How to calculate a double roof for home. How to calculate the length of the rafted two-tie roof, taking into account the load - the rules of the calculation. Calculation of the parameters of the rafter

Metal tile appeared in a series of roofing materials relatively recently, but rapidly gained popularity. This is explained simply - with proper laying, such a cover ensures reliable protection of the house from atmospheric precipitation, while giving the roof to a reliable imitation of the natural classical tile.

The popularity of this coating is also based on the fact that its styling does not represent much difficulty, and with her the owner of the house should cope even independently, naturally, having an assistant, but without resorting to hiring brigades. A clear profile of metal tile allows, without much difficulty, combine neighboring sheets, and make a mistake even if desired is very difficult. But all this will be fair only if a high-quality suit is mounted under such a roof. To figure out how many boards go timeds will need for its creation will help calculator calculating sawn timber for crate under metal tile.

Below will be a few comments about working with the program.

The scope roof has a system of inclined planes (skates). The construction of the rafter system is selected and calculated, given the presence of supports for it, the type of coating, the size and shape of the blocking building. Special calculation will help you choose the desired size of the rafter foot and ensure the strength of the roof.

Types of soling systems of a two-tie roof

The scheme of the solo system is selected based on the conditions of the amount of supports for it and the distance between them.

Sweeping rafters are based on the external bearing walls of buildings and for additional internal supports, if the distance between the main supports exceeds 4.5 m. The rafter foot is based on the support bar (Mauerlat), which transmits the weight from the roof on the building wall. The upper end is connected with a skate run and another rafter foot.

1, 2 - hanging the rafter system. 3, 4 - Sloping System. A - Rifle, B - tightening, C - Rigel, D - Run, E - Mauerlat, F - Troops, G - Rack.

The hanging type of rafter systems has a tightening at the level of the lower support nodes or above them and does not imply intermediate supports. The distance between the external supporting supports should not exceed 6.5 m. This variant of the device of the rafter design can be attributed to triangular farms. The distance in the plan between them is accepted by 1.3-1.8 m.

Composition of coating

Roof

Eternite roofs are flat or wavy sheets of asbestoscert. This is a cheap view of the roofing coating, which is easy enough to install. Recently, research has shown its harmful effect on human health.

Slave roofs include slate. They are constructed from natural material layered shale structure. EuroShorter, Ondulin are descendants of an ordinary slate. They are compressed fiberglass or cellulose, which are impregnated with bitumen.

Metal coating is often used in the construction of residential buildings. It reliably protects the house from atmospheric influence, has low weight and not laborious in installation. To this type of roofs can be attributed to the professional flooring, galvanized steel, alucyc.

Rolls belong to soft roofing. They are waterproof, resistant to environmental impact and are convenient in installation. These include such types:

ruberoid (Rubext, glass astronomist, EuroRuberoid, Tol, etc.);
bitumen-polymer (glassizol, glazing, linocur, etc.);
membrane roofs (PVC, thermoplastic membranes, films made of synthetic rubber, etc.).

If earlier tiled roofs were only ceramic, then today there are: cement-sand, bituminous and metal tile.

Wooden roofs are rarely used due to the difficulty of the device. They are trimmed, danucleus, shroves, lemeh, dwarf.

Svetopropy roofs are made of polymeric materials and glass. These include cellular polycarbonate, corrugated polyvinyl chloride, triplex, polyester, etc.

Grussol

Roofing flooring or dooming is the base for the roof. It is made from boards or bars. When a metal, wooden or tiled roof, the lamb bar is accepted by a cross section:

50x50 mm at a distance between the rafters - 1.0-1.1 m;
50x60 (h) mm at a step of rafted - 1.2-1.3 m;
60x60 mm at a step - 1.4-1.5 m.

For other species, you can use 2.5 cm boards thick. Under the rolled roof it is satisfied with double flooring from the board. The working lower layer is laid perpendicular to the direction of the rafted with transits. The top is placed at an angle of 45 ° to the underlying layer. The width of the boards for it is made not more than 8 cm, and the thickness is 2 cm.

