The attic is both another floor where you can live and a beautiful external appearance of the entire private house. Even if the attic will be used only in the summer season and will not be heated, nevertheless, this space under the roof in any case forms a strong “cushion of air” that traps heat inside the entire building.

Building an attic roof with your own hands is possible, but only if you are a specialist with extensive experience or you need help from such a person, because this part of the house has a complex structure.

Mansard roof with your own hands can be erected under various roofing structures, but the most popular are broken and gable. To choose the required design, you need to analyze these two types in detail.

Also, the person who carries out the construction needs to decide on the type of rafter system for the attic roof. It is necessary to create a mansard roof pie. Let's take a closer look at them.

Types of rafter system

The construction of an attic floor or a house with an attic begins with the construction of a rafter system. Different types of roofing refer to one of two types of rafter systems. In total, there are two types of rafter system for mansard roofs:

1. Hanging;
2. Layered.

Do-it-yourself mansard roof, its construction begins with the choice of rafter system. These two types have their own distinctive nuances. The choice of one type or another depends on the location of the (main) walls of the building. Let's look at each variety separately in more detail.

Hanging system

The rafter system of the attic roof is called hanging because its support (hanging rafters) is located on the outermost walls with load-bearing capacity. This happens if the building does not have load-bearing partitions, but only walls from the outside.

This type of construction can only be used in a situation where the distance between the external walls does not exceed eight meters. Because this design creates a huge load on the base of the main walls.

To make the load on the base much less, construction elements such as vertical bars (headstocks), tie rods, support beams, and struts are used.

So, struts are structural elements that pull up floor beams and are intended to connect and transfer loads. The construction head hangs the tie to the ridge part of the roof.

In this truss structure, bars that are quite thick are used to create floor beams. The cross-section of such bars is 100×200 millimeters. In order not to make a mistake in calculations, you need to trust a professional, because the reliability of the floor depends on this.

Layered system

A distinctive feature of this design is that it rests not only on the walls, but also on the partitions built on the base of the building. Therefore, at the design stage of the attic space, it is necessary to carefully consider all the elements of the foundation structure if you are planning to install a strip foundation. Load-bearing partitions will be built on it. A layered rafter structure is a more suitable option for building an attic, because it can withstand much greater pressure than the previous system. The layered variety guarantees reliability for floor beams.

If your roof has a broken structure, then the attic rafter system should be combined. This means that a hanging system is suitable for ridge rafters, and a layered system is suitable for side rafters.

Installation of a roof with an attic

During the construction of a brick building, the front side of the attic is also made of brick. This simplifies the process, since you do not have to calculate the parameters of all roof elements. However, it must be remembered that the walls must be on a reliable foundation. They must also have the required thickness, because the pediment creates enormous pressure on the foundation of the building.

If the roof of your attic house will be used as an additional floor, then the pediment should be made of brick or foam blocks. This will create a room under the roof.

In order for the under-roof space to have an acceptable height with a gable roof and spaciousness, the angle of each slope should be 45 degrees. The size of the angle depends on the width of the side of the building (end). If the angle is made smaller, the space of the room under the roof will also decrease. If the angle is large, then the height will be enormous; the attic and its rafter system will put a huge load on the foundation. Also, the expenditure of funds will be unjustified.

Installation of a gable roof is much easier than for an attic with a sloping roof. Since, to build the first one, straight rafters for the attic roof are used, kinks and other connections, which are additional, are eliminated. But the broken roof of the attic allows you to build a more spacious room, and thanks to this design the ceilings will have the desired height. The design of the sloping mansard roof not only creates space, but also makes the structure solid. The complexity of this design lies in the fact that it has a huge number of connecting nodes. All these connections must be made according to the rules, then you can guarantee high quality.

Before purchasing material for a certain type of attic roof truss system, you need to carry out a design with the required dimensions.

Attic room project

When you draw a diagram of your attic space, draw it in a variety of views to better study how the assembled components are placed. It is necessary to correctly calculate the height of the roof ridge - this is the most important, because the area of ​​​​the room under the roof depends on this element. It is impossible to collect unnecessary things in a project; all calculations must be accurate.

In addition to the height of the ridge, it is necessary to make calculations of the height of the ceiling, as well as the size of the under-roof space.

The distance from the attic floor to the roof ridge should be two and a half meters. If this distance is less, then it is not an attic room, but just an attic.

In order for the elements to have accurate values ​​and be positioned correctly, it is necessary to rely on a figure that has right angles (rectangle or square). The rectangular figure is a section of the attic. Starting from the sides of the section, you can determine the required angles (45-50 degrees). You can also determine the location of the roof ridge, rafters and other structural elements.

