How to make a rafter system for an attic roof. Mansard roof rafter system, design and calculation

Just a roof without additional elements or an unheated attic suits few people. An excellent alternative to these two solutions is the construction of an attic. In order for it to fully fulfill its functions, it also requires the roofing to be performed using a special technology.

Distinctive features

All attic roofs have one important feature - these are supporting walls, which are noticeably higher than in the case of a cold attic. The slope, clearly divided into flat and relatively steep, must be done as carefully as possible. It even makes sense to invite professionals, because saving on their services, as practice shows, is irrational and only leads to harmful consequences. You can still do the work yourself, but preparing an attic project is much more difficult than with a conventional roof.

A layer of waterproofing must be installed to prevent moisture from penetrating into the room. The outer covering is always created only from materials that are both light and strong. The interior finishing is carried out mostly using plasterboard sheets and materials based on it. Load-bearing structures are made exclusively of wood or metal. From insulation to roofing trim, it is required to leave an empty gap for maximum ventilation.

Unlike a simple attic, the attic is always equipped with convective forced ventilation. Thanks to it, stagnant air rises to the ridge of the roof and leaves it through the aerators. And at the same time, fresh air flows pass inside with the help of eaves vents. Continuous circulation helps maintain a pleasant microclimate. Problems with excess humidity and stuffiness completely disappear.

Varieties

The mansard roof comes in different formats. A broken roof is equipped on all slopes with a pair of pitched planes, one of them is flat, and the other with a large slope. The first plane tilts by 20–30 degrees, the bottom by 60–80 degrees. This solution is recommended for private houses with a maximum width of 6 m. Difficulties when working with a sloping roof are justified by the emergence of a full-fledged upper floor, the rafters are supported by racks, and the lower belt turns out to be the base for the floors.

Half hip roof- this is a solution that rests on the Mauerlat through a symmetrical rafter system. Miniature slopes are made above the gables. A hip roof is always more complex than a gable roof, especially in terms of the construction of rafters. Dormer windows in hip roofs are most often placed in the same plane as the roofing pie. But if the windows are not closed tightly enough, the attic will be flooded with rain and melt water.

Danish format differs from a simple hip one in the presence of pediments that improve the lighting of the attic through vertical openings. The rafters of hip roofs have no breaking points and go straight. The upper end of the corner ribs rests on the ridge, the length of which is determined by the characteristics of the rafters. Hip sloping roofs are also sometimes made broken. A hipped mansard roof is close to a hip roof, except for the fact that it does not have a ridge.

Multi-pinch type performed as a combination of several gable blocks. A feature of this type is its sophisticated geometry with a lot of kinks. A vault, dome, cone and some other structures can also be created, but these are more complex options, so only qualified specialists should perform such work. Aesthetic qualities and external unusualness allow the most complex ideas to be realized. A semi-mansard roof is installed in cases where it is very important to use the space to the fullest extent possible and install vertical glazing on the floor.

Shape selection

The gable format is the easiest to work with and allows you to save on materials used. But you have to “pay” for everything – and in this case, the “payment” is a reduction in the available usable area. In addition, you will have to build the walls at an angle, which will prevent tall furniture and interior items from being placed inside. For a separate bedroom, this option is optimal, but if you need to create another room, then it is better to choose some other arrangement scheme.

Sloping roofs are the most popular among consumers, under which it is easiest to create a high-quality living area. By eliminating windows protruding from slopes, the technology can be simplified, but the cost of materials will increase. If in the first place are considerations such as obtaining an unusual type of upper surface and the most intense precipitation, then it is worth choosing the multi-pinch option. It features impressive resistance to mechanical stress. If any difficulties arise, you should additionally consult with specialists for a particular home.

A shed roof is not suitable for arranging an attic, because it can only be equipped with a large slope by strengthening the rafters and increasing the cost of roofing. Hip and half-hip (sometimes also called Danish) formats make it possible to build a spacious room with an acceptable ceiling height. But in this case, rafters are more difficult to build than when using one slope, and the total cost of the work is noticeable for almost all customers.

Taking into account the additional layers in the roof, it turns out that there should be at least 250 cm from the floor to the ridge of the roof. To build a two-level attic, you will have to reserve more than 5 m from floor to ceiling. When thinking about the geometric shape and size of the building, you should always pay attention to how the windows will be installed. Having placed them in the plane of the roof, you will have to take care of the finishing to prevent precipitation from getting inside.

Rafter system

What are they?

Under the attic, you can build a rafter complex of one of three main types, namely:

• layered;
• suspension;
• combined.

A suspended rafter system, supported only by ridge purlins and mauerlats, is laid using top and bottom tie-downs. On slopes exceeding 400 cm in length, the lower parts of the rafter legs must be reinforced with uprights or struts to prevent sagging. The advantage of the hanging option is that it is all located in areas not used by people, and allows you to provide a lot of free space.

Layered frames are formed in cases where heavy roofing material is located on top. Regardless of the type of design, the height of the ceilings in residential attics cannot be less than 230 cm. The layered look is ideal if a load-bearing partition is located in the middle of the house. The load from the structure is distributed evenly across it and along the outer walls. Organizing the frame in this way is easy and convenient, but at the same time there should be a maximum of 700 cm from the external walls to the internal one. The suspended version is useful if the building does not have load-bearing partitions or columns, so it will not be possible to transfer pressure from the roof to them. The reference points in this case are the ridge run and the Mauerlat.

If the roof is small (area no more than 50 m²), you can build rafters according to the simplest scheme. It includes “legs” and a drawstring oriented horizontally. When the building is large, you will have to use ties, racks and struts to strengthen it, but strengthening results in a decrease in the usable available area. You cannot use the elementary type if there is more than 14 m from one wall of the structure to the other. But when the roof is supported in the middle not by a partition, but by columns, then mixed rafters are used.

The idea is simple: some of the rafters transfer the mechanical load to the columns, while other elements are made hanging. The advantage of this step is obvious, it reduces the need for additional parts and does not put undue pressure on the foundation of the house. In any case, the arrangement of the attic and its type are thought out at the time of design, since the characteristics of the walls, foundation, rafters and roof are closely interrelated. The decision to remodel a finished house or to add an attic to an ordinary house means the need to rework all calculations and diagrams. Work becomes especially difficult on difficult soils where groundwater is high.

Calculation

During the period of operation, attic rafters must fully (with a reserve) bear the load:

• their own mass;
• roof pie;
• the highest possible gusts of wind;
• average annual load from snow and ice;
• peak loads from precipitation.

If the roof is very steep (more than 60 degrees), you can safely neglect the pressure caused by snow and rain. But the impact of winds, even relatively weak ones, increases significantly. When calculating, a couple of parameters are taken into account: the cross-section of the rafters together with the beams, they are also called tie rods, and the distance when installing them. You should not assume that the size of wooden beams increases with increasing loads on them. The greatest rigidity of structures is achieved when using logs with a diameter of 12–20 cm or when taking lumber with a cross-section of 4–20 cm, while the installation step is 50–120 cm.

Without special engineering knowledge and information about the construction of a house, it will not be possible to calculate the construction more accurately. Online calculators are unable to give anything other than preliminary estimates. Calculations made with their help will need to be checked additionally. It is not necessary to consult with specialists, but you can simply rely on ready-made numbers. Let the load from snow on a flat projection of the slope be equal to 100 kg per 1 m², its slope is 60 degrees, and the span length is 450 cm (before the struts), and the rafters are spaced at intervals of 1.2 m.

For example, the front covering is represented by slate. The actual mass of the snow load is 100x0.25 (0.25 is the slope coefficient). Specific gravity of slate with a typical profile = 25 kg per 1 m², and the total specific gravity is 50 kg per square meter. To recalculate the specific weights per linear meters of rafters, you need to multiply the resulting figure by the installation step. Then the cross-section of the rafters is selected according to the span lengths; but it is important to take into account that ready-made schemes are only suitable for relatively simple options, and if the roof is large or complex, then you will have to turn to professionals.

Correct calculation of the roof should take into account not only the load that it creates, but also pressure from the wind, from the snow mass (the average maximum value is taken according to long-term observations in a specific area). The wood for the rafters is selected in such a way that there are a maximum of three shallow knots per 1 linear meter, the size of which is no more than 3 cm along the longest edge. The wood should not have a single through crack, and the highest permissible moisture content can be 18%.