Rafyla

Wooden rafters are applied log, cut for one kant, from sawdow forest (timber, board laid on the edge). For sprinkling rafters, the round cross section of the log is suitable. The diameter of them is 12-20 cm. The advantages of using the log compared to the board or bar are as follows:

wood savings (to withstand the same loads for round, need a smaller diameter of the source material);
above the limit of fire resistance;
less metallic fasteners;
higher indicators of rigidity and durability.

Calculation of the sprinkle leg

A 18-1.5 m is allowed between the rapid legs. The cross section is determined by the calculation, based on the strength, as well as the rigidity of the structure. For this, the estimated constant load on the rafter is determined, which includes the calculation of constant loads on one mongon meter of the roof and snow load.

Load distribution scheme: α - roof inclination angle, q - General permanent loads, q

The initial data for calculation is accepted:

step setting of the rafter legs;
the angle of inclination of the roof;
width and height of the roof.

The choice of parameters, as well as the selection of most coefficients depends on the roofing material and the detailed composition of the roofing cake.

For inclined roofs, constant loads are calculated by the formula:

The rafting leg is also calculated on the rigidity (deflection). Regulatory load is used here:

α - roof inclination angle;
n, n c - reliability coefficients for loads from snow - 1.4, loads from the roof - 1.1;
g - Weight 1 m 2, which perceives the rafter foot (roofing, drying, rafters);
a - step of the rafting legs (along the axis).

S G - the weight of the snow per 1 m 2, which depends on the climatic area;
c e - the coefficient of snow demolition due to the effect of wind and other atmospheric influences depends on the mode of operation of the roof;
c T - thermal coefficient.

The coefficients with E and C T are accepted according to the requirements of the SP 20.13330.2011 Section 10 "Snow Loads" in accordance with 10.5 and 10.6. For a private house with a scope roof with a roof slope of over 20 °, the coefficients C E and C T are equal to one, therefore, the formula of snow cover:

μ is a coefficient that depends on the angle of inclination of the roof and is determined according to the application "M" SP 20.13330.2011:

for roofs with an angle of inclination less than 30 ° μ \u003d 1;
for roofs with an angle of inclination above 60 ° μ \u003d 0;
in other cases for angle of inclination of 30 °<α<60° µ = 0,033 х (60°-α).

The weight of snow cover in areas can be clarified in the joint venture 20.13330.2011 "load and impact", where the area of \u200b\u200bthe area on the application map is also determined.

Snow Potion Weight S G

District	I.	II.	III	IV.	V.
S G kg / m 2	80	120	180	240	320

Since the rafter foot is bending from exposure to her loads, it is checked for the strength of the bent element, according to the formula:

M.< m и R и W нт

M - bending calculated moment;
R and - the calculated resistance of the bending of wood;
m and - coefficient reflecting the working conditions;
W NT - the moment of resistance of this section;
R and \u003d 130 kg / cm 2 - for pine and fir;
m and equal to 1.0 - for sections with a height of up to 15 cm and 1.15 - for sections height more than 15 cm.

In an individual, the moment of resistance and the moment of inertia for the material of the rafter is calculated. According to the data obtained, the desired size of the structural elements is selected.

The proposed calculation is exemplary and requires an addition in the form of an extremely permissible length of the reference elements, the arrangement of spacer or retaining beams and racks.

Example number 1.

Consider tiled ceramic roofs on a two-tie roof in the Moscow region (III climatic area).

Angle of inclination 27 °; cos α \u003d 0.89; Step raftered along the axis - 1.3 m; The estimated span of the rafter - 4.4 m. The drying age is taken from a bar of 50x60 mm.

The weight of the roof is 1 m 2:

roof weight - 45 kg;
the weight of the rafter foot - 10 kg.

Total: G H \u003d 62 kg / m 2

q \u003d (1.1 x 62 x 0.89 + 1.4 x 126 x 0.89 2) x 1,3 \u003d 260 kg / m.

q H \u003d (62 x 0.89 + 126 x 0.89 2) x 1,3 \u003d 201 kg / m
M \u003d 0.125 x q x l 2 \u003d 0.125 x 2,60 x 440 2 \u003d 62 920 kg ∙ cm

The moment of resistance:

The moment of inertia (I), which is necessary from the condition of a possible deflection F \u003d 1/150 L; E \u003d 100 000 kg / cm 2; QH \u003d 201 kg.

