At what distance do the rafters. The pitch of the rafters of a gable roof. Hip roof truss system
The construction of the roof truss system and the subsequent roofing are the most important stages in any construction. This matter is very complicated, 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 lean-to structure roofs. 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 shed 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 completed high school. But this simplicity does not affect the strength and reliability of the entire structure.
- Even if the leader independent construction the owner of the site has never before 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 appearance shed 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 (A) 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, it is 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 is not shown - on frame structure. 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 purpose of this element is uniform distribution loads from rafter legs on 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 the installation of vertical racks required height h.
The solution is simple, but the design is, 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 in the case when, due to its great length, require a certain amplification (this will be discussed below).
The rigidity of the entire truss system is already embedded 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 a strapping or transverse bars 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. WITH opposite side located capital wall 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 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 you can already take external as selection criteria design decoration of the building under construction, the features of the territory of the site, the convenience of laying communications of the storm water collection system, etc. 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 shed roofs that it has essential. 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). For distances up to 12 meters, you will have to install a vertical stand in the center, which should rest either on reliable overlap, 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, based on capital walls, and with tying these racks with contractions, with the installation of the same struts both 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 | Valid type 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 a "hot" technology, with a mandatory top dressing of fine gravel embedded in 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 no 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 wavy sheets 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
The distance between the rafters under the metal tile in without fail takes into account the forces resulting from the wind, snow load, own weight of structures, roofs. In addition, the following factors affect the pitch of the rafters under the metal tile:
- the location of the pipes - the wooden elements of the roof should be 25-35 cm from the chimney, should not interfere with straight trajectories ventilation ducts, fan pipes;
- roof configuration - it is necessary to have a rafter leg at the junction of the ridge of a gable, hipped roof.
All wooden elements of the truss system are made from coniferous trees, the humidity of which does not exceed 20%.
The step of the rafter legs is calculated at the design stage for budgeting. This will significantly reduce the amount of waste, cuttings of sawn timber.
What you need to know when choosing the optimal distance between the rafters?
The scheme of the roof with hanging rafters.
Having collected the loads present during the strength calculation, the designer evenly distributes them on bearing walls. The principle of calculation is the same for layered, hanging rafters, only the schemes for fastening the elements in the ridge, on the Mauerlat, differ.
The minimum, maximum step of wooden rafters under the metal tile is regulated by 0.7 m, 1.2 m, respectively.
When choosing a step of 60 - 100 cm, the length of the rafters cannot exceed 6 m, with its decrease, a run-up of up to 1.2 m is allowed. If you put your feet more often than 60 cm, this will unnecessarily make the roof heavier and increase the construction budget. If you increase the step more than 1.2 m, the bearing capacity and the resource of the structure will sharply decrease.
A solid crate of wood-containing boards adds strength and rigidity to the truss system. In this case, it is allowed to increase the step by 0.3 - 0.2 m compared to a periodic crate made of a bar or edged board. However, to save the construction budget, a continuous crate for metal tiles is used extremely rarely. The material has sufficient strength and rigidity due to additional transverse profile ribs.
A step of more than 1.2 m is not used even when using rolled metal rafters, despite a sufficient margin of safety of the material. This is due to the possible deflection of the roof sheets during heavy snowfalls, hurricane winds.
The cross section of the beam from which the rafter legs are made also affects the pitch of the rafters, since the area of \u200b\u200bsupport of the crate and the weight of the roof change. The best option is considered to be a beam of 150 x 50 mm with a discharged crate in increments of 4 - 7 cm, depending on the pitch of the transverse wave.
Calculation example for a gable roof
When implementing a project, specialists at the initial stage know roofing material. In order to find out the recommended pitch of the rafters, you can use the SNiP tables, and then adjust the value in accordance with the operating conditions. An example table is shown below:
| Leg section (cm) | Rafter pitch (cm) depending on their length (m) | ||
| 5 | 4 | 3 | |
| board 20 x 2 | 70 | 120 | – |
| board 18 x 2 | – | 100 | – |
| board 16 x 2 | – | 70 | 130 |
| timber 22 x 6 | – | 120 | – |
| timber 20 x 5 | – | 110 | – |
| timber 18 x 5 | – | 90 | 150 |
| log 180 | 90 | 150 | – |
| log 150 | – | 90 | 150 |
| log 140 | – | 70 | 140 |
| log 130 | – | – | 110 |
The table values correspond to the rafters of simple single-gable roofs. First, the section of the leg, the length of the element, the distance between the centers of the log, the beam is obtained automatically. At the next stage, the length of the slope in the ridge is divided by the pitch of the rafters with the addition of one. Thus, the number of legs is counted, rounding the number up. Then it remains to adjust the distance between the wooden rafters in fact. For example, with a ridge length of 7.5 m, a rafter leg with a section of 16 x 2 cm (board) 4 m long, you get:
7.5 / 0.7 \u003d 10.7 + 1 \u003d 11.7 pcs. round up to 12 rafters.
