Do-it-yourself mansard roof: structure and construction technology. Calculations and construction of the rafter system for an attic roof Build an attic roof with your own hands

24.10.2023

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 of areas 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 to be covered and the architectural design; it is better to choose simple types of attic roofs so that the 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;
sheathing, 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 with metal plates, corners, and 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, then the cut must be exactly 90°, the elements are applied at the ends, 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.

A house with an attic is not just additional living space, but also a presentable appearance of the entire structure. Even if the room under the roof is not heated and is used only in the summer, it still has a powerful “air cushion” that helps retain heat inside the entire building.

Making an attic on your own will be difficult, especially if you do not have the relevant experience, because it is a fairly massive and complex structure.

An attic room can be installed under various types of roofs, but the most popular is a broken or gable structure. According to their structure, they are slightly different from each other.

In order to decide which design will be more suitable for your home and will be easier to install, you need to consider both options in more detail. In addition, the master who will be involved in the construction of the attic roof must figure out which of the two types of rafter system structures to choose.

Any roof belongs to one of the existing two types of rafter systems; it is a layered and hanging structure. Each of them has a different feature, and which one to choose depends on how the load-bearing walls of the structure are located.

Hanging structure

A hanging structure is a rafter system that rests only on the outer main walls. This happens when in the house itself, except for the external walls, there are no major partitions.

This design can only be used if the distance between two main walls is no more than 8 m, since this system puts a high load on the foundation. To reduce it, various elements are used in the hanging system, such as tie rods and headstocks, struts and crossbars. For example, the headstock hangs the tie to the ridge connection, and the struts pull the beams to the rafters.

For floor beams in a hanging system, hewn logs or fairly thick bars installed on an edge are used. Their cross-section must be at least 100x200 mm. The floor in the attic should be as reliable as possible, and in order not to make mistakes in the parameters, it is better to entrust the calculations to a specialist.

Layered system

The layered system, unlike the hanging one, is supported not just by two external load-bearing walls, but also by permanent partitions installed on the foundation. Therefore, when planning the construction of an attic, it is necessary to think in advance about the design of the strip foundation on which the permanent partitions will be installed. The layered system is perfect for installing an attic because it can withstand high loads compared to the hanging version. It provides a good base for the floor beams and therefore for the attic floor.

If you make a broken version of the attic roof, then it makes sense to use a combined roofing system, that is, the side rafters are installed in a layered manner, and the ridge rafters are installed in the form of a hanging system.

Do-it-yourself mansard roof: video, photo

When building a house from blocks or bricks with an attic, its front side is often built from the same material. This is convenient because you don’t have to calculate the parameters of these roof elements and assemble them from bars to lift onto the wall. But it is important to understand that the walls of the building must be on a reliable foundation and have good thickness, since such a pediment puts a significant load on the main structure.

If the attic serves as another floor year-round, then a gable wall made of foam blocks or bricks is an excellent option for creating a living space under the roof.

In order for attic rooms with a gable roof to be spacious and have a normal height, the angle of the roof slopes should be approximately 45-50°, depending on the width of the end part of the structure. If you take a smaller angle, the volume of the room will significantly decrease. Increasing the steepness of the slopes will make the roof unreasonably high, it will become heavier, will have greater windage under wind loads, and the cost of materials will be inappropriate.

Of course, the installation of a gable roof is simpler compared to a broken structure, since straight rafters are used without additional connections or any kinks. But the broken design allows you to make the room in this part more spacious, and the ceilings correspondingly higher.

The broken system is much more complex in design, calculations, and roofing, but it not only creates a more spacious space under the roof, but also gives solidity to the entire structure. Its main difficulty lies in the large number of complex connecting elements. All connections must be made in accordance with the technology, otherwise the roof will turn out to be unstable.

If the walls are built of brick or stone, then it is better to lay out the front parts in advance during the general laying. In this case, in order to create a unique rafter system, aligned with the finished gables, you can install intermediate rafters and special supporting fastenings to them.

Before purchasing and preparing material for a particular system, you need to draw up a design project with the appropriate dimensions - it will become the main guide for preparing and assembling elements during installation.

Video: rafter system for a sloping attic roof

Attic project

When developing a scheme for building an attic, it is better to do this in different projections in order to clearly understand how the elements of the rafter system will be placed. It is important to correctly calculate what the height of the roof ridge should be, since the size of the area depends on it.

When preparing a design diagram for constructing a roof for an attic, it is necessary to calculate the height of the ceiling, ridge and total area of the room.

The minimum height from the floor to the ridge is 2.5-2.7 m, but if this distance is smaller, then the room cannot be called an attic; the name attic is more suitable for it. This indicator is established by SNIP standards.

In order for all the elements to be accurately drawn and have the correct location in the overall system, it is necessary to start from a figure with right angles, namely a square or rectangle - a cross-section of the attic space being created. Based on the width and height of the future room, you will never be mistaken with the angles at which the roof slopes are located, with the location of the rafters, ridge and other supporting elements. Having found out these parameters, they must be immediately entered into the drawing.

