It is pointless to argue about the importance of the roof for any building. It is not for nothing that over a dozen different types of roofs have been invented in the history of mankind, from simple to quite complex in design and construction. An important element in planning the construction of a roof is the step between the rafters - strong bars that are the basis of the structure. This will be discussed in this article.
The distance between the base of the roof slopes is not a constant value and depends on the following components:
- type of roof;
- slope angle;
- the type of roofing material to be installed;
- rafter section dimensions.
Before proceeding with the process of erecting the upper structure of the house, a calculation should be performed by determining the optimal distance between the rafters.
Gable roof rafter pitch
The most widespread in our country are gable roofs. They are a structure that has two parallel planes, with an angle of inclination relative to the horizon from 20 to 50 degrees.
With an insufficient slope of the gable roof in snowy areas, there is a danger of accumulation of large snow masses, which can lead to the destruction of the structure. An increase in the slope angle in regions with a predominance of strong winds is also fraught with a high load and the risk of breaking not only the roof, but the entire structure as a whole.
Mansard roof truss system
Most private houses have an exploited under-roof space called an attic. This design is characterized by an increased height of the slope, which is caused by the need to create a living space of a comfortable height. As a rule, the slopes of the mansard roof are broken, having a varying angle of slope. For their installation, a double truss system is used.
The steepness of the lower slopes of the mansard roof significantly exceeds the slope of their upper extensions. The plane load perceived by them is not great. Thanks to this, the rafters in the lower part can be installed with a maximum pitch. The upper ridge slopes are recommended to be mounted with a reduced gap from each other.
Rafters in a shed roof
For outbuildings and some private houses, roofs with one slope are used. Due to the limited angle of inclination, high pressure is exerted on them. Experts recommend using lumber of increased cross-section for the rafters of a single-pitched roof, with the installation of a minimum step from each other.
When calculating the distances at which roof beams are installed, special attention should be paid to the amount of snow load in a particular area. With a small slope, this characteristic is of great importance. Roofing material for such roofs is best chosen with a minimum dead weight, which will reduce the bending load.
Hip roof truss system
The hip roof truss system is considered the most difficult in construction. This type is called four-pitched, since the roof is formed not only by side, but also by additional end slopes, where the installation of rafters is carried out not on the ridge, but on the corner bowstrings. This places special demands on the organization of the roof frame.
Under the hip roof, the attic is not often arranged. This is due to the small angle of inclination of the rafters and the roof as a whole. In the case of an increase in the angle of the slopes to the horizon, the distance between the rafters is increased, with a decrease, vice versa. An additional aspect of the calculation is the roofing material used.
The dependence of the pitch of the rafters on the roofing material
In addition to variable snow and wind loads, a constant (static) one also acts on the roof, the force of which depends on the roofing material used. It is no secret that different types of roofs have their own weight, which can differ by 10 or more times.
The right choice of material affects not only the top, but also all other parts of the structure of a residential building and other buildings. Not without reason, when designing the foundation, it is necessary to decide in advance on the choice of the roof.
Roofing from profiled sheet
Currently, one of the most common roofing materials is a profiled sheet, which is produced galvanized or followed by a polymer coating. The distinguishing features of the profiled sheet include the following parameters:
- High corrosion resistance;
- As a result, a long (more than 15 years) service life;
- Easy installation even without the necessary qualification;
- Small sheet weight (weight 1 m 2 is 4-5 kg).
Since this roofing material does not exert a high load on the truss system, the distance between the elements is chosen as much as possible for a particular angle of inclination. In addition, the profiled sheet does not require high strength characteristics from the roof lathing. All this together allows minimizing the total load on the foundation and walls.
Roofing from a metal tile
The second common type of steel roofing materials is metal tiles. This type of profiled sheet, which successfully imitates natural clay material, but with a lower mass (10 or more). A feature of the rafters under the metal tile is the smaller section size.
When choosing at what distance to install the rafters, first of all, you should be guided by the dynamic load. Like a profiled sheet, a metal tile is not demanding on the size of the rafter legs and is well mounted on a crate made of an inch coniferous board. All this makes a metal roof low-cost.
Rafter system for ondulin
In the 21st century, corrugated sheet materials were replaced by a more durable and lightweight analogue - ondulin. Among others - the most lightweight material. The weight of the sheet does not exceed 6 kg.