The specification of the size allows you to calculate the center-to-center distance for mounting after installing the outer legs:
7.5/12 = 62.5 cm.
Dormer windows are located between adjacent rafters, in the places where pipes and chimneys pass, the legs are displaced by the distance specified in SNiP. All other elements of the system remain in place, the area of adjacency to the pipes, if necessary, is enhanced:
- a bed is cut into two adjacent legs;
- a short rafter cuts into it at one end, the second adjoins the element of the opposite slope in the ridge;
- the offset legs in the upper part rest on a ridge run attached to at least two roof trusses.
Thus, the system receives the necessary rigidity without losing bearing capacity fire safety requirements are met wooden parts roofs.
Rafter leg material
The material of the rafters is often a beam of 25 x 10 cm - 15 x 4 cm, which allows to reduce the construction budget.
When choosing lumber of natural moisture, the developer is guaranteed to shrink the structure in the first year and a half by 5-7 cm in height. By increasing the estimate point for the arrangement of the truss system by 70%, you can purchase glued laminated timber, significantly reducing structural loads, and doubling the roof resource.
The distance between the rafters will remain unchanged, however, instead of a planed beam of 17.5 x 5 cm, recommended by building codes for five-meter legs spaced every 0.6 m, you can get by with a glued beam of a smaller section of 15 x 4 cm. Transportation costs will decrease, work at height will be facilitated , cut material.
Prefabricated rafters from boards are used with the truss fastening scheme of the same name hip roof. The upper slopes are made of single boards, the lower ones are made of three boards sewn with self-tapping screws with an offset in the rows.
The choice of metal rafters is justified with a complex configuration of the roof, an abundance ventilation pipes, chimneys, which cannot be bypassed in compliance with the requirements of SNiP, fire safety. In this case, the step between the rafters is maximized, since rolled metal is much stronger than lumber.
If the rafters are attached at the bottom to the Mauerlat, the step of the legs is not critical, the elements can, if necessary, move to the desired distance in any direction. If the scheme of support on puffs, which are floor beams, is used, it is much more difficult to displace individual elements. In this case, the amount of cutting waste increases when sheathing the draft ceiling, the floor of the attic or attic space.
Construction of the roof of a building milestone in the construction of a house, while it is necessary to calculate the pitch of the rafters as accurately as possible, since the reliability and service life of the roof will depend on this.
If the master does not pay attention to the calculations and installs the rafters, focusing only on his own eye, then the frame will turn out to be either too heavy, moreover, expensive, or fragile.
General calculation rules
The step of the rafters is the distance from one to the other rafter leg. It is believed that such a distance is set in the range from 60 cm to 100 - 120 cm (determined by optimal width, dimensions must be taken into account. waterproofing materials and heater).
The exact installation step of the rafters for gable roof can be calculated as follows:
- measure the length of the slope along the cornice of the roof;
- we divide the measurement data by a certain step (we determined a step of 1 m - we divide by 1, if the step is 0.8 m - we divide by 0.8, etc.);
- add 1 to the resulting number;
- the result is rounded up (in the direction of increase) - we see the number of rafters for installation on one slope of a gable roof;
- we divide the length of the slope by the resulting number and get the exact step between the rafters.
For example, the length of the roof slope is 30.5 meters, given the width of the insulation and waterproofing rolls, a step of 1 meter is selected.
30.5 m / 1 m = 30.5 + 1 = 31.5. Rounding up gives a result of 32. 32 rafters are required for the frame for the roof slope.
30.5 m / 32 pcs. \u003d 0.95 cm - the distance (step) between the centers of the rafters.
However given formula does not take into account the nuances of certain roofing materials, therefore, in the future, the article will consider how to calculate the correct pitch of the rafters for the most popular coatings.
It is especially worth highlighting the rafter system during the construction of a hip roof (envelope). The construction of such a roof begins to be built precisely from the hip legs, into which the rest of the rafters then crash.
The hip, which has a length of over 6 m, is often reinforced by sewing it together from two elements. Otherwise, the installation and calculation of the pitch of the rafters for a hip roof are similar to the installation and calculation of a gable roof.
Rafter system for ceramic and metal tiles
The use of metal tiles in the construction of private sector houses is the most common phenomenon, which is facilitated by a number of its positive qualities.