First of all, you need to calculate the middle of the width of the front wall. Further from this point, the height of the ridge, the attic ceiling, the location of the walls (racks) and the size of the eaves overhang are determined.

Due to the fact that each of these structures has a certain number of connecting nodes with different configurations, it would be nice to draw each of these connections separately in order to understand in detail the features of the pairing of all the elements that are connected at this point.

All rafter systems include basic and additional elements, which may not be found in every structure. The main components of the attic roof include:

floor beams (the basis for the remaining elements of the system). They are laid on main walls.

A rafter leg consisting of two sections (in the case of a broken pattern) or straight in a gable system. The top rafter in this case is called the ridge rafter, since it forms the highest point of the roof - the ridge, and the rafters that form the walls of the attic are called side rafters.

Mauerlat is a powerful beam that is attached to the main side walls. It is necessary to install rafter legs on this element.

A ridge board or beam is an integral element for a gable roof, but is not always used when installing a broken roof.

Constructions are supporting elements that are required to strengthen a broken and gable structure. In the first case, the side and ridge rafters are attached to it, and in the latter, the stand acts as a good support for a long rafter. Moreover, the racks are the frame for covering and insulating the attic walls.

Diagonal connecting elements additionally fasten the longitudinal beams or posts and rafters, thereby making the structure even more durable.

Inter-rafter purlins are installed in the case of a broken roof for structural rigidity.

Attic floor beams are used in both versions of the system - they connect the racks with them, and they act as a frame for the ceiling.

In order to be sure that the project is developed without errors, it would be a good idea to show it to a specialist. It will determine how correctly you selected the attic parameters to the length and width of the walls of the building.

Video: calculating a mansard roof using software

Material parameters for the construction of an attic roof

When the graphic element is ready, then, based on the dimensions set on it, you will be able to calculate the amount of materials that will be needed for the construction of the attic roof. It is necessary to select materials according to their characteristics, which must meet environmental and fire safety requirements.

For wood, it is necessary to provide an antiseptic treatment, which will significantly reduce the flammability of the materials. For construction you will need:

boards for rafter legs, the cross-section of which is selected based on the results of calculations, which you will learn about a little below.

Beam of 150x200 or 100x150 mm - for floor beams, depending on the width between load-bearing walls, rafter system, as well as for purlins, valleys or diagonal legs - if, of course, they are provided for by the design.

Beam from 100x150 or 150x150 mm, intended for laying the Mauerlat.

Typically, timber 150x150 or 100x100 mm is used for racks.

Unedged board for the subfloor, as well as some fasteners.

Annealed steel wire with a diameter of 3-4 mm - for fastening some parts.

Bolts, nails, staples of various sizes, angles of various configurations and other fasteners.

Lumber for counter battens and sheathing for roofing material - depending on the type of roof.

Vapor barrier and waterproofing membranes.

Insulation materials intended for roof thermal insulation.

Roofing material and special fasteners.

Rafter section

Rafters provide a roofing element that absorbs the main external loads, which means special requirements are placed on their cross-section.

The size of the required lumber depends on many parameters - from the step between the rafter legs, the length of these legs between the support points and ending with the wind and snow load that falls on them.

The geometric parameters of the rafter system are easily determined in the drawing. But to understand other parameters, you will have to refer to reference materials and perform some calculations.

It's no secret that snow load differs in different regions of our country. Below in the figure you will see a map on which all of Russia is divided into zones demonstrating the snow load.

In total, 8 zones are distinguished (the last one is considered extreme and can not be considered for the construction of an attic roof).

Sg is an indicator in the table (carefully study the map and the table attached to it).

μ is a correction factor that depends on the steepness of the roof slope.

For example, if the roof slope angle is less than 25°, then - μ=1.0; if from 25 to 60°, then μ=0.7; if it is more than 60°, then the snow will not linger on the roof, and the snow load is not taken into account.

If the attic roof is of a broken structure, then for its different sections the load may have different values.

The angle of inclination of the roof can be determined by a simple ratio of the height and base of the triangle (usually half the width of the span) or using a protractor according to the drawing.

This indicator also largely depends on the region where the structure was built, on the height of its roof and on the characteristics of the environment.

And again, for the calculation you will need to determine the initial data from the map and the table attached to it.

The calculation for this task will be carried out using the following formula:

Wp = W × k × c

W – value in the table, depending on the specific region.

k – coefficient taking into account the location and height of the building (see table).

The letters in the table indicate the following zones:

A - open areas, forest-steppes, steppes, tundra, deserts, forest-tundra, sea coasts, reservoirs and large lakes.
B – urban areas, areas with frequent wind obstacles, artificial or relief, at least 10 m high, wooded areas.
B – dense urban development, building heights from 25 m.