Construction of the structure and laying of the “pie”

Frame: device

Drawing up a competent project and calculating the exact dimensions of the elements in it is only half the battle. It is also necessary to be able to implement what is planned properly. The work of constructing the frame using a simplified method allows you to make a broken mansard roof in two stages. First, the rafter trusses are assembled on the ground, then they are laid on the prepared walls. For assembly you need boards with a section of 150x50 and 100x50 mm, their length is exactly 600 cm.

To build a rafter frame with your own hands, you need to do the following:

• prepare beams for the lower chord of the truss, taking into account overhangs of 250–270 mm on all sides;
• if the length of the beam is insufficient, increase it by nailing an overlay of a suitable cross-section;
• attach vertical posts to the beam laid out on the ground, forming the walls of the future attic;
• secure the ceiling beams and ridge supports;
• supplement them and the corners of the structure with a pair of boards for marking under the hanging rafters;
• cut off the elements exactly according to the location and attach them;
• from the remains of lumber, build the lower legs of the rafters in the same way and nail them to the frame;
• repeat all the same steps when installing the remaining trusses.

In most cases, front gables are equipped with windows or doors leading to balconies. To simplify the work, it is advisable to construct all belts and racks on the ground. Having received the necessary frames, they are lifted one by one and sequentially, moving from the first pediment, they are fixed in the right place. It is easy to avoid the pediment from falling - you just need to install spacers and attach them firmly to the walls. The placement of all the following trusses should occur exactly as shown in the drawing.

The exposed rafters are attached to the walls by screwing brackets into the second highest crown or using steel angles and zinc-coated screws. If the walls are made of brick or other capital blocks, the connection of the rafters is achieved through the Mauerlat. A wooden beam placed around the entire perimeter is attached to studs or anchor-type bolts. Such a structure must be separated from the stone surface by waterproofing (a layer of roofing material). At this point, the work with the rafters themselves can be considered complete.

Waterproofing

To ensure the safety of the roof for many years to come, it is very important to lay a number of layers of materials that provide reliable cover from negative factors.

Be sure to use diffusion membranes that simultaneously perform the following functions:

• do not allow the wind to pass through;
• block the penetration of precipitation;
• freely conduct water vapor out.

The first of the canvases is rolled out in the lower segment of the roof; it must be attached to the boards with a construction stapler. When installing all subsequent panels, an overlap of 0.1–0.15 m is provided. When the entire base is covered, the sheathing can be filled. Then the final coating is applied. The installation and technological nuances of the work depend on how it will be.

Instead of simple waterproofing, in the attic it is best to use materials with minimal accumulation of condensation. They help prevent the insulation layer from getting wet. Films made of polymer materials without perforation are considered the best option for such a coating. Whatever type is used, a ventilation gap of 50 mm is allocated for it in the cake. By using polyethylene rolls with an outer aluminum layer, it is possible to simultaneously guarantee heat retention in the attic.

Reinforced polypropylene is invariably superior to polyethylene because it is stronger and less susceptible to UV damage. One side of such a film has anti-condensation properties; it is made from a mixture of cellulose and viscose. As a result of laboratory tests, it was possible to prove that anti-condensation coatings absorb a lot of water and retain it inside without the formation of drops. If you change the conditions that created the condensation, the material will dry out quite quickly. Of course, you should carefully choose which side to put on the outside.

At sharp angles of roof inclination, waterproofing is reliably provided by windproof or vapor barrier membranes. If the slopes are relatively flat, then be sure to use a film that protects against condensation. Diffusion membranes are required in roofs that have one air outlet: two or more ventilation gaps can usually be done with simple materials. Moisture-proof films over living areas are placed in two layers. Before installation, they should be stored in a dark, temperature-stable area, away from heaters and incandescent lamps.

Insulation

The insulation is laid out from the inside in a layer of at least 200 mm. With such a thickness, the level of thermal insulation will be sufficient and guarantees prevention from both winter hypothermia and summer overheating. If the thermal protection layer is too small, the snow will warm up. Continuous melting and hardening will quickly deteriorate even the most reliable roofing materials. If the attic is not protected from above, you will have to use powerful air conditioners on hot summer days.

According to professionals, you can properly insulate an attic roof using foam glass, mineral wool or expanded polystyrene. Foam materials do not absorb water, and plastics are more flammable than cotton insulation. If you use extruded polystyrene, you can simultaneously provide decent sound insulation. Using foam glass, you can insure yourself against fire, frost, and rotting under the influence of high humidity. The advantage of cotton wool is its affordable cost and ease of use; its basalt variety is distinguished by its increased strength.

Insulating materials are fixed using lathing. It is formed on the basis of planks. The width of an individual block is 100–150 mm, its thickness is 50 mm. By choosing thermal protection that is impervious to moisture, you can sometimes abandon the vapor barrier. But experienced experts believe that such a step is reckless in any case. After all, it is unknown how the conditions inside the roofing pie will change over time, and how severe weather disasters it will withstand.

To prevent the formation of cold bridges in an attic intended for winter living, in addition to the main layer of protection, it is necessary to provide another layer - it surrounds the rafters and their legs. Of course, the rafters are no longer visible visually, and you need to immediately note where exactly they go. Otherwise, the subsequent fastening of materials and structural elements will turn out to be a very difficult task, bordering on a gamble. A film permeable to water vapor is always placed over the thermal insulation. The need for insulation materials is calculated based on data on the internal volume of the room, but a reserve should also be provided so that overspending due to defective work and other reasons does not affect the result.

Ecowool can also be used as insulation. Its advantages are obvious, but all work must be carried out by strictly trained teams with special equipment. There is nothing to think about installing such an insulating layer yourself. The disadvantage of the ecological variety of cotton wool is its composition. Due to the presence of cellulose flakes, the material is highly flammable. Penofol is used to enhance the effect of other thermal protection options, but by itself it is extremely rarely necessary.

Additional elements: installation

Even when the roof covering is laid, this does not mean that all the work is completed.

It is necessary to install additional elements that perform quite diverse functions:

• make the edges of the slopes more orderly in appearance;
• cover internal and external ribs;
• isolate the cake from the seepage of precipitation, dust particles and various insects and small birds.

When installing corrugated sheets, various additional parts are used. Almost all of them have to be installed at the last stage of work on the roof, but certain types need to be installed before laying the sheets. All these details should be studied in advance so as not to destroy already prepared structures and not recycle them from scratch. The drip rails are supposed to be attached to the rafters along the line of the lower eaves strip, and before the sheathing is filled. Such elements are mandatory in low-rise buildings that are not equipped with drainage systems.

Valleys or valleys are concave corners of the joining planes of the slopes. It is in these places that roof leaks most often occur, so special attention must be paid to them when working. The bottom of the valley is placed before the profile is laid out on continuous sheathing of boards. The width of the sheathing should be 0.6 m in both directions. The upper strips are shaped like a simple angle with the same cross-section as the bottom part. They are laid out after the corrugated sheet is laid and attached.

If the roof is flat, the valleys should be covered with mastic, and on steeper structures a waterproofing strip should be placed under the steel corners. The width of this strip is 0.2 m greater than the width of the part being installed, and the exit on the right and left should be the same - 100 mm each. The abutment strip, which encircles the perimeter of the base of the brick chimney, is installed in approximately the same way as the valley; it is divided into two parts. The lower strips must be covered with a waterproofing carpet. The upper edges are inserted into grooves, the depth of which is approximately 15 mm.

The lower edges of the chimneys are sealed with a sealant, then a covering is installed, and when the corrugated sheeting is laid, the cake is covered with the upper edge. Junctions to walls can be created without double-layer metal protection. The bottom strip is simply replaced with adhesive waterproofing, which is placed along the joining line. To finish a large area, it is necessary to lay planks with an overlap of 0.1 m. Additional elements are fixed above the corrugated sheet in two planes.

The roof is attached with self-tapping screws measuring 0.19 x 0.48 cm, they are installed in increments of 0.4 m. The eaves strips are installed only after the installation of the structures holding the gutters. This requirement does not apply when using short brackets. If the planks have not yet been installed, the end is protected with ventilation tapes or mosquito nets. The end strips for corrugated sheeting are attached to the boards at the ends; the high ribs of these elements extend above the slope exactly to the same level as the profiles.

