Types and schemes of rafter systems

When designing any residential building, architects pay special attention to the roof, as it performs not one but several functions, depending on its design features. It should be noted that not all future homeowners are satisfied with the usual gable roof, although it can be called the most reliable, since it has only two pitched planes and one junction between them. Many are attracted by more complex constructions, which add to the structure a special appeal and originality. Other, more practical homeowners, prefer mansard structures, which are simultaneously able to perform the role of the roof and the second floor.

Types and schemes of roofing systems

The basis of any roof is an individual truss system, which has its own design features. Make the choice of the desired roof skeleton will be much easier if you first figure out what types and schemes of the rafters are used in construction practice. After receiving such information, it becomes more clear how complicated such constructions are in the installation. Especially it is important to know if the skeleton for the roof is supposed to be erected independently.

Basic functional tasks of the

system When constructing a pitched roof structure truss system is a framework for the coating and to keep materials "roofing pie".With a competent installation of the frame structure, the necessary conditions will be created for the proper "work" of insulated and unheated roof types, which protect the walls and interior of the house from various atmospheric influences.

When choosing the type of rafters, you have to take into account a lot of versatile criteria.

. The roofing structure is also always the final architectural element of the exterior of the building, maintaining its stylistic direction in its own way. Nevertheless, the structural features of truss systems first of all must meet the requirements of strength and reliability, which must correspond to the roof, and only then - already aesthetic criteria.

The frame of the rafter system forms the configuration and the angle of the roof. These parameters largely depend on natural factors specific to a particular region, as well as on the desire and capabilities of the homeowner:

• Number of precipitation in different periods of the year.
• Direction and average wind speed in the area where the construction will be erected.
• Plans for the use of space under the roof - the arrangement in it of residential or non-residential premises, or its use only as an air layer for thermal insulation located below the premises.
• Variety of planned roofing material.
• Financial opportunities for the homeowner.

Atmospheric precipitation and the force of wind currents give a very sensitive load on the structure of the roof. For example, in regions with heavy snowfalls, it is not necessary to choose a rafter system with a small angle of slope of the skates, since snow masses will linger on their surface, which can lead to deformation of the frame or roofing or to leaks.

If the area where the construction is to be built is famous for its winds, it is better to choose a structure with a slight slope of the ramp so that the sudden gusts do not rip apart the individual elements of the roof and roof.

Basic elements of the roof structure

Details and components of the

rafters Depending on the type of rafter system chosen, the structural elements used can vary considerably, however, there are parts that are present in both simple and complex roof systems.

Basic parts of the standard

truss system. The main elements of the pitched roof pit system are:

• Rafter legs forming the roof slopes.
• Mauerlat - a wooden beam, fixed on the walls of the house and serving to fix the lower part of the rafter feet on it.

• A horse is the joint of the skeletons of two skates. It is usually the highest horizontal line of the roof and serves as a support on which the rafters are fastened. The ridge can be formed by rafters, fixed together at a certain angle or fixed on a ridge board( run).
• Battens are racks or beams that are mounted on rafters with a certain pitch and serve as the basis for the flooring of the selected roofing material.
• Supporting elements, where you can carry the ladders, girders, racks, struts, screeds and other details, serve to increase the rigidity of the rafter legs, support the ridge, the binding of individual parts in the overall design.

In addition to the above structural details, it can include other elements, whose functions are aimed at strengthening the system and the optimal distribution of roof loads on the walls of the building.

The roofing system is divided into several categories depending on various features of its design.

Attic space

Before proceeding to the consideration of different types of roofs, it is worthwhile to understand what an attic space can be, since many owners use it successfully as economic and full-fledged residential premises.

Before choosing a rafter system, you should immediately decide what role the attic of the

is assigned to. The structure of pitched roofs can be divided into bezcherdachnye and attic. The first option is called precisely because the space under the roof has a small height and is used only as a warming room on top of the building of the air layer. Such systems usually include a single-pitched roof or having several skates, but located at a very small angle.

