The construction of a semi-attic allows you to give the house an expressive, aesthetic appearance. But the rafter system of a semi-mansard roof requires a special design approach.
Advantages of a semi-attic
The issue of increasing the usable area of the house by arranging an additional upper floor is one of the most pressing in private construction. The construction of a full second (third or more) floor requires serious financial investments and significantly increases the final cost of construction work. The most popular solutions include the construction of an attic roof - this allows you to equip additional living spaces directly under the roof. The walls and roof of the attic floor are roof slopes. If there is a desire to create vertical walls in the attic floor, partitions are installed.
A semi-attic is a fundamentally different approach to arranging an additional floor. A semi-attic refers to a living space, the side walls of which are formed by a vertical building structure and a roof slope.
The vertical part of the side outer wall of the attic does not exceed 1.5 meters.
Unlike the attic, in the semi-attic the side vertical walls are load-bearing. The advantages of this design include rational use of internal space and the ability to perform practical vertical glazing.
Significant heat loss occurs through the roof structures of the house, so when building an attic floor, special attention must be paid to the thermal insulation of the roof. It is much easier to insulate a half-attic, since its walls are built from the same material as the entire frame of the house. It should be noted that the final cost of constructing a semi-attic floor is higher than an attic floor. In addition, it is necessary to take into account some features of the arrangement of a semi-attic rafter system.
Designing a semi-attic roof
When developing a project for a semi-attic roof frame, it is important to choose the right angle of inclination of the roof. Due to the architectural features of such a building, the roof is rarely made high, so as not to disturb the proportions of the building. But at the same time, the roof must successfully cope with operational loads, including snow. A semi-attic is usually equipped with a pitched or gable roof. It must be taken into account that the rafter system must be non-thrust, so as not to transfer the thrust load to the walls of the attic.
The prepared diagram of the rafter system should reflect not only the location of the structural elements, but also the principles of their fastening. To prevent the rafters from transmitting thrust to the walls, a roof frame with layered rafters is erected, and the rafter legs must be fastened in a special way, with certain degrees of freedom. The non-thrust system is usually used in the construction of buildings made of stone, brick and other block materials.
The installation of a system with layered rafters requires laying a mauerlat and installing a ridge girder, which must rest on gables or special strictly vertical posts.
In order for the rafter to bend and not transfer thrust to the walls, one of its supports must be fixed, but be able to rotate freely. In this case, the second support is movable and freely rotating. This installation of rafters can be done in three different ways.
Installation of non-propelled layered rafters: method No. 1
The lower part of the rafter leg can be hemmed with a support beam, or a tooth can be cut into it to rest against the mauerlat. In this case, in the upper part of the rafters it is necessary to make a horizontal cut with a bevel. The depth of this cut should not exceed A= 0.25h, and the length of the support area should not be more h– rafter section height. The bevel of the trim allows you to avoid the spacer load when bending the rafters - a cut without a bevel will rigidly rest against the purlin with its side cheek. The length of the beveled cut must be at least two A.
If it is not possible to trim the top of the rafter, it must be hemmed with a piece of board of the same section as the rafter leg and secured on both sides with wooden nails or mounting metal plates. The upper ends of the rafter legs are laid freely on the ridge beam. In a gable structure, fastening to the purlin is carried out according to the principle of a sliding support, while the rafter legs are not fastened together. Thus, this version of a gable roof can be considered as a complex of two separate single-pitch structures adjacent to each other.
The hemming of the upper part of the legs of the rafters or the sawing is done horizontally. Installing rafters with a change in the pattern of support of the rafter legs on the purlin leads to the occurrence of thrust loads.
Installation of non-propelled layered rafters: method No. 2 and method No. 3
Installing rafters in this way is the most common option for installing a non-thrust structure when building a gable roof. The lower part of the rafter leg is carried out on a slider, while the top needs to be secured, for this purpose:
- the rafters rest against the purlin or against each other and are connected using wooden pegs or jagged metal plates;
- the upper parts of the rafter legs are fastened with a bolt or nail connection.
Particular attention is paid to the principle of attaching the lower part of the rafters to the Mauerlat. It is necessary to secure the rafters in the design position, for which one nail is driven into the side surface at an angle on both sides. Either a single long nail can be driven in from above or a flexible steel plate can be installed. You can also use steel corners - in this case, the rafter is fixed on both sides with corners, and nails are not driven into it. Additionally, these elements of the truss structure are fastened with flexible wire strands - they prevent wind overturning of the roof without interfering with the main fastening to work as a slider.