On a gable roof with slopes in the shape of a rectangle, pieces of wood are nailed to the ends before the main covering is installed. Their role is to form a kind of border around the entire perimeter; it will make the layout of the sheets more accurate. End extensions, representing an angle with unequal width of the shelves, are mounted with the overlap of one of the shelves of the final wave of the sheet. The ribbed variety is equipped with another rib oriented along the fold line. This design simultaneously increases the strength and aesthetic characteristics of the parts.

A ridge strip is invariably used on any roof with slopes. It not only covers the “crown” of the roof mechanically, but also completes the visual image of the structure as a whole. Ridge strips are installed after placing a ventilated seal along the entire installation line, duplicating the roof topography in this place. The sheathing is installed continuous, covered with reinforced waterproofing. The ridge strips are pinned to the convex corrugations using self-tapping screws; the fastener alignment step can reach 300 mm.

Regardless of the type, snow guards are installed only on continuous sheathing. When the attic is built in the form of several steps, it is necessary to retain the falling snow for each of them separately. The same structures are placed under entrance groups and under windows. Extensions that stop the snow mass should be placed 350–500 mm from the edges of the overhangs, in a straight line or according to the checkerboard rule. Attachment is ensured using self-tapping screws with washers that increase density.

A different approach is practiced on a tiled roof. There the dobors are made of clay; Moreover, their list differs significantly. There are skates of bizarre configurations, reminiscent of a lily or even an eagle. There are units for ventilation systems. Non-standard areas are sheathed with elements in the shape of the letters Y, T, X. Nozzles, ribbed grooves, roofing umbrellas made from various types of metal are also used.

When working on a seam roof, in addition to installing the valley, special attention must be paid to the ridge assembly and connection points. Since seam structures can accumulate charges of static electricity, it is unacceptable to use them without lightning rods. The choice of extensions for hip and half-hip roofs is determined by the type of structural material used. Maximum effort must be spent on retaining snow and ensuring adequate water drainage. Gutters and ridges must be equipped with special plugs.

Beautiful examples

When creating attic roofs for private houses, attention is paid not only to their technical characteristics, but also to their external attractiveness. The photo shows an elegant mansard roof covered with red tiles. Its construction clearly turned out to be not an easy task - at least all the geometric kinks are worth it. But the result, especially when complemented by a window of complex design, is clearly worth the effort.

The half-hip roof, shining in the sun due to the metal coating, looks very good. The hipped structure cannot be considered simple, but it was possible to create a high attic with windows stretched upward. Some customers prefer options with a balcony, and experienced builders know how to satisfy this request. This is what a frame country house might look like, from the attic of which there is access to a covered area. The external fencing, made of figured wooden elements, not only ensures complete safety, but also gives the building as a whole additional charm.

Here is an alternative solution: the balcony is equipped not at the end of the roof, but in its long plane. Thanks to this, it was possible to make the structure oblong at the cost of reducing the width. Exit to the outside is provided not by doors, but by rising window sashes. But a balcony-type window successfully performs its function even with a noticeably smaller area. The photo shows one of these systems, in which metal railings are used on the sides, and high-strength glass is installed in the front plane.

A full hip roof can have a very bizarre geometric shape. These are not only many slopes, but also curved curved surfaces. The high complexity of the work and its high cost are justified by its good compatibility with decorative wall elements and interesting design effects. If you don’t want to go for any radical refinements, you can simply choose a gable design and implement it as efficiently as possible. This can be done with a calm geometry, while creating quite comfortable conditions for those living in the attic.

For information on the construction of an attic roof, see the following video.

An attic in a house is always interesting, beautiful and profitable. However, not every master will undertake to do all the work independently. Reasons: ignorance of technological subtleties and the complex rafter system of the attic roof. But you can build an attic yourself, the main thing is a good design and a sober assessment of your own strengths and financial capabilities. And we will advise and tell you what types of rafters there are, and we will analyze the structure of the rafter system of the attic roof of various types.

The drafting must take into account all the nuances. If miscalculations are made, the developer runs the risk of ending up with something different from what was planned. The simpler the roof, the more convenient it is to make it yourself. Types of roofs are:

1. Gable, where the slopes descend on both sides;
2. A broken line, consisting of two or more slopes of different angles of inclination;
3. Hip with a triangular shape of slopes;
4. Semi-hip - end-type slopes are located approximately half the height distance;
5. Dome for polygonal or round buildings;
6. Vaulted - in cross-section, such a roof has the shape of an arc.

The attic roof is distinguished as ventilated and non-ventilated. The type is selected depending on the climatic characteristics of the region, for example, in areas with high rainfall it is better to build ventilated facilities.

Types of rafter systems

The rafter system of the attic roof is selected depending on the layout of the building and differs as follows:

1. Layered rafter system attics are installed when the load-bearing partition runs through the middle of the building. The design redistributes the weight load and is suitable for buildings where the distance between the external wall panels and the internal support system does not exceed 7 m.
2. Hanging rafter systems applicable in the absence of internal partitions and walls. Supported by a mauerlat and a ridge girder, they are suitable for buildings where the distance between the external walls and the structure does not exceed 14 m.
3. Combined rafters Attics are most often needed in buildings where columns are installed instead of partitions. It turns out that part of the rafter structure rests on columns, and part is made in a hanging version. The absence of auxiliary elements, reduced load on the foundation and no cluttering elements are the main advantages of the system, which is why this option is used most often.

Important! The types of rafter systems are selected at the design stage in order to correctly calculate the required strength of the foundation. In the case when the decision to build an attic arises at the final stage of construction, an accurate diagram of the truss system of the attic roof and a complete recalculation of the weight of the house taking into account new data will be required. The process cannot be neglected, especially in areas with weak soil. Otherwise, the end result will be that the house will quickly subside, and groundwater will render the foundation unusable in a short time.

Structural features of the rafter system

The main components are little different from a conventional gable roof:

• Mauerlat is the base of the roof that bears the weight.
• Rafters are elements of the system that form the inclination of the slopes. The top is fixed to the ridge, the bottom - to the mauerlat or stand.
• Post - an element that supports the ridge or back of the rafter leg.
• Struts are needed to strengthen and support the rafter legs. The strut has an oblique cut and serves to prevent the rafters from bending under the weight of the mass.
• Ties - a horizontal tie of a pair of rafters, placed in the upper or lower part.

Important! Rafter elements are often made from the highest grade wood. A timber with a moisture content of no more than 15-18% is purchased and pre-treated with anti-rotting compounds and antiprenes.

Assembly diagram of the rafter system for the attic

An attic rafter system is quite a troublesome task, so it is better to entrust the assembly to a specialist. But if this is not the case, tips and videos will help you complete the simplest design yourself.

1. The mauerlat beam is laid on the top frame of the walls. If the house is log, you can get by with upper crowns reinforced with brackets.
2. Install floor beams. Mounting on the mauerlat or protrusions of wall panels. The simplest fastening is without extension, supported on the walls, but with extension is when the beam is carried outside the perimeter of the house to create an overhang. In this case, the distance between the end of the beam and the wall panel should be at least 0.5-1.0 m.
3. Vertical racks are installed. To do this, determine the middle of the floor beam, then equal intervals are set aside from it - the distance should be equal to the width of the attic room.
4. The puffs are secured to the racks, and it turns out that each pair of racks looks like the letter “P”.
5. Installation of the lower rafter elements is carried out with fastening to the rack. Fasteners - self-tapping screws or nails, fasteners on the mauerlat in the form of a movable fastening slider, compensating for the shrinkage effects of the timber.
6. Installation of rafters for the upper part of the attic roof is carried out by connecting each pair with a metal plate or bar.
7. Final processing includes laying a waterproofing membrane and sheathing. The lathing for soft roofing material is solid, for profiled sheets and other hard materials it is sparse.

The proposed installation of the rafter system is the simplest. It is quite possible to equip such a structure with your own hands, you just need to make the correct calculations, the rafter system, drawings of the attic roof, and diagrams will help you complete the work without errors.

Rafters with extension behind the wall panel

This option is used when there is a small amount of internal space. You will have to rest the rafter leg on the upper floor beam. Mauerlat is not needed here, but reinforcing struts are required. To strengthen the base, you can fill in a reinforced concrete belt. Attaching the floor beams to the monolithic belt is done with anchors, into which support posts are inserted to the maximum thickness of the beam.