The attic structure, which has a sufficiently large height of the ridge, can be used in various ways, to be insulated and insulated. To such variants it is possible to carry a mansard or two-slope variant. If you choose a roof with high ridge, then it is mandatory to take into account the wind loads in the region where the house is built.

Slope of skates

To determine the optimal inclination of the roof slopes of the future residential building, first of all you need to look at the already built low-rise neighbor's houses. If they stand for more than a year and stand up to the wind load, their design can be safely taken as a basis. In the same case, when the owners set a goal to create an exclusive original project, unlike the nearby buildings, it is necessary to familiarize yourself with the structural and operational features of various rafters and make the appropriate calculations.

The figure shows a simplified view of the wind impact on the pitched roofs of the

. It should be taken into account that the change in the tangent and normal values ​​of the wind force depends on how large the slope of the roof slopes is, the more steep the angle, the greater the value of the normal forces and less tangents. If the roof is sloping, then the design is more affected by the tangential load of the wind, since the lift increases on the leeward side and decreases from the windward.

The consolidated load of wind and snow can force to reinforce individual elements of the

rafter system. Winter snow load should also be taken into account when designing the roof. Usually this factor is considered in combination with wind load, since on the windward side the snow load will be much lower than from the leeward slope. In addition, there are places on the slopes where snow will necessarily be collected, giving a big load to this area, so it should be strengthened with additional rafters.

The slope of the roof slopes can vary from 10 to 60 degrees, and it should be selected not only taking into account the consolidated external load, but also depending on the roofing to be used. This factor is taken into account because the roofing materials differ in their mass, to fix them requires a different number of elements of the rafter system, which means that the load on the walls of the house will vary, and how big it will also depend on the angle of the roof slope. Of particular importance are the characteristics of each coating for resistance to moisture penetration - many roofing materials in any case, one or another slope is needed to ensure free flow of storm water or melting snow. In addition, when choosing the slope of the roof, you need to think in advance how the cleaning and repair work on the roof will be carried out.

When planning a particular angle of the roof slopes, you need to know, the fewer joints between the cover sheets, and the more they are hermetic, the less you can make the slope of the ramp, of course, if you do not intend to arrange a residential or utility space in the attic space.

If, for a roof covering, a material consisting of small elements is used, for example ceramic tiles, then the slope of the stingrays must be made steep enough so that the water never lingers on the surface.

Given the weight of the roofing material, you need to know - the heavier the coating, the greater the angle of the skates, since in this case the load is correctly distributed to the rafter system and bearing walls.

The following materials can be used to cover the roof: metal tiles or profile sheet, galvanized steel, corrugated asbestos-cement and bituminous-fibrous sheets, cement and ceramic tiles, roofing material, soft roofing and other roofing materials. The following illustrations show the permissible angles of steepness of skates for different types of roofing.

The presented diagram will help to determine the ratio of the steepness of skates and the planned roofing material

Basic constructions of the roofing systems

First of all it is necessary to consider the basic types of truss systems relative to the location of the walls of the house that are used in all roof structures. The basic options are divided into a layered, hanging, and combined, that is, including in its design elements of both the first and second type of systems.

slab system In buildings where internal load-bearing walls are provided, a layered rafter system is often installed. Mounting it is much simpler than hanging, since the inner load-bearing walls provide a reliable support for its elements, and in addition, this design will require fewer materials.

Typical design of the built-in

rafter system. For rafters in this system, the ridge is the defining reference point on which they are fixed. The unassailable form of the collapsible system can be arranged in three versions:

• In the first variant, the upper side of the rafters is fixed on a ridge support, called sliding, and their lower side is fixed by cutting to the mauerlat. In addition, the rafters at the bottom are fixed to the wall using wire or staples.

Rigid legs fastening to Mauerlat

• In the second case, the rafters in the upper part are cut at a certain angle and joined together by means of special metal plates.