If you use rigid fasteners with a large number of nails or self-tapping screws, the attachment point for the lower part of the rafter will transfer the spacer load to the power plate.
Features of the third installation method include rigid pinching of the ridge assembly, while in the lower part the rafters are fastened to a slider. It should be noted that this design provokes the occurrence of a strong bending moment in the ridge unit, which can cause its destruction. In this case, the deflection of the rafters outside the ridge unit is minimal. There are certain difficulties with independently calculating the maximum bending moment of such a ridge unit, so it is recommended to use calculation formulas for beams with two supports (single-span). The device of the nodal connection with rigid pinching of the rafter legs in the upper part makes it possible to construct a rafter system with a certain margin of safety.
Features of the construction of a non-thrust rafter system
All three installation options provide for special fastening of the rafters: one end of the rafter is mounted on a sliding support that allows rotation, and a hinged connection is used to secure the second end, allowing only rotation. Modern fasteners (plates) are easy to use and allow you to successfully fix rafter legs to the sliders and hinges of the system. Traditional fastening options using staples, nails, scrap boards and bars can also be used. It is important to choose the right type of fastener so that it fully fulfills its task: it allows the rafter leg to slide in the support or prevents it.
The calculation scheme, which is used when developing a rafter system project, is based on the assumption of a uniformly distributed load on the roof, that is, it is assumed that all points of the planes of the roof slopes are affected by the same force. In reality, loads on roof slopes are affected unevenly, depending on the wind rose, the orientation of the house relative to the cardinal points (snow drifts melt faster on the south side), etc.
Installing rafters in all three ways ensures the necessary static stability of the rafter system, if the key condition is met: the ridge run must be rigidly fixed.
To ensure the necessary rigidity of fixation of the ridge girder, its ends are inserted into the gables of the attic half. This prevents it from moving horizontally. If you support the ridge girder only on the racks, the uneven load on the slopes can lead to a displacement of the roof, in the case where on one of the slopes the load is close to the design load, and on the other it has decreased significantly.
Increased structural rigidity
To increase the stability of the rafter system, you can use a horizontal screed, which should be nailed to the posts supporting the ridge girder. In a non-thrust design, the contraction does not function in the absence of high snow loads, but in a pre-accident situation it works in tension. Such situations include deflection of the ridge girder under increased load and uneven subsidence of the foundation. Contractions are usually mounted at a height of about 2 meters from the floor of the attic so that they do not interfere with the free movement of people around the room.
When installing a non-thrust rafter system according to the second and third options, you can install a slider (a unit that supports the rafter on the mauerlat) with the end of the rafter leg moved outside the wall. This design is more statically stable, including more successfully resisting uneven loads.
To increase the stability of a non-thrust system with layered rafters, it is recommended to rigidly secure the bottom of the racks supporting the purlin by cutting into the beam and attaching it to the floors in order to turn the hinge unit for supporting the lower end of the rack into a rigidly pinched structure. If we are talking about a semi-attic made of stone or brick, in which the ridge girder is securely fixed in the gables, additional strengthening of the racks is not required, but it is advisable to install emergency stops.
Scrum installation has its own characteristics. When arranging assemblies with the installation of bolts or studs, you need to carefully consider the manufacture of holes for fasteners. Their diameter must exactly match the diameter of the bolt or stud or even be 1 mm less than this value. In the event of an emergency, the clamp begins to work only after it selects a gap between the bolt and the wall of the hole. During this period of time, the rafter legs in the lower part will “spread” by a certain distance (its value depends on the height at which the scrum is installed), as a result of which the mauerlat may be shifted or damaged. In difficult cases, the roof eaves may be damaged, and the rigidly fixed Mauerlat will force the light walls to move apart.
When installing rafters for the attic, all technological requirements must be met so that the supporting structure can fully perform the tasks assigned to it. Trusses and other associated elements must be installed so that the finished structure can withstand wind and snow loads for a particular region. All these points are further clarified during the calculation process. If desired, you can install the rafters for the attic yourself, saving money on the services of third-party workers.
Rafter fastening diagram.
Basic information about roof rafters
An attic is a room under the roof; it is located on the attic floor of a building. This technique allows you to competently plan the growth of used areas without significant material costs. You can live in the attic no worse than in any other room. But to do this, it needs to be properly equipped and, in particular, the rafters for the roof must be correctly installed.