Firstly, this is a small weight of the coating, which facilitates installation and helps to reduce loads on supporting structures.
Secondly, sheets of metal tiles can be quickly closed large areas roofs, which is very convenient, especially if you choose a gable roof option.
The step of the rafters under the metal tile is set in the range from 60 to 95 cm, since the relatively small weight of the roof does not require increased resistance. Due to the low weight of the coating, the thickness of the rafters can also be reduced.
As for the thickness thermal insulation material, used to insulate roofs made of metal tiles, experts believe that when installing an attic under it, for greater confidence in reliability, thermal insulation of 20 cm can be used, in other cases 15 cm is enough.
A feature of roofs covered with metal tiles is the possibility of condensation.
This can be avoided by organizing ventilation during the installation of the rafters: for this, several holes (about 10 mm in diameter) must be drilled in the rafters at a short distance from the top.
As for the installation of a frame made of rafters under a coating such as natural (ceramic) tiles, it is necessary to remember its large weight.
In comparison with other modern materials, tiles are 10 times heavier or more. Given this feature, experts recommend using exclusively dry wood for it in order to avoid sagging after drying.
For rafters in this case, you need to use a beam with a section of 50 - 60 mm * 150 - 180 mm; the step width of the rafter legs is set in the range of 80 - 130 cm, while the greater the degree of roof slope, the greater the distance between the axes of the rafters.
The pitch of the rafters is also dependent on their length: the greatest length will require the smallest distance, and vice versa. Otherwise, the roof frame will lose the necessary stability.
Given the size of the tile (as a rule, its length does not exceed 40 cm), it is necessary to correctly calculate the width of the step of the crate stuffed onto the rafters.
From the length of the slope, you need to subtract the length of the bottom row and the number of centimeters between the crate and the last bar.
Frame for ondulin, corrugated board and soft roof
Relatively new on the market of materials are such types of roofing as corrugated board and ondulin. At the same time, they are successfully used both in the construction of a gable and hip roof.
The weight of these materials is almost equal to the weight of the metal tile, so the calculation of the width of the rafter pitch will be similar to the calculation when laying metal sheets. The pitch of the rafters for corrugated board is determined from the range of 60 - 90 cm, for ondulin - 60 - 100 cm.
The sufficient thickness of the rafters themselves when covering the roof with ondulin and corrugated board is 50 * 200 mm.
If it is necessary to increase the distance between the centers of the rafters, then you can increase the strength of the transverse crate.
The rule for installing a batten under a corrugated board is similar to installing a batten for a metal tile: the last board must be taken wider than the rest (usually 15 cm thicker).
The crate for ondulin must be made solid to increase the resistance of the material to various weather conditions.
Speaking about the device of the truss system for a soft roof, it is worth remembering the types of such material presented on the markets: this is a roll type of roofing and bituminous tiles.
The name itself suggests that for a soft roof it is necessary to solid foundation which will withstand heavy snow cover, gusts of wind and heavy rains.
The main requirements for roof frames for soft roofing are that they must be strong and even.
Strength must be calculated for the thickness of the snow typical for the region in which the structure is being built, and for the average weight of an adult male, so that troubleshooting is possible.
A flat roof should be for the reason that to exclude the possibility of sagging under the influence of the above weather phenomena.
Between the axes of the rafters for a roof frame with a soft roof, the step should be small, no more than 50 cm.
If the step is still larger, you will need to make a rough crate, on which the main, solid one will already be mounted.
The counter-lattice will help the soft roof not to bend and increase its service life by an order of magnitude. For a continuous crate, a 30 mm board or a 20 mm OSB board is more often used.
If soft roof is provided as a covering for a hip roof with the organization of an attic space, then it is necessary to think about its insulation, having thought over the filing for laying insulation, hydro and vapor barrier.
These are all the subtleties of the roof frame device for a soft roof.
Rafter for slate roof
Despite the richness and variety of modern materials, the good old slate remains quite popular. The use of expensive roofing is far from always justified, and it is then that an asbestos-cement sheet comes to the rescue.
The weight of slate is quite impressive, while its installation does not require any kind of grandiose crate. This is because such a roof in itself is quite strong.
For erection roof frame in this case, rafters with a section of 150 * 40 mm and a beam with a section of 35 * 35 mm for the crate are required.
Lumber for the construction of the frame should be stacked and kept for some time to give the same level of moisture. 
After the drying process is completed, the bend must be determined. Rafter legs are recommended to be installed with the concave part (tray) up - so if water gets on the rafters, it will slide down, bypassing the attic space.
Before starting the installation, the beams are checked for the content of knots in them and rejected, since the knotted material may not withstand the weight of the roof.
