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The most important structure of the house, which affects the entire structure as a whole, is its roof. The main design features of the roof depend on many factors, such as the maximum allowable load on the walls, the type of construction, the type of roofing material, etc. The hip roof, the truss system of which is not quite simple, is nevertheless quite a popular construction during construction. Its main advantage is considered to be its excellent self-cleaning ability, as well as good resistance to heavy snow and wind loads.
Design features of the hip roof
The hip roof has found wide application in construction due to its strong design features, durability and rather original design, which has a beautiful appearance.
The roof structure allows for a spacious living attic floor with stunning inset windows, while the streamlined shape reduces aerodynamic loads from strong winds.
The truss system of the hip roof consists of four slopes: two of which are lateral (having the shape of a trapezoid), and two more are hip (in the form of triangles). Thus, the structure has two vertices, united by a ridge run.
Main structural units
- Skate run- the main bearing axis in the upper part of the roof, which is the junction of all four slopes. It is made from edged boards 50x200 mm.
- Diagonal (sloping rafters)- an important load-bearing element of the frame, connecting the corners of the house with the horse run. It is carried out from the same board as the ridge run.
- Side roof rafters- made from a board 50x200 mm. It is attached to the ridge run and the side walls of the building or the Mauerlat. Their main task is to evenly distribute the lateral load on the load-bearing walls.
- Shortened rafters (spiders)- a board sawn at a certain angle, which is attached to the diagonal rafters and the hip part of the wall of the house or Mauerlat. Thus, there is no connection between the sprigs and the horse run.
It is important to follow the basic rules for linking structural units; the reliability and strength of the entire structure will depend on the quality of their fastening. To do this, use only high-quality lumber and "ruffed" nails.
Scheme of connection of the main components of the structure
Types of hip roofs
There are quite a lot of options for the execution of hip roofs, in addition to the standard one, there are also: (half-hip Dutch and Danish, hipped roofs, as well as broken roofs).
- If, for example, the length of the hip roof slope is less than the side ones, such a design is called half-hip (Dutch). Such a design with dignity withstands strong blast loads, and thanks to sharp slopes, snow almost never lingers on it for a long time. This type is more similar to the classical one, however, in terms of its characteristics, it significantly exceeds it.
- The Danish half-hip roof is a little more difficult to implement. The design difference lies in the fact that the hip part is already located not from below, but from above, a vertical pediment, which can be replaced with a beautiful frame with glass.
- For buildings with walls of the same length (square), a hipped roof is perfect. Unlike the hip one, which has a ridge run, the hipped one does not have one. The design is as follows, four absolutely identical roof slopes converge at one top point. thus forming a pyramidal geometric figure.
- Broken roofs due to the complexity of the design are very rare. However, their appearance is so mesmerizing that for a long time you can’t take your eyes off her. It represents itself, a set of many slopes, arranged at different angles relative to the walls. With your own hands, without having enough experience behind you, it is very problematic to make such a roof, so it is better to entrust this matter to professional roofers.
Do-it-yourself hip roof
Correct calculations are the key to the reliability and durability of any roof. Having drawn the design diagram correctly, you can easily assemble it yourself, while having 2-3 partners as an apprentice. It will not be necessary to resort to the help of a team of builders, it is enough to do everything according to the plan and adhere to the given calculations.
Tilt angle
When designing any roof, its angle of inclination is chosen based on climatic conditions, which in Russia are very different, depending on the region. If the building is being built in a region with heavy snowfall prevailing in winter, then it is desirable to make the angle of inclination large, so the snow cannot linger on the roof and will constantly slide off it under its own weight.
In the southern regions, where precipitation is quite rare, and only in the form of rain, but strong gusts of wind are not uncommon, roofs are erected with a slight slope. The main task of which is to resist these wind loads.
Also an important factor in calculating the slope is the type of roofing. The fact is that some of them have a recommended corner height limit, which should not be neglected. And so, in order not to make mistakes, read each of them:
- Slate - Recommended Slope Angle 15º - 65º. Failure to comply with these parameters can lead to moisture ingress between the joints of the sheets;
- Ceramic tiles - the best sloped angle for slopes 35° - 65°. Neglecting the slope recommended by the manufacturer will lead to the possibility of condensation;
- Metal tiles - the minimum slope for this material is 13°, the maximum is not set by manufacturers;
- Soft tiles - the optimal size of the slope is considered to be no less 15º. Roof installation can be carried out at any other value of the angle above the minimum;
- Ondulin - any slope angle is not less than 5°, the step of the crate will directly depend on the size of the corner.
- Metal seam roofing - should be used when the slope of the slopes is over 25° degrees.
Correct area calculation
In order to correctly calculate the total surface area of the hip roof, we first need to calculate the area of \u200b\u200beach slope separately, then add the resulting numbers together. As we remember, the slopes of the hip roof are the geometric shapes of two trapezoids and triangles. Remembering the school curriculum, it is easy to calculate their total area.