On specially developed tables, you can determine the log diameter for the rafter.

The diameter of the log (cm) depending on the W and J (for bricken, one kant).

Legend	13	14	15	16	17	18	19
J.	1359	1828	2409	3118	3974	4995	6201
W.	211	263	324	393	471	559	658

According to the table below, we determine the diameter of the log - 18 cm.

Example number 2.

Take all the data from the previous example, but for the roof from Ondulina. It is necessary to calculate the cross section of the rafting leg from the bar.

Angle of inclination 27 °; cos α \u003d 0.89; Step raftered along the axis - 1.3 m; The estimated span of the rafter - 4.4 m. The drying age is taken from a bar of 50x60 mm.

The weight of the roof is 1 m 2:

the weight of the roof from Ondulina - 3.4 kg;
dooming - 0.05 x 0.06 x 100 x 550/25 \u003d 7 kg;
the weight of the rafter foot - 10 kg.

TOTAL: GN \u003d 20.4 kg / m 2

q \u003d (1.1 x 20.4 x 0.89 + 1.4 x 126 x 0.89 2) x 1,3 \u003d 207.6 kg / m.

qH \u003d (20.4 x 0.89 + 126 x 0.89 2) x 1,3 \u003d 153.3 kg / m
M \u003d 0.125 x q x l 2 \u003d 0.125 x 2.08 x 440 2 \u003d 50 336 kg ∙ cm

The moment of resistance:

The moment of inertia (I), which is necessary from the condition of a possible deflection F \u003d 1/150 L; E \u003d 100 000 kg / cm 2; QH \u003d 153.3 kg.

We take a timber with a height of 15 cm. For a bar with a height of more than 14 cm RI \u003d 150 kg / cm 2. Therefore:

On the table, determine the size of the cross section of the bar for the rafter.

Width (b) and height (H) of timber depending on W and J.

Legend
Legend	8	9	10	11	12	13	14
	1829	2058	2287	2515	2744	2973	3201
	261	294	327	359	392	425	457
	2250	2531	2812	3094	3375	3656	3937
	300	337	375	412	450	487	525

We accept for a rafter bracer with a cross section of 10x15 cm.

The resulting formulas can be used to calculate other roof coatings. At the same time, the load on the rafter foot based on their selected option is calculated. The formulas may change:

length rafted;
step rafters;
roof slope angle;
snow load, which is selected according to the construction region;
weight of the root.

The conjugation of the rafter feet between themselves and the run should be reliable. This ensures the absence of a destructive returner on the walls of the building. Wooden structures It is necessary to inspect from time to time, so when the removal rafter faces the distance from the top of the attic overlap to the bottom mark of the Maurolalate, not less than 400 mm is taken.

Duct roofs and today are the tradition of private house-building. The correct roof device is a durable, durable and beautiful house.

Online calculators for calculating roofing and roof are mandatory tools present in the arsenal of architects and professional construction companies. Although, in principle, such calculators are also useful and simple owners of country sites, which westing the construction of the house with their own hands (there will also be required to calculate the roof). And not surprising, because the quality and accuracy of such calculations directly affect not only the durability of the entire roofing structure, but also on the general view of the house. In this section of the site, the best calculators are collected to calculate the roofs that will help you in the most common cases during self-building at home! Here you will find useful tools for calculating the area of \u200b\u200bthe three-piece roof, the number of slate, the area of \u200b\u200bthe tent roof, the length of the rafter legs, the height of the skate and much of the other! All online calculators were created by experienced specialists, each tool is accompanied by detailed explanations and instructions for the calculation.

What are the advantages of our online calculators? From their numerous (and often paid) analogs, they differ in that they do not need to download to the local computer. For calculations, complex, carefully proven algorithms are used, and the results of the calculations are outlined in a simple and accessible form. Another advantage is that you can add a page with an online calculator to bookmark the browser and use at any time!

