Calculate the distance between the rafters. Distance between wooden rafters under metal tile Maximum and minimum rafter step

In the construction of the house it is important that the roof frame and its rafter design were reliable. To do this, it is necessary to know the optimal size of the gap between the rafters. How to properly carry out calculations for a solid system of a two-tie roof, taking into account various roofing materials, our specialists will tell in this article.

How to correctly calculate the distance between the rafters (for a double roof)

Distance under various roofing materials

Experts advise: determining the step between rapid supports, consider the roofing material from which the roof of the two-tie roof will be created. Consider the most common roof coating options suitable for private houses.

1. Profile - For this roofing material, we need a digital indicator from 60 to 90 centimeters (with an increase in the step to at least a single meter, you will have to install additional transverse boards with a large cross section - 5 × 10 cm). At the same time, under the professional flooring it will be necessary to install the crate, which will ensure the possibility of fastening the mandatory vertical components - the chimney, the ventilation system.
2. Ceramic tile - the roof of such a material has a rather heavy weight, therefore the load on the rafter system will be higher than when coating the roof of the corrugated floor. Accordingly, the distance we expect, will be different: from 80 centimeters to 1 meter 30 centimeters. But in this embodiment, the steep slope is also taken into account (if the angle of inclination is 15 degrees, then the gap will be minimal - 80 cm, at 75 degrees - 130 cm).
3. Metal tile - this roofing material is lighter than the previous one and sold immediately in the sheet form, so the thickness of the component of the rafter system is reduced, and, therefore, the distance between the elements in it is reduced. For a rafter material with a cross section of 15 × 5 centimeters, the gap must be seamless from 60 centimeters to 95 centimeters. Such a distance will allow quality to warm the attic room (for this it is necessary to place the insulation material directly between the rafters). The feature of the installation of the rafter design under the metal tile is that the supports are installed on top of the ski run (usually their mounting is made on the ski bar from the side). But in this case, you should not forget about the ventilation holes near the upper roof.
4. Ondulin - this material is called "erectifier", and it is perfect for the roof of private residential buildings. For a rafter design for ONDULIN, rafters are used from a 5 × 20 centimeters boards, which provides some safety margin (and rapid runs are taken into account). The distance between such rapid boards is standard - from 60 to 90 centimeters, and a wooden beam for the crate should be a cross section of 4 × 5 cm, with an inter-axis step of 60 cm.
5. Slate is one of the most common roofing materials in our country, the rafters should be selected under it with a cross section of 5 × 10/5 × 150 centimeters. The distance between them will be slightly in a smaller range - 60-80 cm. The peel from a wooden bar has its gap between the elements, which directly depends on the angle of the roof slope angle: with a small slope - from 45 cm, with a larger - from 60 cm.

Thus, the total digital indicators to determine the distance between the rafters (depending on the roof material) will range in the following limits: a minimum is 60 cm, and maximum - 130 cm. If you yourself cannot decide on the choice of such a digital indicator, you should contact To qualified specialists for help.

One of the important stages of any construction is the construction of a roof of the building, the basis of which is the installation of the rafter system. From how correctly the step of the rafter is chosen, i.e. the distance between them, the uniform distribution of the roofing weight on the frame, the reliability of the roof and the duration of its operation will be completely dependent. With any minor calculation error, damage and collapse of the whole roof may occur.

Collect the required settlement values \u200b\u200bfor setting a step

The rafter system includes the following components:

• farms;
• skate and sidebars;
• maurylalat;
• diagonal elements.

Farms consist of a riglel, bases, rafting legs, binding and fasteners. Stropile legs are beams located along the skates, the lower ends of which are connected to the Mauerlat, and the top - with runs.

Step rafters is the exact distance between two rapid legs.

To obtain an accurately specified value, you must first find out the values \u200b\u200bof some important values \u200b\u200bfor this.

All calculations on the roof covering system correctly produce at home design. This responsible business can be held or entrusted to its specialists. The more accurate the calculations, the stronger will be the base for the roof.

To properly produce all the required calculations, including the size of the step of the rafter, you need to know:

• constant and temporary loads;
• their size;
• the corner of the skate;
• kind of roofing;
• material manufacturing rafters;
• roof type.