Important! The external structure forms a cornice: for wooden houses the width is from 0.5 m, for those made of concrete and stone – from 0.4 m.

Scheme of work:

1. Install the outermost floor beams that form the outline of the overhangs. The section of the beams is 150*200 mm.
2. The remaining beams are mounted along a cord stretched between the outer beams: the distance between them is equal to the pitch of the rafter legs. Insulated roofs require a rafter pitch of 0.6 m; if rafters are installed with the specified pitch, they can be made from timber with a section of 50*150 mm.
3. Having cut out the tenons, prepare the supports.
4. Install the corner posts and secure them with temporary supports.
5. Using a plumb line, determine the location of the support points of the beams and select holes for them.
6. Install row posts and a pair of load-bearing supports in the centers of the attic gable.
7. Lay purlins from 50*150 mm boards. Secure the purlins with corners.
8. Connect the supports with bars, also securing them with corners to the purlins.
9. Fasten the crossbars using temporary fasteners with an inch. The deviation from the edge of the frame is 300-350 mm.
10. Make a template for the bottom row of rafters: attach the blank board to the end of the purlin and beam, determine where to cut off the excess, try it on and trim it.
11. Install the end rafter posts.
12. Make a template for the top of the rafter legs.
13. Try on the template and build a tier, how the rafter system will be, photos of the attic roof will clearly show the entire structure.
14. If the templates fit perfectly, make the required number of rafter legs, mount them in place, strengthen the crossbars with the headstock to avoid their sagging and firmly sew them to the ridge area. The lower part does not require rigid hemming, it should be free.

The final completion is the installation of the gable frame, sheathing and roofing material. If it is not entirely clear how to complete this project, watch a video from professionals; the material will help you understand the intricacies of construction.

Attic from frame modules

The mansard roof rafter system involves a version of frame modules that is much simpler than the previous one. It is not groups of individual supports that are mounted on the ceiling, but ready-made block modules of the side walls of the future attic room. Similar designs of mansard roofs and their rafter system allow you to work not at height, but below, calculating and measuring every step. The step-by-step process is as follows:

1. Make the walls of the attic according to the design in advance, with the longitudinal beams acting as purlins and support elements. Together with the racks, lay out these elements on a flat area and mark the sockets for the support points of the side walls with squares - make cuts along them.
2. Select a spike on the racks.
3. Connect the longitudinal beam with the vertical posts and you get a frame module (double). These are the future walls of the attic.
4. Lift the frames up and install them in place. Temporarily secure the installed frames with spacers and then fasten them with brackets.
5. Select sockets at the edges of the beams for mounting the lower row of rafters; if necessary, modify the sockets with a chisel.
6. The upper rafter tier is made on the ground, for which the blanks are first adjusted to the required elements.
7. The base of the upper triangle of the attic structure is a stretcher, and its length is equal to the distance between the installed planes (vertical) of the already mounted frames.
8. Select sockets along the edges of the stretch, and spikes on the lower heels.
9. Assemble rafters for the attic of the upper tier, mount a crossbar for additional fastening, and reinforce the ridge assembly with a triangular-shaped wooden overlay.
10. Pre-production of rafter legs for the attic will allow you to avoid working at height. You only need to cut the top bevel, which rests on the top post of the wall panel and on the tension of the upper trusses.
11. Try on the lower rafter part to the end, mark the tenon shape area on the lower heel, cut out the tenons according to the drawing made.

Now all that remains is to move upstairs and raise all the rafters. First install the trusses, securing them to the upper frame of the walls, and then install the lower part, attaching them to the ceilings (beams) with brackets. It turns out to be a completely comfortable floor, the rafter system for which was assembled on the ground. To make it easier to understand the task of building an attic roof, a modular rafter system, watch the video. All other stages are carried out according to the standard scheme of a conventional gable structure; the attic and rafter system are shown above.

There are several roof options under which you can place a comfortable living space. In order to ensure the maximum volume of the attic space under the roof, it is necessary to select the optimal angle of inclination of the slopes and not to forget about the snow and wind load on the roof. We will look at the most popular designs of attic rafter systems in the middle zone.

The design of the attic roof truss system

A mansard roof makes it possible to obtain additional usable space with a relatively small financial investment, which is why this architectural solution has gained great popularity. So what is called an attic?

Attic (from the French mansarde) is an usable attic space (both residential and non-residential premises), formed on the top floor of a house, or the top floor of a part of a house, with an attic roof.

Wikipedia

https://ru.wikipedia.org/wiki/Attic

The attic is located within the load-bearing walls of the building and rests on them through the mauerlat, horizontal beams (strings) and rafters. The larger the attic space, the greater its useful volume, which is achieved by increasing the angle of inclination of the slopes and is formed by a more complex rafter system. The location of the rafters of the attic roof depends on the structure, which can be of different types, namely:

1. Tent or pyramidal structure with a minimum volume of under-roof space.

   The slopes of the tent structure rest on the side rafters and the central post, so the volume of the under-roof space here is minimal

2. A hip or half-hip roof, in which the main living space is located under trapezoidal slopes.

   The rafters of the hip roof form two triangular and two trapezoidal slopes

3. A gable structure, which is a symmetrical gable roof with gables cut in at right angles, which provides a significant volume of attic space.

   The multi-gable roof allows you to equip a full attic floor

4. A gable symmetrical roof with an attic is a classic option, characterized by ease of installation and resistance to wind influences due to its rigid structure.

   A gable roof requires the least amount of working time and low consumption of building materials

5. The rafter system of an attic sloping roof provides the maximum volume of living space at a relatively low cost.

   A sloping roof is the optimal solution in terms of the ratio of the cost of construction to the volume of usable space in the attic

The rafter system must withstand constant loads, which consist of the weight of structural elements, insulation and roofing. In addition, there are variable loads depending on the strength of the wind and the weight of the snow on the roof. The choice of the cross-section of load-bearing elements and the method of connecting them should be aimed at creating the most durable and rigid structure that evenly distributes the load on the walls of the building.

Depending on the width of the building, different types of attic rafter systems are used, which are divided into hanging, layered and combined.

1. Hanging rafters are those that rest on the walls of the building through the mauerlat and tie, and form a ridge in the upper part. With this connection method, there is no intermediate support, and the bursting pressure on the walls of the house is reduced with the help of crossbars, racks and struts. The hanging rafter system is usually used when the building width is no more than 6 m.

   To compensate for bursting forces in suspended rafter structures with a span of up to 6 m, tie rods and crossbars are used

2. Layered rafters are called rafters with intermediate support on the internal wall of the house. They are used when the width of the building is from 6 to 16 m. The larger it is, the more elements are used to evenly distribute the load.

   Layered rafters have one or more supports inside the house

3. The combined type of rafter system is used in mansard roofs with variable slope angles. The most typical example is a broken mansard roof, where the lower rafter legs are layered and supported by a post and a mauerlat, and the upper ones are mounted as hanging rafters supported by a tie rod and a headstock. When constructing mansard roofs, all types of rafter systems are used, and their choice depends on the structure in which they are used.

   In the design of a sloping roof, the upper rafters are hanging, and the lower ones are layered

Scheme of the rafter system of the attic roof

To erect a roof, you must have a project that specifies the list and size of structural elements, as well as the method of connecting them. To understand the principle and sequence of installation, you need to know the purpose of the elements of the rafter group and the way the roof adheres to the walls of the building. The attic roof consists of the following elements:

• the connecting element between the wall of the building and the rafter group is the Mauerlat, which is attached to the walls of the house with studs, brackets or anchors;
• strings are attached to the Mauerlat parallel to the short wall of the building, and beds are installed along the long side;
• vertical posts are mounted on the central floor;
• the ridge girder rests on the posts;
• the upper part of the rafters rests on the ridge girder, and the lower part is connected to the tie, forming a cornice overhang;
• the rafter legs in the upper part are connected by crossbars;
• on hip roofs, diagonal rafters and shortened eaves are used;
• trusses serve as additional support for the diagonal rafters;
• for intermediate fastening of rafters, racks and struts are used;
• if necessary, the rafters are lengthened with fillets.

The main load-bearing elements of the attic roof are rafters, beams and tie rods, as well as vertical posts and a ridge girder.