At the very beginning, it is necessary to determine the middle of the width of the front wall. The midpoint of the width of the front wall will help determine the height of the roof ridge and ceiling, the location of the stud walls, and the dimensions of the eaves overhang.

Due to the fact that any structure has a certain number of connecting nodes that have different locations. It is better to draw each connecting element separately in order to find out all the features of the connection with each other.

A diagram of the rafter system for the attic roof must also be prepared. Each rafter system design and its variety has primary and secondary elements. Main components:

• The first main element is the floor beams. They are mounted to form the basis of other parts of the rafter structure. Floor beams are laid on the load-bearing walls of the house.
• The structure also consists of a rafter leg. It is straight in a gable roof or consists of two parts in a sloping roof. In the latter version, the rafter that is located at the top is called the ridge rafter because it creates highest point, which is the ridge of the roof. Other attic rafters form walls and are called side rafters.
• The next element is timber. This is the most important part in a gable roof structure. However, most often timber is not used when constructing a sloping roof.
• Mauerlat. This is also a powerful beam, which is laid on top along the perimeter of the outer wall. The rafter legs are installed on the Mauerlat.
• Another component is the racks. This is a support for strengthening a particular roof structure. Two types of rafters are attached to the broken roof: side and ridge. In another type of roof, a support for long rafters acts as a post.
• Bevels. They are the connecting element for the racks. Also, bevels are longitudinal beams that give the structure additional strength.
• The next part is the attic floor beams. These are connecting nodes for racks, as well as a base for arranging the ceiling.
• Inter-rafter purlins. Their installation is carried out in a sloping roof to provide rigidity.

If you compiled the project yourself, then it needs to be checked by a professional. If so, he may make some adjustments.

Characteristics of materials used

If the drawing is made, then it is necessary to carry out calculations based on it: how much material is needed to build the attic. Products must meet the required properties. They must also be environmentally friendly and fireproof. For wood, you need to carry out specially designed treatment using antiperines. Thanks to this treatment, you can increase the level of fire resistance of wood.

Therefore, the following materials will be useful for construction:

1. The first material is boards. They will be intended for rafter legs. The section is selected according to the calculation results.
2. A beam whose cross-section is 150×200 millimeters (may be different). It is intended for floor beams. The choice of section depends on the type of rafter system and the distance between the load-bearing walls of the building. The timber is also used for purlins and valleys. If these elements are in the project at all.
3. Another beam, the cross-section of which is 150×150 (maybe different), to lay another beam - the mauerlat.
4. The next material is unedged board. It is necessary to lay the subfloor.
5. The wire is made of steel, which should have a diameter of four millimeters. It will be needed to hold some parts together.
6. It is necessary to collect products for fastening: nails, bolts, staples, corners.
7. Another material is a sheet of metal, the thickness of which should be one millimeter.
8. Timber intended for sheathing and antiseptic-treated timber (counter-lattice). The choice of polymaterials depends on the type of roof.
9. Products used for roof insulation.
10. Films designed for waterproofing and vapor barrier of the space under the roof.
11. Roofing material and components for its fastening.

Required rafter section

Rafters are roof parts that bear the main pressure, so their cross-section must meet certain requirements.

The size of the required timber depends on different standards:

1. The first parameter is the step between the rafter legs.
2. Length of rafter legs between support points.
3. The last parameter is snow and wind load.

Almost all of these parameters can also be calculated from the drawing.

Step-by-step installation instructions

A do-it-yourself roof with an attic does not end at the design stage. Do-it-yourself installation of an attic roof must be carried out step by step, according to a specific algorithm of actions. Then you will get high quality. Installation is practically no different, regardless of whether you have a sloping roof or a gable roof. How to build a roof with an attic and how to do it correctly? Let's consider each stage of installation separately.

Fastening the Mauerlat

It is necessary to make a frame for the attic roof. The first stage is securing a powerful beam (mauerlat) to the side of the walls. The rafter legs will be installed on it. Its installation is carried out on a waterproofing layer of roofing felt.

Thanks to this element, the pressure will be distributed evenly across the base of the building.

Fastening is carried out using metal pins. The depth of insertion of metal pins should be 150 millimeters. If the beam is fastened to the wall wooden house, then it passes with the help of wooden edges.

How to make a rafter system? Installation of the rafter system begins with the installation of wooden beams to create the ceiling. These components are attached to a powerful log at the top. The rafter legs are attached to these components.