One of the indicators that must be taken into account when calculating the timing step, constant and temporary loads are considered. These include:

• the weight of roofing and rafter design;
• the weight of the inner finish of the roof;
• weight of snow cover;
• human weight conducting roof service.

It should be noted that these data are taken in special tables developed by scientists, depending on climatic zones, according to various territorial regions.

The angle of the skate can be determined, knowing the length of the wall at home and the height of the roof. The cooler roof, the items set more, since the load on such roofs will be transmitted mainly on the bearing walls. Learning further calculations, the length of the rafter is easily calculated. Most often they have standard quantities: 4 and 6 m.

For the manufacture of roofing system, the wood of coniferous trees is well suitable. The sawn timber should be high-quality, without bitch, rot. Before working, all wooden elements need to be treated with antiseptic special compositions.

The step of the rafter will depend on the type of roof, i.e. from the functional features and its shape. The magnitude of a simple and complex roof will be different.

What will affect the type of roofing on the step of the rafter should be considered in more detail.

General technology for calculating the distance between rafyles

Making all the necessary measurements, you can make a constructive calculation of the step of the rafter. Based on the practice, this indicator is in the range from 0.6 to 1.0 m.

To independently correct this calculation, you need to follow the following technology:

1. The total length of the roofing slope is taken.
2. The optimal step of the rafter farm is selected.
3. The length of the skate must be divided into a step of rafters.
4. The unit adds to the value.
5. For an integer number, the result is rounded in the biggest.
6. Such a calculation is the number of rafting farms (rafting feet) located on one roof slope.
7. Now the whole length of the roofing slope is divided into the resulting value indicating the number of farms. Thus, the step of the rafter is determined.

It should be noted that this calculation is made in the center of future rafters. However, the calculations cannot be considered accurate and constant. In each case, the construction of the roof of the house is also taken into account angle of the roof, and the features of the selected roofing material, and other indicators. In this regard, it is necessary to consider the features of the choice of the step of the rafted for the most common roofing materials: metal and ceramic tiles, professional flooring, slate and ondulin.

Features when choosing a distance between rafters for metallic and ceramic tiles

Metal tile as roofing is extremely common in both urban and country construction. The design of the rafting roof system itself when using metal tile will differ little from the general scheme. However, due to the fact that this building material has a small weight, rafters and other elements of the system can take a smaller cross section, i.e. with a smaller margin of strength. The distance between the rafters when using metal tile is 60-95 cm. Performance of all work on the installation of the roof from metal tile is much easier than from other roofing materials. The feature of the device of the crates of this material is that the board near the eaves should be thicker than 1.5 cm. Usually, the cross section of a rafter from metal tile is 50x150 mm.

Ceramic tile is a roofing material having a significant weight, which is 10 times more than the weight of the metal tile. In this regard, it is necessary to more thoroughly approach the calculation of the rafting roof system. It should be slightly increased - to 60x180 mm. The average distance between rafters for coating from ceramic tile is installed in the range of 0.8-1.3 m. It is necessarily taken into account the angle of slopes of the slopes: the distance between the rafters is made more than above the roof.

The length of the rafter legs in this case will have a strong impact on the result. The distance between the rafters is reduced with an increase in their length.. With their long-length, there may be increased loads that can be significantly reduced if you additionally install a system of subproofing supports of racks and other elements.

Features when choosing a step rafters for slate, professional flooring and ondulin

The most common roofing material is slate. This is due to its low cost, simplicity of installation, the possibility of replacement during damage to individual elements of the roof.

The features of the crates for slate is its weelle type, consisting of any type of board or timber, but with their obligatory cross section of at least 30 mm. This is necessary for the correct and high-quality distribution of slate weight on the crate.

The optimal distance between the rafters with a combination of loads from the weight of slate sheets should be 80 cm. It is worth constantly taking care of the strength of the strength of the rafting system, which can be due to different unforeseen circumstances. Otherwise, its establishment for slate roof is not different from other options.

Now you should pay attention to some features when installing a rafting system for such roofing materials such as professional flooring and ondulin.

The weight of the professional flooring and ondulin is much easier than that of ceramic tiles or slate, so the installation technology of the rafter for these materials is practically no different from the installation of metal tiles. The distance between the roof rafters from the professional flooring is 60-90 cm, and from Ontulina - 60-100 cm.