The small thickness of ondulin sheets at slope angles of less than 15 ° requires the construction of a continuous crate of plywood sheets, for example, which will require an appropriate rafter pitch. This should be taken into account in the calculations.
slate roof
Not so long ago, a wavy material from an asbestos-cement mixture, called slate, was widespread. High mass and fragility are the main disadvantages, however, even today he finds his fans in the construction of various outbuildings.
A high mass, comparable to the weight of a clay tile, will not allow the use of the same truss system as under a metal tile. Building codes define a minimum angle of slope for a slate roof of 22 degrees or more. Otherwise, the load from the material itself and the truss system with the crate exceeds the permissible parameters. The step of the inclined bars, as well as their cross section, are selected individually in each case.
Polycarbonate roof
In recent years, more and more often on the roofs of verandas and gazebos, an artificial polymer material, polycarbonate, has been used. Produced in two versions - monolithic and honeycomb. The first in its properties is similar to ordinary quartz glass, but significantly exceeds it in strength. The second one has less mechanical properties, but high thermal insulation and light transmission.
Cellular polycarbonate is standardly much lighter than a monolithic counterpart. It is used as a roof without the use of lathing, provided that the step does not exceed ½ of the width of the sheet of material. The high strength of the monolithic analogue also makes it possible to avoid elements transverse to the rafters. Sufficient flexibility allows you to cover semi-circular roofs on a metal frame, the pitch of which does not exceed 0.9 meters.
Thematic material:
Rafters under a soft roof
The original pattern can be obtained through the use of soft roofing materials, which are spread with an adhesive layer. They are installed on a continuous crate made of plywood or OSB. The step of the rafters should allow you to fix the sheets, so it is chosen as a multiple of ½ of the width. Given the standard dimensions of plywood 1520x1520 mm, the center distance between the rafters will be: 1520: 3 = 506 mm.
Rafter step for insulation
The installation of residential under-roof spaces is often combined with the laying of insulation sheets in the rafter gap. The most common plates with dimensions of 600x1000mm. These parameters are used as starting points.
Rafter pitch calculation scheme
According to building codes, the pitch of the roof rafters is in the range of 0.6 - 1 meter. Its final calculation is performed according to a simple formula, depending on the total length of the roof. For the calculation, you must perform the following list of actions:
- determine how much distance should be between the rafters for your specific building conditions. According to the reference book, the magnitude of wind and snow loads in the area is determined.
- the length of the roof is divided by the desired distance by adding one. The result will be equal to the number of rafter legs that are installed on one roof slope. If the value is not an integer, it is rounded off.
- the length of the roof is divided by the number of rafters calculated above, we get the final step in meters.
For example, with a slope of 30 degrees, the maximum distance between the rafters of a gable roof under a metal tile is 0.6 measure. The length is assumed to be 16 meters. Consequently:
- 16:0,6+1=27,66;
- rounding the result, we get 28 rafters per slope;
- 16:28 \u003d 0.57 meters - the center gap of the rafter legs for these specific conditions.
As you can see, the calculation technology is not complicated, but this is just an approximate scheme. Taking into account many other parameters mentioned above can make certain adjustments.
The construction of the roof truss system and the subsequent roofing are the most important stages in any construction. This matter is very complex, associated with comprehensive preparation, which includes the calculation of the main elements of the system and the acquisition of materials of the desired section. Not every novice builder will be able to design and sanitize a complex structure.
However, often in the construction of adjoining buildings, utility or auxiliary buildings, garages, sheds, gazebos and other objects, the special complexity of the roof is not required at all - the simplicity of design, the minimum amount of material costs and the speed of work, which are quite feasible, come first. for independent performance. It is in such situations that the rafter system becomes a kind of "lifesaver"
In this publication, the main focus is on the calculations of a shed roof structure. In addition, the most typical cases of its construction will be considered.
The main advantages of shed roofs
Despite the fact that not everyone likes the aesthetics of a building over which a pitched roof is mounted (although the question itself is ambiguous), many owners of suburban areas, when building buildings, and sometimes even a residential building, choose this option, guided by a number of advantages similar design.
- Materials for a shed truss system, especially if it is being built over a small outbuilding, will require very little.
