Calculation of the rafter system of a gable roof. Types and diagrams of rafter systems: overview and recommendations for installing a roof rafter system Plan of a complex pitched roof in detail

The construction of a country house or cottage always involves the use of a rafter system similar to that used in the construction of residential buildings. The material for such rafters is usually wood.

The rafter system can be made not only in the form of a triangle, but also in the form of other structures. But no matter what material and what form will be used, first of all, you still need to know what a rafter plan is.

What you need to know to develop a rafter plan

In order to save living space, attic rafter systems are chosen, since it is with their help that it becomes possible to equip an additional living room in the attic.

In general, a process such as designing a rafter system can be considered quite complex, since it requires certain skills, knowledge and skills. Therefore, to carry out all the necessary calculations and competently draw up a drawing, it is best to use the services of a specialist who already has some experience in such work.

The most important parameters that must be taken into account, starting from the roof design stage, are:

• Roof slope angle
• Selection of rafter section
• Roof type
• Material to be used for roofing
• Calculation of the rafter system

The level of slope of the slopes must be taken into account when selecting materials and when calculating the strength of the supporting structure necessary for any roofing work.

Most of the materials that can be used for such purposes can have a very noticeable impact on the design of the rafter system as a whole. Therefore, it is necessary to choose the material that will be used to cover the roof very carefully, with all responsibility, and this must be done during the design process.

The drawing of the rafter system must be calculated with special care, since all possible errors and shortcomings that are made when assessing loads may well lead not only to damage and deformation of the rafters, but also to the complete destruction of the roof already during its operation, up to the complete collapse of the roof.

Development of a rafter plan

The process of developing a rafter plan includes procedures such as:

• Construction of modular axes linked to the thickness of the building’s load-bearing walls. In this case, on the plan itself, the projection of the crowning cornice is shown on the outer wall using a contour line.
• Ventilation and pipelines must also be indicated on the plan; their location must certainly be taken into account when arranging elements in the rafter system design.
• Based on the selected roof structure, a plan is developed. In this case, the walls and the fastening of the rafters in the ridge must be taken into account directly on the sketch.

Using such a sketch allows you to draw a plan of the rafter system, with the mauerlats, longitudinal struts and racks, a rafter beam, and rafter legs indicated on it.

The selection of a suitable distance between adjacent rafters is carried out based on:

• from the weight of the material chosen for roofing,
• scaffolding that will be used in this case,
• The pitch of the rafters can be changed due to the need to pass ventilation pipes or a chimney through them.

Also, ventilation and pipes can be passed through by interrupting the legs of the rafters, for which their ends are supported on special wooden jumpers, which are located between the adjacent rafters, and secured using a special rafter cut.

If we are talking about gable roofs, then the dormer windows should be on the gables, which, in turn, are located at the ends, which cannot but increase the efficiency of attic ventilation in the summer.

Features of the design of a roof with four slopes imply the display on the plan of eaves resting on diagonal rafter legs, as well as dormer windows located on the hips.

In cases where the space under the roof is planned to be used for the construction of an attic floor, this should also be shown in the drawing in the form of upper beams that will serve as support for the rafters.

Also, we should not forget that the layout of the rafters should be developed simultaneously with the plan for the various designs of sections of the building.

The drawing must take into account the data of all distances between the modular axes of the proposed structure, since all indicators of the thickness of future walls are associated with them.

Directly in the plan itself, the distances between the chimney, ventilation and racks must be indicated.

In addition, the plan should display callouts indicating all the required cross-sectional values ​​and lengths of all available parts.

A hip roof, provided it is constructed correctly, is distinguished not only by its presentable appearance, but also by increased strength, which allows it to effectively withstand precipitation and strong winds. In this article we will talk about the structure of the rafter system of a hipped roof, consider the types of such frames, and also describe a detailed work plan for their construction.

Comparative characteristics of frame types: tent and hip

The category of roof with four slopes includes 2 types of frame systems, which schematically look like square (hipped structure) and rectangular (hip roof) envelopes. In our country, the envelope roof is quite popular. The main feature of hipped roofs is the absence of gables. To construct the rafter system of a hipped roof, in both cases hanging and layered rafters are used. Their assembly methods are standard for roofs with any number of slopes.

Distinctive features of hipped roofs of various designs:

• In the case of a hip frame, the roof consists of four isosceles triangles whose vertices touch at one point. In this case, the functions of the ridge are assigned to the central support beam in layered structures, or to the top point of the hanging rafter truss.
• A hip-type roof assumes the presence of two triangular and two trapezoid-shaped slopes. In this case, the trapezoidal slopes are adjacent to the ridge beam with their upper ribs, and the triangular slopes with their vertices. In this case, all four slopes touch each other with lateral ribs.

