Attic rafter system can be of different configurations, with correct installation It is distinguished by reliability and functionality. The rafter structure is a powerful frame, capable of withstanding the load not only of the entire roof, but also the influence of external natural factors.
The frame made of rafter boards is the basis of the entire roofing system. attic structure , which is capable of supporting the weight of the entire roofing system. Before you equip the roof for the attic, you need to know in what order to install all the necessary elements of the rafter structure.
The structural elements of the roof truss system intended for the attic are:
- Mauerlat. The basis of the entire roofing structure, which able to withstand and evenly redistribute the load from the roof system to the supporting walls. Mauerlat consists of boards that are attached to the external walls of the building, and elements of the rafter structure are also attached to them;
- Beam posts or rafter legs, which form the frame of the roof structure. Boards for rafter legs should bear the load roofing pie together with the outer covering;
- Vertical racks. Racks are installed for holding the central part of the rafters and protecting them from bending, as well as to support the ridge beam;
- Runs. Additional bars that are installed at an angle for supporting rafter legs;
- Ridge beam. Mounted on long systems (more than 7 meters) and serves for creating structural rigidity;
- . An additional wooden structure that is attached to the rafter system and serves as a base for the roof.
In addition, there are additional elements: beams, purlins, crossbars, which are installed in various parts of the roof frame to create rigidity and strength of the structure as a whole.
Mansard roof truss system: drawings and photo of the plan below.
Rafter drawing plan
Types of rafter systems for mansard roofs
Roof truss structures for a warm room may be different, and accordingly, the installation of such structures will be different. In addition, the rafter system may have:
- Hanging structure. It rests on the side walls of the room with one edge of the structure and at the top when connecting the rafters - on the ridge element;
- Layered design. Most often it is installed in buildings with a span of more than 10 m. With this structure of the roof structure, the rafter system has support on external walls and a partition inside the building.
Rafter systems for attics can be installed during installation:
- designs;
- roofs;
- Broken gable;
- roofs;
- designs;
- Dome system (cone);
- Vault system.
The classic look of an attic space is represented by a rectangular structure, which is mounted inside the covering, resting its upper corners on the slopes, and the lower corners are included in the support system.
Layered rafters
Installation of attic roof rafters and pitch calculation
The decisive indicator for calculating the pitch of the roof rafters in a warm room is the choice of the external roof covering. Yes, for different types It is necessary to install the rafters for the attic roof as follows:
- Under . The pitch between boards with a section of 50 by 50 mm should correspond to 60-80 cm;
- Under . A beam with a cross section from 50x100 mm to dimensions 50x150 mm is required. The pitch when installing under slate should be 600-800 mm;
- Under . When the cross-section of the rafter leg is 50x150 mm, the step size should not exceed 95 cm and should be at least 60 cm;
- Under . The section of the beam can be 50x100 mm, as well as 50x150 mm. With such a board, the step must be taken at least 60 cm and no more than 90 cm.
Besides, great importance when calculating the step has roof slope. If the slope is 15%, then the distance between the rafter boards is recommended to be at least 80 mm. As the degree of slope of the roof slope increases, the distance between the rafters increases proportionally.
Rafter pitch
How to move rafters beyond the wall line
The rafters extend beyond the line of the outer wall in order to increase the attic living space. The peculiarity of this method is that the support of the lower rafter beam is the floor board, and not the Mauerlat board.
Wherein install reinforcing struts under the extreme part of the triangular sides.
In this case, it is not always advisable to install a Mauerlat, but Concrete pouring must be done, since floor beams will be attached to the concrete with anchors.
When the rafters are moved beyond the outer line, a cornice should be formed, the width of which for houses made of wood should be at least half a meter, for structures made of stone or concrete - at least 400 centimeters.
Removing the rafters beyond the line of the external wall must be done in the following sequence:
- Install external slab beams, with a cross-section of at least 15*20 cm. They serve as the outline of the overhangs and should form a rectangle (based on their roof shape);
- Pull the cord between the outer beams and install the remaining beams in increments of 0.6 m (for a warm room);
- Measure this distance from the left to the right edge, which should correspond to the short leg of the triangle, and mark the points by cutting out sockets for installing the extreme supports;
- Make supports the dimensions of the timber nests are 10*15 cm. The length of the support boards should be more than 10 cm;
- Install temporary spacers for mounting corner posts;
- Using a plumb line on a cord attached to the posts, check the uniformity of the points selections for supports;
- In the central part of the attic gables install two supports;
- Install purlins on supports, firmly attaching them with corners;
- Connect opposite supports with bars, also attach them to the purlins using corners. Install a temporary support under each beam;
- The beam, which serves as a crossbar, temporarily fasten with an inch at a distance of 200-300 mm from the edge. To make it convenient to mount the top of the rafter structure, install temporary plank flooring;
- From edged boards it follows make templates, along which opposite trusses are then mounted:
- The template is made by applying the workpiece to the beam and the end of the purlin, and corresponds to the rafters of the bottom row. Mark the groove lines to size to eliminate excess;
- Install the rafter legs from the end, and then from the lower level of the attic;
- Next according to the template install the top rafter frame;
- To avoid sagging of the crossbars, it is necessary to the trusses fasten the headstocks from below - in a hinged way, from above - with a rigid fastening.
The rafter boards are attached to the walls using wire ties and the gable frame is installed.
Removing the rafters from the wall
How to calculate the rafter system
Before calculating the rafter system, it is necessary to definitely know the shape of the roof.
It should be taken into account that for comfortable living in the attic the height of the walls of the room must be at least two meters, and the length - from three meters.
The attic project involves the calculation of a rafter system that matches the size and nuances of the building.
If a layered system is provided, then additional support needs to be installed.
In addition, you should keep in mind:
- The ridge beam must be installed when the roof length is more than seven meters, since it significantly makes the structure heavier;
- Don't forget about the skylight system, for which it is necessary to additionally construct a frame;
- Necessarily take into account the loads from climatic factors: wind, snow, which may be important for determining the roof overhang;
- A lot of roofing cake, which is determined on the basis of one sq. meters of its entire structure. In this case, it is necessary to multiply the result by a coefficient (from 1.5 to 3) for a margin of safety.
In addition, the characteristics of the flooring and the performance of the roof should be taken into account.
Calculation example
Installation of the rafter system
Installation should begin with the floor beams, which are attached to the mauerlat, and the rafter legs are attached to them. It is important to consider.
- Mark the installation location of the ridge element and supports in the center of the beams;
- At equal distances, install racks made of boards equal in cross-section to the floor beams. It should be fastened with corners, having previously been temporarily secured with nails to determine the accuracy of installation;
- The first pair of racks is fastened with bars made of bars;
- Rafters are attached to the resulting structure in a U-shape, which are installed either on the Mauerlat or on the floor beam by cutting a groove;
- Install ridge rafters by connecting them with bolts and washers or metal plates;
- The rigidity of the structure is provided by struts, which are attached to the center of the side rafters and the post and headstock, which are mounted in the center of the tie.
Other trusses are made in a similar way and are secured together by purlins. The distance between farms can be from 60 to a meter.
To secure the assemblies of the attic structure and give them strength it is necessary to fix them with staples. Next, the sheathing is installed.