Rafter fasteners in this case are made with nails, optimal length which - 15 - 20 cm.
Nails should pierce the timber through, however, the peeking ends should never be bent, since it is necessary to maintain the mobility of the structure.
With drying and deformation of the tree, this technique will prevent cracking of the slate sheets.
The lathing for the device of a slate roof can be continuous or sparse. Solid is made from OSB sheet or plywood and are more often used when laying flat slates.
Sparse is typical for laying on it wave slate. For a sheet with a standard size of 1.75 m, the crate pitch is about 80 cm. There is no point in making the crate more frequent, since the slate has a sufficient margin of safety.
After analyzing the materials of the article, you can independently engage in the construction of a gable and hip roof frame, determining for yourself their features and properties of roofing materials.
It will not be superfluous to recall that the calculation rafter pitch- a very responsible occupation, and it is necessary to approach its markup responsibly, since this will avoid mistakes and speed up the progress of work in the future.
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 with two parallel to the plane, with an angle of inclination relative to the horizon from 20 to 50 degrees.
With an insufficient slope of the roof of a gable roof in snowy areas, there is a danger of accumulation of large snow masses, which can lead to structural failure. 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. Typically, stingrays mansard roof broken lines with a varying angle of inclination. 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 given to the magnitude of the 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 called four-slope, since the roof is formed not only by the side, but also by additional end slopes, where the installation of the rafters is carried out not on the ridge, but on the corner bowstrings. This presents special requirements to 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's no secret that different kinds 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, to replace wavy sheet materials a more durable and lightweight analogue came - 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, artificial polymer material- polycarbonate. 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. Which are installed on solid crate 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 that standard sizes 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 locality.
- 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. Hence:
- 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.
Stropilina is one of individual elements load-bearing structure roof, with the help of which its slope is formed. In the design, the rafter is attached with its upper end to the ridge, and the lower end rests on the Mauerlat, with a straight slope, or on a rack (with a sloping roof). Rafters are made from edged boards section 150x60 mm or timber 150x100 mm. The distance between the rafters at which they are located from each other after installation is called a step, which can be in the range of 600 - 1200 mm.
Rafter systems their types
Depending on the type of installation of rafter legs, systems are divided into 3 types:
What may determine the installation step of the rafters
The step of the roof rafters depends on such factors, How:
Taking into account all these indicators when calculating, you can get a solid and reliable roof structure, which for a long time will be a high-quality support for the roof.
It is the calculation, subject to the basics of regulatory loads, allows you to choose the right distance between the rafters. As a rule, the standard values can be determined from the Sheaves, and the calculated ones are derived on their basis separately for each structure.
At the same time, it is customary to use rafter legs with a section of 150x50 mm with an optimal distance between the rafters within 0.8 - 1.8 m / p. but it should be remembered that when the slope of the roof slope changes, the distance between the rafters also changes.
Calculation of the truss structure
The strength and stability of the entire roof directly depends on the quality of the calculation for the selection of the section of the rafter legs and the distance between them. Regardless of which type of coating is chosen: profiled sheet, slate or metal tile, the initial calculation should remain unchanged. After all, each calculation is based on structural strength under mechanical loads, and other effects are no longer important.
When calculating the choice of the optimal distance between the rafters for the roof, are based on the following parameters:
- Type of roofing.
- View of the truss system and design features of the roof.
- feasibility and economy.
For a small house, the design calculation for the roof can be done by yourself. True, the method of calculating the elements for the roof truss system is rather complicated, and it is recommended to do it using programs specially created for this. Especially if you need to calculate complex broken roof with a large area, most likely, it will not be possible to do without a specialist. At the same time, the calculation of the step of the rafters will also be based on the standards - the minimum step is 0.6 m, the maximum step is 1.2 m.
Method of calculation
Produced in this way.
- The length of the building is measured along the eaves.
- The resulting length is divided by the estimated distance between the rafters. For example, the estimated pitch of the rafters will be 0.8 m / p. (mean distance is considered to be 950 mm).
- After performing this action, one should be added to the result obtained, and the resulting amount should be rounded. Thus, the required number of rafters is obtained on one side of the slope. After that, the length of the building must be divided by the number of rafters received, and as a result, the exact axial pitch of the rafters is determined.
Example, - building length 26.5 m / p. the distance between the rafters is supposed to be 0.8 m. So:
- 26.5 m ˸ 0.8 m = 33.1 33.1+1 = 34.1. As a result, after rounding, it turns out that 34 rafters need to be installed on one slope.