On a note! When calculating online, construction standards are used, GOST and SNilation, which are adopted in the Russian Federation and the world. In addition, the global practice of modern construction is taken into account.

When building a roof, you can not save on the materials so that in the future did not have a leakage, but also there should be no excess, so calculation of roof Must be as accurate as possible.

What depends on the calculation of the roof?

If the house is ready, just look at its roof to determine the front of the measuring work. Simple rafal structures will mean easy computing, for example, will not be difficult to find out how to correctly calculate the two-screw roof, not to mention the single one. However, more complex options are very common. In particular, the pyramidal, broken attic or a semi-haul four-tight roof will create certain difficulties for beginners. But even the crowned building multi-line design can be quick and, most importantly, is correctly calculated in terms of material costs, if you know all the necessary formulas.

Roofing Calculator

Specify all surfaces for the coating.

Type of sheets	Metal tile metal	Need: - - - -
Sheet Working size, not full!	X. cm
Surface	Add everything rectangular Plots roofing L \u003d. m H \u003d. m.
Surface	Add everything triangular Plots roofing L \u003d. m x \u003d. m.
Surface	Add everything trapecoidal Plots roofing L \u003d. X \u003d. M \u003d m.

First of all, it should be remembered that from how many rods did not consist of the roof, all surfaces are either simple geometric figures, or they can be broken on them. Further, the calculator for calculating the roof requires operating in the process of calculations with such concepts as the real and efficient area of \u200b\u200bthe coating. The first is its own leaf dimensions, and the second - taking into account the adhesion laid above. In other words, some of the material must be deducted, since it will overtakely with other sheets. The percentage of losses depends on the tilt of the skate and characteristics of the coating (waste from metal tile more than from the roll material).

Typical solution how to calculate the roof area

An option with one or two slopes is the easiest, to calculate the size you only need to know the length of the house, the rafter leg, as well as the sink (cornice and front). If you add to all right and multiply, we get the following formula: S \u003d (L d + 2L FS) (L CH + L COP)where L D. - the length of the end wall of the house, L FS.and L KS. - the length of the front and cornice sweep, respectively, and L CH -Stropyl foot. In other words, the calculator calculating the roof of the house can be used without getting off on it, and having done all the measurements from the ground, the attic and attached to the stepladder wall. But do not forget that in this way you get the area of \u200b\u200bonly one slope, for the full picture the result must be multiplied by 2.

More complex designs usually require measurements directly to the surface, that is, if there are no coatings, then on the finished crate, and if you need to know how to calculate the renewal of the roof, then on its old shelting. Learning the length and width of each roof plane, draw the exact layout, after which we divide on the simplest geometric shapes. For example, a semi-haul consists of two trapezes, two rectangles and four triangles. The usual broken roof roof on the projection will look like one large square or rectangle. Multi-type construction will differ only in a large number of above geometric shapes.

Formulas that are prompting how to calculate the area of \u200b\u200bthe roof can be found in the school textbook, but for your convenience they will be given later. So, we have already calculated a rectangle, but the formula was composed of many parameters, in fact it looks like S \u003d AB.where a. and b. - Continuable sides of the figure. The trapezium can be calculated as follows: S \u003d H (A + B) / 2where h. - Height. This option is most convenient due to the fact that the sides, and, consequently, the angles between them and the base can be unequal. To determine the area of \u200b\u200bthe triangle we take the formula S \u003d BH / 2where b. - reason, and h. - Height-high on it. If at least one angle is 90 degrees, you can use the formula S \u003d AB / 2where a. and b. - Kartets.