In another situation, their installation can be carried out on walls insulated from moisture. Fastening is carried out thanks to the corners to the inside of the powerful beam. Next you need to find the middle of these elements in order to understand where the support and ridge posts are located.

The racks will help determine the width of the walls of the attic space.

The cross-section of the bars intended for the constructed racks must be similar to the cross-section of the wooden floor beams. They are attached to each other thanks to specially designed corners. They are secured with nails, and then everything is leveled using a building level.

Then the layered rafters are installed. Then a narrow notch is cut out. Thanks to the narrow recess, the rafters are installed on a powerful beam. Installation is carried out using brackets.

Then the ridge rafters are installed. They are fastened together thanks to a metal plate. The grandmother joins the skate. This was the completion of one part of the rafter structure. The rest are built in the same way.

After the attic is built, it is waterproofed. After this you will be able to get a full-fledged roofing pie, and the construction of the house with your own hands is completed.

Do-it-yourself attic roof is a complex and responsible process. To build a roof for a house, you must also follow safety precautions while working. If you do not have any experience in this work, then it is better to entrust the roofing to professionals who will do everything efficiently and at a high level.

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

A 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 structure, which can be of different types, namely:

1. 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

2. 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

3. 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

4. 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

5. 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.

1. 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

2. 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

3. 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 extended 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 to different types mansard roof, 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 into a groove. To construct a gable roof, the following main components are used:

1. A ridge unit that provides a connection between the rafter legs and the ridge purlin.
2. Places where the crossbar connects the rafters to give greater strength and rigidity to the trusses.
3. Attachment points for struts and posts that provide additional support to the rafters.
4. 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 the broken mansard roof, five rafter elements

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 is large, 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 recalculating their quantity in 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:

1. 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.
2. If 25 m 3 of lumber is purchased, then it will weigh 25 ∙ 540 = 13,500 kg.
3. 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:

1. On walls with walled studs, a mauerlat is mounted around the perimeter. If available inside the building load-bearing wall We lay a bench or purlin on it of 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.

2. Cable ties with cornice extensions are attached to the Mauerlat parallel to the short wall.
3. Vertical posts are placed on the tie rods, delimiting the attic space.
4. 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

5. The lower and then the upper rafters are installed, which are attached to the ridge part.
6. To strengthen the lower and upper rafters, struts, headstocks and ribs are used.
7. 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.

When starting to build an attic, you need to have a good project. The type of roof should be harmoniously combined with the appearance of the entire building. When choosing the design of the upper floor, you need to find out how the rafter system of the attic roof is structured and what its pitch is. The design of the rafter system is the basis of the roof. All components, supports, the distance between them, material and fences are important. This is the supporting skeleton of the roof, which determines its reliability and durability; in addition, the rafter system allows it to perform its direct function - to protect it from bad weather. If you plan to build an attic with your own hands, you need to choose not very complex circuit designs. The rafter system largely depends on what type of roof will be chosen, what rafter pitch and what type of attic roof will be preferable. The project must contain the distance between the rafters, the spacing of the beams, and take into account both the roof’s own weight and the load caused by natural precipitation. In addition, all components must be resistant to temperature changes.

Types of attic roof

Rafter system and components for various types attic structures have their differences. At the same time, the structure should not be very heavy, so as not to load the walls of the building, reliable and durable, and the pitch of the rafters should be optimal. There are different types of attic roofs:

• Gable, with two slopes on the sides.

• A broken line, consisting of two or more slopes with different angles of inclination.

• Hip, where two or more slopes have a triangular shape.

• Semi-hip, with end slopes located approximately at a distance of half the height.

• Dome, for buildings with a polygonal or round shape.

• Vaulted, having the shape of an arc in section.

The type of roof is divided into ventilated and non-ventilated structures. Depending on the climate, a building of one type or another is chosen. For humid climate zones with high rainfall, it is preferable to build ventilated roofs. In such roofs, the layer of air between the roofing material and the insulation performs an additional protective function. Unventilated, broken, more suitable for dry climates.

Features of the attic roof

The characteristic features of an attic roof, in contrast to standard roofs, is the impact on the structure not only from the outside, but also from the inside. External in the form of precipitation and wind and internal in the form of condensation arising due to the difference in temperature indoors and outdoors. Therefore, the structure of the upper floor and the rafter system must have additional vapor barrier and thermal protection - layers of material laid at some distance from each other. For additional thermal insulation, mineral wool is usually used; together with moisture-proof material and waterproofing on the roof, they form good protection. A small distance between the layers will provide ventilation to the roof.