Mansard roof rafter system.
Before installing rafters for the attic, you need to choose the appropriate type of structure. Rafters can be layered or hanging.
Layered rafters for attic roofs are best installed in buildings that have a load-bearing intermediate wall. To install a layered rafter system for an attic roof, it is necessary that 2 load-bearing walls are located at a distance of no more than 7 m from each other.
If there are no internal walls, the only option is hanging rafters for the attic roof. The standard design includes rafters and a lower chord - a tie. The Mauerlat is used as a supporting element. Wire and staples are used to secure the rafters. Installation is carried out taking into account the expected load level.
Features of installation of the rafter system
Installation of roof truss system.
Before you begin installing rafters for the attic roof, prepare everything you will need during the work process:
- Unedged board.
- Wooden beams.
- Thermal insulation material.
- Nails.
- Annealed wire with a diameter of 3-4 mm.
- Leg-split.
- The boards are 15 cm wide and 4-5 cm thick.
- Moisture-proofing material.
There are several different types of attic roofing systems, namely:
- Triangular.
- Asymmetrical.
- Symmetrical.
- Broken.
One of the most important design aspects is the calculation of the roof slope angles. When performing this stage, the following features must be taken into account:
- Climatic conditions of the region.
- Type and characteristics of materials used for construction and finishing.
- Personal preferences of the home owner.
Mounting points for the rafter system.
The greater the angle of inclination of the roof slope, the less free space there will be in the attic room. However, if the angle is too small, the roofing system will be more difficult to clean from sediment and dirt. Over time, this will lead to a decrease in system reliability. Therefore, it is very important to choose the optimal roofing material for the existing conditions.
Correct installation of rafters for the attic roof ensures the strength and stability of the roof. When performing this work, you must follow a number of rules. Firstly, the structure is constructed from wooden beams with a section of 100x100 mm or 150x150 mm. Secondly, the system is carefully waterproofed. Typically, roofing felt or roofing felt is used as waterproofing.
The frame structure is laid on reinforced concrete bases. To fasten the supporting unit, wire and metal brackets are used. Quite often a tongue-and-groove connection is used. It is important that the wood used to construct the rafters has a moisture content of no more than 15%. If possible, the choice should be given to coniferous species.
A disinfectant atmosphere must be created. It is strictly forbidden to use damp timber. Because of them, the entire rafter system can simply collapse. Therefore, the bars must be dried before use. Additionally, the wood is impregnated with antiseptic and fire-retardant compounds.
When marking the installation of supports, calculate the installation step so that all rafters are installed vertically in the same plane. A tool familiar to any builder called a plumb line will help you check the verticality of the installation.
To ensure that the parts are held in place as securely as possible, use braces or braces. Upholster vertical posts with suitable materials. Most often, double-sided cladding is performed using plywood and plasterboard. Insulation must be laid between the sheathing sheets.
Step-by-step instructions for installing rafters
Scheme of strengthening the rafters with additional struts.
The process of installing a rafter system for an attic roof begins with laying the top beam. To secure it, you can use nails, screws and metal staples. Bars with a cross section of 150x150 or 100x100 mm are used.
After this, the Mauerlat is installed. It is needed, first of all, to prevent the roof from tipping over in a strong gust of wind. The Mauerlat must be designed and installed in such a way as to withstand the loads that apply to both the roof of the house and its walls. The mauerlat itself is laid out from beams. It is best to use 100x150 mm bars. You can also use boards with a thickness of 50 mm or more.
The selected material should be laid horizontally, having previously calculated the size of the wall surface. A waterproofing material must be installed under each block or board, which will protect the elements of the Mauerlat from the harmful effects of moisture.
Finally, the rafter legs are installed. These structural elements can be purchased ready-made or made independently. First, the pitch of the rafter legs is calculated, after which markings are applied to the mauerlat. To do this, you need to put marks on the rafter frame and the mauerlat. Professionals recommend installing rafters in increments of 1-1.2 m. Lay the outer rafters towards the front. It is important that the edge line of the gable and the top of the legs are at the same level.
Rafters are made of bars or boards. It is important that the boards are straight.
It is better to refrain from using material with knots; the maximum permissible number of knots is 3 pieces per linear meter.
Types of rafter structures.
Next, you need to take the twine and stretch it between the outer rafters. In this case, it will serve as a level for mounting the remaining legs. Finally, you will need to connect the upper parts of the rafters together in pairs and install the ridge beam. It will be needed if the roof is more than 7 m in length, and the rafter frame weighs relatively much.
