Calculation of the distance between the rafters from the length. The optimal distance between the rafters of a gable roof

The gable roof is the most popular design in private housing construction. The truss system of a gable roof should provide a support platform for mounting the roof. Properly calculated pitch of the rafters of a gable roof allows you to ensure the strength and stability of the structure to all external loads, create a durable and reliable roofing. This article discusses the design features of the truss system, the calculation and installation procedure. This information will allow you to correctly understand the methodology for creating a gable roof, so that during construction you do not ask unnecessary questions to workers.

The distance between the rafters for a gable roof

Among the people involved in the construction of a private or country house, there are constant discussions about the most successful roof design and the number of supporting elements. In order to understand these opinions and take one side or another, it is necessary to consider the general structure of the roof.

There are two types of rafter construction:

hanging.

Layered.

They are used on relatively small houses with a length of supporting elements of not more than 6 m. The structure consists of a number of truss trusses having the shape of an isosceles triangle. The trusses are installed on a strapping made of timber (Mauerlat), interconnected by batten strips. The bearing capacity of hanging rafters is relatively small, but the simplicity of design, economy and high speed of installation are their advantages. There are quite a few options for implementing hanging rafters, which is explained by the prevalence of small buildings that do not need a complex and massive roof structure.

Design layered truss system somewhat more difficult. Along the perimeter of the ceiling of the upper floor, a strong timber is laid - Mauerlat. Two (or more) vertical racks are installed along the longitudinal central axis, the height of which determines the angle of inclination of the slopes. A ridge run is installed between the posts, which runs along the entire length of the roof and serves as a reference line for the rafter legs. Each of them has two points of support - at the bottom it is a Mauerlat, and at the top - a ridge run.

For the formation of additional support, which excludes sagging of the supports, struts are used - inclined strips attached to the rafter legs at an angle close to a straight line and abutting in the lower part against the central lower bar - lying.

The step lag for the roof is the distance between two adjacent rafters. It is determined by the number of lags evenly distributed along the length of the longitudinal axis of the roof. The main supporting structures for the roof are rafters and lathing, forming inclined surfaces with a given geometry and area. The angle of inclination determines the wind and snow loads, and, with an increase in the angle, the wind load increases, and with a decrease, the snow load on the roof.

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What determines the pitch of the rafters

Consider the factors that determine the step between the rafters of a gable roof, in more detail. It must be immediately taken into account that the number of rafters determines the bearing capacity. Reducing their number complicates the installation of insulation, contributes to the sagging of the laths of the crate and the roof installed on them.

At the same time, too frequent placement of rafters also creates difficulties in the installation of insulation. It has to be adjusted in width, which creates waste, i.e. waste of material. Therefore, the size of the heat insulator is often used as a criterion for determining the pitch of the rafters. For example, many types of mineral wool are 60 cm wide, which is quite suitable for most gable roof designs.

In addition, the pitch of the rafters directly depends on their number. This is a calculated value, which is determined based on the bearing capacity of the supporting elements. The loads acting on the roofing, as well as the weight of the roofing itself, are quite large, so a stable and durable structure is needed to accept them. It must be borne in mind that the type of rafter system also matters, since layered rafters are much heavier than hanging rafters, they form a noticeable load on the walls and foundation of the house.

Wind and snow loads are external factors that affect the roof structure. The weight of snow in winter can crush or even break a roof if its design is not properly designed. The SNiP applications contain special data on the average annual amount of snow in different regions. Some of them have up to half a ton of snow per square meter.

In addition to snow, wind creates serious loads. At the same time, if the snow load is static, then the wind effects are sudden and uneven. The wind can rise at any time of the year, both in winter and in summer, which makes us take it seriously. When choosing the angle of inclination, you should find out the strength and direction of the prevailing winds in the region, find out about the possibility of hurricane gusts. Available in SNiP applications.

All these factors determine the parameters of the truss system and the distance between the individual supports.

The dependence of the pitch of the rafters on the material of the roof

There are many types of roofing. Most of them are noticeably outdated and are little used in modern construction. The most popular today are:

profiled sheet.

metal tile.

It should be noted that profiled sheet and corrugated board are one group of profiled coating. Some sources consider them to be different names for the same material, others separate them by wave height. The profiled sheet has a higher wave height, and the corrugated board is somewhat flatter. The first type can be used not only as a roof covering, but also as a material for the construction of fences, fences, metal garages, etc.

The corrugated board has a smaller wave and is intended for laying as a roof. Both materials have a common specific feature - profiling is performed only in the longitudinal direction, which expands their capabilities and allows you to make roofs for round roofs and canopies.

The step of the rafters of the gable roof under the corrugated board is selected taking into account this feature of the material. If the value is too high, it will be possible for the roof to sag between the rafters. In addition, there will be an excessive load on the battens, which may not be ready for it. An important parameter also becomes the area of ​​​​the slope. The pitch of the rafters of a shed roof under corrugated board is much less than that of a gable roof, since the length of the supporting elements and the magnitude of the load in it increase significantly and require an increased number of supports.

The metal tile looks like a canvas made of natural ceramic tiles. In all its operational qualities, it is very similar to corrugated board or profiled sheet, but physically it has an important feature - the presence of not only longitudinal, but also transverse waves. This allows you to slightly increase the step between the rafters of a gable roof under a metal tile, or be guided when choosing the size of a heat insulator.

When using slate or ondulin, the pitch of the rafters is taken according to the degree of rigidity of these materials. Alternatively, increase the density of the lathing, or install a solid version of thick plywood.