One of the options for connecting the rafter legs in the area of ​​the ridge

The lower edge of the rafter's feet is fastened to the Mauerlat with movable fasteners.

Sliding fastenings of rafter legs on the Mauerlat

• In the third version, the rafters are rigidly fastened in the upper part by brusks or treated boards horizontally parallel to each other on both sides of the rafters connected at an angle, and a ridge run is jammed between them.

Scheme of pinch ridge grip at the top of the rafters

In the lower part for fastening the rafters, as in the previous case, sliding attachments are used.

It is necessary to explain why it is sliding locks that are often used to fix the rafters on the Mauerlat. The fact that they are able to rid the load-bearing walls from excessive stress, since the rafters are not fixed rigidly, and when shrinking the structure they are able to move without deforming the general construction of the roofing system.

This type of attachment is used only in the on-board systems, which also distinguishes them from the hanging variant.

However, in some cases, a spacer system is used for the layered rafters, in which the lower end of the rafters is rigidly fixed to the Mauerlat, and to remove the load from the walls, tightenings and struts are built into the structure. This option is also called complex, since it includes elements of a nasal and hanging system.

For the construction of private houses is most often used is a collapsible system, so a few words should be said about the installation work.

• The waterproofing material is laid on the bearing walls of the house - most often it is ruberoid.
• The waterproofing is fixed using Mauerlat anchorages - this can be a large cross-section beam( for example, 120 × 150 or 150 × 150 mm).

• On the Mauerlate the rafters are fastened to sliding or rigid fasteners. Rarely often the rafters are additionally fixed on the inner side of the wall with the help of wire twisting. To do this, a crutch is screwed into the wall 250 to 300 mm from the surface of the Mauerlat, to which the wire is screwed, and then fixed to the rafter. Such fasteners will keep the roof unscathed during a strong wind.

Scheme for additional fastening of the rafter leg on the Mauerlat with wire twisting

In the diagram the numerals are:

1 - rafters;

2 - Mauerlat;

3 - brick wall;

4 - counter-rail;

5 - wire twisting;

6 - the fastening element.

• At the top of the rafters can be connected in one of the ways described above.
• To form the overhang of the tie beam or the rafter feet themselves are pulled out beyond the edges of the outer bearing walls. This design will protect the walls during the rain. The width of the overhang should be 500 ÷ 600 mm.
• Then the rafter system is strengthened by struts, struts and purlins.

Board flooring will make the work more comfortable and safe

Before beginning the installation operations for the installation of the rafter system it is recommended to at least temporarily lay the boards on the joists. This simple adaptation will secure the work and make them more comfortable.

Hanging system

Hanging rafter system is installed in buildings where there are no capital partitions inside the building, and the distance between the side bearing walls varies from 6 to 11 m and more. In this case, the roof construction is completely supported by the bearing walls and gives them a high spacer load. Therefore, that a little to weaken the tension, additional fastening horizontal elements are used, with which the rafter pairs are pulled together - these structural details are called bolts or puffs.

A typical example of a suspended roof structure

The crossbars can be fixed anywhere in the height of the rafters. They are often used as beams of attic flooring, laying on the Mauerlat.

Options for the construction of the suspended truss system

For this type of construction the rafters are made of a board with a cross section of approximately 50 × 200 mm, but for each specific structure, individual calculations must be made, which is best entrusted to specialists.

• The first step in this construction on the side load-bearing walls is to install the Mauerlat.
• Further, the rafters at the bottom are cut into the Mauerlat, and the upper ones can be connected in one of the three ways described above. Usually, first one rafter is built, which is mounted on the ground, then it is raised to the height and adjusted in place. After that, this pair is used as a template for making the remaining pairs.
• After all pairs have been mounted, they are taken up in turn and installed on the Mauerlate, at a distance of the calculated step.
• The next step is to prepare a ridge run, which will be associated with individual rafter pairs at the top. When installing the run, it is very important to keep the distance between the rafter legs.
• Further, on each of the rafter pairs are fastening boards. They are fixed for rigidity on both sides of the rafters and additionally fixed to the Mauerlat with special metal perforated corners.