How to properly install thermal insulation and waterproofing

Rules for rafter systems

When constructing an attic roof, strict adherence to the standards and recommendations regarding the design of the rafter system and their spacing is necessary. The main ones:

• The timber or board for making rafters should be selected from high quality wood that is well dried (with a moisture content of no more than 15%).
• The size of the rafters should be maintained at least 100x100 mm in cross section.
• It is not allowed to insert beams into the lower crown; this can weaken the structure.
• Be sure to treat all wood components with a fire retardant and antiseptic to prevent fungus and rot.
• The angle of inclination of the rafters is from 30 to 60 degrees.
• The rafters are fastened with metal corners or metal brackets and special nails; the strapping is done with wire.

• The height of the rafter system varies from 2.5-3.5 meters, and the broken structure allows a height of up to 4 m.

• Particular care should be taken to design and calculate components and window openings, rafter spacing, because After installing the rafters, it will be difficult to change the parameters of the roof windows.

Rafter materials

The rafter system of the attic roof can be constructed from various materials. Modern industry makes it possible to use not only wood, but also lightweight metal beams and assemblies. The most common are:

• metal structures;

• reinforced concrete structures, used mainly for industrial buildings;

• wooden structures;

• combined designs.

The material should be determined based on the design parameters of the building, its size and application. Metal and concrete rafter systems are usually used on industrial buildings. In private and small-sized houses, wooden structures are often preferred. Wood is easier to process, the roof structure is not so heavy, a rafter system made of wood is easier to install and is much more environmentally friendly.

Calculation of the rafter system

In order for the roof to last a long time, reliably perform its functions and not require constant repairs, it is necessary to make accurate calculations before starting construction. You should take into account the roof’s own weight, depending on its material, the amount of precipitation and wind load. In accordance with the calculations, the type of rafter structure and the installation pitch of the rafters are selected. We list the main types of rafter systems:

• hanging;

• sloping roof rafter system;

• layered system;

• combined.

Calculations for systems with a sloping structure and sloping roofs are easier and faster than for hanging rafters. The most common are combined rafter structures of pitched roofs. It is recommended to entrust the calculation of complex rafter systems to professional designers. Calculation using complex formulas and coefficients should give the load value per meter of square rafter system. For residential buildings, the standard average load is 50 kg per m².

Design diagram of the rafter system

Lathing and Mauerlat

The design of the sheathing is directly related to the type of roofing. For soft types of coating (for example, ondulin), the sheathing must be continuous. When using slate, metal tiles or corrugated sheets, the boards on the sheathing should be placed at a distance of 25-40 cm. For the manufacture of sheathing, an edged board with a thickness of 40-50 mm is usually used. If the roof has a low slope, snow retention structures should be installed.

For stone buildings, such a part of the rafter system as the Mauerlat is common. Its task is to compensate part of the load of the rafters on the walls of the house. In addition, Mauerlats connect the roof structure and the building. As a rule, the Mauerlat is attached using anchors to a concrete belt on top of the walls. In small wooden houses made of timber or chopped, the role of a mauerlat can be performed by the last crown.

Rafter system supports

The structure of the attic roof rafter system is distinguished by its mounting on the Mauerlat:

• In wooden houses made of timber, the Mauerlat can be fixed to the upper crown.
• In houses with a frame, the rafters can rest on the top frame.
• In houses made of brick and stone, the support is the lower crown.

Important! In all cases, it is imperative to waterproof the support beams. For this, as a rule, roll-type waterproofing materials are used.

In the case of mounting the beds on poles, the dimensions of the poles should be 100x145 mm ± 5 mm. If the bench is mounted on a wall or ceiling, you can install a narrow board between them. Lezhen can not be used for a hipped roof if beams without roof struts are used.

Installation

Let us briefly describe the order in which rafter systems for pitched roofs are installed. You should start with the installation of the Mauerlat on which the rafter system will rest. It is made from timber measuring approximately 10x15 cm and takes on the load of the rafters. Waterproofing in the form of roofing felt or similar material is placed under the timber. The Mauerlat is fixed with studs or with cement mortar.

If the roof has a broken or combined structure, the most common form of truss is U-shaped. It is recommended to install such trusses at the bottom, then lift them and install them on the roof. The frame is assembled from a 5x15 cm board or 10x10 cm timber and is mounted on the roof at a distance of 0.5-2 meters. The distance between the trusses determines the load that the roof must withstand. The smaller the distance between the rafters, the greater the weight the structure will withstand. The most common are triangular trusses.

Important! The outer trusses should be installed first, connecting them with a ridge. The ridge is leveled horizontally using a level, after which intermediate trusses can be installed.