Instruction how to calculate the roof of the house

Above, we brought an example of calculating a complex roof by drawing up its projection. You can go easier and take a plan at home, where the roof is displayed on the plane schematically, then determine the area and multiply to the slope coefficient. For example, in order to find out how much the rolls of the soft coating are required, based on the fact that one roller is enough for 3 square meters, the formula is taken N \u003d SK / 3. Here S. - the area of \u200b\u200bthe created projection, K. - The slope coefficient that can be found from the table:

If you are wondering how to calculate the height of the roof, this task can be solved according to the above indicators. For example, the width of the house is 10 meters, and the position of the position of the rafter foot - 35 degrees. We take half the width and multiply on the slope coefficient equal to 35 degrees, it turns out to be 5. 0.79 \u003d 3.95. This is the desired height of the skate. At the same time, if you know the angle of the skate, it is necessary to correctly select the material relative to the slope steepness, which can also be done using data from the table, but also another:

For ONDulina, the roofing calculator will be somewhat different, since it is known that the real area of \u200b\u200bone sheet is 1.82 square meters, but decreases due to the upper and side alternation of neighboring sheets to 1.62 m 2. It is with an effective meaning and will have to work by calculating the ratio between the roof and material area. In other words, the number of sheets of Ondulin is calculated by the formula N \u003d s k / s lwhere S K. - Roof area, and S L. - material dimensions.

How to calculate roof from metal tile?

It is known that roofing metal rolling is one of the most durable materials used to cover the roof. With proper care, such a coating will serve up to 50 years and even more in conditions of moderate impact of climatic factors. In order to calculate how many metal tiles need, it is necessary to know its dimensions, and, having solved the task how to calculate the size of the roof, proceed to the determination of the number of sheets of the material. However, both stages can be combined. To do this, use the formula N \u003d (l ck / in l) (in ck / l l)where L CK. - Skate length, In L. - Width of the sheet, In ck. - width of the skate, and L L. - Leaf length.

With any calculations, the length of the slope must be taken with the cornice and with a deduction of the skate lining.

There are other tasks except to calculate the roof, for example, you need to identify other elements necessary for the roof covering. In particular, you will need endands, skates, sink elements and cornices. It is no longer able to determine their quantity, but in the route meters, taking into account the adhesive, which, usually, is 10-15%. Also, we should not forget about the fasteners, such as or long screws that are required at least 9 pieces per sheet of material. As for the waterproofing, one roll is usually enough for 75 square meters of the roof, taking into account the adolescents this number will decrease by approximately 15%. Thus, the roof area needs to be divided by 63.75 to find out how many waterproofing rolls you need.

Design and competent calculations of the elements of the rafter design - the key to success in construction and in the subsequent operation of the roof. It is obliged to resist the aggregate of temporary and permanent loads, while the construction is minimized.

To make calculations, you can use one of the numerous programs laid out on the network, or do it manually. However, in both cases, it is necessary to clearly know how to calculate the roof rafters to thoroughly prepare for construction.

The rapid system determines the configuration and strength characteristics of the pitched roof that performs a number of significant functions. This is a responsible enclosing structure and an important component of the architectural ensemble. Therefore, in the design and calculations of the rafter feet should avoid flaws and try to exclude shortcomings.

As a rule, in project developments, several options are considered, of which the optimal solution is selected. The choice of the best option does not mean that you need to create a certain number of projects, to perform for each accurate calculations and, as a result, preferred the only one.

The course of determining the length, assembly slope, the cross section of Stropilin is in the scrupulous selection of the form of the structure and the size of the material for its structure.

For example, in the formula for calculating the carrying capacity of the rafter leg, the parameters of the cross section of the most suitable material are initially introduced. And if the result does not comply with the technical standards, then the lumber size increases or decrease, until maximum compliance achieves.

Method for finding an angle of inclination

At the definition of an angle of the slope of the scope design there are architectural and technical aspects. In addition to the proportional configuration, the most suitable for the style of the building, the impeccable solution must be considered:

Snow load indicators. In localities with an abundant precipitation, roofs with a bias from 45 ° and more are erected. Snow departments are not delayed on the ridges of such steepness, so that the total load on the roof is reduced, the total load on the roof is reduced, stodil and construction as a whole.
Wind load characteristics. In areas with gustful strong winds, coastal, steppe and mountainous areas, low-pitched structures of the streamlined form are built. The steepness of the rods usually does not exceed 30º. In addition, the wind prevent the formation of snow deposits on the roofs.
Mass and type of roofing. The greater the weight and smaller elements of the roof, the cooler need to build a rafter frame. It is necessary to reduce the likelihood of leakage through compounds and reduce the specific coating weight per unit horizontal roof projection.