Mauerlat joint assembly - rafter and screed

• The nail of the connecting elements of the rafter system is usually carried out by nails, but after the elements are assembled and leveled, they are rigidly fixed with bolts through the metal plates and corners. Only such fastening will make the construction reliable and durable.
• If the distance between the walls reaches 10 ÷ 11 m, then the system should be further strengthened by racks and slopes.

Both suspended and stratified systems are used in the installation of various roof structures, which will be discussed below.

Roof shapes and their roofing systems

Roofs can have one or more ramps connected in different ways. Each of the structures is formed by an individual frame system, the main elements of which are rafters. The names of the roofs directly depend on their constructions:

The basic types of roof structures

So, depending on the specific conditions, the following roof constructions are used depending on the type and architectural features of the building:

• Single roof.
• Flat.
• Gable construction.
• Hinged, four-sided.
• Semi-high.
• Multi-clutch.
• Hinged.
• Broken or mansard roof.

Now, knowing how each type of roof looks, it is worthwhile to figure out what they are and what kind of truss system they have.

Single-pitched roof

An example of a single-pitched roof on a residential house

As you can already understand from the title, this roof has one ramp, located under a slope. If the structure is small in size and completely erected from brick or concrete, the rafters of the structure are laid on the facade carrier high and on the back low wall. If between the building facade and the rear wall the distance is six or more meters, then between the front and rear wall are mounted retaining racks.

Strengthening rafters of a saddle roof with racks and postsoles

In addition, such structures can be formed entirely from a wooden beam or logs, this option is resorted to if the rafter system is installed on load-bearing brick walls having one height.

Basic Elements of Roof Deck Construction

A single-deck wooden truss structure designed for a building with a wall-to-wall distance of six meters or more consists of the following elements:

1 - Supporting truss.

2 - Support stand, which serves as a support for the rafters.

3 - The rafter's leg.

4 - Ridge run, on which the upper sides of the rafter legs are fixed.

5 - Left, serves for fixing the front pillar and the strut.

6 - Mauerlat, on which the underside of the rafters is fixed by the method of cutting.

The complexity of the gable roof system directly depends on the distance between the bearing walls, that is - the length of the rafters themselves. Examples are shown in the illustration below:

Dependence of the complexity of the gable roof system from the distance between the bearing walls

1 - Simple lining rafters in the construction of a single-pitched roof, with a distance from the front to the rear wall of 3 to 4.5 m.

2 -bearing walls is 5 to 6 m, the rafters are supported by struts attached to the Mauerlat.

3 - The construction with the distance between the walls from 6 to 7.5 and more meters is supported by stands( pasterns) supported by struts.

Such complex system variants can be mounted between brick or concrete bearing walls.

Single-pitched roofs can rarely be found above residential buildings. More often they are mounted over verandas, outbuildings, utility objects and garages.

This design can be called the easiest to install, especially in those cases when all calculations are correctly performed. Another positive quality of a saddle roof is a small consumption of building materials.

The biggest disadvantage of a single-deck construction is a small overburden, so it can be called cold, since a small air gap will not keep heat in the premises of the house.

It is very important to correctly calculate the slope of a saddle roof, which will primarily depend on the roofing material to be used for the coating. There are recommended minimum gradients for all roofing. To determine this parameter, you can use the table below:

If a concrete roofing is chosen, the minimum angle of the slope of the ramp can be determined from the table or following the installation instructions for the material.

The simplest calculations of the

rafter system parameters If you have determined the angle of the ramp, you can immediately determine the elevation of the gable roof part using the formula below:

The scheme for calculating the "roof triangle"

The formula for calculating the elevation of the roof facade looks as follows:

Lbc =Ldd × tgA;

Ld - the distance between the front and rear wall;

tgA is the slope of the roof slope.

After this, it will be easy to calculate the length of the rafters, which are suitable for the calculated structure( without taking into account the eaves).

