Through what distance the rafters are placed when constructing roofs. Calculation of the pitch of the rafters for various roofing materials Step of the rafters for the roof

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

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

Pros and cons of a pitched roof for a house

Newbies in the construction business will be delighted that such a single-slope structure is quite simple and can be done by hand. True, it is impossible to call the work the simplest one, but with detailed instructions a pitched 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:

Profitability. For the construction of the roof, you do not need a lot of building materials, on which the bulk of the funds are spent.
The simplicity of the rafter system and the shed structure as a whole. Most for beginners. Installation will be easier than with a gable roof.
The building will be lightweight. This means that there is less stress on the walls and foundation.
Thanks to this shape, the pitched roof perfectly resists wind load, as well as the weight of snow that accumulates on the surface.
The angle of inclination is very different, depending on the needs. It ranges from 5 ° to 45 °.
If you make the angle of a pitched roof small, then it can be used for various purposes. For example, if it is a shed, then install a tank for heating the liquid. If this is a living space, then on a pitched roof, you can equip a wonderful place to relax. Alternatively, installing solar panels as an alternative power source.
The versatility of a lean-to construction. It can be coated with almost any material commercially available. It all depends on the operating conditions and the selected angle of inclination.

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

Cons of a pitched roof:

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

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

Calculation of the roof structure of a single-pitched type

This is the first step before installing the rafter 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 select the following data:

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

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

As a result, the angle of the slope will depend on the height of the rise. The second option provides for the creation of supports, on which the run will fit. The second method saves building materials.

For drawings, you need to know the following nuances:

The drawing of the future pitched roof must have all the necessary information about the elements. The dimensions, distances between them, fastening features, etc. are indicated. An example of a similar drawing of a pitched roof is shown below.

Choosing the angle of a pitched roof

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

The designations are as follows:

Lс - the length of the used rafter;
Lbс - 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 the desired angle of the pitched roof.

Taking into account the basic values, it is possible to calculate all the parameters of a shed 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 a basis. In this case, the formula is as follows:

When you have decided on the angle of the pitched roof, then you need to calculate the future height of the pediment. For this, the formula is as follows:

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

Note! This rafter length does not include a canopy on the rear or front of the room.

The choice of the angle of the slope is influenced by many criteria. The main one is the choice of roofing material. Each of them is recommended to buy for a particular angle of inclination. Here are guidelines for popular roofing materials:

For the device of corrugated board, the slope must be at least 8 °.
When using metal tiles, you will need to make a roof with an angle of inclination of 30 °.
For a slate device, indicators are needed from 20 ° to 30 °.
As for rolled roofing materials (roofing material, bituminous tiles and soft roofing), the angle of inclination should be 5-7 °, not less.

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

Varieties of shed roof truss system

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

Now that we have figured out the structure of the rafter system and learned its types, we can consider the process of creating a shed roof itself.

Installation work on the creation of a pitched roof

Having in 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 rafter system is as follows:

For safety, the building should be covered with beams. They fit 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. Fixing step -500-800 mm.
Mauerlat is laid on top of the beams. This is a massive timber that will serve as a support. It fits on the rear bottom wall of the building.
To move safely on the roof, wooden planks are laid on the floor beams. It is temporary.
Now you need to build a pediment wall. It is made of the same material as the building itself. You can use a lighter material. For example, if the walls are brick, then the pediment is raised by means of bars or boards.
The floor beams must be covered with waterproofing and embedded in the wall. The pediment rises to the selected height according to the drawings.
On the finished pediment, you can fix the Mauerlat. It turns out that the two Mauerlats are parallel to each other.
Marking is applied to the lower wall for fastening the rafter legs. The fastening elements themselves are fixed.
To firmly fix the rafter, based on the drawings, grooves are cut out on it. This is a good mounting option. The grooves are in two places, above and below, to enter the Mauerlat. There are other methods of fixing the rafter leg, as shown in this photo.
After that, the legs are fixed with special corners and fasteners. From above, at the pediment, the legs are screwed tightly. But the lower part is done depending on the selected shed roof truss system. It can be rigidly fixed or made sliding.
There is a certain sequence of inserting rafter legs. First, the extreme elements of the rafter system are mounted. A cord is pulled between them, which serves as a guide and level for subsequent rafters. Do not forget that the pitch of the rafters corresponds to the pitch of the floor beams.
The rafters, which are already installed, are connected to the floor joists by means of struts, struts and other elements to give them stability. We talked about them above. Fixation is carried out with corners and brackets made of metal.
Advice! If you want to lengthen the rafters and bring them out of the wall, then "filly" are attached to the bars. So you can protect the adjacent part of the structure from precipitation.
When the construction of the pitched roof is ready, you can proceed with the insulation and the creation of the roofing cake.

The photo shows what layers the correct insulated single-pitched roof should consist of.

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

As for the lathing for laying roofing material, it is selected depending on what kind of roofing material it will be. For example, a solid sheathing of boards or plywood is needed when installing soft tiles and other roll materials. If metal tiles, corrugated boarding, slate, ondulin and other types of rigid roofing are used, then the lathing is done at random. The pitch depends on the roofing material.

