Simple online calculator will accurately calculate the length of the rafters, the length of the overhang of the rafters, the cut angle of the rafters. Start calculating the rafters now!
Do-it-yourself rafter system
This calculator is indispensable for those who decided to make do it yourself rafters... A smart online calculator will accurately calculate the length to the rafter overhang, the overhang length, the cut angle and the distance from the edge of the rafter to the start of the cut. The online calculator is suitable for calculating the rafters of a gable roof and a 1-pitched roof.
The permissible range of the angle of inclination of the roof is from 20 ° to 60 °, the smaller the angle, the less lumber will be needed for the farm, but the larger the angle, the more spacious it will be under the roof of the second floor of the house. If you choose an angle of 30 °, then for a building width of 10 m, the elevation of the ridge above the upper floor will be 2.5 m.The length of the rafter legs will be 7 meters, of which 6.2 are above the house, and the rest will be out of the roof. The minimum departure size is taken to be 50 cm for safety from bad weather. Rafters with a length of 7 meters are considered the maximum allowable for an inclined design to the ridge of the roof, if the length of the rafters is more than 7 meters, additional reinforcement of the gable roof in the form of beams is required. When calculating rafters on a gable roof the step between the individual lags is 80-130 cm... The exact step size depends on the weight of the roof, rainfall and wind load in your area of construction. All rafter blanks must be treated with antiseptic and fire-fighting compounds.
We offer a professional free calculation of the rafter system gable roof using an online calculator site, 3D visualization and detailed drawings. Detailed calculations of the roof and roof, all materials, lathing, rafters, Mauerlat. Try calculating a gable roof now!
Our online calculator rafter system will calculate the gable roof:
- calculation of the length of the gable roof rafters
- number of rafters and step
- calculation of the area of the gable roof and the angle of inclination
- calculation of the roof lathing
- the number of sheet roofing materials (for example, corrugated board, metal tiles, slate)
- parameters of vapor barrier and insulation
To form the calculation of the gable roof calculator, you need to measure and enter the following dimensions in the appropriate windows:
The section (thickness x width) and the pitch of the rafters depend on the angle of inclination of the roof, its type, length rafter leg, the maximum withstand basic loads, as well as on the type and weight of the roof covering, and even to some extent on the width of the insulation. If you do not know where to get the standard parameters of rafters and battens, our article will help you " Optimal cross-section, pitch of the lathing and rafter legs, depending on the type of roof ».
The calculator calculates materials for the roof based on the dimensions you entered roofing sheet and from the estimated value of the roof area. We advise you to buy the amount of roofing materials for the roof, boards and beams for the rafter system with a small margin, it is always better to hand over the leftovers to a hardware store than pay a lot of money for the delivery of a missing pair of boards.
Be careful! From how accurate the values you enter, the online calculator will be able to calculate the gable roof so reliably.
Simplify your calculations and save time, the program will draw itself rafter plangable roof and will display the results of calculating a gable roof according to the data you entered in the form of a drawing of a gable roof in different angles review, and its interactive 3d model.
On the tab “ 3 D- View»You can better see your future gable roof in 3D. In our opinion, visualization in construction is a very necessary feature.
If you have a gable roof with different slopes in your project, you should calculate using the calculator twice - for each slope separately.
Specify the parameters of wooden rafters:
B- rafter width, important parameter determining the reliability of the rafter system. The desired cross-section of the rafter (in particular, the width) depends on: loads (constant - the weight of the lathing and roofing cake, as well as temporary - snow, wind), the material used (quality and its type: board, timber, glued timber), the length of the rafter leg, the distance between the rafters. You can determine the approximate section of the timber for the rafters using the table data (the width value is greater importance from 3 columns, for example, with a rafter length of up to 3000 mm and a step of 1200 mm, the desired width is 100 mm). When choosing the width of the rafters, be sure to take into account the recommendations made in SP 64.13330.2011 " Wooden structures"And SP 20.13330.2011" Loads and impacts ".