If you need to increase the distance between the rapid legs, it is necessary to strengthen the design of the system with transverse elements of the crate.

The device of the crate for the profile is very similar to the device of the crate of metal tiles. It is important to remember that in this case the last board should have a slightly large thickness than everyone else.

The feature of the installation of the lattice for ONDulin should be considered the need for a solid type of it for high-quality resistance to various loads. In some cases, it is possible to use a shunt-type fraud, but then the step between the rafters should be not more than 30 cm.

Thus, when you can produce all the necessary measurements, knowing the basics of the installation of the rafter system for the main materials for the roof (tiles, corrugated flooring, slate and ondulin), you can correctly calculate the distance between the rafyles.

On the importance of the roof for any structure to argue meaninglessly. No wonder in the entire history of mankind, more than a dozen different types of roofs were invented from simple to quite complicated in design and construction. An important element when planning the construction of the roof is a step between rafters - durable bars, which are the basis of the design. This will be discussed in this article.

The distance between the basis of roofing rods is not a permanent value and depends on the following components:

• kind of roofing;
• the angle of tilt of the skate;
• the species of the proposed roofing material;
• the size of the cross section of the rafter.

Before proceeding to the construction process of the top construction of the house, calculate the calculation, determining the optimal, distance between the rafters.

Rapid roof rafters

Duscal roofs received the greatest distribution in our country. They represent a construction having two parallel planes, with an angle of inclination relative to the horizon from 20 to 50 degrees.

With an insufficient bias, the roof of the bone roof in the snow-covered areas is the risk of accumulating large snow masses, which can lead to the destruction of the structure. The increase in the corner of the rods in the regions with the predominance of strong winds is also fraught with high load and the risk of fault not only the roof, but also the structure as a whole.

Horry roof

Most of the private houses have an exploited underpowering space called attic. This design is distinguished by the increased slide height, which is caused by the need to create a residential room of a convenient height. As a rule, the slots of the attic roof are broken, having a changing angle of the slope. For their installation, a double rafter system is used.

The steepness of the lower semi-column of the attic roof significantly exceeds the tilt of their continuation. Plague load perceived by them is not large. Due to this, the rafters at the bottom can be installed with a maximum step. The upper skate rods are recommended to mount with a reduced gap from each other.

Single roof rafters

For household buildings and some houses in private, roofs that have one skate are used. Due to the restriction of the angle of inclination on them there is high pressure. Experts are recommended for a single-piece roof rafter use a lumber of an increased cross section, with the installation of the minimum step from each other.

When calculating the distance on which the roof beams are installed, special attention should be paid to the magnitude of the snow load in a particular area. With a small slope, this characteristic is of great importance. The roofing material for such roofs is better to choose with a minimum one's own mass, which will reduce the bending load.

Slinged Walm Roof System

The most complex in construction is considered the rafting system of the holm roof. This species is called a four-page, since the roof is formed not only by side, but also additional end skates, where the installation of the rafter is carried out not at the horse, but on the angular tents. This makes special requirements for the organization of roofing frame.

Under the holm roof, the attic is not satisfied. This is associated with a small angle of inclination of the rafted and the roof as a whole. In the event of an increase in the angle of the rods to the horizon, the distance between the rafters is increased, with a decrease - on the contrary. An additional aspect of the calculation also used the roofing material.

The dependence of the step rafters from the roofing material

In addition to snow and wind loads related to variables, there is a constant (static), the force of which depends on the roofing material used on the roof. It is no secret that various types of roof have their own mass, which may differ at 10 or more times.

The correct choice of material has an impact not only on the upper, but also on all other parts of the design of a residential building and other buildings. No wonder, when designing a foundation, it is necessary to decide in advance with the choice of roof.

Roofing from the professionalist

Currently, one of the most common roofing materials is a profiled sheet produced by galvanized or subsequent polymer coating. The following parameters will be attributed to the distinctive features of the professionalist:

1. High corrosion resistance;
2. As a result, long-term (more than 15 years) service life;
3. Easy installation even without the necessary qualifications;
4. The low mass of the sheet (weight 1 m 2 is 4-5 kg).

Since this roofing material does not have a high load on the rafter system, the distance between the elements is selected as possible for a particular angle of inclination. In addition, the professionalist does not require high strength characteristics from the roof crate. All this together allows you to minimize the overall load on the foundation and walls.