With– a coefficient that depends on the prevailing wind direction (wind rose of the region), as well as on the angle of inclination of the roof.

With this coefficient, the matter is much more complicated, since the wind can have a dual effect on roofs. So, it has an overturning, direct effect on the roof slopes. However, at small angles, the aerodynamic effect of the wind is of particular importance - it raises the slope plane due to the resulting lift forces.

As you have already noticed, the diagrams that accompany the tables indicate the areas of the roof that are subject to maximum wind loads, and also indicate the corresponding coefficients used for the calculation.

It is worth noting that at slope angles up to 30° (in the area of ridge rafters), the coefficients are indicated both negative (directed upward) and with a plus sign. They somewhat dampen the wind load, and in order to reduce the impact of lifting forces, you need to carefully secure the roofing material and rafter system in this area, using additional connections (for example, annealed steel wire).

Once the snow and wind loads are calculated, they can be summed up and, taking into account the design features of the system, the cross-section of the rafter boards can be determined.

Please note that these data are indicated for the most commonly used coniferous materials (spruce, pine, larch or cedar). In the table you can see the maximum length of the rafters between the supports, the section of the board depending on the pitch between the rafters and the grade of the material.

The total load value is indicated in Kilopascals (kPa). Converting this value into the usual kilograms per m2 will not be difficult. 1 kPa ≈ 100 kg/m².

As for the size of the board along its cross-section, it is rounded up to the larger side of standard lumber sizes.

What tools will you need to install an attic roof with your own hands?

Of course, during work you cannot do without a set of tools, the list of which includes:

screwdriver, electric drill;
building level, tape measure, plumb line and square;
chisel, axe, hammer, chisel;
jigsaw, circular saw, hacksaw;
carpenter's knife

If the work takes place surrounded by competent mentors, step by step and carefully, and the tools are of high quality, the process will be much faster.

Do-it-yourself mansard roof: main steps + video

It is important to strictly follow the sequence of work, because this is the only way the structure will be strong and reliable.

Mauerlat fastening.

The installation of any rafter system should begin with attaching a powerful support beam - Mauerlat - to the end of the side walls of the buildings. It is convenient to install rafter legs on it. It is made from high-quality timber 100x150 mm. The Mauerlat is laid on roofing felt waterproofing laid along the upper end of the wall (regardless of the material).

Thanks to the Mauerlat, the load is evenly distributed across the walls and transferred to the foundation. It is fixed to the wall using metal studs, which are previously embedded in a crown or concrete belt running along the upper edge of the wall of the structure or with 12 mm anchor bolts. They must go into the wall at least 150-170 mm. If the Mauerlat is installed on a wall made of wood, then the beams are attached to it using wooden dowels.

Installation of the rafter system.

Installation of the rafter structure begins with the installation of floor beams, which can be mounted on top of the mauerlat (if you plan to move the beams outside the room, increasing its area). In this design, the rafter legs are fixed directly to the floor beams.

Otherwise, they can be laid on waterproofed walls and secured with brackets or corners to the inner edge of the Mauerlat. This option is used if the rafter legs need to be fixed directly to the mauerlat.

The posts should be at the same distance from the middle of the floor beam. In the future, they will determine the location of the walls of the room, namely its width.

The bars for the racks must have a cross-section corresponding to the size of the floor beams. The racks are attached to the beams using wooden plates and special corners. But first, they are fastened with nails, after which they are leveled using a plumb line and a building level, and only then are they thoroughly secured with the expectation of upcoming loads.

As soon as the first pair of racks is installed, they are fastened on top with a block (tightening). It, in turn, is connected using metal corners to the racks.

When the tie is secured, you will have a U-shaped structure. On the sides, layered rafters are installed on it, which are laid on the mauerlat or attached to the floor beam with the second end.

A groove (special notch) is cut into the installed supports for the timber or in the rafters. With its use, the rafters are installed on the mauerlat beam and secured with metal brackets.

To ensure structural rigidity, struts can be installed from the base of the rack to the middle of the side rafters. If this turns out to be not enough, and you do not mind the material, then it would be a good idea to strengthen the overall structure with contractions and additional racks.

Then the middle is calculated on the puff. A beam will be attached to this place, which will support the ridge connection of the upper hanging rafter subsystem.

The next stage is the installation of ridge rafters. They can be fastened with various connections - these can be powerful bolts with metal washers or plates, or a metal plate.

After installing them, the headstock is attached to the middle of the tightening and the ridge.

Upon completion of work on one part of the truss structure, it is necessary to do 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 best option would be an interval of 600 mm, which will give the structure the necessary stability and rigidity and will be convenient for insulation using standard mineral wool mats. But this significantly makes the structure heavier and increases the cost of materials.

First, the side parts of the system assembly are installed, then the intermediate parts. They are connected to each other by purlins, which are installed between the upper ends of the racks and work like spacers. So, we get a rigid structure of the attic rafters, where there will already be a ready-made frame for finishing the walls.