The diagram indicates the dimensions of the elements of the rafter system, their location, angles of inclination and methods of insertion at the connection nodes. Information about the location of double rafters, the presence of additional supports, and the dimensions of eaves and gable overhangs is also required.

The diagram is the main document for assembling the rafter system; it reflects all the necessary parameters. However, before cutting the material, it is necessary to check the calculations again and create templates for the main parts. If there is no project, you need to carry out calculations and create a diagram yourself.

Mansard roof rafter spacing

Before starting work, you need to select the pitch of the attic roof rafters. The distance between the rafters and the eaves (in the case of a hip roof) depends on several factors:

• building size;
• type of rafter system;
• constant and variable load on the roof;
• sections of rafters, racks and slopes;
• type of roofing;
• type and pitch of sheathing;
• insulation sizes.

For rafters, sheathing and counter-lattens, softwood material is selected in accordance with SNiP II-25, and the load on the rafters is calculated according to SNiP 2.01.07 and ST SEV 4868. Based on what is stated in the building codes and regulations, we can say that for rafters less than 9 m applicable beam cross-section from 50X150 to 100X250 mm with a pitch of 60 to 100 cm. The size of the building affects the design of the truss and the presence of racks, struts and crossbars, the use of which increases the strength of the rafter legs and allows you to increase the pitch between the rafters to 120 cm or more . Usually, to select a step, reference tables are used, which contain recommendations taking into account the length of the rafters and the cross-section of the beam.

Table: dependence of the pitch between the rafters on the section of the beam and the length of the rafters

The type of roofing used also affects the choice of rafter spacing, because different materials have different weights:

• tiles, depending on the type, weigh from 16 to 65 kg/m2, slate - 13 kg/m2. Such heavy coverings imply a reduction in the pitch of the rafter legs to 60–80 cm;
• the weight of metal coatings and ondulin does not exceed 5 kg/m2, so the pitch of the rafters can be increased to 80–120 cm.

On hip roofs, in any case, the step of the roofers is chosen to be 50–80 cm to give the slope greater rigidity.

In addition, the installation step of the rafters depends on:

The length of the rafters and sheathing of the attic roof

When doing independent calculations, the dimensions of some structural elements of the roof have to be calculated based on the existing dimensions of the building and the angle of inclination of the slopes. The length of the rafters sometimes has to be adjusted for different types of attic roofs, selecting the optimal dimensions of the entire structure as a whole.

Let's assume that the main dimensions of the building are known and it is necessary to calculate the length of the rafter joists for several proposed options for the angle of inclination and type of roof. Let half the width of the building L be 3 m, and the size of the eaves slope be 50 cm.

Additional calculations show that increasing the angle of inclination of the lower slope from 60 to 70 o will increase the width of the attic by 10%.

The length of the sheathing connecting the rafter legs is determined taking into account the gable overhangs that protect the facade walls from precipitation. The length of the gable overhang depends on the height of the building and is selected in the range from 40 to 60 cm. Therefore, the total length of the slope will be equal to the length of the house, increased by twice the length of the overhang.

Let's assume that the length of the house is 10 m, and the gable overhang is 0.6 m. Then the dimensions of the sheathing must be calculated taking into account the length of the slope, equal to 10 + 0.6 ∙ 2 = 11.2 m.

The parameters of the sheathing should be calculated taking into account the length of the gable and eaves overhangs

Any adjustment to the project requires a careful recalculation of the parameters of the rafter system, taking into account the changes that have arisen.

Video: calculation of the attic roof

Knots of the rafter system of the attic roof

The nodes of the roof truss system represent the junction of individual elements into a single structure, which allows you to evenly distribute the load on the walls of the building. The connection is made with nails, self-tapping screws or bolts using overhead wooden elements or metal squares and plates, as well as by connecting to a groove. To construct a gable roof, the following main components are used:

1. A ridge unit that provides a connection between the rafter legs and the ridge purlin.
2. Places where the crossbar connects the rafters to give greater strength and rigidity to the trusses.
3. Attachment points for struts and posts that provide additional support to the rafters.
4. A cornice assembly in which the rafters are attached to a tie rod or mauerlat, forming a cornice overhang.

Nodal connections of the rafter system must be made in such a way as to ensure the most rigid fastening of the elements to each other

A characteristic feature of a gable sloping roof is the knot where the upper and lower rafter joists, the vertical post, the crossbar and the purlin are connected. Such a complex connection requires the use of mortises, bolts, steel plates and construction staples.

In the most complex unit of a broken mansard roof, five rafter elements are connected

The most complex component of a hip mansard roof is the junction of the side or diagonal rafters with the mauerlat. The side rafter in the lower part rests on the corner beam of the mauerlat and on the embedded beam; in another option, a vertical post or truss is placed between the embedded beam and the rafter leg. The upper part of the hip rafters is attached to the ridge purlin using bolts or nails.

The corner rafters of a hip roof bear the greatest load, so their connection to the Mauerlat must be thought out most carefully

The described units are used most often when installing rafter systems of various designs and allow you to install load-bearing elements on your own. For efficient and high-quality assembly, drawings and production of templates with verified angles of joints and inserts are required.

Video: rafter system components

Calculation of the rafter system of the attic roof

The rafter system is the basis of the roof, so it is important to choose the design that is most suitable for the climatic conditions of the region and the existing requirements for the size of the residential attic. After selecting the design, the angle of inclination of the slopes and the height of the ridge are calculated for the required dimensions of the attic room. Calculations are made taking into account the size of the cornice using the following formulas:

The meaning of trigonometric functions can be found in reference tables.

Table: values ​​of trigonometric functions for different slope angles

The most difficult thing when designing mansard roofs is counting lumber. Calculating the number of rafters required and matching them with a standard length of 6 m can sometimes be quite difficult. Let’s assume that we have chosen the hip roof, the most difficult to calculate, measuring 10X13 m, taking into account the eaves overhangs 80 cm long and the slope angle of 45 degrees. Then the side rafters will have a length of 5 / sin 45 o = 7.04 m. Therefore, the standard six-meter beam will have to be lengthened. Typically, for rafters a little more than 6 m long, a 100X200 mm beam or a 50X250 mm board is used.

If the building is large, it requires rafters longer than the standard size of 6 m, so the beam has to be extended

As for the horizontal floor beam, since the width of the building is 10 m, the tie rods should consist of two parts, which either rest on the internal wall of the building, or are joined together by reinforcing elements and rest on the purlin. For tightening and purlins, use timber with a cross section of at least 50x200 mm. Along the perimeter of the building there is a mauerlat, for which timber 150X150 mm or 200X200 mm is used. According to the scheme we have chosen, the perimeter of the building is 39.6 m, so installing the Mauerlat will require seven six-meter beams. The dimensions of all other elements of the rafter system will not exceed 6 m.

The weight of the lumber of the rafter system is calculated by summing the lengths of all elements with a certain cross-section and converting their quantity into cubic meters. This is necessary to determine the mass of the entire roof, and is also necessary when purchasing and transporting material. The calculation is made according to the table, and then the obtained values ​​are multiplied by the weight of 1 m 3 of lumber.

Table: calculation of the amount of lumber in 1 m3 and the volume of one unit of material

Pine lumber weighs 505 kg/m 3 at 12% humidity, and 540 kg/m 3 at transport humidity 25%. Here are some examples of calculations:

1. If 1 m 3 of material with a cross section of 50X200 mm contains 16.6 boards, then the weight of one board will be 540 / 16.6 = 32.5 kg.
2. If 25 m 3 of lumber is purchased, then it will weigh 25 ∙ 540 = 13,500 kg.
3. If 100 boards 25X200 are required, then you need to buy 100 / 33.3 = 3 m 3 of wood, which will weigh 3 * 540 = 1,620 kg.

It is important to note that it is advisable to purchase edged lumber with the lowest moisture content so that after installation it does not warp or crack, especially for large-section timber. For the construction of a rafter system, the wood moisture content should not exceed 18%.

Installation of attic rafter system

Installation of a rafter system with a residential roof space requires careful preparation. It is necessary to install convenient scaffolding, decking and ladders, as well as provide workplaces with safety ropes. Workers must be provided with protective clothing, protective equipment and working equipment. It is necessary to select a flat place on the ground for pre-assembling the trusses, marking the corners and making templates. All wooden elements must be treated with antiseptic and fire-retardant compounds.

