Installing a gable roof is considered a very practical and correct solution when constructing a residential or commercial building. This option combines relative simplicity of execution and reliability, ease of maintenance and long term services. In this material we will talk about how to install the rafter system gable roof with your own hands, what are its varieties, and how to calculate the sizes of its individual elements. Our step-by-step instructions will help you deal with any complications that may arise during the work process.
A roof with two slopes has a whole list of advantages:
- ease of calculations;
- various options execution;
- saving materials;
- possibility of natural outflow of water;
- low probability of water leakage due to the integrity of the structure;
- possibility of arrangement attic space or attics;
- reliability and long service life;
- convenience of preventive repairs.
Types of gable roofs
Let's consider the main types of roofs with two slopes, the rafter system in which will differ slightly in design.
Symmetrical gable roof
This is the simplest gable roof, however, is the most reliable and in demand. Symmetrical slopes allow you to distribute the load on the Mauerlat and load-bearing walls evenly. In this case, the type and thickness of the insulating layer do not affect the choice roofing material. Thick rafter beams have a sufficient margin of safety, so they will not bend. In addition, spacers can be installed at your discretion.
Among the disadvantages of this option, one can note only that the angle of the slopes is too sharp, which makes it difficult to use. attic floor and creates “dead” zones that have no use.
Roof with two asymmetric slopes
If the angle of inclination of the slopes is made more than 45º, you can use some unused areas of space. It will even be possible to arrange a living space in the attic. However, some additional calculations will be required, since the load on the walls will become uneven.
Broken roof with external or internal fracture
This configuration makes it possible to place a spacious attic or attic under the roof. However, in this case, more complex engineering calculations will be required.
The design of rafters for arranging a roof with two slopes
The design of the gable roof truss system assumes the presence of the following components:
- Mauerlat. It is a durable beam made of oak, pine, larch or other strong wood, which is laid along the perimeter on the load-bearing walls of the building. The purpose of the Mauerlat is to evenly distribute the load. The cross-section of the bars is chosen based on their structure - solid or glued, as well as on the age of the building. The most commonly used beams are 100×100 or 150×150 mm.
- Rafters. The entire structure is created from such elements (read also: " "). Connecting at the top point, two rafters form a truss. They are made from logs or strong bars.
- Puff. This part serves to connect the rafters and ensure their rigidity.
- Runs. In those places where the rafter legs are joined, a ridge purlin is attached, onto which the ridge will subsequently be mounted. And with the help of side girders, the rafter frame is given additional strength. The expected load determines the size and number of such elements.
- Rafter stand. This is a vertical beam that partially takes on the weight of the roof. If the design of a gable roof is simple, then one such beam is placed in the center. A long span may require three bars - one in the center and two on the sides. If an asymmetrical roof is being erected, then the location of such a beam is determined by the length of the rafter legs. Under the rafters for a sloping roof, racks are placed on the sides to free up space for movement. Beams are placed in the center and sides if there are two rooms.
- Struts. These are the supports for the rack. If significant winds and precipitation are expected in winter, longitudinal as well as diagonal racks are installed.
- Sill. The rafter stand rests on it, and the struts are also attached.
- Lathing. The selected roofing material is attached to it, and you can also move on it during work. Fix the sheathing perpendicular to the rafters. Please note that the lathing allows you to evenly distribute the mass of roofing material throughout the rafter system.
The installation diagram of the gable roof truss system will significantly facilitate all construction work. How such a roof scheme will look depends on the type of roof.
Please note that the material for the rafter system must be of the highest quality, treated with fire retardants and antiseptics. There should be no knots or cracks on the beams for rafters, mauerlat and racks. Only a small number of knots firmly seated in the wood are allowed on the sheathing.
Calculation of frame elements for a gable roof
Laying Mauerlat on walls
This element is mounted on the load-bearing wall along its entire length. If we are talking about a log house, then the upper crown can serve as a mauerlat. For buildings made of aerated concrete or brick, you will need a Mauerlat equal to the length of the wall. Sometimes this part can be laid between the rafters.
If there is insufficient length of material for the Mauerlat, several pieces can be spliced together. In this case, the edges are filed at 90º and joined using bolts - wire, dowels or nails are not suitable.
There are two ways to lay a mauerlat on top of a load-bearing wall:
- symmetrical in the center;
- with a shift in the desired direction.