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

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

Conclusion

The creation of a roof, be it a gable or a pitched roof, is a dangerous, laborious and responsible process. That is why caution and strict adherence to the instructions for creating the structure is required. Only then can the best result be achieved.

The content of the article

When building a roof, first of all, the type of rafter system is chosen. This means that the rafters must be hanging or layered, or the entire rafter system will consist of both rafters, that is, combined. It is not difficult to calculate the distance between the rafters, knowing the magnitude of the loads that will act on the entire roof.

Loads are temporary and permanent. Constant loads include:

the weight of the materials of the rafter system itself;
weight of roofing material;
the weight of the elements of the roofing pie, if the roof is made insulated;
weight of the interior decoration of the attic ceiling.

Temporary loads include: the weight of the snow cover, the weight of a person during the production of roofing works and maintenance of the roof during the operation period, the wind load and the weight of possible water flows in the summer.

What are the calculations based on?

The distance between the roof rafters is also calculated based on the selected material and the cross-section of the rafters. All calculations are carried out at the design stage of the house by specialists from design organizations. To do this, they use reference documents and building codes and regulations governing one or another step of the rafters, the step of the lathing and other calculated values.

When building a private house, rarely does anyone order a project where, on the basis of calculations, it is recommended what distance between the rafters must be maintained. Most often, developers rely on the experience of the craftsmen and trust them to carry out all calculations on site. However, there are those who wish to calculate the rafter system themselves and build the roof on their own.

In this case, they must first of all decide on the type of roof, choose which attic will be - heated residential or cold, since the type of rafter system and the calculation of the distance between the rafters directly depend on these parameters

The distance between the rafters of a pitched roof

The calculation for a pitched roof is the simplest. The rafter system does not provide for racks and braces - only the rafters themselves. Such a roof is usually installed in utility rooms, garages, saunas, etc.

The pitch of the rafters of a pitched roof is shown in the table below and depends on the section of the timber:

If the developer wants to independently calculate the loads on the rafter system, it will be useful for him to familiarize himself with such documents as SNiP 2.01.85 "Loads and Impacts" and "Changes from SNiP 2.01.85", which contains maps for the climatic regions of Russia.

Coniferous wood is chosen as the material for the construction of the truss system, the moisture content of which is 20-22%. Boards, beams and other types of lumber should be flat without curling, rot, knots and blue.

All wooden elements should be treated with antiseptics and fire retardants to protect the wood from decay and fire. The material used, the length of the rafter legs and the section of the beam also affect the calculations (see the table):

Approximate calculation

The step of the rafters is nothing more than the distance between the rafter legs. As a rule, for residential private houses, this figure is 0.6-1.0 m.

The step size of the rafters is influenced by a significant number of factors. The calculation of the required number of rafter legs is done in the following way:

The length of the roof slope is measured. After that, the resulting value is divided by the selected indicator of the step between the rafters.
Then one is added to the resulting value and rounded up to get an integer. This gives the number of required rafter legs for a given length of one roof slope.
After that, the entire length of the roof slope is divided by the resulting integer (the number of rafter legs) and, as a result, the distance between the axes of the future rafters is obtained, which is called the pitch of the rafters.
The axis should run in the center of the rafter. However, for different types of roofing, the pitch of the rafters may vary; it also changes depending on the slope angle of the roof slope.

For example: the length of the roof slope is 16 meters, and the step between the rafters is 0.6 meters. Therefore, 16 / 0.6 + 1 = 27.66 = 28 meters (rafters are necessary for the device of the ramp)

The greater the slope angle, that is, the steeper the roof, the larger the step of the rafters. This is due to the fact that the load on steep roofs is not distributed over the entire roof plane, but for the most part is transferred to the load-bearing walls.

Rafters for ceramic tiles

Ceramic tiles are a material that has a decent weight. Therefore, for the device of roofing from tiles, the cross-section and length of the rafters should be calculated, given that one square meter of ceramics weighs almost ten times the weight of the metal tile.

If it is supposed to tighten the rafters in the structure of the rafter system, then its cross section should be increased.
The rafters themselves should be made of dry healthy wood, their cross-section should be 50x150 or 60x180 mm.
The pitch of the rafters is made in the range of 0.8 -1.3 m for ceramic tiles, and its exact definition depends on the slope angle of the slopes.

The higher the roof, the wider the pitch of the rafters can be. For example, with a slope angle of 15 degrees, the step will be 80 cm, and if the slope angle rises to 75 degrees, the distance between the rafter legs will increase to 1.3 m.

Another circumstance affects the size of the step of the rafters - this is the length of the rafter legs. The longer they are, the smaller their step is. This is due to the fact that at the maximum length of the rafters, increased deflection loads are created. They can be reduced by arranging a system of supporting racks, struts and other elements of the rafter system, which take on some of the loads from the rafters.

Metal roof rafters

The rafter system for metal tiles is not much different from other rafter structures. But due to the fact that it has a weight several times less than ceramic tiles, rafters and all other elements of the roof structure can be made with a lower margin of safety, i.e., a smaller section. The difference in weight of clay and metal tiles is about 35 kg per 1 sq. M.