If you are still afraid to make a mistake, the specialists from whom you will purchase roofing material can correctly calculate, or you can use any of the online calculators that are convenient for you, which are full on the Internet.
Having accurately indicated all the parameters of the future roof, they will help to calculate everything with an accuracy of up to a square meter.
Calculation of the truss system
For an accurate calculation of the rafter system, you must use the table below of the relationship between length and their placement.
| Roof angle ratio | Correction factor for corner rafters | Correction factor for intermediate rafters |
| 3:12 | 1.016 | 1.031 |
| 4:12 | 1.027 | 1.054 |
| 5:12 | 1.043 | 1.083 |
| 6:12 | 1.061 | 1.118 |
| 7:12 | 1.082 | 1.158 |
| 8:1 2 | 1.106 | 1.202 |
| 9:1 2 | 1.131 | 1.250 |
| 10:12 | 1.161 | 1.302 |
| 11:12 | 1.192 | 1.357 |
| 12:12 | 1.225 | 1.414 |
Based on the above table, the length of the rafter leg is equal to its product of the coefficient and the projection. The use of the table will help to make all the necessary calculations as accurately as possible.
The calculation itself is carried out in the following sequence:
- Using a regular rail, find the laying (horizontal projection) of the intermediate rafter leg. Find your slope coefficient in the table and multiply by the presented coefficient;
- From the ridge run to the attachment point of the lower part of the stacking leg, we measure the length of the rafter;
- In the same way, multiplying the correction factor by the laying (horizontal projection), we find the length of the overhang of the rafters. Or you can use the Pythagorean theorem (see Fig. 1).
- Now find the length of the corner rafters. It will be easier to visualize this using the figure below.
Installation of rafters
Frame reinforcement
In order to give the structure greater rigidity, it must be strengthened with additional corner braces and vertical posts. Their required number is calculated based on the maximum load of the truss system. The value includes the weight of: roofing cake and coating, as well as the mass of snow and wind loads.
After the hip roof truss system is reinforced, you can safely proceed with the installation of the crate. Its step and design depends on the type of roofing material you choose. For example, under it should have a solid carpet.
Structures with hanging rafters are in demand when building a roof supported only on the outer walls of the house. This principle of construction is applicable for both gable and hip roofs.
Design features of the hip roof
The calculation and construction of a hip roof is much more difficult than the construction of single-pitched and dual-pitched structures. The four-pitched hip roof has two slopes in the form of a trapezoid, and two triangular slopes (hip). This configuration allows you to withstand high wind loads, reliably protect building structures from external influences. In addition, the resulting spacious attic space can be used as a living space (windows for natural light are mounted on the roof slopes).
A four-pitched roof with a ridge run can be erected in two ways: with layered or hanging rafters. The use of layered roofs allows you to make the roof lighter, simplifies the calculation and installation. But in this case, it is required that the building has a load-bearing middle wall. Hanging rafters in the construction of a hip roof can be used with a small width of the building and the absence of internal walls. The operational load is transferred to the outer walls of the building.
The angle of inclination of the slopes of a four-pitched roof with hanging rafters should be more than 40 °.
The hanging rafters of the hip-type roof rest either on the floor beams or on the Mauerlat. The design of the truss system requires accurate calculations and the preparation of detailed drawings indicating the principles for mounting fasteners. For small buildings of the correct geometric shape, calculations can be performed independently, in other cases it is recommended to turn to professionals, since design errors will cause a significant decrease in the reliability of the roof during operation.
At the first stage of calculations, it is necessary to choose the angle of inclination of the hip roof, which directly affects its height. For a system with hanging rafters, the optimal angle of inclination is 40 - 60 °. The higher the ridge is located, the more material will be required to build the roof. At the same time, a high roof is the best option for regions that are characterized by a large amount of precipitation. A flatter roof has less windage and better resists wind loads.
When choosing the angle of inclination of the hip roof, it is recommended to adhere to the golden mean rule and proceed from aesthetic considerations. You can choose the angle of inclination of the slopes, and based on this, calculate the height of the ridge. Or vice versa, determine the desired height of the roof, and then calculate the angle of its inclination.
When calculating the hip roof, it is required to ensure the correct positioning of the ridge run. It should be located strictly parallel to the load-bearing side walls, exactly along the central axis of the building and equidistant from the end walls. Otherwise, the center of gravity of the roof will be shifted, which will lead to an uneven distribution of the load on the truss structure and load-bearing walls, which is fraught with deformation and destruction of the roof.
The drawings prepared as part of the development of the project must contain information about the location, cross section, shape and size of all elements of the truss system. Their appearance and design features, attachment features, span width, ridge length, roof height are taken into account.