A similar design with U-shaped trusses is optimal for a roof width of no more than 6 meters. For roofs exceeding this parameter, a design with an additional central support made of timber is recommended. The rafter legs and trusses in the upper part are connected to each other by horizontal beams. To make a reliable and durable attic rafter system, you should use coniferous wood. The timber, well dried and sanded, is carefully checked for the presence of knots on all elements and discarded. Fastening is carried out with metal corners, brackets at equal distances and overlays.

Construction of the roof truss system

The difficulty lies in the fact that it is necessary to take into account several important components: snow load, gusts of wind, slope angle, weight of the rafters themselves, insulation, waterproofing, roofing materials. Rafters can be combined, metal or wood.

The attic roof should be light so as not to load the foundation. Developers are increasingly using thin-walled metal rafters for mansard roofs; their cost is much higher than wooden ones, but the speed and ease of installation of such systems more than makes up for this drawback.

In independent construction, the rafter system of an attic roof is traditionally made of wood, so we will take this material as a basis.

Good to know

In order to correctly calculate the truss structure of the attic, it is necessary to take into account 3 types of loads acting on the roofing system. First, you should calculate the weight of the attic roof itself: roofing material, sheathing, counter-lattice, waterproofing, rafters, attic insulation layer, vapor barrier, finishing. To do this, you will need to know the weight of each material per 1 m2; such parameters are indicated in the instructions and certificates of the manufacturers.

For example, polymer-bitumen waterproofing will require 5 kg/m2, one square meter of mineral wool weighs 10 kg, standard sheathing made of 25 mm boards - 15 kg, ondulin approximately 3 kg, metal tiles - the heaviest roofing material. When calculating the load, add up all the indicators and multiply by a correction factor of 1.1.

Secondly, the design of the attic roof rafter system must withstand snow loads; in some areas this figure exceeds more than 500 kg per m2. Formula for calculating snow load:

S=Sg x µ, where

Sg is the mass of snow on 1m2 of horizontal surface, the indicator is established by regulatory documents for each climatic region separately;

µ - coefficient depending on the slope of the roof: an angle of 25 o - coefficient 1.0, 25-60 o - 0.7, if the slope is above 60 o the coefficient is not taken into account.

And finally, wind loads. To calculate them, the formula is used:

W = Wo x k, where

Wo – normative data, which are determined individually for each district;

k – correction factor for different types terrains and building heights.

Based on the total load on the rafter system of the attic roof, the length, pitch and cross-section of the rafter leg are determined. Below we have provided a table of recommended parameters for installing a rafter system in a temperate climate zone (Moscow region):

Distance between attic roof rafters, m	Leg length, m
	6	5.5	5.0	4.5	4.0	3.5	3
	Cross section of beams, mm
0,6	50*200	50*200	50*175	50*150	50*150	40*175	40x150
0,9	75*250	75*200	75*175	75*175	50*200	50*175	50x150
1,1	100*200	75*200	75*200	75*175	75*175	75*150	75x150
1,4	100*200	100*200	75*200	75*200	75*200	75*175	75x150
1,75	100*250	100*200	100*200	100*200	75*200	75*200	75x150
2,15	—	100*250	100*250	100*200	100*200	100*175	100x150

Other elements of the attic roof rafter system have their own parameters:

• the Mauerlat is made of timber 150*150, 100*150, 100*100 mm;
• crossbar – 100*200-150 mm;
• purlins – 100*200-150-100 mm;
• valleys, diagonal legs – 100*200 mm;
• tightening – 50*150 mm;
• strut – 150*150, 100*100 mm.
• hemming board – 25*100 mm.

Important: Wooden rafters must comply with GOST 8486-86(83). There can be no more than 3 knots per 1 m of a leg; the size of the knots should not exceed 30 mm along the long side. Through cracks are unacceptable. Wood moisture content is less than 18%.

Rafter system of a gable mansard roof, drawing of the main elements of the truss

Main nodes

The truss structures of attic roofs, regardless of whether they include many interfaces and butt joints, are connected to each other, cut into a tie and a mauerlat, have auxiliary elements of the system: crossbars, headstocks, supports or struts, and are additionally fastened with staples, bolts, clamps. The design of the rafter system of the attic roof must provide for the uniform distribution of all loads on the base and load-bearing structures of the building.

Scheme of the attic roof rafter system, main components and elements

Depending on the architectural solution, the type of attic roof is determined, in turn, not only its usable area depends on the configuration of the roof, but also what type of rafter system is applicable in each specific case: suspended or layered.