The step of the rafters under the metal tile, as a rule, is made 0.6-0.9 m. Metal tiles are widely used to cover country houses, in which attic rooms are often provided, therefore, the roof is made insulated. The step of the rafters in such structures is adjusted to the dimensions of the insulation, which is inserted between the rafter legs.

The roof frame must be reliable and durable. But it is difficult to achieve this without competently performed calculations. In the process of carrying out the calculations, it is determined at what distance to put the rafters on the roof.

What can an incorrect or inaccurate calculation of the loads to which the rafter structure will undergo? To the most negative consequences, ranging from deformation of the rafter legs and damage to the roof covering and ending with the collapse of the base of the roof frame. Therefore, when designing buildings, the list of mandatory calculations contains data on what the distance between the roof rafters should be. There is a certain methodology that allows you to calculate this value.

Method for calculating the distance between the rafters

The distance between the roof rafters is called the rafter pitch. As a rule, the pitch of the rafter legs in the roof structure usually exceeds one meter, and the minimum gap ranges from 60 centimeters.

The calculation of the required number of rafters for a roof of a certain length and the pitch of the rafters is made as follows:

Roof structure for metal tiles

In the construction of suburban private real estate, metal roofing can be found most often. This roofing material is similar to clay tile decking, but has a number of advantages over it. Sheet metal shingles are easy to install, so the roof can be erected in a shorter time, the rafter system for metal shingles is also not difficult.

Metal tiles are lighter than ceramic products, the difference in weight sometimes reaches 35 kilograms per square meter, depending on the thickness of the products (read also: ""). Due to a significant reduction in the weight of the roofing, it becomes possible to reduce the thickness of the elements of the rafter structure and the dimensions of the cross-section of the sheathing bars, to increase the pitch of the rafters.

Under the metal roofing, the rafter legs are mounted with a distance of 600 to 950 millimeters, while the cross-section of the construction material is 150 by 50 millimeters. According to experts, in this case, if you place a 150 mm thick insulation between the rafters, then such thermal insulation will create comfortable conditions for staying in the attic room. At the same time, for greater reliability, it is advisable to choose a 200 mm insulation.

When installing the rafters, to ensure ventilation of the space that is filled with insulation, holes are drilled in the rafters near the upper roof with a diameter of 10-12 millimeters.

The technology for creating a rafter system for metal tiles does not differ significantly from structures for other types of roofing materials. The only feature is that for the rafters, the upper support is mounted on the ridge girder from above, and not on the side of the ridge beam. The presence of a free zone between the rafters ensures air circulation under the roof deck, and this, due to the use of metal material, reduces the risk of condensation.

Shed roof rafter system, main advantages and characteristics ").

The distance between the rafters of the gable roof is made taking into account the size of the heat insulator, which is laid between them. The approximate step between the rafter legs is 1-1.2 meters (read: ""). Rafters regulate the size of the roof overhang.

The construction of the roof truss system and the subsequent roofing are the most important stages in any construction. This is a very complex matter, coupled with comprehensive preparation, which includes the calculation of the main elements of the system and the acquisition of materials of the required section. Not every novice builder will be able to design and sanitize a complex structure.

However, often in the construction of outbuildings, utility or utility structures, garages, sheds, gazebos and other objects, the special complexity of the roof is not required at all - the simplicity of the design, the minimum amount of costs for materials and the speed of work, which are quite feasible, come first. for self-execution. It is in such situations that the rafter system becomes a kind of "magic wand"

In this publication, the main focus is on the calculations of a pitched roof structure. In addition, the most typical cases of its construction will be considered.

The main advantages of pitched roofs

Despite the fact that not everyone likes the aesthetics of the building over which the pitched roof is mounted (although the question itself is controversial), many owners of suburban areas when erecting buildings, and sometimes even a residential building, choose just this option, guided by a number of advantages similar construction.

Materials for a single-pitched rafter system, especially if it is being built over a small outbuilding, will require very little.
The most "rigid" flat shape is a triangle. It is he who underlies almost any rafter system. In a lean-to system, this triangle is rectangular, which greatly simplifies the calculations, since all geometric relationships are known to everyone who graduated from high school. But this simplicity does not in any way affect the strength and reliability of the entire structure.
Even if the owner of the site, who is leading independent construction, has never previously encountered the construction of a roof, the installation of a single-pitched rafter system should not cause him excessive difficulties - it is quite understandable, not so complicated. Often, when blocking small outbuildings or other adjoining structures, it is quite possible to do not only without calling a team of specialists, but even without inviting assistants.
When erecting a roof structure, the speed of work is always important, of course, without loss of quality - you want to protect the structure from the vagaries of the weather as quickly as possible. According to this parameter, the single-pitched roof is definitely a "leader" - there are practically no complex connecting nodes in its design that take a lot of time and require high-precision adjustment.

How significant are the disadvantages of a single-pitched rafter system? Alas, they are, and they also have to be reckoned with:

An attic with a pitched roof is either not assumed at all, or it turns out to be so small that you have to forget about its wide functionality.