Lc = Lbc / sinA

or

Lc = √( Lcd² + Lbc²)

It is easy to find the values ​​of trigonometric functions in the corresponding tables.

By the way, these formulas are quite suitable for calculating any roofing structure - you just need to be able to split the rafter system into triangles. For example, for a gable roof, Lbc simply becomes the height of the ridge over the overlap.

In order not to force the reader to look for reference data for self-calculation, two calculators are given below, which allow us to quickly calculate the basic parameters of the "roof triangle".

Calculator for calculating the height of the "truss triangle"

The calculator allows you to determine the height of the "truss triangle".Depending on the type of roof, this may be an excess, as in the case of a single-pit roof, or the height of the ridge( fracture) for other structures.

Similarly, the length of the horizontal projection of the rafter should be differentiated. If for a single-pitched roof this is simply the distance between the stacks, then in other cases there may be other "layouts".For example, for a symmetrical gable roof this will be half the length of the span.

The calculator for calculating the length of the rafters

The calculation is based on the horizontal projection( Ld) and the height of the truss triangle, previously defined( Lbc).

If desired, you can include in the calculation and width of the eaves, if it is created by the projecting rafters.

Gable roofing system

Double-sloped rafter systems - the most popular for single-story private houses. They look neat, fit well in any style of construction, are reliable and can be used, depending on the angle of their slope, to equip the attic for living rooms, utility rooms or simply to create an air gap that keeps the heat in the building.

The gable roof is one of the most common constructions of the

. The saddle girder system can be sheared or hanging, built on wooden beams or reinforced concrete, it is left cold or it is reliably insulated with special materials.

Double-sided rafter system with a mansard room.

The rafters in this roof construction rely on two bearing walls, which have the same height. Two rectangular sloping surfaces of the system can form an equilateral or versatile triangle.

The second version of the rafter system is convenient because one of the roof planes is mounted at a large angle and there will be almost no snow on its surface, so it is best to arrange it on the leeward side of the house, where snow drifts occur most.

A gable roof with different steep slopes and lengths.

The roofs of gable roofs are lined with boards or lined with brick, making them a kind of continuation of the wall. The pedimental triangular elements of the roof are often called forceps, and the gable construction is gable.

An example of the location of fastening and retaining elements in a two-sloped nylon structure.

Calculations of the length of the rafters, corners and the height of the ridge( or the middle pillar as in the diagram) are carried out on the same principle as for a single-pitched roof.

The attic of a gable roof can turn into a full living room

If it is planned to equip a living space in the attic, then the rafter system is strengthened by a minimum number of retaining elements, so their location must be carefully calculated. Typically for this option, tightening is used, installed in the upper part of the structure - they can be used as a frame under the roofing of the attic ceiling. At the bottom of the rafters are supported by racks. They become an excellent base for the crate, on which the material of the wall covering is fixed. In this version the rafters are fastened together on the ridge of the roof at an angle to each other 85 ÷ 90 degrees.

Video: useful information on the planning of the gable roof system

Hinged and semi-fine roof rafters system

Hinged roofs have four slopes, the pediments have a triangular, sloping shape, and the side rails of the structure are trapezoidal. It is the triangular ramp that is called the hip - it joins the trapezoidal plane at a certain angle.

The hip roofs of the

are very original. Hip and half-shaft truss systems are almost identical and differ only in one feature: if in the hip construction all four slopes are located from the ridge to the eaves, then the half-tile end faces of the roof do not reach the cornice line.

The rafters of trapezoidal skates in these roof systems rely on long structural bearing walls, and triangular surfaces on short side walls. In addition, both in the hip and in the half-hail construction used diagonally installed rafters. They connect the upper part of the outer trusses with the corners of the structure and serve to support the rafters that form the hip.

In the semi-valley structures, the end triangular ramps are shortened, so they are suitable for regions with a large wind load and are planned so that the end side of the building is turned to the windward side.