Method for calculating the distance between the rafters

There are two calculation options:

Engineering calculation using appropriate formulas and techniques.

Using online calculators, giving an answer after entering their own initial data.

The first method is only suitable for a professional roof system designer. For an unprepared person, it is extremely difficult to perform such calculations, since various specific data, coefficients, tabular values ​​are needed, which are difficult to find and must be used correctly. Calculations obtained using online calculators are also not recommended for use in real construction, but as an option to refine or verify the results of calculations performed by specialized organizations.

Video description

In the video you can see what the step of the rafters should be:

Conclusion

In conclusion, it should be recalled that all design and calculation activities must be carried out by trained and specially trained specialists. The pitch of the rafters is an important and crucial value that determines the bearing capacity of the roof. The damage caused by the inability to take on existing loads is quite serious and can call into question the possibility of living in a house, so it is necessary to take this issue as seriously as possible.

Before the construction of the truss system and the organization of the roof, a number of simple measures must be carried out, which will be the key to the integrity of the structure. This includes choosing the type of roof.

It can be hanging or layered, or maybe a combined version. This is when two types are combined in one building.

Live loads are snow cover on the roof in winter, water flows from rain in summer, wind, the load that a person exerts when carrying out maintenance work during the operation of the roof, etc.

Permanent loads include the weight of the rafter system itself, the weight of the roofing material and the roofing pie, the mass of interior decoration, if it is planned to organize an attic in the attic of the building.

When creating a project for a single-pitched or dual-pitched roof, first of all, they choose the type of truss structure, the angle of inclination of the roof slopes, as well as materials for the construction of the structure. When calculating the distance between the rafters, one should take into account the loads that will affect the roof of the building during operation.

• The weight of the roofing material;

• The weight of the building materials from which the roof truss frame is built;

• Weight of insulation, vapor barrier, waterproofing;

• The weight of the finishing material of the attic or residential attic space.

The following temporary loads also affect the roof of the structure:

• Snow weight;

• The weight of a worker performing maintenance and repair of the roof.

For the correct calculation of the pitch of the rafters, it is necessary to take into account the cross section of the elements of the structure under construction, the presence of thermal insulation of the roof, the type of lathing and roofing. Calculations should be performed on the basis of SNiP 2.01.85 "Loads and impacts".

Video on how to calculate the truss system:

Scheme for calculating the distance between the rafters

All calculations are carried out at the design stage of the building. They are carried out by design engineers of the organization where the house project was ordered.

If the project has not been drawn up and the person relies only on the experience of the masters who are entrusted with the construction of the roof, then in this case you need to familiarize yourself with the relevant documentation. These are SNiP 2.01.85 "Loads and Impacts" and "Changes from SNiP 2.01.85".

There is a detailed calculation scheme and a map of the country's climatic zones.

Further, they are determined with the type of roofing system and the purpose of the attic space. Indeed, depending on whether it is an unheated attic or a living room, the loads on the rafters will be different, and, consequently, the course of calculations also changes.

The calculations must necessarily take into account the climatic zone where the work is carried out, the structural material of the rafters and its cross section.

So, the pitch of the rafters is the distance between the rafter legs. It can vary within 0.6 m - 1.0 m.

Calculation progress:

1. First, the length of the roof slope is measured. Further, this value is divided by the step length of the rafters of the selected material. This indicator is taken from the SNIP and is unique for each building material and also depends on the beam section used;
2. one is added to the result of previous calculations and rounded up. Thus, an integer value is obtained and it indicates the required number of beams;
3. the length of the roof slope is divided by the resulting integer. The result will show how many beams are needed to build a high-quality and durable roof.

Experts point to the following feature of roofs with a steep slope. When erecting them, you can reduce the distance between the rafters. This is due to the transfer of the load from the beams to the wall of the house.

The distance between the rafters for different types of roofs

However, the calculation of the distance between the rafters cannot be carried out so unambiguously. After all, this indicator also depends on the type of structural material used for the roof.

The distance between the beams for a roof made of metal

The average weight exerted on the roof is 35 kg/m². To withstand it, the roof must have a step of 0.6-0.9 m. In this case, a beam with a section of 50x150mm is used.

However, metal tiles are often used in the construction of country houses and cottages. And in such structures, the attic space is often equipped as a living room.

This leads to the installation of a roofing pie and all kinds of heaters, which, in turn, put an additional load on the rafters. Therefore, it is recommended to increase the cross section of the beam for beams. This is especially true for regions with low air temperatures in winter. The recommended dimensions of the rafters are 50x200mm.

In addition, the distance between the rafters can be adjusted to the width of the insulation. This will not only increase the bearing capacity of the roof, but also simplify the arrangement of the heat-insulating layer, and reduce the consumption of insulation.

The distance between the beams for the roof of corrugated board

The recommended rafter pitch for a roof is 0.6 m - 0.9 m. However, here it is necessary to take into account the operational characteristics of the corrugated board itself. If the step is large, then the corrugated board will “sag” under its own weight, thereby changing the geometry of the roof and its technical characteristics.

To prevent this, you need to mount additional boards with a large section as a crate. They will act in some way as rafters.

The cross section of the rafters for roofing from corrugated board is 50x100 mm or 50x150 mm. The crate is made of a board with a section of 30x100 mm.

The distance between the beams for a roof made of ceramic tiles

Ceramic tiles are a heavy material for roofing. It exerts a load on the rafters in the range of 40-60 kg per m². That is why the distance between the rafters in this case will be minimal - 80-130 cm. The greater the weight, the smaller the distance. However, the latter indicator may decrease, depending on the angle of the roof. The larger it is, the less often you can mount beams.

