Times of the same type gray houses are far in the past. Today everyone is trying to make their home unusual and original. There is also a return to construction fashion of such decorative elements, such as bay windows, cornices, mezzanines, as well as the construction of different types of attics, which give the house originality. For example, a thoughtfully designed rafter system mansard roof creates an opportunity for minimum costs significantly expand the usable area of the house.
How to build it correctly and efficiently - this is discussed in our article.
Types of rafter systems
Advice: if you need to significantly increase the area of the house due to the attic, choose multi-pitched roofs.Broken design rafter system the mansard roof is difficult to implement, but gives originality to the house
The structure of the rafter system of the attic roof
The backbone of the attic is its frame. It is on this that the roofing, thermal insulation cake, interior lining, various engineering systems and communications.
So that during operation the rafter system of the attic roof can withstand heavy loads, it combines the main elements and components in a special way. This is done in order to distribute the load on the load-bearing walls of the house.
The main elements of the truss structures of mansard roofs are:
- Mauerlat;
- rafters directly (hanging and layered);
- side and ridge girders;
- connecting elements (spacers, struts, diagonal connections).
Attic, rafter system
Please note: The load on an attic roof is on average about 200 kg/m2, so the rafters must have a certain margin of safety to withstand it.The strength of the system depends on its elements and the reliability of the connecting nodes. The most common types of parts connection:
- using screws;
- using bolts;
- tongue and groove - when one part has a groove, and the other has a ridge that is inserted into this groove;
- welded
The choice of one type of connection or another depends on the expected loads, the characteristics of the material used and technical features designs.
Calculation of the rafter system of an attic roof with a different number of slopes
Having decided on the design of the attic space, we begin to install the roof frame. At the same time, its main elements and components are determined by a calculation formula that will help select the profile, length and cross-section of system elements, the pitch of their location, and methods of connecting parts. Considering the characteristics of the attic roof, part of the room will have a low ceiling.
Advice: in places where the attic ceiling is too low, you can place niches for storing things, various modular cabinets, shelving.Roof truss system: drafting
First, they decide on the choice of the mansard roof frame scheme. In construction, rafters are divided into layered and hanging. Layered ones rest on the walls of the house and are installed in buildings where the distance between the walls does not exceed 6.5 m, while hanging ones are mounted on a tie rod and a mauerlat. If the width of the spans is large, the rafter system must be strengthened with additional connections.
Various schemes-projects of the rafter system of the attic roof, their differences
There are special formulas for calculating expected loads.
To determine the snow load, use the formula: S=Sg*µ.
Wherein:
S - snow load,
Sg - weight of snow cover per 1 m 2 area (this indicator can be found in SNIP - section “Rafter systems”),
µ - coefficient depending on the angle of inclination of the roof (it is 1.0 - for flat roofs with a slope of 25 degrees, and 0.7 for roofs with a slope of 25 to 60 degrees).
To calculate the wind load, the following formula is used:
W = Wo*k
Wherein:
Wo is the norm of wind load, determined according to the SNIP table individually for each region of the country,
k is a coefficient that determines the fluctuation of wind load depending on the height of the house and the type of terrain where it is located.
To calculate other elements of the attic roof and the cross-section of the rafters, you can use a special online calculator. It is necessary to specify the roofing material, the material for the manufacture of the attic floors, and the program will provide a calculation of the sheathing, the section angle and the distance between the rafters of the attic roof.
Online calculation program
Materials for the manufacture of the rafter system
Most often, the frame for an attic roof is made of wood. In this case, you should select durable wood that can withstand temperature changes and rot. First grade material is suitable for these purposes. coniferous species and larch.
Advice: To protect the rafter system, the wood should be treated with a special antiseptic and fire retardant compound.
Impregnation of attic roof rafters with antiseptic
If heavy loads are expected on the roof, then they can be used metal rafters mansard roofs. They can rely on wooden beams, or the entire structure is made entirely of metal.
The rafter structure of the attic roof consists of trusses. And the rafters for the attic (legs) are the constituent elements of each truss. The number of trusses is determined by the length of the façade and the pitch of their installation.
Truss - metal rafter system for mansard roof, photo
The metal roof structure is strong and durable, but it also has disadvantages associated with delivery and installation, as well as its high cost.
Construction technology for the frame of a gable roof attic
The design of the attic roof rafter system is selected depending on the type of roof, as well as on the developed attic design. The most simple option is a gable roof.
