
The most common option for attaching rafters to the ridge is a butt connection:
In the construction industry, various options for rafter splicing are used everywhere, and when choosing a specific technology, you need to pay attention to the design characteristics of the rafter system, which are influenced by:
Rafters can be spliced as follows:
Each type of rafter system has its own characteristics and is only suitable for a certain type of roof structure. Exactly from correct installation rafters depend not only on the reliability, but also on the strength of the roof, so this stage of work must be approached with maximum responsibility.
Construction of a reliable rafter system is one of the most difficult tasks when constructing the roof of a country house, cottage or garage. And yet, do not rush to give up - today we will refute the popular belief that such work is beyond the capabilities of a beginner. Knowing the rules for calculating, sawing and installing a roofing frame, you can build a roof no worse than specialists. In turn, we will try not only to talk about the structure, design and construction features of various types of rafter systems, but also share the secrets of experienced craftsmen.
Any, even the most shabby roof is based on a strong power frame called a rafter system. The rigidity of the roof, and therefore its ability to withstand even the strongest wind and snow loads, depends on how correctly this structure is installed.
The rafter system is the roof’s power frame, which absorbs all wind and snow loads
The best material for making rafters (trusses) is considered to be timber or a thick board made of coniferous wood. And there is an explanation for this - pine or spruce lumber is relatively light in weight, and the presence of natural resins makes it quite durable. Even if the timber has a slight residual moisture, it will not move when dried, which is no less important factor than ease of use and long service life.
Depending on the size of the roof, the supporting elements of the structure can have a cross-section from 50x100 mm to 200x200 mm or more. In addition, the length of the roof directly affects the number of rafters, because they are installed in small increments - from 60 cm to 1.2 m.
The main requirement for a wooden frame is the ability to withstand bending and torsion. For this reason, a triangle shape is best for timber frame trusses. Moreover, they can consist of several parts:
Additional elements of the rafter system make the roof frame more durable, rigid and stable
When choosing a roof frame design, it is important to find that golden mean that will allow you to obtain a strong and reliable structure with minimum costs. For this reason, you can deviate a little from the established canons, if the matter does not concern the rigidity of the entire structure. For example, it is quite possible to do without fillies, and form the eaves overhang using longer rafter legs. Or use not a solid Mauerlat, but pieces of timber laid only in the places where the rafter legs are attached - it all depends on the engineering ingenuity and experience of the roofer.
Depending on the roof structure and the purpose of the attic space wooden frame may consist of several types of rafters:
To make an informed choice, you need to understand the features of various types of rafter systems and know the strengths and weak sides each design.
Since the principle of fastening hanging rafters does not require additional support points, this design is used for buildings no more than 6 m wide. Installation of unsupported trusses involves fastening each pair of legs to opposite main walls, while their upper parts are fixed directly to the ridge girder.
A roof frame with hanging rafters transfers only vertical forces to the walls, therefore it has simpler attachment points to load-bearing walls
During operation, a force acts on the hanging rafters, tending to push the structure apart. To compensate for the bursting force, a crossbar made of wooden beam or metal profile pipe. If the attic space will be used for household purposes, then the upper lintel is secured as close to the ridge as possible, and the lower edges of the pairs of rafter legs are connected with ties. This scheme allows you to increase the useful height of the attic without at all reducing the strength of the frame. By the way, if the lower lintels are made from timber with a cross-section of more than 100x100 mm, then they can also be used as load-bearing beams. It is necessary to ensure reliable connection puffs and rafter legs, since significant expansion forces are also applied to the place of their attachment.
Layered rafters require the installation of at least one support, so they are used for buildings with internal load-bearing walls. Maximum length a single span should not exceed 6.5 m, otherwise the strength and rigidity of the roof frame will suffer. To increase the width of the roof, the rafter system is reinforced with intermediate supports. Even one additional post allows you to increase the width of the roof up to 12 m, and two - by more than 15 m.
A system with layered rafters is an ideal option when you need to build a large roof width
The stability of layered trusses can be increased by using a sub-rafter frame with purlins, racks and struts. In addition, this rafter system requires much lower lumber costs. The versatility, durability and cost-effectiveness have long been appreciated by both construction companies and individual developers, most often using them in their projects roofing structures with layered beams.