Roof truss system
The main elements of the rafter system of the hip-type roof include:
- mauerlat / floor beams (support for rafter legs);
- ridge run (an element that, together with the rafters, determines the configuration of the roof);
- ordinary side rafters (connect the ridge and load-bearing walls);
- diagonal (corner, slanting) rafters (directed from the corners of the walls to the ridge);
- central rafter hip;
- sprigs (shortened rafter legs connecting the rafters with the Mauerlat);
- struts and racks (used as additional supports);
- crossbars (provide a rigid connection between the rafter legs in pairs);
- sprengel (acts as an additional support for the diagonal rafter).
During the construction of a hip roof using hanging rafters, a ridge run is not installed. Instead, central trusses are mounted - rafter legs connected by crossbars for rigidity. The rafter system in the central part of the future hip roof is carried out in exactly the same way as in the construction of a gable roof. Roof trusses are recommended to be made on the ground according to a pre-prepared template in order to accurately comply with all dimensions. When installing trusses, it is necessary to check the verticality of each structure. It is important that the extreme truss trusses are at the same distance from the corresponding end walls of the building: this will ensure the correct geometry and symmetry of the hips.
After mounting a row of trusses in the ridge part of the resulting system (on both slopes), bars or boards are mounted that connect the trusses to each other. Then, rafters are attached to the extreme trusses, resting on the corners of the building. At the next stage, the central hip rafter is mounted (on each triangular slope) and the sprigs.
Roof trusses can be based on a Mauerlat or floor beams. When developing a project, it should be borne in mind that in the second case, the step of laying the beams must correspond to the step of the rafters. If the truss system provides for the installation of trusses on the Mauerlat, then the puffs located at the bottom of the trusses will not only ensure the rigidity of the structure, but can also serve as floor beams.
Lower tightening can be used if the span does not exceed 6 meters. If hanging rafters are mounted in a span of 6 to 7.5 meters, it is necessary to use crossbars in the upper part. With a span length of 7.5 - 9 meters, the upper part of the rafters should be tied with a puff using a headstock (rack). If the span is from 9 to 10 meters, the previous type of structure should be reinforced with struts.
Before proceeding with the installation of the truss system, it is necessary to check the geometry of the walls of the building. The upper part of the walls (Mauerlat, floor beams) must be located strictly horizontally.
Principles for the manufacture and installation of rafters
Installation of diagonal rafters is a key stage in the construction of a hip roof. It is important to ensure the correct geometry of the structure so that the truss system evenly distributes the operating loads of the roof.
The diagonal rafters are longer than the side rafters, they rest on the corners of the building frame, and in the upper part they are connected to the ridge element of the roof. Rafter half-legs (shortened) - sprigs, in turn, rest on the sloping ones. The rafters are subject to increased strength requirements, as they carry an increased load, acting as the supporting elements of the system. The total load on the diagonal rafters is twice that of conventional rafter legs. The lower part of the rafters rests against the Mauerlat or a beam laid at the corner of the wall, or rests on them, depending on the design principle - expansion or non-expansion.
Sloping rafters can be made from durable glued beams of the required length. But, most often, double boards are used, spliced in compliance with certain requirements. Splicing a diagonal rafter leg allows:
- increase the resistance of the element to loads due to the double section;
- to make a continuous beam of the required length;
- unify the dimensions of the details of the hip roof.
Unification allows you to use the same material for the manufacture of diagonal elements as for standard rafter legs - the use of boards of the same standard size simplifies design solutions when designing and installing nodes of the truss system.
One or two supports are installed under the diagonal rafter. The boards are spliced along the length so that the joints are located at a distance of 0.15L from the center of the support. Accordingly, the length of the boards for the manufacture of rafters is selected depending on the length of the span and the number of required supports. In particular, if a hip roof requires a diagonal rafter 10 meters long, it is recommended to use boards 7 and 3 meters long to position the post 1/4 of the span from the top end of the rafter. In this case, the structure will be able to withstand the design loads - it is not recommended to place supports under the middle part of the rafter.
The role of support under the diagonal rafter is a strut or stand made of timber or paired boards. The angle of installation is of no fundamental importance if the strut rests against a solid reinforced concrete floor (with laying a waterproofing layer). If the rack rests against the bed, the installation angle is usually 35 - 45 ° to the horizontal plane.
Additional supports are installed according to the following principle. A span of up to 7.5 meters requires the use of one brace. If the span is 7.5-9 meters, a support is installed at the bottom of the rafter, or a truss truss is mounted. With an increase in the length of the span, an additional support is installed. If the ceiling is not strong enough, it is necessary to lay an additional intermediate beam to stop the uprights.
Sprengel - a beam that crosses the angle formed by two walls adjacent to each other. A truss truss is a structure in which the rafters are supported by supports that lie on the trusses. The whole system is reinforced by two struts. For the manufacture of a trussed truss, a beam of 100 × 150 mm is used for beams, 100 × 100 for racks and 50 × 100 for struts.