The main elements of the rafter system of a gable mansard roof are:
- linear type parts (columns, beams, rod systems);
- planar elements (panels, slabs, flooring);
- spatial parts (vaults, shells, volumetric elements).
Thanks to the use of modern building materials and techniques, installation of the frame under the roof can be done independently. The work process for installing mansard roof rafters is also called raftering.
Instead of a detailed drawing, it is enough to draw a simplified sketch of the roof frame, which will indicate all the parameters necessary for installing and assembling the rafters.
Advice: The wood should be dried before starting all work.First, the Mauerlat is marked and installed. It is fixed to the walls of the building.
Before laying the Mauerlat, waterproofing is laid underneath it
Installation of a wooden frame
At the end, the rafter legs are cut in order to secure them firmly to the Mauerlat. Nails, staples, and corners can be used for fastening.
Fixing the timber to the mauerlat
At the top junction of the rafters, their ends are also cut at an angle. Next they are tightened. For this, small boards are used, which are connected to the rafters using nuts, nails, and studs. If necessary, struts and spacers are installed.
Performing a puff on a skate
Important: give Special attention the quality of fastening of parts, because the stability of the structure depends on this.
Installation of sheathing
A good tutorial about the rafter system of an attic roof - video:
Bottom line
The attic can be built from modern quality materials, have a beautiful unusual shape, but if the rafter system is erected incorrectly, all work will be nullified. Therefore, it is so important to know the principle of the roof truss system and correctly calculate its main elements in order to build a high-quality attic structure.
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 of the room.
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.
- Rafter leg, straight in gable system roof 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.
- A ridge board or beam is a mandatory 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.
- Beams attic floor They are used in all versions of the attic - they connect the racks, and they also serve as a frame for the ceiling.
- Inter-rafter purlins are installed in the broken form of the roof for structural rigidity.
To be sure that the prepared project is 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 the requirements of fire and environmental safety. 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 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, so 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 snow load is not taken into account at all.
It is typical that if the attic roof has broken structure, then for its different sections 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. Thus, it has a direct, overturning effect directly on roofing slopes. But at small angles special meaning takes the aerodynamic effect of the wind - it tries to raise the plane of the slope due to the resulting lifting 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 maximum length 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). Convert this value into more familiar kilograms per square meter- 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 to standard sizes lumber to a greater extent.
| 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 amount of 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 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 brackets 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 fixing the tightening it will be U-shaped design. 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 ridge rafters, which can be fastened together 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 both the necessary rigidity and stability of the structure, and will be convenient for insulation using standard mats mineral wool. 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 metallic profile or metal tiles, 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 them to professionals or carry out all actions under supervision experienced craftsman, and with the utmost care and precision.
The attic roof must have great strength. The rafter system of such a roof is subject to serious loads and its design must be calculated in such a way that these loads are evenly transferred to the walls and foundation of the building.
Attic design options
An attic is a building whose facade is partially or completely the surface of the building's roof (sloping or broken). An attic differs from a used attic in that the line of intersection of the roof and facade is located from the floor level at a height of no more than 1.5 meters. Use attic room can be done in different ways - it can be a living room, gym, utility room or greenhouse.
Attics can be installed in the following types of roofs:
Gable. The most simple form– symmetrical forceps. In such roofs the pediment is triangular. The advantages of this type of roof are reliability and ease of installation. For houses with a width of up to 6 meters the best option is a gable roof with an angle of 45 degrees. If the width of the building is more than 6 meters, pointed roofs (angle of inclination - 60 degrees) should be made. Gable gable roofs do not make it possible to build large attics.
Asymmetrical(with stingrays different lengths and tilt angle) gable roofs have original look and allow you to realize the most daring architectural solutions. However, such roofs require professional calculations and have a rather complex design.
Broken gable roof- This is one of the most suitable types of roofs for installing an attic. Its design allows the use of under-roof space with maximum effect. In addition, it significantly reduces the cost of building materials. Each slope of such a roof is divided into two parts with different angles of inclination (usually the slope of the upper part is 30 degrees, and the lower part is 60 degrees).
This is one of the types of roofs with two slopes. Its frame is practically no different from the frame of a conventional symmetrical roof, the peculiarity of the floor hip roof– two small slopes (hips) above the gables.
It’s as easy as shelling pears to equip a comfortable and spacious additional floor. The attic fits perfectly into their design.
Advantages of hip mansard roofs:
- The rafter system of the hip roof can withstand significant wind loads, because it lacks pediments.
- This type of roof allows you to install large overhangs that protect the walls and foundation of the house from precipitation.