- The most "rigid" flat figure is a triangle. It is he who underlies almost any truss system. In a shed 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 affect the strength and reliability of the entire structure.
- Even if the owner of the site, who is leading an independent construction, has never previously encountered the construction of a roof, the installation of a shed truss 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, naturally, without loss of quality - you want to protect the building from the vagaries of the weather as quickly as possible. According to this parameter, the shed roof is clearly the "leader" - in its design there are practically no complex connecting nodes that take a lot of time and require high-precision adjustment.
How significant are the shortcomings of a single-pitched truss system? Alas, they exist, and they also have to be reckoned with:
- An attic with a shed roof is either not supposed 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 ensuring sufficient thermal insulation of the premises located under a pitched roof. Although, of course, this can be corrected - nothing prevents the roof slope itself from being insulated or from placing an 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 implications. First, 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 influence 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.
- Another drawback, perhaps, can be attributed to very conditional and subjective - this is the appearance of a pitched roof. It may not appeal to lovers of architectural delights, they say, it greatly simplifies the appearance of the building. This can also be objected to. Firstly, the simplicity of the system and the cost-effectiveness of erection often play a decisive role in the construction of auxiliary structures. And three times - if you look at the overview of projects of residential buildings, you can find very interesting design options, in which the emphasis is on a shed roof. So, as they say, tastes differ.
How is a shed truss system calculated?
General principles of system calculation
In any scenario, a shed roof system is a structure of rafter legs installed parallel to each other. The name itself - “layered” indicates that the rafters rest (lean) on two rigid points of support. For ease of perception, we 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 (IN) located above the other (BUT) to 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 support points ( d) - most often this is the length or width of the building being built. Second leg - excess h. Well, the length of the rafter leg between the fulcrum becomes the hypotenuse - L. Base angle (α) determines the slope of the roof slope.
Now let's consider the main aspects of choosing a design and performing calculations in more detail.
How will the required slope of the 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 slope - is common, but this can be achieved in various ways.
- The first is that even at the stage of developing a building project, the height of one wall (shown in pink) is immediately laid in excess of 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 building walls, it extremely simplifies the creation of the roof truss system itself - almost everything is already 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 racks of the frame on one side are higher by the same amount h compared to the opposite.
In the illustrations above and in those that will be placed below, the diagrams are made with simplification - the Mauerlat passing along the upper end of the wall, or the strapping beam - on the frame structure is not shown. This does not fundamentally change anything, but in practice, this element, which is the basis for the installation of the truss system, cannot be dispensed with.
What is a Mauerlat and how is it attached to the walls?
The main task of this element is to evenly distribute the load from the rafter legs to the walls of the building. Rules for the selection of material and on the walls of the house - read in a special publication of our portal.
- The following 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 quite simply eliminated by fastening the transverse bars (boards) of the crate and sewing the rectangular gable part of the roof from the front side. The remaining pediment triangles 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 shed trusses. This method is good because, after carrying out the calculations, it is possible to perfectly assemble and fit one truss, and then, taking it as a template, make the required number of exactly the same structures on the ground.
It is convenient to use such technology when, due to their large length, they require a certain amplification (this will be discussed below).
The rigidity of the entire rafter system is already incorporated in the design of the truss - it is enough to install these assemblies on the Mauerlat with a certain step, gain a foothold on it, and then connect the trusses with strapping or transverse battens of the crate.
Another advantage of this approach is that the truss performs both the role of the rafter leg and the floor beam. Thus, the problem of thermal insulation of the ceiling and filing of the flow is greatly simplified - everything for this will be ready right away.
- Finally, one more case - it is suitable for the situation when a shed roof is planned over an extension being built near the house.
On the one hand, the rafter legs rest on the racks of the frame 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 rest on a horizontal run fixed on it, or on individual fasteners (brackets, embedded bars, etc.), but also aligned horizontally. The attachment line of this side of the rafter legs is also made in excess h.
Please note that despite the differences in approaches to the installation of a shed system, the same “rafter triangle” is present in all options - this will be important for calculating the parameters of a 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 in order to ensure free flow of storm water and melted snow.
On a stand-alone building, there are already certain choices. Of course, the option is rarely considered in which the truss 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 back or to one side.