The installation of the Mauerlat is carried out on a pre-laid waterproofing layer of roofing felt. This will protect the wood from rotting.
It is worth taking the process of attaching the Mauerlat responsibly, since in strong winds it must withstand a particularly large load.
The following consumables can be used as fastenings for the Mauerlat:
- Anchors that are indispensable for monolithic materials.
- Wooden dowels. These parts are used in houses made of timber and logs, although they require additional fastenings.
- Staples.
- Reinforcement or special studs. This option is preferable for buildings made of foam or aerated concrete.
- Knitting or steel wire is an auxiliary fastening element that is almost always used.
Assembling trusses or rafter pairs
Trusses can be assembled using one of the following methods:
- The beams for the rafters are assembled and attached directly to the roof of the building. This process is quite labor-intensive, since all measurements, trimming and coupling of beams will have to be done at height. However, you can do it on your own, without the involvement of technology.
- Trusses or rafter pairs can be fixed to the ground, and then the finished elements can be raised to the roof of the building. On the one hand, this simplifies the process of installing the rafters, and on the other, due to the large weight of the structure, lifting it to the top will require special equipment.
Please note that you should start assembling rafter pairs only after marking has been applied. And if you make a template in advance, for which you take two boards equal to the length of the rafters and connect them together, then all the pairs will turn out to be absolutely identical.
Installation of rafters
After assembly and lifting to a height, the gable roof rafters are installed wooden house. To fix them on the Mauerlat, cuts are made at the bottom of the rafters. The first to install are two trusses at opposite ends of the roof.
After this, a rope is pulled between the starting pairs, along which all other trusses will be aligned and the ridge will be installed.
Now you can mount the remaining pairs, observing the calculated step between them. In cases where the pairs are assembled directly on the roof, a ridge girder is attached between the two end trusses. The rafters are subsequently installed on it.
The procedure for installing rafter halves may differ according to the opinions of professionals. Some people prefer to lay the beams in a checkerboard pattern so as not to overload the foundation and walls during work. Others are inclined to install pairs of rafters in series. Be that as it may, rafter legs may need supports and posts - it all depends on the size of the roof and the shape of the trusses.
Skate attachment
A ridge is an element that is formed by attaching rafters at the highest point. As soon as all the parts of the rafter system for a gable roof have been installed, all structural elements should be thoroughly secured.
Installation of sheathing
The presence of sheathing is mandatory when constructing any roof. It not only supports the roofing material and allows it to be securely fastened, but also makes it possible to move along the roof while working.
The distance between individual boards is selected based on the type of roofing material:
- soft roofing is laid on a continuous sheathing without gaps;
- for metal tiles you need lathing in increments of 35 cm (between the two bottom rows - 30 cm);
- slate and corrugated sheeting can be laid on the sheathing in increments of 44 cm.
Results
Thus, in order to assemble a rafter system for a roof with two slopes, many nuances should be taken into account and any possible complications should be provided for. We hope that our tips will help you cope with this difficult task and create a high-quality and durable roof for your home.
When designing any residential building, architects pay special attention to the roof, since it performs not one, but several functions at once, depending on its design features. It must be said that not all future homeowners are satisfied with an ordinary gable roof, although it can be called the most reliable, since it has only two pitched planes and one joint between them. Many are attracted to more complex designs, which add special attractiveness and originality to the building. Other, more practical homeowners prefer attic structures, which can simultaneously serve as a roof and a second floor.
The basis of any roof is an individual rafter system, which has its own design features. It will be much easier to choose the right roof frame if you figure out which ones in advance. types and diagrams of rafter systems used in construction practice. After receiving such information, it will become more clear how difficult such structures are to install. This is especially important to know if you plan to build the roof frame yourself.
Main functional tasks of rafter systems
When arranging pitched roof structures, the rafter system serves as a frame for covering and for holding materials “ roofing pie" With proper installation of the frame structure, the necessary conditions will be created for the correct and non-insulated types of roofs, protecting the walls and interior of the house from various atmospheric influences.
The roof structure is also always the final architectural element of the exterior design of a building, supporting its stylistic direction with its appearance. However, the design features of rafter systems must first of all meet the strength and reliability requirements that the roof must meet, and only then the aesthetic criteria.
The frame of the rafter system forms the configuration and angle of inclination of the roof. These parameters largely depend on natural factors characteristic of a particular region, as well as on the desires and capabilities of the homeowner:
- Precipitation in different periods of the year.