- The hip roof structure is rigid (thanks to the corner ribs) and is much less susceptible to deformation.
- Houses with hip roofs they look solid and fit organically into the architectural ensemble.
The disadvantages include the complexity of the design, mandatory arrangement skylights on the roof for lighting and the fact that short (end) hips slightly reduce the usable roof area. Windows need to be given special attention when designing a roof. If they are located in the plane of the slopes, then they will have to be closed when it rains. Vertical windows more practical, but their design is quite complicated.
Calculation of frame elements
When creating a project, first of all you need to decide on its configuration, design and roofing material. By selecting certain type roofs, you can make the necessary calculations; Based on them, the parameters of all elements of the rafter system are established.
is carried out taking into account the amount of precipitation falling in a given area and the average wind force (data are given in SNiP).
Weight " roofing pie» is easy to determine - specific gravity of all materials (vapor barrier, waterproofing, insulation and sheathing) per sq. m of roofing is multiplied by the total roof area. The loads on the roof, its weight, shape and angle of inclination of the slopes determine the parameters of the rafters.
Typically, for the construction of the rafter system of attic roofs, they are used structural elements from durable wood(larches, pine trees). Rafters, due to increased loads (on average, they are 200 kg/m2), must be at least 70 mm thick. Rafter step in the mansard roof design is shorter than in others - the distance between the rafters is about 50 cm.
In order to create the necessary safety margin, a multiplying factor is used in the calculation. For large buildings, it is possible to install a metal rafter system; it is calculated in accordance with technical characteristics hardware used (can be found in reference books).
Thanks to the computerization of the entire country, it became possible to calculate using the Internet. Calculators allow you to determine:
- Roof surface area.
- Angles of inclination of ridge and side rafters.
- Quantity of insulating materials.
- The length of the rafters.
- Recommended cross-section of mauerlats, rafters, struts, sheathing.
- The area of the attic and the entire under-roof space.
- Rafter step.
- The number of rows of sheathing and the distance between them.
- The number and volume of sheathing and rafters.
Construction of the rafter system
The rafter system is, of course, the fundamental element of the roof. How well it is designed and how correctly it is made determines the functionality and durability of the roof. Her 
components:
- Mauerlat;
- purlins (ridge and side);
- beds or support beams;
- rafters (sloping and hanging);
- struts, support posts, diagonal struts.
All required parameters elements are determined during calculation. When installing mansard roof use layered and hanging rafters. Hanging ones are used when the rafter system rests only on two main walls. In case of additional support on the carrier central wall or beams (supporting transverse beams) layered rafters are used.
In order to choose the right rafter system correctly, you should pay attention to:
- roof functionality;
- the probable amount of precipitation in the area;
- total roof load
Correct connection of all components guarantees the strength of the roof. The main fastening units in the rafter system (see photo below):
- Mauerlatny. produced in two ways. The hard way used when installing layered rafters and ensures a strong connection between the rafters and the Mauerlat. Fastening is done using corner hardware and a support bar or by cutting (a “saddle” is cut out in the rafter leg, with which it rests against the mauerlat. The rafter is attached to the mauerlat with nails and metal staples). arranged by cutting out a recess in the mauerlat for the rafter and securing it with a metal corner).
- Beam.
- Skate.
- As a rule, to the skate and support beams rafters are secured using threaded connections, staples and roofing hardware (metal corners of various profiles and shapes).
- An important structural unit is a rigid structure of interconnected rafters. They are needed to evenly redistribute the load on the main walls of the house. Connections of rafter elements made of timber are made by cutting and are additionally strengthened using threaded connections, anchors and roofing hardware. To avoid sagging and bending of large trusses, additional supports are created - purlins or transverse struts and beams.
Sloping mansard roof design
The peculiarity is that usually both types of rafters are used in its design. The upper slope (from the bend to the ridge) is made of hanging rafters, which rest on posts or a side girder.
To prevent bending, they are equipped with horizontal ties. When installing the lower slope (from the bend to the ceiling), layered rafters are used, supported by the Mauerlat and a side girder.
To increase the stability of the structure, struts are installed. In some cases, layered rafters are attached to a mauerlat lying on floor beams that protrude significantly beyond the walls of the building.
The lower slopes of the rafter system have a large angle of inclination (about 60 degrees), the upper slopes are flat (from 30 degrees). Hanging trusses make it possible to do without a ridge girder; they can be assembled on the ground.
The best option is to connect layered and hanging rafters end-to-end.
