Types and schemes of truss systems: an overview and recommendations for the installation of a roof truss system. Installation of rafters: step by step instructions Choosing a truss system

The roof of the building protects it from the cold, rain and wind. It is as important an element as the exterior walls and foundation. The truss system is the supporting frame of the roof. It takes on all the loads: from structures, from snow and wind. In order to avoid problems during operation, the roof structure of the house must be strong and reliable. Do-it-yourself installation of the truss system should be performed only after careful preparation and study of all the necessary information.

Roof and roof

Before you start building the roof of a private house, you need to distinguish between two concepts. Non-professionals are often confused, but builders clearly separate the definitions of roof and roofing. The roof is the entire structure that separates the building from the street above. The roof structure of a private house includes rafters, all other load-bearing elements, thermal insulation material, roofing.

Rafters - load-bearing roof structures

The roof is the top part of the roof. It is also roofing.. Roofing requires careful selection of material. After all, the reliability of waterproofing and comfort of living will depend on it.

System Requirements

To properly mount the truss system with your own hands, you must take into account a certain set of rules. Without taking them into account, the structure will not be able to effectively resist negative influences from outside.

The first thing to consider is durability. All elements must withstand the load without destruction. The device of the roof truss system involves a preliminary calculation of the supporting structures for the first limit state. It is he who checks the elements of the truss system for strength.

The truss system must be strong and rigid

The second requirement is rigidity. The maximum deflection is taken into account here. The roof structure of a wooden house or any other should not sag too much. Permissible deformations in the middle of the span are equal to the length of this span divided by 200. Before starting construction, the design of the truss system must be calculated according to the second group of limit states - for rigidity.

Do-it-yourself roof rafters are made taking into account that the structure is light in weight. Otherwise, the load on the walls and foundations increases greatly. It is for this reason that wood has become widespread as the main material. The wooden truss system has sufficient strength, but weighs relatively little. Attention should be paid not only to the design of the roof, but also to correctly choose the roofing material. It shouldn't be too heavy. Ceramic tiles have lost their popularity not only because of the cost, but also because the roof of the house, its walls and foundations must be reinforced under it.

The weight of the roofing material for a wooden truss structure should not be too large

Special requirements are placed on the quality of the material. The manufacture of wooden elements should be carried out only from good raw materials. It is worth considering the following recommendations:

• For the main elements, wood of 1 or 2 grades is used. Grade 3 can only be used for battens and other small parts.
• Rafter structures of pitched roofs are recommended to be made from coniferous species. They are more resistant to decay and other troubles because they contain resin. With the same cross section, the allowable span for hardwood will be less.
• Before starting work, all elements must be treated with an antiseptic. This stage of preparation allows you to prevent many troubles in the future. Also, if desired, you can treat the tree with flame retardants. This will increase fire resistance.
• It is better to buy wood from the northern regions, which is harvested in the winter. This material is of the highest quality.

Construction parts

The scheme of the truss system includes many elements. To understand the drawings and correctly perceive the information, you need to know at least the basic ones. So what is the roof made of?

Ridge, cornice and slopes - the main part of the roof

First of all, it is a ridge, a cornice and slopes. These elements are the main parts. The ridge is the topmost part of the structure. Cornice or overhang - lower. Slopes are inclined surfaces that are located between the ridge and the eaves.

The construction of the truss system requires knowledge of the load-bearing elements. These include:

• Mauerlat - timber, which is laid along the edge of the walls of the building. Mauerlat is needed to evenly transfer the load from the rafter legs, which are supported pointwise. Usually, for its manufacture, a bar with dimensions of 150x150 mm or 200x200 mm (for large buildings) is used.
• Rafter legs are inclined beams that transfer the load from the own weight of the roof, snow and wind to the Mauerlat. Such beams are usually installed from the ridge to the eaves. But when erecting a hip roof, elements appear that have only one of the specified points. They are supported on a ridge or on a cornice. Such details are called spawns. They usually have the same section as the rafters. In fact, sprigs are rafter legs cut off on one side.
• Run - a beam on which the elements of the roof rest. The run can be installed under the racks. Another option is a ridge run (crossbar). The rafters rest on it at the highest point. The cross section of the run depends on its span, usually 200x200 mm is taken.
• Slanting legs are needed only for hip roofs. They are diagonal rafters resting on the Mauerlat at the corners. The cross section is taken enlarged, usually 150x200 or 100x200 mm.
• The design of the wooden roof involves the presence of puffs, struts and racks. They are designed to reduce the load on the main elements. When building a house with your own hands, it is important to remember that the racks cannot be supported on the floor span. Installation is possible only on the underlying walls or on runs thrown between the walls. It is possible to mount such elements on the ceiling only if it is designed for such a load and reinforced in the desired area.
• The crate is needed in order to make the base under the coating. For metal tiles and seam roofing, the lathing can be sparse from boards with a thickness of 32-40 mm. For bituminous tiles, you need a solid base of boards 25-32 mm thick or moisture-resistant plywood.
• In order to make a departure of the cornice, filly is installed. They become a continuation of the rafters. The filly is attached to the rafter for a length of at least 1 m. The section of the element is usually taken as 50x100 mm.

Bearing elements of the hip roof

Another element of the truss system is the truss. This is a one-piece structure, which consists of rafters, puffs, struts and racks, rigidly interconnected. The truss has a triangular shape, and inside it is divided into several smaller triangles, which provides it with good stability.

Roof shapes

Pitched roof roofs come in a variety of shapes. It is worth highlighting here:

Types of rafters

There are two designs:

• with layered rafters;
• with hanging rafters.

The device of the roof of a wooden house is possible only with the use of the first. This is due to two rules:

• hanging rafters must be rigidly attached to the Mauerlat;
• in a wooden house, the rafters must be hinged to the Mauerlat.

These two statements contradict each other, so the truss system of a wooden house can contain only layered elements.

In a wooden house, only layered rafters are mounted

Layered beams are elements that rely on the Mauerlat at the bottom point and on the ridge run at the top.. This allows you to reduce the horizontal thrust that acts on the walls when the rafters try to part and take a horizontal position. Elements can be reinforced with struts or struts. Contractions in this case can be placed through one pair of legs.

Hanging tanks rest only at the lowest point on the Mauerlat. Above, they simply rest against each other. So that the system of wooden elements does not part, be sure to make puffs. It is better to install them on each pair of legs. This option is characterized by a strong thrust effect on the outer walls, but it allows you to get more free space inside the attic.

Connections

Before you make a rafter system with your own hands, you need to carefully study the nodes. To build your house, it is not worth saving time or money. Only in this case the result will please for many years.

The main nodes of the connection of the rafters

The attachment points of the roof truss system, which deserve special attention, are as follows:

• fastening the Mauerlat to the wall;
• fastening rafters to the Mauerlat;
• fastening the rafters at the top point;
• splicing rafters along the length.

Mauerlat to the wall

This knot can be done in several ways. The choice largely depends on the material of the wall. The construction of a building from brick, blocks or concrete allows the use of the following methods:

• on the wire;
• on staples;
• on studs;
• on the anchor with the device of a monolithic belt along the edge of the wall.

The connection of the Mauerlat with the wall during the construction of brick buildings is carried out using anchors

Rafter to Mauerlat

Fasteners are carried out in two ways:

• tough for buildings made of brick, concrete or concrete blocks;
• articulated for wooden houses.