Roofing from metal tileage

The second common type of steel roofing materials is a metal tile. This kind of professional leaf, successfully imitating natural clay material, but with a smaller mass (10 or more). A feature of rafters for metal tile is a smaller section.

When choosing, at what distance, install rafters, first of all, should be guided by a dynamic load. Like a professional sheet, metal tile is not demanding of the size of the rafter feet and is well mounted on the crate of an inch coniferous boards. All this makes the metal roof of a small-time.

Scroll system for Ondulin

In the 21st century, a more durable and light analogue came to the change of wavy sheet materials - Ondulin. Among others - the most lightweight material. The mass of the sheet does not exceed 6 kg.

The small thickness of Ondulin sheets at the corners of the skates is less than 15 o, requires the arrangement of a solid crate of plywood sheets, for example, which will require the corresponding step of the rafter. This should be paid attention to the calculations.

Slate roof

Not so long ago, the widespread material was wetted from an asbesto-cement mixture, called slate. High mass and fragility are the main disadvantages, however, he finds his fans in the construction of various economic buildings.

The high mass, comparable to the weight of the clay tiles, will not allow the same rafter system as under metal tile. Construction standards defined the minimum angle of the roof of the roof from slate in 22 o and more. Otherwise, the load from the material and the rafter system with the crate exceeds the permissible parameters. The step of inclined bars, like their cross section, are selected individually in each case.

Polycarbonate roofs

In recent years, an artificial polymer material - polycarbonate has become more and more often on the roofs of the veranda. Available in two versions - monolithic and cellular. The first in its properties is similar to ordinary quartz glass, but significantly surpasses its strength. The second has smaller mechanical properties, but high thermal insulation and light effect.

Cellular polycarbonate is standardly much easier than a monolithic fellow. It is used as a roof without the use of the crate under the condition that does not exceed the ½ width of the material sheet. The high strength of the monolithic analog also allows to avoid transverse rafyles of elements. Sufficient flexibility allows semicircular roofs on a metal frame, the step of which does not exceed 0.9 meters.

Thematic material:

Raftered under the soft roof

The original pattern can be obtained due to the use of soft roofing materials, accumulating with the adhesive layer. Install that are installed on a solid crate of plywood or OSP. The step of the rafter should allow the fastening sheets, so it is chosen to a multiple ½ width. Subject to the standard sizes of plywood 1520x1520 mm, the mid-scene distance between the rafters will be: 1520: 3 \u003d 506 mm.

Step rafted under the insulation

Installation of residential underpants spaces are often combined with styling of insulation sheets in a rapid gap. The most common plates with dimensions of 600x1000mm. These parameters and use as starting.

Scheme calculating step rafters

For construction standards, the pitch of the roof rafters is located in the range of 0.6 - 1 meter. Its calculation is performed according to a simple formula, depending on the total length of the roof. To calculate, you must perform the following list of actions:

1. determine how much distance should be between rafters for your specific construction conditions. According to the directories, the magnitude of wind and snow loads is determined in the area.
2. the roof length is divided into the desired distance, adding a unit. The resulting result will be equal to the number of rafting legs, which are installed on one rope of the roof. In the event that the value is not an integer, it is rounded.
3. the roof length is divided into the calculated above the number of rafters, we get the final step in meters.

For example, when the slope of the slope of 30 degrees, the maximum distance between the solid roof rafters is 0.6 measure. Length is assumed to be 16 meters. Hence:

1. 16:0,6+1=27,66;
2. rounding the result, we obtain 28 rafters on one slut;
3. 16: 28 \u003d 0.57 meters - the inter-axis interval of the rafter feet for these specific conditions.

As can be seen, the calculation technology is not complicated, but this is only an approximate scheme. Consideration of many other parameters specified above can make certain adjustments.

-\u003e calculation of the rafter system

The main element of the roof, perceiving and opposing all types of loads, is Slinge system. Therefore, in order for your roof to reliably oppose all environmental impacts, it is very important to make the correct calculation of the solo system.

For self-calculation of the characteristics of the materials required for the installation of the rafter system, I cite Simplified formulas calculation. Simplifications are made in the direction of increasing the strength of the structure. This will cause some increase in lumber consumption, but on small roofs of individual buildings it will be insignificant. This formulas can be used when calculating two-tie attic and attic, as well as single-sided roofs.