Waterproofing attic roof

As soon as you have built the rafter system, you can begin finishing it with insulation and other related materials.

It is worth noting that the first coating on top of the rafters should be a waterproofing and windproof film. It is attached to the rafters using a stapler and staples, starting from the cornice. The canvases are laid with an overlap (200 mm), and then the joints are glued together with waterproof tape.

A counter-lattice is placed on top of the waterproofing, which will better fix the film on the surface and create a ventilation distance between the roofing and windproof material. Typically, the counter-lattice is made of boards 50-70 mm thick and 100-150 mm wide.

A sheathing is fixed perpendicular to it, on which the roofing material is laid. As for the pitch between the slats, it is calculated depending on the size and type of sheet roofing material, taking into account the overlap required for it.

If you are using a soft roof, then plywood sheets are usually attached to the counter-lattice.

How the roof covering is installed

The roofing material is fixed to the prepared plywood or sheathing. Typically, its installation begins from the roof eaves and then one by one, from one of the edges - depending on the type of roof. The roofing sheets themselves are installed with an overlap. If metal tiles or a metal profile are used for the coating, then this material is secured using special self-tapping screws with elastic gaskets. Typically, fasteners are matched to the color of the material.

The most difficult stage in covering a sloping roof is the transition from layered side rafters to ridge rafters. Some difficulties may also arise if the roof has projections for arranging the roof above windows or balconies.

Moreover, if a chimney pipe goes onto the roof, it requires a separate design of the hole in the insulating layer and rafter system, and on the roof - a device around reliable waterproofing. It is worth noting that the work of constructing any roof, including such a complex one as an attic roof, is very important and dangerous, and therefore requires increased safety measures. If you do not have experience in such construction processes, then it is better to entrust their implementation to specialists or invite an experienced craftsman, under whose supervision, perform all actions carefully and carefully.

The attic is the roof under which the living rooms are located. The shape of the attic roof can be different, but most often the attic is equipped under a gable roof. The most rational solution to obtain the maximum usable area of a residential attic is a mansard roof with a broken slope line.

The stages of building a mansard roof with your own hands are in many ways similar to the construction of a regular roof, as are the names of the elements that make up its frame. These include:

Mauerlat - a support beam that transfers the load from the rafters to the walls of the building;
Floor beams - boards that form the attic floor and the ceiling of the lower floor;
Racks - vertical supports that support the rafter system;
Purlins – horizontal supports for rafters;
Crossbars are transverse horizontal elements that tighten the roof slopes together, otherwise they are called puffs;
Rafters - boards that form the main contour of the roof;
Suspension - a suspended rack that supports the tightening and redistributes the load between the rafters;
Lathing - boards or sheets of plywood designed for laying roofing on top of them and transferring the load to the rafter system;
Rabs are boards fixed along the axis at the bottom of the rafters and designed to form a roof overhang.

The cross-section of roofing elements is determined using calculation; the article presents the most commonly used materials in private construction.

Construction of a sloping mansard roof and its differences

As already mentioned, a roof with broken slopes is somewhat different from a simple gable roof. The difference lies in the shape of the opposite slopes: they are not a straight line, but consist of two slopes connected at an obtuse angle. The roof can be either symmetrical or have different shapes of opposite slopes - it depends on the project.

Thanks to the broken shape, the usable volume of the attic space significantly increases. The bottom of the rafters is usually set at an angle of about 60 degrees to the horizontal, and the support posts supporting these rafters act as the frame for the interior walls. The upper part of the rafters is most often installed at a slight angle, from 15 to 45 degrees - this allows you to save materials, but maintain the functionality of the roof and its resistance to snow loads.

Vertical posts supported by floor beams, purlins and tie rods connecting them form a parallelepiped that limits the internal dimensions of the attic. To give the structure additional rigidity, struts are installed between the floor beams and the lower rafters. After installing the upper rafters, hanging supports - headstocks - are installed to strengthen the truss and eliminate sagging of the crossbars. To further strengthen the lower rafters, they are pulled together with the racks using contractions. The elements are fastened using nails and bolts or studs.

Calculation of the dimensions of the attic roof

The main condition for a comfortable attic installation is the ceiling height - it should not be lower than 2.5 meters. To ensure such a height of the room, the break line of the attic roof must be at a height of at least 2.8 meters, taking into account the thickness of the insulation layer and the internal lining of the attic, as well as the thickness of the finished floors.

Before you start purchasing materials and building a roof, you need to draw a detailed drawing that will indicate the overall dimensions of the house, the line of the slopes and the height of the attic.