Rigid fastening can be with or without a notch. The cut is recommended to be done on the rafters, and not on the Mauerlat, as this weakens it. In both cases, the leg is rigidly fixed with nails, screws, staples or metal corners.

With rigid fastening, it is better to make a cut on the rafters and fix the structure with fasteners

For hinged fastening, a special part is used - a sled. They allow the beam to move without obstacles when the walls of the building shrink.

Articulation allows the beam to move

Additionally, rafter legs are attached to the wall. This is necessary so that the roof is not blown off by the wind. For fastening, a twist of two wires with a diameter of 4 mm is used, fixed to the wall on an anchor or ruff. In a wooden house, twisting can be replaced with staples. Fastening is carried out on each beam or through one.

At the skate level

Layered elements rest on a ridge run with a notch. Additionally, on both sides they make an overlay from the board. An overlay is also needed for hanging elements. It can be wooden or metal with holes for self-tapping screws.

The ridge run and rafters are connected using a cut

Rafter splicing

There are several methods for splicing roof rafters with your own hands. The choice between them largely depends on the experience of the master. The splicing point is located at a distance of 0.15 of the span from the support. At the same time, not only the ridge run and the Mauerlat are considered supports, but also the struts and racks.

Splicing rafters along the length

There are five ways:

• butt joint;
• oblique cut;
• overlap;
• compound legs;
• paired legs.

To build a quality roof, you need to carefully study the technology, choose the right type of rafters and how to connect elements at important nodes. This is especially important when building a truss system with your own hands.

As a rule, softwood lumber is used.

For various elements and details of the wooden truss system, a tree of a certain type and variety is used. When using lumber in a rafter-beam system, the following properties and indicators of wood should be taken into account: bending strength, compression, chipping, wood density and its moisture content.

Wooden truss structures must necessarily correspond to the special degree of fire resistance of the room. They must necessarily be treated with special fire retardants and.

There is a huge variety of options and elements for the device of wooden truss structures. There are the following types of roof structures: layered or hanging rafters, combined, with a puff, etc. The most popular truss structures are layered and hanging.

To avoid sagging of the entire structure to the lower end of the beam, using band steel clamps, a horizontal puff is attached to support the beams of the entire attic floor. If the span is up to 12 m, then struts are introduced into the structure of the rafters, which reduce the estimated length of all rafter legs.

Hanging wooden rafters work both in compression and bending.

Below we consider the types of truss structures:

1. conventional hanging rafters
2. double hanging rafters

It is not uncommon to increase the entire area of ​​\u200b\u200bthe attic in the system of wooden hanging rafters, puffs are not used, but struts are used.

Mauerlat roof

In this case, the rafter legs are cut into the Mauerlat itself. The lower plane should lie on the wall, and certain cuts must be made in the upper one for proper connection with the rafter legs.

All struts rest against the end of the wooden one. In this case, the loads that the tightening would compensate for are directly transferred to all walls. As a result, this solution of a wooden truss system is possible only if there is a special massive structure.

Hanging rafters are parts and elements of truss structures that are located in the same vertical plane and are connected to each other using cuttings, bolts, nails, clamps and brackets.

There is a combined truss system - this is the installation of both a layered and a hanging truss structure, which alternate in turn. Where there are no intermediate supports, hanging truss systems are used, and where present, layered truss systems.

Rafter with tightening

They are used for spans up to 15 m. in special puffs. They are mounted at the height of the building between two rafters and tied. And longitudinal struts will prevent lateral bending.

Roof rafter tightening

All structures with retaining wooden beams must be assembled in the form of truss structures reinforced with special supports that will rest on the transverse beams and all load-bearing walls, as well as in the form of trussed systems. The concept of sprengel is a structural element of the type of an open triangular rod system, which is attached to the main truss supporting structures.

The structural rigidity of this roof is given by a longitudinal brace or strut. The use of struts reduces the overall load on the entire structure. Vertical struts are usually attached to or uprights using notches, trunnions, steel plates.

Truss hanging wooden truss systems

Sprengel

The entire load from the rafter legs goes to the racks, which transfer it further to the main carriers. With this design, the load will be distributed between all load-bearing walls. Racks are attached at the ends of the main load-bearing walls. The lower ends of all racks are fixed with suspension trunnions.

Sprengel beams are produced from solid solid wood or glued plank array. Usually, they are of small height. Good and high-quality bearing capacity of trussed beams is carried out with the help of a trussed system and wooden beams supporting it.

Schrengel beams can cover huge spans. Sometimes they are completed with steel belts.

Complex structures of the truss system

Produced by the type of truss trusses. Lattice trusses are divided into types according to the shape of their gaps: triangular, trapezoidal or parallel belts. Usually, lattice trusses are produced symmetrically, but other options are possible, for example,. A common lattice truss includes top and bottom chords, racks and braces.

A reliable and high-quality connection of load-bearing wooden structures with central supports into one common system is called a frame. Racks and beams connected in a frame are necessarily fastened or included in each other. To date, there are two main types of frames - two-hinged and three-hinged. Double-hinged frames are equipped with a crossbar that runs across the entire width of the finished frame. These frames are best suited for structures with a small angle of inclination. Three-hinged frames consist of two equal halves, which support each other in the region of the roof ridge. Three-hinged frames are used where a more significant angle of inclination is needed.

Calculation of truss structures and the final selection of their elements and parts trust specialists. There are huge loads. In addition to its own weight, it is affected by wind loads, heavy rains, hail, snow and ice. The roof quite often undergoes a variety of: from temperature to seismic.

Rafters perform a number of significant roofing functions. They set the configuration of the future roof, perceive atmospheric loads, and hold the material. Among the rafter duties are the formation of even planes for laying the coating and providing space for the components of the roofing pie.

In order for such a valuable part of the roof to flawlessly cope with the listed tasks, information about the rules and principles of its construction is needed. The information is useful both for those who are building a gable roof truss system with their own hands, and for those who decide to resort to the services of a hired team of builders.

In the device of the truss frame for pitched roofs, wooden and metal beams are used. The starting material for the first option is a board, log, beam.

The second is constructed from rolled metal: a channel, a profile pipe, an I-beam, a corner. There are combined structures with steel most loaded parts and wood elements in less critical areas.

In addition to the "iron" strength, the metal has a lot of disadvantages. These include heat engineering qualities that do not satisfy the owners of residential buildings. Disappointing need for the use of welded joints. Most often, industrial buildings are equipped with steel rafters, less often private change houses assembled from metal modules.

In the case of self-construction of truss structures for private houses, wood is a priority. It is easy to work with it, it is lighter, “warmer”, more attractive in terms of environmental criteria. In addition, nodal connections do not require a welding machine and welder skills.

Rafters - a fundamental element

The main "player" of the frame for the construction of the roof is the rafter, among the roofers called the rafter leg. Beds, braces, headstocks, girders, puffs, even Mauerlat may or may not be used depending on the architectural complexity and dimensions of the roof.

The rafters used in the construction of the gable roof frame are divided into:

• Layered rafter legs, both heels of which have reliable structural supports under them. The lower edge of the layered rafter rests on the Mauerlat or on the ceiling crown of the log house. The support for the upper edge can be a mirror analogue of an adjacent rafter or a run, which is a beam horizontally laid under the ridge. In the first case, the truss system is called spacer, in the second, non-spacer.
• hanging rafters, the top of which rests against each other, and the bottom is based on an additional beam - puff. The latter connects the two lower heels of adjacent rafter legs, resulting in a triangular module called a truss truss. The tightening dampens the tensile processes, so that only a vertically directed load acts on the walls. The design with hanging rafters, although it is spacer, does not transfer the spacer itself to the walls.