- The direction and average speed of the wind in the area where the building will be erected.
- Plans for the use of space under the roof - arranging residential or non-residential premises, or using it only as an air gap for thermal insulation of the rooms below.
- Type of planned roofing material.
- Financial capabilities of the homeowner.
Atmospheric precipitation and the strength of wind currents place a very sensitive load on the roof structure. For example, in regions with heavy snowfall, you should not choose a rafter system with a small slope angle, since snow masses will linger on their surface, which can lead to deformation of the frame or roofing or to leaks.
If the area where the construction will take place is famous for its winds, then it is better to choose a design with slight slope ramp so that occasional sudden gusts do not disrupt individual elements roofs and roofs.
Main elements of roof structure
Parts and components of rafter systems
Depending on the chosen type of rafter system, the structural elements used can vary significantly, however, there are parts that are present in both simple and complex systems roofs
The main elements of a pitched roof rafter system include:
- Rafter legs that form the roof slopes.
- - a wooden beam fixed to the walls of the house and used to fix the lower part of the rafter legs on it.
- A ridge is the junction of the frames of two slopes. It is usually the highest horizontal line of the roof and serves as the support to which the rafters are anchored. The ridge can be formed by rafters fastened together at a certain angle or fixed on a ridge board (purlin).
- Sheathing is slats or beams mounted on rafters at a certain pitch and serving as the basis for laying the selected roofing material.
- Supporting elements, which include beams, purlins, racks, struts, ties and other parts, serve to increase the rigidity of the rafter legs, support the ridge, and connect individual parts into an overall structure.
In addition to the mentioned design details, it may also include other elements, the functions of which are aimed at strengthening the system and optimally distributing roof loads on the walls of the building.
The rafter system is divided into several categories depending on different features of its design.
Attic space
Before we look at different types roofs, it is worth understanding what the attic space can be, since many owners successfully use it as utility and full-fledged residential premises.
design pitched roofs can be divided into non-attic and attic. The first option is called that way because the space under the roof has small height and is used only as an air layer insulating the top of the building. Such systems usually include or have several slopes, but located at a very slight angle.
An attic structure that has a sufficiently high ridge height can be used in different ways, be insulated and not insulated. Such options include an attic or gable option. If you choose a roof with a high ridge, then it is imperative to take into account the wind loads in the region where the house is built.
Slope slope
To determine the optimal slope of the roof slopes of a future residential building, first of all you need to take a closer look at the low-rise neighboring houses that have already been built. If they have been standing for more than one year and can withstand wind loads, then their design can safely be taken as a basis. In the same case, when the owners set a goal to create an exclusive original project, unlike the neighboring buildings, it is necessary to familiarize yourself with the design and operational features of various rafter systems and make the appropriate calculations.
It should be taken into account that the change in the tangent and normal values of the wind force depends on how large the slope of the roof slopes is - the steeper the angle of inclination, the greater the importance of normal forces and the less tangent forces. If the roof is flat, then the structure is more affected by the tangential wind load, since the lifting force increases on the leeward side and decreases on the windward side.
Winter snow load should also be taken into account when designing the roof. Usually this factor is considered in conjunction with the wind load, since on the windward side the snow load will be much lower than on the leeward slope. In addition, there are places on the slopes where snow will certainly accumulate, putting a large load on this area, so it should be reinforced with additional rafters.
The slope of roof slopes can vary from 10 to 60 degrees, and it should be chosen not only taking into account the consolidated external load, but also depending on the roofing that is planned to be used. This factor is taken into account because roofing materials differ in their weight; to secure them, a different number of elements of the rafter system is required, which means that the load on the walls of the house will also vary, and how large it will be also depends on the angle of the roof. Of no small importance are the characteristics of each coating in terms of resistance to moisture penetration - many roofing materials in any case require one or another slope to ensure the free drainage of storm water or melting snow. In addition, when choosing a roof slope, you need to think in advance about how the cleaning process will be carried out and repair work on the roof.
When planning a particular angle of the roof slopes, you need to know that the fewer joints between the sheets of roofing, and the more airtight they are, the less you can make the slope of the slope, of course, if you are not planning to arrange a residential or utility room in the attic space.
If a material consisting of small elements is used to cover the roof, for example, ceramic tiles, then the slope of the slopes must be made steep enough so that water never lingers on the surface.