Drawing - dimensions of the attic roof

Technology for constructing a sloping mansard roof

Install a Mauerlat around the perimeter of the house. In wooden buildings, the top beam or log serves as the mauerlat. In stone - brick or block - buildings, the mauerlat beams are attached to studs or anchors, fixed in the walls during laying at a distance of no more than 2 meters. The mauerlat is leveled along the inner plane of the wall, and the remaining outside wall is later covered with decorative masonry. Mauerlat timber made from dry softwood usually has a cross-section of 100 or 150 mm. The timber is sawed off to the required length, the anchor pins are straightened if necessary and the timber is placed on top of them. Tapping lightly with a hammer. Indentations from the studs remain on the timber; a hole of the required diameter is drilled along them. You can also mark the timber using a tape measure, but the likelihood of error in this case is higher. Roll waterproofing is laid on the wall; you can use ordinary roofing felt in two layers. The Mauerlat is put on the studs and the nuts are tightened.
For floor beams, coniferous timber with a section of 100x200 mm is usually used. The floor beams are placed either on top of the mauerlat, extending 0.3-0.5 meters beyond the plane of the walls, or in specially designed pockets in the masonry. In the first case, the beams are secured using corners and self-tapping screws. To make the ceilings even, the beams are laid in strict sequence: first, the outermost ones in level, then, by pulling the string, the intermediate ones are aligned along them. The pitch of floor beams is usually from 50 to 100 cm, but the most convenient is a step of 60 cm, which allows you to lay insulation boards without trimming. To level the height of the beams, they are hemmed or pads made from boards are used. If the beams are placed in special pockets in the masonry, their ends must be treated with coating waterproofing and wrapped with roofing felt. Align them in the same way.
Racks are installed on the outer floor beams. The outer racks are made of 100x150 mm timber; the height and installation line of the racks are determined according to a previously prepared drawing. The racks are leveled using a level and plumb line and temporarily secured with jibs in perpendicular directions - along and across the axis of the roof. This will allow you to install the racks without deviation in any direction. The jibs are made from any board and nailed. A string is pulled between the outer drains and the remaining racks are placed along it with a pitch equal to the pitch of the floor beams, that is, on each beam. All racks are secured in the same way as the outer ones. You should end up with two rows of posts of the same height, running parallel to each other.
Purlins from 50x150 mm boards are laid and secured on the racks, the purlins are secured to 150 mm nails and to corners using self-tapping screws. Place crossbars made of 50x200 mm boards on the purlins with the narrow side down - this will increase their rigidity. Since there will be no load on the crossbars during operation, such a section of the board is quite sufficient; however, in order to prevent their deflection and increase reliability during the installation process, when installing the crossbars, temporary supports made of boards no thinner than 25 mm are placed under them. The top of the crossbar is fastened with one or two boards - also temporarily, until the rafters are installed. In this case, the boards should not be placed in the middle of the tightening - there they will interfere with further installation, but retreating about 30 cm. After installing the racks, purlins and crossbars, you have a rigid structure that limits the interior spaces of the attic. To increase its strength, it is subsequently secured with struts and contractions.
Installed from 50x150 mm boards. First, a template is made from a 25x150 mm board - it is easier and faster to process. A board of the required length is applied to the upper purlin, the shape of the cut is drawn directly on the board and it is cut out. Apply the template to the purlin in the places where the rafters are installed, and if it matches everywhere, then the upper part of all rafters can be made according to the template. The lower part, resting on the mauerlat next to the floor beams, is cut out in place each time. The rafters are secured using corners and self-tapping screws and nails.
To make the upper rafters, you need to mark the center of the roof. This can be done using a temporary stand nailed to the Mauerlat and an extreme tie from the end of the roof so that one edge of the board runs along the center line of the roof. The rafters are aligned along this edge. Next, prepare a template from a 25x150 mm board, placing it at the edge of the installed board at the desired level and to the purlin on which the lower rafters rest. Mark the upper and lower cuts and cut out the template. Apply it alternately to both sides of the roof, checking how accurately its center is marked. If the rows of racks are made in parallel, then there should be no problems with installing the upper rafters - they will all have the same size.
The required number of rafter legs is made according to the template. The rafters are installed on purlins and connected at the top using overhead metal plates or cutting boards with self-tapping screws. In the purlin, the rafters rest on the notches and are secured to the corners. In order for the rafters to stand straight, they are secured using struts, installed with the lower end on the ties. This is how all the rafters are placed. Attach hanging racks - pieces of board 25x150 mm. The upper edge of the board is fixed at the junction of the rafters, the lower edge - to the tie.
Place struts under the lower rafters from 50x150 mm boards, resting them with the lower oblique cut against the floor beam and securing them to the corners, and attach the upper edge to the side of the rafter leg, nail it to one or two nails, then drill a through hole and secure it to a bolt or stud. . After installing the lower struts, remove all temporary supports and posts.
Sew up the gables, leaving door and window openings. If the floor beams are laid in wall pockets, fillies are attached to the lower rafters - boards that continue the line of the rafters and form the roof overhang. When laying floors on top of the mauerlat, the beams already protrude to the required distance, and there is no need for fillers.
, corresponding to the type of roofing - continuous or sparse. Waterproofing is placed on the sheathing and installation of the roof covering, for example, begins.