Installation of the rafter system
Installation diagram
Installation of attic roof sheathing
Depending on the type of external roof covering provided, there are two lathing options: solid and sparse.
Solid is most often installed when covering:
- Roll. In this case, the lathing is installed in two floorings: the lower one - in 30 cm increments from 20 cm bars, the upper one - from 50x20 boards, which are nailed at an angle relative to the lower flooring of 30-45°;
- Slate flat asbestos-cement;
- Flexible tiles.
The sparse type is set when:
- Steel, metal coating. The bars, the cross-section of which is 5x5 cm, are laid perpendicular to the rafters in increments of 20-30 cm. Installation is carried out from the eaves upwards. A flooring of 70 cm wide boards is mounted on the overhang. Butt-joined bars are attached along the ridge and ribs;
- Metal tiles;
- Asbestos cement slate;
- Clay tiles.
The pitch of laying the sheathing and the thickness of the boards directly depend on the roofing covering and are calculated individually depending on the load and the specifics of the installation.
ATTENTION!
The sparse sheathing bars should be nailed offset so that the joints in adjacent rows are not located on the same rafter beam.
Sheathing boards should be slightly less than the length of the slope.
Lathing
Conclusion
Thus, it has its own installation features. They must be taken into account, since the attic is an additional place to live, and it must meet all the criteria for a given function.
Useful video
In this video you will learn everything about the rafter system of the attic roof:
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In modern private construction, the rafter system of the mansard roof makes it possible to increase living space and create an additional half-floor. This design is distinguished by the variety of design options, their reliability and versatility. It is convenient for installing attic and dormer windows and accessing a small balcony on the roof. Such a constructive completion of the building makes it possible to organize additional living space instead of a conventional attic. The attic level is formed thanks to a specific rafter system and a large angle of inclination.
What type of attic space should I choose?
For the first time, attics began to be inhabited in Europe after the Second World War, when there was not enough full-fledged housing for everyone. However, in our time, the attic, as luxury housing under a roof, has become very fashionable. The construction of mansard roofs began in the dacha sector, in country cottages, and in new houses in order to add usable space.
Today, installation of a mansard roof truss system has become much easier and more affordable, thanks to the offer of the latest developments and the availability of building materials. High-quality insulation and new methods of sealing the attic roof have turned an ordinary attic into a cozy room. This made it possible to protect the living space under the cold roof from cold and negative weather factors. And the rafter system of the attic roof allows you to vary the configuration, size and shape of the under-roof space. Options for building an attic:
- cold summer - country;
- insulated - for full year-round living.
Mansard roof rafter system - photo:
The side walls of the attic inside have different shapes walls:
- symmetrical and asymmetrical;
- single-level and two-level;
- vertical (with additional storage on the sides);
- partially vertical (the bevel for the ridge starts approximately from the middle of the wall);
- inclined;
- beveled triangular (in the shape of the slopes of the attic roof);
- broken (attics of complex shape).
The total volume of the attic space, which is provided by a tetrahedral (hip) or gable roof, depends on the bevel angle. With proper finishing of the interior and thoughtful design, the room can be aesthetically pleasing and complete for habitation, even with strongly sloping walls.
When the under-roof space should be designed for housing, it is important:
- bring down all communications;
- determine the layout and functionality of 1 or more compartments;
- provide ventilation, heat and waterproofing;
- take care of additional insulation for the winter;
- let down all the amenities if it is an isolated room for one person.
Architect's advice: The living space inside the attic is planned to be convenient for movement and comfortable for life support. Therefore, the room dimensions should be at least 3 m wide, and there should be enough space above the head to move freely with raised arms.
Preliminary calculation of the rafter system of the attic roof is very important. All points must be thought out in advance when entering into the preliminary design of the attic. Sometimes it is necessary to replace the roof, and the decision to add an attic comes in the process of choosing the roof configuration.
Attention: The construction of the attic roof structure of the rafter system must be carried out taking into account the fact that it will create additional load on the foundation and walls, which is harmful for a house that is not new. And although this will not destroy the main structure, it can cause additional shrinkage.
It is not too late to abandon the idea of arranging an additional residential floor if the building is dilapidated and the soil is not suitable for multi-story buildings. Only specialists can correctly calculate the total load construction organization or an architect, he will also suggest the optimal configuration (geometry) of the attic space, so as not to spoil the appearance of the house. The angle of inclination of a new building is determined at the design stage. It depends on the following factors:
- climatic conditions of the region;
- roofing materials;
- functionality of interior spaces.
Mansard roof rafter system - drawings
It is impossible to plan an attic room without special windows. It is important to consider their location at the design stage, that is, before installing the rafter system. Ultimately, not only the appearance of the house, but also the reliability of the entire structure will depend on the proper placement of window openings, which influence the pitch between the supports. It is also necessary to consider the method of fastening the frame of the attic windows, and their height is dictated by the ease of maintenance inside the attic.
Where to start building the attic rafter system:
The rafter frame is the base or skeleton of the attic. And if you are interested in how to make a rafter system for an attic roof, you should start by studying existing experience so as not to invent anything and avoid any annoying mistakes. If the rafter “cap” is installed and mounted correctly, then sheathing it from the outside and inside will not be difficult.
The rafter system of the attic roof is assembled with your own hands in order:
- Mauerlat;
- beam base;
- frame racks;
- runs;
- hanging rafters of the upper slopes.
Advice: When constructing an attic, all wood must be dry and seasoned, treated with a special antiseptic or antifungal aerosol. Logs and dry timber should have a moisture content of about 18-20%, no more.
Let's consider the next stage of work - a diagram of the rafter system of the attic roof. Design basis:
- main racks,
- floor beam,
- side rafter,
- ridge rafter,
- top harness,
- brackets for fastening.
How to make a mansard roof for a small cottage?
All work on the construction of the rafter system of a gable mansard roof can be done with a small team of improvised workers.
If you want to build a cold summer attic over a small dacha, it is not difficult; it is important to think about how you can get to the upper room:
- along external attached steps;
- from the inside, like an attic staircase.
Light boards, timber and small diameter logs are suitable for the prepared perimeter of a country house. However, the integrity and reliability of the lightweight attic structure will depend on the reliability of the connections between the rafter system and the floor beams. You can use strapping, screws, nails, bolts, etc.
The racks are laid in order, supported by the base and ceiling beams, then the rafter legs of the first level of the slopes are attached to them. The main components of the attic rafter system are fastened with either construction staples or strapping made of hardened wire. Sometimes an additional connection with reinforcement with staples or wire is required.
The upper beam of the attic floor is attached to these supports - this is a ridge post that “assembles” the rafters under the upper slope. Next, the rafter legs for the upper level of the slopes are secured, after which the rafter legs are connected to the main floor beams.
When the base is ready, all the supports are fastened with strapping and lathing, for additional reliability, so that the rafter system is strong and convenient for laying insulation, waterproofing and roofing material. The simplest design of a country attic is covered with waterproofing and covered with slate. And don't forget about the sediment drainage system.