If the roof is smaller, it will be enough to tie the top of the legs with guy wires. You can use the braces directly as attic ceiling beams in the future. In strong winds and snow, these elements will take on a certain part of the load.
Finally, the sheathing is installed, moisture insulation and thermal insulation material are laid, the roof is installed, and the walls and ceiling of the attic are finished.
If there are windows in the attic roof, the work is performed in the same sequence, but at the stage of installing the rafters, window openings are laid into which window frames will later be installed. Do not forget that the attic must have a size of at least 3x2.2 m. Otherwise, living in such a room will be extremely uncomfortable.
A mansard roof, made in accordance with all the rules, will be a wonderful decoration for any home and will serve for decades. Pay due attention to the design of the rafter system and approach this task with all responsibility. You will not only save money, but will also control every stage of the work, which will allow you to be completely confident in the quality of its completion. Good luck!
Using all possible space, giving the house originality and significantly reducing heat loss through the roof - these are the tasks that the attic solves. If there is a certain margin of safety at the foundation, in this way you can turn a one-story house into a two-level one. Another attractive thing is that you can build an attic roof with your own hands even without special construction skills. It is important not to make a mistake with the choice of materials and do everything according to the rules.
Windows on a regular floor are located in the walls. In attics there are no or almost no walls. They are replaced by a roof. That’s why windows are made special: they not only must let in sufficient light, but also withstand wind and snow loads, which are much greater on the roof than on the walls.
Dormer windows
When planning an attic, you should take into account the recommendations of SNiP. They recommend making the window area no less than 10% of the floor area. So if the attic is divided into several rooms, each should have a window.
Of all the methods shown in the photo for installing skylights with an attic, inclined installation is the easiest to implement. In this case, it is necessary to ensure the proper degree of waterproofing of the junction, and also to use special models with reinforced frames and reinforced glass - the load on the surface can be significant.
Advantages of a sloping roof window:
- more light, less sharp boundaries of light and shadow;
- the roof surface remains flat, its relief is not complicated;
- relatively easy installation.
When planning such a window, it is necessary to remember that its area increases with increasing angle of inclination. At what height is it more convenient to install such a window and how its height increases in centimeters depending on the inclination, look at the photo.
The steeper the slope relative to the floor, the smaller the window height should be.
The width of the window frame should be 4-6 cm less than the pitch between the rafters. Then it can be easily installed without disturbing the structure of the frame. If the window is wider, it is necessary to make a reinforced beam above it and calculate the load.
If you need to have a larger window, it is easier to place two narrow ones side by side. They look no worse than one big one, and there will be fewer problems.
When installing a dormer window, the roof geometry becomes more complicated: a valley appears on top and on the sides. Because of this, the rafter system becomes more complex both during planning and during assembly. The complexity of laying the roof covering also increases. All valleys are the places where leaks are most likely to occur. Therefore, everything needs to be done very carefully. In regions with a lot of snow, it is advisable to install snow guards over such windows so that they are not blown away in the event of a sudden meltdown.
Installation of a vertical dormer window in an attic roof
The advantage of such a window is that you can stand next to it at full height. But they let in less light, the terrain becomes more complex and the roof becomes more problematic.
A recessed window is usually used if there is access to a balcony through it. In other cases, this method of arrangement is not the best option: little light gets in, the shadows turn out to be very deep, which is tiring for the eye, the geometry also becomes more complex, although not to the same extent as in the previous version.
The easiest way is to make a window at the end of the attic. In this case, a reinforced frame or reinforced glass is not needed. Just high-quality glass is quite enough. It is this option that can most often be seen in country attics: this is the most inexpensive option that can easily be implemented with your own hands.
Rafter system
When independently building private houses with an attic, they usually choose a broken roof. It allows you to get a room of significant area, larger than under a gable.
With the same width of the base (of the house), the attic space under a sloping roof is larger than under a regular gable roof. The rafter system is becoming more complex, but a gable roof with an attic under a sloping roof is still more popular
The design of the sloping mansard roof is such that the overhangs can be lowered quite low, giving the house an interesting look. But the long overhang of the roof serves not only a decorative role. They also cover the upper part of the wall from precipitation and divert the bulk of the water away from the foundation. Although when planning you need to keep in mind that in strong winds they increase windage. Because of this, it is necessary to use more powerful boards and beams. Therefore, the size of the roof overhang is chosen based on several considerations, the main one of which is weather conditions.