Today, the roofs of country houses amaze with the elegance of their design, whimsical shapes and variety of configurations. Such complex structures can be built in only one way - by combining both types of rafter systems in one frame.
The combination of layered and hanging trusses allows you to obtain a rafter system of any configuration
Even for the construction of not the most complex sloping roofs, both rafter systems are used at once. Right triangles located on the sides are layered rafter structures. And they are connected due to the upper tie, which at the same time plays the role of a tightening for the upper hanging rafters.
Since two types of roof frames are used in the construction of roofs, we will consider the installation technology of each structure separately. However, before starting construction work, it is necessary to study methods of fastening structural elements to each other.
It was already mentioned above that hanging rafters are most often used in the construction of small or undemanding buildings. In this case, a log house is an almost ideal option, since you can do without a mauerlat. The lower part of the rafter legs is attached to the upper crown or the edges protruding beyond the perimeter of the walls ceiling beams(matits). In the latter case, the tie must be moved upward - this will allow the timber to be placed over the finishing log and make the attic more comfortable.
To increase the height of the attic space, the tie should be installed as close to the top of the roof as possible
The geometry of the slopes depends on how well the beams for the rafters are prepared. A cord stretched between nails driven into the outer beams will help to level the supporting surfaces.
Before installing the trusses, the supporting surfaces are aligned with the cord
The method of fastening the rafters depends on many factors - the type of support beams, their cross-section, features of the roof overhang, etc.
In order to simplify the process of marking and installing the roof frame, use vertical slats installed along the center line of the roof
In order for the rafters to have the same dimensions and configuration, they are made according to a pre-made template. To make it, we suggest using the following instructions:
The simplest template allows you to get roof trusses of the same size and configuration
In order for the structure to successfully cope with thrust loads, the thrust tooth at the end of the rafter leg is inserted into a recess on the floor beam
Several methods are used to fasten trusses - it all depends on the type of support beams, the design of the roof frame and the cross-section of its elements
To attach the crossbar to the rafters, overlays from sections of inch boards are used
After the template is lowered to the ground, it is disassembled and cuts are made according to the applied markings. In addition, a separate pattern is constructed according to which the ends of the rafter legs will be cut. The manufacture and assembly of hanging rafters is most often done below, lifting the finished structures onto the roof. If the weight and dimensions of the assembled trusses do not allow them to be pulled up manually, then the assembly is carried out on site. In this case, the components of the rafter system are fixed with nails ranging in size from 100 to 200 mm.
In order to lift and install the trusses, you will need the help of at least one person. Trying and plumbing the rafters alone is an extremely difficult task - you will have to attach them to the struts more than once and descend from the roof many times to check the deviation from the vertical plane.
With the help of a rafter tooth, it is possible to obtain such a reliable connection that only one nail can be used for final fixation
When lifting the assembled rafters upward, first mount the outer structural elements, and then the central and intermediate ones. To strengthen the structure, a support is installed under each leg:
Having aligned the hanging rafters to the level, they are fixed with temporary spacers. After this, the lower ends of the beams are nailed to the matrix or floor beams.
Various temporary structures significantly simplify the process of installing rafters at level
There is no need to resort to newfangled methods of fixation using various corners and perforated plates. The reliable “old-fashioned” method of fastening using nails 200 mm long or construction staples will be much better both in terms of strength and reliability, and in cost. At this stage, you don’t have to worry about the structure looking flimsy.. After the remaining elements of the rafter system are installed and the sheathing is completed, the structure will acquire the necessary rigidity and stability.
The process of manufacturing and installing layered rafters is generally very similar to the construction of a suspended roof frame. The main difference is at the top point and is due to the fact that the tops of the layered beams rest on the ridge girder. In this case, the connection with the latter is performed in several ways:
If the design of the wooden frame provides for the support of trusses on the side purlin, then the rafters are connected end-to-end, and in the places adjacent to the purlin, recesses are made.
To fasten layered rafters, use nails, construction staples or linings made of wood and metal
To ensure structural strength, the notches should not be too deep. Experts recommend making recesses no more than a quarter of the thickness of the timber or a third of the width of the board.