An attic from layered rafters is made in approximately the same way, but the tops are reinforced with thicker timber - for sufficient structural strength. Such a system will functionally replace the support beam of the upper slopes. They will become the supporting frame of the attic roof and the basis for cladding the walls and ceilings indoors - photo:
The lower level has options for attaching the support to the upper points of the rafters - on the side girder of the racks, on the gables, or only on the racks, that is, without installing the side girders. And the lower points of the rafters of both lower slopes should rest on the floor beams, and preferably without insertion.
Under a roof made of heavy piece materials, it will be necessary to reduce the interval between the rafters, and also add sheathing to their cross beams. This scheme is often used for the construction of mansard roofs of complex configurations.
It is important to build a rafter attic, knowing some design features. Therefore, experts recommend learning a few lessons on how to properly make a rafter system for an attic roof. We start with the Mauerlat.
1. Mauerlat is the foundation around the perimeter of the house on which the entire rafter system is attached. Therefore, the reliability of fastening the lower beams to this perimeter will literally determine whether “the roof will be torn off” due to unfavorable weather and climatic phenomena. A high-quality Mauerlat will not allow the attic roof to come off during a tornado or tip over during powerful hurricane winds. Reliable fastening of the truss structure to the perimeter of the building evenly distributes the load of the roof on the walls and foundation of the house.
2. It is better to choose boards and beams that are strong, not knotty, and at least 40 mm thick. It is better to use dry treated wood for the Mauerlat, optimally timber with a cross section of 150x100mm. After preparing the perimeter of the walls for laying the rafters, the timber or board must be laid horizontally, checking the level along the entire perimeter of the walls.
3. On the crowns of walls or columns of a building frame type or brickwork, a layer of waterproofing recommended for the type of building material must be laid. This is necessary so that the moisture in the walls and base of the rafter system does not transfer to them. For waterproofing, bitumen, roofing felt or roofing felt, and other modern waterproofing materials are suitable.
4. We fasten the beam at the base to the walls with bolts or staples; additionally, the fastening can be strengthened with wire strapping. The studs for the Mauerlat are mounted into the wall during masonry. The Mauerlat beam is treated with an antifungal agent so that it is not susceptible to destruction.
5. When everything is ready to install the rafter legs, it is important to mark the base where they will be attached. Ready-made rafter legs can be ordered from a workshop and then assembled yourself, rather than spending a lot of time making them. For convenience, they can be laid out on those sides of the house where they will be laid around the perimeter of the attic.
6. Check the racks for loosening and vertical shift. If this is the case, then do not think that the problem will go away with the installation of roofing materials. The additional weight of the structure will only increase its instability. Therefore, all flaws should be eliminated at this stage - reinforce the fastening with braces and ties.
7. Experts recommend maintaining an equal interval (step) between the rafters - about 80-120 cm. The easiest way is to stretch twine between the outer rafters to use it as a marking and level for the remaining rafter beams. The racks are made not only in one horizontal plane, but also aligned exactly vertically - check the plumb line.
8. Vertical racks are good basis for future walls of the attic living space, so they must be perfectly smooth. The inside will be covered with wooden or plywood panels, plasterboard, fiberboard or chipboard. Do not forget to lay the appropriate insulation between them, which is intended for the roof and attic.
9. To secure the posts to the drains of the upper timber, use metal staples or nails. With the completion of this stage of work, the installation of the rafter frame is completed. At the last stage, the rafters are connected in pairs and attached to the ridge beam.
10. Don't forget to leave gaps for skylights or doorways for stairs. Installation of dormer windows is carried out after the walls of the internal cladding are equipped.
11. You can do without a ridge beam, but it is necessary if the attic roof is long - more than 7 m. But it increases the total mass of the rafter system. It is enough to fasten the tops of the rafters with ties. The final stage is lathing for thermal and waterproofing and roofing materials. When the roof is almost ready, they proceed to the installation of roof windows and interior decoration of the room.
12. It is better to calculate the quantity of consumables and wooden beams in advance using tables and drawings, but it is better to take into account the minimum and maximum consumption - with different spacing between the racks. Ideally, the design is expected to be lightweight and reliable, at low cost. Important points We suggest studying the arrangement of the rafter system of the attic roof in the video at the end of the article.
A structurally complex attic under aesthetic roofing materials looks much more interesting than a regular hip roof, but only specialists can do it. When the decision is made to replace the old roof with a more modern roof, take the opportunity to build an attic. Although the more complex structure of the attic roof rafter system is a little burdensome in terms of the amount of work, the additional living space and the unique appearance of the house will delight your children and grandchildren for many years.
There are several roof options under which you can place a comfortable living space. In order to ensure the maximum volume of the attic space under the roof, it is necessary to select the optimal angle of inclination of the slopes and not to forget about the snow and wind load on the roof. We will look at the most popular designs of attic rafter systems in the middle zone.
The design of the attic roof truss system
Mansard roof makes it possible to obtain additional usable space with a relatively small financial investment, which is why this architectural solution has gained great popularity. So what is called an attic?
Attic (from the French mansarde) is an usable attic space (both residential and non-residential premises), formed on the top floor of a house, or the top floor of a part of a house, with an attic roof.
Wikipedia
https://ru.wikipedia.org/wiki/Attic
The attic is located within the load-bearing walls of the building and rests on them through the mauerlat, horizontal beams (strings) and rafters. The larger the attic space, the greater its useful volume, which is achieved by increasing the angle of inclination of the slopes and is formed by a more complex rafter system. The location of the rafters of the attic roof depends on the design, which can be different types, namely:
- Tent or pyramidal structure with a minimum volume of under-roof space.
The slopes of the tent structure rest on the side rafters and the central post, so the volume of the under-roof space here is minimal
- A hip or half-hip roof, in which the main living space is located under trapezoidal slopes.
The rafters of the hip roof form two triangular and two trapezoidal slopes
- A gable structure, which is a symmetrical gable roof with gables cut in at right angles, which provides a significant volume of attic space.
The multi-gable roof allows you to equip a full attic floor
- A gable symmetrical roof with an attic is a classic option, characterized by ease of installation and resistance to wind influences due to its rigid structure.
A gable roof requires the least amount of working time and low consumption of building materials
- The rafter system of an attic sloping roof provides the maximum volume of living space at a relatively low cost.
A sloping roof is the optimal solution in terms of the ratio of the cost of construction to the volume of usable space in the attic
The rafter system must withstand constant loads, which consist of the weight of structural elements, insulation and roofing. In addition, there are variable loads depending on the strength of the wind and the weight of the snow on the roof. The choice of the cross-section of load-bearing elements and the method of connecting them should be aimed at creating the most durable and rigid structure that evenly distributes the load on the walls of the building.
Depending on the width of the building, different types of attic rafter systems are used, which are divided into hanging, layered and combined.
- Hanging rafters are those that rest on the walls of the building through the mauerlat and tie, and form a ridge in the upper part. With this connection method, there is no intermediate support, and the bursting pressure on the walls of the house is reduced with the help of crossbars, racks and struts. The hanging rafter system is usually used when the building width is no more than 6 m.
To compensate for bursting forces in suspended rafter structures with a span of up to 6 m, tie rods and crossbars are used
- Layered rafters are called rafters with intermediate support on the internal wall of the house. They are used when the width of the building is from 6 to 16 m. The larger it is, the more elements are used to evenly distribute the load.