Tilt angle
Depends on the roofing material, but most of all - on the region and weather conditions. The classic version is shown in the figure: the lower slopes in relation to the plane of the attic floor are inclined by 60°, the upper slopes by 30°. Based on these data and the parameters of your building, you can calculate all lengths. Just take into account that according to SNiP, the ceiling height in the attic cannot be less than 2 m. Then, by definition, this is an attic. A person will feel comfortable if the ceiling is raised to a height of at least 2.2-2.3 m. Based on this, according to the rules of geometry, calculate the required lengths.
In the classic version, the load from precipitation on the side surfaces may not be taken into account. Precipitation can only be retained on the upper part, the angle of inclination of which is less than 45°.
In general, the inclination of the side surfaces usually varies between 45° and up to 80°. The steeper the slope, the greater the windage it has, this must be taken into account: in regions with strong winds it is better to make flatter roofs. Then wind loads will be perceived much better.
Types of rafter systems for sloping roofs
The design of a sloping mansard roof is one of the options for the rafter system (the most common)
To make the frame of a sloping roof with your own hands, pine lumber is most often used, grade no lower than 2. The choice of cross-section of timber and boards depends on the size of the roof, the selected roofing covering (its weight), wind and snow loads in the region, and the pitch of rafter installation. All these parameters are taken into account in the calculation. The methodology is prescribed in SNiP 2.08.01-89 and TKP 45-5.05-146-2009.
One of the options for constructing a frame with hanging rafters
The figure above shows a drawing of a frame with hanging rafters. It can only be implemented if the base of the upper triangle is no more than 4.5 meters (in this case, this is the width of the attic room). If more, you will have to make layered rafters, which should rest on the load-bearing wall in the middle (the attic will be divided into two parts by a row of beams).
Another version of the upper part is shown in the photo below (the picture is clickable). In this case, the side rafters are reinforced with struts. They significantly increase the rigidity of the system.
There is a second way to achieve a similar effect - to establish contractions - in the figure they are only outlined with barely visible lines. The length of the side rafter leg is divided by three, and contractions are established in these places. They will be needed if the roof covering will have a significant weight.
Option for installing a sloping roof truss system - with struts that increase the rigidity of the system
For a building that is small in size, the roof frame can be generally simple: at the top there are two hanging rafters, a tie rod, floor beams, racks and side rafters (pictured below).
Construction of a rafter system for a broken mansard roof for a small house
How to calculate a sloping roof
The attic sloping roof of a small house (no more than 6-7 meters wide) has been built so many times that, based on experience, we can say what materials should be used. Many parameters are dependent on other materials. For example, the installation step of the rafters is tied to the parameters of the insulation. To ensure that there is as little waste as possible during insulation and installation is simpler, it is necessary that the distance from one rack to another be slightly less than the width of the insulation (20-30 mm). So, if you are going to use mineral wool, its width is 60 cm. Then the racks need to be installed so that the gap between two adjacent ones is 57-58 cm and no more.
The width of the board for the rafter leg is again determined based on the insulation. For the central zone of Russia, the required thickness of basalt wool is 200-250 mm. That's not all. In order for the thermal insulation to dry, a ventilation gap of 20-30 mm is required (without it, condensation will gradually rot the wood and render the mineral wool unusable). In total, it turns out that the minimum width of the rafter leg should be 230 mm. The thickness of the board is at least 50 mm. This is in regions with light winds and not very heavy snowfalls. To summarize, for all rafters - ridge and side - a board of 230 * 50 mm is required.
If lumber with such characteristics turns out to be too expensive, it will be possible to do the insulation in two directions: partly along the rafters, partly, filling the sheathing, across. You can lay a minimum of 100 mm of basalt wool, therefore you can take a standard board 50*150 mm and leave a 50 mm ventilation gap, or order a non-standard 130*50 mm. It's up to you to see which is more profitable for the money.
For racks and beams, it is better to take a beam of at least 80 * 80 mm, better - 100 * 100 mm. Especially in areas with difficult weather conditions - heavy snowfalls or strong winds.
Order a more accurate calculation from specialists. This is a long process consisting of collecting loads from the roofing material, the structural elements themselves, wind and snow loads. After which, according to a certain formula, elements are selected. For more detailed information on how the calculation is carried out, see the following video.