| Rafters length, mm | Rafter pitch, mm | Rafters section, mm |
| Up to 3000 mm | 1200 | 80x100 |
| Up to 3000 mm | 1800 | 90x100 |
| Up to 4000 mm | 1000 | 80x160 |
| Up to 4000 mm | 1400 | 80x180 |
| Up to 4000 mm | 1800 | 90x180 |
| Up to 6000 mm | 1000 | 80x200 |
| Up to 6000 mm | 1400 | 100x200 |
Y- the height of the roof, the distance from the ridge to the ceiling of the attic. Affects the angle of inclination of the roof. If you plan to equip a non-residential attic, you should choose a small height (you will need less material for rafters, waterproofing and roofing), but sufficient for inspection and maintenance (at least 1500 mm). If it is necessary to equip a living space under the arch of the roof, to determine its height, it is necessary to focus on the growth of the tallest family member plus 400-500 mm (approximately 1900-2500 mm). In any case, you must also take into account the requirements of SP 20.13330.2011 (updated edition of SNiP 2.01.07-85 *). It should be remembered that precipitation can linger on a roof with a small angle of inclination (low height), which negatively affects its tightness and durability. However, a high roof becomes more vulnerable to strong wind gusts. The optimum tilt angle is between 30-45 degrees.
X- The width of the roof (without overhangs) is determined by the width of the outer perimeter of your house.
C- the size of the overhang, an important structural element of the roof that protects the walls and foundation from precipitation, is determined taking into account climatic conditions Your region (SP 20.13330.2011) and the general architectural idea. For single and two-storey houses without the organization of an external water drain, not less than 600 mm. If you arrange a drainage system, you can reduce it to 400 mm (SNB 3.02.04-03). According to the requirements of IRC-2012, paragraph R802.7.1.1 (International Building Code for 1-2 apartment individual residential buildings) maximum length free overhang of rafters, which does not require the arrangement of additional support struts, 610 mm. The optimal overhang is 500 mm.
Z Is the distance from the top edge of the rafter to the saw. The size Z associated with the width of the rafter by a simple ratio - no more than 2/3 of its width (neglect of this rule significantly reduces the bearing capacity of the rafter). A gash is necessary to attach the rafters to the Mauerlat - a support that absorbs loads from the roof and redistributes to load-bearing walls.
By checking the item "Black and white drawing" you will receive a drawing close to the requirements of GOST and you can print it without wasting colored paint or toner.
Calculation results:
Length to the overhang of the rafter- this size should be used to mark the rafters to the Mauerlat.
Overhang length will show how far it is necessary to release the rafter outside the perimeter of the house to obtain a given roof overhang ( WITH) protecting from bad weather.
Having calculated the total length of the rafter and overhang not hard to find out required amount lumber of the required length and estimate how many reagents are needed to treat wood from decay.
Calculation of the angle and section of the rafters: the cut angle is the angle at which the ends of the rafters must be cut to connect to each other. At the same angle to the edge of the rafter, the beginning of the saw should be measured. To maintain the same angle, it is advisable to use a template on all rafters.
The rafter system is the main part of the blood, which takes all the loads acting on the roof and resists them. To ensure the high-quality functioning of the rafters, it is required correct calculation parameters.
How to calculate the rafter system
To make the calculation of the materials used in the rafter system on their own, simplified calculation formulas are presented in order to increase the strength of the system elements. This simplification increases the number of materials used, but if the roof is small, then such an increase will be imperceptible. Formulas allow you to calculate the following types roofs:
- single-slope;
- gable;
- attic.
Video: calculation of the rafter system
Calculation of the load on the rafters of a gable roof
For the construction of a sloped roof, a strong supporting frame is required, to which all other elements will be attached. When developing a project, the required length and area are calculated cross section rafter beam and other parts of the rafter system, which will be subject to variable and constant loads.
To calculate the system, you need to take into account the peculiarities of the local climate Loads that act constantly:
- the mass of all elements of the roof structure, such as roofing material, lathing, waterproofing, thermal insulation, inner lining of the attic or attic;
- weight of equipment and various subjects, which are attached to the rafters inside the attic or attic.
Variable loads:
- load caused by wind and precipitation;
- the mass of a worker who performs repairs or cleaning.
Variable loads also include seismic loads and other types of special loads that place additional requirements on the roof structure.