Mounting the top of the diagonal rafters
The upper end of the rafters is attached to the ridge part of the outer truss truss when installing a system with hanging rafters. This may require the use of a sprengel or surf (a short board with a thickness of 50 mm or more), to which the ends of the diagonal rafters sawn at the required angle are attached. If the surf is placed indented from the ridge, you get a Danish half-hip four-pitched roof. The following types of fasteners can be used to fasten the rafters in the upper part:
- perforated plates;
- nails;
- twisting from wire rod;
- clamps.
The sprockets are attached to the rafters by cutting or with the device of cranial bars (the second option allows you to get a more rigid structure). The cross section of the bars, which are sewn onto the rafters on both sides, is 50 × 50 mm. The sprockets should be supported on the rafters with a shift so that the joints of the bars do not form at one point.
A four-pitched roof is familiar to most developers. But its second name - hip can bewilder even an experienced builder. It's all about the triangular end slopes (hips), which replaced the vertical gables.
Why did the creators of such a roof need to complicate the construction of a gable roof, you ask?
There are several reasons for this:
- The aerodynamics of a hip roof is better than that of a gable roof. Therefore, it steadfastly resists strong winds.
- Triangular slopes make the roof rigid and reliable.
- The hip design makes it possible to install wide cornice overhangs along the perimeter of the building, protecting the facade of the building from rain.
- The aesthetic appearance of such a roof is better than a gable roof.
The device and varieties of hip roofs
In order to understand how a hip hipped roof is arranged, consider its main elements.
The design of the hip impassable roof
As can be seen from the diagram, the main elements of this roof are the same as those of a gable roof. Here there is a ridge run, rafters and mauerlat for attaching them to the wall, racks that support the ridge and struts that unload the middle part of the rafter legs.
The wind beam holds the rafters together during the installation of the roof, and the filly lengthens them, forming roof overhangs. Differences begin with diagonal rafters forming hip slopes. Short rafter legs adjacent to the diagonal rafters are called rafters. To reduce the deflection of long hip beams, sprengels are placed under them. This is the name of short T-shaped racks-stands, cut into the Mauerlat with their ends.
Depending on the width of the building and the presence of internal walls on hip roofs, two types of truss structures are used:
- hanging;
- layered.
The name of each speaks for itself. Hanging rafters rest only on the outer walls. In the upper and lower parts, they are connected by horizontal tie-beams, which ensure the rigidity of the structure. The rafters in the ridge joint rest on vertical posts, in the middle part - on struts, and the ends are placed on the outer walls.
Structural schemes of hanging and layered truss systems of hip roofs
In addition to the classic hip roof, there are several varieties of it, created for reasons of aesthetic appeal:
- half-hip 4-pitched (Danish);
- gable semi-hip (Dutch);
- tent (4 identical hip slopes);
- hip with a broken slope.
Calculation features
The process of calculating a hip roof can be divided into three stages:
- The choice of the angle of inclination of the slopes, depending on the type of roofing material.
- Determination of the lengths of the structural elements of the roof, based on the drawings of the cross-section of the building and the plan of the floor to be covered.
- Selection of the cross section and pitch of the rafters along their length, taking into account the type of wood used and the normative snow load of the construction region.
The angle of inclination of the slopes depends on the material of the roof. Therefore, when making a diagram of a truss structure, it is necessary to take into account its minimum value recommended by the standards (in degrees):
- for slate - 22;
- soft tiles - 11;
- metal tiles - 14;
- corrugated board - 12;
For a roof made of a waterproof membrane, the angle of inclination of the slopes can be any. Based on the minimum allowable slope value, its actual value is chosen depending on the purpose of the attic space.
If a living space is built under the hip roof, then its slopes should have an angle of inclination that allows comfortable movement within the "living area".
The actual length of the structural elements of the roof is easiest to determine by drawing the truss system in a scale convenient for measurements.
Knowing the length of the rafters, their pitch and cross section can be found in the table. Here the dependence of the geometric dimensions of the rafters on the type of wood and the magnitude of the snow load of the construction region is indicated.
Selection of the section of the rafters and their pitch depending on the length, type of wood and snow load
This table can also be successfully used in reverse order. By choosing the pitch and section of the rafters, the type of wood and the amount of snow load, you can easily find the maximum length of the rafters allowed by the standards.
The cross section of the Mauerlat beam must be no less than the cross section of the rafter leg. Most often it is 10x15 cm, 15x15 cm or 15x20 cm. The cross section of the ridge beam is usually equal to the cross section of the rafter legs.
For the lathing, a board 25 mm thick is used, stuffing it at the interval recommended for the selected roofing. For the installation of a solid flooring on the roof frame, an OSB plate with a thickness of 12-15 mm is used.
Mounting Features
Judgments circulate on the Internet that the installation of a hip roof is very difficult and time-consuming. There is some truth in this, but, in essence, the assembly of this structure is not much different from the construction of a conventional gable roof.
Hip roof for a gazebo - invaluable assembly experience
The process of installing a hip roof truss system includes several stages:
1. A mauerlat is laid along the perimeter of the walls. In this case, it is placed on steel threaded studs embedded in the masonry and tightened with nuts. At the docking sites (at the corners of the house and at the splicing points), landing planes are selected on the Mauerlat, cutting off half of the beam.