A broken attic roof usually does not need insulation - only the walls and ceiling of the attic are insulated. The air space created under the rafters ensures good ventilation of the attic, reduces heating of the attic rooms in the summer and provides additional thermal insulation in the winter. Therefore, when covering the gables, it is important to leave ventilation windows in the upper part of the roof, above the attic floors.

Video - instructions for constructing an attic roof

In an effort to effectively use the entire available space of a country house, many owners equip the attic. When doing this, you need to be prepared to arrange the roof in a certain way. At its core, an attic is a converted attic and requires certain design solutions and some alterations in thermal insulation and roofing. In general, the construction of an attic roof for a country house is not much different from the construction of other types of roofs. But due to the operational characteristics of the attic roof and the requirements placed on it, it is necessary to have knowledge and understanding of the specifics of the arrangement of this type of roof.

Types of mansard roofs

Like any construction work, the construction of an attic roof begins with the design stage and selection of the most suitable attic roof for the structure, its type and type. For the attic, shed roofs or regular and sloping gable roofs are used. In addition, the appearance of the roof is influenced by the materials used and the design features of the roof itself.

Depending on the structural features of the building itself, several standard roof solutions are used during the construction of the attic. Mansard roofs: photos and description

Gable roof for a single-level attic. This option is a regular gable roof, under which an attic is located. During design and construction, no major difficulties arise due to the simplicity of calculations and the ease of construction of the truss structure. The main disadvantage of this roof design is the small interior of the attic with rather low ceilings.

Broken gable roof for a single-level attic. Unlike a conventional gable roof for an attic, a broken structure uses 4 pitched planes located at different angles. This type of roof structure is somewhat more complex to design and construct, but its undeniable advantage is the full-size interior space.

Single-level mansard roof with remote consoles. The design of this type of roof is more complex compared to the previous ones. But the spacious room and full-fledged vertical windows compensate for the shortcomings in the complexity of design and construction. The design feature of an attic with such a roof is its displacement and extension beyond one of the sides of the house, and the roof is more like a pitched one.

Two-level mansard roof with mixed type of support. Roofs of this type are the most difficult to design and construct. Such roofs are designed in conjunction with the house, as one whole, due to the multi-level placement of rooms.

Various mansard roof designs are not much different in design from conventional pitched roofs. Of course, there are certain design features, but in general they are the same as gable or single-pitch, and consist of the following main elements:

. Roof. The outer part of the roof, which serves as protection against various atmospheric phenomena.

. Lathing. Most often, wooden boards to which the roof is attached, as well as insulating materials.

. Ridge run. The upper part of the entire truss structure.

. Rafters. These are the stiffening ribs of the entire roof structure; they can be layered or hanging. Layered rafters are used for the attic roof.

. Mauerlat. This structural element consists of beams laid along the perimeter of the external walls and connected to the walls using special fasteners. The entire rafter structure is attached to the Mauerlat.

.Diagonal connections. To ensure the reliability and strength of the entire rafter structure, the rafters are connected to longitudinal beams and vertical posts using diagonal connections or bevels.

. Internal supports. To give the roof stability, the rafters and/or ridge girder are supported by vertical beams.

. Insulation layer. Due to the fact that the attic roof and the interior premises are practically one whole, to maintain temperature and humidity conditions, a multi-layer insulation cake is laid between the roof and the walls of the room. The insulation consists of hydro- and vapor barriers, sound and noise insulation, as well as a thick layer of thermal insulation. In addition, proper insulation of the attic roof is important for the safety of the roof itself.

Mansard roof construction technology

When designing and constructing an attic roof, many builders and designers, either out of ignorance or doing their work poorly, make serious mistakes in insulation, ventilation and truss structure. The result is an attic roof, which literally after a couple of seasons becomes unusable, fungus and mold appear, and the roof begins to leak or completely collapse. This happens due to a violation of the mansard roof construction technology.

Due to the fact that the attic roof is maximally drawn to the walls of the interior, and in this case it is quite difficult to obtain excellent heat transfer performance, the entire attic roof structure must have excellent thermal insulation, ventilation and a properly constructed rafter structure using wood treated with fire-bioprotectants.

To make your attic roof reliable and durable, you need to know the following:

The thickness of the rafters must be more than 250 mm. For such rafters you can use laminated veneer lumber;
Use materials as thermal insulation that will not lose their properties in the event of increased humidity. For example, extruded polystyrene foam or foam glass;
between the roof and the thermal insulation layer we make full ventilation with vents and hoods, through which air will circulate under the entire surface of the roof;
on the inside, along the entire surface of the thermal insulation, it is necessary to install a vapor barrier layer;
On the outside of the rafters, a layer of waterproofing and, if necessary, a layer of sound insulation are laid under the roof.