Installation of the structure for ondulin

The step of the rafter legs under the ondulin should be 60-100 centimeters. For the manufacture of rafters, lumber with a section of 200 × 50 mm is used. This is enough to create the most durable and reliable truss frame.

It should be noted that under this roofing material it is necessary to make a continuous crate. Due to this, the material will better resist snow loads and solar exposure.

Sometimes a thinned type of crate is used. For its manufacture, a wooden beam is used. The distance between adjacent elements should be less than 30 centimeters. This option, as a rule, is more expensive compared to a continuous crate.

Rafter system under slate

Slate roofing is considered the most common in Russia. The main reason is the low cost of this roofing material, the ease and speed of installation work. Also an important advantage is the possibility of replacing individual damaged slate sheets with new ones.

The distance between the rafter legs for a slate roof should be 80 centimeters. This distance is considered the most optimal.

The crate under the slate should be thinned out. For its manufacture, a board or timber with a cross section of at least 30 millimeters is used. It is this thickness of the timber or board that is required for the qualitative distribution of the weight of the roofing and winter precipitation.

When erecting a rafter system, one should remember about a constant margin of safety. It may be needed in case of bad weather and under mechanical stress.

Rafter frame for a soft roof

Soft roofing includes soft tiles, bitumen-polymer and bituminous roll materials, as well as roofing membranes. The main advantages of this type of roof include low weight, as well as the absence of the need to build a massive rafter system.

The minimum pitch of the rafters is 60 centimeters, and the maximum is 150 centimeters. When erecting a rafter frame under a soft roof, the angle of inclination of the slopes should be taken into account. In other words, the smaller the slope of the roof slopes, the less you need to make the distance between the rafter legs for a continuous crate.

The distance between the rafters also depends on the material from which the crate will be made. The greater the thickness of the plywood or OSB sheet, the greater the pitch of the rafters can be.

Roof made of sandwich panels

Roofing of this type, as a rule, is erected on hangar-type buildings or houses made of sip panels. Sandwich panels have bending rigidity, so their installation does not require the installation of traditional rafter legs.

If the spans from the top of the wall to the ridge of the gable roof are small, then the sandwich panels are mounted without additional supports.

With a span length of more than 400 centimeters, it is necessary to install additional runs. When building a roof from sandwich panels, a traditional truss frame is often erected on a residential building. However, in this case, the distance between the rafter legs can be made large, since they serve as a support for the runs.

Choose the distance between the rafters based on the length of the bearing walls and the length of the material for the runs. Roofing made of sandwich panels is able to withstand high operational loads.

Construction of a truss frame for polycarbonate

Recently, polycarbonate is often used in the construction of roofing. It is used in the construction of sheds, winter gardens and arbors. The rafter frame and crate are made of metal or wood.

Polycarbonate differ in weight, which depends on the thickness of the sheet. The step of the crate for polycarbonate should be from 60 to 80 cm. The crate made of metal or wood is attached to the rafters (straight or arched).

The distance between the rafter legs for polycarbonate, as a rule, is 150-230 cm. To correctly calculate the distance between the rafters, it is necessary to take into account the glazing area, the thickness and dimensions of the sheets. It should also be remembered that polycarbonate sheets are mounted with small gaps.

A shed type of roof is rarely seen in private housing construction. Although, according to some, this is in vain, because the installation of a shed roof is much easier than the installation of a gable roof. On the other hand, such a roof design will not be able to keep the heat in the room so well. That is why shed roofing is most often used to build a garage, country house or barn.

True, if the work on thermal insulation is correctly performed, then the structure may well be warm. In this case, a living room is made under a pitched roof. Let's look at the advantages of a shed roof, what types of truss systems exist, how the design is calculated. In addition, we will consider how to install this type of roof.

Pros and cons of a shed roof for a house

Beginners in the construction business will be delighted that such a shed construction is quite simple and can be done by hand. True, it is impossible to call the work the easiest, but with detailed instructions, a shed roof will be created. But before considering the design features of the roof, you need to find out its features and advantages. They characterize this type of roof.

Advantages of a pitched roof:

1. Profitability. For the device of the roof, a lot of building materials are not needed, on which the bulk of the funds are spent.
2. The simplicity of the truss system and the shed structure as a whole. The best thing for beginners. Installation will be easier than with a gable roof.
3. The building will have a small weight. This means that there is less load on the walls and foundation.
4. Thanks to this shape, the shed roof perfectly resists the wind load, as well as the weight of snow that accumulates on the surface.
5. The angle of inclination is very different, depending on the needs. It varies from 5° to 45°.
6. If you make the angle of a shed roof small, then it can be used for various purposes. For example, if this is a barn, then install a tank for heating the liquid. If this is a living space, then on a shed roof you can equip a great place to relax. Alternatively, install solar panels as an alternative power source.
7. The versatility of a one-slope building. It is covered with almost any material available on the market. It all depends on the operating conditions and the chosen angle of inclination.

Despite all its advantages, a shed roof has its drawbacks. This is not surprising, since nothing is perfect, but it is better to know about the cons and use them profitably.

Cons of a shed roof:

• The first concerns insulation. There is no more space with an air gap under the structure, so the issue of insulation should be taken more seriously. If you do not make thermal insulation of the structure, then in summer the attic will be too hot, and in winter, on the contrary, it will be supercooled. In either case, the temperature (high or low) will be transmitted to the house. Correct calculations and high-quality insulation will help eliminate this;
• when creating a ceiling immediately under the roof, made at a slight angle, the house will not have an upper air gap and an attic. And in this case, living space cannot be organized;
• due to a slight slope, which reaches from 5 to 10 °, snow and moisture will accumulate on a shed surface.