2. The further sequence of work depends on the width of the overlapped span (roof area). This point must be taken into account at the stage of drawing up a drawing or a roof diagram.
Racks supporting the ridge beam can be dispensed with if the width of the building (span) is less than 7.5 meters. With a house width of 6 to 7.5 meters, the hanging rafters in the upper part must be connected with a crossbar (a beam with a section of 50x100 mm).
If the width of the building is small (up to 6 meters), then lower puffs (floor beams) will be sufficient to ensure the rigidity of the truss system.
Having laid the Mauerlat, the central axis is marked on the end walls. Two extreme racks are set along it and fastened with temporary struts to the floor beams. If the building is covered with panels, then a central beam is laid along them (the cross section is the same as that of the Mauerlat). The lower ends of the extreme racks are fixed on it.
The initial stage of installation - the installation of vertical racks under the ridge
Intermediate racks are placed in increments of 1-2 meters. If the house is covered with beams, then the racks can be mounted on them, fixing them with brackets or self-tapping screws.
3. A ridge beam is laid on the racks, the places for installing the rafter legs are marked on the Mauerlat and they are mounted. To attach the rafters to the Mauerlat, a notch is used (a cutout is made on the rafter leg for tighter contact).
Cutting the rafter leg into the Mauerlat increases the reliability of the joint
4. Hip (sloping, diagonal) rafters are fixed with the lower end to the Mauerlat, and with the other end to the junction of the ridge beam and the extreme ordinary rafters.
After that, short rafter legs (spiders) are attached to them.
Anyone who wants to make a hip roof with their own hands must remember that the main attention here is paid to the quality of assembly of nodes. It is very responsible to approach the installation of the ridge beam, the joining of the diagonal rafters with the ridge and with the sprigs.
The joint of the sprig with the hip rafter
On large roofs, the standard length of the beam (6 meters) is not enough to make a solid diagonal rafter. Therefore, it is assembled from two parts, securely fixing them together.
The overhangs of the hip roof are made by stuffing on the rafter legs trimmings of a beam or a thick board (filly) that extend beyond the perimeter of the walls by 50-100 cm.
Having finished the installation of the truss system, the crate is nailed to it and the roofing material is laid.
The roof protects the building from the penetration of adverse atmospheric phenomena into the premises. To guarantee the reliability and strength of roof structures, it is necessary to choose the right type of roof and know all its structural elements. The load from the coating and snow cover is taken over by the truss system. Most often, a hip roof becomes the best option. But what is she like?
What is a hip
The design of the hip roof is a four-pitched system. In the center of which is a ridge or just a junction point of the slopes. Roof slope - sloping surface,
This type is best suited for covering buildings that are close to a square in terms of, that is, having a large width. During the construction, there are no gables, the walls around the entire perimeter are of the same height. The optimal value of the angle of inclination in degrees will be a value from 20 to 45.
Its main parts are:
Structural elements of a hip roof
The device of the hip roof truss system assumes the presence of the following elements:
hip roof elements - Rafter legs (rafters)- the main load-bearing structures (only available for rectangular hips) are inclined beams, resting at one end on the Mauerlat, and at the other on the ridge crossbar.
- Narozhniki- rafter legs, resting with the upper and lower ends on the sloping legs. Mauerlat often acts as a lower support. These elements are the main structural parts of a square hip roof. With a rectangular shape of the building in plan, they are used in conjunction with conventional rafters, the pitch and section are the same.
- Slanted legs- diagonal rafters forming end slopes. At the lowest point, they rest on the corner of the building. They usually have a larger cross section than ordinary rafter legs. They are relied upon by the guards.
- Ridge crossbar- a horizontal beam located in the central part of the building (absent with a square building). The design of the hip roof assumes the presence of racks along it (with a gable roof, the support occurs on the gables). It is the top support for inclined beams.
- Mauerlat- a beam installed along the edge of the wall from the inside. Provides lower support for the rafters, evenly distributes the vertical component of the load along the walls and perceives the horizontal (thrust). In a log or log house, the upper crown of the wall structure serves as the Mauerlat.
- Struts- inclined racks supporting rafters, slanted legs or crossbar. Intermediate supports allow you to reduce the cross section of the bearing elements. The hip roof truss system involves the installation of struts at an angle of 60 or 45 degrees relative to the horizontal plane.
- Racks- vertical intermediate supports.
- Sprengel- horizontal beams diagonally laid in the corner of the building. They provide support under the rack set to support the skew leg. This design transfers the load to perpendicular walls and is used when it is not possible to install the rack on the floor. For example, it is impossible to install a support post in the middle of a reinforced concrete slab, since the slab can withstand a certain load, in which the main component is the mass of furniture, equipment and people.
- fight- a horizontal element that tightens the rafters preventing them from moving apart, can be located at the Mauerlat level or higher.