Here it is already possible to take the external design of the building under construction, the features of the territory of the site, the convenience of laying communications for the storm water collection system, etc. as selection criteria. But you should still keep in mind certain nuances.
- The optimal location of a shed 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 slope turns into a kind of wing - the wind tries to tear the roof up. It is for pitched roofs that this is of paramount importance. 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 slope: with a rectangular building, it can be placed 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, they practice the rule that the free length of the rafter leg should usually not exceed 4.5 meters. With an increase in this parameter, additional elements of structural reinforcement 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 (strut), located at an angle of 45 °, and resting from below on a rigidly fixed support beam (lying). At distances up to 12 meters, it will be necessary to install a vertical rack in the center, which should be based either on a reliable ceiling, or even on a capital partition inside the building. The rack also rests on the bed, and in addition, a strut is also installed on each side. This is all the more relevant 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 without additional support to do in any case will not work.
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, relying on capital walls, and linking these racks with contractions, installing 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 truss system.
wood screws
What angle of slope will be optimal?
In the vast 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 single-slope 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 side, but this does not mean at all that the wind on the other side is completely excluded. The steeper the angle of inclination, the greater the resulting lifting force becomes, and the greater the shear load will be experienced by the roof structure.
In addition, shed 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 ...
Too gentle slope, with a slope angle of up to 10 degrees, is also not very desirable, for the reason that the load on the truss system from snow drifts increases sharply. In addition, with the onset of snowmelt, it is very likely that ice will appear along the lower edge of the slope, making it difficult for the free flow of melt water.
An important criterion for choosing the slope angle of the slope is the intended one. It is no secret that for various roofing materials there are certain "frameworks", that is, the minimum allowable roof slope angle.
The slope angle itself can be expressed not only in degrees. It is more convenient for many masters to operate with other parameters - proportions or percentages (even in some technical sources you can find a similar system of measurements).
Proportional calculus is the ratio of the span length ( d) to the slope height ( 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 easily converted from one value to another.
The red lines show the conditional division of roofs: up to 3 ° - flat, from 3 to 30 ° - roofs with a small slope, from 30 to 45 ° - medium steepness, and above 45 - steep slopes.
The blue arrows and their corresponding numerical designations (in circles) show the established lower limits for the use of a particular roofing material.
 |
|||
|---|---|---|---|
| № | Slope | Type of acceptable roofing (minimum slope) | Illustration |
| 1 | 0 to 2° | Completely flat roof or sloped up to 2°. At least 4 layers of rolled bituminous coating applied using the “hot” technology, with a mandatory top dressing of fine gravel embedded in the molten mastic. | |
| 2 | ≈ 2° 1:40 or 2.5% | Same as in point 1, but 3 layers of bituminous material will be enough, with obligatory sprinkling | |
| 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 rolled bituminous materials - at least two layers glued to the mastic in a hot way. 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 (single line). | |
| 6 | ≈ 11÷12° 1:5 or 20% | Soft bituminous tile | |
| 7 | ≈ 14° 1:4 or 25% | Flat asbestos-cement slate with reinforced profile. Decking and metal tiles - practically without restrictions. | |
| 8 | ≈ 16° 1:3.5 or 29% | Sheet steel roofing with folded connection of adjacent sheets | |
| 9 | ≈ 18÷19° 1:3 or 33% | Slate asbestos-cement corrugated regular profile | |
| 10 | ≈ 26÷27° 1:2 or 50% | Natural ceramic or cement tiles, slate or composite resin tiles | |
| 11 | ≈ 39° 1:1.25 or 80% | Roofing from wood chips, shingles, natural shingle. For lovers of special exotics - reed roofing | |
Having such information and having outlines for the future roofing, it will be easier to determine the slope angle of the slope.
metal tile
How to set the desired slope angle?
Let's turn again to our basic "rafter triangle" scheme, posted above.
So, to set the required slope angle 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 value of the tangent is a tabular value that is easy to find in reference literature or in 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, which 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 this criterion becomes decisive.
Calculator for calculating the excess of the upper point of the installation of the rafter leg
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:
- Profitability. For the device of the roof, a lot of building materials are not needed, on which the bulk of the funds are spent.
- 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.
