The Device And Installation Of The Rafter System, As Well As A Step-by-step Description Of The Stages Of Work

2024 Author: Bailey Albertson | [email protected]. Last modified: 2023-12-17 12:53

Device and step-by-step installation of the rafter system

The basis of a beautiful and reliable roof is the solid construction of the truss system. It is important to mount it in such a way that it will serve for many years, especially in difficult places of contact with the walls of the building, chimneys and pipes of the ventilation system. Depending on the weight of the snow, the wind load and the weight of the roof, it is necessary to choose the correct pitch of the rafters and the scheme for performing the joints of the individual elements of the rafter group. We will consider options for attaching parts of the structure to floor beams and ridge, ways to increase the load capacity of rafter legs and step-by-step installation of trusses and a complex roof in general.

Content

• 1 The device of the rafter system

  • 1.1 Options for the rafters

    • 1.1.1 Single-pitched rafter system
    • 1.1.2 Gable and broken roof structures
    • 1.1.3 Four-slope rafter systems
    • 1.1.4 Construction of the supporting frame of hipped roofs
    • 1.1.5 Multi-gable rafter groups
  • 1.2 Arrangement of the rafter system around the pipe

  • 1.3 Installation of the roof over the old coating

    1.3.1 Video: replacing the roof without dismantling the old one

  • 1.4 Step of rafter legs when installing a roof

    1.4.1 Table: selection of length, pitch and section of rafters

  • 1.5 Construction of complex roofs

    1.5.1 Video: complex roof construction

  • 1.6 Nodes of the truss system

• 2 Installation of the rafter system

  • 2.1 Fastening rafters to floor beams
  • 2.2 How to correctly make cuts on rafter beams

  • 2.3 Installing the rafter system with your own hands step by step

    • 1 Recommendations for self-installation
    • 2.3.2 Video: device and installation of the rafter system

Rafter system device

The construction of the roof is the final stage in the construction of a 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 roof and insulation are mounted, is called the rafter system. The device 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 on the walls of the house along the perimeter, and consists of the following elements:

• floor beam or tightening - a horizontal bar resting on the Mauerlat;
• hanging or layered rafter legs, which are attached at the bottom to a puff or mauerlat, and at the top they are connected and form a ridge;

• run - a bar connecting the trusses of the rafter group;

  

  Depending on the type and size of the roof, rafter systems are layered, hanging or combined, but their main elements are largely repeated

• racks, crossbars, struts and scraps are auxiliary elements that are necessary to give strength to the rafters and the entire roof structure;

• rafters - used on hip roofs and are shortened rafters;

  

  The diagonal rafters of the hip roof are fastened with braces and trusses to ensure an even distribution of the load

• sprengels - designed to give strength to the diagonal rafters of the hip roof;
• filly - used to lengthen rafter legs and rafters and form a cornice overhang;
• frontal boards - are attached to vertically cut rafters or filly and are used for mounting drips, wind bars and drainage system brackets;
• counter-lattice - mounted on rafters and used to create a ventilation gap between the waterproofing layer and the roofing material;
• lathing - stuffed perpendicular to the counter-lathing and serves to fasten the roofing material.

More complex types of roofs are formed from a combination of pitched, hipped and hip types, their rafter system is also assembled from the described elements.

The basis of any truss and truss system is the rigid triangular connection, which gives the roof structure strength and allows it to withstand the weight of snow and wind

Rafter options

A rafter system of any kind is designed to create inclined pitched surfaces, from which precipitation flows down without accumulating on the roof. In addition, the sloped surface better resists multidirectional wind loads. When constructing a rafter system, the following types of rafters can be used:

• rafter legs of a hanging type, rest only on the outer walls of the building and a tightening, and are connected to each other by crossbars, struts and struts;

• layered rafters have additional supports on the inner walls of the house and are rigidly fastened with the help of auxiliary elements;

  

  Hanging rafters do not have a rigid support in the place of the ridge connection, and the layered ones rest on the inner wall of the building through the rails, rack and girder

• combined systems are used in the construction of a mansard sloping roof or other structures, when hanging rafters are used in the upper part of the truss, and layered rafters are placed in the lower part.

Different types of roofs are assembled from these types of rafters. Consider the most popular options for the device of pitched systems of various configurations.