- crate- boards or bars of small section, laid perpendicular to the rafters on top of them. They serve as the basis for roofing material. A do-it-yourself hip roof is often erected with the installation of a sparse crate (through one board), but you need to remember that in especially critical places (valleys, cornices) the crate is solid.
- Control grille- bars or boards of small section. In the construction of the roof are not always used. They are installed on top of the rafter legs, parallel to them under the crate. Needed to raise the crate above the insulation between the rafters, thereby providing the necessary ventilation gap.
- Filly- boards attached to the lower end of the rafters, providing the necessary overhang of the eaves.
Some of these elements are missing in the construction of a simple roof, the mandatory structures for the hip are:
- conjurers;
- sloping legs;
- Mauerlat;
- crate.
Preparatory work
Before you make a hip roof, you need to make several design decisions, namely:
Table for calculating the pitch of hip roof rafters - rafter step;
- section of rafters and sloping legs;
- roof slope.
The step of the rafters depends on the purpose of the roof space and the width of the building. The larger the span of the rafter leg, the less you have to take a step. If the space under the roof will be used as an attic floor or a heated attic, additional insulation will be required.
Warming is carried out using three types of materials, depending on which the step is selected:
- rigid mineral wool slabs - rafter pitch 58 or 118 cm;
- polystyrene foam (polystyrene or extruded) - rafter pitch - 60 cm;
- polyurethane foam (foam) - any step.
Installation diagram of rafters in accordance with roof windows These values are due to the convenience of workers. If we take a step of supporting structures of 58 cm when using mineral wool, then convenient installation of standard slabs with a width of 60 cm will be ensured.
The manufacturer recommends that the thermal insulation material be a few centimeters wider than the distance between the clean rafters, this will ensure the most snug fit and prevent the appearance of cracks and cold bridges. The appointment of a size of 118 cm provides for laying plates in two strips in width.
When using expanded polystyrene with a standard width of 60 cm, installation with a spacer is not required. The material is held between the supporting structures by glue, special nails and the bottom battens. The gaps between the wooden elements and the slabs of heat-insulating material are filled with mounting foam or sealant.
Polyurethane foam in the form of foam removes the requirements for rafter spacing. The material can take any form given to it, which provides freedom of action in this matter.
If skylights are installed, their dimensions must also be taken into account. The clear distance between the inclined beams is taken 4-6 cm more than the width of the window. If roof insulation is not provided, choose a convenient rafter pitch, usually 1 meter.
Supporting the rafter legs on the truss The cross section of the rafters is taken by calculation, but in the general case, you can specify the following values:
- 5x15 cm for spans up to 3 m;
- 5x20 cm for spans up to 4 m;
- 7.5x17.5 for spans up to 5 m;
- 7.5x200 for spans up to 6 m.
The values are given for a rafter pitch of 0.9. As the distance increases, the cross section must also increase. The cross section of the oblique legs is also taken a little more.
Installation
Do-it-yourself hip roof is a feasible task, but you need to know the main knots for connecting structures.
The connection of the rafter legs at the top point depends on the type of rafter. They can be:
- layered;
- hanging.
The top ones rest on the crossbar. To do this, a notch is made in a horizontal beam. Fastening is done with nails.
Hanging rafter legs provide for the absence of a crossbar. They are most often used when it is necessary to organize a free layout and the absence of a central wall. In this case, there is no support under the junction. Inclined beams are fastened together with nails. Additionally, at the junction, wooden linings 22-25 cm thick are provided on both sides of the rafter legs. These linings are tightened with studs or bolts.
To fix the rafters at the lowest point, a notch is made in the Mauerlat. Inclined elements are installed and fixed with nails or metal corners. The spears are joined end-to-end to the slanting elements, at the same level.
To resist the wind loads of the roof, trying to rip it off, twists of wire are provided that connect the lower end of the rafters to the wall. In the wall, the twist is fixed on a ruff (fixing device).
When building walls from wooden materials, brackets can be used instead of twists. Twists or staples are installed on each rafter leg or through one.
If you build the truss system correctly with a competent selection of the section and the pitch of the rafters, the roof will last a long time.
Hip roofs have many advantages. They are beautiful, reliable in all weather conditions, the four-sided design allows you to effectively insulate the house from the side of the roof. Some difficulty is the device of the truss system. We will deal with its schemes and calculations in this article.
Hip roofs, sometimes called Dutch and Danish, are distinguished by good quality, reliability and spectacular European design. The truss base of such roofs consists of many basic and reinforcing elements that require drawings or three-dimensional drawings, accurate calculations and execution.
Hip roof varieties
Hip roofs, in addition to the basic classical design, consisting of two trapezoidal slopes and two triangular end hips, also include their varieties:
- Half hip double slope.
- Semi-hip four-slope.
- Shatrovaya.
- Hip-pediment.
Each variety has its own scheme of the truss system. Next, we consider and calculate the classic hip roof.