Despite all the obvious disadvantages, a shed roof is an ideal option for creating a garage and other buildings on the site.

Calculation of the construction of a single-pitched roof

This is the first stage before the installation of the truss system. It is recommended to draw up a detailed plan or drawing, which will be guided by when working. To create this schema, you need to highlight the following data:

• the total width of the roof construction, as well as the length of the spans that is formed between the bearing walls;
• slope angle, desired or obtained;
• the length of the single-pitched roof;
• selected roofing material;
• what is the height and width of the load-bearing walls.

Note! When a shed roof is created for a barn, garage or country house, you can simply raise the front wall of the structure above the back.

As a result, the angle of the slope will depend on the height of the rise. The second option involves the creation of supports, on which the run will fit. The second way allows you to save building materials.

For drawings, you need to know the following nuances:

The drawing of the future shed roof should have all the necessary information about the elements. The dimensions, distances between them, fastening features, etc. are indicated. Below is an example of such a drawing of a pitched roof.

Choosing the corner of a pitched roof

The angle of the slope is chosen taking into account the fact that the resulting roof forms a triangle, one corner of which will always be right. The legs are the floor beams and the gable part of the building, and the rafters serve as the hypotenuse. This is clearly seen in this diagram.

The designations are as follows:

• Lc - the length of the rafter used;
• Lbc - our leg, indicating the height of the pediment from the floor beam to the roof plane;
• Lsd - the width of the building;
• A - the selected or desired angle of a pitched roof.

Given the basic values, it is possible to calculate all the parameters of a single-slope structure. There is a formula for this. The first is used when the width of the building and the planned height of the pediment are taken as the basis. In this case, the formula is:

When you have decided on the angle of the shed roof, then you need to calculate the future height of the gable. For this, the formula is:

In this case, the length of the roof rafter legs is calculated as follows:

Note! This length of the rafters does not take into account the canopy from the rear or the facade of the room.

Many criteria influence the choice of slope angle. The main one is the choice of roofing material. Each of them is recommended to buy for a particular angle of inclination. Here are recommendations for popular roofing materials:

1. For the installation of corrugated board, the slope must be at least 8 °.
2. When using metal tiles, you will need to make a roof with an angle of inclination of 30 °.
3. For a slate device, indicators from 20 ° to 30 ° are needed.
4. As for rolled roofing materials (roofing material, shingles and soft roofing), the angle of inclination should be 5-7 °, no less.

Advice! A roof without a heating system in an area where there is a lot of snow in winter, the ideal solution would be a single-pitch roof with a slope of 40°, regardless of the roofing material. So all precipitation will quickly descend from it.

Varieties of the truss system of a shed roof

There are three options for creating a truss system. The choice of design depends on the size of the room and its type.

Now that we have dealt with the design of the truss system and learned its types, we can consider the process of creating a shed roof.

Installation work on the creation of a pitched roof

Having on hand the drawings and the selected type of system, you can get to work. You will also need the appropriate tools and lumber. The installation of the truss system is performed as follows:

1. For safety, the building should be covered with beams. They are placed on the wall. To extend their service life, roofing material is glued to the wall. It will protect the beams from moisture and decay. You need to position the floor sticks in the same way as the rafters. Fastening pitch -500-800 mm.
   
   
2. Mauerlat is laid on top of the beams. This is a massive beam that will serve as a support. It fits on the back bottom wall of the building.
3. To safely move around the roof, flooring from wooden boards is laid on the floor beams. He is temporary.
   
   
4. Now you need to build a gable wall. It is made from the same material as the building itself. You can use lighter material. For example, if the walls are brick, then the pediment rises by means of bars or boards.
5. Floor beams must be covered with waterproofing and walled into the wall. The pediment rises to the chosen height, according to the drawings.
6. On the finished pediment, you can fix the Mauerlat. It turns out that two Mauerlat are parallel to each other.
7. Markings are applied to the lower wall for attaching the rafter legs. The fastening elements themselves are fixed.
8. To firmly fix the rafter, based on the drawings, grooves are cut on it. This is a good mounting option. The grooves are in two places, top and bottom, to enter the Mauerlat. There are other methods of fixing the rafter leg, as shown in this photo.
   
   
9. After that, the legs are fixed with special corners and fasteners. From above, at the pediment, the legs are screwed rigidly. But the lower part is made depending on the chosen truss system of a pitched roof. It can be rigidly fixed or made sliding.
   
   
10. There is a certain sequence of inserting rafter legs. First, the extreme elements of the truss system are mounted. A cord is stretched between them, serving as a guide and level for subsequent rafters. Do not forget that the step of the rafters corresponds to the step of the floor beams.
11. The rafters that are already installed are connected to the floor beams through racks, struts and other elements to give them stability. We talked about them above. Fixation is carried out with metal corners and staples.

    Tip! If you want to lengthen the rafters and bring them out of the wall, then “fillies” are attached to the bars. So you can protect the adjacent part of the structure from precipitation.

    

12. When the construction of a shed roof is ready, you can begin to insulate and create a roofing pie.

The photo shows what layers the correct insulated shed roof should consist of.

Insulating material is laid between the rafters. He has to hold on tight there. After that, a counter-lattice for ventilation is made on top. A waterproofing film is laid on the counter-lattice. It protects the insulation from moisture, which can ruin it.

As for the crate for laying roofing material, it is selected depending on what kind of roofing material it will be. For example, a solid crate of boards or plywood is needed when installing soft tiles and other rolled materials. If metal tiles, corrugated board, slate, ondulin and other types of hard roofing are used, then the crate is done in a row. The step depends on the roofing material.