When installing, the following factors must be taken into account:
- The lumber used for its construction must be dry (humidity no more than 15%).
- All wooden structural elements should be treated with antiseptic liquids before installation.
- The minimum cross-section of the rafters is 10×15 cm, the Mauerlat – 15×15 cm.
- It is best to use coniferous wood, without cracks, with a minimum number of knots.
- Particular attention should be paid to the installation of windows.
Installation instructions for rafters
Required tool:
- hacksaw (gasoline or electric saw);
- axe;
- hammer;
- screwdriver;
- metal square;
- construction cord;
- marker or pencil;
- plumb line;
- level.
Installation technology:
- First, lay the Mauerlat on the supporting walls and securely fasten it. As a rule, fastening elements are pre-provided in the walls.
- Mount the beds (if necessary). They are located parallel to the Mauerlat at the distance specified in the project. Large-section timber or sanded carriages are used as beds.
- Racks (at least 10 cm thick) are installed on the beds, which will serve as a support for the purlin and as a base for the attic walls. The racks must be given a strictly vertical position using a plumb line and building level, and then securely fasten them (you can make mortises in the beds at the fastening points, but this is not necessary) using corner metal elements and staples.
- The racks are secured with struts.
- Side purlins are installed on the racks (strictly horizontally), and they are firmly fixed with hardware.
- Install the outermost layered rafters on both sides and fasten them according to the design.
- Stretch the construction cord and place the rafter legs along it one by one.
- Hanging rafter trusses are installed (if the upper slope is made with a ridge girder, then install it first, and then install the top row of rafters).
- Arrange a frame for windows if they are provided for in the project.
- They arrange the sheathing.
After installation, you can begin to create a “roofing cake”.
For more information on DIY installation, watch the video.
Let's sum it up
An attic is the most rational way to arrange a roof. The designs of many types of roofs make it possible to arrange such a room. Hip and sloping gable roofs are especially suitable for this purpose (this type of roof will also allow you to save on building materials). If you correctly calculate the design and strictly follow the installation technology, a roof with an attic will decorate the house and significantly increase the living space.
A living space located in the attic is called an attic. The advantage of the attic is obvious - it is an opportunity to increase usable space at home, without spending too much money. At the same time, the rafter system of the attic roof must meet the standards of strength and reliability. These indicators determine how well the basic protective functions of the roofing system will be performed.
The most profitable is considered to be a mansard roof, each angle of the slope of which is different from the rest. This allows you to make more profitable use of the attic space.
There are two types of rafters for the attic: layered and hanging.
Layered rafters are used on those buildings where there is an intermediate load-bearing wall. Thus, on one side the rafters rest on outer wall buildings, and on the other hand on specially created supports or an internal wall. 
Please note that a layered rafter system is only possible if the distance from one load-bearing wall to another does not exceed 7 meters.
Hanging rafters are used in cases where the building does not have internal main walls. The most simple types hanging trusses consist of rafters and lower belt, that is, puffs. The support is the mauerlat. Depending on the expected loads, the rafter system is additionally reinforced with brackets mounted in the walls with wire. To construct the frame, boards are used, the length of which depends on the length of the span between the trusses.
The mansard type of roof is more often used in the construction of private residential buildings. There are several reasons for this:
This type of structure is not difficult to install; the rafter system of the mansard roof does not cause difficulties even for novice builders. It does not require large financial investments. The result is a comfortable room and roof for living. Practically - another floor in the house.
It will not be a problem to organize an attic space in an already finished house, and the changes will not affect the supporting structures of the house. In order to remake old roof into the attic. It is only necessary to demolish old roof and build a new one in its place.
However, pay attention to the building's foundation, soil and bearing structures, since the attic roof is heavier and more massive. So, if possible, it is advisable to take into account the construction of an attic roof at the planning stage. Thus, it will be more convenient to calculate the rafter system of the attic roof.
Design of the attic roof truss system
There are several types of mansard roof:
- symmetrical;
- broken line;
- asymmetrical;
- triangular.
It should also be noted that it is possible to install single-level and multi-level attics with different geometric shape premises. This cannot but affect the appearance of the house.
No less important when constructing an attic roof is the angle of the roof slopes. It depends on the following factors:
- on the climate of the area;
- from the material used;
- from the architectural preferences of the owner.
However, please note that if you take the roof angle too high, this will reduce the number usable area attics. Too small an angle of inclination will lead to difficulties in the operation of the roof itself: cleansing from precipitation, strength.