In accordance with the technological specifics of the rafter legs, the structures constructed from them are divided into layered and hanging. For structural stability, they are equipped with struts and additional racks.

For the arrangement of supports for the top of the layered rafters, beds and girders are mounted. In reality, the truss structure is much more complicated than the elementary patterns described.

Note that the formation of a gable roof frame can generally be carried out without a truss structure. In such situations, the alleged planes of the slopes are formed by slegs - beams laid directly on the bearing gables.

However, we are now specifically interested in the device of the gable roof truss system, and it can involve either hanging or layered rafters, or a combination of both types.

Subtleties of fastening rafter legs

The rafter system is fastened to brick, foam concrete, aerated concrete walls through the mauerlat, which in turn is fixed with anchors.

Between the Mauerlat, which is a wooden frame, and the walls of these materials, a waterproofing layer of roofing material, waterproofing, etc. is necessarily laid.

The top of the brick walls is sometimes specially laid out so that something like a low parapet is obtained along the outer perimeter. So it is necessary that the Mauerlat placed inside the parapet and the walls do not burst the rafter legs.

The rafters of the frame of the roofs of wooden houses rest on the upper crown or on the ceiling beams. The connection in all cases is made by cutting and duplicated with nails, bolts, metal or wooden plates.

How to do without furious calculations?

It is highly desirable that the cross section and linear dimensions of the wooden beams be determined by the project. The designer will give clear calculation justifications for the geometric parameters of the board or beam, taking into account the entire range of loads and weather conditions. If there is no home design development master at his disposal, his path lies on the construction site of a house with a similar roof structure.

You can ignore the number of storeys of the building under construction. It is easier and more correct to find out the required dimensions from the foreman than to find them out from the owners of a shaky unauthorized construction. After all, the foreman is in the hands of documentation with a clear calculation of the loads per 1 m² of roof in a particular region.

The installation step of the rafters determines the type and weight of the roofing. The heavier it is, the smaller the distance between the rafter legs should be. For laying clay tiles, for example, the optimal distance between the rafters will be 0.6-0.7 m, and for a profiled sheet, 1.5-2.0 m is acceptable.

However, even if the step required for the correct installation of the roof is exceeded, there is a way out. This is a reinforcing counter-lattice device. True, it will increase both the weight of the roof and the construction budget. Therefore, it is better to deal with the step of the rafters before the construction of the rafter system.

Craftsmen calculate the pitch of the rafters according to the design features of the building, tritely dividing the length of the ramp into equal distances. For insulated roofs, the step between the rafters is selected based on the width of the thermal insulation boards.

On our website you can find, which may also help you a lot during construction.

Rafter structures of layered type

Rafter structures of the layered type are much simpler in execution than their hanging counterparts. A justified plus of the layered scheme is to provide full ventilation, which is directly related to the longevity of the service.

Distinctive design features:

• Mandatory presence of support under the ridge heel of the rafter leg. The role of the support can be played by a run - a wooden beam resting on racks or on the inner wall of the building, or the upper end of an adjacent rafter.
• The use of Mauerlat for the construction of a truss structure on walls made of brick or artificial stone.
• The use of additional runs and racks where the rafter legs, due to the large size of the roof, require additional support points.

The minus of the scheme is the presence of structural elements that affect the layout of the internal space of the operated attic.

If the attic is cold and the organization of useful premises is not supposed to be in it, then the layered construction of the truss system for the installation of a gable roof should be preferred.

A typical sequence of work on the construction of a layered truss structure:

• First of all, we measure the height of the building, the diagonals and the horizontalness of the upper cut of the skeleton. When identifying vertical deviations of brick and concrete walls, we eliminate them with a cement-sand screed. Exceeding the heights of the log house we squeeze. By placing chips under the Mauerlat, vertical flaws can be dealt with if their magnitude is insignificant.
• The floor surface for laying the bed must also be leveled. He, the Mauerlat and the run must be clearly horizontal, but the location of the listed elements in the same plane is not necessary.
• We process all wooden parts of the structure before installation with fire retardants and antiseptic preparations.
• We lay waterproofing on concrete and brick walls for the installation of a Mauerlat.
• We lay the Mauerlat beam on the walls, measure its diagonals. If necessary, we slightly move the bars and turn the corners, trying to achieve the perfect geometry. Align the frame horizontally if necessary.
• We mount the Mauerlat frame. The splicing of the beams into a single frame is carried out by means of oblique cuts, the joints are duplicated with bolts.
• We fix the position of the Mauerlat. Fasteners are made either with brackets to wooden plugs laid in the wall ahead of time, or with anchor bolts.
• We mark the position of the bed. Its axis should recede from the Mauerlat bars at equal distances on each side. If the run will be based only on racks without lying down, the marking procedure is carried out only for these columns.
• We install the bed on a two-layer waterproofing. We fasten it to the base with anchor bolts, connect it to the inner wall with wire twists or staples.
• We mark the installation points of the rafter legs.
• We cut out racks according to uniform sizes, because our bed is set to the horizon. The height of the racks must take into account the dimensions of the section of the run and the bed.
• Installing racks. If provided by the project, we fix them with spacers.
• We lay the run on the racks. We check the geometry again, then install the brackets, metal plates, wooden mounting plates.
• We install a trial rafter board, mark the places of trimming on it. If the Mauerlat is set strictly to the horizon, there is no need to adjust the roof rafters in fact. The first board can be used as a template for making the rest.
• We mark the installation points of the rafters. Folk craftsmen for marking usually prepare a pair of slats, the length of which is equal to the gap between the rafters.
• According to the markup, we install the rafter legs and fasten them first at the bottom to the Mauerlat, then at the top to the run to each other. Every second rafter is screwed to the Mauerlat with a wire bundle. In wooden houses, the rafters are screwed to the second crown from the top row.

If the rafter system is done flawlessly, the layered boards are mounted in random order.

If there is no confidence in the ideal structure, then the extreme pairs of rafters are installed first. A control twine or fishing line is stretched between them, according to which the position of the newly installed rafters is adjusted.

The installation of the truss structure is completed by installing the filly, if the length of the rafter legs does not allow the formation of an overhang of the required length. By the way, for wooden buildings, the overhang should “go beyond” the contour of the building by 50 cm. If the organization of the visor is planned, separate mini-rafters are installed under it.

Another useful video about the construction of a gable truss base with your own hands:

Hanging truss systems

The hanging type of truss systems is a triangle. The two upper sides of the triangle are folded by a pair of rafters, and the puff connecting the lower heels serves as the base.

The use of tightening allows you to neutralize the effect of the thrust, therefore, only the weight of the crate, the roof, plus, depending on the season, the weight of precipitation, acts on walls with hanging truss structures.

The specifics of hanging truss systems

Characteristic features of hanging type truss structures:

• Mandatory presence of a puff, made most often of wood, less often of metal.
• The ability to refuse the use of Mauerlat. A frame made of timber will be successfully replaced by a board laid on a two-layer waterproofing.
• Installation on the walls of ready-made closed triangles - roof trusses.