And in order to protect the insulation from the inside of a shed roof, you need to sheathe it with a vapor barrier film. Now we can say that the shed roof is completely ready.

Note! If a shed roof is made for a barn or other non-residential structure, then it is not necessary to insulate it. It is better to spend them for another purpose.

Conclusion

Creating a roof, whether it is a gable or single-pitched, is a dangerous, time-consuming and responsible process. That is why caution is required and strict adherence to the instructions for creating a structure. Only then can the best result be achieved.

The distance between the rafters is one of the key parameters that affect the strength of the structure. Competent calculation of the installation step of the rafters allows you to build a roof that is resistant to high operational loads.

Roof loads and rafter system calculation

The development of a single-pitched or dual-pitched roof project begins with the choice of the type of truss system, the angle of inclination of the slopes (roof height) and materials for the construction of the structure. The calculation of the distance between the rafter legs is carried out taking into account the loads that the roof will experience during operation. Permanent loads include:

• the weight of the materials from which the truss system is made;
• roofing weight;
• weight of roofing cake materials (waterproofing, vapor barrier, insulation);
• the weight of the finishing elements of a residential attic or attic.

In addition to permanent loads, the roof also experiences temporary ones, which include:

snow cover weight;

the weight of a person during the maintenance and repair of the roof.

A step is the distance between the rafters of one slope. When calculating a shed, gable or complex roof, the following scheme is usually followed:

• the length of the future roof slope is measured;
• the resulting value is divided by the optimal numerical value of the pitch of the rafters;
• one is added to the obtained value, the result is rounded off;
• the length of the roof slope is divided by the rounded result.

The final result will determine how far the rafter legs should be placed. The determination of the step cannot be extremely accurate, since it is necessary to take into account a number of additional factors, including the width of the insulation, the particular installation of the crate for various types of roofing material. If a roof with a chimney is being designed, the pitch can be adjusted according to its location so that it is not necessary to remove part of the rafter in the future and install a supporting structure, such as a special rafter system.

The distance between the rafters under the slate

Slate is a traditional roofing material. Its advantages include such characteristics as resistance to external influences (excluding mechanical ones) and low cost. Slate allows you to create a roofing, the repair of which can be reduced to the replacement of individual elements. Slate is heavy and requires the installation of a sufficiently powerful truss system. The calculation of the distance at which it is necessary to put the rafters under the slate is carried out taking into account the cross section of the beam for the manufacture of rafter legs.

The optimal solution is to install the system under the slate, in which the gap between the rafters must be at least 800 mm. In order for the slate structure to withstand not only the weight of the material, but also increased external loads, the crate is made of timber or boards with a cross section of at least 30 mm. When calculating the truss system for slate, it should be read that this material has rather large restrictions on the choice of the angle of inclination of the slopes.

Rafters for metal roofing

Metal tiles are actively used as a practical and aesthetic roofing material when arranging a shed, gable, hip or complex roof. The frame for the metal tile is built according to standard principles. To calculate at what distance it is better to place the rafters, it is necessary to take into account the loads and the angle of the roof. The metal tile is characterized by relatively low weight, so it can serve as a replacement for the old roofing of slate or ceramic tiles. In this case, the rafters do not need to be strengthened or the pitch of their installation changed.

The standard step of rafters for metal tiles is 600-900 mm. The cross section of the elements can be 50-150 mm - this is enough to create a reliable frame for a metal tile. But if it is planned to use insulation, the layer of which in areas with low winter temperatures should be 200 mm, it is recommended to use a 200x50 beam for rafters under metal tiles so as not to mount an additional system that holds the insulation. The gap between the rafters under the metal tile is best adjusted to the width of the sheet or roll heat insulator.

Decking: rafters and crate

The professional flooring belongs to easy and convenient roofing materials in application. Galvanized or coated with a decorative and protective layer, corrugated board can be used both for mounting a shed roof of a utility room or garage, and for a gable roof of a residential building. How to calculate the distance required to install the rafters under the corrugated board?

To ensure the necessary rigidity of the structure, it is enough to install the rafters under the corrugated board in increments of 600-900 mm. In this case, it is necessary to pay attention to the angle of the roof. The calculation shows that with high external loads, it is better to lay the corrugated board on the system with a minimum step. But if the distance between the rafters under the corrugated board is close to the maximum, and the angle of the roof slope is small, then the structure is strengthened by using a more frequent crate. In this case, the step of the crate under the corrugated board should be about 50 mm, the width of the elements should be at least 100 mm.

Rafter system for soft roofing

Soft roofing includes bituminous and bitumen-polymer roll materials, roofing membranes, as well as soft tiles. A soft roof is characterized by a relatively low weight and no need to install a massive truss structure.

The minimum distance between the rafters is 600 mm, the maximum is 1500 mm. When installing a support under a soft roof, it is important to take into account the angle of inclination of the slopes: the smaller the angle, the smaller the distance between the supports for a continuous crate should be. The choice of step is also influenced by the thickness of the material for the crate - the thicker the sheet of plywood or OSB, the greater the installation step of the rafter legs can be.

Ondulin: calculation of rafters

Ondulin (bituminous slate) is laid on a flat, continuous crate made of sheet material. This allows the roofing to successfully resist wind and snow loads. The crate under the ondulin rests on the rafters, which should be located in increments of 600 - 1000 mm, depending on the angle of inclination of the gable or shed roof.