- The building will have a small weight. This means that there is less load on the walls and foundation.
- Thanks to this shape, a shed roof perfectly resists wind loads, as well as the weight of snow that accumulates on the surface.
- The angle of inclination is very different, depending on the needs. It varies from 5° to 45°.
- 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.
- 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 shed 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:
- For the installation 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 from 20 ° to 30 ° are needed.
- 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:
- 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.
- 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.
- To safely move around the roof, flooring from wooden boards is laid on the floor beams. He is temporary.
- 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.
- Floor beams must be covered with waterproofing and walled into the wall. The pediment rises to the chosen height, according to the drawings.
- On the finished pediment, you can fix the Mauerlat. It turns out that two Mauerlat are parallel to each other.
- Markings are applied to the lower wall for attaching the rafter legs. The fastening elements themselves are fixed.
- 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.
- 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.
- 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.
- 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.
- 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 service life and the final reliability of the roof lie in the correct preparatory work, which includes the correctly chosen distance between the rafters. It is from this element of the supporting frame that the load distribution on the supporting frame directly depends, an error in the calculations of which can lead to deformation and collapse of the entire roof. So, the calculation of the total distance between the truss elements is one of the most important tasks in planning and calculating the load-bearing house.
Basic calculation technology
Rafter pitch is the exact distance between two legs of one truss truss. Most often, in private construction, the distance between the legs is about one meter, but the exact figures should come from a detailed calculation of the bearing capacity of the selected type of roofing system. In order to independently perform such a calculation, you must adhere to the following scheme of actions:
- Having measured the eaves of the roof structure, it is necessary to determine the total length of the roof slope.
- The resulting value must be divided by the selected and most optimal step of the rafters. In other words, if exactly one m is chosen in the rafters, then the length of the slope must be divided by this unit of measurement.
- One is added to the result, after which you can round the finished value. It is this method that allows you to determine the number of roof trusses on one roof slope.
- Now it’s worth dividing the length of the roof slope by the resulting number of trusses, which will allow you to determine the pitch of the rafters.
It is worth recalling that this method of calculating such a building element as the pitch of the rafters cannot be considered extremely accurate, because in such calculations it is necessary to take into account the features of the selected roofing material, which can be a problem in the absence of proper experience in this matter. It is for this reason that methods will be described below that will allow you to choose the right rafter pitch for popular roofing materials.
Ceramic tiles and rafter installation
The main feature of the manufacture and installation of a truss bearing system for ceramic tiles is the extremely large weight of the roofing material, which in its totality is ten times greater than the weight of any roofing material.
As a rule, this type and size of roofing material provides for up to 60 kg per square meter of truss bearing system. All this becomes the reason for the use of only dry lumber on the roof, which eliminates the possibility of further deformation during drying and pressure.
When using a wooden beam on the roof, the cross section of which is 150x50 mm, the step between can vary from 70 to 120 cm.
In addition, the distance between the rafter legs may also depend on the overall slope of the roof.
Do not forget about the length of the rafter-type legs themselves. The longer this length is, the smaller the distance should be between the legs of the rafters, otherwise the supporting frame of the roof will be deprived of maximum strength and stability.
Experts recommend using no more than 80 centimeters of pitch between trusses if the roof slope is up to 45 degrees. Special attention should be paid to the lathing system when using ceramic roofing material on the roof.
To determine such a step, it is necessary to take into account the characteristics of each individual element of the roofing material, namely each tile. In order to perform the correct calculation of the crate step for such material, it is necessary to subtract the length of the lowest row and the distance between the last bar and the row of the crate from the pitched length.
As a rule, all varieties of such roofing material have a length of no more than 40 cm. When laying the tiles, they are overlapped, which takes up to 9 cm from the bottom row. In other words, the correct step in this calculation is from 31 to 35 cm.
Metal tiles and laying methods
As a rule, the use of metal tiles in private construction is considered the most common, for which there are a number of reasons and positive characteristics of this roofing material on the roof.
If we compare such a roofing type material with the one described above, then several striking differences can be noted, each of which can be safely considered a positive feature of the material. First, it is worth recalling the simplicity and speed of installation of such material, which is made in a sheet type, allowing you to cover a significant area of \u200b\u200bthe roof at a time.