Based on the first point, there are certain difficulties in providing sufficient thermal insulation for the premises located under the pitched roof. Although, of course, this can be corrected - nothing prevents the roof slope itself from being insulated, or by placing the insulated attic floor under the rafter system.
Shed roofs, as a rule, are made with a slight slope, up to 25 ÷ 30 degrees. This has two consequences. Firstly, not all types of roofing are suitable for such conditions. Secondly, the significance of the potential snow load increases sharply, which must be taken into account when calculating the system. But on the other hand, with such slopes, the effect of wind pressure on the roof is significantly reduced, especially if the slope is correctly positioned - to the windward side, in accordance with the prevailing winds in this area of the terrain.

Another drawback, perhaps, can be attributed to very conditional and subjective - this is the appearance of a pitched roof. It may not be to the liking of lovers of architectural delights, they say, it greatly simplifies the appearance of the building. One can object to this too. First, the simplicity of the system and the economy of construction often play a decisive role in the construction of auxiliary structures. And threefold - if you look at the overview of projects of residential buildings, you can find very interesting design options, in which the emphasis is placed on a pitched roof. So, as they say, tastes differ.

How is a shed rafter system calculated?

General principles of system design

In any scenario, a single-slope roof system is a structure of layered rafter legs installed parallel to each other. The name itself - "layered" means that the rafters rest (lean) on two rigid points of support. For the convenience of perception, let us turn to a simple scheme. (By the way, we will return to the same scheme more than once - when calculating the linear and angular parameters of the system).

So, two points of support of the rafter leg. One of the points (V) located above the other (A) by a certain excess value (h)... Due to this, a slope of the slope is created, which is expressed by the angle α.

Thus, as already noted, the construction of the system is based on a right-angled triangle ABC, in which the base is the horizontal distance between the pivot points ( d) - most often this is the length or width of the building being erected. Second leg - excess h. Well, the length of the rafter leg between the points of support becomes the hypotenuse - L. Base angle (α) determines the steepness of the roof slope.

Now we will consider the main aspects of choosing a design and carrying out calculations in somewhat more detail.

How will the required slope be created?

The principle of the location of the rafters - parallel to each other with a certain step, with the required slope angle of the ramp - is common, but this can be achieved in different ways.

The first is that even at the stage of development of the building project, the height of one wall (shown in pink) is immediately laid with an excess h relative to the opposite (yellow). The two remaining walls, running parallel to the roof slope, are given a trapezoidal configuration. The method is quite common, and although it somewhat complicates the process of erecting walls, it extremely simplifies the creation of the roof rafter system itself - almost everything is ready for this.
The second method can, in principle, be considered a variation of the first. In this case, we are talking about frame construction. Even at the stage of project development, it is laid in it, then the vertical struts of the frame on one side are higher by the same amount h compared to the opposite.

In the above illustrations and those that will be posted below, the diagrams are made with a simplification - the Mauerlat passing along the upper end of the wall is not shown, or the strapping bar is on the frame structure. This does not fundamentally change anything, but in practice you cannot do without this element, which is the basis for the installation of the rafter system.

What is a Mauerlat and how is it attached to walls?

The main task of this element is to evenly distribute the load from the rafter legs to the walls of the building. The rules for the selection of material and on the walls of the house - read in a special publication of our portal.

The next approach is practiced when the walls are of equal height. The excess of one side of the rafter legs over the other can be ensured by installing vertical racks of the required height h.

The solution is simple, but the design turns out, at first glance, somewhat unstable - each of the "rafter triangles" has a certain degree of freedom to the left - to the right. This is easily eliminated by fastening the transverse beams (boards) of the sheathing and sewing the rectangular gable part of the roof from the front side. The pediment triangles remaining on the sides are also sewn up with wood or other material convenient for the owner.

rafter mount

Another solution to the problem is the installation of a roof using single-pitch trusses. This method is good in that it is possible, after carrying out the calculations, to ideally assemble and fit one truss, and then, taking it as a template, make on the ground the required number of exactly the same structures.

This technology is convenient to use when, due to its great length, they require a certain amplification (this will be discussed below).

The rigidity of the entire rafter system is already incorporated in the structure of the truss - it is enough to install these assemblies on the Mauerlat with a certain step, fix on it, and then connect the trusses with strapping or transverse beams of the sheathing.

Another advantage of this approach is that the truss plays the role of both rafter legs and floor beams. Thus, the problem of thermal insulation of the overlap and the filing of the flow is greatly simplified - everything for this will be immediately ready.

Finally, one more case - it is suitable for a situation where a pitched roof is planned over an extension being erected near the house.

On the one hand, the rafter legs rest on the frame racks or on the wall of the extension being built. On the opposite side is the main wall of the main building, and the rafters can be supported on a horizontal run fixed on it, or on individual fasteners (brackets, embedded bars, etc.), but also horizontally aligned. The line of attachment of this side of the rafter legs is also made with an excess h.

Please note that despite the differences in approaches to the installation of a shed system, all variants have the same "rafter triangle" - this will be important for calculating the parameters of the future roof.

In which direction should the roof slope be provided?

It would seem - an idle question, however, it is necessary to decide on it in advance.

In some cases, for example, if there are no special options - the slope should be located only in the direction from the building to ensure free drainage of storm water and melted snow.