Rafters for ondulin are made of timber with a section of 200 × 50 mm. When choosing at what distance to put the rafter legs for the structure under the ondulin, it is recommended to take into account the width of the insulation material in order to simplify its installation. This calculation allows you to reduce the financial costs of arranging the roof.

Sandwich panel roof

Sandwich roofing is most often erected on sip-panel houses or hangar-type buildings. A feature of the sandwich is its bending rigidity, which makes it possible to dispense with the installation of traditional rafters. Small spans from the ridge of a gable roof to the upper part of the wall (or the distance between the supporting structures of a shed roof) allow the installation of a sandwich without additional supports.

If the span exceeds 4 meters, additional girders must be installed. To install a sandwich roof on a residential building, a traditional rafter system is often installed, but in this case the rafters can be positioned with a large step - they serve as a support for the girders. The distance between the rafter legs is selected based on the length of the available material for the runs and the length of the load-bearing walls. The technical parameters of the sandwich allow the roof to withstand high operating loads.

Polycarbonate: erection of the supporting structure

Polycarbonate has recently been actively used as a roofing material. First of all, polycarbonate is in demand in the construction of gazebos, sheds, winter gardens. The crate and truss system for polycarbonate can be made of wood or metal.

Polycarbonate varies in weight depending on the thickness of the sheet. The crate for polycarbonate is recommended to be done in increments of 600-800 mm. The crate (wooden or metal) is mounted on rafters, which can be straight or arched. Usually the gap between the rafters for polycarbonate is from 1500 to 2300 mm. In order to correctly calculate at what distance it is better to bleed the rafters, it is necessary to take into account the glazing area, the dimensions and thickness of the sheets, and take into account that polycarbonate is attached with gaps for thermal expansion.

The distance between the rafters of a gable and single-pitched roof

Find out what distance between the rafters you need to make for a gable and shed roof. The maximum distance between the rafters for metal tiles, ondulin and soft roofing.

The distance between the rafters: principles and examples of calculating the pitch of the truss system

The task of correctly calculating the distance between the rafters is very responsible. Not only the reliability and durability of the roof, but also all subsequent work on it will depend on how seriously you begin to solve it: laying insulation, installing roofing, installing additional elements. If you manipulate the step of the rafters under the roof sheets, as many do, then it is not a fact that a heater will then enter between the rafters. If you focus only on insulation, the very first winter with its abundant Russian snow will crush the truss system. That is why the whole point is to choose the optimal rafter pitch for all slopes, and now we will teach you this skill.

What determines the pitch of the rafters?

So, the distance between the rafters is determined by such important factors:

1. The shape of the roof (gable, single-pitched or multi-pitched).
2. Roof angle.
3. The parameters of the timber that is used for the manufacture of rafters (width, thickness).
4. The design of the truss system (layered, hanging or sliding).
5. The totality of all loads on the roof (covering weight, atmospheric phenomena, etc.).
6. Lathing material (20x100 or 50x50) and its parameters (solid, with gaps of 10 cm, 20 cm or solid plywood)

And each of these parameters must be taken into account, which is exactly what this article is about.

Decorative rafters: 0% load

First of all, decide on the most important point: the type of roof and its purpose. The fact is that the roof of a residential building in winter can withstand a large cap of snow, a constant wind at a height and it is often insulated from the inside, but completely different requirements are imposed on the rafter system of a small gazebo hidden under the crowns of trees.

For example, if you are building a pergola in its classical sense, then it does not matter at all what exactly the distance between the rafters will be - this is already a purely aesthetic factor:

In the above illustration, it can be seen that even in such a building there is a step of rafters. After all, here it provides both an aesthetic factor and the rigidity of the structure itself. But the step is chosen arbitrarily.

Functional rafters: detailed calculation

We approach the main question: what distance should be between the roof rafters of a residential building? Here, be patient and carefully study all the nuances.

Item 1. Wall length and rafter spacing

First of all, the step of installing rafters on the roof of a residential building is usually chosen according to the structural size of the building, although taking into account many other factors.

For example, it is easiest to install rafters in increments of 1 meter, so for a wall 6 meters long, 7 rafters are installed as standard. At the same time, you can save money by placing them with a distance of 1 and 2 meters, and you get exactly 5 rafters. It can also be placed with a distance of 2 and 3 meters, but reinforced with a crate. But it is highly undesirable to make a step of rafters more than 2 meters.

Item 2. Influence of snow and wind loads on the shape of the roof

So, we settled on the fact that the average distance between the rafters of an ordinary roof is 1 meter. But, if there is a significant snow or wind load in the area, or the roof is more or less flat or simply heavy (for example, covered with clay tiles), then this distance must be reduced to 60-80 cm. But on a roof with a slope of more than 45 degrees, it can be even zoom to a distance of 1.2m-1.4m.

Why is it so important? Let's figure it out. The fact is that the air flow collides on its way with the wall under the roof of the building, and turbulence occurs there, after which the wind hits the eaves of the roof. It turns out that the wind flow, as it were, goes around the slope of the roof, but at the same time trying to raise it. And in the roof at this moment there are forces that are ready to rip or overturn it - these are two windward sides and one lifting.

There is another force that arises from wind pressure and acts perpendicular to the slope, trying to push the roof slope inwards. And the greater the angle of inclination of the roof slope, the more important are the safe wind forces and the less tangential. And the larger the angle of the slope, the less often you need to put rafters.

To understand whether you should make a high roof or a flat one, this map of the average wind load will help:

The second point: in the Russian region, such an atmospheric phenomenon as snow constantly affects the standard roof of a house. And here, too, you need to consider that the snow bag usually accumulates more on one side of the roof than on the other.