On the basis of the calculation methods below, the programmer Andrei Mutovkin (Andrei-Mutovkin's business card - Mutovkin.rf) has developed a program for calculating the solo system. At my request, he generously allowed to place it on the site. You can download the program.

The calculation technique was prepared on the basis of SNiP 2.01.07-85 "load and impact", taking into account the "change ..." from 2008, as well as on the basis of the formulas given in other sources. I developed this technique many years ago, and time confirmed its correctness.

To calculate the rafting system, first of all, it is necessary to calculate all loads acting on the roof.

I. Loads acting on the roof.

1. Snow loads.

2. Wind load.

On the rapid system, except the above, the load from the elements of the roof is also available:

3. The weight of the roof.

4. The weight of the draft flooring and doom.

5. The weight of the insulation (in the case of a warmed attic).

6. The weight of the solo system itself.

Consider all these loads.

1. Snow loads.

To calculate snow load, we use the formula:

Where,
S - the desired snow load, kg / m²
μ - coefficient depending on the roof slope.
SG - Regulatory Snow Load, kg / m².

μ is a coefficient depending on the roof slope α. Dimensional value.

It is possible to approximately determine the angle of the liner of the roof α as follows the resulting of the height of H on half of the span - l.
The results are reduced to the table:

Then, if α is less than or equal to 30 °, μ \u003d 1;

if α is greater than or equal to 60 °, μ \u003d 0;

if a 30 ° calculate the formula:

μ \u003d 0.033 · (60-α);

SG - Regulatory Snow Load, kg / m².
For Russia, it is accepted on a card 1 of the mandatory application 5 SNiP 2.01.07-85 "Loads and Impact"

For Belarus, the regulatory SG light load is determined
The technical code of the established practice of Eurocode 1. Impact on the design part 1-3. General impacts. Snow loads. TKP EN1991-1-3-2009 (02250).

For example,

Brest (I) - 120 kg / m²,
Grodno (II) - 140 kg / m²,
Minsk (III) - 160 kg / m²,
Vitebsk (IV) - 180 kg / m².

Find the maximum possible snow load on the roof of 2.5 m high and a long span 7m.
The structure is in the der. Babenki Ivanovo region RF.

On the card 1 of the mandatory application 5 SNiP 2.01.07-85 "load and exposure" define SG - regulatory snow load for the city of Ivanovo (IV district):
SG \u003d 240 kg / m²

Determine the angle of the liner of the roof α.
For this, the height of the roof (H) is divided by half of the span (L): 2.5 / 3,5 \u003d 0.714
And on the table we will find the angle of the slope α \u003d 36 °.

Since 30 °, calculation μ We produce according to the formula μ \u003d 0.033 · (60-α).
Substituting the value α \u003d 36 °, we find: μ \u003d 0.033 · (60-36) \u003d 0.79

Then S \u003d SG · μ \u003d 240 · 0.79 \u003d 189kg / m²;

the maximum possible snow load on our roof will be 189kg / m².

2. Wind load.

If the roof is cool (α\u003e 30 °), then due to its sail, the wind presses one of the rods and strives to overturn it.

If the roof is common (α, then the lifting aerodynamic force arising when it is driving with its wind, as well as turbulence under the sips tend to raise this roof.

According to SNiP 2.01.07-85 "Loads and Impact" (in Belarus - Eurocode 1 Exposure on structures Part 1-4. General impact. Wind exposures), the regulatory value of the medium component of the wind load WM at the height Z above the ground surface should be determined by the formula. :

Where,
Wo is the regulatory value of wind pressure.
K is a coefficient that takes into account the change in wind pressure in height.
C is an aerodynamic coefficient.

K is a coefficient that takes into account the change in wind pressure in height. Its values, depending on the height of the building and the nature of the terrain, are reduced to Table 3.

C - aerodynamic coefficient,
which, depending on the configuration of the building and the roof, can take values \u200b\u200bfrom minus 1.8 (the roof rises) to plus 0.8 (the wind presses on the roof). Since our calculation is simplified in the direction of increasing strength, the value C is taken equal to 0.8.