Scheme and main elements
To perform the calculation of the truss system, you need to familiarize yourself with its basic scheme, the main and auxiliary elements.
The main elements of the truss system
The main elements include (see the figure below):
- Mauerlat. It is a beam fixed along the perimeter of the outer walls, indented from the outer edge. Attaches to the wall. Mauerlat disperses the load from the pressure of the rafters, connects the truss system with the walls of the house, and is the basis of the roof.
- Skate. Upper crossbar for fastening the rafters of the roof slopes. The height of the ridge depends on the angle of inclination of the slopes. Gives the system rigidity and strength.
- The central rafters of the slopes. The ends of the ridge are supported on the sides of the Mauerlat. There are 4 such elements in the system. - 2 pcs. on every slope.
- The central rafters of the hips. The ends of the ridge are supported on the end sides of the Mauerlat. There are 2 such elements in the system. - 1 pc. on every hip.
- Skew legs (diagonal, corner rafters). Connect the corners of the Mauerlat with the ends of the ridge. They are part of the supporting structure. There are 4 of them in the rafter system.
- Intermediate rafters of slopes. They are installed parallel to the central rafters of the slope between them with the same pitch, relying on the side of the Mauerlat and the ridge beam. If the length of the ridge is insignificant, they may not be used.
- Shortened rafters of slopes. They are installed parallel to the central rafters of the slopes and have a variable length - the closer to the corner, the shorter. They rely on the side of the Mauerlat and slanting legs. The number of elements depends on the installation step.
- Shortened hip rafters or sprigs. They are installed parallel to the central rafters of the hips and have a variable length - the closer to the corner, the shorter. They rely on the end part of the Mauerlat and oblique legs. The number of elements depends on the installation step.
Scheme and main elements of the truss system
You can read more about attaching rafters to the Mauerlat in our article.
The above elements are basic, basic. Other elements are designed to reinforce the main ones and are used in critical buildings, for example, for residential buildings:
- Vertical racks for supporting the ridge beam. They rely on crossbars (see below), laid parallel to the end of the house or a bed located along the longitudinal axis of the building (if there is a main wall under it).
- Crossbars or puffs. The rafter legs of the slopes are connected in pairs. They serve as a support for racks and diagonal struts (see below). They can serve as floor beams if they are built into the Mauerlat or installed directly into the longitudinal walls of the house. If the puffs are placed closer to the ridge, they will become the basis of the attic ceiling.
- Diagonal braces (braces). They are used to increase the rigidity of the system if the length of the rafters is more than 4.5 m. The use of struts allows you to reduce the cross section of the rafters, which they reinforce.
- Sprengel. Beam installed in the corners of the Mauerlat. Serves for mounting a stand that supports and reinforces the oblique leg.
- Wind beam. It serves to resist the deformation of the rafter legs in gusty, strong winds. It is attached to the rafters of the slopes from the inside, obliquely, on one or both sides - it depends on the wind load in the construction area.
- Filly. An element of a smaller section than the rafters themselves. Extends the leg of the rafters to provide a roof overhang when a single piece is not available due to limited lumber length or for cost reasons.
Gain elements
Calculation of the truss system
The calculation of the system includes the choice of the angle of inclination of the slopes and hips and the calculation of the lengths of its main and auxiliary elements.
The choice of the angle of inclination of the longitudinal and end slopes
The choice of the angle of the slopes and hips ranges from 25-45 ° and depends on the desire to have an attic, the roofing material adopted, the assessment of static (roof weight) and dynamic (wind, snow) loads.
In hipped roofs, the angle of inclination of the hips and slopes is the same. In hip roofs, the same angles are also often taken in terms of aesthetics, but they may differ if this is the architect's idea.
Recommendations for the use of roofing materials
For a better understanding of the calculation algorithm, let us consider as an example the hip roof of a house with sides of 8 and 12 m, and a ridge height of 2.5 m. We will take the angle of inclination of the slopes at 35 °, and the angle of inclination of the hips - 45 °.
Calculation of the main truss elements
The classic hip roof consists of two slopes in the form of trapezoids connected in a ridge, and two hips - end slopes in the form of triangles.
First you need to remember some formulas from the school algebra curriculum. This is the ratio of the lengths of the sides of a right triangle, expressed in terms of the trigonometric function of the angle and the Pythagorean theorem.
Trigonometric functions of an acute angle of a right triangle
Let's depict the frame of the truss system in an axonometric view:
Let's calculate the main elements of the truss system.
1. Calculate the length of the central hip rafter CD, which is the height of an isosceles triangle (hip) and the hypotenuse of a right triangle whose height is equal to the height of the ridge (CE = 2.5 m). Angle of inclination of the hip α = 45°. Sin 45° = 0.71 (according to the Bradis table).
According to the trigonometric relation:
- CD = CE / sin α = 2.5 / 0.71 = 3.52 m
2. Determine the length of the skate K. To do this, from the previous triangle we find the length of the base ED, using the Pythagorean theorem:
House length: BL = 12 m.