On a detached building, there are already certain options for choosing. Of course, it is not enough when an option is considered in which the rafter system is positioned in such a way that the direction of the slope falls on the front part (although such a solution is not excluded). Most often, the slope is organized backward or to one side.

Here you can already take as the selection criteria the external design of the building being erected, the features of the site, the convenience of laying communications for the storm water collection system, etc. But you should still keep in mind certain nuances.

The optimal location of a pitched roof is to the windward side. This allows you to minimize the wind effect, which can work with the lifting application of the force vector, when the ramp turns into a kind of wing - the wind is trying to tear the roof up. This is of the utmost importance for pitched roofs. When the wind blows into the roof, especially at small angles of steepness of the slopes, the value of the wind effect will be minimal.
The second aspect of the choice is the length of the ramp: with a rectangular building, it can be positioned along it or across it. It is important to consider here that the length of the rafters without reinforcement cannot be unlimited. In addition, the longer the span of the rafters between the support points, the thicker the lumber used for the manufacture of these parts should be in cross-section. This dependence will be explained a little later, already during the calculations of the system.

However, the rule of thumb is that the free length of the rafter leg should usually not exceed 4.5 meters. With an increase in this parameter, additional structural reinforcement elements are necessarily provided. Examples are shown in the illustration below:

So, with a distance between opposite walls from 4.5 to 6 meters, it will already be necessary to install a rafter leg (brace), located at an angle of 45 °, and resting from below on a rigidly fixed support bar (bed). At distances of up to 12 meters, you will have to install a vertical post in the center, which must rest either on a reliable overlap, or even on a capital partition inside the building. The rack also rests on the bed, and in addition, a brace is also installed on each side. This is all the more important due to the fact that the standard length of lumber usually does not exceed 6 meters, and the rafter leg will have to be made composite. So, in any case, it will not work without additional support.

A further increase in the length of the slope leads to an even greater complication of the system - it becomes necessary to install several vertical racks, with a step of no more than 6 meters, with support on the cap walls, and with the connection of these racks with fights, with the installation of the same struts on each rack, and on both outer walls.

Thus, you should think carefully about where it will be more profitable to orient the direction of the roof slope also for reasons of simplifying the design of the rafter system.

wood screws

What is the optimal slope angle?

In the overwhelming majority of cases, when it comes to a pitched roof, an angle of up to 30 degrees is chosen. This is due to a number of reasons, and the most important of them has already been mentioned - the strong vulnerability of the shed structure to the wind load from the front side. It is clear that, following the recommendations, the direction of the slope is oriented to the windward direction, but this does not mean that the wind from the other side is completely excluded. The steeper the slope angle, the more significant the generated lifting force becomes, and the greater the breakdown load will be experienced by the roof structure.

In addition, pitched roofs with a large angle of inclination look somewhat awkward. Of course, this is sometimes used in bold architectural and design projects, but we are talking about more "mundane" cases ...

A too gentle slope, with a slope angle of up to 10 degrees, is also not too desirable, for the reason that the load on the rafter system from snow deposits increases sharply. In addition, with the beginning of snow melting, it is very likely that ice will appear along the lower edge of the slope, which makes it difficult for the free flow of melt water.

An important criterion for choosing the angle of steepness of the slope is the conceived. It is no secret that for various roofing materials there are certain "frames", that is, the minimum permissible roof slope angle.

The very angle of the slope of the slope can be expressed not only in degrees. It is more convenient for many craftsmen to operate with other parameters - proportions or percentages (even in some technical sources you can find a similar measurement system).

Proportional calculus is the ratio of the span length ( d) to the lifting height of the ramp ( h). It can be expressed, for example, in a ratio of 1: 3, 1: 6, and so on.

The same ratio, but in absolute terms and reduced to percentages, gives a slightly different expression. For example, 1: 5 - this will be a slope of 20%, 1: 3 - 33.3%, etc.

To simplify the perception of these nuances, below is a table with a graph-diagram showing the ratio of degrees and percentages. The scheme is fully scaled, that is, it can be used to easily translate some values into others.

Red lines show the conditional division of roofs: up to 3 ° - flat, from 3 to 30 ° - roofs with a low slope, from 30 to 45 ° - medium steepness, and above 45 - steeply sloped slopes.

Blue arrows and the corresponding numerical designations (in circles) show the established lower limits for the use of a particular roofing material.