The advantages of the hanging scheme include the space under the roof free from racks, which allows you to organize an attic without pillars and partitions. There are disadvantages.

The first of these is the limitation on the steepness of the slopes: their slope angle can be at least 1/6 of the span of a triangular truss, steeper roofs are strongly recommended. The second disadvantage is the need for thorough calculations for the competent device of cornice nodes.

Among other things, the angle of the truss truss will have to be set with jewelry accuracy, because. the axes of the connected components of the hanging truss system must intersect at a point, the projection of which must fall on the central axis of the Mauerlat or the lining board replacing it.

Subtleties of long-span hanging systems

Puff - the longest element of the hanging rafter structure. Over time, it, as is typical of all lumber, deforms and sags under the influence of its own weight.

Owners of houses with spans of 3-5m are not too concerned about this circumstance, but owners of buildings with spans of 6 meters or more should think about installing additional parts that exclude geometric changes in tightening.

To prevent sagging in the installation scheme of the truss system for a large-span gable roof, there is a very significant component. This is a pendant called a grandmother.

Most often, it is a bar attached with wooden surfs to the top of the truss truss. You should not confuse the headstock with the racks, because. its lower part should not come into contact with the puff at all. And the installation of racks as supports in hanging systems is not used.

The bottom line is that the headstock, as it were, hangs on a ridge knot, and a tightening is already attached to it with the help of bolts or nailed wooden plates. Threaded or collet type clamps are used to correct slack.

Adjustment of the tightening position can be arranged in the zone of the ridge knot, and the headstock can be rigidly connected to it with a notch. Instead of a bar in non-residential attics, reinforcement can be used to manufacture the described tightening element. It is also recommended to arrange a headstock or suspension where the puff is assembled from two bars to support the connection area.

In an improved hanging system of this type, the headstock is complemented by strut beams. The stress forces in the resulting rhombus are extinguished spontaneously due to the competent arrangement of the vector loads acting on the system.

As a result, the truss system pleases with stability with a slight and not too expensive upgrade.

Hanging type for attics

In order to increase the usable space, the tightening of the rafter triangles for the attic is moved closer to the ridge. A perfectly reasonable move has additional advantages: it allows you to use puffs as the basis for filing the ceiling.

It is attached to the rafters by cutting with a semi-frying pan with a duplication of a bolt. It is protected from sagging by installing a short headstock.

A noticeable drawback of the attic hanging structure is the need for accurate calculations. It is too difficult to calculate it on your own, it is better to use a ready-made project.

Which design is more cost effective?

Cost is an important argument for an independent builder. Naturally, the price of construction for both types of truss systems cannot be the same, because:

• In the construction of a layered structure for the manufacture of rafter legs, a board or beam of small section is used. Because layered rafters have two reliable supports under them, the requirements for their power are lower than in the hanging version.
• In the construction of a hanging structure, the rafters are made of thick timber. For the manufacture of puffs, a material similar in cross section is required. Even taking into account the rejection of the Mauerlat, the consumption will be significantly higher.

Saving on the grade of material will not work. For the bearing elements of both systems: rafters, purlins, beds, Mauerlat, attendants, racks, lumber of the 2nd grade is needed.

For crossbars and puffs working in tension, you will need the 1st grade. In the manufacture of less responsible wooden slips, the 3rd grade can be used. Without counting, we can say that in the construction of hanging systems, expensive material is used to a greater extent.

Hanging trusses are assembled in an open area next to the object, then transported assembled upstairs. To lift weighty triangular arches from a bar, you will need equipment, for which you will have to pay rent. And the project for complex nodes of the hanging version is also worth something.

Video instruction on the installation of a truss structure of a hanging category:

There are actually many more methods for constructing truss systems for roofs with two slopes.

We have described only the basic varieties that are actually applicable for small country houses and buildings without architectural ideas. However, the information provided is sufficient to cope with the construction of a simple truss structure.

At the heart of each roof is a large number of beams, rafters, racks and girders, which are collectively called the truss system. Over the centuries-old history of types and methods of its organization, a lot has accumulated, and each has its own characteristics in the construction of knots and cuts. We will talk in more detail about what the gable roof truss system can be and how the rafters and other elements of the system should be attached in more detail.

The design of the gable roof truss system

In the context of a gable roof is a triangle. It consists of two rectangular inclined planes. These two planes are connected at the highest point into a single system with a ridge beam (run).

Now about the components of the system and their purpose:

• Mauerlat - a beam that connects the roof and walls of the building, serves as a support for the rafter legs and other elements of the system.
• Rafter legs - they form the inclined planes of the roof and are the support for the crate under the roofing material.
• Ridge run (bead or ridge) - combines two roof planes.
• A puff is a transverse part that connects opposite rafter legs. Serves to increase the rigidity of the structure and compensate for bursting loads.
• Beds - bars located along the Mauerlat. Redistribute the load from the roof.
• Side runs - support the rafter legs.
• Racks - transfer the load from the runs to the beds.

Filly may still be present in the system. These are boards that extend the rafter legs to form an overhang. The fact is that in order to protect the walls and foundation of the house from precipitation, it is desirable that the roof ends as far as possible from the walls. To do this, you can take long rafter legs. But the standard lumber length of 6 meters is often not enough for this. Ordering non-standard is very expensive. Therefore, the rafters are simply grown, and the boards with which this is done are called “fillies”.

There are quite a few designs of truss systems. First of all, they are divided into two groups - with layered and hanging rafters.

With hanging rafters

These are systems in which the rafter legs rest only on the outer walls without intermediate supports (bearing walls). For gable roofs, the maximum span is 9 meters. When installing a vertical support and a strut system, it can be increased up to 14 meters.

The hanging type of gable roof rafter system is good because in most cases there is no need to install a Mauerlat, and this makes the installation of rafter legs easier: no need to make cuts, just mow the boards. To connect the walls and rafters, a lining is used - a wide board, which is attached to studs, nails, bolts, crossbars. With such a structure, most of the bursting loads are compensated, the impact on the walls is directed vertically downwards.

Types of truss systems with hanging rafters for different spans between load-bearing walls

Gable roof truss system for small houses

There is a cheap version of the truss system when it is a triangle (photo below). Such a structure is possible if the distance between the outer walls is not more than 6 meters. For such a rafter system, it is possible not to calculate the angle of inclination: the ridge must be raised above the puff to a height of at least 1/6 of the span length.

But with this construction, the rafters experience significant bending loads. To compensate for them, they either take rafters of a larger section or cut the ridge part in such a way as to partially neutralize them. To give greater rigidity in the upper part, wooden or metal plates are nailed on both sides, which securely fasten the top of the triangle (also see not the picture).

The photo also shows how to grow rafter legs to create a roof overhang. A notch is made, which should go beyond the line drawn from the inner wall upwards. This is necessary to move the incision site and reduce the likelihood of a rafter breaking.

Ridge knot and fastening of rafter legs to the backing board with a simple version of the system

For mansard roofs

Option with the installation of a crossbar - used when. In this case, it is the basis for filing the ceiling of the room below. For reliable operation of this type of system, the crossbar notch must be hingeless (rigid). The best option is semi-pan (see the picture below). Otherwise, the roof will become unstable to loads.

Please note that in this scheme there is a Mauerlat, and the rafter legs should extend beyond the walls to increase the stability of the structure. To secure them and dock with the Mauerlat, a cut is made in the form of a triangle. In this case, with an uneven load on the slopes, the roof will be more stable.

