We offer professional free estimates rafter system gable roof by using online calculator and the website, 3D visualization and detailed drawings. Detailed calculations of the roof and roofing, all materials, sheathing, rafters, mauerlat. Try calculating a gable roof right now!
Our online calculator rafter system will calculate the gable roof:
- calculating the length of gable roof rafters
- number of rafters and pitch
- calculation of gable roof area and angle of inclination
- calculation of roof sheathing
- number of sheet roofing materials (for example, corrugated sheets, metal tiles, slate)
- vapor barrier and insulation parameters
To generate a gable roof calculator calculation, you need to measure and enter the following dimensions in the appropriate boxes:
The cross-section (thickness x width) and pitch of the rafters depend on the angle of inclination of the roof, its type, the length of the rafter leg, the maximum main loads that can be withstood, as well as the type and weight of the roof covering, and even to some extent on the width of the insulation. If you don't know where to get it standard parameters rafters and sheathing, our article will help you “ Optimal cross-section, pitch of sheathing and rafters depending on the type of roof ».
The calculator calculates the materials for the roof, based on the dimensions of the roofing sheet you entered and on calculated value roof area. We recommend buying the quantity of roofing materials for the roof, boards and beams for the rafter system with a small reserve; it is always better to hand over the remainder to hardware store than to pay a lot of money for delivery of a missing pair of boards.
Be careful! The online calculator will be able to calculate a gable roof depending on how accurate the values you enter.
Simplify your calculations and save time, the program will draw the rafter plangable roof and will display the results of calculating a gable roof based on 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 a three-dimensional view. In our opinion, visualization in construction is a very necessary opportunity.
If your project has a gable roof with different slopes, you should make the calculation using the calculator twice - for each slope separately.
Rafters are the basis of any roof. They bear the main load associated with the weight of the roof, wind and snow pressure. For long-term and trouble-free operation of the roof, it is important to make accurate calculations of these loads, determine the strength characteristics of the rafters, their cross-section, length, quantity, as well as the volume of material required for the arrangement roof frame. All these calculations can be done independently.
Calculation of rafters using online programs
The easiest way to calculate rafters is with an online calculator. You specify the initial data, and the program calculates the necessary parameters. Existing programs vary in their functionality. Some of them are complex in nature and calculate many parameters of the rafter system, others are much simpler and involve the calculation of one or two indicators. Among the comprehensive services, we should highlight the Stroy-calc series of construction calculators for calculating the parameters of roof rafters with one and two slopes, an attic and hips.
The Stroy-calc calculator is used to calculate the parameters of roof rafters with one, two slopes, an attic and hips
The program also takes into account roofing material, i.e., together with the calculation of the rafter system, you can obtain data on required quantity finishing coating from:
- ceramic tiles;
- cement-sand tiles;
- bitumen shingles;
- metal tiles;
- slate (asbestos-cement slabs);
- steel seam roofing;
- bitumen slate.
In order to obtain the required result, the following information is entered:
- roof characteristics: roofing material, base width, base length, rise height, overhang length;
- rafter characteristics: rafter pitch, type of wood for rafters;
- characteristics of the sheathing: width, board thickness, distance between rows;
- snow load on the rafters: selecting the region of snow load on the map.
The program contains drawings of roof types, which show data entry parameters in graphical form. The result displays information on:
- roof - angle of inclination, surface area, approximate weight of roofing material;
- rafters - length, minimum cross-section, quantity, volume of timber for rafters, their approximate weight, layout (drawing);
- lathing - number of rows, distance between boards, number of boards, their volume, approximate weight.
Online calculators, of course, cannot take into account the design features of rafters in all situations. To obtain accurate data for a specific roof option, all calculations must be done manually. We offer you methods for calculating loads on rafters (snow, wind, roofing pie), as well as determining rafter parameters (section, length, quantity, pitch). Based on these data, it will also be possible to calculate the amount of wood required for arranging the rafter system.
Calculation of the load on the rafters
The rafters hold up the roof. Therefore, loads are transferred to them both from external natural factors, and on the weight of the roofing pie (sheathing, insulation, hydro- and vapor barrier). The main external loads are associated with the influence of snow and wind.
Snow load
Snow load is determined by the formula: S =μ ∙ S g, where:
- S is the desired load value;
- μ - coefficient determined by the slope of the roof (the greater the slope, the lower this coefficient, since the snow will melt, so its pressure will be less);
- S g is the norm of snow pressure in a specific area of the country (kg/m2), calculated based on the results of long-term observations.
The angle of the roof is calculated from its main triangle
To determine the coefficient μ, it is necessary to know the angle of inclination of the slope. It often happens that the width and height of the roof are given, but the angle of inclination is unknown. In this case, it must be calculated using the formula tg α = H/L, where H is the height of the ridge, L is half the width of the building (on the gable side), tg α is the tangent of the desired angle. Next, the value of the angle itself is taken from special tables.
Table: the value of the slope angle according to its tangent
| tan α | α, deg |
| 0,27 | 15 |
| 0,36 | 20 |
| 0,47 | 25 |
| 0,58 | 30 |
| 0,70 | 35 |
| 0,84 | 40 |
| 1,0 | 45 |
| 1,2 | 50 |
| 1,4 | 55 |
| 1,73 | 60 |
| 2,14 | 65 |
Let's assume that the house has a width of 8 m and a height at the ridge of 2.32 m. Then tg α = 2.32/4 = 0.58. From the table we find that α = 30 o.