Considering the weight of the roofing material, you need to know that the heavier the covering, the larger the angle of the slopes should be, since in this case the load will be correctly distributed over the rafter system and load-bearing walls.
The following materials can be used to cover the roof: or profile sheet, galvanized steel, corrugated asbestos concrete and bitumen-fiber sheets, cement and ceramic tiles, roofing felt, soft roofing and other roofing materials. The illustration below shows the permissible slope angles for various types of roofing coverings.
Basic designs of rafter systems
First of all, it is worth considering the basic types of rafter systems relative to the location of the walls of the house, which are used in all roof structures. Basic options are divided into layered, hanging, and combined, that is, including elements of both the first and second types of systems in its design.
fastenings for rafters
Layered system
In buildings where internal load-bearing walls are provided, a layered rafter system is often installed. It is much easier to install than a hanging one, since the internal load-bearing walls provide reliable support for its elements, and in addition, this structure will require less materials.
For rafters in this system, the defining reference point is the ridge board, on which they are fixed. The non-thrust type of layered system can be arranged in three options:
- In the first option, the upper side of the rafters is fixed on a ridge support, called a sliding one, and their lower side is fixed by cutting to the mauerlat. Additionally, the rafters in the lower part are fixed to the wall using wire or staples.
- In the second case, the rafters in the upper part are cut at a certain angle and connected to each other using special metal plates.
The lower edge of the rafter legs is attached to the Mauerlat with movable fasteners.
- In the third option, the rafters are rigidly fastened in the upper part with bars or treated boards located horizontally, parallel to each other on both sides of rafters connected at an angle, and a ridge girder is clamped between them.
In the lower part, sliding fasteners are used to secure the rafters, just as in the previous case.
It is necessary to explain why sliding fasteners are often used to secure rafters to the mauerlat. The fact is that they are able to relieve load-bearing walls from excessive stress, since the rafters are not rigidly fixed, and when the structure shrinks, they have the ability to move without deforming general design roofing system.
This type of fastening is used only in layered systems, which also distinguishes them from the hanging version.
However, in some cases, for layered rafters, a spacer system is used, in which the lower end of the rafters is rigidly fixed to the Mauerlat, and to relieve the load from the walls, tie-downs and struts are built into the structure. This option is called complex, as it includes elements of a layered and hanging system.
The basis of beautiful and reliable roof is robust design rafter system. It is important to install it so that it serves long 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 pitch of the rafters and the design of the joints of the individual elements of the 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.
Construction of the rafter system
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 on the purpose of the attic space. It is mounted on a Mauerlat fixed to the perimeter walls of the house and consists of the following elements:
- floor beam or tie - a horizontal beam resting on the mauerlat;
- hanging or layered rafter legs, which are attached in the lower part to a tie or mauerlat, and in the upper part they are connected and form a ridge;
- purlin - a beam connecting the trusses of the rafter group;
Depending on the type and size of the roof, rafter systems can be layered, suspended or combined, but their main elements are largely repeated
- racks, crossbars, struts and tie-downs are auxiliary elements that are necessary to give strength to the rafters and the entire roof structure;
- sprigs - used on hip roofs and are shortened rafters;
The diagonal rafters of the hip roof are fastened with flanges and trusses to ensure even distribution of the load
- trusses - designed to give strength to the diagonal rafters of a hip roof;
- fillies - used to lengthen rafter legs and spouts and form a cornice overhang;
- frontal boards - attached to vertically cut rafters or fillets and are used for mounting drip edges, wind strips and drainage system brackets;
- counter-lattice - mounted on the rafters and used to create a ventilation gap between the waterproofing layer and the roofing material;
- sheathing - stuffed perpendicular to the counter-lattice and used to fasten the roofing material.
More complex types of 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.
Rafter options
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 used to assemble different types of roofs. Let's consider the most popular options for installing pitched systems of various configurations.
Shed roofs are used in construction 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 sheet roofing material is used, the sheathing pitch should be reduced to 10 cm, the overlap should be increased to 15 cm, and the joints of the sheets should be additionally sealed.
Gable and broken attic structures
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 are distinguished by the largest volume of built-in attic; the frame system here is represented by a combination of hanging and layered rafters with different slope angles.
Gable rafter systems are characterized by simplicity of design, high strength and minimal consumption building materials, such roofs are often used in budget dacha construction.