№	Slope value	Type of roofing allowed (minimum slope level)	Illustration
1	from 0 to 2 °	Completely flat roof or with an angle of inclination up to 2 °. At least 4 layers of rolled bitumen coating, applied by "hot" technology, with the obligatory top dressing of fine gravel, sunk into the molten mastic.
2	≈ 2 ° 1:40 or 2.5%	The same as in point 1, but 3 layers of bituminous material will be enough, with mandatory dressing
3	≈ 3 ° 1:20 or 5%	At least three layers of bituminous roll material, but without gravel backfill
4	≈ 9 ° 1: 6.6 or 15%	When using roll bitumen materials - at least two layers, hot glued to the mastic. It is allowed to use some types of corrugated board and metal tiles (according to the manufacturer's recommendations).
5	≈ 10 ° 1: 6 or 17%	Asbestos-cement slate corrugated sheets of reinforced profile. Euroslate (odinilin).
6	≈ 11 ÷ 12 ° 1: 5 or 20%	Soft bituminous shingles
7	≈ 14 ° 1: 4 or 25%	Reinforced flat asbestos-cement slate. Decking and metal tiles - practically without restrictions.
8	≈ 16 ° 1: 3.5 or 29%	Roofing sheet steel with folded joints of adjacent sheets
9	≈ 18 ÷ 19 ° 1: 3 or 33%	Asbestos-cement corrugated slate, regular profile
10	≈ 26 ÷ 27 ° 1: 2 or 50%	Natural ceramic or cement piece tiles, slate or composite polymer tiles
11	≈ 39 ° 1: 1.25 or 80%	Roof covering made of wood chips, shingles, natural shingles. For lovers of special exoticism - stone roof

Possessing such information and having plans for the future roofing, it will be easier to determine the slope angle.

metal tile

How to set the required ramp angle?

Referring again to our basic "rafter triangle" scheme posted above.

So, to set the required slope angle of the slope α , it is necessary to ensure the elevation of one side of the rafter leg by an amount h... The ratios of the parameters of a right-angled triangle are known, that is, it will not be difficult to determine this height:

h = d × tg α

The tangent value is a tabular value that is easy to find in reference books or tables published on the Internet. But in order to simplify the task for our reader as much as possible, a special calculator is placed below that will allow you to perform calculations in just a few seconds.

In addition, the calculator will help to solve, if necessary, the inverse problem - by changing the slope angle in a certain range, select the optimal value of the excess, when exactly this criterion becomes decisive.

Calculator for calculating the excess of the upper point of installation of the rafter leg

Specify the requested values and click the "Calculate the value of excess h"

Basic distance between the support points of the rafters d (meters)

Planned roof slope α (degrees)

How to determine the length of the rafter leg?

In this matter, there should also be no difficulties - for two known sides of a right-angled triangle, it will not be difficult to calculate the third, using the well-known Pythagorean theorem. In our case, when applied to the basic scheme, this ratio will be as follows:

L² =d² +h²

L = √ (d² +h²)

When calculating the length of the rafter legs, one nuance should be taken into account.

With small slope lengths, the length of the rafters is often increased by the width of the eaves overhang - this will make it easier to mount the entire unit later. However, with large lengths of rafter legs, or in the case when, due to circumstances, it is necessary to use material of a very large section, this approach does not always seem reasonable. In such a situation, the lengthening of the rafters is used with the help of special elements of the system - filly.

It is clear that in the case of a single-pitched roof, there can be two eaves overhangs, that is, on both sides of the building, or one - when the roof is attached to the wall of the building.

Below is a calculator that will quickly and accurately calculate the required rafter leg length for a pitched roof. Optionally, you can carry out calculations taking into account the eaves overhang, or without it.

Calculator for calculating the length of the rafter leg of a shed roof

Enter the requested values and click the "Calculate rafter leg length L"

Elevation height h (meters)

Basic length d (meters)

Calculation conditions:

Required width of the cornice overhang ΔL (meters)

Number of overhangs:

It is clear that if the length of the rafter leg exceeds the standard dimensions of commercially available lumber (usually 6 meters), then you will either have to abandon the formation with the rafters in favor of the filly, or resort to splicing the timber. You can immediately assess the consequences of this "pouring out" in order to make the best decision.

How to determine the required cross-section of the rafters?

The length of the rafter legs (or the distance between the points of their attachment to the Mauerlat) is now known. The parameter of the height of the rise of one edge of the rafter was found, that is, there is also the value of the slope angle of the future roof. Now you need to decide on the section of the board or timber that will be used for the manufacture of rafter legs and, in conjunction with this, the steps for their installation.

All of the above parameters are closely interconnected and must ultimately correspond to the possible load on the rafter system in order to ensure the strength and stability of the entire roof structure, without distortion, deformation or even collapse.

Principles of calculating the distributed load on the rafters

All loads falling on the roof can be divided into several categories:

Constant static load, which is determined by the mass of the rafter system itself, roofing material, lathing to it, and with insulated slopes - by the weight of thermal insulation, inner lining of the ceiling of the attic, etc. This total indicator largely depends on the type of roofing material used - it is clear that the massiveness of the corrugated board, for example, cannot be compared with natural tiles or asbestos-cement slate. And yet, when designing a roofing system, they always strive to keep this figure within 50 ÷ 60 kg / m².
Temporary loads on the roof due to the influence of external causes. This is undoubtedly the snow load on the roof, which is especially typical for roofs with a slight steepness of the slopes. The wind load plays a role, and although it is not so great at small slope angles, it should not be completely discounted. Finally, the roof must also support the weight of a person, for example, when carrying out any repair work or when cleaning the roof from snowdrifts.
A separate group is extreme loads of a natural nature, caused, for example, by hurricane winds, anomalous snowfalls or rains for a given area, tectonic tremors of the earth, etc. It is almost impossible to predict them, but when calculating for this case, a certain reserve of strength of structural elements is laid.