In order to choose the optimal angle of inclination of the rafaline, the project must be taken into account all the requirements listed. The steepness of the future roof is obliged to comply with the climatic conditions chosen for the construction of the terrain and the technical data of the roofing coating.

True owner owners in the northern windless areas should be remembered that with increasing angle of inclination of the rafter, the consumption of materials is increasing. The construction and arrangement of the roof of the steepness of 60 - 65º will cost approximately one and a half times more expensive than the construction of an angle of 45º.

Neighborhoods with frequent and strong winds should not be too short enough to save on savings. Necessary gentle roofs lose in architectural terms and do not always help reduce the number of expenses. In such cases, the increase in the insulating layers is most often required, which in counterweight expectations of the economy leads to the rise in the cost of construction.

The sloping slope is expressed in degrees, as a percentage or in the format of dimensionless units displaying the ratio of half of the field of flight to the height of the installation of the skate run. It is clear that degrees outlines the angle between the ceiling overlap line and the line of the skate. Percentages rarely enjoy due to the complexity of their perception.

The most common method for setting the angle of inclination of rafting legs, used both by the designers of low-rise buildings and builders, these are dimensionless units. They in shares transmit the ratio of the length of the overlapping span to the height of the roof. The facility is easiest to find the center of the future frontal wall and will install a vertical rail in it with a rink height mark than to postpone the angles from the edge of the skate.

Calculation of the length of the rafter

The length of the rafylic is determined after the angle of inclination is selected. Both specified values \u200b\u200bcannot be attributed to the number of accurate values, because In the process of calculating the load as a steepness, and after it, the length of the rafting leg can change slightly.

The main parameters affecting the calculation of the length of the rafter include the type of roof of the roof, according to which:

The outer edge of the rafter feet is trimmed with a flush with the outer surface of the wall. The rafters in this situation do not form an abuser, protecting the design of precipitation. For the protection of the walls, the drainage is installed, fixed on the rituit to the end edge of the Stropilin of the cornice board.
Cropped flush with a wall of rafters are increasing with lumps to form an eaves. Fakes are fixed to rafalines with nails after the construction of a rafter frame.
The rafters are initially reproduced taking into account the length of the cornese swell. In the lower segment of the rafter feet choose wrinkles in the form of angle. For the formation of wrinkles, retreat from the lower edge of the rafter to the width of the eaves. Words are needed to increase the reference area of \u200b\u200bthe rafter feet and for the reference node device.

At the stage of calculating the length of the rafter feet, we need to consider the options for fastening the roof frame to Mauerlat, to the crossing or to the top crown of the cut. If the installation of the Stropilin flush with an external contour of the house is designed, then the calculation is carried out along the length of the upper rib rafting, taking into account the size of the tooth, if it is used to form a lower connecting node.

If the rafter legs are rebounded with a carnese removal, then the length is calculated on the upper edge of the rainfall along with the sink. It should be noted that the use of triangular wrists significantly accelerates the rates of the construction of a rafter frame, but weakens the elements of the system. Therefore, a coefficient of 0.8 is used when calculating the bearing capacity of strings with selected angle.

Traditional 55 cm. However, the scatter can be from 10 to 70 and more. The calculations use the projection of the cornese removal on the horizontal plane.

There is a dependence on the strength characteristics of the material, on the basis of which the manufacturer recommends the limit values. For example, the slate manufacturers do not advise the root for the contour of the walls over a distance of more than 10 cm so that the snow mass accumulating along the rumble could not damage the edge of the cornice.

Cool roofs are not accepted to equip wide overlines, regardless of the material of the eaves are not wider than 35 - 45 cm. But structures with a bias up to 30º can perfectly add a wide eaves, which will serve as a peculiar canopy in areas with excess solar lighting. In the case of designing roofs with cornisse, 70 and more cm, they are strengthened with additional support racks.

How to calculate the carrying ability

In the construction of rafal frames, lumber are used made of coniferous wood. The harvested bar or the board must be no lower than the second grade.

The rafting legs of the pitched roofs work according to the principle of compressed, curved and compressed-curved elements. With the tasks of resistance to compression and bending, a second-class wood is perfectly coping. Only if the design element will work on stretching, the first grade is required.