Skate length:
- CF \u003d 12 - 2.478 x 2 \u003d 7.044 m
3. The length of the corner rafters CA can also be obtained from the Pythagorean theorem for triangle ACD. Half the width of the house AD = 8 / 2 = 4 m, CD = 3.52 m:
4. The length of the central rafters of the slope GF is the hypotenuse of the triangle, the legs of which are the height of the ridge H (CE) and half the width of the house AD:
The intermediate rafters of the slopes have the same length. Their number depends on the pitch and section of the beams and is determined by calculating the total load, including weather.
These tables correspond to the atmospheric loads of the Moscow region
| Rafter pitch, cm | Rafter length, m | ||||||
| 3,0 | 3,5 | 4,0 | 4,5 | 5,0 | 5,5 | 6,0 | |
| 215 | 100x150 | 100x175 | 100x200 | 100x200 | 100x250 | 100x250 | — |
| 175 | 75x150 | 75x200 | 75x200 | 100x200 | 100x200 | 100x200 | 100x250 |
| 140 | 75x125 | 75x125 | 75x200 | 75x200 | 75x200 | 100x200 | 100x200 |
| 110 | 75x150 | 75x150 | 75x175 | 75x175 | 75x200 | 75x200 | 100x200 |
| 90 | 50x150 | 50x175 | 50x200 | 75x175 | 75x175 | 75x200 | 75x200 |
| 60 | 40x150 | 40x175 | 50x150 | 50x150 | 50x175 | 50x200 | 50x200 |
Let's compare the maximum, average and minimum section of a beam with a length of 4.717 m (see the values for 5.0 m).
At section 100x250 mm the step will be 215 cm. With a ridge length of 7.044 m, the number of intermediate rafters will be: 7.044 / 2.15 = 3.28 segments. We round up - up to 4. The number of intermediate rafters of one slope - 3 pcs.
- 0.1 0.25 4.717 3 2 = 0.708 m 3
At section 75x200 mm the step will be 140 cm. With a ridge length of 7.044 m, the number of intermediate rafters will be: 7.044 / 1.4 = 5.03 segments. The number of intermediate rafters of one slope - 4 pcs.
The volume of lumber for both slopes:
- 0.075 0.2 4.717 4 2 = 0.566 m 3
At section 50x175 mm the step will be 60 cm. With a ridge length of 7.044 m, the number of intermediate rafters will be: 7.044 / 0.6 = 11.74 segments. We round up - up to 12. The number of intermediate rafters of one slope - 11 pcs.
The volume of lumber for both slopes:
- 0.05 0.175 4.717 11 2 = 0.908 m 3
Therefore, for our geometry, the optimal option from the point of view of economics would be a section of 75x200 mm with a step of 1.4 m.
5. To calculate the lengths of the shortened slope rafters MN, you again have to remember the school curriculum, namely the triangle similarity rule.
Similar triangles on three sides
The large triangle that we need to reinforce with shortened rafters has known dimensions: GF = 4.717 m, ED = 2.478 m.
If the shortened rafters are installed with the same step as the intermediate ones, their number will be 1 in each corner:
- 2.478 m / 1.4 m = 1.77 pcs.
That is, two segments are formed with one shortened rafter in the middle. A small triangle will have a leg, 2 times smaller than ED:
- BN = 2.478 / 2 = 1.239 m
We compose the proportion of similar triangles:
Based on this ratio:
At this height, the cross section of the rafters is taken according to the table - 75x125 mm. The total number of shortened rafters of both slopes is 4 pcs.
6. Determining the length of shortened hip rafters (spreaders) is also performed from the ratio of similar triangles. Since the length of the central hip rafters CD = 3.52 m, the step between the shortened rafters may be greater. With AD \u003d 4 m, shortened rafters with a step of 2 m will be one on each side of the central hip rafter:
- (2 3.52) / 4 = 1.76 m
With such a height, we take the rafter section 75x125 mm. The total number of shortened rafters of both hips is 4 pcs.
Attention! In our calculations, we did not take into account the overhang.
Calculation of the roofing area
This calculation comes down to determining the areas of a trapezoid (slope) and a triangle (hip).
Let's do the calculation for our example.
1. The area of one hip with CD = 3.52 m and AB = 8.0 m, taking into account the overhang of 0.5 m:
- S \u003d ((3.52 + 0.5) (8 + 2 0.5)) / 2 \u003d 18.09 m 2
2. The area of one slope at BL = 12 m, CF = 7.044 m, ED = 2.478 m, taking into account overhangs:
- S \u003d (2.478 + 0.5) ((12.0 + 2 0.5) + 7.044) / 2 \u003d 29.85 m 2
Total roofing area:
- S Σ \u003d (18.09 + 29.85) 2 \u003d 95.88 m 2
Advice! When buying material, consider cutting and inevitable losses. The material produced by large area elements is not the best option for hip roofs.