The total loads are expressed in kilograms per square meter of roof area. (In technical literature, they often operate with other quantities - kilopascals. It is easy to translate - 1 kilopascal is approximately equal to 100 kg / m²).

The load falling onto the roof is distributed over the rafter legs. Obviously, the more often they are installed, the less pressure will fall on each running meter of the rafter leg. This can be expressed by the following relationship:

Qр = Qс × S

Qр- distributed load per linear meter of rafters, kg / m;

Qc- total load per unit of roof area, kg / m²;

S- the step of installing the rafter legs, m.

For example, calculations show that an external impact of 140 kg is likely on the roof. with an installation step of 1.2 m, 196 kg will be needed for each running meter of the rafter leg. But if you install the rafters more often, with a step of, say, 600 mm, then the degree of impact on these structural details decreases sharply - only 84 kg / m.

Well, according to the obtained value of the distributed load, it is already easy to determine the required cross-section of lumber that can withstand such an effect, without deflection, torsion, fractures, etc. There are special tables, one of which is shown below:

The estimated value of the specific load per 1 running meter of the rafter leg, kg / m					Section of lumber for the manufacture of rafter legs
75	100	125	150	175	from round timber	from a board (timber)
					diameter, mm	thickness of the board (timber), mm
						40	50	60	70	80	90	100
Planned length of rafters between support points, m						board (timber) height, mm
4.5	4	3.5	3	2.5	120	180	170	160	150	140	130	120
5	4.5	4	3.5	3	140	200	190	180	170	160	150	140
5.5	5	4.5	4	3.5	160	-	210	200	190	180	170	160
6	5.5	5	4.5	4	180	-	-	220	210	200	190	180
6.5	6	5.5	5	4.5	200	-	-	-	230	220	210	200
-	6.5	6	5.5	5	220	-	-	-	-	240	230	220

Using this table is a snap.

In the left part of it, the calculated specific load on the rafter leg is found (with an intermediate value, the nearest one is taken to the larger side).

Along the found column, they go down to the value of the required length of the rafter leg.

In this line, on the right side of the table, the required parameters of lumber are given - the diameter of the round timber or the width and height of the bar (board). Here you can choose the option that is most convenient for you.

For example, calculations gave a load value of 90 kg / m. The length of the rafter leg between the support points is 5 meters. The table shows that you can use a log with a diameter of 160 mm or a board (timber) of the following sections: 50 × 210; 60 × 200; 70 × 190; 80 × 180; 80 × 180; 90 × 170; 100 × 160.

The point is "small" - to determine the total and distributed load.

There is a well-developed, rather complex and cumbersome calculation algorithm. However, we will not overload the reader with an array of formulas and coefficients in this publication, but suggest using a calculator specially designed for this purpose. True, to work with it, you need to make a few explanations.

The entire territory of Russia is divided into several zones according to the likely level of snow load. In the calculator, you will need to enter the zone number for the region in which the construction is being carried out. You can find your zone on the map below:

The level of snow load is affected by the angle of the roof slope - this value is already known to us.

Initially, the approach is similar to that in the previous case - you need to determine your zone, but only by the degree of wind pressure. The schematic map is placed below:

For the wind load, the height of the roof being erected matters. Not to be confused with the excess parameter considered earlier! In this case, it is the height from ground level to the highest point of the roof that is of interest.

The calculator will ask you to determine the construction area and by the degree of openness of the construction site. The criteria for assessing the level of openness in the calculator are given. However, there is a caveat.

It is possible to speak of the presence of these natural or artificial obstacles to the wind only if they are located no further than at a distance, no more than 30 × H, where N Is the height of the house being built. This means that to assess the degree of openness for a building with a height of, for example, 6 meters, you can take into account only those signs that are located no further than within a radius of 180 meters.

In this calculator, the pitch of the rafters is variable. This approach is convenient from the point of view that by varying the value of the step, you can track how the distributed load on the rafters changes, which means that you can choose the most acceptable option in terms of selecting the required lumber.

By the way, if the pitched roof is planned to be insulated, then it makes sense to bring the step of installing the rafters to the dimensions of standard insulation boards. For example, if basalt wool pits with a size of 600 × 1000 mm will be used, then it is better to set the rafter pitch either 600 or 1000 mm. Due to the thickness of the rafter legs, the distance "in the light" between them will be 50 ÷ 70 mm less - and this is almost ideal conditions for the most tight fit of the insulation blocks, without gaps.

However, let's get back to the calculations. All other data for the calculator is known and calculations can be performed.

The task of correctly calculating the distance between the rafters is a very responsible one. Not only the reliability and durability of the roof will depend on how seriously you start solving it, but also all subsequent work on it: laying insulation, installing roofing, installing additional elements. If you juggle the step of the rafters under the roofing sheets, as many do, then it is not a fact that insulation will then enter between the rafters.

If you focus only on insulation, the very first winter with its abundant Russian snow will crush the rafter system. That is why the whole point is to choose the optimal rafter pitch for all slopes, and we will teach you this skill now.

What determines the pitch of the rafters?

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

Roof shape (gable, single-pitched or multi-pitched).
Roof inclination angle.
Parameters of the timber used for the manufacture of rafters (width, thickness).
The structure of the rafter system (layered, hanging or sliding).
The aggregate of all loads on the roof (coating weight, atmospheric phenomena, etc.).
Sheathing 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.