The angle of inclination of the slope depends on the wind load In most areas Russian Federation the problem of snow load is acute - the rafter system must perceive the fallen mass of snow without deformation of the structure (the requirement is most relevant to single-pitched roofs). With a decrease in the angle of inclination of the roof, the snow load increases. Arrangement shed roof with a close to zero tilt angle requires the installation of rafters with a large cross-sectional area, with a small pitch. You will also need to constantly clean it. This also applies to roofs with an inclination angle of up to 25 °.
Snow load is calculated by the formula: S = Sg × µ, where:
- Sg is the mass of snow cover on a flat horizontal surface with a size of 1 m 2. The value is determined according to the tables in SNiP "Roof systems" based on the required area in which the construction is being carried out;
- µ - coefficient taking into account the angle of inclination of the roof slope.
At an angle of inclination of up to 25 0, the value of the coefficient is 1.0, from 25 o to 60 o - 0.7, over 60 o - the value of snow loads is not involved in the calculations.
Precipitation affects roof calculation Wind load is calculated by the formula: W = Wo × k, where:
- Wo - the value of the wind load, determined according to the tabular values, taking into account the nature of the area where the construction is underway;
- k is a coefficient that takes into account the height of the building and the nature of the terrain.
With a building height of 5 m, the value of the coefficients is kA = 0.75 and kB = 0.85, 10 m - kA = 1 and kB = 0.65, 20 m - kA = 1.25 and kB = 0.85 ...
Roof rafter section
It is not difficult to calculate the size of the rafter beam, given the following point - the roof is a system of triangles (applies to all types of roofs). Having overall dimensions building, the value of the angle of inclination of the roof or the height of the ridge and using the Pythagorean theorem, the length of the rafters from the ridge beam to the outer edge of the wall is determined. The length of the cornice is added to this size (in the case when the rafters protrude beyond the wall). Sometimes the cornice is made by mounting fillies. When calculating the roof area, the lengths of the filly and rafters are summed up, which allows you to calculate the required number roofing material.
The cross-section of the timber for the rafters depends on many parameters. To determine the section of the timber used for the construction of any type of roof, in accordance with the required length of the rafter, the step of its installation and other parameters, it is best to use reference books.
The range of rafter bar sizes ranges from 40x150 to 100x250 mm. The length of the rafter is determined by the angle of inclination and the distance between the walls.
An increase in the slope of the roof entails an increase in the length of the rafter beam, and, accordingly, an increase in the cross-sectional area of the beam. This is necessary in order to provide the necessary structural strength. At the same time, the level of snow load is reduced, which means that the rafters can be installed with a large step. But by increasing the step, you increase the total load that will act on the rafter.
When making a calculation, be sure to take into account all the nuances, such as moisture, density and quality of lumber, if a roof is built from wood, the thickness of the used rolled metal - if the roof is made of metal.
The basic principle of calculations is as follows - the amount of load acting on the roof determines the size of the cross-section of the timber. The larger the cross-section, the stronger the structure, but the greater its total mass, and, accordingly, the greater the load on the walls and foundation of the building.
How to calculate the length of the gable roof rafters
The rigidity of the structure of the rafter system is a mandatory requirement, and its provision excludes deflection when exposed to loads. The rafters bend in the event of errors in the design calculations and the step size with which the rafter is installed. In the case when this defect is identified after the end of the work, it is necessary to strengthen the structure with the help of struts, thereby increasing its rigidity. With a rafter length of more than 4.5 m, the use of struts is mandatory, since the deflection will in any case be formed under the influence of the beam's own weight. This factor must be taken into account when performing calculations.
The length of the rafters depends on their location in the system Determining the distance between rafters
The standard step with which the installation of rafters in a residential building is carried out is about 600-1000 millimeters. Its value is influenced by:
It is not recommended to artificially decrease or increase the step of the rafters. The determination of the required number of rafters is taking into account the step with which they will be installed. For this:
- The optimal installation step is selected.
- The length of the wall is divided by the selected step and one is added to the resulting value.
- The resulting number is rounded to the nearest whole.