Such requirements are determined by certain natural and physical phenomena. But first things first:

A large thickness of the rafters is required to be able to lay a 20 cm thick layer of thermal insulation between them, and this in turn entails an increase in the mass of the entire roof structure, which is supported by the rafters.

The wood for the entire structure is treated with special means to protect against fire and microorganisms, which is a strict requirement of SNiP. This will protect it from damage by fungi and increase its service life.

If you use such popular materials as mineral and glass wool for thermal insulation, you can only gain in ease of installation and lightening of the entire structure as a whole. But cotton wool, no matter what it is, is cotton wool that absorbs water like a sponge, cakes and loses its insulating qualities. If you choose a material other than polystyrene and foam glass, you should focus on complete resistance to moisture, low heat transfer coefficient and relatively low weight.

A thermal insulation thickness of 20 cm is necessary because in our latitudes it is very cold in winter and very hot in summer. A feature of the attic design is large heat losses in winter and rapid heating of the room in summer. A large layer of thermal insulation will prevent heat loss and penetration inside. But this is only one of the reasons, the second is the safety of the roof. The fact is that the heat that escapes from their premises in winter warms up the roof, on which there is a layer of snow and partially causes it to thaw, and snow is a natural insulation. Melted snow at sub-zero temperatures turns into ice, which has no thermal insulation properties, it weighs down the roof and ultimately destroys the roof itself. And since up to 100 cycles of thawing and freezing can occur in one day, the roofing material will fail in just one season. In summer, the room becomes incredibly hot and stuffy, and you need to install an air conditioner, or even two. But these inconveniences can be avoided by installing a thick layer of proper thermal insulation.

Equally important is proper roof ventilation. It will help cool the roof, both in summer and winter, and also remove excess moisture from under the roof. All this will ensure comfortable living in the attic, protect against the appearance of mold, fungi and rot, and in addition will protect the roof from destruction in winter.

Regarding steam, hydro and sound insulation, everything is simple. Vapor barrier allows excess moisture from the premises to pass through and prevents its penetration from the outside; waterproofing protects thermal insulation materials and the room from accidental moisture ingress. And sound insulation reduces the noise level from impacts of rain, hail and wind on the roof surface.

Phased construction of an attic roof

Carrying out all the work to create a roof for an attic requires builders to have some experience in this area. Unlike ordinary pitched roofs, building an attic roof with your own hands is somewhat more difficult due to the installation of angled windows in the roof itself and the broken structure of the slopes. To build an attic roof with your own hands, you must adhere to the following stages of work:

Design

The first thing you have to do is develop a roof project. To do this, you can turn to specialists or, if you are good with a computer, do everything yourself in an architectural program. Also at this stage, all the necessary calculations of loads, the angle of inclination of roof slopes, etc. are carried out. To do everything correctly, you should turn to a document such as SNiP “Loads and Impacts” for the necessary information.

Construction of the rafter frame

This stage of work is the most labor-intensive, and for a do-it-yourself attic roof to be made with high quality, the combined efforts of 3 to 4 people will be required. We begin the construction of the attic roof by laying and securing the mauerlats along the entire perimeter of the house, using timber with a section of 100x100 mm.

Construction of an attic roof photo:

After this, we install a frame for the attic space, the racks of which will also serve as supports for the rafter structure. To do this, we use a beam with a cross-section no smaller than the cross-section of the longitudinal beams on which the racks will rest. First of all, we install vertical posts at the beginning and end of the building. We fix them to the longitudinal beams using special stamped metal corners and self-tapping screws. To facilitate all fastening work, we use a screwdriver. Now we lay the jumper over the racks and secure it.

We stretch the cord between the two resulting arches, and if everything was done correctly, it will be strictly horizontal, if not, you will have to disassemble one of the arches, trim it a little and reinstall it. Now, using a stretched cord, we install similar arches with the step provided for the rafters. We connect the resulting arches with jumpers, which we secure with stamped corners or nail plates.

Having assembled the frame of the future interior space, we proceed to install the rafters. We start with those that have the greatest angle of inclination and are on the same level with the frame of the attic room. There are no particular difficulties here. The beam for the rafters is cut to the required design length, a groove is cut at the base of the beam for installation on the Mauerlat, and the top is cut at a certain angle. After which each rafter is installed in place and fixed to the main structure.

The next step is a little more difficult, since you will have to install the upper rafters. The difficulty lies in maintaining a certain angle and centering of the entire structure. To make the task easier, you can first make a template from two long boards that will exactly repeat the future connected rafters. Using this template, we cut the rafters on the ground and then install them in place. The rafter installation algorithm is the same as for the interior frame arches.

To complete the installation of the rafter structure, we nail the sheathing. For lathing, both ordinary boards and sheets of plywood or chipboards can be used. This will depend on the type of roofing materials.