Layered rafters have one or more supports inside the house
- The combined type of rafter system is used in mansard roofs with variable slope angles. The most typical example is a broken mansard roof, where the lower rafter legs are layered and supported by a post and a mauerlat, and the upper ones are mounted as hanging rafters supported by a tie rod and a headstock. When constructing mansard roofs, all types of rafter systems are used, and their choice depends on the structure in which they are used.
In the design of a sloping roof, the upper rafters are hanging, and the lower ones are layered
Scheme of the rafter system of the attic roof
To erect a roof, you must have a project that specifies the list and size of structural elements, as well as the method of connecting them. To understand the principle and sequence of installation, you need to know the purpose of the elements of the rafter group and the way the roof adheres to the walls of the building. The attic roof consists of the following elements:
- the connecting element between the wall of the building and the rafter group is the Mauerlat, which is attached to the walls of the house with studs, brackets or anchors;
- strings are attached to the Mauerlat parallel to the short wall of the building, and beds are installed along the long side;
- vertical posts are mounted on the central floor;
- the ridge girder rests on the posts;
- the upper part of the rafters rests on the ridge girder, and the lower part is connected to the tie, forming a cornice overhang;
- the rafter legs in the upper part are connected by crossbars;
- on hip roofs, diagonal rafters and shortened eaves are used;
- trusses serve as additional support for the diagonal rafters;
- for intermediate fastening of rafters, racks and struts are used;
- if necessary, the rafters are lengthened with fillets.
The main load-bearing elements of the attic roof are rafters, beams and tie rods, as well as vertical posts and a ridge girder.
The diagram indicates the dimensions of the elements of the rafter system, their location, angles of inclination and methods of insertion at the connection nodes. Information about the location of double rafters, the presence of additional supports, and the dimensions of eaves and gable overhangs is also required.
The diagram is the main document for assembling the rafter system; it reflects all the necessary parameters. However, before cutting the material, it is necessary to check the calculations again and create templates for the main parts. If there is no project, you need to carry out calculations and create a diagram yourself.
Mansard roof rafter spacing
Before starting work, you need to select the pitch of the attic roof rafters. The distance between the rafters and the eaves (in the case of a hip roof) depends on several factors:
- building size;
- type of rafter system;
- constant and variable load on the roof;
- sections of rafters, racks and slopes;
- type of roofing;
- type and pitch of sheathing;
- insulation sizes.
For rafters, sheathing and counter-lattens, softwood material is selected in accordance with SNiP II-25, and the load on the rafters is calculated according to SNiP 2.01.07 and ST SEV 4868. Based on what is stated in the building codes and regulations, we can say that for rafters less than 9 m applicable beam cross-section from 50X150 to 100X250 mm with a pitch of 60 to 100 cm. The size of the building affects the design of the truss and the presence of racks, struts and crossbars, the use of which increases the strength of the rafter legs and allows you to increase the pitch between the rafters to 120 cm or more . Usually, to select a step, reference tables are used, which contain recommendations taking into account the length of the rafters and the cross-section of the beam.
Table: dependence of the pitch between the rafters on the section of the beam and the length of the rafters
The type of roofing used also affects the choice of rafter spacing, because different materials have different weights:
- tiles, depending on the type, weigh from 16 to 65 kg/m2, slate - 13 kg/m2. Such heavy coverings imply a reduction in the pitch of the rafter legs to 60–80 cm;
- the weight of metal coatings and ondulin does not exceed 5 kg/m2, so the pitch of the rafters can be increased to 80–120 cm.
On hip roofs, in any case, the step of the roofers is chosen to be 50–80 cm to give the slope greater rigidity.
In addition, the installation step of the rafters depends on:
The length of the rafters and sheathing of the attic roof
When doing independent calculations, the dimensions of some structural elements of the roof have to be calculated based on the existing dimensions of the building and the angle of inclination of the slopes. The length of the rafters sometimes has to be adjusted for different types of attic roofs, selecting the optimal dimensions of the entire structure as a whole.
Let's assume that the main dimensions of the building are known and it is necessary to calculate the length of the rafter joists for several proposed options for the angle of inclination and type of roof. Let half the width of the building L be 3 m, and the size of the eaves slope be 50 cm.
Additional calculations show that increasing the angle of inclination of the lower slope from 60 to 70 o will increase the width of the attic by 10%.
The length of the sheathing connecting the rafter legs is determined taking into account the gable overhangs that protect the facade walls from precipitation. The length of the gable overhang depends on the height of the building and is selected in the range from 40 to 60 cm. Therefore, the total length of the slope will be equal to the length of the house, increased by twice the length of the overhang.
Let's assume that the length of the house is 10 m, and the gable overhang is 0.6 m. Then the dimensions of the sheathing must be calculated taking into account the length of the slope, equal to 10 + 0.6 ∙ 2 = 11.2 m.
The parameters of the sheathing should be calculated taking into account the length of the gable and eaves overhangs
Any adjustment to the project requires a careful recalculation of the parameters of the rafter system, taking into account the changes that have arisen.
Video: calculation of the attic roof
Knots of the rafter system of the attic roof
The nodes of the roof truss system represent the junction of individual elements into a single structure, which allows you to evenly distribute the load on the walls of the building. The connection is made with nails, self-tapping screws or bolts using overhead wooden elements or metal squares and plates, as well as by connecting to a groove. For construction gable roof The following main components are used:
- A ridge unit that provides a connection between the rafter legs and the ridge purlin.
- Places where the crossbar connects the rafters to give greater strength and rigidity to the trusses.
- Attachment points for struts and posts that provide additional support to the rafters.
- A cornice assembly in which the rafters are attached to a tie rod or mauerlat, forming a cornice overhang.
Nodal connections of the rafter system must be made in such a way as to ensure the most rigid fastening of the elements to each other
A characteristic feature of a gable sloping roof is the knot where the upper and lower rafter joists, the vertical post, the crossbar and the purlin are connected. Such a complex connection requires the use of mortises, bolts, steel plates and construction staples.
In the most complex unit of a broken mansard roof, five rafter elements are connected
The most complex component of a hip mansard roof is the junction of the side or diagonal rafters with the mauerlat. The side rafter in the lower part rests on the corner beam of the mauerlat and on the embedded beam; in another option, a vertical post or truss is placed between the embedded beam and the rafter leg. The upper part of the hip rafters is attached to the ridge purlin using bolts or nails.
The corner rafters of a hip roof bear the greatest load, so their connection to the Mauerlat must be thought out most carefully
The described units are used most often when installing rafter systems of various designs and allow you to install load-bearing elements on your own. For efficient and high-quality assembly, drawings and production of templates with verified angles of joints and inserts are required.
Video: rafter system components
Calculation of the rafter system of the attic roof
The rafter system is the basis of the roof, so it is important to choose the design that is most suitable for the climatic conditions of the region and the existing requirements for the size of the residential attic. After selecting the design, the angle of inclination of the slopes and the height of the ridge are calculated for the required dimensions of the attic room. Calculations are made taking into account the size of the cornice using the following formulas:
The meaning of trigonometric functions can be found in reference tables.