26.5 m/s ˸ 34 art. = 0.77 m - this value is the distance between the rafters along their central axes.
But that's only general technique calculation, which does not take into account the peculiarity of the planned roofing. Therefore, it is recommended by experts to calculate the step between the rafters for a certain roofing material and insulation, for example, for the most popular roofing metal tile today.
Roof structure for metal roofing
metal tile visually imitates ceramic roof tiles. It is made from thin sheet steel by cold stamping. Thanks to polymer coating, has a high resistance to weathering and a rather attractive visual appearance, is not afraid of sudden temperature changes.
The advantage of metal tiles
Often used in the construction of most mansard roofs.
The cross section of wooden rafters under a metal roof is usually standard 150-50 mm, but the distance between them can be from 600 mm, but not exceed 900 mm (depending on their angle of inclination, which can vary between 22 - 45 degrees). This limitation of the pitch of the rafters is due to the fact that the crate under the metal tile is mounted with a distance from each other within 300 mm. The standard timber, which is used for the crate, has a section of 30x50 mm or 50x50 mm. And this means that each rafter is subjected to additional load.
The stability of the roof structure against various mechanical loads depends on four factors:
An important factor in the calculation of the truss structure, is the estimated maximum load on the roof, the formation of which includes:
- The weight of the entire truss structure.
- The weight of the crate under the cover.
- Weight of insulation and roofing.
- Snow load (determined according to a special, unique for each region, reference book).
- Wind load (also according to a special guide for the region).
- The weight of a person with a tool (repair work, estimated weight - 175 kg / m²).
When installing the rafter system, the distance of the rafter legs should not exceed an average value of 0.9 m / p. except for certain, foreseen in advance cases.
If, when calculating the loads, any inaccuracy is made in the selection of material for the roof and the location of the rafters, it may occur its deformation and destruction of the roofing. Robust design the roof will be guaranteed only with the correct calculation of the section of the rafters and their installation step.
It should be remembered. Universal value calculation roof structures does not exist. Each building requires an individual calculation.
Rafters for a shed roof
Shed roofs can often be found on small outbuildings. They can also be used in private residential buildings, but quite rarely. In such cases, the angle of inclination of the roof is rather small, and with such an arrangement of the load-bearing floor beams, they are under a lot of pressure, especially in winter.
Therefore, for a shed roof, load-bearing floor beams are installed from a beam of large section from 60x150 to 100x220 mm, depending on the width of the overlapped span. At the same time, the distance at which the rafters are laid from each other should be within 400 - 800 mm, depending on the angle of the roof.
For pitched roof not required complex structure rafters, they can simply be laid on the walls, without even using a Mauerlat. In regions where there is enough snowy winters with a lot of snow, it is recommended to build a roof slope at a maximum angle of 35 ⁰ and place the roof in the direction of the wind. This reduces windage and leads to its self-cleaning.
Gable roof
Represents a structure assembled from rafters interconnected in the form of a triangle. The upper part, which rests on the ridge, and the lower part on the Mauerlats, located parallel to each other on opposite walls. In simple words, this is a roof consisting of two opposite slopes, connected by a ridge.
Double pitched roof structure, depending on its area, is mounted from separate rigid elements that enhance the strength of the roof. These include racks that support rafters, puffs that connect rafters to each other, jibs, girders, support beams, etc.
For a gable roof, often the rafters are mounted taking into account the insulation in increments of 0.9 - 1.2 m / p. In this case, the strength of the mounted structure will be the highest if the resulting triangle is isosceles. In regions with strong winds, rafters are recommended to be mounted with a slope of approximately 20 ⁰, and in snowy areas optimal angle should be 45⁰.
Although the gable roof is considered classic, it has several alternative "related" types.
mansard roof
For mansard roof, behind design parameter to determine the step between the rafters and their number, a load is taken in the range of 40-60 kg for every 1 m / p. rafters, and the maximum deflection from its length is 1/250. Usually, with a properly selected section, this distance along the centers of the rafters is, as for a gable roof, 0.6 - 1.2 m / p.
It should be noted that the average load on the attic is approximately 200 kg / m2. So, with the standard calculation of the section of the rafters, it is recommended to add a small percentage of the margin of safety.
hip roof
Among all roof structures, it is considered one of the most difficult . It's almost a hipped roof., while the rafters of the end slopes are attached with their upper ends to the corner bowstrings, and not to the ridge. Therefore, certain requirements may be imposed on this type of roof during construction. In this case, the rafters are installed similarly to a gable roof at a distance of 60 cm - 1.2 m / p.
Attic rooms under such a roof are made in rare cases, since its slopes “eat up” some area of the attic room, especially in height.