Four-slope rafter systems
Four-pitched roofs are formed by two trapezoidal and two triangular slopes and have complex design 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.
Construction of the supporting frame of hip roofs
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.
The rafters of the tent system converge at the top at one point and are fastened to each other with ties; in the lower part they are fixed with the help of cuts
Hip roofs give the building a unique appearance, but are characterized by increased consumption of roofing and lumber. Most often they are used on outbuildings, gazebos, and in a truncated version - as roofs for bay windows.
Multi-gable rafter groups
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 rafter system of a multi-gable roof forms eight triangular slopes, at the junction of which valleys are located
Roofs of this type are designed to provide natural lighting to the 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.
Installing a roof over an old covering
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 to dismantle the old roof, you can lay a new covering directly on top old roof. To do this, you need to know exactly where the rafter beams with counter-lattice and sheathing boards go.
In my 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.
Video: replacing the roof without dismantling the old one
The pitch of the rafter legs when installing the 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:
- roof type;
- the length of the slopes and the angle of inclination;
- type of roofing material;
- rafter section;
- expected wind and snow load.
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.
Table: selection of length, pitch and section of rafters
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 step has an indirect influence on the choice of steps. insulation material. For example, the standard width of the 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.
Installation of complex roof structures
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 tent element. Even a conventional multi-gable roof with gables on 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”. TO design work Professional specialists should be involved, 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 the selection of 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 mounted 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.
Video: installation of complex roofs
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 assembly quality of the units, since in these connections the load is evenly distributed from the load-bearing elements to the 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 paid 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 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 that are used on various types roofs, the same principles of connecting parts are used. As fastening elements Nails, self-tapping screws, bolts, perforated metal strips and angles of various designs are used.
Installation of the rafter system
Before starting the construction of the rafter system, it is necessary to carry out preparatory measures to ensure efficient and quick assembly. It is necessary to create safe conditions for 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:
- protractor (small), level, construction pencil, cord;
- chain saw for rough cutting and trimming;
- circular saw, jigsaw;
- electric drill, screwdriver;
- hammer, chisels.
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.
Fastening the rafters to the floor beams or tightening them in the lower part is done in various 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.
How to properly make cuts on rafter beams
During the assembly of the rafter system, it is necessary to join elements with different angles of inclination. For marking cuts, cuts and corner connections 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 the following sequence.
- The timber is placed on the mauerlat and ridge girder; vertical lines and the exact position of the tie-in are marked according to the level.
- The angle of inclination is fixed on the cutter, and the dimensions of the insert are measured with a tape measure or square.
- Using a square and a protractor, the measurement results are transferred to the workpieces, after which the cutting angles and dimensions of the notch tenons are marked.
- The necessary cuts are made on the marked workpiece.
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, use a level to mark vertical angle joint, and then the desired abutment angle 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.
Do-it-yourself rafter system installation step by step
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 it is quite possible to assemble it 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.
- On threaded rods reinforced belt or the last crown of walls along the perimeter are mounted solid beams Mauerlat to ensure uniform distribution of the load from the rafter system to the walls of the building.
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
- Floor beams or tightenings are attached to the Mauerlat using brackets, metal corners or bolts. When using long and massive rafter legs, vertical posts are mounted in the middle of the floor beams, and ridge purlins are attached to them.
- The first blank for the truss is installed from one edge of the roof (on the gable). An insert is made on the rafter legs, and they are attached to the mauerlat, floor beams and ridge girder.
Roof trusses on the gables are installed first
- The second blank is installed in place of another pediment.
- Both trusses are fixed in a vertical position, which is controlled by a level or plumb line.
- Guide cords are stretched between the installed trusses.
Guide cords are stretched between the trusses installed on the gables to control the correct position of the intermediate elements
- Intermediate rafter structures are installed with the selected pitch. All of them must be aligned vertically and along the stretched cords.
- A ridge and additional horizontal purlins are installed (if they are provided for in the design).
- The rafters are reinforced with crossbars, racks and other elements provided for by the project.
After installing all trusses, horizontal purlins and additional reinforcing elements are installed
- On hip roofs, row rafters are first installed, supported by a ridge girder and a mauerlat, and then diagonal rafters and soffits are installed alternately.
- With the help of gable and front boards, overhangs are formed that protect the walls of the building from precipitation.