After this, you can begin work, which takes place in the following sequence:

1. On walls with walled-up studs, a mauerlat is mounted around the perimeter. If there is a load-bearing wall inside the building, we lay a beam or purlin on it that is the same height as the mauerlat.

   If the house is being built from building blocks, then the Mauerlat is most conveniently laid on threaded rods, walled into the wall during its laying.

2. Cable ties with cornice extensions are attached to the Mauerlat parallel to the short wall.
3. Vertical posts are placed on the tie rods, delimiting the attic space.
4. The racks are connected to a tie that serves as the ceiling of the attic space. The trusses installed in this way are connected to each other by horizontal girders.
   

   Vertical posts, top ties and horizontal purlins form the frame of the attic space

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

   After installing all the rafter joists, all that remains is to lay the sheathing and nail the front board

We looked at the assembly of the rafter system using the example of a broken mansard roof. The construction of other structures consists of similar operations and mainly consists of performing work according to the design installation diagram, which reflects the methods of connecting the elements of the rafter system. With carefully calculated drawings, a team of four people is able to install a roof with a rafter system of any complexity.

Video: installation of an attic roof

We examined the rafter group of the attic roof, its design, calculations, as well as a diagram and description of the main components. They offered an option for step-by-step installation of load-bearing structures of the attic, attached illustrations and videos that explain the procedure for assembling the structural elements of the attic roof. Now its successful construction depends only on the careful fulfillment of the requirements of instructions and technologies and the availability of certain skills for the performers to carry out construction work. We wish you success.

The installation of an attic roof allows you to significantly increase the usable area and rationally organize the space of a low-rise building. However, its construction often frightens home craftsmen because the process is too complex and labor-intensive.

There is no need to be afraid, because the result will provide a beautiful roof and comfortable additional rooms. And in order for the result of the work to please the owner and household members, you need to know what rules are used to construct the rafter system of an attic roof, and what is the easiest and best way to arrange it.

When we mention mansard roofs, we immediately recall a pentagonal gable structure of impressive size over a log house, concrete or brick walls. Visual memory suggests that its slopes must certainly have different slopes, i.e. the bottom of the roof simply has to be much steeper than the top. Due to the difference in the angles of inclination, a convex fracture is formed, which gave the roof the popular name “broken”. The term has justifiably migrated to the technical definitions of attic structures. It reflects the essence of the usual standard in the device, but often has nothing in common with the configuration. Despite the fact that the design of all mansard roofs necessarily includes two parts, their presence cannot always be determined visually.

Purely based on external indicators, the predominant number of attic structures can be divided into:

• Triangular roofs, the lower and upper parts of which have an equal slope. Outwardly, they resemble traditional gable structures without kinks in the plane of the slopes.
• Pentagonal roofs with slopes having convex corners. This category clearly demonstrates the presence of two joined parts in the design.

In both of these varieties, the rafter system consists of two tiers stacked on top of each other. The lower structure forms the useful space of a residential attic with a height of 2 to 2.5 m, so that moving inside it is not difficult. The second tier creates the shape of the roof top and is allowed to be of arbitrary height.

By varying the angle of inclination of the upper and lower rafter legs, you can obtain the optimal roof shape in your own opinion. It is believed that a pentagonal attic, the corners of which are in contact with an imaginary circle, looks best.

Note that the principle of constructing a sloping roof is suitable not only for gable rafter systems. Interpreting the basic method, the attic can be organized in hip, single-pitched, hipped and other roofing structures.

Sometimes an existing structure is converted into an attic, the construction of which did not use “broken” technology. However, these roofs cannot a priori be classified as attic. True, if the rafter legs have sufficient power, no one bothers to use the crossbars of pitched rafter systems as ceiling beams, and the supports of additional purlins as beams for cladding the attic.

We found out that the main feature of an attic roof is the presence of two adjacent rafter structures connected into a triangle or pentagon of a shape that is attractive to the owner. In their construction, standard ones are used:

• Layered, according to which the lower tier of the attic is built and used in the construction of the upper part.
• Hanging. In accordance with it, only the upper part of the structure is built.

If, to simplify, the section of the attic roof is divided into two halves, you will get a trapezoid at the bottom and a triangle at the top. The inclined sides of the trapezoid are allowed to be exclusively layered, and the sides of the triangle are layered and hanging.

Basic diagrams of rafter systems

A “classic of the genre” is rightfully considered to be the pentagonal diagram of the rafter system of an attic roof with support posts forming the walls of the interior. Its section is conventionally divided into simple geometric shapes. In the center there is a rectangle, on the sides of which there are two mirrored rectangular triangles, and an equilateral triangle on top.

Standard attic construction

The layered rafters of the lower part of the structure rest at the bottom on the mauerlat, and with the upper heel on the right or left purlin. The part of the mansard roof frame that crowns the structure is made up of hanging rafter arches. They are supplemented with a suspension headstock in the middle if they are intended to cover a span of more than 3 m. The headstock cannot be connected to the arch tightening with a notch, like a support post. Its job is to prevent the tie from sagging - it is not a support, but a suspension.

The supports-racks of the layered rafters of the lower part rest through the beam on the ceiling. If it is necessary to increase stability, struts are installed under the supports. The posts are connected to the frame and purlins by notches, the joints are duplicated with metal corners and toothed plates. If the floor is concrete, bitumen waterproofing is laid under the floor. The bed can be laid not on the ceiling, but on brick pillars or on leveling boards. When constructing an attic on a wooden floor, you can do without the beams altogether and embed the racks directly into the beams.

The rather steep lower parts of the slopes of attic roofs are practically not affected by the snow load; precipitation does not linger on them. However, steeply installed rafters have another problem - gusty winds will tend to overturn and tear off the roof. Therefore, attaching the system to the Mauerlat must be taken very seriously. In an attic situation, each rafter is tied to the walls with twists, and not through one, as in conventional pitched structures.

Method of moving rafters beyond the wall line

It often happens that the planned attic structure creates too narrow an internal space. It can be expanded by moving the rafter legs outside the walls. Those. the rafter leg will rest not on the mauerlat, but on the beams of the upper floor. This case, in theory, does not need a Mauerlat at all. But reinforcing struts in the scheme with the removal of rafters are used without question, because there is no support at all under the extreme part of the side triangles.

The installation of the Mauerlat can be eliminated, but pouring a monolithic reinforced concrete belt for attaching beams to brick walls is highly desirable. The floor beams are attached to the monolithic belt with anchors, and support posts are driven into them to a maximum of 1/3 of the thickness of the beam. An important point: moving the rafters outside the wall is simply required to form a cornice for wooden houses with a width of at least 0.5 m, for concrete and stone houses at least 0.4 m.

Technology for constructing a rafter structure with the rafter leg extending beyond the wall:

• We install the outermost floor beams that define the contour of the eaves overhangs. Because the ceiling will be loaded, the section of the beams is taken from 150x200mm. If, when laying the starting beam, it turns out that the walls do not form an ideal rectangle, we try to correct the flaws by changing the position of the beams.
• We lay and fix the remaining bars along the laces stretched between the fixed outer beams. We control the height and pitch of the beams before fastening. The distance between the floor elements is equal to the step between the rafter legs. For insulated roofs, the optimal rafter installation pitch is 0.6 m, because it is equal to the width. If the rafters will be installed with a similar frequency, they can be made from 50x150mm boards.
• From the left and right edges we set aside a distance equal to the length of the short leg of the right triangle. At the marked points, carefully use a chisel to select nests a third of the height of the beam under the outer supports.
• Let's make supports by cutting out tenons. They need to be made according to the size of the selected nests. For the manufacture of corner supports, a beam with a cross-section of 100×150 mm is suitable, and two load-bearing supports for the gable sides of the roof should be made from it. For ordinary racks, 50×100 mm timber is sufficient. The material for the supporting elements should be longer than the design height by the length of the tenon, but it is better by 10 cm in case of errors during cutting.
• We install the corner posts and fasten them with temporary spacers. We connect the posts with lace.
• We use a plumb line to check the points in the beams for selecting nests for row supports and select the indicated holes.
• We install row posts and two load-bearing supports in the centers of the attic gables.
• On the installed supports we lay purlins - boards with a section of 50x150mm. We fasten the purlins with corners. It is not necessary to use as many nails as in the corners of the holes. Two or three are enough for each plane. As a result of laying the boards, the frame of the walls of the future attic is obtained.
• We connect the supports installed opposite each other with bars, attaching them to the purlins with corners. These elements will serve as tensile crossbars. Therefore, for their manufacture you will need 1st grade lumber with a cross-section of 100×150mm. For each installed crossbar, a temporary support from a 25x150mm inch is needed.
• We temporarily fasten the crossbars on top with the same inch, retreating 20-30cm from the edges of the frame. Temporary thin flooring of one, two or three boards is needed for ease of installation of the upper part of the rafter system.
• We make a template for the rafters of the bottom row from an inch. To do this, we apply a blank board to the end of the purlin and beam. Then we outline the lines of the grooves along which the excess will be sawed off. We try it on and trim the excess if necessary.
• We make rafter legs using the template. If there are doubts about the flawlessness of the construction, then it is better to cut out only the upper groove first. By placing the rafter in its proper place, you can then adjust the lower groove after the fact without unwanted damage to the material.
• We install the end rafter legs, which will need to be connected again with lace.
• Using the lace as a guide, we install the rafter legs of the lower tier of the attic.
• Similarly, we make a template for the upper part of the rafter system. In order to find the line of the top cut, we temporarily sew a board onto the gable support.
• Let's make a mirror version of the previous template. The rafters of the upper tier will rest against each other.
• Let's try both templates on the roof. If everything is normal, we use them to make the required number of upper rafters from 50x150mm boards.
• We are constructing the upper tier of the rafter system.
• To prevent the crossbars from sagging, we install headstocks of the required size to each upper truss. We firmly sew them only to the ridge area; the bottom should not be rigidly fixed.