When building the roof, it is necessary to remember that the wind forces seeking to lift or disrupt the roof can reach significant values, and therefore, the bottom of each rapid leg must be carefully attached to the walls or to the matzam.

This is done by any means, for example, with the help of annealed (for softness) with a steel wire with a diameter of 5 - 6mm. With this wire, each rafter foot is screwed to the matsam or to the ears of the slab overlap. It's obvious that than the roof is harder, the better!

Determine the average wind load on the roof of a single-storey house with the height of the skate from the ground - 6m. , an angle of slope α \u003d 36 ° in the village of Babenki Ivanovo region. RF.

3 applications 5 in "SNiP 2.01.07-85" find that Ivanovo region refers to the second wind area Wo \u003d 30 kg / m²

Since all buildings in the village are below 10m., The coefficient K \u003d 1.0

The value of the aerodynamic coefficient C is taken equal to 0.8

the regulatory value of the average component of the wind load WM \u003d 30 · 1.0 · 0.8 \u003d 24kg / m².

For information: If the wind blows into the end of this roof, it acts on its edge (breaking) force to 33.6 kg / m²

3. The weight of the roof.

Different types of roof have the following weight:

1. Slate 10 - 15 kg / m²;
2. Ondulin (Bituminous Slate) 4 - 6 kg / m²;
3. Ceramic tile 35 - 50 kg / m²;
4. Cement-sand tiling 40 - 50 kg / m²;
5. Bituminous tile 8 - 12 kg / m²;
6. Metal tile 4 - 5 kg / m²;
7. Professional flooring 4 - 5 kg / m²;

4. The weight of the draft flooring, the root and the rafter system.

The weight of the black flooring is 18 - 20 kg / m²;
The weight of the lamb 8 is 10 kg / m²;
The weight of the actual stage system 15 is 20 kg / m²;

When calculating the final load on the solo system, all the above loads are summed up.

Now I will open you a little secret. The sellers of certain types of roofing materials as one of the positive properties note their lightness, which, according to their assurances, will lead to a significant savings of sawnwood in the manufacture of a rafter system.

As a refutation of this statement, I will give the following example.

Calculation of the load on the rapid system when using various roofing materials.

Calculate the load on the rafter system when using the heavyweight (cement-sand tile
50 kg / m²) and the easiest (metal tile 5 kg / m²) of the roofing material for our house in the village of Babenka Ivanovo region. RF.

Cement-sand tile:

Wind Loads - 24kg / m²
Roof Weight - 50 kg / m²
Grub weight weight - 20 kg / m²

TOTAL - 303 kg / m²

Metal tile:
Snow Loads - 189kg / m²
Wind Loads - 24kg / m²
Roof Weight - 5 kg / m²
Grub weight weight - 20 kg / m²
The weight of the solo system itself - 20 kg / m²
TOTAL - 258 kg / m²

It is obvious that the existing difference in settlement loads (only about 15%) will not be able to lead to any tangible savings of lumber.

So, with the calculation of the total load q, acting on the square meter of the roof, we figured out!

I especially pay your attention: when calculating, carefully follow the dimension !!!

II. Calculation of the rafter system.

Slinge system It consists of individual rafters (rafter feet), therefore the calculation is reduced to the definition of the load on each rapid leg separately and the calculation of the cross section of a separate rafting leg.

1. Find a distributed load on the pattern meter of each rapid leg.

Where
QR is a distributed load on a rabbown meter of a rafter foot - kg / m,
A - distance between the rafters (step rafter) - m,
Q is the total load acting on the square meter of the roof - kg / m².

2. Determine the working plot of maximum LMAX length in the rafter foot.

3. Calculate the minimum cross section of the material of the rafter.

When choosing a material for rafters, we are guided by the table of standard lumber sizes (GOST 24454-80 lumber of coniferous rocks. Dimensions), which are reduced to Table 4.