- A waterproofing film with a sag of no more than 20 mm and counter-lattice bars are attached to the rafters, which ensure ventilation gap between waterproofing and roofing. Then a longitudinal sheathing is laid, which serves as the basis for the roofing.
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.
Video: design and installation of the rafter system
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.
The roof performs a number of important functions in creating decent living conditions, coupled with providing visual appeal. It is quite reasonable that it is considered a significant structural component of the building. The rafter frame is responsible for the formation of the roof structure. It must withstand the load, determine the configuration and be combined with the exterior of the house.
Only a well-chosen roof base can cope with the tasks at hand. Making the right choice is much easier if the owner country estate All possible types and schemes of rafter systems are known, the specifics of their construction and scope of application are clear.
The list of roof responsibilities goes beyond weather protection. Although confronting weather phenomena in a specific area, without a doubt, tops an impressive list of tasks.
The roof, as the final architectural touch, complements the appearance of the building, gives it a stylistic direction or completely deprives it. The rafter system as the basis of the roof structure must meet the entire range of technical and aesthetic requirements placed directly on the roof.
Factors in choosing the “backbone” of the roof
The rafter system is an indisputable accessory of pitched roofs, which:
- sets the configuration and steepness;
- holds the finishing coating and components of the roofing pie;
- creates conditions for the flawless operation of roofing system elements.
Choosing a roof ultimately comes down to determining the ideal version of the rafter system, which, in addition to the personal preferences of the home owner, is also influenced by such compelling factors as:
- The amount of winter and summer precipitation characteristic of the area in which construction is planned.
- The strength and direction with the speed of the winds prevailing in the region.
- The owner’s desire to use the space under the roof to organize utility or residential premises.
- Type of finishing roof covering.
- Financial capabilities of the owner.
Climatic data greatly influences the choice of roof and the design of the rafter system. In regions with abundant snowfall, it is not advisable to erect structures with a slight steepness, which contributes to the formation of snow deposits. In areas with gusty winds, on the contrary, streamlined and low-sloping shapes are preferred, which will be difficult to be torn off and carried away by a powerful weather phenomenon.
It is clear that the flat design is not suitable for the arrangement of useful premises in it. For those wishing to equip the space under the roof, there are rafter systems designed for construction in regions with varying degrees of wind loads.
If there is no need to use an attic, a roof of a complex or simple configuration can be built without it. There are a lot of options, including various combinations of basic versions, familiarization with which will give an idea of the essence of building a rafter system of any type.
In order not to suffer from guessing about the most rational shape and angle of inclination of a pitched roof, it is enough to take a closer look at the surrounding low-rise buildings.
The proven configuration can be safely taken as a basic option in order to adjust and modify it in accordance with the requirements of the future owner and the technical characteristics of the roofing. If you don’t want to copy your neighbors, you should familiarize yourself with the design and operational specifics of various rafter systems.
Basic options for rafter systems
A pitched roof can be simplistically represented as a set of slopes - planes along which atmospheric water “rolls”. The slopes are formed by the ribs of the rafter legs - the main elements of the rafter system. The classification of pitched roofs and their corresponding rafter systems is made depending on the number and configuration of the slopes. According to the indicated characteristics, their ranks include:
- Single-pitch. Roofs with one slope are installed mainly over utility buildings, extensions, and verandas. rest on two walls or two rows of racks. One of the walls or one row of supports must be higher than the other so that water can flow along the plane formed by the rafters without obstacles.
- Gable. Roofs with two rectangular slopes are most often found in domestic spaces. Rafter legs gable systems rest on two walls of a rectangular box of the house. In the classic version, the area of both slopes is equal, as is the height supporting walls. True, design solutions with slopes of different areas and supporting walls of different heights have become common.
- Hip. Otherwise called hipped, based on the number of pitched planes. Rafter legs hip system form a pair of trapezoidal and a pair of triangular slopes. The rafters of the trapezoidal components rest on the long walls of the box, and the triangular ones rest on the short end walls. In plan, the hip roof looks like a postal envelope. Looks impressive and can be used everywhere. The hipped category includes roofs with shortened triangular slopes, which are strongly recommended for construction in areas with high wind loads.
- Tent . A roof that consists of triangular slopes converging at one vertex. The minimum number of slopes is 4, the upper limit is unlimited. The rafters of the tent system rest on walls or supports of equal height. They prefer to erect tent structures over verandas and gazebos. Variations in the steepness of hipped roofs allow them to be installed in regions with any wind load.