These two types of roofs can also have a nylon or suspension construction of rafters, depending on the presence of internal capital partitions in the building.

This diagram shows the scheme of the hinged truss system:

Sample scheme of the roof hip roof system

As one or the other roof structure may or may not have an attic space. If the angle of the roof is small, then the overburden requires increased insulation, otherwise the premises of the house will quickly become damp.

It should be noted that even with a large slope of skates, this system is not suitable for building residential or business premises under it, since ramps on four sides considerably limit the attic space.

Elements of the construction of the hip or half-tusk roof truss system.

The slopes of the roofs of the hip and half-horn roof systems are usually located at an angle of 10 ÷ 12 degrees in an unclassified construction, and 25 ÷ 30 degrees when arranging in the attic of small rooms.

To cover the hip systems most often used piece roofing material or bitumen shingles. If you use large sheets of corrugated board or metal shingles for the roof, an unacceptably large amount of waste forms during their cutting.

Video: design and installation of the hip roof

Hinged truss system

The roof tent system consists of four ramps having the shape of an isosceles triangle, the upper corners converging at one point, the pyramid type. For the sake of fairness, we note that there may be more skates in the hipped structure, but in any case, the rafters of this system rest on equal walls of the structure.

Tent roof system - all diagonals converge at one point.

As can be seen in this diagram, triangular roof slopes - hips are formed by four diagonal rafters that form the roof ribs. They in the upper part of the roof converge at one point, and their lower side are fixed at the corners of the "box" of the house. These elements are the backbone of the frame, on which the rafters of the skates are fixed. Shaped roofs are able to withstand high loads, so they are perfect for buildings built in the windy regions of the country.

Exemplary design of the roof tilt roof system

Tent roofs can be built according to the principle of a tilting or suspended roof system, the choice of which also depends on the presence of a central support or internal bearing partitions.

To cover this kind of roof, a soft bitumen decorative roof is good - it will look great on the slopes, and also will not give a waste when performing cutting.

Hinged rafter system - very difficult to install

It should be noted that the tent structure can be called difficult to install, probably, therefore, it is rarely found on modern private houses. With its arrangement, a beam-tight system is used, reinforced with struts and struts.

Tent roofing systems can be built at different angles, depending on whether the attic will be set up and what function is assigned to it. Calculation of the height of the central part of the structure is made according to the above formula.

broken roofing systems. The roof of a broken type is usually made for a residential attic.

Broken roof rafter systems are used when it is planned to equip a living room in an attic space, since this construction forms the maximum spacious area of ​​future rooms. Each of the two slopes of a broken rafter system consists of two planes - the top and side.

Example of dimensional dimensions of the broken roof skylight

The upper parts of the skates are the roof of the structure, while the side parts immediately perform two functions - both the walls and the roofs.

The main elements of the roof truss system and the loads acting on them

As can be seen in this diagram, the construction of the broken roof is quite complicated, since each of the trusses consists of four stitched rafters, two of which form the upper, and the other two form the lower tier.

• The lower tier of the rafters rests on the joists and the girders installed between them or on the mauerlat fixed on brick or concrete walls. In addition, these rafters are fixed to the inner part of the wall by wire twists.
• The upper side of the side rafters is fixed at an angle to the runs installed and secured to the top of the racks.
• The upper tier of the rafter legs is fixed with its underside for the same runs, and the upper side for the ridge run.
• Runs of the middle part of the structure are connected with each other by a ceiling beam, overlapping the attic.
• The upper tier of the rafters can be hanging and stratified. It is designed to form the skeleton of a roof and a ridge.
• The angle of the rafters of the lower and upper tiers is chosen individually, but the ideal is considered to be the option when the angle of the rafter on the ridge is 120, and on the joints of the rafters of the lower and upper tiers 125 ÷ 130 degrees.
• The lining fixed to the truss system can be solid or thin, depending on the chosen roofing.
• For a broken system any roofing material can be used, but its thermal conductivity should be taken into account if the attic is insulated and heated.
• The entire structure is recommended to be closed with a waterproofing windproof film.