The roof structure of the attic roof consists of the following elements:
- rafters;
- skate;
- racks;
- struts;
- sheathing;
- Mauerlat;
- roof;
- connecting elements.
Construction of an attic roof
Installation of rafters - photo Installation of the attic roof rafter system is carried out in stages. Since it is a rather complex and important process on which the longevity of the entire attic structure depends.
When constructing a rafter system, you must know and follow the following rules:
Installation and calculation of the attic roof rafter system
Construction of an attic roof for a country house
In a small country house attic - the rafter system is built according to the same rules listed above. The main task will still be the correct calculation of the load to which the roof will be subjected. Why is this so important in construction? country house? Often, in winter period suburban areas remain empty. Thus, the roof of the house may be under very big amount snow cover, which creates a significant load on all elements of the house, including the rafters for the attic.
If you decide to build the roof yourself, you must follow the following procedure for installation work:
- racks are cut into the floor beams;
- rafter legs are installed for the lower slopes;
- the upper beam is attached to the attic floors;
- a ridge post is cut into the attic floor beam for the upper slope;
- then rafter legs are installed for the upper slopes;
- Additional fastenings are installed at the intersection of rafter legs and floor beams.
The rafter system of the attic roof must have several layers. Care needs to be taken regarding processing building material, about thermal insulation and waterproofing. Choose durable, dried material, without knots or cracks, check the integrity. Flaws wooden products significantly affect the strength capabilities of the truss structure.
I continue the story about how I build my house, and today I will talk about the rafter system of the house. I was thinking about what kind of system to make, and after carefully weighing all the pros and cons, I settled on one option, which one? Read on - I'll tell you everything!
In this article I will talk about how I drafted the rafter system, how I calculated the pitch of the rafters, how the rafters of the attic roof were installed, and I will also tell you how the rafters of my house are attached.
A short outline of the article:
- Selection of rafter system
- Calculation of rafter pitch
- Preparing rafter blanks
- Brief conclusion about the article
- Home news
Now let's take a closer look at each point.
Selection of rafter system
When I was planning the house, there were many variations on the type of roof of the house. The fact that the roof will be mansard was not even discussed, but what shape?
Initially I wanted to do broken roof- a la the 90s, but when I started calculating the floor beams of the house, I realized my mistake and began to look for another option. In this version I got a big deflection ceiling beams in the ceiling of the first floor. This was unacceptable - we had to think further.
Part of the first version of my house
In the end, I settled on a gable mansard roof, with a wall height at the mauerlat of 120 cm. This height turned out to be quite convenient for my roof angle. Without bending, I can freely reach the wall of the house with my hand, albeit resting my forehead on the ceiling)))
The appearance turned out to be very attractive. Installation of the roof of such a roof was also convenient; you can walk on the roof freely. There was a small problem with the material, but I waited a little and they cut it for me the necessary board.
Calculation of rafter pitch
I chose the pitch and cross-section of the rafters based on calculations, the principle is the same, only not the entire length of the rafter is taken into account, but only its horizontal projection.
In general, of course, there are specialized formulas that take into account the average snow load, depending on the region. In a separate article, I plan to tell you how to calculate the rafter system for any region. I practically neglected this, simply taking the load as for covering a house.
The distance between the roof rafters was 60 centimeters, the thickness of the rafters gable roof or, more correctly, the cross-section turned out to be 180x50 mm. This is quite enough in our area, there is practically no snow, here is a photo, you can see the date for yourself))) This moment of course infuriates me in our climate, but what can I do...
Pay attention to the snow on the roadsides and on the roofs of houses Of course, sometimes it drops 60-70 centimeters over the winter, but this happens probably once every 10-15 years. Only our winds blow almost incessantly, and everything is swept away from the roofs. Such beautiful roofs as in the photo below, you practically won’t find it in Transbaikalia...
Beauty!!! Preparing rafter blanks
After all the calculations were done, I simply selected optimal angle roofs, taking as a basis the fact that I can’t get boards longer than 6 meters (only one sawmill in the village cuts 6 meters, and then only a five and a beam), overhangs of at least 60 centimeters from the wall, appearance should be attractive.
Directly in Vizio, I placed two boards directly on the facade design, choosing the most optimal angle. When I finished with the angle, I measured the distance from the ridge to the mauerlat (the project was initially done to scale, so as not to clash with dimensions later), drew a drawing in a compass, printed it out, and made rafters for the roof according to the drawing.
Drawing of a part of the Mauerlat 
Entire rafter drawing 
Drawing by the skate An important fact will make the correct gash of the rafters. You can see how to cut a structure in my drawing and in this video; Larry told me how to do it in different ways.