Next, the rafter legs are screwed to the walls with wire ties. Then the pediment frame is installed, along which it needs to be sheathed. Finally, the sheathing is installed at a pitch corresponding to the characteristics of the roofing material.

Method with frame modules

The technology differs from the previous method in that it is not individual supports that are installed on the floor, but modules-blocks of the side walls of the future attic that are completely prepared for fastening.

The block method of constructing a rafter system allows you to optimize the construction of an attic roof, because the construction of modular elements is carried out on the ground. In quiet conditions without a sense of altitude, it is easier to achieve precision node connections.

The process of installing a block mansard roof:

• Based on a pre-made design, we manufacture the frames of the attic walls. Using this method, longitudinal beams play the role of purlins and beds. We lay them out together with the racks on a flat area and use a square to mark the sockets for the supports of the side walls. We make cuts along the measured lines.
• We cut out spikes on the racks, the size of which must correspond to the size of the nests.
• We connect the longitudinal beam with vertical posts, we get two modular frames - these are the walls of the attic.
• We lift the frames up and install them in the intended place. We temporarily fix the position of the walls with spacers, then attach them to the floor beams with brackets.
• Using a chisel, we select sockets at the edges of the beams for installing the lower row of rafters. They need to be placed in one line. To maintain the geometry, it’s easier to first mark them with a chainsaw, then modify them with a chisel.
• We perform the upper rafter tier of the attic on the ground, having previously fitted the blanks to the installed elements. To ensure an accurate fit, we temporarily nail a board to the end of the future roof so that one of its edges clearly follows the central axis of the rafter system. The base of the upper attic triangle serves as a stretcher. Its length is equal to the distance between the outer vertical planes of the installed frames. We select nests along the edges of the guy wires, and spikes on the lower heels of the rafters.
• We assemble the trusses of the upper tier, for reliability we install an additional crossbar, and we reinforce the ridge assembly with a triangular wooden overlay.
• Before we move to the roof, we make preparations for the rafter legs. We try them on to the frames laid out on the ground. It is more convenient to “cut” them in one fell swoop, grabbing several pieces with a clamp. We cut out only the upper bevel, taking into account the fact that it will rest partly on the wall post, partly on the stretch of the upper rafter trusses.
• We try on the bottom rafter to the end. In the area of ​​its lower heel we draw the shape of a spike, repeating the configuration of the nest in the beam. We cut out the thorns.
• We move the trusses of the upper tier and the rafters of the lower tier to the roof. We first install the trusses, attaching them to the upper frame of the walls with staples, then the rafters of the lower part, attaching them to the floor beams with the same staples.

The subsequent stages of roof construction are carried out according to standard rules. Drawings for a mansard roof, clearly representing the structure, will introduce you in detail to the described principles of constructing a rafter system. Thanks to the production of joints by cutting half a tree, the strength and rigidity of the frame as a whole increases, which will eliminate the need to install additional struts.

The disadvantage of this method is that the finished modules are quite difficult to transport to the roof. To transfer the assembled blocks there without the use of lifting equipment, a minimum of 4 people will be required.

Board and nail rafter system

It is impractical to build a powerful attic over small country houses, but you still want to save space on a small plot. For owners of small buildings there is an excellent option - a lightweight board and nails layered structure. The method should appeal to those who love saving, because the construction does not use solid timber.

For the manufacture of each of the supporting elements, two boards are used, between which spacer sections of the bar are installed. The cavity formed by the bars explains why the system is lightweight compared to its solid counterparts. To ensure spatial rigidity, wind braces are installed connecting the supports to the rafter legs. The lathing, in turn, will make its contribution to strengthening the structure.

The popular way to develop a layout

For a successful work result, a project is very desirable. It is not a fact that the presented drawings with dimensions are suitable for furnishing a particular home. Typology in construction is now not at all welcome. If there is no documentation at all, it is better to make at least a sketch of the future roof, not forgetting the height of the ceilings in the attic. Wherein:

• Proportions must be observed, because an attic that is too large can turn a small house into an awkward, mushroom-like structure.
• It must be remembered that the lower part of the attic roof is built using layered rafter legs, and they optically lower the overhang and overlap the upper part of the high windows. There will be no noticeable overhanging effect when constructing an attic according to the scheme with the rafters removed.
• Do not forget that the height of the attic room must ensure freedom of movement. It is this landmark that is required to correctly determine the height of the racks of the attic walls.

You can select the best roof proportions using the traditional template-layout method. According to it, bars or boards are laid out on a flat, spacious area, repeating the contour of the building in real size. By changing angles and moving components, you can achieve the optimal configuration. The elements need to be fixed with nails and immediately measure the lengths of beams, rafters, tie rods, and posts. The resulting dimensions will help in making templates.

The video will demonstrate the calculations and layout of the rafter system for an attic roof:

The basic options and diagrams for the installation of an attic rafter structure that we have given will help you decide on the choice of the optimal type of rafter structure.

In modern private construction, the rafter system of the mansard roof makes it possible to increase living space and create an additional half-floor. This design is distinguished by the variety of design options, their reliability and versatility. It is convenient for installing attic and dormer windows and accessing a small balcony on the roof. Such a constructive completion of the building makes it possible to organize additional living space instead of a conventional attic. The attic level is formed thanks to a specific rafter system and a large angle of inclination.

What type of attic space should I choose?

For the first time, attics began to be inhabited in Europe after the Second World War, when there was not enough full-fledged housing for everyone. However, in our time, the attic, as luxury housing under a roof, has become very fashionable. The construction of mansard roofs began in the dacha sector, in country cottages, and in new houses in order to add usable space.

Today, installation of a mansard roof truss system has become much easier and more affordable, thanks to the offer of the latest developments and the availability of building materials. High-quality insulation and new methods of sealing the attic roof have turned an ordinary attic into a cozy room. This made it possible to protect the living space under the cold roof from cold and negative weather factors. And the rafter system of the attic roof allows you to vary the configuration, size and shape of the under-roof space. Options for building an attic:

• cold summer - country;
• insulated - for full year-round living.

Mansard roof rafter system - photo:

The side walls of the attic inside have different wall shapes:

• symmetrical and asymmetrical;
• single-level and two-level;
• vertical (with additional storage on the sides);
• partially vertical (the bevel for the ridge starts approximately from the middle of the wall);
• inclined;
• beveled triangular (in the shape of the slopes of the attic roof);
• broken (attics of complex shape).

The total volume of the attic space, which is provided by a tetrahedral (hip) or gable roof, depends on the bevel angle. With proper finishing of the interior and thoughtful design, the room can be aesthetically pleasing and complete for habitation, even with strongly sloping walls.