With such a scheme, almost the entire load falls on the rafters, therefore they must be taken with a larger section. Sometimes the raised puff is reinforced with a suspension. This is necessary to prevent it from sagging if it serves as a support for ceiling sheathing materials. If the puff is short, it can be secured in the center on both sides with boards nailed to the nails. With a significant load and length, there may be several such insurances. In this case, boards and nails are also enough.

For big houses

With a significant distance between the two outer walls, a headstock and struts are installed. This design has high rigidity, since the loads are compensated.

With such a long span (up to 14 meters), it is difficult and expensive to make a one-piece puff, because it is made from two beams. It is connected by a straight or oblique cut (picture below).

For reliable docking, the junction is reinforced with a steel plate mounted on bolts. Its dimensions should be larger than the dimensions of the cut - the extreme bolts are screwed into solid wood at a distance of at least 5 cm from the edge of the cut.

In order for the circuit to work properly, it is necessary to correctly make the struts. They transmit and distribute part of the load from the rafter legs to the puff and provide structural rigidity. Metal strips are used to reinforce the connections.

When assembling a gable roof with hanging rafters, the cross-section of lumber is always larger than in systems with layered rafters: there are fewer load transfer points, therefore, each element has a greater load.

With rafters

In gable roofs with layered rafters, their ends rest on the walls, and the middle part rests on load-bearing walls or columns. Some schemes burst walls, some do not. In any case, the presence of a Mauerlat is mandatory.

Bezporny schemes and knots of cuts

Houses made of logs or timber do not respond well to spacer loads. For them, they are critical: the wall can fall apart. For wooden houses, the gable roof truss system must be non-expansion. Let's talk about the types of such systems in more detail.

The simplest non-spacer scheme of the truss system is shown in the photo below. In it, the rafter leg rests on the Mauerlat. In this embodiment, it works on a bend, without bursting the wall.

Pay attention to the options for attaching the rafter legs to the Mauerlat. In the first, the support platform is usually beveled, while its length is no more than the cross section of the beam. The depth of the cut is no more than 0.25 of its height.

The top of the rafter legs is laid on the ridge beam without fastening it to the opposite rafter. Two shed roofs are obtained according to the structure, which adjoin (but do not connect) one with the other in the upper part.

It is much easier to assemble the option with rafter legs fastened in the ridge part. They almost never give a thrust on the walls.

For this scheme to work, the rafter legs below are attached using a movable joint. To fix the rafter leg to the Mauerlat, one nail is hammered from above or a flexible steel plate is placed from below. See the photo for options for attaching rafter legs to a ridge run.

If the roofing material is planned to be heavy, it is necessary to increase the bearing capacity. This is achieved by increasing the cross section of the elements of the truss system and strengthening the ridge assembly. It is shown in the photo below.

Strengthening the ridge assembly for heavy roofing material or with significant snow loads

All of the above gable roof schemes are stable in the presence of uniform loads. But in practice, this almost never happens. There are two ways to prevent the roof from sliding in the direction of greater load: by installing a brace at a height of about 2 meters or by struts.

Options for truss systems with contractions

The installation of contractions increases the reliability of the structure. In order for it to work normally, at the places where it intersects with drains, you need to attach nails to them. The cross section of the beam for the scrum is used the same as for the rafters.

They are attached to the rafter legs with bots or nails. Can be installed on one or both sides. The knot for attaching the bout to the rafters and the ridge run, see the figure below.

In order for the system to be rigid and not “crawl” even under emergency loads, it is enough in this embodiment to provide a rigid fastening of the ridge beam. In the absence of the possibility of its displacement in the horizontal, the roof will withstand even significant loads.

Rafter systems with braces

In these options, rafter legs, which are also called struts, are added for greater rigidity. They are installed at an angle of 45° with respect to the horizon. Their installation allows you to increase the span length (up to 14 meters) or reduce the cross section of beams (rafters).

The strut is simply substituted at the required angle to the beams and nailed from the sides and bottom. An important requirement: the brace must be cut accurately and fit snugly against the uprights and the rafter leg, excluding the possibility of its deflection.

Systems with rafter legs. Above is a spacer system, below is a non-spacer system. The nodes of the correct felling for each are located nearby. Below - possible schemes for attaching the strut

But not in all houses, the average load-bearing wall is located in the middle. In this case, it is possible to install struts with an angle of inclination relative to the horizon of 45-53°.

Bracing systems are necessary if significant uneven shrinkage of the foundation or walls is possible. Walls can sit differently on wooden houses, and foundations on layered or heaving soils. In all these cases, consider the installation of truss systems of this type.

System for houses with two internal load-bearing walls

If the house has two load-bearing walls, two rafters are installed, which are located above each of the walls. Beds are laid on the intermediate load-bearing walls, the load from the rafter beams is transferred to the beds through the racks.

In these systems, a ridge run is not installed: it gives expansion forces. The rafters in the upper part are connected to one another (cut and joined without gaps), the joints are reinforced with steel or wooden plates, which are nailed.

In the upper non-expansion system, the expanding force is neutralized by tightening. Please note that the puff is placed under the run. Then it works efficiently (the top diagram in the figure). Stability can be provided by racks, or jointing - beams installed obliquely. In the spacer system (in the picture it is below), the cross member is a crossbar. It is installed above the run.

There is a variant of the system with racks, but without rafters. Then a rack is nailed to each rafter leg, which rests on the intermediate load-bearing wall with the second end.

Fastening the rack and tightening in the rafter system without a rafter run

To fasten the racks, nails for 150 mm and bolts 12 mm are used. Dimensions and distances in the figure are in millimeters.

The frame format stands out among a number of types of roofing. It can be done in quite different ways, but in any case, you will need to calculate the rafters and install them according to all the rules. With proper knowledge of the problem, you can solve it on your own without resorting to specialists.

Features and forms of the roof

The frame roof can only be installed with spans no longer than 1220 cm, while the gap from one truss to another is a maximum of 0.6 m. The dimensions of the frame fragments are determined by the span distances and the calculated snow load. Rafters can be either freely installed or accepting loads from attic elements. In the case of a broken roof, it is possible to provide a ceiling height sufficient for a residential attic, and it will look best on a square building.

The multi-gable roof is considered the most complex and hardly accessible variation for amateur builders. A balanced truss system effectively withstands even very high loads, while having an excellent "appearance". Since the slope is steep, the risk of snow retention will be minimal. But at the same time, all structural elements will have to be calculated very carefully, and a lot of waste will appear in the process. In addition, the valley will have to survive exposure to a significant amount of snow.

Purpose and types of systems

Mauerlat can be used in a variety of rafter systems. The mass of the roof of the house varies depending on the area occupied by the slopes and the materials used. But in any case, the load created is very solid. When there is a ridge on the structures, a truss frame must be provided, with legs resting against the walls. Force is applied along several vectors at once, and in the cold season, the accumulation of snow only exacerbates the problem.

Mauerlat is designed to eliminate this shortcoming and prevent the destruction of the walls. This word means a beam of significant section, which can be both wooden and steel. In most cases, they take the same material that was used to form the rafters, but be sure to achieve continuity of the strapping or create strong and especially stable joints. The use of Mauerlat is abandoned only in log houses or in buildings built using frame technology - and even there they have their own parts that perform a similar task. When it is not possible to make a non-breaking block, all fragments must be exactly the same length.