Studying the plan of the rafter system of a hipped roof, we can conclude that the choice of the configuration of a hipped roof depends on the shape of the building. That is, square houses are covered with hipped structures, and rectangular houses are covered with hip roofs. In this case, you can use any roofing materials, both hard and soft.

When drawing up drawings of the rafter system of a hipped roof, you should clearly indicate the geometric shape, as well as indicate the position of individual elements and projections of the slopes with exact dimensions.

As a rule, hip and hip-type rafter systems are combined with traditional ones - single-pitched, gable and sloping roofs within one object.

To support a hipped structure, you can use a mauerlat, which is the top frame on concrete or brick walls, as well as the top crown of a log frame. Layered technology is used in cases where it is possible to install upper and lower supports under each rafter leg.

• The Mauerlat must be reinforced to withstand the pushing forces in the event of rigid fixation of the rafter legs with wooden plates or metal corners.
• If the upper part of the leg is fixed rigidly, and the lower part is hinged, the Mauerlat can be fixed in the usual way. In this case, when the load on the frame increases, the rafters will be able to move slightly.
• The bursting load and pressure on the Mauerlat will be leveled by using rigid fastenings on the lower part of the rafters and hinged fastenings on the upper heels.

Please note that the method of laying the Mauerlat and the entire rafter system should be provided for at the building design stage. In the absence of internal load-bearing walls and the impossibility of placing supporting elements for the central part of the roof, hanging rafter technology is used. However, most often they install an inclined type of stable frame, having provided for the presence of load-bearing structures in advance.

When constructing hip and hip frames, the following specific components of the rafter system of a hipped roof are used:

• Diagonal legs from which the ridges of the slopes are made. In hip-type frames, such slanting legs combine the corners of the roof with its highest point. Hip frames involve joining the ridge beam consoles to the corners using diagonal rafters.
• Cornices (half-legs) are elements mounted at an angle of 90 degrees to the cornices. Since they connect to diagonal rafters and are parallel to each other, their length will vary. Roof slopes are created from such elements.

The same structural elements are used to create valleys, with the only difference being that the corners are made concave.

It is the installation of slanted rafters that poses the greatest difficulty. Moreover, these elements will bear an increased load, since they serve as a supporting element for fastening in the upper part of the ridges, that is, they act as a ridge. Therefore, before starting work, it is necessary to calculate the rafter system of a hipped roof.

In general, the process of erecting a roof with four slopes includes the following steps:

1. Laying mauerlat on walls made of brick or concrete. In log houses, this element is the upper crown.
2. Installation of a central support beam under a hip frame or assembly of support structures for a hip roof.
3. Installation of layered rafter legs under one or another structure.
4. Attaching diagonal rafters that align the corners of the roof with the central peak or ends of the ridge.
5. Marking and installation of spigots.

If a hanging type of rafter system is assumed, then the first stage of creating a tent structure will be the placement of a central truss in the shape of a triangle. When creating a hip-type structure, several trusses are attached at the starting stage.

Construction of a hip roof

Since private construction mainly uses hip roofs with layered rafters, let us consider in more detail the process of installing a hipped rafter system of this design. The support for the structures will be the floors placed on the Mauerlat.

Fixation using the cutting method will be performed only at the junction of the ridge with the rafters, so the Mauerlat can be installed on conventional fasteners. In the building under consideration, the box of the house has dimensions of 8.4 × 10.8 m. The roof on the plan will exceed the dimensions of the house by 40-50 cm on each side - this is the width of the eaves overhang.

Plan for laying supports on the Mauerlat

Depending on the material used to construct the walls of the building, the mauerlat can be laid in various ways.

• In the upper part of the walls made of gas silicate or foam concrete blocks, you need to pour a reinforced concrete belt in which to place anchors for subsequent fixation of the Mauerlat.
• When constructing brick walls, a side of 1-2 bricks is made in their upper part so that a recess is formed in the center of the wall for a wooden frame. As the bricks are laid, wooden plugs are placed between the bricks, to which the Mauerlat will be fixed with brackets.

For the Mauerlat you will need a beam with a cross section of 100×150 or 150×150 mm. When planning the use of space under the roof, thicker beams should be used. The frame elements are joined with oblique notches, followed by reinforcement with nails, screws or screws, and in the corners with staples.