The attic can be cold, for example, if it is mounted over a summer cottage or if it is insulated, if it serves as the second floor for a capital private house.

Multi-deck roofing system

Multi-slope roof - the most complex of all

structures The multi-deck roofing system can be called the most complicated of all existing ones, as it often includes different roof shapes - it can be a gable and one-pitch, hipped, hip or half-combining. A similar option is chosen for houses with complex internal planning, and in recent years they have become more and more.

A variety of variants of multi-pitched roofs

Complex roof trusses are built over buildings that have T- or L-shaped form, as well as with more intricate configurations, with decorations, window openings, balconies under roofs and other elements. Therefore, to make it easier to understand such a design, it is divided into separate simple figures( rectangles, triangles, trapezoids), over which and this or that rafter system is planned.

When dividing a building into individual sectors, it is necessary to select the main part of the roof, to which adjoins will adjoin. Ridge runs of all attachments will be joined to the racks of the main rafter system.

Combination of several types of rafters on one roof

Since the multi-slope version of the roof consists of different rafter systems, making up the design of the future structure, you need to think over which roof structure and which sectors of the building it is best to choose.

Some useful recommendations for the choice of the roof system

All the above versions of the roofs can be installed on wooden, brick, erected from other materials of the structure. When choosing a roofing system for a particular building, you need to decide on several factors:

• It is decided in advance whether the premises or living quarters will be located in the attic space. If they are planned, it is better to choose a gable or broken roof skylight, but sometimes they can be arranged under a hip or gable construction.
• Depending on the internal construction of the house, that is, the presence of internal bearing partitions, a padded or hanging system is selected.

In addition, the number of allocated sectors of the house is taken into account. If there are several of them, the roof constructions for each of them are determined.

• There should be clarity with the type of roofing material that the roof is planned to cover, since the design of the rafter system also depends on it.
• It is necessary to provide for climatic features of the region - wind and snow load on the roof.
• The correct location of the house relative to the prevailing wind rose should be determined.
• Finally, you need to calculate your financial capabilities by estimating the necessary quantity of materials and their cost.

If there is no experience in the design and calculation of truss systems, the best way is to seek help from specialists who will offer different options for roofs and help to make all calculations. For fans of doing everything on their own, in addition to the above algorithm for calculating the "roof triangle", as a "bonus" we propose an algorithm for calculating the distributed load on rafters - this will help determine the cross-section of sawn timber for making rafter legs.

Load Calculator for

Truss System The initial data for calculations will be the construction region, the type of planned roofing, the angle of the roof slope. The calculation includes the step between the rafters - this value can be changed, achieving an acceptable value of the distributed load per running meter of the rafter.

The resulting value will be the basis for selecting the beam section( log diameter) for rafter legs in the table below:

Asto use the table?

For example, the value of the distributed load is 100 kg / bg.m. The design of the roof assumes the length of the rafters between the support points - 6 meters. By the table we see that we are satisfied with the second line from below. From it you can choose the required dimensions of the rafter's section: it is a log with a diameter of 200 mm or a beam with dimensions in the section of 70 × 230;80 × 220;90 × 210 or 100 × 200.

It's simple. It remains only to calculate the distributed load.

To begin with - by maps, determine the zones of your region by the level of snow and wind load:

Map of distribution of the territory of the Russian Federation for zones by the level of snow load

Map of the territory of the Russian Federation for zones according to the level of wind pressure

In the calculator, you will be asked to specify the zone and the sign of the openness of the space. There everything is clearly defined, but there is one nuance. Characteristic signs of the closure of the construction site should be located no further than in a radius of 30 × h, where h is the height of the roof that is being erected above the ground level. For example, the calculation is for a roof, located at an altitude of 6 meters. We estimate the surrounding space in a circle with a radius of 180 meters.

Having obtained the calculated value, it is possible to determine with lumber for the manufacture of rafter legs.