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

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

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

Good to know

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

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

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

S=Sg x µ, where

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

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

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

W = Wo x k, where

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

k – correction factor for different types of areas and building heights.

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

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

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

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

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

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

Main nodes

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

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

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

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

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

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

Hanging and layered rafters of the attic roof

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

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

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

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

The shape of the attic roof depends on the area to be covered and the architectural design; it is better to choose simple types of attic roofs so that the beams and racks do not clutter up the space inside.

Attic, rafter system of hip hip roof

Stages of installation of the attic rafter system

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

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

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

Docking technology

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

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

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

How to properly attach layered rafters for an attic

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

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

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

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

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

Sliding fastening of the attic rafter system

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

How to build up and strengthen attic rafters

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

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

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

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

Options for extending the rafter leg

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

Ways to strengthen the rafter leg

How to join rafters at the top

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

Upper rafter connection on a ridgeless mansard roof

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

Joining rafters on a ridge beam

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

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

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.

More and more architectural, original houses are appearing, decorated with bay windows, superstructures, and mezzanines. Attics are becoming fashionable, expanding the usable area of ​​the house. But attic roofs, unlike a simple gable roof, require complex rafter systems. Correctly calculating them and carrying out installation is not at all easy. Below we will try to briefly highlight this issue and provide useful recommendations from experts.

At the design stage of a house, the roof structure must be calculated. Calculations using complex formulas should give a value for the load per meter of a square rafter system. For residential buildings, the standard load is 50 kg/m2.

In accordance with the calculations, the type of attic truss structure is selected. The main varieties include:

• hanging rafter system;
• sloping roof rafter system;
• layered gable roof system;
• combined.

The most common are combined rafter systems for pitched roofs. It is recommended to entrust the calculation of complex rafter systems to professional designers.

Advice!

To increase the usable area of ​​the building, you should choose a multi-slope mansard roof design.

Rafter roof elements

Experienced specialists will perfectly understand what is being discussed in the article, since they know all the terms and names of structures. To make it clear to everyone, here are the common names of elements:

• Mauerlat - a beam attached to the upper crown or wall of the house on which the rafter system rests;
• Floor beams are a wooden structure that plays the role of an attic floor and, at the same time, the ceiling of the room below;
• Posts are vertically mounted posts on which rafters and beams are attached.
• Purlins - beams (boards) located horizontally serve as support for the rafters;
• Crossbars are horizontal beams in a U-shaped truss. They serve as a support and tighten the pitched rafters; they are also called “tightenings”;
• Rafters - timber or boards that form the basis of the roof structure;
• Suspension - a rack whose task is to support the crossbar, facilitating its operation, is also installed horizontally;
• Sheathing - a board or plywood base on which the roofing material is laid;
• The filly is a board that serves as the basis for installing the overhang and is installed at the bottom of the rafter system.

Rafter system calculations

The choice of truss structure largely depends on the size of the building, according to which the span length is determined, i.e. distance between main posts. For small houses, preference can be given to a gable structure.

Structural calculations are carried out to determine the load, in accordance with standards and building regulations. The basic rule for an attic roof is to limit its height, which should not be less than 2.5 meters indoors. Thus, the roof must have a minimum height of 2.80 m, since it requires laying an insulating layer and finishing inside the attic itself.

You should definitely make a design drawing, on which you should put all the dimensions and display the frame elements as much as possible. The drawing should show the dimensions of the house, the angle of the rafters, and the height of the roof.

Advice!

To make accurate calculations for all loads on the roof and its elements, it is recommended to use a calculator located on many sites dedicated to the construction of roofs.

It is enough to enter the type of roofing, the material of the attic roof frame and dimensions. The program will calculate the section angles and pitch of the rafters and give recommendations on the design of the sheathing.

Calculation of the rafter system

Attic roof installation technology

You should start with the installation of the Mauerlat, which is laid along the perimeter of the upper edge of the walls, if the house is brick or block. In houses made of timber or chopped with mauerlat, the upper crown can serve. The timber from which the Mauerlat is made must have cross-sectional dimensions of 100x100 mm or 150x150. Coniferous wood for timber must be well dried. The Mauerlat beams are fixed with anchors or studs to the walls in increments of approximately two meters. Waterproofing is placed under the Mauerlat, usually of a roll type (roofing felt).

Next, you should begin installing the ceiling. Beams 150x200 mm, placed on the Mauerlat, should protrude beyond the walls of the house by about 0.3-0.5 m. The beams are fastened with corners and screws (wood screws), starting from the outer ones, then intermediate ones.

Important!

When laying, use a cord to control the horizontal level so that the beams lie in the same plane.

The distance between them is, as a rule, 0.5-1.0 meters; if you plan to lay insulation, the standard sheet width of which is 0.6 m, then it will be more convenient to withstand the same spacing of the beams.