Layered system, resting the foot on the ridge beam and Mauerlat

Layered rafter legs rest on the load-bearing walls of the attic, and are supported in the middle by intermediate supports; in such systems, loads are transferred exclusively to bending. Hanging ones rest only on attic walls, they are usually installed where there is no internal load-bearing wall, they do not create a horizontal load, only compression and bending.

A hanging system is installed if the distance between the wall supports is no more than 6.5 m; installing an additional support makes it possible to cover an attic up to 12 meters wide; if you need to cover a wider area, then each 3 meters has its own support.

Hanging and layered rafters of the attic roof

If the attic design provides for not one, but several slopes, as in a classic attic roof, then hanging (upper) and layered (lower) rafters usually alternate.

Watch how the rafter system of mansard roofs is installed; the video lesson will help you understand all the intricacies of the construction of a broken structure.

The load-bearing elements of the system ensure the strength and stability of the entire attic roof structure. The load-bearing elements of an attic roof are: sheathing, rafters, and mauerlat. The design features of the system are determined by the type of attic roof: single-pitched, hip, multi-pitched, gable, etc.

Mansard roof truss system, layout diagram of single-pitched floor units

The shape of the attic roof depends on the area covered and the architectural design, for the best choice simple types attic roofs so that beams and racks do not clutter up the space inside.

Attic, rafter system of hip hip roof

Stages of installation of the attic rafter system

The technology for installing an attic roof requires a certain sequence:

• Mauerlat installation;
• laying cross beams;
• installation of vertical racks;
• tightening the side posts or installing a ridge beam;
• step marking and installation of rafter legs;
• installation of auxiliary units: crossbars, struts, rafter legs;
• lathing, waterproofing, roofing material.

Attaching the Mauerlat is an important step for the design of the entire system; it is the basis of the design

Docking technology

Despite the fact that the algorithm for constructing a rafter system is quite simple, installing attic roof rafters requires a competent approach to the installation of docking units. The main load in the system falls on the legs, so the safety and strength of the roof, and the attic as a whole, depend on the quality of their installation on the Mauerlat, as well as on the reliability of their connection to each other.

Rafter system of the attic roof, photo of attaching hanging rafters to the Mauerlat

There are 2 options for connecting the rafters to the Mauerlat: sliding and rigid. In wooden attic structures, it is impossible to make all connections rigid, since wood, under certain conditions, compresses and expands, and with a rigid connection, thrust loads arise on the load-bearing units, which together leads to deformation of the elements of the attic rafter system.

How to properly attach layered rafters for an attic

Important: A rigid connection is used if the rafters are layered, then the leg is rigidly attached to the mauerlat, but at the same time, on the ridge, between each other or on the run, the system nodes must be attached with a sliding connection.

If a rigid fastening system is used on the attic roof, then it is necessary to exclude any forces: sliding, torques, turns, shifts. For rigid fastening there are two connection methods:

• notch in the rafter leg;
• support beam patch.

The saddle (notch) is made on the leg, the cuts should ensure a tight fit of the parts, and should not exceed 1/3 of the height of the beam. For rigid fastening, the rafter is notched against the mauerlat, 2 nails are driven from the sides, at an angle to each other, crosswise, the third nail is driven from above, vertically. It is recommended to further strengthen the fastenings metal plates, corners, bolts.

The sliding method of connection is that a recess for the leg is cut out in the Mauerlat, then the parts are connected to each other with a special metal corner - a slide. This is how the layered system is attached.

Sliding fastening of the attic rafter system

Regardless of the method of connecting the attic rafter system, the rafters and Mauerlat are screwed together with wire or additionally connected with anchors to prevent the roof from shifting due to strong gusts of wind. The struts, headstocks, spacers and headstocks are secured with brackets and clamps.

How to build up and strengthen attic rafters

Often the rafter leg is not long enough for the timber, so they are built up to avoid ordering special boards and to avoid increasing the cost of attic construction.

Important: Since the rigidity of the rafter system is lost at the joining points, connections should be made where the bending moment tends to zero.

Rafters made of timber are joined with an oblique cut. Inclined cuts are made in the parts, their length should be equal to twice the section, and the ends should be of a height equal to the cross-section of the beam, multiplied by a factor of 0.15. The joint is secured with bolts. This connection of beams harmoniously fits into the design of the attic, and allows you to leave the load-bearing elements of the roof open.

Sometimes attic rafters are attached with an overlap, the boards should overlap each other by at least a meter, then they are fastened with nails or bolts in a checkerboard pattern. If attic rafters are built up end-to-end, the cut should be strictly 90°, the elements are applied end-to-end, boards are laid on both sides, then the structure is secured with bolts or nails.