That is why in such places where such a bag is possible, it is necessary to insert paired rafter legs or make a continuous crate. The easiest way to determine such places is by the wind rose: single rafters are placed on the windward side, and paired rafters on the leeward side.

If you are building a house for the first time, then you will not find your own worldview, but determine the average snow load for your area according to official data:

Point 3. The issue of insulation and the standard width of mats

If you will insulate the roof, then it is advisable to set the pitch of the rafters under the standard dimensions of the insulation boards, which are 60, 80 cm and 120 cm.

Modern heaters today are sold in standard widths, usually at the same standard rafter spacing. If you then take them and adjust them to existing parameters, then there will be a lot of waste, cracks, cold bridges and other problems.

Point 4. The quality and strength of the lumber used

Of great importance is also what kind of material you use to build the truss system. So, for each type of wood there is its own regulatory documentation, which concerns its bearing capacity:

Because for the manufacture of the roof truss system in Russia, pine and spruce are most often used, their bending strength and features of use have long been prescribed. If you use wood of other species, then you can display the correction factor.

In addition, if there are sections, cuts or bolt holes on the rafter, in this place it is necessary to calculate the bearing capacity of the bar with a factor of 0.80.

Item 5. Distance between puffs and floor beams

One more thing: if the roof is built with interconnected roof trusses, and their lower belt is used simultaneously as floor beams, then the distance between the trusses must be made within 60-75 cm to take into account the design of the future floor.

Item 6. Loads on truss nodes

So, here are the main loads that act on the roof truss system:

1. Static, which includes the weight of the rafter system itself, the weight of the roof, snow lying on the roof and additional elements.
2. Dynamic, which includes wind force, unexpected damage to the roof, the weight of a person and equipment for repairs, and similar factors.

And all these factors are able at a certain moment to act on the roof at the same time, and therefore there is such a thing as a critical value. This is exactly the value of the loads at which the roof does not withstand and deforms.

Therefore, if the building is being built with significant spans, then steel truss trusses are necessarily used. The fact is that there is no tension in such rods, and the entire load falls on the nodes - here they are affected by compressive and tensile forces. And the distance between such farms is calculated depending on the type of roof and the design of the roof itself.

Usually, a unified truss is placed with a span that is a multiple of six, and therefore a distance is made between the truss nodes that is a multiple of one and a half meters.

Item 7. Weight of the rafter system and roofing cake

Do not forget that the main purpose of the rafters is to hold the entire roof on itself, and its weight is crucial:

Point 8. Ease of installation of roofing

The distance between the rafters is also influenced by such a factor as the selected roofing. The higher the slope of the roof, the more roofing materials will be used. And the heavier they are, the more often you will have to put rafters under them. But what about a full slab? The fact of the matter is that it also has its own weight:

Each type of roof has its own optimal rafter pitch. After all, many standard sheets at the edges need to be fixed directly to the rafter or crate, and it is important that they match. Otherwise, roofing work will easily turn into a living hell at a height, believe me.

That is why, even before starting installation, it is necessary to make a layout, check everything several times. And to know some important subtleties for each type of coating.

Determining the totality of loads on the roof as a whole and the rafters separately

So, we have determined that, in addition to other design factors, a whole set of loads simultaneously acts on the roof truss system: the weight of the truss system, a snow cap, wind pressure. After you add all the loads together, be sure to multiply them by a factor of 1.1. So you all count on unexpected favorable conditions, that is, lay an additional 10% percent strength.

And now you just have to divide the total load by the planned number of rafters and see if each of them will cope with its task. If it seems that the design will be frail - feel free to add 1-2 rafters to the total, and you will be calm for your home.

You need to make a calculation for destruction, i.e. to the full load that acts on the roof. All these loads are determined by the technical characteristics of materials and SNiPs.

The standard roof structure is rafters, lattice runs, and each of these elements works only on the load that puts pressure on it, and not on the overall roof as a whole. Those. each individual rafter has its own load, total, but divided by the number of rafter legs, and by changing the step of their location, you change the load collection area on the rafters - reducing it or increasing it. And, if it is inconvenient for you to change the pitch of the rafters, then work with the parameters of the section of the rafter legs, and the total bearing capacity of the roof will increase significantly:

In this calculation, try to ensure that the longest rafter in your project is no more than six and a half meters, otherwise, splice along the length. Now let's explain in more detail. So, on roofs with a slope of up to 30 degrees, the rafters are the so-called "bendable elements". Those. they work specifically for bending, and there are certain requirements for them. And the possibility of deflection of the rafters is calculated according to a special formula, and if the result exceeds the norm, then the rafters are increased in height and a new calculation is made again.

But on the roof with a warehouse slope of more than 30 degrees, which rafters are already considered “bendable-compressed” elements. That is, they are affected not only by a uniformly distributed load, which causes the rafters to bend, but also by forces that are already acting along the axis of the rafter. In simple terms, here the rafters not only bend a little under the weight of the roof, but are also squeezed from the ridge to the Mauerlat. In addition, the crossbar, which usually holds back two rafter legs, must also be checked for tension.

As you can see, even a person who is far from construction can cope with such calculations. The main thing is to take everything into account, be attentive and ready to spend a little more time on design, so that later all the work goes like clockwork!

The distance between the rafters: what step should be between the rafters

Detailed instructions on how to correctly calculate the distance between the roof rafters of different structures, taking into account the amount of loads and the material used.