Table: values of trigonometric functions for different slope angles
The most difficult thing when designing mansard roofs is counting lumber. Calculating the number of rafters required and matching them with a standard length of 6 m can sometimes be quite difficult. Let’s assume that we have chosen the hip roof, the most difficult to calculate, measuring 10X13 m, taking into account the eaves overhangs 80 cm long and the slope angle of 45 degrees. Then the side rafters will have a length of 5 / sin 45 o = 7.04 m. Therefore, the standard six-meter beam will have to be lengthened. Typically, for rafters a little more than 6 m long, a 100X200 mm beam or a 50X250 mm board is used.
If the building has big sizes, then it requires rafters longer than the standard size of 6 m, so the beam has to be extended
As for the horizontal floor beam, since the width of the building is 10 m, the tie rods should consist of two parts, which either rest on the internal wall of the building, or are joined together by reinforcing elements and rest on the purlin. For tightening and purlins, use timber with a cross section of at least 50x200 mm. Along the perimeter of the building there is a mauerlat, for which timber 150X150 mm or 200X200 mm is used. According to the scheme we have chosen, the perimeter of the building is 39.6 m, so installing the Mauerlat will require seven six-meter beams. The dimensions of all other elements of the rafter system will not exceed 6 m.
The weight of the lumber of the rafter system is calculated by summing the lengths of all elements with a certain cross-section and converting their quantity into cubic meters. This is necessary to determine the mass of the entire roof, and is also necessary when purchasing and transporting material. The calculation is made according to the table, and then the obtained values are multiplied by the weight of 1 m 3 of lumber.
Table: calculation of the amount of lumber in 1 m3 and the volume of one unit of material
Pine lumber weighs 505 kg/m 3 at 12% humidity, and 540 kg/m 3 at transport humidity 25%. Here are some examples of calculations:
- If 1 m 3 of material with a cross section of 50X200 mm contains 16.6 boards, then the weight of one board will be 540 / 16.6 = 32.5 kg.
- If 25 m 3 of lumber is purchased, then it will weigh 25 ∙ 540 = 13,500 kg.
- If 100 boards 25X200 are required, then you need to buy 100 / 33.3 = 3 m 3 of wood, which will weigh 3 * 540 = 1,620 kg.
It is important to note that it is advisable to purchase edged lumber with the lowest moisture content so that after installation it does not warp or crack, especially for large-section timber. For the construction of a rafter system, the wood moisture content should not exceed 18%.
Installation of attic rafter system
Installation of a rafter system with a residential roof space requires careful preparation. It is necessary to install convenient scaffolding, decking and ladders, as well as provide workplaces with safety ropes. Workers must be provided with protective clothing, protective equipment and working equipment. It is necessary to select a flat place on the ground for pre-assembling the trusses, marking the corners and making templates. All wooden elements must be treated with antiseptic and fire-retardant compounds.
After this, you can begin work, which takes place in the following sequence:
- On walls with walled studs, a mauerlat is mounted around the perimeter. If there is a load-bearing wall inside the building, we lay a beam or purlin on it that is the same height as the mauerlat.
If the house is being built from building blocks, then the Mauerlat is most conveniently laid on threaded rods, walled into the wall during its laying.
- Cable ties with cornice extensions are attached to the Mauerlat parallel to the short wall.
- Vertical posts are placed on the tie rods, delimiting the attic space.
- The racks are connected to a tie that serves as the ceiling of the attic space. The trusses installed in this way are connected to each other by horizontal girders.
Vertical posts, top ties and horizontal purlins form the frame of the attic space
- The lower and then the upper rafters are installed, which are attached to the ridge part.
- To strengthen the lower and upper rafters, struts, headstocks and ribs are used.
- The sheathing and front board are installed on the eaves overhang.
After installing all the rafter joists, all that remains is to lay the sheathing and nail the front board
We looked at the assembly of the rafter system using the example of a broken mansard roof. The construction of other structures consists of similar operations and mainly consists of performing work according to the design installation diagram, which reflects the methods of connecting the elements of the rafter system. With carefully calculated drawings, a team of four people is able to install a roof with a rafter system of any complexity.
Video: installation of an attic roof
We examined the rafter group of the attic roof, its design, calculations, as well as a diagram and description of the main components. They offered an option step-by-step installation load-bearing structures of the attic, attached illustrations and videos that explain the procedure for assembling the structural elements of the attic roof. Now its successful construction depends only on the careful fulfillment of the requirements of instructions and technologies and the availability of certain skills for the performers to carry out construction work. We wish you success.
A house with an attic is not only an additional living space, but also a respectable appearance for the entire building. Even if the room under the roof is made unheated and is used only in the summer, it still creates a powerful “air cushion” that helps retain heat inside the entire building.
And about that - read on our portal.
Attic project
When drawing up a diagram for the construction of an attic, it is best to do this in different projections in order to see and understand the placement of all elements of the rafter system. It is very important to correctly calculate the height of the roof ridge, since the size of the area under it will directly depend on it.
When drawing up a design diagram for the construction of an attic roof, you need to calculate the height of the ridge, ceiling and total area premises.
The minimum height from the floor to the ridge should be 2.5-2.7 m, but if this distance is less, then the room is not an attic, it can only be called an attic. This parameter is established by SNIP standards.
So that all elements are drawn accurately and have the desired location in common system you need to start from a figure with right angles, that is, a rectangle or square - a cross-section of the attic space being created. Based on the sides (height and width of the future room), it will be almost impossible to make a mistake with the magnitude of the angles at which the roof slopes are located, with the location of the ridge, rafters and all supporting elements. When determining these parameters, they must immediately be entered into the drawing.
First you need to find the middle of the width of the front wall. Starting from this point, the parameters of the height of the ridge, the future ceiling of the attic, the location of the wall studs and the size of the eaves overhang are determined.
Due to the fact that each of the structures has a certain number of connecting nodes, which have different configurations, it would be a good idea to draw each of these connections separately in order to understand their features of interconnecting all the elements connecting at this point.
Any rafter system consists of basic elements and additional ones, which may not be present in every structure. The main components of an attic roof include:
- Floor beams, which are the basis for the remaining elements of the rafter system. They are laid on the main walls of the building.
- A rafter leg, straight in a gable roof system or consisting of two sections - in a broken pattern. In this case, the top rafter is called the ridge rafter, since it forms the highest point of the roof - and the rafters that form the walls of the attic are called side rafters.
- Ridge board or timber - required element for a gable roof, but is not always used when installing a broken roof model.
- Mauerlat is a powerful beam attached to the main side walls of the building. Rafter legs are installed on this element.
- Racks are the supporting elements necessary to strengthen a gable and broken structure. In the latter case, the ridge and side rafters are attached to it, and in the first, the stand is a reliable support for a long rafter. In addition, the racks serve as a frame for insulating and covering the walls of the attic.
- Diagonal bracing members or bevels additionally secure posts or longitudinal beams and rafters, making the structure more durable.
- Attic floor beams are used in all versions of the attic - they connect the racks, and they also serve as the frame for the ceiling.
- Inter-rafter purlins are installed in a broken roof for structural rigidity.
To be sure that the prepared project has been developed correctly, you need to show it to a specialist. Only he will be able to determine whether the attic parameters are correctly selected for the width and length of the walls of the building.