The rafter systems are arranged from a board or timber, pick them up with a margin of strength, focusing on the standard dimensions of the volumetric lumber.

Calculations of the bearing capacity of the rafter feet are carried out in two states, this is:

Estimated. A condition in which the design is destroyed as a result of the applied load. Calculations are carried out for the total load, which includes the weight of roofing pie, the wind load taking into account the flooding of the construction, the mass of snow, taking into account the linker's slope.
Regulatory. The state at which the rafter system begins, but the destruction of the system does not occur. It is usually impossible to operate the roof in such a state, but after carrying out repair operations, it is quite suitable for further use.

In the simplified estimated version, the second state is 70% of the first value. Those. To obtain regulatory indicators, the calculated values \u200b\u200bmust be trally multiplied by the coefficient of 0.7.

Loads depending on the climatic data of the construction region are determined by the cards attached to the SP 20.13330.2011. The search for regulatory values \u200b\u200bon the cards is extremely simple - you need to find a place where your city is located, a cottage settlement or another closest settlement, and reflect the readings about the calculated and regulatory value from the card.

The averaged information about snow and wind load should be adjusted according to the architectural specificity of the house. For example, the value taken from the map must be distributed over the skates in accordance with the wind roses composed for the terrain. You can get a printout with it in a local meteorological service.

From the windward side of the construction, the snow mass will be much smaller, therefore the calculated indicator is multiplied by 0.75. From the leeward side, snow deposits will accumulate, so they multiply here at 1.25. Most often to unify material for the construction of the roof, weathered part of the design are built from a paired board, and the implanted part is arranged with rafalines of their single board.

If it is unclear which of the skates will be from a leeward side, and what is the opposite, then it is better to multiply by 1.25. The stock of the strength does not prevent at all, if it does not increase the cost of the sawn timber.

The setting weight of the snow is still adjusted depending on the roof steepness. From the skates installed at an angle of 60º, the snow will immediately slide without the slightest delays. In the calculations for such steep roofs, the correction factor does not apply. However, with a lower slope, the snow will already be able to delay, therefore the additive in the form of a coefficient of 0.33, and for 40º it, but already 0.66 is used for 50º.

Wind load is determined in a similar way according to the corresponding map. Correct value depending on the climatic specificity of the region and from the height of the house.

To calculate the bearing capacity of the main elements of the designed rafter system, it is required to find the maximum load on them, summing up temporary and constant values. No one will strengthen the roofs before the snowy winter, although in the country it would be better to put the safety vertical struts in the attic.

In addition to the mass of snow and the grace of winds, the calculations requires accounting for the weight of all elements of roofing pie: installed on top of the rafaline crate, the roof, insulation, internal binder, if used. Weight of steam and waterproofing films with membranes, it is customary to neglect.

Information about the weight of the materials is indicated by the manufacturer in technical passports. Data on the mass of the bar and boards are taken in approximation. Although the mass of the crate on the meter of the projection can be calculated by taking as a basis the fact that the cubic meter of sawn timber weighs an average of 500 - 550 kg / m 3, but a similar amount of OSP or plywood from 600 to 650 kg / m 3.

The values \u200b\u200bof the loads are denoted in the CB / m 2. However, Stropilina perceives and keeps only the load that directly presses on this linear element. In order to make the calculation of the load specifically on the rafter, the combination of natural tables of loads and the mass of roofing pie is multiplied by a step of installation of the rafter.

The load value given to the linear parameters can be reduced or increased by changing the step - the distances between the rafalines. Correcting the area for collecting the load, the optimal values \u200b\u200bare achieved in the name of a long service of a carcass of the pitched roof.

Determination of the cross section of Stroplin

Stropile legs of roofs of various steepness perform ambiguous operation. On the rafter, gentle structures operates mainly bending moment, another compressive force is added to the analogues of steep systems. Therefore, in the calculations of the cross section, the rafters necessarily takes into account the slope.