A T-shaped roof is characterized by a tie-in of two wings at a certain angle. Because of this, it is necessary to form a valley. The outer rafters will rest against the support boards. In addition to them, there will also be basic parts that are directly fixed to the wall. In order for everything in the valley to correspond to the task being solved, wooden elements 3.8 cm thick are used. The crate is supposed to be made monolithic, the coating is attached to it with clamps every 50 cm. steel, you can slightly reduce this figure.

A reinforcing belt is often equipped under the Mauerlat. This is especially important if you plan to insulate the roof and provide reliable waterproofing. Such a belt is formed from the same mixture that is used to build the foundation. Completely the entire formwork is poured with concrete in one step, the slightest individual layers are unacceptable. In the aerated concrete wall, intermediate jumpers are cut down at the top line of blocks - and a practical gutter immediately appears. The Mauerlat is attached either with a tie wire, or with reinforcing bolts (but they will not help in any way without a reinforcing belt), or with building studs.

Having dealt with the support for the rafters, you need to find out what they can be, and what is more correct to use to support the roof. Hanging rafters are used if there is no main wall inside the building, their support points are located exclusively on the outer contours.

Such supports were in demand during the construction of:

• residential buildings with one span;
• production facilities;
• various pavilions;
• attic.

This option should not be underestimated, thanks to engineering developments, suspended rafters are able not to bend, covering spans of 15–17 m. But it is important to understand that they gain all their capabilities only in close interaction with other details. You will have to use puffs, and grandmas, and crossbars. The simplest truss is made of two beams connected in the upper position; in configuration, such a device is close to a triangle. The horizontal connection of the frame parts is provided by a tightening (a beam made of wood or a metal profile).

Due to the tightening, the transfer of thrust to the walls is excluded, while the force applied in the horizontal plane is suppressed. The outer walls experience the action of only those forces whose vector is oriented vertically. Builders do not always place a puff at the very bottom, often it is set at the very ridge. In preparation for the construction of the attic, this element is most often placed higher than the base of the rafter legs. Then it will be possible to make a floor, on the ceiling of which you will not have to beat your head with any careless movement.

Hanging rafters for spans longer than 6 m must be reinforced with hangers and braces. In this case, the monolithic puff is replaced by one assembled from a pair of connected beams. In the classical scheme (triangular hinged), the grassroots bases abut against horizontal parts. For the normal functioning of the system, it is required that the height of the ridge is at least 15% of the span of the trusses. The rafters act on the bend, but tightening does not allow them to move to the sides. In order for the beams to bend less, the ridge knots are cut in with the expectation of eccentricity (the occurrence of a bending force opposite in vector).

Mansard attics are built for the most part with the help of triangular arches on three hinges, and the puffs are assigned the function of floor beams. The components of the tightening are bolted by means of an oblique or direct cut. Raised tightening can also be used in the construction of rafters under the attic. The higher it rises, the more the ceiling can be raised. But it is important to remember that at the same time, the loads on all elements also increase. The transfer of forces is carried out on the Mauerlat with the help of a movable mount, which dampens dimensional changes due to changes in humidity and temperature.

The rafters can be subjected to uneven loading, since it is higher on one side. This leads to a shift in the same direction of the entire system. You can eliminate such an unpleasant effect if you take out the rafters beyond the contour of the walls. The tightening with such a decision ceases to be a support, it transfers either tensile effects (if an attic is being arranged), or stretched-bending ones (when an attic is being built). Hinged arches with the inclusion of a crossbar differ from the previous version by replacing the sliding support with an identical one in function - rigid. Due to the change in the type of supports, the type of stresses generated also becomes different, the rafter system turns into a spacer.

The puff is formed in the upper lobe of the arch. Its purpose is to endure no longer a stretch, but a compressive effect. Additional tightening, reinforcing the crossbar, is needed with a significant load. Arches with suspensions and struts complement the arch systems with headstocks. Such a system is needed for significant spans (from 6 to 14 m). The struts that correct the resulting bend must rest against the headstock. Regardless of the specific type of truss system, it is necessary to carry out all the details and their connections with each other as clearly as possible.

Not always hinged rafters can perform the task. Then the slanting elements come to the rescue. This type of rafters is used under hip roofs and under roofs equipped with a valley. Their length is longer than in the usual case. In addition, they become supports for the shortened rafters of the slopes. That is why the load on the rafters is about 50% more than in other structures.

Thanks to the increased length, it is possible to:

• resist significant impacts;
• form beams without cuts;
• bring the parts to a single size by pairing the boards.

To build a hip roof with many spans, the diagonal legs are provided with supports. Such supports are made in the form of standard struts or racks of timber, or a pair of connected boards. Support through a lining made of wood and a waterproofing layer is made directly on the reinforced concrete floor. The struts are placed at an angle of not less than 45 and not more than 53 degrees, at the bottom such a detail rests on the beds. The angle of installation is less important than the ability to fix parts of the rafters at the point experiencing the strongest load.

Sloping rafters placed in openings up to 750 cm should be held by struts only in the upper lobe. With a length of 750 to 900 cm, a truss truss or rack is additionally mounted below. And if the total span length exceeds 9 m, then for maximum reliability in the middle you need to put a rack, no other support will do. If the selected floor is unable to withstand the load, it will have to be reinforced with a beam. The type of support in the ridge is determined by how many intermediate supports are used, what they are, how the key layered rafters are made.

In addition to the type of rafters, you need to clearly understand their material. Both wooden and metal structures can be good, but only each in its place. Even the high strength of the metal does not allow to push the usual wood. The tree has proven its benefits for thousands of years, and now it is even gaining popularity due to its excellent ecological characteristics. Boards and timber can be bought at an affordable price, and if something has not been taken into account, it is always easy to saw off the desired fragment or build up a part right on the construction site.

Sometimes there are problems associated with the operation of the created structures. Wooden rafters will have to be carefully treated with antiseptics, as well as means that block the development of mold colonies and insects. The combustibility of wood is suppressed due to regular processing, and in addition, it is too difficult to find the necessary components for slopes longer than 7 m. Before installation, the walls are laid with a mauerlat, made from a log frame or based on a block of timber. The thickness of the structures is at least 180 mm, this is the only condition for a uniform distribution of loads.

Metal rafters are inevitably heavier than wood rafters for the same section. Therefore, the walls need to be strengthened, the work on their construction becomes more expensive and longer. It will not be possible to mount metal blocks manually; cranes will be required. It is impossible or very difficult to adjust the dimensions, the geometry of the rafters, so you will immediately have to build the walls as accurately as possible and eliminate errors during their construction. The slightest mistake can make an expensive block almost useless in practice.

Metal rafters are connected by welding, and welded joints are inevitably weakened, as corrosion develops rapidly there. The cost of the work is very high, and when performing them, it is necessary to comply with the requirements of fire and electrical safety. But there is such an indisputable advantage as the ability to support a roof slope from 700 cm and longer. If you use a special anti-corrosion paint, the durability of metal structures is fully guaranteed. All these advantages allow you to quickly and comfortably build industrial buildings with a significant height and length of spans.

How to choose: what to consider?

The truss system should be chosen as correctly and clearly as possible.

When looking for a suitable solution, you need to pay attention to the following points:

• strength;
• the ability to support the slopes and the roof as a whole of a certain size and geometry;
• creating a positive aesthetic image of the building as a whole.