Installation of roof truss system

Installation of support posts and purlins

The next stage is the installation of racks. For them, a 100x150 mm beam is used, which is fastened to the front floor beams. It is necessary, using a plumb line, to check the verticality of each support and fix it with jibs. Intermediate supports are also installed strictly vertically on the beams, forming two parallel rows.

Next comes the installation of purlins, which can be made from boards 100-150 mm wide and 40-50 mm thick. The purlins are fixed using nails and corners with screws. Then, on top of the purlins, plank crossbars are laid, for rigidity, installed at the end.

Advice!

As a result, the outline of the future attic space is formed. To provide additional strength, the supports should be strengthened with struts and braces.

Installation of rafter elements

Installation of rafters starts from the bottom. A board 40-50 mm thick and 150 mm wide is suitable for them. We rest one end on the mauerlat close to the floor beams, and the other is attached to the purlins using angles, screws and nails. To install rafters at the top of the roof, mark the center line of the roof. All rafters must be the same length. To do this, you should make a template board, making cuts on it at both ends. Then you can saw off the rest of the rafters using the template.

The rafters are mounted on purlins, fixed at the top with metal plates. On the purlins, the beams are secured with edge-to-edge cuts and secured with corners on self-tapping screws.

For strength, the lower rafters should be strengthened with struts (board 50x150 mm). After securing the struts, the temporary stops can be removed.

Installation of rafters

Lathing

In cases where floor beams are laid in wall pockets, fillers should be secured to the lower rafters to provide a roof overhang. If the floors lie on the mauerlat, then fillers are not needed, since the beams should protrude beyond the walls to form an overhang.

The sheathing is installed depending on the intended covering of the attic roof. Either the sheathing will be solid or with gaps. A waterproofing layer should be laid on top of the sheathing, after which you can begin sewing up the gables and laying the roofing material - metal tiles, corrugated sheets or slate.

Roof sheathing under metal tiles

Attic insulation

If the attic roof has a broken structure, then, as a rule, it is not insulated, since the air layer under the rafters protects the premises, while simultaneously ventilating the space under the roof. To do this, when sewing up the gables, you should leave ventilation windows (holes) above the attic floor. Thermal insulation should be done only inside the attic room.

Thermal insulation of the attic has its own characteristics, since the rooms have triangular or trapezoidal ceilings. Builders consider insulation to be one of the complex technological tasks in the construction of attic spaces. The main thing is to lay the thermal insulation so that on the sloping ceiling and on the fences it does not shrink during operation.

Attic insulation

The reliability of the roof frame with a residential attic depends on how well the installation of the attic roof rafters is carried out. The complexity of this process is explained by the need to take into account several important components that affect the truss structure.

The rafter system for mansard roofs was developed by the French architect F. Mansart in the 17th century. What’s surprising is that many of the technical solutions for attic living spaces that he proposed are still relevant today. It was thanks to Mansar that the fashion for high ceilings and large windows in attics appeared - they significantly increased the level of comfort for the people living in them.

Types of mansard roofs

The roof rafter system comes in two types:

• layered - in this case, the beams rest on the load-bearing walls of the house;
• hanging - all elements of the rafter structure are connected into a truss and a common frame and mounted on the outer supports.

The type of mansard roof being erected depends on the design of the rafter system:

1. Single slope inclined. The roof has a plane that rests on walls of different heights.
2. Gable. It is a roof with two planes diverging to the sides at a certain angle.
3. Broken. It is a type of gable roof. Consists of planes with a broken surface.
4. Half-hip and hip. These roofs have four slopes.
5. Tent. Such a roof can be conical, pyramidal, or domed.
6. Vaulted. It has parabolic or rounded outlines.

Most often you can find a gable version of the mansard roof. This fact became decisive for the architecture of many domestic cities and towns.

When a gable mansard roof truss system is being erected, drawings for it are drawn up taking into account certain data, including:

• geometric parameters of the structure;
• type of roofing material;
• climatic and weather loads;
• relief of the site and surrounding area.

When developing a project, it should be remembered that if it is necessary to have a large usable attic area, the angle of inclination of the rafters must be made smaller.

The procedure for calculating rafters

A competent and accurate calculation of the mansard roof rafter system will allow you to build a strong and reliable structure that can last for many years.

When performing calculations, take into account:

• weight of attic elements;
• wind and snow loads.

Since these indicators vary in different climatic zones, the design of the rafter system of roofs with an attic can differ significantly. The method for calculating rafters when creating layered structures is simpler than hanging ones. In some cases, roofers use combined options for arranging the frame.

When an attic is to be built, it is advisable to entrust rafter drawings and complex calculations to professionals with extensive experience in such work. The fact is that when performing calculations, mathematical formulas and different coefficients are used.