Creating an Insulation Pie

Having installed the rafters and sheathing, we begin to create the insulating layer. To do this, first of all, we lay a vapor barrier on the inside of the rafters and fix it to the rafters with brackets. Next, we lay the thermal insulation material and carefully ensure that it fits closely to the rafters and does not leave any gaps. On top of the thermal insulation, in increments of 50 cm, we fill the lathing, which will hold all the thermal insulation.

On the outside of the rafters we lay a layer of waterproofing, which will protect against accidental penetration of moisture. Finally, we lay the roof on top of the waterproofing.

Construction of an attic roof: video tutorial

The variety of ready-made attic roof projects is very extensive. They can be with or without windows, rounded or strictly straight, with one slope or several. But no matter what the attic roof is, its construction will require the knowledge and skills of a construction master.

As experienced builders say, an attic can be installed in a house if there is a roof. The type of roof affects how much this measure will increase the usable area, whether it is comfortable to use this room and how complex the work will be required. The most common types of roofs for arranging a residential under-roof space are considered to be gable roofs with straight and broken slopes.

The rafter system of the attic roof is designed in such a way as to free up space in the center, where the height of the ceilings reaches an acceptable height, placing the bulk of the supporting elements at the edges. This article will tell you what the roof frame consists of, how to choose the best design option and perform installation correctly.

Types of rafter systems

When starting to design a rafter system for an attic roof, pay attention to the layout of the house. Based on the types of supports, choose the appropriate device option:

Layered. This type of rafter frame is suitable for houses in which a load-bearing partition runs in the middle. Then the weight of the roof structure is distributed between it and the external walls of the structure. This is an easy and rational way to organize the frame, but it is suitable if the distance between the external walls and the internal support does not exceed 7 m.
Hanging. This type is used when there are no load-bearing partitions or columns inside that are used to transfer the weight of the roof to them. Hanging rafters rest on the mauerlat and ridge girder. For roofs up to 50 sq.m. m, with a low roof weight, the simplest configuration is used, consisting of rafter legs and a horizontal tie. To cover a large structure, this structure is reinforced with racks, braces, and struts. These elements increase the stability of the roof, but “eat up” the usable area of the attic. The permissible distance between the walls of the structure for hanging rafters is 14 m.
Combined. A mixed type of rafter system is used when support columns are installed in the middle of the house instead of a load-bearing partition. It turns out that some of the rafters can be leaned on the columns, and the rest can be mounted as hanging ones. This method is quite often used for arranging attic roofs, since it allows the use of fewer auxiliary elements, reducing the load on the foundation and without cluttering the roof space.

Please note that the installation of the attic must be planned at the project creation stage, because the type, weight and design of the rafter system are necessary for calculating the foundation. If the decision to erect an attic roof arose at the final stage of construction, it is necessary to recalculate the weight of the house taking into account new data in order to check whether the foundation can withstand the additional load, especially if the site has complex soil and a small distance between the surface and groundwater.

Calculation of rafter system elements

According to building codes, a room is called residential if the height from the floor to the ridge is at least 2.5 m and there are sources of natural light, that is, windows. Therefore, the main parameter of the attic roof that needs to be calculated is the angle of inclination of its slopes. The catch is that if you lay down a slight slope, the height of the ceilings in the attic will be lower than allowed by the rules. And, if you make covered slopes, the roof will turn out to be very heavy, expensive and unstable. Therefore, it is used, the slopes of which change the slope, its upper rafters have an acute angle of 30 degrees, and the lower ones - 60 degrees.

Ceiling angle and height

An important stage in the design of an attic roof is the calculation of the cross-sectional size of the elements of the rafter system. The easiest way to find out the recommended size is in a reference table with calculated values that take into account the length, distance between adjacent elements, type and quality of the material. However, if the roof is of non-standard size, it is necessary to perform a calculation based on calculating the total load from the weight of the roof that falls on the rafter system. The calculation scheme also takes into account temporary loads in the form of the mass of fallen snow, which are reflected in the climate coefficient, which characterizes the weather at the construction site.

To create the rafter system of an attic roof, wood is used, but this is not advisable in all cases, since in order for the rafters to cope with the load, it is necessary to increase the cross-section of the lumber used, which further increases the weight of the structure. To break out of this vicious cycle, it is necessary to abandon wood in favor of stronger metal rafters.

Rafter system design

The components of the rafter frame of an attic roof are no different from the design of other types of pitched roofs. It includes:

In most cases, the elements of the rafter system are made of high quality wood. To avoid deformation during operation, it must be dried to a humidity of 15-18%, treated with deep penetration antiseptic impregnation and fire retardant if you plan to install the chimney on the roof.

Assembly sequence

It is better to assemble the rafter system with the help of an experienced craftsman, since even lifting heavy, long beams is problematic. It is not recommended to carry out installation in rain and snow, as the moisture content of the wood will increase during operation. Typically the build process looks like this:

The reliability of the attic roof truss system depends, first of all, on the correctness of the calculations, therefore, if you are not confident in your engineering abilities, it is better to use a standard project created by a professional architect.