When the under-roof space should be designed for housing, it is important:

• bring down all communications;
• determine the layout and functionality of 1 or more compartments;
• provide ventilation, heat and waterproofing;
• take care of additional insulation for the winter;
• let down all the amenities if it is an isolated room for one person.

Architect's advice: The living space inside the attic is planned to be convenient for movement and comfortable for life support. Therefore, the room dimensions should be at least 3 m wide, and there should be enough space above the head to move freely with raised arms.

Preliminary calculation of the rafter system of the attic roof is very important. All points must be thought out in advance when entering into the preliminary design of the attic. Sometimes it is necessary to replace the roof, and the decision to add an attic comes in the process of choosing the roof configuration.

Attention: The construction of the attic roof structure of the rafter system must be carried out taking into account the fact that it will create additional load on the foundation and walls, which is harmful for a house that is not new. And although this will not destroy the main structure, it can cause additional shrinkage.

It is not too late to abandon the idea of ​​arranging an additional residential floor if the building is dilapidated and the soil is not suitable for multi-story buildings. Only specialists from a construction organization or an architect can correctly calculate the total load; he will also suggest the optimal configuration (geometry) of the attic space, so as not to spoil the appearance of the house. The angle of inclination of a new building is determined at the design stage. It depends on the following factors:

• climatic conditions of the region;
• roofing materials;
• functionality of interior spaces.

Mansard roof rafter system - drawings

It is impossible to plan an attic room without special windows. It is important to consider their location at the design stage, that is, before installing the rafter system. Ultimately, not only the appearance of the house, but also the reliability of the entire structure will depend on the proper placement of window openings, which influence the pitch between the supports. It is also necessary to consider the method of fastening the frame of the attic windows, and their height is dictated by the ease of maintenance inside the attic.

Where to start building the attic rafter system:

The rafter frame is the base or skeleton of the attic. And if you are interested in how to make a rafter system for an attic roof, you should start by studying existing experience so as not to invent anything and avoid any annoying mistakes. If the rafter “cap” is installed and mounted correctly, then sheathing it from the outside and inside will not be difficult.

The rafter system of the attic roof is assembled with your own hands in order:

• Mauerlat;
• beam base;
• frame racks;
• runs;
• hanging rafters of the upper slopes.

Advice: When constructing an attic, all wood must be dry and seasoned, treated with a special antiseptic or antifungal aerosol. Logs and dry timber should have a moisture content of about 18-20%, no more.

Let's consider the next stage of work - a diagram of the rafter system of the attic roof. Design basis:

• main racks,
• floor beam,
• side rafter,
• ridge rafter,
• top harness,
• brackets for fastening.

How to make a mansard roof for a small cottage?

All work on the construction of the rafter system of a gable mansard roof can be done with a small team of improvised workers.

If you want to build a cold summer attic over a small dacha, it is not difficult; it is important to think about how you can get to the upper room:

• along external attached steps;
• from the inside, like an attic staircase.

Light boards, timber and small diameter logs are suitable for the prepared perimeter of a country house. However, the integrity and reliability of the lightweight attic structure will depend on the reliability of the connections between the rafter system and the floor beams. You can use strapping, screws, nails, bolts, etc.

The racks are laid in order, supported by the base and ceiling beams, then the rafter legs of the first level of the slopes are attached to them. The main components of the attic rafter system are fastened with either construction staples or strapping made of hardened wire. Sometimes an additional connection with reinforcement with staples or wire is required.

The upper beam of the attic floor is attached to these supports - this is a ridge post that “assembles” the rafters under the upper slope. Next, the rafter legs for the upper level of the slopes are secured, after which the rafter legs are connected to the main floor beams.

When the base is ready, all the supports are fastened with strapping and lathing, for additional reliability, so that the rafter system is strong and convenient for laying insulation, waterproofing and roofing material. The simplest design of a country attic is covered with waterproofing and covered with slate. And don't forget about the sediment drainage system.

An attic from layered rafters is made in approximately the same way, but the tops are reinforced with thicker timber - for sufficient structural strength. Such a system will functionally replace the support beam of the upper slopes. They will become the supporting frame of the attic roof and the basis for cladding the walls and ceilings indoors - photo:

The lower level has options for attaching the support to the upper points of the rafters - on the side girder of the racks, on the gables, or only on the racks, that is, without installing the side girders. And the lower points of the rafters of both lower slopes should rest on the floor beams, and preferably without insertion.

Under a roof made of heavy piece materials, it will be necessary to reduce the interval between the rafters, and also add sheathing to their cross beams. This scheme is often used for the construction of mansard roofs of complex configurations.

It is important to build a rafter attic, knowing some design features. Therefore, experts recommend learning a few lessons on how to properly make a rafter system for an attic roof. We start with the Mauerlat.

1. Mauerlat is the foundation around the perimeter of the house on which the entire rafter system is attached. Therefore, the reliability of fastening the lower beams to this perimeter will literally determine whether “the roof will be torn off” due to unfavorable weather and climatic phenomena. A high-quality Mauerlat will not allow the attic roof to come off during a tornado or tip over during powerful hurricane winds. Reliable fastening of the truss structure to the perimeter of the building evenly distributes the load of the roof on the walls and foundation of the house.

2. It is better to choose boards and beams that are strong, not knotty, and at least 40 mm thick. It is better to use dry treated wood for the Mauerlat, optimally timber with a cross section of 150x100mm. After preparing the perimeter of the walls for laying the rafters, the timber or board must be laid horizontally, checking the level along the entire perimeter of the walls.

3. A layer of waterproofing recommended for the type of building material must be laid on the crowns of walls or columns of a frame-type structure or brickwork. This is necessary so that the moisture in the walls and base of the rafter system does not transfer to them. For waterproofing, bitumen, roofing felt or roofing felt, and other modern waterproofing materials are suitable.

4. We fasten the beam at the base to the walls with bolts or staples; additionally, the fastening can be strengthened with wire strapping. The studs for the Mauerlat are mounted into the wall during masonry. The Mauerlat beam is treated with an antifungal agent so that it is not susceptible to destruction.

5. When everything is ready to install the rafter legs, it is important to mark the base where they will be attached. Ready-made rafter legs can be ordered from a workshop and then assembled yourself, rather than spending a lot of time making them. For convenience, they can be laid out on those sides of the house where they will be laid around the perimeter of the attic.

6. Check the racks for loosening and vertical shift. If this is the case, then do not think that the problem will go away with the installation of roofing materials. The additional weight of the structure will only increase its instability. Therefore, all flaws should be eliminated at this stage - reinforce the fastening with braces and ties.

7. Experts recommend maintaining an equal interval (step) between the rafters - about 80-120 cm. The easiest way is to stretch twine between the outer rafters to use it as a marking and level for the remaining rafter beams. The racks are made not only in one horizontal plane, but also aligned exactly vertically - check the plumb line.

8. Vertical posts are a good basis for the future walls of the attic living space, so they must be perfectly level. The inside will be covered with wooden or plywood panels, plasterboard, fiberboard or chipboard. Do not forget to lay the appropriate insulation between them, which is intended for the roof and attic.

9. To secure the posts to the drains of the upper timber, use metal staples or nails. With the completion of this stage of work, the installation of the rafter frame is completed. At the last stage, the rafters are connected in pairs and attached to the ridge beam.

10. Don't forget to leave gaps for skylights or doorways for stairs. Installation of dormer windows is carried out after the walls of the internal cladding are equipped.

11. You can do without a ridge beam, but it is necessary if the attic roof is long - more than 7 m. But it increases the total mass of the rafter system. It is enough to fasten the tops of the rafters with ties. The final stage is lathing for thermal and waterproofing and roofing materials. When the roof is almost ready, they proceed to the installation of roof windows and interior decoration of the room.

12. It is better to calculate the amount of consumables and wooden beams in advance using tables and drawings, but it is better to take into account the minimum and maximum consumption - with different spacing between the racks. Ideally, the design is expected to be lightweight and reliable, at low cost. We suggest studying the important points of arranging the rafter system of an attic roof in the video at the end of the article.

A structurally complex attic under aesthetic roofing materials looks much more interesting than a regular hip roof, but only specialists can do it. When the decision is made to replace the old roof with a more modern roof, take the opportunity to build an attic. Although the more complex structure of the attic roof rafter system is a little burdensome in terms of the amount of work, the additional living space and the unique appearance of the house will delight your children and grandchildren for many years.