- Broken. They are also called attic, because it is the broken technology that allows you to create the most spacious rooms under the roof. Rafter legs of broken structures are installed by analogy with gable systems, but are constructed in two tiers. The lower rafters rest on the walls of the box being equipped, the upper ones on the supports of the lower tier of the rafter frame.
The listed types of roofs and rafter structures have numerous variations on the pitched theme. For example, a gable roof may have a regular gable gable at one end and a hip on the opposite side, or it may be supplemented single-pitch construction above the porch in the middle of the main slope.
When two gable systems are combined crosswise, a composite roof with four wooden gables or stone gables is formed. In the arrangement of boxes with a T-shaped or L-shaped configuration, several types of rafter systems are often involved simultaneously. The upper tier of a sloping roof can be built using hip technology.
A truss structure of any complexity can be represented as a set simple shapes. To make it easier to understand the intricacies of construction, it is better to conditionally divide the object into separate blocks. They will tell you how to build each of the parts and connect the basic types of rafter frames listed above to each other.
Overview of pitched rafter structures
In order to understand the abundant variety of structures and the possibilities of their layout, we will consider the main types of rafter systems and the corresponding diagrams.
Type #1 – lean-to rafter frame
Most shed roofs are classified as non-attic, because regardless of the steepness, the space they create under the roof is not large in volume. However, if you want to build a strictly horizontal ceiling, a ceiling separating the attic from the main rooms is still built.
The scheme depends on the size of the span to be covered with a single slope:
- If the distance between the upper and lower supports of the rafter leg is less than or equal to 4.5 m, additional struts and racks are not used.
- If the span is in the range from 4.5 m to 6 m, a bench is laid near the high wall. A strut is rested against it - a rafter leg that ensures the rigidity of the rafter closer to the top of the span.
- If a span of 6m to 9m is to be covered, the beams are laid on both sides and the rafter legs rest against both beams.
If it is necessary to cover a larger span, it is divided into sectors with the distances indicated above. At the border of adjacent sectors, racks for purlins are installed, and within the sector, beds and struts are installed according to the described rules. For construction in regions with high wind activity, single-pitch rafter structures are supplemented with diagonal wind braces from the inside.
In plan, the diagram of a single-pitch rafter frame resembles a series of parallel beams. A roof with one slope is not very beautiful, but it is very economical. Optimal angle slope from 4º to 12º, a greater slope is not prohibited.
It is advisable to equip structures with low slopes with continuous sheathing and waterproofing, which is not necessary for steep roofs. As finishing coating It is better to use corrugated sheets or roofing metal for low structures for arranging steeper structures.
Type #2 – rafter systems for gable roofs
Gable rafter frames are built on reinforced concrete floors and wooden beams, mainly with attics. The most common type of roof has a huge number of low and high, insulated and cold modifications.
Depending on the architectural and technical specifications object rafter legs used in the construction of gable roofs are divided into:
- Layered. These are rafters that have a strong support under the upper and lower heel. They are manufactured and installed like the rafters of pitched roofs. Layered rafter systems are constructed over boxes that have an internal load-bearing wall. It is needed as a supporting structure for the ridge girder. The role of a wall can be played by a number of supporting posts or columns. In the simplest layered scheme with a span of up to 5 m, the tops of the rafters rest on a purlin, which rests on a beam through support posts. Rigidity is provided by struts. Schemes for more substantial spans are equipped with contractions, headstocks and additional runs.
- Hanging. Hanging type rafters have only a lower support; their tops rest against each other. The elements of the hanging rafter frame are immediately made in the shape of a triangle, so you can dispense with the Mauerlat. In such cases, the function of the Mauerlat is trusted to the base of the triangle - a tightening used to compensate for the thrust on the roof from the weight of the snow, the roof and the system itself. Hanging technology is used in the arrangement of small boxes that do not have internal support for the ridge girder. If it is necessary to cover long-span structures, the hanging system is equipped with headstocks, struts, ties, etc.
Depending on the technical characteristics of the roof, the sheathing is arranged continuous or sparse. Low slopes up to 12º are completely covered with a waterproof carpet, high ones - only in places of possible leaks: along the eaves, ridge, valleys, around pipes and other roofing passages.