Single slope rafter system

Shed roofs are used in the construction of country houses, garages, baths and utility rooms. Such roofs are made using the simplest rafter system, which can become more complicated with an increase in the length of the slope. 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 to put an additional vertical stand with symmetrical slopes.

The choice of the design of a single-pitched rafter system depends on the length of the ramp, while the use of composite beams is allowed

As the length of the ramp increases, the structure of the rafter system is complicated by rigid triangular elements and fights, 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 lathing step 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 mansard structures

The gable type of roofs, traditional for the entire territory of 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 provided by crossbars and side posts, which serve as the walls and ceiling of the attic.

Gable and sloping mansard roofs are very popular in suburban construction due to the ability to equip an additional residential under-roof space

Sloped gable roofs are distinguished by the largest volume of the 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 distinguished by simplicity of design, high strength and minimal consumption of building materials; such roofs are often used in budget suburban construction

Four-slope rafter systems

Four-pitched roofs are formed by two trapezoidal and two triangular slopes and have a complex structure of the rafter system with a support frame, on which ordinary and diagonal beams are mounted. The space between the rafter joists is filled with rafters, and additional support for the diagonal legs are sprengels resting on corner lintels.

Four-pitched rafter systems are characteristic of hip and semi-hip roofs, under which a spacious attic room can be placed

Four-pitched roofs are perfectly protected from multidirectional gusts of wind and give the building a special chic, but their disadvantage is the rafter system, which is expensive and difficult to install.

The basis for the truss system of the 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 somewhat different design with truncated triangular slopes.

The device of the supporting frame of hipped roofs

The rafters of the hipped roofs in the upper part converge at one point and form a polyhedral pyramid. To increase the strength of the connection of the rafter legs, special docking elements, sheathing beams and additional cords are used.

The rafters of the tent system converge at the top at one point and are attached to each other with ties, in the lower part they are fixed with saws

Hip roofs give the structure a unique look, but they are distinguished by an increased consumption of roofing and lumber. Most often they are used on outbuildings, gazebos, and in a truncated version - as the roofs of bay windows.

Multi-gable rafter groups

Multi-gable roofs are pitched fragments cut at right angles to each other and forming internal corners or valleys at the junction. 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 the multi-gable roof forms eight triangular slopes, at the junction of which valleys are located

Roofs of this type are designed to provide natural illumination of the under-roof space and have a very attractive appearance, but they are rather difficult to install and insulate.

The device of the rafter system around the pipe

The passage of ventilation and chimneys through the roof sometimes requires the displacement of the rafter legs in violation of the selected step between them. But in the presence of pipes of sufficiently large dimensions, combined into one block, this is not enough. It is necessary to cut the rafters at the place of passage of the pipes and connect the cut sections with other rafters with bars fixed to the corners. The distance between the pipe and the wooden elements must correspond to a fire gap of 130–150 mm.

The rafter system around the chimney is built taking into account the fire gap, and the cutout is reinforced with additional racks

Next, the trimmed rafters are fastened using vertical struts to the puffs 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-combustible heat-insulating material.

Installation of the roof over the old coating

In the process of service, the roofing 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 a long time, then the repair can be done quickly and efficiently. When there is no time to dismantle the old roof, you can lay the new roof directly over the old roof. To do this, you need to know exactly where the rafter beams with counter-battens and lathing boards pass.

According to personal opinion, compiled on the basis of practical experience, for a new roofing it is better to choose corrugated board, metal tile 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

Step of rafter legs when roofing

When installing the roof, the rafters are installed at a certain distance from each other. This distance is called the 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;
• section of rafters;
• estimated wind and snow load.

The pitch and number of rafters can be selected based on recommendations and adjusted according to 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

Rafter length, m	Rafters step, cm	Rafters section, mm
Until 3	60	50X150
Up to 3.5	90	50X175
Up to 4	110	75X175
Up to 4.5	140	75X200
Up to 5	175	100X200
Up to 5.5	200	100X250
Until 6	140	100X200

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 joint sections with different types of slopes. On such roofs, a beam with a section of 50X150 and 100X200 mm serves as rafters, and the pitch is selected in the range from 60 to 120 cm.

When building roofs with a habitable attic room, a bar of a larger section is chosen, and rafters are installed more often to increase the strength of the truss

According to the observations of the author of this article, the dimensions of the insulation material have an indirect influence on the choice of the step. 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. Zealous owners choose a step multiple of 59 cm in order to mount the insulation mats between the rafters tightly and without gaps.