Online calculators vs. notebook and pencil

For the correct calculation of the cross-section of the rafters and the step of their installation, there are many complex formulas today. But remember that such formulas were at one time developed more so that it was possible not so much to ideally calculate the roof structures, but to study the work of such elements.

For example, today simple online programs are popular that calculate the parameters of rafters well. But it's ideal if you can set specific tasks yourself and calculate everything you need. It is important to understand to the smallest detail what exactly happens in the rafter system during operation, what forces are acting on it and what loads. And a computer program cannot always take into account everything that the human brain notices. Therefore, we advise you to do all the calculations manually.

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 withstands a large cap of snow, constant wind at a height and it is often also 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 distance between the rafters it will have - this is already a purely aesthetic factor:

In the above illustration, it can be seen that even such a building has its own rafter pitch. Indeed, here it provides both the aesthetic factor and the rigidity of the structure itself. But they choose a step in an arbitrary way.

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

Point 1. The length of the wall and the choice of the pitch of the rafters

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

For example, the easiest way is to install rafters in 1 meter increments, so 7 rafters are standard for a 6 meter long wall. 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 take a step of the rafters more than 2 meters.

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

So, we stopped at the fact that the average distance between the rafters of a conventional roof is 1 meter. But, if there is a significant snow or wind load in the area, or the roof is more or less sloping or just 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 increase 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 there are turbulences, after which the wind hits the eaves overhang of the roof. It turns out that the wind flow, as it were, bends around the slope of the roof, but at the same time trying to raise it. And at this moment, forces arise in the roof that are ready to rip it off or overturn it - these are two windward sides and one lifting side.

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

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

The second point: in the Russian region, an atmospheric phenomenon such as snow constantly affects a 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 places where such a bag is possible, you need to insert paired rafter legs or make a solid crate. The easiest way to identify such places is by the wind rose: single rafters are placed on the windward side, and paired 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:

Clause 3. Issue of insulation and standard width of mats

If you are going to insulate the roof, then it is advisable to place the rafter pitch under the standard dimensions of the insulation plates, which are 60, 80 cm and 120 cm.

Modern insulation today is sold in a standard width, usually at the same standard rafter pitch. If you then take them and adjust to the already existing parameters, then there will be a lot of waste, cracks, cold bridges and other problems.

Item 4. The quality and strength of the lumber used

It is also of great importance what kind of material you use for the construction of the rafter system. So, for each type of wood there is its own regulatory documentation that relates to its bearing capacity:

Because for the manufacture of roof truss systems in Russia, pine and spruce are most often used, their bending strength and features of use have long been spelled out. If you use wood of other species, then it will be possible to display a correction factor.

In addition, if there are sections, cuts or bolt holes on the rafters, at this point you need to calculate the bearing capacity of the bar with a factor of 0.80.

Item 5. Distance between tie rods and floor beams

Another point: if the roof is built with trusses connected to each other, and their lower chord is used simultaneously as floor beams, then the distance between the trusses must be made within 60-75 cm in order to take into account the design of the future floor.

Item 6. Loads on roof truss assemblies

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

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

And all these factors are capable of simultaneously affecting the roof at a certain moment, and therefore there is such a thing as critical value. This is exactly the value of the loads at which the roof does not withstand and deforms.

Therefore, if a building is being built with significant spans, then steel trusses are necessarily used. The fact is that there is no stress 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 trusses is calculated depending on the type of roof and the structure 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 nodes of the truss in 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 support the entire roof, and its weight is critical in this case:

Item 8. Convenience 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 the solid crate? 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 along the edges need to be fastened directly to the rafter or crate, and it is important that they match. Otherwise, the work on roofing will easily turn into a living hell at a height, believe me.

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

Determination of the totality of loads on the roof as a whole and the rafter separately

So, we have determined that, in addition to other design factors, a whole set of loads simultaneously acts on the roof rafter system: the weight of the rafter system, a cap made of snow, wind pressure. After you add all the loads together, be sure to multiply them by a factor of 1.1. So you all rely 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 structure will be frail - feel free to add 1-2 rafters to the total, and you will be calm about your home.

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

The standard roof structure is rafters, lattice girders, and each of these elements is triggered only by the load that presses 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 pitch of their location, you change the area of collection of the load on the rafters - by decreasing 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 load-bearing capacity of the roof will increase significantly:

With this calculation, try to ensure that the longest rafter in your project is no more than six and a half meters, otherwise, splicate along the length. Let's explain in more detail now. So, on roofs with a slope of up to 30 degrees rafters are the so-called "bendable elements". Those. they work precisely in bending, and there are certain requirements for them. And the possibility of deflection of the rafters is calculated using 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 "bend-compressed" elements. That is, they are affected not only by a uniformly distributed load, which causes the bending of the rafters, but also by the forces that are already acting along the axis of the rafter. In simple terms, here the rafters not only sag slightly under the weight of the roof, but also squeeze from the ridge to the Mauerlat. In addition, the crossbar, which usually holds the two rafter legs, must be checked for tension.

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