The quality and durability of the roof largely depend on the correct calculation of the pitch of the rafters. It affects the laying of insulation, the fastening of roofing material and the installation of additional parts. Pay attention only to the requirements for the distance under the roofing sheets, then there may be problems with the insulation boards. And vice versa, adjusting the size of the insulation can make the frame too weak, and in winter there will be a threat of collapse. How to correctly calculate the distance between the roof rafters? We will talk about this in our article.

As a rule, the pitch between the rafters depends on several factors. But usually the distance fluctuates between 0.6 and 1.2 meters. These figures are rounded, in practice the distance may differ by several centimeters downwards. For an accurate determination, the following calculations must be performed:

1. Determine the length of the slope by measuring along the eaves of the house. Suppose that it turned out 17.8 meters.
2. Divide the figure obtained by the planned step of the rafters. If it was decided that the distance between the beams would be 0.8 meters, then 17.8 / 0.8 = 22.25.
3. Further, we round the result up and add one: 23 + 1 = 24. At this stage, the number of rafters required is determined.
4. Now we calculate the distance between the axes of the beams. To do this, the length of the slope must be divided by the number of rafters: 17.8 / 24 \u003d 0.74 m.

So, you will determine the real distance at which the rafters for a roof made of metal or some other material should stand.

Often, when planning a roof frame, specialized calculators are used. They enter basic data and get the finished result. Nevertheless, you should not completely trust the program, since only a person can take into account some conditions. When calculating, you can understand how the system works, what loads are acting. If necessary, adjustments are made to strengthen or facilitate the design. Self-calculation will help to more accurately determine the required pitch of the rafters of a gable and single-pitched roof.

Step calculation depending on the roofing material

For each coating, its own standards and dimensions are developed for the truss system. The main factors are the strength of the material, its weight and resistance to external loads. Consider the main types of coatings.

Decking

The step of the rafters under the corrugated board can vary from 0.6 to 0.9 m. The final result depends on additional conditions, which we will discuss below. If for some reason the step should be larger, a transverse board with a large section is added. In this case, usually the rafters themselves are chosen with dimensions of 50x100 or 50x150 mm.

In addition to the rafters, a crate of 30x100 millimeters is used. The gap between the boards should be about 0.5 meters. It can be more, it all depends on the type of corrugated board and the height of the wave. Sheathing boards protruding beyond the boundaries of the eaves should have a thickness of 1.5 cm more than usual. This is done based on the need to mount ventilation, a chimney or a drain.

Ceramic tiles

The main difficulty in designing a roof frame for ceramic tiles is the large weight of the material for the roof. It is 10 times heavier than corrugated board and accounts for 40 to 60 kg per square meter.

Under such a coating, dry beams are used, with a moisture content of only 15%. Their cross section should be either 50x150 or 60x180 mm. With such indicators, the maximum allowable distance between the rafters can be 1.3 meters. The minimum allowable step through which the rafters can be placed is 0.8 m. The roof slope affects the final decision: at 15 °, the step is 0.8 m, at 75 ° - 1.3 m.

The length of the rafter leg is also taken into account, the shorter it is, the larger the gap, and vice versa. In addition, if the slope is less than 45 °, and movement is planned on the surface, the beams are placed in increments of no more than 0.85 m.

The distance between the boards of the crate is selected so that each intersection of the tiles has its own base. The standard length of the material is 400 mm, and the amount of overlap during installation varies between 55 and 90 mm. It turns out that the distance between the central axes of the crate can be either 310 or 345 millimeters.

metal tile

In recent years, the question has been particularly acute: how to determine the distance between the rafters under the metal tile? It imitates more expensive ceramic material, but at the same time it has the positive properties of corrugated board. Installation of such a coating is simple and does not require large financial costs. All this makes the material attractive for the roofs of private houses.

The mass of metal tiles is less than ceramic, so a simpler frame is required. The section of the beams is reduced to 50x150 mm and the step between the crate is increased. The step of the rafters under the metal tile varies between 0.6 and 0.95 m.

Ondulin

The allowable step for covering from ondulin is 0.6-0.9 meters. The standard section of the rafters is 50x200 millimeters. Such dimensions will allow to withstand the load of the roofing pie on the gable roof.

On top of the counter-lattice, a crate of bars measuring 40x50 millimeters is attached. The pitch between the central axis is 600 mm.

Additional factors

When calculating the pitch of the rafters, attention is paid not only to the type of roofing. Many other points are taken into account, data on which can be found in reference books and SNiPs. Here are some of the factors:

1. Snow and wind loads. The more snow falls in winter and the stronger the winds blow, the smaller the distance between the beams should be. But, if you increase the angle of the roof slope over 45 °, then it is allowed to increase the step.
2. Choice of heater. To reduce the cost of insulation boards, it is recommended to take into account their standard sizes. They produce mats with a width of 600, 800 and 1200 mm. If this condition is neglected, then a large number of undercuts will appear, cold bridges and construction will be delayed.
3. lumber quality. It takes into account the type of wood, grade and section. As mentioned above, strength is affected by how well the beam was dried. When buying wood, pay attention to evenness and the presence of defects in the form of knots and traces of pests.
4. Floor beams and puffs. If you equip the attic floor under a gable roof, then the maximum distance between the rafters should be 0.75 meters.

The calculation of the distance between the beams for a gable and single-pitched roof is different. Even if he makes several slopes, for each it is necessary to make a calculation individually. This is especially true for buildings with different lengths of cornices.

Taking into account all these factors, it is possible to determine how far the rafters should be installed. Although all calculations can be done independently, since reference data is freely available, it is better to turn to professionals. They have experience in designing, they will quickly determine the required distance between the rafters. So, you will avoid possible mistakes and be sure of safety.