- The length of the wall is divided again by the resulting number, thereby determining the desired step of mounting the rafters.
Truss system area
When calculating the area of a gable roof, you need to take into account the following factors:
- The total area, which consists of the area of two slopes. Based on this, the area of one slope is determined and the resulting value is multiplied by the number 2.
- In the case when the sizes of the slopes differ among themselves, the area of each slope is determined individually. The total area is calculated by adding the values obtained for each slope.
- In the case when one of the slope angles is greater or less than 90 o, in order to determine the area of the slope, it is "split" into simple shapes and calculate their area separately, and then add the results.
- When calculating the area, the area of chimneys, windows and ventilation ducts is not taken into account.
- The area of gable and cornice overhangs, parapets and firewall walls is taken into account.
The calculation of the rafter system depends on the type of roof For example, a house is 9 m long and 7 m wide, the rafter is 4 m long, the eaves overhang is 0.4 m, and the pediment overhang is 0.6 m.
The value of the area of the ramp is found by the formula S = (L dd + 2 × L fs) × (L c + L ks), where:
- L dd - wall length;
- L fs - the length of the gable overhang;
- L c - the length of the rafter bar;
- L ks - the length of the eaves overhang.
It turns out that the area of the slope is S = (9 + 2 × 0.6) × (4 + 0.4) = 10.2 × 4.4 = 44.9 m 2.
The total roof area is S = 2 × 44.9 = 89.8 m 2.
If a tile or a soft covering in rolls is used as a roofing material, then the length of the slopes will be 0.6–0.8 m less.
The size of the gable roof is calculated in order to determine the required amount of roofing material. With an increase in the angle of inclination of the roof, the consumption of material also increases. The stock should be about 10-15%. It is caused by overlapping stacking. To determine the exact amount of material, taking into account the slope of the slopes, it is best to use reference books.
Video: gable roof truss system
How to calculate the length of the rafters of a hip roof
Despite the variety of types of roofs, their structure consists of the same elements of the truss system. For hip type roofs:
Video: hip roof truss system
What affects the angle of inclination of the rafters
For example, the slope of a pitched roof is about 9–20 о, and depends on:
- type of roofing material;
- climate in the region;
- functional properties of the structure.
In the case when the roof has two, three or four slopes, then in addition to the geography of construction, the purpose will also have an impact attic space... When the purpose of the attic is to store various property, then a large height is not required, and if used as a living space, equipment of a high roof with a large angle of inclination will be required. Hence it follows:
- appearance front of the house;
- used roofing material;
- influence of weather conditions.
Naturally, for areas with strong winds optimal choice there will be a roof with a low angle of inclination - to reduce the wind load on the structure. This also applies to regions with hot climates, where rainfall is often minimal. In areas with a large amount of precipitation (snow, hail, rain), a maximum angle of inclination of the roof is required, which can be up to 60 °. This angle of inclination minimizes the snow load.
The angle of inclination of the slope of any roof largely depends on the characteristics of the climate. As a result, for the correct calculation of the angle of inclination of the roof, it is necessary to take into account all the above factors, therefore the calculation will be carried out in the range of values from 9 o to 60o. Very often, the result of calculations shows that perfect angle the slope ranges from 20 ° to 40 °. At these values, the use of almost all types of roofing materials is allowed - corrugated board, metal tiles, slate and others. But it should be borne in mind that each roofing material also has its own requirements for the construction of roofs.
Without the dimensions of the rafters at your disposal, you cannot begin the construction of the roof. Take this issue seriously. Do not limit yourself only to the calculations of the rafter system, the choice of its design and the determination of the acting loads. Building a house is a whole project in which everything is interconnected. In no case should you consider separately such elements as the foundation, Basic structure walls, rafters, roofing. A high-quality project necessarily takes into account all factors in an integrated manner. And if you plan to build housing for your own needs, then the best solution there will be an appeal to specialists who will solve pressing issues and carry out design and construction without errors.