Table 4. Nominal size of thickness and width, mm

Board thickness - Section Width (B)	Board width - section height (H)
16	75	100	125	150
19	75	100	125	150	175
22	75	100	125	150	175	200	225
25	75	100	125	150	175	200	225	250	275
32	75	100	125	150	175	200	225	250	275
40	75	100	125	150	175	200	225	250	275
44	75	100	125	150	175	200	225	250	275
50	75	100	125	150	175	200	225	250	275
60	75	100	125	150	175	200	225	250	275
75	75	100	125	150	175	200	225	250	275
100		100	125	150	175	200	225	250	275
125			125	150	175	200	225	250
150				150	175	200	225	250
175					175	200	225	250
200						200	225	250
250								250

A. Calculate the cross section of the rafter foot.

We specify an arbitrarily width of the section in accordance with the standard dimensions, and the height of the section is determined by the formula:

H ≥ 8,6 · LMAX · SQRT (QR / (B · RIPS)) if the slope of the roof α

H ≥ 9.5 · LMAX · SQRT (QR / (B · RIPS)) if the slope of the roof α\u003e 30 °.

H - the height of the section cm,


B - the width of the section cm,
RiPridge - wood resistance to bending, kg / cm².
For pine and fir riesg is equal to:
1 grade - 140 kg / cm²;
2 grade - 130 kg / cm²;
3 grades - 85 kg / cm²;
SQRT - Square root

B. We check whether the magnitude of the deflection is stacked.

The normalized material deflection under load for all roof elements should not exceed L / 200. Where, L is the length of the work area.

This condition is performed with the faithfulness of the following inequality:

3,125 · QR · (LMAX) ³ / (b · h³) ≤ 1

Where,
QR is a distributed load on a rabbown meter of a rafter foot - kg / m,
LMAX is a working plot of a rafter foot of the maximum length m,
B - the width of the section cm,
H - the height of the section cm,

If the inequality is not respected, then increase B or h.

Condition:
Roof angle α \u003d 36 °;
Step rafted a \u003d 0.8 m;
Working plot of the rafter foot of the maximum length LMAX \u003d 2.8 m;
Material - pine 1 grade (Rizg \u003d 140 kg / cm²);
The roof is a cement-sand tile (the weight of the roof is 50 kg / m²).

As it was calculated, the total load acting on the square meter of the roof is q \u003d 303 kg / m².
1. Find a distributed load on the pattern meter of each rafter foot QR \u003d A · Q;
QR \u003d 0.8 · 303 \u003d 242 kg / m;

2. Choose the thickness of the chalkboard for rafters - 5cm.
Calculate the cross section of the rafting leg with the width of the section 5cm.

Then, H ≥ 9,5 · LMAX · SQRT (QR / B · RIPS)Since the bias of the roof α\u003e 30 °:
H ≥ 9.5 · 2.8 · SQRT (242/5 · 140)
H ≥15.6 cm;

From the table of standard sizes of sawn timber, choose a board with the nearest cross section:
width - 5 cm, height - 17.5 cm.

3. We check whether the magnitude of the deflection is stacked. For this should be observed inequality:
3,125 · QR · (LMAX) ³ / b · h³ ≤ 1
Substituting values, we have: 3,125 · 242 · (2.8) ³ / 5 · (17,5) ³ \u003d 0.61
Value 0.61, which means the cross section of the rafted material is chosen correctly.

The cross section of the rafted, installed in increments of 0.8m, for the roof of our house will be: width - 5 cm, height - 17.5 cm.

The distance between rafters for metal tile necessarily takes into account the efforts folded from the wind, snow load, their own weight of structures, roofs. In addition, the step of rafters under metal tile of the following factors are affected:

• the location of the pipes - the wooden elements of the roof must defend from the chimney by 25-35 cm, should not interfere with direct trajectories of ventilation channels, fan pipes;
• roof configuration - it is necessary to have a rafter foot at the place of the jacket of the skate of the forcep, the tent roof.

All wooden elements of the rafter system are made of coniferous trees whose humidity does not exceed 20%.

The step of the rafter feet is calculated at the design stage to compile estimates. This will significantly reduce the amount of waste, trimming lumber cutting.

What do you need to know when choosing the optimal distance between rafyles?

Roof circuit with hanging rafters.

Having gathered under the strength calculation, the loads present, the designer evenly distributes them on the bearing walls. The principle of calculating the same for urban, hanging rafters, differs only by the fastening of elements in the skate, on Mauerlat.

The minimum, the maximum step of wooden rafters for metal tile is regulated by 0.7 m, 1.2 m, respectively.