Video: professional calculation of a mansard roof using special software
Material parameters for the construction of an attic roof
If the graphic design is ready, then, based on the dimensions marked on it, you can calculate the amount of materials required for the construction of the attic roof. Materials must be selected according to their characteristics, which must meet fire and environmental safety requirements. For wood, it is necessary to provide special treatment with fire retardants, which will reduce the flammability of the material. So, for construction you will need:
- Boards for rafter legs. Their cross section is selected based on the results of special calculations - this will be discussed in more detail below.
- A beam having a cross-section of 100×150 or 150×200 mm is for floor beams, depending on the chosen rafter system and the width between the load-bearing walls, as well as for purlins, diagonal legs or valleys - if they are provided for in the design.
- Beam with a cross section of 100×150 mm or 150×150 mm for laying the Mauerlat.
- For racks, timber 100 × 100 or 150 × 150 mm is usually used.
- Unedged board for laying the subfloor and some fasteners.
- Annealed steel wire with a diameter of 3-4 mm - for fastening some parts together.
- Nails, bolts, staples different sizes, corners of various configurations and other fasteners.
- A metal sheet with a thickness of at least 1 mm is for cutting out overlays.
- Lumber for sheathing and counter-lattens for roofing material - depending on the type of roof chosen.
- – for thermal insulation of the roof.
- Waterproofing and vapor barrier membranes.
- Roofing material and fastening elements for it.
What section of rafters are required?
Rafters are roofing elements that will bear the main external loads, therefore the requirements for their cross-section are quite special.
The size of the required lumber will depend on many parameters - on the step between the rafter legs, on the length of these legs between the support points, on the snow and wind load that falls on them.
The geometric parameters of the rafter system design are easy to determine in the drawing. But with the remaining parameters, you will have to refer to the reference material and make some calculations.
Snow load is not the same for different regions of our country. The figure below shows a map on which the entire territory of Russia is divided into zones according to the intensity of the snow load.
There are eight such zones in total (the last, eighth, is rather extreme and cannot be considered for the construction of an attic roof).
Now you can accurately determine the snow load, which will depend on the angle of the roof slope. For this there is the following formula:
S = Sg × μ
Sg– table value – see the map and the table attached to it
μ — correction factor depending on the steepness of the roof slope.
- If the slope angle is me 25°, then μ=1.0
- With a slope from 25 to 60° - μ=0.7
- If the roof is steeper than 60°, then it is considered that snow does not linger on it, and the snow load is not taken into account at all.
It is typical that if the attic roof has a broken structure, then for different sections of it the load can have different values.
The slope angle of the roof can always be determined either with a protractor - according to the drawing, or by a simple ratio of the height and base of the triangle (usually half the span width):
Wind load also mainly depends on the region in which the building was built and on the characteristics of its surroundings and the height of the roof.
And again, for the calculation, the initial data on the map and the table attached to it are first determined:
The calculation for a specific building will be carried out according to the formula:
Wp = W × k × c
W– table value, depending on the region
k– coefficient taking into account the height of the building and its location (see table)
The following zones are indicated by letters in the table:
- zone A - open areas, steppes, forest-steppes, deserts, tundra or forest-tundra, wind-exposed sea coasts, large lakes and reservoirs.
- zone B – urban areas, wooded areas, areas with frequent wind obstacles, relief or artificial, at least 10 meters high.
- zone IN– dense urban development with an average building height above 25 meters.
With– coefficient depending on the predominant wind direction (wind rose of the region) and on the angle of inclination of the roof slopes.
With this coefficient the situation is somewhat more complicated, since the wind can have a dual effect on the roof slopes. So, it has a direct, overturning effect directly on the roof slopes. But at small angles, the aerodynamic effect of the wind takes on special importance - it tries to raise the slope plane due to the resulting lift forces.
The drawings, diagrams and tables attached to them indicate areas of the roof exposed to maximum wind loads, and indicate the corresponding coefficients for calculation.
It is characteristic that at slope angles of up to 30 degrees (and this is quite possible in the area of ridge rafters), the coefficients are indicated both with a plus sign and negative, that is, directed upward. They somewhat dampen the frontal wind load (this is taken into account in calculations), and in order to neutralize the effect of lifting forces, it will be necessary to very carefully secure the rafter system and roofing material in this area, using additional connections, for example, using annealed steel wire.
Once the wind and snow loads have been calculated, they can be summed up and, taking into account the design features of the system being created, the cross-section of the rafter boards can be determined.
Please note that the data is given for the most commonly used coniferous material (pine, spruce, cedar or larch). The table shows the maximum length of the rafters between the support points, the section of the board depending on the grade of the material, and on the pitch between the rafters.
The value of the total load is indicated in kPa (Kilopascals). Converting this value into more familiar kilograms per square meter is not difficult. With completely acceptable rounding we can accept: 1 kPa ≈ 100 kg/m².
The dimensions of the board along its cross-section are rounded up to standard lumber sizes.
| rafter section (mm) | Distance between adjacent rafters (mm) | ||||||
|---|---|---|---|---|---|---|---|
| 300 | 600 | 900 | 300 | 600 | 900 | ||
| 1.0 kPa | 1.5 kPa | ||||||
| higher | 40×89 | 3.22 | 2.92 | 2.55 | 2.81 | 2.55 | 2.23 |
| 40×140 | 5.06 | 4.60 | 4.02 | 4.42 | 4.02 | 3.54 | |
| 50×184 | 6.65 | 6.05 | 5.28 | 5.81 | 5.28 | 4.61 | |
| 50×235 | 8.50 | 7.72 | 6.74 | 7.42 | 6.74 | 5.89 | |
| 50×286 | 10.34 | 9.40 | 8.21 | 9.03 | 8.21 | 7.17 | |
| 1 or 2 | 40×89 | 3.11 | 2.83 | 2.47 | 2.72 | 2.47 | 2.16 |
| 40×140 | 4.90 | 4.45 | 3.89 | 4.28 | 3.89 | 3.40 | |
| 50×184 | 6.44 | 5.85 | 5.11 | 5.62 | 5.11 | 4.41 | |
| 50×235 | 8.22 | 7.47 | 6.50 | 7.18 | 6.52 | 5.39 | |
| 50×286 | 10.00 | 9.06 | 7.40 | 8.74 | 7.66 | 6.25 | |
| 3 | 40×89 | 3.06 | 2.78 | 2.31 | 2.67 | 2.39 | 1.95 |
| 40×140 | 4.67 | 4.04 | 3.30 | 3.95 | 3.42 | 2.79 | |
| 50×184 | 5.68 | 4.92 | 4.02 | 4.80 | 4.16 | 3.40 | |
| 50×235 | 6.95 | 6.02 | 4.91 | 5.87 | 5.08 | 4.15 | |
| 50×286 | 8.06 | 6.98 | 6.70 | 6.81 | 5.90 | 4.82 | |
| total snow and wind load | 2.0 kPa | 2.5 kPa | |||||
| higher | 40×89 | 4.02 | 3.65 | 3.19 | 3.73 | 3.39 | 2.96 |
| 40×140 | 5.28 | 4.80 | 4.19 | 4.90 | 4.45 | 3.89 | |
| 50×184 | 6.74 | 6.13 | 5.35 | 6.26 | 5.69 | 4.97 | |
| 50×235 | 8.21 | 7.46 | 6.52 | 7.62 | 6.92 | 5.90 | |
| 50×286 | 2.47 | 2.24 | 1.96 | 2.29 | 2.08 | 1.82 | |
| 1 or 2 | 40×89 | 3.89 | 3.53 | 3.08 | 3.61 | 3.28 | 2.86 |
| 40×140 | 5.11 | 4.64 | 3.89 | 4.74 | 4.31 | 3.52 | |
| 50×184 | 6.52 | 5.82 | 4.75 | 6.06 | 5.27 | 4.30 | |
| 50×235 | 7.80 | 6.76 | 5.52 | 7.06 | 6.11 | 4.99 | |
| 50×286 | 2.43 | 2.11 | 1.72 | 2.21 | 1.91 | 1.56 | |
| 3 | 40×89 | 3.48 | 3.01 | 2.46 | 3.15 | 2.73 | 2.23 |
| 40×140 | 4.23 | 3.67 | 2.99 | 3.83 | 3.32 | 2.71 | |
| 50×184 | 5.18 | 4.48 | 3.66 | 4.68 | 4.06 | 3.31 | |
| 50×235 | 6.01 | 5.20 | 4.25 | 5.43 | 4.71 | 3.84 | |
| 50×286 | 6.52 | 5.82 | 4.75 | 6.06 | 5.27 | 4.30 | |
Tools
Naturally, during work you cannot do without tools, the list of which includes:
- Electric drill, screwdriver.