Complex roof construction

Complex roofs include multi-level architectural solutions that often feature a mixture of styles, such as a pitched roof with a bay window or a combination of a hip structure with a hipped roof element. Even a conventional multi-gable roof with tongs 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 marriage and the loss of expensive materials.

Complex roofs need to 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 component parts, and valleys, vertical posts and horizontal ridge-type beams can be mounted at their junctions.

When installing complex rafter systems, it is important to ensure that there is a gap for under-roof ventilation on all slopes, otherwise condensation will damage the rafters, battens and the insulation layer

Video: the device of complex roofs

Truss system nodes

The nodes connecting the elements of the rafter group perform the function of ensuring a rigid and durable fastening of parts. Increased requirements are imposed on the quality of assembly of units, since in these joints there is an even distribution of the load from the load-bearing elements to the puffs, floor beams and Mauerlat. The main types of connections that are used when installing rafters include the following nodes:

• ridge - the junction of the upper part of the rafter legs;

• cornice - connection of the lower part of the rafters with a mauerlat or tightening;

  

  The main bearing units of the rafter system must be performed in accordance with increased requirements for the level of withstand loads

• knots of connection of struts and crossbars with a rafter leg.

There are also particularly complex joints, for example, the junction of the diagonal rafters of the hip roof to the purlin and the Mauerlat or the junction of the sloping roof, where five parts of the rafter system are connected.

When assembling a sloping roof, special attention should be paid to the node of the transition of hanging rafters to layered ones, since five load-bearing elements are connected in them at once

Consider the attachment point for rafters, racks, girders and puffs using the example of a broken mansard roof. In it, the vertical rack is connected with a tie-in with a horizontal girder and a tightening, then a lower rafter leg is mounted to them, which rests on the tightening using a tie-in and a metal bracket. Then the upper truss is fastened with ridge ties and also cuts into the tie and is fixed to the bracket. In other nodes of the rafter system, which are used on various types of roofs, the same principles of joining parts are used. Nails, screws, bolts, perforated metal strips and corners of various designs are used as fasteners.

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 a safe environment for work, prepare a place for cutting and making templates, and ensure the availability of lumber and fasteners. During the installation process, you will need working drawings and the following tools:

• goniometer (malka), level, construction pencil, cord;
• chain saw for rough cutting and trimming;
• circular saw, jigsaw;
• electric drill, screwdriver;
• hammer, chisels.

Before assembling, it is necessary to make templates of the same type of elements of the rafter system and make sure of their high-quality joining and good fit at the installation site.

Roof trusses need to 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 of the preparatory work is cutting sawn timber to size, impregnating the elements with fire retardant and antiseptic compounds and natural drying for at least a day.

In the absence of design documentation for the roof, it is important to select in advance the methods of fastening the rafter legs in the ridge and eaves, as well as design solutions for connecting parts in various docking and other nodes

Fastening rafters to floor beams

Fastening the rafters to the floor beams or tightening in the lower part is done in 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 enough to be attached to the beams with a plank assembly or using metal plates, cutting the beam at the required angle and using taps.

The choice of the 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

With large values of the length and weight of the rafter legs and the expected snow and wind load, the connection must be made with a frontal cut, single or double tooth. In this case, under-beams are used to ensure a snug fit of the threaded rods. Before installation, it is necessary to create templates that will ensure the correct cutting of materials at the cutting unit and a 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 holes for the threaded studs 90 located ^on the upper plane of the trusses as it will provide a tight fit and reliable fastening parts together without displacement and misalignment.

How to make cuts on rafter beams correctly

In the process of assembling the rafter system, it is necessary to dock elements with different angles of inclination. For marking cuts, cuts and corner joints, building levels and goniometric tools are used, and templates are made for mass production of the same type of parts. The cuts on the rafters can be made in the following sequence.

1. The beam is exposed to the Mauerlat and the ridge girder, vertical lines and the exact position of the inset are marked according to the level.
2. The tilt angle is fixed on the bevel, and the dimensions of the inset are measured with a tape measure or a square.
3. With the help of a square and a goniometer, the measurement results are transferred to the workpieces, after which the cutting angles and the dimensions of the cutting spikes are marked.
4. The necessary cuts are made on the marked workpiece.