Do-it-yourself mansard roof: installation procedure
The design of the Mauerlat on mansard roofs is no different from the standard version. If or logs, you can use the upper crown as a mauerlat. It is only pre-treated with impregnation with high protective properties.
If the wall is made of foam blocks, a reinforced monolithic belt is placed on top of it. On a brick wall or made of shell rock or other similar materials, the installation of such a belt is not necessary. Waterproofing is laid in two layers on the wall, and on top is a timber treated with an antiseptic - 150 * 150 mm or a log. It is secured with embedded studs.
When assembling all elements, long nails are used - at least 150 mm long. In the most critical places, it is better to connect three or more elements using bolts or studs with double-sided threads. It is advisable to strengthen all joints with steel plates or corners.
First way
Installation of attic roof rafters is done in two ways. First: they assemble the parts on the ground, then lift them up in finished form. There, the outer structures, which will become pediments, are put up first. They are placed vertically and secured. It is often more convenient to secure them with long bars nailed to the wall (temporary). The following assembled structures are inserted into the prepared recesses in the Mauerlat (they are made at the required pitch). They are positioned strictly vertically and carefully secured. If necessary, additional temporary spacers are installed to fix them in the desired position. Side beams are installed.
How to build a sloping roof in this way and assemble the nodes, see the video below.
Second way
The second method - the construction of a sloping roof is carried out sequentially by assembling elements directly on site. This method is more convenient if the structure is large and when assembled it can only be lifted using special equipment (crane).
First, the floor beams are laid. Stands and ties are attached to them, and temporary spacers are installed to hold them in the vertical direction. Next, the upper and side rafter legs are assembled, and the tie rods and jibs are installed.
During installation, the following sequence of actions is observed: first, the outermost elements are installed and adjusted to the desired position, and securely fastened. If necessary, use temporary spacers. A fishing line, rope, and cord are stretched between them, which will serve as a guide for the installation of all subsequent elements. This simple move allows you to get the ideal geometry (don’t forget to check the slope angle, verticality or horizontality).
On top of the racks, tie-downs are attached - bars, to which the side rafters are then fixed and onto which the tie-down of the upper triangle is installed. The ties are secured using metal corners. Since the beams are long, they sag. This is later eliminated - after installing the upper rafter legs - with the help of vertical beams of fixed or adjustable height. And temporarily they can be supported with racks (so as not to pull the entire system).
To make it easier to maintain the desired angle when installing the side rafter legs, templates are made according to which cuts are made. But since the geometry of buildings built with your own hands is rarely ideal, adjustments may be necessary. To check the resulting angle of inclination, another template is knocked down from several boards, which is used to check the correct installation.
If the standard length of lumber - 6 meters - is not enough, either order the required length (expensive) or increase it. When building up, two boards measuring at least 0.6 meters (30 cm on each side of the joint) are nailed to the joint. They are nailed on both sides or bolts are used.
A reliable way to build rafters. The length of the “patch” is at least 60 cm
After installing the side rafters, all that remains is to install the top ones. A template is also made for them, pre-cut on the ground, and installed on top.
The top part can be made in different ways. Its structure depends on the width of the base. How to make it, look at the photo below.
Since the structure of the attic sloping roof does not provide for the presence of a ridge, a beam is placed in the middle to tighten it, to which the slopes are attached, fixing the triangle in the required position.
Nodes and their drawings
When installing a rafter system, questions may arise regarding the assembly of nodes—the intersections and connections of several structural elements. In the photo you see drawings of key connections.
The second option for connecting the side layered rafters and the upper triangle. Bolts are used for more secure fastening.
How to make a do-it-yourself fastening of the upper tee and rafter leg on an attic roof
Methods for attaching rafter legs to the mauerlat or, as in this case, to the side beam are shown in the figure below. To make it easier to mount a heavy element, a thrust board (bar) is nailed to the bottom of the rafter, which limits its movement: the board rests against the edge and does not allow it to sink lower.
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:
- Gable, where the slopes descend on both sides;
- A broken line, consisting of two or more slopes of different angles of inclination;
- Hip with a triangular shape of slopes;
- Semi-hip - end-type slopes are located approximately half the height distance;
- Dome for polygonal or round buildings;
- 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:
- 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.
- 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.
- 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! 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.
- 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.
- 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.
- 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.
- The puffs are secured to the racks, and it turns out that each pair of racks looks like the letter “P”.
- 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.
- Installation of rafters for the upper part of the attic roof is carried out by connecting each pair with a metal plate or bar.