Options for extending the rafter leg

If the cross-section of the material is not enough, then the boards are reinforced. Paired rafters consist of two or more boards that fit tightly together; this structure is stitched with nails in a checkerboard pattern. Composite rafters are made from two boards, between which liners are inserted with a length of 2 board heights. The distance between the liners should not exceed 7 foot heights. The top of composite rafters may consist of a single plank.

Ways to strengthen the rafter leg

How to join rafters at the top

There are several options for connecting the rafters of the attic roof to each other at the top. If a ridge is not provided, the boards are cut at an angle, fastened together with nails, and additionally with the help of metal and wooden overlays. Hanging systems for complex raftering of a multi-slope mansard roof are fastened into a tenon with a single or double tooth.

Upper rafter connection on a ridgeless mansard roof

If the rafter system provides a ridge, then the rafters can be attached to the ridge beam with an overlap, or by sawing the ends at the desired angle, the joints must be reinforced with metal or wooden overlays.

Joining rafters on a ridge beam

It is better to assemble trusses on the ground, and then lift and install the structure on the attic floor. First of all, you need to make a template. To do this, the board is placed in place, the corner of the cut is drawn for the upper joint, and a groove is marked for fastening to the Mauerlat, then the second board is tried on in the same way.

On the ground, according to the marks obtained, the boards are sawed down, joined together, the template is lifted onto the roof and tried on. If the geometry of the attic roof is met, then the entire rafter system can be made according to one template, but in case of small deviations, it is recommended to do only the top cut and joining, and make the tie-in into the Mauerlat locally.

An attic space equipped as an attic is one of the options for increasing the usable area of ​​the house. The roof of such a room must be strong, and its rafter system must be able to withstand heavy loads.

Types of roof structures, advantages and disadvantages

When constructing an attic, a rafter system is used, which differs in shape and type of structure. The roof can be:

1. Gable. The easiest way to install a structure is a symmetrical gable roof.

It has a frontal view in the shape of a triangle. If the width of the house does not exceed 6 meters, then the angle of inclination in such a roof can be within 45 degrees. If the house width is more than 6 meters, the angle should be increased to 60 degrees.

The advantage of such a mansard roof is the ease and speed of installation, the reliability of the structure and its ability to withstand significant loads.

The disadvantage is the small space inside the room, which does not allow you to design a large attic

Installation of a gable roof rafter system https://www.youtube.com/watch?v=3ykQjiMMUbA

1. Three-slope and four-slope. It has another name - asymmetrical, having slopes of different slopes and lengths.

The advantage of such a roof is its beautiful design and originality.

The disadvantage is that such a roof is much more expensive and has a complex shape that requires scrupulous calculations.

1. Broken gable. Such stingrays attic structure have two parts located at different angles of inclination.

The advantage of a sloping roof is that in this option you can use the attic space as an attic with maximum efficiency. In addition, the rafter system of a sloping mansard roof is the most economical.

1. Half-hip. One of the types of gable roofing. A characteristic feature is two slopes (hip) above the front part of the roof.
2. Hip. It consists of trapezoidal slopes on both sides of the long roof and triangular slopes on both sides of the short one.

The advantage of half-hip and hip roofs is that, due to the absence of gables, they are able to bear significant loads. They have low windage. The rafter system of such roofs makes it possible to install an overhang of significant dimensions, which will serve as protection from atmospheric phenomena. The construction of such roofs is more durable.

The disadvantage is the difficulty of installation. Hips reduce the overall space of the attic. Hip and half-hip roofs require windows, which must be given special attention at the design stage. Windows located in the slope itself are easier to manufacture and install, but must be closed during precipitation. Vertical window openings are much more convenient, but their equipment and installation are much more complicated.

Design of a rafter system for a hip roof

Material for the rafter system

The materials used for the manufacture of load-bearing structural elements must be durable, withstand temperature changes, have a low specific gravity and be resistant to moisture. The most suitable material is wood. Conifers with high strength and minimal rotting are chosen for the construction of the structure. These can be larch, pine or spruce. The finished timber must be treated with an antiseptic and fire-resistant material. Also, the roof rafter system can be made of laminated veneer lumber, but this will entail an increase in the length of the run.

The rafter system can be made of lightweight metal structures. This roof option is easy to install, easy to operate and maintain, but costs much more.

Main elements of the rafter system

The basis on which the internal and external cladding of the attic space is mounted is the rafter structure. There are often cases when the internal space between the roof and the cladding is used for laying various types of communications.