Places for saw cuts are marked in several stages using a construction pencil and a goniometer

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 small and transferred to the part.

According to the author of the article, cutting the material according to a single sample is not an unnecessary operation, since the time lost for making templates is more than compensated for during the installation process, which is significantly accelerated and becomes more rational and high-quality. You need to pay attention to the good condition of the goniometer and use only proven copies.

DIY installation of the rafter system step by step

In order to save money, many owners assemble the roof of the house on their own. With some building experience, this decision is quite justified, since even complex roofs are quite possible to assemble with your own hands, having project documentation. In the absence of a project, you yourself need to make a drawing of the future structure with the main parameters and dimensions of the elements of the rafter system.

The truss blanks can be assembled on the ground or directly on the roof. Usually a triangle is made from two side beams and a bottom tightening, all other elements are mounted after the truss is installed in a vertical position. Each structure must be made according to a template made in advance and tested at the installation site. With significant length and weight of structural elements, assembly is carried out in stages.

Installation is carried out in the following sequence.

1. Solid Mauerlat beams are mounted on the threaded rods of the reinforced belt or the last crown of the walls around the perimeter to ensure even distribution of the load from the rafter system to the walls of the building.

   

   In the houses of their concrete or building blocks, the Mauerlat is installed on studs embedded in the armored belt, in wooden buildings its role is usually played by the last crown of the wall

2. Floor beams or tightening beams 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 girders are attached to them.

3. The first blank for the truss is installed from one edge of the roof (on the gable). An inset is made on the rafter legs, and they are attached to the Mauerlat, floor beams and ridge girder.

   

   The first to be installed are roof trusses on the pediments

4. The second workpiece is set in place of the other pediment.
5. Both trusses are fixed in a vertical position, which is controlled by a level or plumb line.

6. Guide cords are pulled between the installed trusses.

   

   Guide cords are pulled between the trusses installed on the gables to control the correct position of the intermediate elements

7. Intermediate truss structures are installed with the selected step. All of them should be aligned vertically and along the tight cords.
8. Ridge and additional horizontal girders are mounted (if provided by the design).

9. The rafters are reinforced with crossbars, uprights and other elements provided for by the project.

   

   After installing all trusses, horizontal girders and additional reinforcing elements are mounted

10. On hip roofs, at first, ordinary rafters are installed, resting on a ridge girder and a Mauerlat, and then diagonal rafters and rafters are alternately placed.
11. With the help of gable and frontal boards, overhangs are formed that protect the walls of the building from precipitation.

12. A waterproofing film with a sag of no more than 20 mm and counter-lattice bars are attached to the rafters, which provide a ventilation gap between the waterproofing and the roofing. Then the longitudinal lathing is laid, which serves as the basis for the roofing.

    

    Installation of a waterproofing film, counter battens and lathing completes the assembly of the rafter system

Experience shows that when the rafters are more than 6 m long, it is necessary to build them up at the joints using a spike, double-sided linings and using threaded rods or bolts installed in increments of 15 to 20 cm. The joint must be reinforced with additional struts or struts. In 2010, using this technology, the author installed a roof with a rafter leg length of more than eight meters; so far, no deflections and other changes in shape have been found on the slopes.

Complex roofs are assembled starting from the main supporting structures on which the rafter system is based. Then, ordinary and diagonal rafter legs, handcuffs and auxiliary elements are installed. In conclusion, the different types of fragments are joined together into a single structure.

Self-installation guidelines

According to the author of this article, who mounted three roofs of varying complexity with his own hands, the installation of the rafter system can and should be carried out by himself. The first roof was cut and assembled according to the blueprint in four days, and on the fifth and sixth days, waterproofing, battens, frontal boards and roofing material were installed. The second roof took three and a half days, and the third was erected in two days. With the growth of skill and with proper planning of work, the installation of the rafter system is significantly accelerated. If you have building experience, then it is not difficult to install a roof with the proper quality. In case of difficulties, it is necessary to involve design engineers or professional builders for consultation, who will help in a difficult situation.

Video: device and installation of the rafter system

We considered options for assembling the rafter system at the joints with pipes, over old roofs, at the points of contact with the Mauerlat, as well as in the case of complex rafter structures. Along the way, we studied some ways of connecting the elements of trusses and rays. The roof can be assembled with your own hands, it is important to strictly follow the step-by-step instructions and strictly observe safety precautions, then success will be ensured.