The second feature of metal tiles on the roof can be considered the extremely low weight of the material, which has a positive effect on installation, work on the roof and the load on the supporting frame of the roofing system.
This feature can be considered the most important, because it is responsible for the lower costs of labor and time in organizing the truss carrier system. When using this roofing material, the pitch of the rafter bearing legs is from 60 to 95 cm, because the reduced weight and size of the roof does not require high load resistance parameters.
With such indicators, it is worth using a heat-insulating material, the thickness of which is at least 15 cm, which is placed between the rafters. When organizing, the thickness of the insulating material should or may be greater, because this is necessary for arranging a residential floor in the attic. This also affects such an element as the thickness of the material that is used to make the rafter load-bearing legs.
All this indicates the absence of significant differences in the truss system for metal roof tiles. This roofing material provides standard knowledge about the construction of truss and roofing systems, which is simply necessary to install. The main difference of such a system may be the fastening of the upper type support to the ridge run, and not through the ridge type beam itself.
The free space at the top of the system, obtained through the installation of rafter legs, is ideal for ventilation of the entire under-roof space, which is often covered with condensate in metal roofing material.
In the event that changes are made to the roof of an old wooden house, it is necessary to completely remove the mauerlat, replacing it with a common top-type crown. In such a crown, it is necessary to put marks and make selections with the desired step, into which the elements of the rafter bearing legs will be installed. This allows you to more accurately calculate the pitch of the rafter bearing legs and install them.
Decking and determining the distance between the racks
When using such a roofing material as corrugated board, the calculation of the correct pitch of the rafter bearing legs is 60-90 cm, which practically coincides with all the types of structures and roofing materials described.
If necessary, put more distance between the elements of the rafter legs, it is necessary to insure the transverse elements of the crate with a greater thickness and cross section. This will strengthen the entire supporting structure, which will extend the life of the entire roof. The step between is about 50 centimeters, when using a board that is at least 10 centimeters in size.
When it comes to such a moment as calculating the crate on the truss system, then do not forget that the last board should be 1.5 centimeters thicker than all the other elements of the system. Before installing the elements of the crate, it is worth remembering the presence of a chimney and a special system that should be on each roof. This will save time on the calculation and alteration of the truss system, and the crate as a whole.
Ondulin and construction installation methods
As in the cases described above, ondulin provides for the calculation of the pitch of the rafter bearing legs from 60 to 100 cm, which makes such sizes standard when using the most popular roofing materials.
The truss trusses themselves are made of lumber with a section of 200x50 millimeters, which is quite enough to ensure that the strength and reliability of the truss system are at the maximum level, and it is easy to install them. It is immediately worth noting the fact that the described roofing material needs a continuous lathing system, which will allow the material to qualitatively resist the loads from snow thicknesses, as well as solar exposure.
In some cases, a thinned type of crate can also be used, the calculation of which is quite simple if a wooden beam is used for this, the step between the elements of which is no more than 30 cm. As a rule, this option is more expensive than necessary for a continuous crate. In other words, it is irrelevant to use the thinned type of system in this case.
Slate and truss structure under it
As a rule, slate coating is considered the most common in our country. The reason for this indicator can be considered the extremely low cost of the material, the simplicity and speed of installation, as well as the possibility of replacing individual sheets in case of damage to individual sections of the roof.
The distance between the rafters for this type of roof should be 80 cm. It is this distance that is considered the most optimal solution when combining the load from the weight of slate sheets.
The crate in such a system needs a thinned type using a board or timber of any type, but of a certain section, which should not be less than 30 mm. Such a thickness of a board or timber is needed for high-quality and correct distribution of weight from the roofing material itself, as well as from winter precipitation.
Do not forget about the constant margin of safety when organizing the truss system, which may be required in case of unforeseen circumstances associated with mechanical loads and bad weather. All other features of the truss and crate system do not have any special differences from the options listed above. In other words, for all other types of coatings, we determine the distance in the same way as for the above roof.
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:
- Determine the length of the slope by measuring along the eaves of the house. Suppose that it turned out 17.8 meters.
- 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.
- Further, we round the result up and add one: 23 + 1 = 24. At this stage, the number of rafters required is determined.
- 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 actual 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 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:
- 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 pitch.
- 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.
- 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.
- 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.