By calculating the weight of the roof, they find out the magnitude of the load, which is expressed in kilograms per “square” of the truss structure. Typically, the average value of this parameter for residential buildings is about 50 kg/m².

Calculations of wind and snow loads in regions with unfavorable climatic conditions indicate that rafter systems for gable mansard roofs should be made with paired rafters and continuous sheathing - they will avoid frame deformations.

Stages of arranging an attic roof

The rafter system consists of the following elements:

• Mauerlat;
• ridge beam;
• rafter legs;
• vertical racks;
• inclined struts.

In order to increase the reliability of the roof frame and give it the necessary rigidity, struts, crossbars, racks, and beam supports are installed between the rafters. The base for the roof covering is made sparse or solid.

Installation of the rafter system of an attic gable roof - a step-by-step process:

1. Install an upper beam with a cross-section of 10x10 or 15x15 centimeters. To fix it to the racks, metal staples, special nails or self-tapping screws are used. In this case, the first beam is assigned the function of a rafter frame.
2. The mauerlat is laid, which is one of the main structural elements - it is subject to considerable loads due to the weight of the roof and the influence of precipitation and wind. To do this, use boards with a thickness of at least 5 centimeters or timber, the smallest section of which is 5 × 10 centimeters. Before laying the boards, a waterproofing layer is installed underneath them so that moist air does not penetrate into the Mauerlat. They are fixed to the walls with staples and nails. Additionally, the Mauerlat is tied to the load-bearing walls using thick metal wire, previously embedded in the walls during their construction.
3. Install the rafter legs, maintaining a gap between them of 60–200 centimeters.
4. First of all, the rafters of the attic roof that are outermost to the gable are installed. Then, using a level, other structural elements are installed.
5. At the top of the frame, the rafters are connected to each other.
6. A ridge beam is installed - it is required for a roof whose length exceeds seven meters. If this parameter is smaller on the roof, then this element is not necessary for the rafter system.
7. Then they begin the construction of the sheathing, laying insulation and water barrier, and then the roofing material.

How to make a rafter system correctly

Before making a rafter system for an attic roof, you should familiarize yourself with a number of rules:

1. Rafters and other elements of the attic living space must be made from beams, the minimum cross-section of which is 10x10 centimeters. Choose high-quality timber, containing no more than 3 defects per linear meter.
2. When fastening the attic frame, special nails, metal staples and wire harness are used.
3. The humidity of wooden elements for constructing a roof with an attic should not exceed 15%.
4. All lumber must be treated with preparations and compounds with an antiseptic effect that protect against rotting.
5. When constructing a roof with an attic, the optimal choice is coniferous wood, which is less susceptible to exposure to humid air.
6. For vertical posts, a wooden beam with a cross section of 10×10 centimeters is used. They are installed in a strictly vertical plane using a plumb line. These racks are the basis of the walls of the future attic. They are then sheathed with sheets of plywood, plasterboard or other finishing material.
7. Before attaching the rafters of the attic roof, you need to pay attention to the laying of the windows, since it will be quite difficult to change anything later.

Installation of a sloping attic roof according to drawings

A sloping roof is a type of gable roof. It is used when it is necessary to increase the volume and living space of the attic space. House owners think about how to make a sloping attic roof when they want to create conditions for more comfortable living in the attic.

The rafter system for such a roof is calculated using the same method as for a gable roof. The main stages of their construction are also similar.

But when erecting a sloping roof, the following rules are adhered to:

1. The boards intended for fixing the rafter legs are insulated along the entire length. Thanks to this measure, heat loss is significantly reduced, thereby creating a more favorable atmosphere in the room.
2. The cross-section of the rafter legs and the pitch of their installation, when creating a mansard roof with an additional slope, must correspond to the calculated data, taking into account possible impacts and containing a safety margin.
3. Since the installation of thermal insulation will lead to the appearance of condensation at the point of contact between the cold environment and the warm one, it is imperative to use a vapor barrier.
4. To create thermal insulation, you need to use natural materials that are fireproof and environmentally friendly.

Features of the arrangement of the attic floor

The installation of attic rafters must be done so that the frame provides maximum reliability, allowing it to withstand the weight of the roofing pie. At the same time, the rafter system must be light in order to reduce the load on the load-bearing walls of buildings.

For this reason, the main material for the construction of attic floors today is still wood that meets these requirements. In this case, ceramic or metal tiles and ondulin are used to cover roofs. These roofing materials allow you to create a reliable coating with excellent performance characteristics.

When arranging the attic floor, you need to remember that it should provide a higher degree of thermal insulation compared to other living spaces. At the same time, it is necessary to perform high-quality hydro- and vapor barrier.

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.