Technical parameters take precedence. Even the most beautiful structures that follow the principles of design will not show their positive qualities if they last too little. Experienced builders always analyze the average annual and seasonal temperatures, the financial capabilities of developers, the maximum possible wind speed and the severity of the overlying roof. The future use of the under-roof space and the scale required for it are also taken into account. Wind, snow and rain should not be underestimated, since these factors can have a very strong effect on the roof, and through it on the rafters.

If it is reliably known that a particular area is characterized by heavy snowfalls, the minimum slope angle is impractical. This point is even more relevant when using flat roofs. Under the pressure of accumulating precipitation, the frame can rapidly deform or water will pour inside. Another thing is when a certain region is often subject to the arrival of cyclones and the strong winds they bring. Here the slope should already be made smaller, then the situation with the disruption of individual structural elements will be practically excluded.

Mistakes can be avoided if you look at houses already built nearby and operated for a long time. By accurately reproducing their roof structure and the rafter system interconnected with it, one can best take into account local specifics. But not everyone follows this path, sometimes the task is to develop an exclusively original project. Then you will have to carefully collect the initial data, carry out scrupulous calculations. In the absence of special knowledge, it is better to attract qualified performers to help.

After analyzing the total load created by wind and snow, it can sometimes be found that certain parts of the truss complex need selective reinforcement. When assessing the required angle of inclination of the roof, attention is also paid to the type of coating used. A heavy metal tile or corrugated board with a very large slope can spontaneously slide down, you have to additionally fix them, complicating your work and increasing the cost of installation. In addition, certain materials have a tendency to retain water or become soaked with it, which can only be combated by making the slope steeper. Creating a good roof and truss system that meets such conflicting requirements is not always accessible to non-specialists.

What does it consist of?

The structure of the truss system, as you can see, is quite complex and even contradictory. Each part of this design has a strictly defined role. So, Mauerlat is a long bars of coniferous wood, and strictly resinous wood is used for work. Such elements are laid out along the external load-bearing walls, attached to the base with anchors or rods of a special design (threaded). This part transfers the load from the roof to the wall.

Next comes such a device as a rafter leg. Under this name appears a wooden beam used to build the contour of the slopes. The shape of the structure is always triangular, because it is the best way to help the roof withstand the destructive effects of winds, snow and other atmospheric processes. Rafter legs are placed at uniform distances along the entire roof, the step cannot exceed 120 cm.

The bed is also of some importance for supporting the roof - this is a wooden block that replaces the Mauerlat in some cases. Beds are placed on the internal supporting walls. They turn into the basis of the roofing triangle. Thanks to them, the slopes do not crawl under their own weight. And it is also worth mentioning about the racks - these are bars with a square section placed vertically. They perceive the pressure exerted downward by the ridge assembly and transmit it mechanically to the inner bearing plane. Sometimes the racks are under the rafters.

Struts are designed to strengthen the entire structure of the roof, they connect the legs and beds into one whole. This detail is shaped like a rhombus. The community formed by the puff and struts is called the farm. In addition to them, you also need a crate, which is thin boards stuffed at right angles to the legs of the rafters. It helps to keep the rafter legs as a single system. Absolutely any roof covering is attached to the crate.

Under soft materials, the crate should be made inseparable, and plywood is considered the best tool. At the very top is a ridge, which logically and physically completes the roofing triangle. The connection of a pair of opposing legs of the rafters is provided by a square piece of wood which prevents the entire roof from collapsing. And at the very bottom of the pitched roof there is an overhang, which extends approximately 0.5 m from the perimeter. Thanks to him, the streams of rain leaving the roof do not flood the outer bearing planes and do not harm them.

Fillies are used only in the situation when the rafter legs cannot be made along the length that would allow organizing the overhang. Connecting with boards of reduced section effectively solves this problem. For fastening the wooden elements of the rafters, it is most often recommended to use clamps, staples. It is undesirable to use nails, because the tree pierced by them becomes weak and fragile after a few years. Therefore, if professionals use connections made directly on the construction site, they use bolts.

But even a bolted connection weakens building structures, albeit relatively slightly. The strongest are the connections with the help of clamps or staples made of metal. Only their industrial production can maximize the quality of products, since deviations from the norms and deterioration in quality are excluded only under strictly standardized and fully controlled conditions. You can assemble a truss structure from completely finished trusses very quickly, there is no risk in using it. Another thing is that it is required to collect information about the necessary characteristics as accurately as possible and transfer it to the manufacturer without distortion.

In addition to these elements, the truss system borders on the valley. This is the name given to a special connection of a geometrically complex roof at points where its trajectory changes. The difference from the ridge is that in such places the roofing parts form a negative angle. The technical essence of the product lies in the fact that the gutter helps to divert liquid to the side. The more complex the configuration, the greater the number of such gutters should be.

The cornice beam serves to abut a strut against it, the other end of which rests against the frontal board, while the dropper is not deformed and its configuration is not distorted. Wind connections are those elements of the truss system that transfer the load created by the wind from the roof to the foundation. They not only increase the overall stability of the structure, but also help to avoid tipping over in case of instability of individual parts. The roof will retain spatial rigidity even with very strong winds.

Horizontal wind connections are such elements as:

• braces;
• parabolic puffs;
• complexes of conventional puffs;
• trusses, complemented by a cross-shaped lattice.

Vertically, the preservation of characteristics under strong air pressure is ensured by wind supports and beams. Sometimes a monolithic reinforcing core is used. Engineers have come up with many other options for designing a wind connection. It is provided with frames and semi-frames, pinched props. In small buildings, rigid (resisting compression) or stretched diagonals are used, some covering two spans at once. The location of each of the elements is accurately reflected in the project documentation.

It is not so difficult to understand the qualitative characteristics of truss systems and their composition, if you show care and diligence. But it is equally important to calculate the quantitative parameters of these systems. If you do not do this or make the calculations incorrectly, you can either spend too much money, or encounter leaks, even with the destruction of individual elements.

• roof bends;
• average annual snow mass;
• unevenness in its distribution along the slopes, depending on the steepness of the slope and the wind rose;
• wind transfer of already fallen snow;

• descent of snow and ice masses, runoff of liquid water down;
• aerodynamic characteristics and windage of the structure;
• differences in the strength of the impact on individual points.

It is not so easy to calculate everything necessary, moreover, by simulating realistic situations and including a reasonable margin of safety in the project. Moreover, it is necessary to pay attention to the addition of various loads, to their cumulative effect. But still, any customer is quite capable of evaluating the quality of the work of designers. The loads applied to the truss systems are divided into three key groups: main, additional and extreme.

The main category includes:

• stable factors - the severity of the roof and roof structures, additional elements installed on top of them;
• long-term effects - snow, temperature;
• periodically changing factors - full calculations of snow and temperature effects, taking into account all the subtleties.

An additional group is the pressure exerted by the wind, builders and repairmen, ice and rain. The extreme category includes all natural and man-made emergencies that may occur in a particular place. Their level is predicted with a margin to ensure the exclusion of unpleasant consequences. When calculating the frame roof and the structures under it, the ultimate load is taken into account, if applied, the entire structure crumbles. Additionally, an indicator or a group of indicators is given, upon reaching which various deformations inevitably appear.