How to calculate the parameters of a gable roof of a private house? You can use an online calculator. But what if there is no way to use the rafter calculator? If you wish, you can calculate the main parameters of the roof construction on paper. I will tell you how to perform calculations in accordance with the loads acting on the rafter system.
| Illustrations | Calculation parameters |
| The severity of the snow. Despite the slope of the slopes, on the roof surface, as shown in the photo, accumulates a large number of snow. The mass of snow cover affects the roof cake, rafters and load-bearing walls. | |
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Wind pressure... Depending on the angle of inclination, the wind influences the roof.
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Roofing material weight... The pie is a multi-layer construction, which, depending on the quantity structural elements, has this or that mass. This means that when calculating with your own hands, you need to find the optimal ratio of the parameters of the cake and the material from which the load-bearing walls are erected. |
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Rafter weight... The stronger the rafters, the heavier they are and the higher their price, and vice versa, a decrease in the strength of the rafters will make the system lighter. Our task, in the calculations, is to choose the parameters of the rafters that will correspond to the mechanical load from the roofing material. |
Calculating the maximum snow weight
The maximum snow weight can be calculated using the formula S = µ · Sg, where:
- S is the amount of snow load (in kg / m 2);
- µ - coefficient of the roof slope (depends on the angle of inclination of the rafters α);
- Sg - standard weight of snow (in kg / m 2).
In order to make calculations according to the proposed formula, let us determine the dependence of the conditional value µ on the angle of inclination α.
The diagram shows the ratio of the slope of the slope and the geometric parameters roof truss, which is formed by diagonal and horizontal beams.
Table 1 shows the already calculated results of dividing such quantities as the height of the roof to the ridge and half of the tightening - the beams forming the ceiling.
An angle of inclination (α) of 30 ° or less corresponds to a coefficient (µ) 1. If the angle is equal to or greater than 60 °, then µ is 0. If 60 °> α> 30 °, then the value of µ can be calculated using the formula: = 0.033 * (60-α).
Parameters of standard snow load in kg / m2:
After the slope coefficient of the rafters and the parameters of the standard snow severity are known, we return to the formula S = µ · Sg, insert the existing parameters and calculate the rafters taking into account the effect of the atmospheric precipitation layer.
Calculating the maximum allowable wind pressure
The importance of calculating wind exposure is due to the following points:
- If the angle of inclination α is greater than 30 °, the windage of the structure increases. Because of this, additional pressure falls on one of the slopes or on the pediment, which negatively affects the state of the structure.
- If the angle of inclination α is less than 30 °, when the air flows around the roof, an aerodynamic lifting force and a turbulence zone under the overhangs are formed.
The calculation of the permissible air flow load is carried out according to the formula Wo K C = Wm, where:
- Wm is the maximum allowable air flow effect;
- Wo - conditional impact of the air flow (determined according to Table 2 and the wind pressure map);
- K is the coefficient of change in the effect of air flow along the height (shown in Table 3 in relation to the height of the building);
- C is the drag coefficient.
The drag coefficient C according to the configuration of the roof and the building may have a value<1,8 (ветер поднимает крышу), >0.8 (the wind presses on one of the slopes). Let's simplify the calculation towards increasing the strength and assume that the value of the coefficient C is 0.8.
Now that all the coefficients are known, it remains to insert them into the formula Wo · K · C = Wm and calculate the maximum allowable value of the effect of the air flow Wm.
Calculation of roof mass
When buying roof coverings, you can find out the weight from the seller or on the package. But in order to calculate in advance what material is suitable, you can use the table. To calculate, you need to calculate the area of \ u200b \ u200bthe roof slopes and multiply by the proposed values.
In addition to the mass of the coating, the load-bearing walls bear the weight of the rafters themselves, lathing boards, counter battens, etc. The average values of the gravity of the elements of the rafter system can be found in the proposed table.
Weight values are based on kilograms per square meter assuming that the distance between the boards of the sheathing is standard 50-60 cm. To calculate the mass of the structure, we find out the area of the slopes and multiply by the proposed values.
It is advisable to round up the calculation results so that the resulting value provides the greatest strength of the rafter system.
Let's sum up
Now you know the factors taking into account the calculation of the roof rafter system, and therefore you can calculate the necessary values yourself, without using the online calculator. More useful information can be found by watching the video in this article. Ask questions of interest in the comments.