The structure consists of the following parts:

1. Rafters. They are one of the main elements of the frame of the entire structure. The angle of inclination of the slope, the design, stability and strength of the structure depend on their shape and quantity.
2. Runs. Designed for connecting rafters.
3. Mauerlat. Rafters are mounted on it. Serves as a foundation for the entire attic structure, evenly distributing the load on the building along its entire perimeter.
4. Lathing. Sheathing material mounted on the rafters to which the roof is attached. In addition, it increases the rigidity of the entire structure.
5. Horse. The place of the upper fastening of the attic roof slopes.
6. Support stand, strut. Spacer elements that strengthen the rafters.
7. Sill. Beam between the front wall and the ceiling. Mounted parallel to the ridge. Serves as a basis for attaching struts and racks. Gives strength and stability to rafters.
8. Puff. A fastener designed to secure rafters.
9. Fillies. A piece of timber that extends the rafters to create the required length of roof overhang.
10. Roof overhang. The lower part of the roof that extends beyond the walls. Designed to protect walls and foundations from the effects of precipitation.

Broken attic structure and its calculation

The attic with a sloping roof is the most used, since the area under the roof can be used with maximum benefit. The reference diagram is considered to be a diagram in the context of which there are elementary figures: a rectangle - in the center, an equilateral triangle - at the top, two right triangle On the sides. Drawings of this design are easy to calculate. The general diagram and individual drawings are drawn onto paper before starting calculations.

A sloping roof is calculated using the following elements:

• calculation of the angle at which the roof will be installed;
• determining the dimensions of ridge and side rafters, as well as elements to strengthen them;
• calculating the dimensions of the sheathing;
• calculation of slope areas;
• determining the mass of materials needed for the roof;
• calculation of load and mass of insulation;
• establishing the required distance between the rafters.

Important! The angle at which the roof is installed should be within 30 degrees in its upper part and 60 degrees for the side rafters.

The length of the side rafters is calculated using the formula. We have the initial data: 0.5 m – roof eaves, 2.5 m – support height, 60 degrees – inclination angle. We apply the formula for calculating the hypotenuse of a right triangle.

L = cornice + height / cosinus 60 = 0.5 + 2.5 / 0.5 = 5.5 meters.

The length for ridge rafters is calculated using the formula for an equilateral triangle. Let’s assume that the base or tie is 4 meters, the angles A at the base correspond to the angle of inclination of the ridge rafters, which is 30 degrees, at the top of the triangle the camber angle is 120 degrees.

L = puff / 2cosinus A = 4 / 2x0.86 = 2.3 meters.

To install a broken attic structure, the minimum permissible cross-sectional dimensions for the rafters are selected: 50 x 100 mm. To determine the weight of the rafter material, select the average density of wood at a humidity of 18 percent. This will be 0.5 tons per cubic meter.

The density and pitch of the sheathing depends on the roofing material. For soft roof plywood sheathing is installed over the entire surface of the rafters. For semi-rigid and rigid roofs large sizes compacted or sparse sheathing is installed. Under a large semi-rigid roof it is necessary to lay a continuous layer of sheathing. Basically, the lathing is installed every 25-35 cm. The width of the board is about 25 cm.

To calculate the area, the structure is divided into geometric shapes. Their areas are calculated separately each, then all data is summed up. For a broken attic structure, the area is divided into 4 parts: 2 side, 2 ridge. Calculate the area of ​​each, double it and then add everything up.

Calculating the weight of the roof is mandatory element. Approximate weight 1 sq.m. roofing can be: slate - from 11 to 14 kg, soft tiles - from 9 to 16 kg, galvanized sheet - from 3 to 6 kg, ceramic tiles - from 50 to 70 kg.

The average load for a sloping roof should be at least 200 kg per linear meter. This will ensure that the snow load and wind are contained on the entire structure. In addition, there are correction coefficients that depend on the inclination of the structure: up to 25 degrees the coefficient is 1, from 25 to 60 degrees - 1.025, from 60 degrees and above - none.

The distance between the rafters is set differently, depending on the roof covering. If the rafters are made with a cross-section of 50x150 mm, then the approximate pitch between them can be:

• for ceramic tiles, slate, ondulin - 80 cm;
• for metal tiles – 60 cm;
• for corrugated sheeting – 90 cm.

Ksenia Skvortsova. Chief Editor. Author.
Planning and distribution of responsibilities in the content production team, working with texts.
Education: Kharkov State Academy of Culture, specialty “Culturologist.” Teacher of history and cultural theory." Experience in copywriting: From 2010 to present. Editor: since 2016.

Comments 0