The snow drift coefficient reflects how much more snow will be deposited on the lee side and in front of objects (parts) that block the air flow. In problem areas, you will have to bring the rafters as close as possible and thoroughly calculate the required thickness of the front material. The most accurate assessment of all parameters can only be given by multiplying any received figures by the reliability factors. As for the wind, the force developed by it is aimed at dropping steep roofs and lifting from the leeward section of a flat roof. We must not forget that the air flow acts simultaneously on the facades and on the roof slopes.

When hitting the facade, the air breaks up into two waves: one goes down and is no longer of interest, and the other tangentially presses the roof overhang, trying to raise it. The action on the slope occurs at a right angle, this area is pressed inward. At the same time, a vortex is formed, which tangentially affects the windward sector of the slope. This vortex bypasses the ridge and begins to create lift already applied to the leeward segment. For your information: when calculating the mass of the roof, you need to take into account the severity of the rafters, insulation, waterproofing and vapor barrier.

The standard load per 1 square meter of the roof is up to 50 kg, regardless of its size and other significant circumstances. By changing the distance from one rafter leg to another, you can set the actual distribution of loads on them. According to most experts, indicators from 60 to 120 cm will be acceptable values. But on an insulated roof, it is worth choosing distances that are equal to one sheet or roll of insulation materials. At the same time, it should be borne in mind that among several suitable options for arranging rafters, the one that gives the best effect with the minimum consumption of materials used is preferable.

When calculating the loads carried by the rafters, they always look at the fact that they do not exceed the ultimate endurance of the roofing material. After all, there is no point in such an excess. If, under the planned impact, the roof will still begin to sag, it is impossible to talk about a solid result. In calculations, the payload from structures connected to truss trusses is calculated according to the contact area that is plotted on the drawing. Such structures include ventilation chambers, attic and ground floor ceilings, and water tanks placed on the roofs. In addition to the amount of pressure on the rafter system, the sharpness of the roof slope is also calculated.

Tilt angle: value

On forums with consultations of specialists and in professional literature, one can find references to three units of measurement of inclination at once. In addition to the usual and expected degrees, there will be percentages and ratios between the parties. Often they get along together even within the same publication or instruction from the manufacturer of roofing materials. But in fact, there is nothing mysterious in this, any consumer can understand the essence. Under the angle of inclination of the roof, experts understand the angle that occurs at the intersection of the horizontal with the roof slope.

In this case, there can be no obtuse angles in principle. Moreover, you can meet a slope steeper than 50 degrees only in decorative elements, all kinds of turrets. The only exceptions to the general rule are the slopes on the lower rows of the rafters of the attic roof. In all other cases, the angles range from 0 to 45 degrees. The relative proportions of the sides are calculated as the ratio between the height of the slope and its projection onto the horizontal. This indicator is equal to half the span for a uniformly constructed roof with a pair of slopes.

On a shed roof, the proportion is equal to one, but in more complex configurations, you still have to carry out all the calculations and estimates yourself, without starting from ready-made values. The slope angle is usually expressed as a fraction, with the numerator and denominator separated by a colon. But when the resulting numbers cannot be rounded to whole numbers, it is recommended to use percentages: they simply divide one by the other and increase it a hundred times. Flat roofs are those that have a slope of no more than 5 degrees; a slope of 6–30 degrees is recognized as small, and all other roofs are considered to be steep. The flat design drastically increases the usable area and is quite wind resistant, but it will need to be manually cleared of snow and strengthen the waterproofing to the limit. The slope is necessarily consistent with the specific material, and the required values ​​\u200b\u200bcan be found in the instructions from the manufacturer. In order to calculate even the most complex and bizarre roof configurations, they are mentally divided into triangles and the angle is calculated separately in each.

Step, length and section of rafters

When it became clear how long the slopes are, what angles formed by these slopes with a horizontal plane, it was time to do the actual calculation of the rafters. If the roof frame is made of a 5x15 cm timber under a metal tile, the mounting pitch sways from 0.6 to 0.8 m. As the slope grows, the gap also increases. If the roof slopes at 45 degrees, you need to put rafters every 800 mm, and for slopes of 75 degrees, you can add another 200 mm.

The next important parameter is the length of the rafters. It is closely related to the step: if the blocks are made long, they are brought together as much as possible, and when a single part is shortened, they are moved apart. When calculating the step of the crate, they proceed from the type of tiles laid on top and from the fact that an integer number of rows should be laid out on each slope. If you get a fraction, it is better to round, reduce or increase the indicator a little. The rafter legs under the metal tile, the cross section of which is 15x5 cm, range from 65 to 95 cm. You cannot increase the step when the cross section of the crate is 3x5 cm.

In order for the insulation to be better ventilated, rows of holes with a diameter of 1–1.2 cm are prepared in the region of the upper edge of the rafters. Ordinary rafters under the corrugated board go every 0.6–0.9 m. with significant cross section. The crate under the corrugated board is assembled from boards with dimensions of 3x10 cm, which are placed at intervals of 0.5 m. The interval must be calculated according to the height and thickness of the materials.

With all the revealed shortcomings of slate, it remains widely in demand. Under the slate roof, rafters with a section of 5x10–15 cm are mounted, 60–80 cm apart from each other. Most often, an average distance of 0.7 m is recommended. Pauses between parts of the crate are calculated according to the steepness of the material. On relatively flat areas, the support of 4 pieces of wood justifies itself. If the roof is made steeper, put 3 bars, separated by 63–65 cm.

We must not forget that due to the responsibility of the truss system, it is better to leave a margin of safety than to make an unreasonably weak type of rafters. For their manufacture, timber is used, dried to a maximum of 15%. A non-edged board of the same dryness can serve as a replacement for a beam. Under the ceramic tiles, a 5x5 cm timber crate is used. In the places marked according to the calculated distance, slate nails or simple self-tapping screws are used.

Installation: technology

The construction of the roof involves the use of a standard range of carpentry tools and an electric drill. If metal structures are used, a grinder will be required for precise cutting. Remember that it is impossible to process metal tiles or corrugated board with it, this can damage the material. A hipped roof without racks is made using puffs that reinforce the structure.

In the hip version, it is necessary to strengthen the runs running diagonally. Paired boards and a particularly strong timber are assigned to them. Connection points always have a support (stand), and the main support is placed about a quarter of the length separating the large rafters from the ridge. Under the gables on a gable roof, rafters of a shorter length are always made. But under the main part of the four-slope structure, extremely long parts can be placed, even more than 7 m. To keep them securely, either a rack is used that transfers stress to the ceiling or a sprengel.

The first step in creating rafters under a broken roof is the formation of a support complex in the form of the letter P. It rests on the floor beams and is held by rafter legs. Next, they put three or more runs, two of them are brought to the corners of the frame, and the rest are placed in the middle of the overlap. The final step in raftering is fixing the legs. It is desirable to make truss systems according to a pattern - to connect two boards that are the same length as the rafters, and pin them to each other with a nail. The template is placed with its edges at the points of attachment of the rafter legs and fixed with a cross member.

An additional template (this time plywood) will help to make a mounting saw. Farms are attached to the Mauerlat, starting from the extreme ones. In order not to confuse with the attachment point of the ridge, the tops of these trusses are tied with a straight rope. The massiveness of the puffs increases as you approach the ridge. If the truss elements are bolted, washers or plates should be used. This will keep the nuts from digging into the wood.

How to install the rafters with your own hands, see the video below.