Type #3 – hip and half-hip system
Hip, or “envelope” roofs, differ from gable structures in that the place of vertical gable gables in their structures is occupied by inclined triangular slopes - hips. The central part of the roof is occupied by a standard gable rafter system, to which the same hips adjoin at an angle.
Diversity in the family of hip structures is achieved through variations with proportions. By changing the ratio of the length of the ridge to the length of the base and the height of the slope, you can get a design that meets any taste and architectural needs.
In the construction of rafter frames the following are used:
- Slab or hanging roof trusses with appropriate structural elements: beds, ridge runs, puffs, etc.
- Diagonal rafters connecting the tops of the outer trusses to the corners of the frame.
- Sloping shortened rafters that form inclined slopes of the hips and parts of the main slopes adjacent to the hips.
Hip structures can be attic or non-attic. I must admit, they are not very suitable for organizing rooms under the roof. Four inclined slopes seriously limit the space. However, for lovers of attic houses there is a Danish variety with a shortened hip. Adherents of non-standard architecture will certainly like the Dutch type, which belongs to the category called “” along with the Danish version.
Rafter systems for hip and roof types are erected with an angle of inclination from 10-12º to 60º. The absolute priority is the classic proportions with a slope of 25-30º.
In addition to penetrations, ridges and eaves overhangs, all convex and concave corners of the hip structure need enhanced waterproofing. The complex configuration of the slopes dictates the use of piece materials in finishing. When cutting metal tiles and corrugated sheets, there will be too much waste.
View #4 – hip roof
A simple hipped hipped structure is a hip roof without a ridge. Its plan layout resembles a square with diagonals running from corner to corner. Triangular slopes are connected at one vertex, which makes the roof similar to a tent. Build over boxes of a clear rectangular or polygonal shape.
In the construction of hip rafter systems, standard layered and hanging principles are used:
- A rafter structure of the layered variety is erected above the box with a central support or load-bearing wall.
- Above an object without interior wall or the supports erect the frame according to the hanging principle.
The steepness and number of slopes depend on the personal preferences of the future owner. The ideal roofing covering for finishing triangular slopes would be piece material, solely because when cutting large sheets, an impressive amount of waste remains. Regardless of the steepness, they prefer to equip tent structures with continuous lathing and a waterproofing carpet.
View #5 – broken rafter system
Rafter frames for broken lines, i.e. are specifically focused on increasing the attic space in order to create domestic or residential premises in it.
Broken technology is mainly used in construction attic roofs, which can be cold in country houses and insulated in permanent residences.
Each slope of a classic sloping roof can be divided into two rectangular parts, creating an external angle between them. Required form obtained by changing the sizes of parts of the slopes, the angles between them and the angle in the ridge zone.
Rafter system mansard type- one of the most complex types of rafter systems: diagrams and drawings of a broken frame introduce you to the complex structure of the structure. It consists of two tiers perched on top of each other:
- The lower tier of the rafter legs rests through the Mauerlat on the beams of a wooden floor, reinforced concrete slabs or the ceiling beam of a wooden house. To support the top of the rafters, purlins are installed, which also serve as support for the bottom of the rafters of the upper tier. The rafters of the lower part of the sloping roof are only allowed to be layered.
- The upper tier of rafters rests with their lower heels on the purlins of the tier located underneath. The purlins serve as the basis for laying ceiling beams attics. In the construction of the upper part, both layered and hanging methods can be used. The task of the top is only to form the ridge part, because the responsibilities for distributing the roofing pie are assigned to the lower part of the attic roof.
The owner chooses the angle of inclination of the lower and upper parts of the slopes according to his own preferences. The ideal shape is considered if the five corners are intersected by an imaginary circle. Solid or sparse sheathing is installed depending on the type of roofing, and there are no restrictions on its choice at all.
It is better to install continuous sheathing and waterproofing on the flatter upper part. On the steep lower part of the slopes, precipitation does not linger, but it is threatened by heavy winds.
To prevent the sloping roof from falling off in areas with frequent strong winds, each rafter is attached with a wire bundle to the wall, and not through one, as is customary when fixing conventional pitched roofs.
Video review of types and shapes of roofs
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The presented diagrams of different types of rafter systems are suitable for arranging a wooden house, brick and foam concrete frame. The only difference is in the fastening of the Mauerlat on wooden and stone walls. Information about the basic types of rafters will help you correctly determine the type and configuration of the roof for a country property.