- Building level and plumb line, tape measure, square.
- Axe, chisel, chisel, hammer
- Circular saw, jigsaw, hacksaw.
- Carpenter's knife.
Installation will be accelerated if the tools for the work are of high quality, and the work will be carried out with competent mentors and assistants, carefully and step by step.
Installation stages
It is necessary to strictly follow the sequence of work - only under this condition the structure will be reliable and durable.
Mounting the Mauerlat
Installation of any rafter system begins with securing a powerful supporting structure to the end of the side walls of the building. timber - mauerlat, on which it will be convenient to install rafter legs. The Mauerlat is made from high-quality timber with a cross-section of at least 100 × 150 mm. It must be laid on roofing felt waterproofing laid along the upper end of the wall (regardless of the material).
Due to the Mauerlat, the load will be evenly distributed over the walls and transferred to the foundation of the building.
The Mauerlat is secured to the wall using metal pins, which are pre-embedded in a concrete belt or crown running along the upper edge of the wall, or with anchor bolts with a diameter of 12 mm. They must go into the wall at least 150 — 170 mm. If the Mauerlat is installed on a wooden wall, then the beams are attached to it using wooden dowels.
Installation of truss structure
- Installation of the rafter system begins with the installation of floor beams. They can be attached to the mauerlat from above if the beams are planned to be moved outside the perimeter of the building and thereby increase the area of the attic. In this design, the rafter legs are fixed to the floor beams.
Floor beams fixed on top of the Mauerlat (Fig. A) - In another case, they can be stacked on waterproofed walls and fastened with corners or staples to the inner edge of the Mauerlat. This option is used when the rafter legs are planned to be attached directly to the mauerlat.
Another option is that only the rafter legs are attached to the Mauerlat - Next, you need to find the middle of the floor beam, since this mark will become a guideline for determining the location of the support posts and the ridge.
- The racks should be located at the same distance from the marked middle of the floor beam. They will subsequently determine the location of the walls of the attic room, that is, its width.
- The bars for the racks must have a cross-section equal to the size of the floor beams. The constructions are attached to the beams using special corners and wooden overlays. However, to begin with, they are first nailed, then carefully leveled using a building level and a plumb line, and only then are they permanently secured, taking into account future loads.
- When the first pair of racks is installed, they are fastened together from above with a bar, which is called a tie. This tightening is also connected to the racks using special metal corners.
- After securing the tie, you will get a U-shaped structure. Layered rafters are installed on its sides, the second end of which is attached to the floor beam or placed on the mauerlat.
- A special recess (groove) is cut into the installed supports for the timber or in the rafters. With its use The rafters are tightly installed on the Mauerlat beam and secured with metal brackets.
- To provide rigidity to the structure, additional struts can be installed from the base of the rack to the middle of the installed side rafters. If this does not seem enough, and saving material is not in the foreground, then you can strengthen the overall structure with additional racks and contractions (they are indicated in the drawing, Fig. A, with translucent lines).
- Next, while tightening, the middle is calculated - the headstock will be attached to this place, supporting the ridge connection of the upper hanging subsystem of the rafters.
- The next step is to install the ridge rafters, which can be fastened together with different connections - this can be a metal plate or powerful bolts with metal plates or washers.
- After installing them, the headstock is attached to the ridge and the middle of the tightening.
- Having completed work on one part of the rafter system, you need to make all the rest according to the same principle. The distance between adjacent rafters in such a system should be no more than 900 — 950 mm, but the optimal interval would probably still be 600 mm - this will provide the necessary rigidity and stability of the structure, and will be convenient for insulation using standard mineral wool mats. True, this makes the structure heavier and will require more materials.
- First, the side parts of the system assembly are installed, and then the intermediate parts. They are connected to each other by purlins, which are installed between the upper ends of the racks and act as spacers. Thus, you will get a rigid structure of the attic rafters, in which the frame for wall cladding will already be ready.
Prices for various types of fasteners for rafters
Rafter fasteners
Waterproofing attic roof
When the rafter system is built, you can proceed to finishing it and accompanying materials.
- The first coating that should be fixed directly on top of the rafters will be a waterproofing and windproof film. it is attached to the rafters using staples and a stapler, starting from the cornice. The canvases are laid with an overlap of 150 — 200 mm, and then the joints are glued together with waterproof tape.
- On top of the waterproofing, a counter-lattice is placed on the rafters, which will more reliably fix the film on the surface and create the necessary ventilation distance between the windproof and roofing material. The counter-lattice is usually made of boards 100 wide — 150 mm and thickness 50 — 70 mm.
- The sheathing is fixed perpendicular to the counter-lattice, on which the roofing material will then be laid. The pitch between the slats must be calculated depending on the type and size of the sheet roofing material, taking into account the overlap required for it
- If a soft roof is chosen, then plywood sheets are most often fixed to the counter-lattice.
Roofing installation
The roofing material is attached to the prepared sheathing or plywood. Its installation usually starts from the roof eaves and proceeds in rows, from one of the edges - depending on the type of roof. Roofing sheets are mounted with an overlap. If a metal profile or metal tile is used for the coating, then such material is secured with special self-tapping screws with elastic gaskets. Fastening elements are usually matched in color to the roofing material.
The most difficult thing in covering an attic sloping roof is the transition from layered side rafters to hanging ridge rafters. There may be certain difficulties if the roof has projections for installing roofs over balconies or windows.
In addition, if a chimney pipe goes onto the roof, it requires a separate design of the hole inside the rafter system and an insulating layer, and on the roof, reliable waterproofing must be installed around the pipe.
You can find out in detail how and what is the best way to cover a roof on our portal; there is a whole section where you can find answers to many questions, including recommendations for reliable insulation of an attic room.