Next, you need to place the ceiling elements on the Mauerlat. They are made from bars with a cross section of 100×200 mm. The central beam is laid first. If the length of the lumber is not enough, it is made from two pieces of timber. Moreover, the connection point should be on a supporting element, for example, a load-bearing wall.

In this case, the beams are laid in 60 cm increments. As a rule, the box has non-ideal dimensions, so the spacing between the beams can be slightly adjusted to smooth out imperfections. The distance from the walls of the house to the outer beams located on both sides should be 90 cm. This is required for the installation of outriggers.

Extensions are attached to the end parts of the floor beams. For convenience, they are first placed only in those places where the rafters will be installed later. They are fastened to the surface of the outrigger mauerlat with nails, and to the beams with dowels, large-section nails, and self-tapping screws, after which the fastening is reinforced with corners.

Assembling the ridge section of a hipped roof

The central section of the hip roof is nothing more than a traditional gable structure. Consequently, its assembly is carried out using technology for pitched roofs. Although such a design usually involves the presence of a beam on which supports for the ridge are placed, in this example the functions of such an element are assigned to the central floor beam.

The ridge section of the roof is done as follows:

• First, a supporting structure is assembled for the rafters, which will rest against the ridge beam with their upper heels. The ridge itself will be supported by three support pillars, of which the middle one is mounted directly on the central beam of the floor. To correctly install the two outer pillars, transverse bars are placed under them on top of the ceiling, spanning at least 5 beams in length. The struts provide additional stability to the structure. The supporting elements of the frame are made of timber with a cross-section of 100×150 mm, and the struts are made of boards 50×150 mm.
• To ensure that all rafters are the same, a template is made for cutting them. To do this, a board of the required length is tried on at the installation site, the cuts are marked, and then all the rafters are cut along it.
• The finished rafters are supported on the ridge beam by the cutting point, and the lower part is secured to the outrigger.

Typically, floor beams are placed perpendicular to the frame so that the support of the rafter legs in the central part of the roof rests on them. Since in the example under consideration the rafters are connected to the extension, the installation of additional supports is necessary. They are placed in such a way as to redistribute the load from the rafters and supports to the walls.

In the end, you need to install three rows of stems on each side. After this, a cornice is attached strictly horizontally to the floor beams and extensions, facilitating further work on the roof.

Fastening the corner extensions of the rafter system

It is necessary to install corner extensions in the corners behind the cornice board.

They are attached like this:

• From the corner to the place of the conventional intersection of the floor beam with the outer support of the frame, a string is pulled.
• A block is placed along its contour in the right place. On the block you need to mark the places where it intersects the floor beam and the corner joint of the cornice. According to the markings, all excess is cut off.
• Using corners, the finished element is attached to the ceiling and mauerlat.

The same actions are performed with all remaining offsets.

Installation of sloped rafters - drawings

The diameter of the diagonal rafters coincides with the dimensions of the ordinary elements. Since in our example the slope of the trapezoidal slopes and hips is different, one of the sloped legs is placed slightly higher than the other.

The process of creating and installing slopes is as follows:

• Using laces, we outline additional lines for marking the cut, pulling it to the corners and the center of the slope from the top point of the ridge beam.
• Determine the angle between the top of the corner stem and the lace. This will be the angle for the bottom cut (α). The upper cut (β) is calculated using the formula: β=90º-α.
• We take a piece of board and cut one edge of it at an angle β. Having attached the workpiece to the place where the upper parts are joined, we combine its edge with the lace. We mark the excess and saw off.
• In another blank for the lower heel, we saw off a section at an angle α.
• Using the templates obtained, the first diagonal rafter is cut out. If there is no whole board of the required length, the element is assembled from two pieces. They are spliced ​​using an inch board, 1 m long, placing it on the outside of the rafters. The finished element can be installed.
• The second half of the diagonal rafters is made in the same way, not forgetting that it should be placed slightly lower than the first. The junction of the two halves of the slope should not coincide with the section where the boards are joined into one piece.
• The boards are joined with nails at a distance of 40-50 cm.
• Next, you need to draw a saw line along the lace on the rafter so that it can be joined to the adjacent diagonal element.

The manufacture of the remaining 3 parts is carried out in the same way. Supports are installed under each of these rafters in the places where the beams meet the corner extensions. Additional supports near the ridge are required if the span exceeds 7.5 m.