When choosing a step 60 - 100 cm, the rafters length cannot exceed 6 m, with its decrease, the disintegration is allowed to 1.2 m. If you put your feet more often than 60 cm, it is overlooking the roof, will increase the construction budget. If you increase the step more than 1.2 m, the carrying capacity will sharply decrease, the structure of the structure.

A solid doomle from the woodconding plates adds strength, rigidity of the rafter system. At the same time, the step increases by 0.3 - 0.2 m compared with the periodic crate from the bar or edged board. However, to save the construction budget, a solid income for metal tiles is extremely rare. The material has sufficient strength, rigidity due to additional transverse profile ribs.

Step greater than 1.2 m is not used even when applying rafted from metal, despite the sufficient stock of the material strength. This is due to the possible roof sheets during abundant snowfall, hurricane wind.

The cross section of the bar, from which the rafter legs are made, also affects the step of the rafted, since the area of \u200b\u200bthe support of the crate, the weight of the roof is changed. The optimal option is considered to be a ram 150 x 50 mm with a discharged cladder with a step of 4 - 7 cm, depending on the step of the transverse wave.

Example of calculating for a bone roof

When the project is fulfilled by experts at the initial stage there is a roofing material. In order to find out the recommended step of the rafter, you can use the SNiP tables, after which it is possible to adjust the value in accordance with the operational conditions. An example of a table is below:

Leg section (cm)	Step rafted (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
bar 22 x 6	–	120	–
bar 20 x 5	–	110	–
bar 18 x 5	–	90	150
log 180.	90	150	–
log 150.	–	90	150
breed 140.	–	70	140
log 130.	–	–	110

Table values \u200b\u200bcorrespond to the rafters of simple single-bone roofs. First, the length of the leg, the length of the element, the distance between the log centers, the bar is automatically obtained. At the next stage, the skate length is divided into a step of rafters with the addition of units. Thus, the number of legs with rounding the number in the large side is calculated. Then remains to adjust the distance between wooden rafters in fact. For example, with a length of the skate of 7.5 m, a rafter foot with a cross section of 16 x 2 cm (board) 4 m long will be:

7.5 / 0.7 \u003d 10.7 + 1 \u003d 11.7 pcs. Round up to 12 rafters.

The size refinement allows calculating the intercentrose distance for mounting after installing the extreme legs:

7.5 / 12 \u003d 62.5 cm.

Hearing windows are located between adjacent rafters, in places of passage of pipes, swelling legs are shifted to the distance specified in SNiP. All other elements of the system remain on the ground, the field of adjustment to the pipes is strengthened if necessary:

• two adjacent legs are lying;
• a short raftered is hampered in it in one end, the second adjoins in a skate to the element of the opposite skate;
• displaced legs in the upper part are based on the ski run, fixed to two rafter farms at least.

Thus, the system gets the necessary rigidity without losing the carrying capacity, compliance with the fire safety requirements of wooden roof parts.

Material of rafter foot

The material of the rafter is more often a timing of 25 x 10 cm - 15 x 4 cm, allowing to reduce the construction budget.

When choosing a lumber of natural humidity, the developer is guaranteed to get a design shrinkage in the first a year and a half by 5-7 cm in height. Increasing the estimate of the estimate to the arrangement of the rafter system by 70%, you can purchase a glued bar, significantly reduced the design loads, to increase the roof resource in half.

The distance between the rafyles will remain unchanged, however, instead of a planed bar of 17.5 x 5 cm, recommended by the construction norms for five-meter feet placed in 0.6 m, can be caught by the glued bar of the smaller section of 15 x 4 cm. The transport costs will be reduced, will be facilitated at height , Curra material.

Prefabricated rafters from boards use the same name of the fastening of the Ferms of the Walm Roof. The upper rods are made of single boards, the bottom of three boards stitched with self-draws with a displacement in the rows.

The choice of metal rafters is justified with a complex configuration of the roof, the abundance of ventilation pipes, chimneys, bypass which, in compliance with SNiP requirements, fireproof is not possible. In this case, the step between the rafters is maximally increasing, as metal rolls are much stronger than lumber.

If the rafters are attached at the bottom to Mauerlat, the step is not critical, the elements can, if necessary, shift to the desired distance to any side. If a tightening scheme is used, which are beams of overlapping, shifted separate items are much more complicated. In this case, the amount of cutting is increasing when the black ceiling is trimmed, the sex of an attic or attic room.