Prices for popular types of corrugated sheets
Corrugated sheet
Video: detailed video tutorial on building a mansard roof
It should be noted that the work of constructing any roof, and especially one as complex as an attic roof, is not only responsible, but also quite dangerous and requires special, increased safety measures. If you have no experience in carrying out such construction processes, then it is better to entrust their implementation to professionals or perform all actions under the supervision of an experienced craftsman, and with the utmost care and precision.
The attic allows you to expand the space of the house and allocate space for additional rooms. The complexity of self-installation is reduced after studying materials about the features of the building. The work of the owners is paid for by the durability and beauty that the rafter system of the created mansard roof receives. This material will help you in its construction.
The support of the entire roof, and therefore the basis of the attic structure, is the rafters. They must be selected in accordance with several parameters, calculated taking into account the characteristics of the materials. The selection options are as follows:
- Load. The sum of the weight of everything that makes up the attic roof, to which 10% is added to avoid errors. The rafters must withstand the weight of the totality of all materials, as well as the load of snow in winter and gusts of wind at any time of the year.
- Installation speed. When constructing prefabricated buildings, it is better to use metal rafters, which are installed by specialists in the shortest possible time.
- Easy to install. At this point, thin-walled metal rafters again win.
- Material cost. Since metal is a priori more expensive, and the complexity of the advanced design of mansard roofs multiplies the price, wooden rafters are much cheaper. For this reason they win in case self-built attics.
Further, as a more traditional option, wooden rafters will be considered. In addition to the above two types, there are also combined buildings, but the rafter system of the attic roof is rarely built with their help. Below are various diagrams of systems that may be useful when building your own attic.
In this article
Choosing the type of attic
Attic spaces have several types, differing in insulation design and structural strength, as well as the type of roof. An insulated attic is suitable for those who intend to turn it into a living space used all year round. As for the cold attic space, it is suitable for dacha owners.
Types of attic buildings vary depending on the slope and shape of the walls:
- Vertical.
- Sheer.
- Triangular with a sloping roof.
- Complex shapes, which are generally called broken shapes.
- Single-level.
- Two-level.
- Symmetrical appearance of the walls.
- Walls of asymmetrical design.
These parameters will help determine the type of attic. The article discusses the three most common of them:
- Classical.
- Triangular.
- Blocky.
For owners of houses based on individual projects, the main characteristics will allow them to create their own unique design.
Development of an individual project
In your own home you want to create maximum uniqueness. Both in the case of choosing your own form, and when using one of the schemes below, the owner needs to make a clear construction plan to avoid problems. Needs customization general drawings for your home, recalculate the parameters taking into account new materials. For success, follow these tips on how to do the project right:
- Create an attic of such a height that you can not only sit and store things, but also walk comfortably. This is especially true in the case of living space.
- Observe the dimensions of the attic. Don't make it too big, otherwise the building will look ugly.
- Do not use wide roof slopes, otherwise the windows will be blocked and the rooms will be darkened.
- The rafter system of the attic roof requires drawings. Don’t waste time on a visual plan; it will help during construction.
Classic scheme
Most often they choose an attic with a pentagonal roof, because this scheme The rafter system of the attic roof gives a larger, more functional space. Supports are used to create the walls of the room. The easiest way to describe the design is using several geometric shapes:
- Rectangle. This is the center of the attic, a space that can be used for any purpose.
- Right triangles: one on the left and one on the right. This space is no longer so versatile.
- The ceiling part is a triangle with equal sides.
This rafter system for the attic roof is not original. . If you want to create a non-standard, perhaps designer attic, on your site, then below is a list of other less common schemes.
Triangular pattern
This is the simplest, although not the most The best way creation. Thanks to the steep slopes of the roof, almost no snow remains on it, as a result of which the load is reduced. But at the same time, there is less living space. Features and rules for the construction of a triangular attic:
- Support - Mauerlat. The weight of the rafters, inclined in appearance, is transferred to it.
- The upper part of the supports is attached to the left and right purlins.
- Hanging rafter arches required for the ceiling part are also used.
- When using hanging rafters and provided that they are the basis for a space more than 3 meters long, a suspension is used. It is installed in the center. The suspension is not a support, so the next point is logical.
- The suspension is not built on the principle of a support strut.
- Considering that the building is susceptible to falling due to gusts of wind, it needs to be additionally secured. For this purpose, the rafters are attached to the walls using twists.
- The rafters of the lower part rest on the ceiling.
- The posts cut directly into the beams, given that the floor is wooden.
Important! Each rafter is attached to the wall, and not through one. This principle is necessary in this particular case.
Block type
The ceiling becomes a support for pre-prepared block modules. The biggest advantage of this system in assembly is that it is simple and carried out on the ground. It is much easier to create this type with your own hands than the others. Two points are important:
- On the ground it is easier to connect the elements and make a stronger bond
- In conditions of height, a person becomes agitated, thereby reducing the quality of the entire building. On earth, errors not only occur less frequently, but are also more noticeable.
At the same time, there is also a drawback. The rafters of the attic roof are quite heavy, which makes it difficult to lift the structure to the floor, and this can only be done with the help of a team of 4 or more people. The task is easier for those who have special lifting equipment, but there are only a few of them.
Installation algorithm:
- Drawing up a project.
- Creation of frames - the foundations of the walls of the attic room. Longitudinal parts are a replacement for standard purlins and beds. They, as well as the racks, are delivered to the assembly site - a flat earthen surface.
- Next, mark the places where they will be attached. support structures sidewalls They should look like lines, which, when subsequently filed, create nests for fastening.
- Installation and fixation for a short period of time. For the second, spacers are used; In addition to being held in place, beams are attached to the frame.
- The beams must have sockets for connection to the rafters in the attic roof. The tools used are a chainsaw and a chisel.
Important! The nests for the rafters must be on the same line, otherwise the structure will look oblique.
- The top tier of attic rafters is also created on the ground. The base of the resulting structure is at the same time a stretcher within the attic system. Nests are created at the edge of the base. Don't forget to decide on the tenons on the lower halves of the rafters.
- All elements of the upper part are connected to each other: a wooden addition for the ridge assembly will help with this. It would be useful to install an additional crossbar.
- Before moving to the attic roof, rafter leg blanks are created. We try them on to the frames laid out on the ground. It is more convenient to cut them in one fell swoop, grabbing several pieces with a clamp. Only the upper bevel should be cut, taking into account the fact that it will rest partly on the wall post, partly on the stretch of the upper rafter trusses.
- The lower rafter is tried on at the end. The shape of the spike is drawn in the area of its lower heel, repeating the configuration of the socket in the beam. Thorns are cut out.
- The upper tier moves to the roof along with the rafter legs of the lower tier. We first install the trusses, attaching them to the upper frame of the walls with staples, then the rafters of the lower part, attaching them to the floor beams with the same staples.
The subsequent stages of roof construction are carried out according to standard rules. Visual diagrams for an attic roof, representing the structure, will introduce you in detail to the described principles of constructing a rafter system. .
Important! The strength of the frame can be increased by using notch joints. This will avoid additional elements, for example, struts.
The given options for attic space schemes are universal: home owners will be able to choose the one that best meets their requirements. Regardless of the type of attic, the main thing is the correct materials and installation of the rafter system. Then the building will last a long time and will be safe for residents.