Video in preparation
I have ridge roof with layered rafters, all the rafters rest on the ridge and therefore it was made quite powerful.
The ridge is made from hardwood boards with a cross-section of 22x50 centimeters and the final cross-section is 22x10 cm, with a ridge length of 9.6 meters. A very powerful and heavy thing, which the six of us somehow shoved into place.
Here the skate is resting on a support Places have been prepared for the ridge in the gables of the house, and additionally two support pillars; as a result, the ridge rests on the ground at four points.
This is the skate sitting in its place in the pediment Lifting and assembling the rafter system
When the rafters were prepared and the ridge of the house was installed, my brother and I began installing the rafters for the attic roof. The rafters were made of pine, so they could be lifted by one person on the ground and carried by another on the second floor of the house.
All the rafters were neatly stacked along the mauerlat outside the house, then I climbed onto the load-bearing central wall of the house, took the rafters, and my brother handed them to me. Of course, you can assemble the rafter system alone, but if you run around and jump, it’s better to immediately call an assistant.
They fastened it at the same time, I to the ridge, my brother to the Mauerlat. In general, correctly calculated and sawed rafters do not go anywhere when you throw them into place. They just sit and wait for you to kill them.
Here you can clearly see how the rafters are nailed together And yes, I forgot to say, markings were previously made according to the calculated distance between the rafters - on the ridge and on the mauerlats of the house, so that the entire roof would be level and all the rafters would be in their places.
Fastening the rafters in frame house does not cause any difficulties. The main thing is not to violate the principle of operation of the nodes frame house and everything will work out.
The rafters are fastened to the ridge with nails in an oblique manner on both sides, then they are pierced through each other, forming a kind of lock that cannot be pulled apart no matter how hard you try.
The rafters on the outside of the ridge were intentionally made a little longer, then the excess was simply cut off with a saw. But it turned out to be a good supply for nailing.
Since the roof is ridged, the question of how to attach the rafters to the Mauerlat did not arise. I simply fastened them with 120 nails, obliquely on both sides. I don't think anything should escape anywhere.
Attaching the rafters to the mauerlat The façade extensions are made from the same rafters, only they are sawn off so that they fit close to each other, as they are located in the same plane. They rest on a pre-released ridge and mauerlat beams. It was a complete improvisation, and time will tell how it behaves. I hope nothing will run away or fall anywhere. Still, it’s not just the two points that hold it in place, but also the sheathing.
Overhangs of the house, soffits not yet completed After installing all the rafters, I began installing the tie rods. My tie rods come with the same pitch as the rafters, and are made of 150x50 cm boards.
In the center the puff is nailed to load-bearing wall, and relies on it. The ends of the ties were hung level, and the rough attic ceiling was subsequently screwed onto them. The roof was held together very firmly, especially after installing the sheathing and ceiling.
I walked freely on top of the ceiling when I was carrying bags of sawdust, and it holds the weight of the sawdust quite calmly.
The rough ceiling, there is now a windbreak on it, and there are 25 centimeters of sawdust on it Let's make a brief conclusion:
The entire process of assembling the rafter system can be divided into several individual stages work.
- Let's find out the distance from the ridge to the mauerlat of the house - to make the correct calculations.
- We calculate the pitch of the rafters and their cross-section. We select based on capabilities and availability of materials for sale.
- We select the optimal angle of the rafter system. I relied on the appeal of the house.
- We calculate the locations of the cuts and their angles, or as I did - we draw a rafter in “ full height».
- We make rafters, leaving a reserve at each end. Saw off from the top after piercing, and from the bottom along the thread - also after installing all the rafters.
- We lay out the rafters along the mauerlat, in their approximate location.
- We lift the rafters into place. We use an assistant, it will be hard for one.
- We pierce the rafters in place. I used five nails to hammer the rafters together, two each to the ridge, and three nails to the mauerlat.
Home news
From home news, nothing particularly unusual happened, I closed the next session, studied all January, the next one in May. Closed pretty well, attached screenshot)))
Kind of a student Lera decided to make a huge dragon with a wingspan of about a meter, we’ll see what happens together! For now, only the frame is ready.
I think it’s time to end the article on this note, I think installing rafters for an attic roof will now not be something supernatural for you, even if you don’t do it yourself, you can definitely control it.
If you have questions or suggestions, or constructive criticism, then welcome to the comments. Don't forget to subscribe for updates.
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