Assembly and installation of hip rafter legs

Using a stretched cord from the ridge to the center of the slope, we measure the lower angle γ and calculate the opposite angle δ=90º-γ. Just as with diagonal parts, templates are made for cuts on the upper and lower heel of the element so that it fits tightly between the diagonal rafters. Having made the central hip rafter, it must be installed in the appropriate place.

Structural rigidity and reliable fastening of the shortest extensions are ensured by installing short extensions between the cornice and corner extensions.

At the next stage, they make templates for the makers:

• A piece of board is sawn off at an angle δ and tried on at the junction with the diagonal leg.
• Excess areas are identified and then sawed off. This template will be needed to create all the flaps that will be installed on one side of the hip. For the other half, the cut on the blanks will need to be done on the opposite side.
• The lower heel of the splices is cut according to a template sawed off at an angle γ. This blank is suitable for creating lower joints on all spigots.

The production of spigots is carried out taking into account the estimated length of the elements and according to the manufactured templates. They will fill the planes of the hips and main slopes. The installation of these parts is carried out so that the junction points of the slopes with the spouts on opposite sides do not converge in one place, that is, apart. The fastening elements for connecting the frames with the diagonal rafters are angles, and with the outriggers and floor beams - jagged plates or angles - whichever is more convenient.

The construction of a roof with a hip frame is carried out using the same technologies as with a hip frame. The only difference is the absence of a ridge in hip roofs. In this case, the installation of the hip roof rafter system begins with joining the diagonal rafters, and then the splices. If hanging rafters are used, the central truss is installed first.

Thus, a detailed study of the features of the construction of hipped roofs will allow you to begin creating a frame structure with skill.

1) Draw the coordination axes of the building.

2) Draw the outline of the walls.

3) Lay Mauerlat along the perimeter of the building on the outer walls.

4) Place a support beam in the corners of the building to support the diagonal rafter legs.

5) At an angle of 45°, draw diagonal rafter legs from the corners of the building.

6) Lay a plank along the inner wall of the building and show the upper purlin.

7) Lay the rafter legs, starting from the support unit, after a certain distance.

8) Lay short rafter legs (springs) along the diagonal rafter legs in a checkerboard pattern.

9) Install the racks every 3000 - 6000 mm, starting from the support unit.

10) If the building width is more than 12 m, place a crossbar at the rafter legs.

11) To form a cornice, a filly is nailed to each rafter leg, and fillies, called shorties, are nailed to the diagonal rafter legs on both sides.

An effective solution for constructing a roof is the use of layered rafters to cover spans of up to 14 m if the building has one internal support and up to 16 m with two internal supports.

The rafters are connected using fastening bolts, staples and nails.

In the case when the distance between supports (external or internal) is more than 7500 mm, in civil buildings the load-bearing foundation of the roof is roof trusses, representing a flat geometrically unchangeable lattice system consisting of individual, interconnected elements (rods). Rafter trusses can be wooden, metal-wood, steel and reinforced concrete. Wooden trusses are called hanging rafters.

The pitch of trusses for spans up to 9 m is 3–4 m, for spans over 10 m – 1.5–2 m.

Hanging rafter diagrams

Dormer windows arranged in pitched roofs for lighting, ventilation of the attic, and access through them to the roof. They can be semicircular, triangular, rectangular in shape. Lighting is provided through a glazed sash measuring at least 0.6×0.8 m. For ventilation, wooden louvered grilles are used, located adjacent to the glazed sash of the dormer window. Dormer windows must be placed in such a way as to ensure through ventilation. It is recommended to place the bottom of the window no higher than 0.8 - 1.0 m from the top of the attic.

Types of dormer windows

a – triangular; b – semicircular; c – rectangular; g – polygonal

1 – glazed parapet; 2 – louvered grille

When designing a house, attention should be paid to the rafter system. A so-called rafter plan must be drawn up, which includes all the construction features of the structure, the pitch of the rafter legs and other points necessary to build a reliable and durable roof that can withstand the design loads.

Types of rafter systems.

Rafter system design

Drawing up a plan for rafters for a hipped roof, a gable roof, or for another structure is a complex and responsible process at the same time. That is why a special program is used to draw up a drawing; it is necessary to take into account calculations of snow and wind loads, the weight of the roofing material, and the dimensions of the house itself. The plan is drawn up by a specialist who has the necessary experience in performing such work. When drawing up a rafter plan, the following parameters are taken into account:

• material for constructing the roof (it can be wood or metal);
• type of roof, its features;
• roof angle;
• section of rafter legs;
• If the listed data is available, you can begin to implement the plan for the rafter system.