- 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:
- Install the outermost floor beams that form the outline of the overhangs. The section of the beams is 150*200 mm.
- 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.
- Having cut out the tenons, prepare the supports.
- Install the corner posts and secure them with temporary supports.
- Using a plumb line, determine the location of the support points of the beams and select holes for them.
- Install row posts and a pair of load-bearing supports in the centers of the attic gable.
- Lay purlins from 50*150 mm boards. Secure the purlins with corners.
- Connect the supports with bars, also securing them with corners to the purlins.
- Fasten the crossbars using temporary fasteners with an inch. Deviation from the edge of the frame is 300-350 mm.
- 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.
- Install the end rafter posts.
- Make a template for the top of the rafter legs.
- 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.
- If the templates fit perfectly, make the required number of rafter legs, mount them in place, strengthen the headstock of the crossbars 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:
- 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.
- Select a spike on the racks.
- Connect the longitudinal beam with the vertical posts and you get a frame module (double). These are the future walls of the attic.
- Lift the frames up and install them in place. Temporarily secure the installed frames with spacers and then fasten them with brackets.
- Select sockets at the edges of the beams for mounting the lower row of rafters; if necessary, modify the sockets with a chisel.
- The upper rafter tier is made on the ground, for which the blanks are first adjusted to the required elements.
- 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.
- Select sockets along the edges of the stretch, and spikes on the lower heels.
- 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.
- 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.
- 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.
The attic is an excellent opportunity to increase the total and usable area of the house. It is installed in the attic and is quite suitable for living, provided that it is designed correctly. The rafter system of the attic roof, drawings of which can be found in this material, is the basis of the entire structure. And it is precisely this that needs to be given the closest attention when designing.
Mansard roof rafter system - drawings
An attic is a room located directly under the roof. Its facade is partially or completely formed by the roof surfaces (according to SNiP 2.08.01-89).
SNiP 2.08.01-89. Residential buildings. Downloadable file (click the link to open the PDF in a new window).
It is a full-fledged residential floor; there can be one or several rooms, depending on the design parameters.
On a note! The word "attic" comes from France. It was the French architect who, in 1630, came up with the idea of usefully arranging attic spaces. And this man’s name was Francois Mansart - hence the name of this type of superstructure.
The peculiarity of attic roofs is not only the special design of the rafter system, but also the need for detailed consideration of other aspects - insulation, moisture and vapor barriers, etc. Since due to the attic, the load on the foundation and walls of the building itself usually increases, then predominantly all of it elements are built from lightweight materials. That is, it is recommended to use wood to create a rafter system; lightweight materials are used as insulation.
The attic can be of impressive size and occupy the entire area of the building, but within its walls. Sometimes it is installed only on part of the floors, and then the rear ones are covered by a regular roof.
Very often, the attic is used in individual construction, because it is an opportunity to increase the living space of the house and make it warmer (heat loss through the roof is reduced by an average of 7-9%). And the costs of arranging an attic will be much less than building a full floor.
In general, building an attic is not very difficult and you can cope with the task yourself. The main thing is to correctly calculate wind, snow and other types of load.
Prices for timber
Types of attics
The design of the attic will directly depend on what shape the roof is supposed to be installed. After all, part of the walls of this room will be formed by the roof slopes. Depending on this, there are several types of mansard roofs.
Perhaps the simplest option for arranging the roof itself and the attic floor. This roof has only one slope, which rests on the multi-level walls of the building. Thus, the slope angle is formed. By the way, it should not go beyond the strictly limited limits - 35-45 degrees (if the slope is less, then snow will constantly accumulate on the roof in winter, which will significantly increase the load on the entire house and will cause the installation of additional supports in the already small in size attic). The rafter system here is extremely simple.
On a note! The rafter structure will not require additional supports if the distance between two walls located opposite each other does not exceed 4.5 m.
Such attic roofs look original, despite the simplicity of their design. Usually, a fairly large window is made on the side of the high wall of the attic, which allows you to get a well-lit room.
Mansard roof with two slopes
This option is also relatively simple to implement and is therefore widely used. The main thing is that the height of the roof itself allows you to arrange a living space underneath it. The rafter system of this roof looks like a regular gable roof; it can be asymmetrical or symmetrical depending on the location of the ridge.
The gables are usually simple and straight, and the room inside will have the shape of a trapezoid or square (the latter option is only possible if the attic space is spacious enough). The height of the ceilings near the walls should not be more than 1.5 m; above that there is a sloping cone-shaped ceiling.