Calculations for structures with a bias up to 30º

On the rafting legs of the roofs of the specified steepness acts only bending voltage. They are calculated at the maximum moment of bending with the application of all types of load. Moreover, temporary, i.e. Climatic loads are used in calculations at maximum indicators.

Stropilin, having only supports under both own edges, the point of maximum bending will be in the very center of the rafter foot. If the rafter is laid on three supports and is composed of two simple beams, then the moments of maximum bending will come to the middle of both of the spans.

In solid rafying on three supports, the maximum bending will be in the area of \u200b\u200bthe Central Support, but because Under the bending site is a support, then it will be directed up, and not as the previous cases down.

For normal operation of the rafter legs in the system, two rules must be completed:

The internal voltage formed in the rafter when bending as a result of the load applied to it, must be less than the calculated resistance of the lumber to bend.
The deflection of the rafter foot should be less than the normalized deflection value, which is determined by the L / 200 ratio, i.e. It is allowed to progress the element only on one two hundredth of its real length.

Further calculations consist in a sequential selection of the sizes of the rafter foot, which as a result will satisfy the specified conditions. For calculating section there are two formulas. One of them is used to determine the height of the board or bar for an arbitrarily given thickness. The second formula is used to calculate the thickness of an arbitrarily given altitude.

In calculations, it is not necessary to use both formulas, it is enough to apply only one. The result obtained in the end is verified by the first and second limit state. If the calculated value turned out to be an impressive margin by strength introduced into the formula, an arbitrary indicator can be reduced to not overpay for the material.

If the calculated value of the moment of bending will be more than L / 200, then an arbitrary value increases. The selection is carried out in accordance with the standard sizes on sale of sawn timber. So choose the cross section until the moment is calculated and the optimal option is obtained.

Consider a simple example of calculations according to the formula B \u003d 6Wh². Suppose H \u003d 15 cm, and W is the ratio M / R zeal. The value of M is calculated according to the formula G × L 2/8, where G is the total load, vertically directed to the rafter foot, and L is the length of the span, equal to 4 m.

R Izg for lumber from coniferous breeds we take in accordance with the technical standards of 130 kg / cm 2. Suppose, we calculated the total load in advance, and it turned out to be 345 kg / m. Then:

M \u003d 345 kg / m × 16m 2/8 \u003d 690 kg / m

To translate into kg / cm divide the result by 100, we get 0.690 kg / cm.

W \u003d 0.690 kg / cm / 130 kg / cm 2 \u003d 0.00531 cm

B \u003d 6 × 0.00531 cm × 15 2 cm \u003d 7.16 cm

We round the result as it should be on the most side and we obtain that for the device rafters, taking into account the load provided in the exemplary, the ram 150 × 75 mm will be required.

We check the result on both states and make sure that the material is suitable for the cross section calculated. σ \u003d 0.0036; F \u003d 1.39

For rafter systems with a bias over 30º

The rafted roofs of a steepness more than 30º are forced to resist not only bending, but also the strength of compressing them along its own axis. In this case, in addition to checking according to the resistance to the bending described above, and the magnitude of the bend you need to calculate the lines of internal voltage.

Those. Actions are performed in a similar manner, but there are several more verification calculations. The arbitrary height or arbitrary thickness of the lumber is defined, with its help, the second parameter of the section is calculated, and then a check is performed for compliance with the above three technical conditions, including compression resistance.

If necessary, in strengthening the carrying capacity of the rafter, arbitrary values \u200b\u200bentered into formulas increase. If the safety margin is quite large and the regulatory deflection significantly exceeds the calculated value, that is, it makes sense to fulfill the calculations by reducing the height or thickness of the material.

Choosing the initial data for the production of calculations will help the table in which the generally accepted dimensions of the lumber produced with us are reduced. It will help to choose a cross section and the length of the rafter feet for the initial computing.

Video about the calculations of Stropilin

The roller clearly demonstrates the principle of performing calculations for the elements of the rafter system:

Performing the calculations of the bearing capacity and installation angle of the rafter - an important part of the design of the roof frame. The process is not easy, but it is necessary to figure it out in it and those who produce calculations manually, and those who use the calculation program. You need to know where to take table values \u200b\u200band what makes settlement values.