The design of the rafter legs depends on:

The attachment point for the rafters to the mauerlat.

• shapes of the future roof;
• the length of the floors and the space to be covered;
• presence of internal supports.

The rafter plan must be drawn up taking into account all parameters. Slab and hanging rafters are used to construct the roof. The leg design can be made in a triangle shape to provide maximum rigidity and strength. If complex trusses will be used, you will additionally have to purchase:

• struts;
• crossbars;
• puffs;
• additional racks;
• rafter beams.

Layered rafters are used for houses where the middle one is used as a load-bearing wall. The rafter structure includes 2 rafter legs, a mauerlat on which they rest from below, and a ridge purlin for support from above, as well as racks. The racks are mounted on a bench, it is placed on the internal load-bearing wall, which makes it possible to correctly distribute all the loads. If there are no internal walls, then the support is on pillars or columns, the spacing between which is 6.5 m.

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Hanging rafters are used when internal supports or walls are completely absent. In this case, the rafter legs will rest only on the outer walls.

Diagram of the truss system for a sloping attic roof.

The structure includes the rafter legs themselves and a horizontal beam in the form of a brace. The lower ends of the beams rest on a special Mauerlat on top of the wall; it allows the load to be distributed evenly. Such rafters can cover a space of 7-12 m. Crossbars are used for reinforcement.

The production of hanging rafters is more complex than layered ones, which is why the latter are used much more often. The cost of hanging rafters is higher, but in some cases they are the only ones that can be used. Combined systems can be used to reduce costs. This makes it possible to make construction simpler and more economical.

The drawing is drawn up using a special program. When drawing up a drawing, the following steps are performed:

1. Modular coordination networks are applied first; they allow you to link all the data on the design of the rafter system to the main walls of the future house.
2. The plan shows all the channels of the ventilation and smoke system, pipelines that will exit through the rafter system during the construction process.
3. A plan for the future selected roof shape is being developed. When drawing up a sketch, you need to take into account the location of the walls.

The diagram must indicate the elements that the roof has: roof ribs, valleys, ridges, etc. It is imperative to take into account what shape the slopes will take, the direction and angle of inclination. The drawing indicates the location of the gables and dormer windows, if any.

Using the roofing system plan, builders will build a strong and reliable structure. The plan must indicate the following parameters:

Design of a single-pitched roof rafter system.

• rafter beams;
• Mauerlat;
• rafter legs;
• puffs and fillies for fastening the legs;
• racks with longitudinal struts, guaranteeing spatial rigidity of the entire rafter system (such elements must be shown in the drawing as a dashed line).

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If you plan to build a metal roof truss system, i.e. special galvanized beams, then it is necessary to use completely different programs designed for design. Only a specialist can do this, otherwise, if the calculations are incorrect, the roof will not withstand the loads. The pitch of the rafter legs is calculated taking into account the building material and the loads from the insulation. For example, for a hip roof, which is constructed of wood, the pitch of the rafters can be:

1. When making rafter legs from beams, the step is 150-180 cm.
2. When making rafter legs from edged boards, the step is 100-120 cm.

It is important that the plan shows the ventilation outlets of the pipes, as reinforcement of the structure may be required.

In some, in order to pass the pipe, it is necessary to saw the rafter leg, and install the remaining ends on special wooden jumpers, which will be located between the adjacent legs. In this case, a saw is used for fastening. Scheme of the rafter system.

Technological rules

Scheme of rafters with a sliding support.

For a hipped roof or other configuration, small dormer windows are provided in the gables to ensure proper ventilation of the attic spaces, especially in the warm season. For example, for a hipped roof, it is necessary to show on the rafter plan the diagonal slanted rafter legs and the ribs resting on them. It is important not to forget about the dormer windows that will be located on the hips.

If you plan to build an attic living space, then the upper beams for lining the walls should be shown on the plan. They will serve as a support for the rafter legs of the entire structure, providing the necessary strength and reliability of the roof. The design scheme is always carried out simultaneously with the development of plans for all structural sections of the building. This allows you to connect them with each other and ensure correct and clear design. As a result, each node will be clearly connected to the others, and the structure will be stable and reliable.

In this lesson we will look at how to compose and rafter plan in AutoCAD (2010). According to current standards, a roof plan must be drawn up for buildings with internal drainage. If the drainage in the building is external and the building is not complex, then such a drawing is not necessary. Next, let's see how to draw a roof plan for a pitched and flat roof of an industrial and public building.