The main disadvantage of a gable roof in terms of arranging an attic is the loss of most of the free space. That is, the lion's share of the room is cut off by the roof slopes. Of course, this free space is usually used as a storage space, but this aspect has a very significant effect on the size of the attic.
Broken mansard roofs
In fact, this is also a kind of gable roof, but its slopes have two parts, located at different angles relative to the ceilings. Due to this, you can get a fairly spacious attic floor, which will be equal in area to almost a full second floor (it will be only 15% smaller than the lower floor). The height from ceiling to floor will be the same throughout the attic and will be about 2.2-2.3 m.
Broken mansard roof - drawing
However, this design involves the construction of a rather complex rafter system. And not every novice master will be able to cope with this task. However, despite this, the sloping roof option is quite common.
Hip roofs, mansard roofs
Such a roof involves the creation of the most complex type of rafter system, requiring the most accurate and painstaking calculations. The surface of the roof itself will have a fairly large area, which is why you will have to spend a lot of money on other materials - insulation, hydro- and vapor barrier films, etc. But in general, the attic turns out to be quite spacious, although parts of the usable area are cut off .
But such a roof has maximum resistance to snow and wind loads. The overhangs can be quite large and will be ready to protect the walls of the building from the effects of precipitation. Such attic roofs look very attractive.
Attention! When arranging a hipped roof, it is important to take care of the need to strengthen the layered rafters - they are the ones who experience the maximum load.
Attic roof rafter system
When installing an attic roof, the rafter system can be made from elements of a layered or hanging type. In the first option, the rafters are installed so that they form a triangle with even edges. In this case, the support is carried out on the mauerlat fixed along the perimeter of the walls, on additional supports installed under the rafters, and the connection of two boards in the ridge area also serves as a support point.
When installing hanging type rafters, supports in the form of additional beams are not provided. They rest only on the walls of the house. Pulls may be used. In this case, the rafters themselves work in bending and compression.
Hanging and layered rafters - example drawing
Creating a rafter system when building an attic is a primary task. It is first important to correctly calculate it and take into account all the subtleties of its construction. To understand what will be discussed, you need to familiarize yourself with its main elements.
Table. Main details of the rafter system.
| Element | Description |
|---|---|
| Mauerlat | This is a beam (or board) that is fixed on the upper end part of the load-bearing wall of the building. The rafter legs will be attached to it. It plays the role of a support and will transfer the entire load from the roof to the walls of the building. |
| Rack | Any vertically located beam that acts as a support for the rafter legs. |
| Floors | This is a series of beams laid horizontally to form the floor of the attic floor. They also play the role of the ceiling of the first floor of the building. |
| Rigel | These beams are located horizontally and are additional reinforcing and supporting elements for the rafters. May also be called "puffs". |
| Rafters | Also called “rafter legs”. They form the frame of the roof and give it its shape. Moisture-proof materials, sheathing and roofing will be attached to them on top. |
| Lathing | Many blocks or sheets of plywood that are attached to the rafters. It is on them that the roofing material will be directly fixed. |
| Suspension | A board that helps distribute the load. Installed under the bolt or tightening. |
| filly | The board that forms the roof overhang is fixed at the bottom of the rafter leg. |
Prices for construction boards
Construction boards
Required calculations
In order to avoid mistakes when designing an attic, it is important to carry out a number of preliminary calculations. Depending on the chosen type of rafter system and type of roof, they may differ. The easiest way is to use a special program, but you can try to do all the calculations manually.
It is important to determine the area of the final roof, the dimensions of the attic, and the width of the floors. The calculation is made based on the following data:
- length and width of the house;
- volumes of precipitation in winter and summer (this will help determine the required roof slope angle);
- the width of the joints between parts of the floors.
An example of calculating the pitch of rafters in the program "Rafters 1.1"
Let's consider an example calculation: the length of the house is 12 m, the width is 3 m. The amount of precipitation in the area indicates that the required roof slope angle should be about 40 degrees. The calculation is made using the formula Hk = L x tgA, where Hk is the required height, L is ½ the width of the building, tgA is the tangent of the angle. Total: Nl = 3/2 x tg40 = 1.26. This means that the recommended roof height should be 1.26 m.
On a note! Most often, when installing mansard roofs, owners opt for broken rafter systems. The methodology for calculating parameters in this case can be found in SNiP 2.08.01-89 and TKP 45-5.05-146-2009.