Individual developers most often resort to installing rafters in the following way:
It is convenient to use a construction square for marking. After the scale is selected, the values of the slope rise and half the span are plotted on the sides of the right triangle. Thanks to this, it will be possible to obtain the slope angle of the slope without resorting to mathematical calculations.
To make rafters, we suggest using the most convenient method:
At first glance, this method is very tricky. However, even a quick glance at the instructions provided is enough to master it perfectly. Of course, you can set aside the necessary distances and make markings using a calculation method, but it will be much easier to get confused when calculating angles and distances.
It should be remembered that the cuts made in the rafter legs must be absolutely identical, otherwise the roof slope will be uneven. To do this, you can use a wooden block as a template. It is only important that its thickness does not exceed 1/3 of the thickness of the workpiece.
For the most common slope angles, there are templates, the configuration of which has already been calculated by professionals. By using one of these patterns, you can significantly simplify the task of marking the corners of notches.
Templates with marked notch angles allow you to simplify the process of making rafters
When choosing timber for large roof trusses, you have to look for a reasonable compromise between the length and thickness of the rafters. The reason for this is the features of the standard range of lumber, in which longer beams have an increased cross-section. On the other hand, their use is not always justified both technologically and due to the increased cost of the structure. The way out of this situation is to lengthen the rafter legs by splicing. The rigidity and mechanical strength timber, so the connection is carried out strictly according to a certain method.
The method of splicing with an oblique cut is that inclined cuts (cuts) are formed on the mating parts of the beams. They should be carried out especially carefully - after combining both parts of the beam, there should be no gaps left, otherwise deformation will appear at the junction.
When splicing with an oblique cut, there should be no gaps or gaps between the mating surfaces, which could weaken the rafter and cause its deformation.
When making cuts, leave a small transverse section with a height of at least 15% of the rafter thickness - the presence of the end part will make the connection more durable. To calculate the optimal length of an oblique cut, it is necessary to multiply the height of the beam at the cutting site by two. The truss is fastened with nails, clamps or bolted connections.
To lengthen the rafter using the joining (stitching) method, the edges of the boards are overlapped and a stand is installed in the center of the junction area. The elements are fastened using nails, which are driven in according to a certain pattern:
Connecting boards by joining allows you to do without additional pads, but requires the installation of additional support in the center of the junction area
In order for the beam to successfully cope with operational loads after joining, the length of the joining section (T) is calculated using the formula T = 0.42 × L, where L is the length of the overlapped span.
The connection by frontal extension is that the edges individual parts the rafters are carefully trimmed and butted together. For fastening, lumber linings with a thickness of at least 1/3 of the section of the main beam are used. The length of the overlays is determined by the formula L = 3 × h, where h is the width of the board.
When splicing with a frontal stop, a monolithic structure will be obtained only with the correct placement of fasteners
All parts are fixed using nails or bolted connections. In the first case, nails are driven in two parallel rows, trying to place the fasteners in a zigzag pattern. The threaded connection is made in a checkerboard pattern, determining the number of bolts depending on the length of the linings.
To build up a rafter leg, it is not at all necessary to use both parts of the same section. With a composite extension, a single element can be lengthened by using two boards that are sewn onto its side planes. The resulting gap is filled with scraps of lumber of length l = 2 × h in increments of L = 7 × h, where h, as before, is the thickness of the element being extended.
Composite extension of rafters allows you to attach crossbars, supports and other structural elements in the most convenient way
When starting to independently design and install a rafter system, be sure to consult with experienced roofers regarding the specifics of constructing roofs in your area. Perhaps their advice will save you from trouble and help you save time and money. In turn, we offer several recommendations that will help make the structure more reliable and durable:
Modern materials and technologies make it possible to build a roof of any configuration and purpose. Given such diversity, it is simply impossible to consider all options in detail within one article. However, based on the basic construction principles discussed here, you can easily cope with the most complex design. The main thing is to pay attention to detail, be attentive and careful in your work. And then the roof will not only be a reliable functional superstructure, but also a true decoration of your home.
Thanks to my varied hobbies, I write on various topics, but my favorites are engineering, technology and construction. Perhaps because I know many nuances in these areas not only theoretically, as a result of studying at a technical university and graduate school, but also with practical side, because I try to do everything with my own hands.