The coefficient μ is determined using the following method:
- at slope angles up to 25 o μ = 1;
- for angles from 25 to 60 o μ = 0.7;
- for steeper slopes μ = 0, i.e. the snow load is not taken into account.
Thus, for the structure under consideration μ = 0.7. The S g value is selected based on the location of the region in which construction is taking place on the snow load map.
The snow load map allows you to determine the snow pressure on the roof in different regions of Russia
Having determined the region number on the map, the value of the standard snow load can be found using the corresponding table.
Table: standard snow load by region
| Region No. | I | II | III | IV | V | VI | VII | VIII |
| S g, kg/m 2 | 80 | 120 | 180 | 240 | 320 | 400 | 480 | 560 |
Let's assume that our house is located in the Moscow region. This is the third region in terms of snow load. S g here is equal to 180 kg/m 2. Then the total snow load on the roof of the house will be S = 0.7 ∙ 180 = 126 kg/m2.
Wind load
Wind load depends on the area of the country where the house is built, the height of the house, the characteristics of the terrain and the slope of the roof. It is calculated by the formula: W m = W o ∙ K ∙ C, where:
- W o - standard value of wind pressure;
- K is a coefficient that takes into account changes in wind pressure at altitude;
- C - aerodynamic coefficient, taking into account the shape of the roof (with flat or steep slopes).
The standard value of wind pressure is determined from the wind load map.
The wind load map allows you to determine the wind pressure on the roof in different regions of Russia
Table: standard wind load by region
| Region No. | 1 a | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| W o , kgf/m 2 | 24 | 32 | 42 | 53 | 67 | 84 | 100 | 120 |
In terms of wind loads, the Moscow region is in the first zone. Therefore, the standard value of wind pressure W o for our case is 32 kg/m2.
The K value is determined using a special table. The higher the house and the more open the area it is built, the greater the value of K.
Table: coefficient taking into account wind pressure at height
Let's take the average height of a house - from 5 to 10 m, and we will consider the area closed (this type corresponds to most areas where suburban construction). This means that coefficient K in our case will be equal to 0.65.
The aerodynamic coefficient can vary from -1.8 to 0.8. A negative coefficient means that the wind is trying to lift the roof (usually with gentle slopes), while a positive coefficient means it is trying to tip it over (with steep slopes). For reliability, let’s take the maximum value of this coefficient, equal to 0.8.
Wind affects roofs with steep and gentle slopes differently
Thus, the total wind load on the house we are considering will be equal to W m = 32 ∙ 0.65 ∙ 0.8 = 16.6 kg/m 2.
Roofing cake weight
The total weight of a square meter of roofing cake will be equal to the sum specific gravity all its constituent elements:
- laths made of coniferous wood (8 - 12 kg);
- roofing(for example, we take corrugated sheeting - 5 kg);
- waterproofing made of a polymer membrane (1.4 – 2.0 kg);
- vapor barrier made from reinforced film(0.9 – 1.2 kg);
- insulation ( mineral wool- 10 kg).
The weight of other types of roofing can be determined using a special table.
Table: weight of various types of roofing
For greater reliability, we take the maximum weight values of the roofing pie components: P = 12 + 5 + 2 + 1.2 + 10 = 30.2 kg/m2. We add a reserve of 10% in case of installing any additional structures or non-standard types coating: P = 30.2 ∙ 1.1 = 33.2 kg/m 2.
Total load on the rafters
The total load on the rafters is calculated by the formula: Q = S+W m +P, where:
Let us recall that the calculation is carried out for the Moscow region, the roofing is corrugated sheeting, the roof inclination angle is 30°: Q = 126 + 16.6 + 33.2 = 175.8 kg/m2. Thus, the total load on one square meter rafters is 175.8 kg. If the roof area is 100 m2, then the total load is 17580 kg.
It is a mistaken belief that reducing the weight of the roofing significantly reduces the load on the rafters. Let's take cement-sand tiles (50 kg/m2) as a coating. Then the weight of the roof will increase by 45 kg/m2 and will be not 33.2, but 76.4 kg/m2. In this case, Q = 126 + 16.6 + 76.4 = 219 kg/m2. It turns out that with an increase in the mass of the roofing covering by 10 times (from 5 to 50 kg/m2), the total load increased by only 25%, which can be considered not such a significant increase.
Calculation of rafter parameters
Knowing the magnitude of the loads on the roof, we can calculate the specific parameters of the material required for installation of the rafter system: cross-section, length, quantity and pitch.
Selection of rafter cross-section
The cross-section of the rafters is calculated according to the formula: H = K c ∙ L max ∙ √Q r /(B ∙ R bend), where:
- K c - coefficient equal to 8.6 at an angle of inclination less than 30 o, and 9.5 at a greater slope;
- L max - the largest rafter span;
- B is the thickness of the rafter section in meters;
- R bend - bending resistance of the material (kg/cm 2).
The meaning of the formula is that required size the cross-section increases with the increase in the largest span of the rafter and the load on its linear meter and decreases with an increase in the thickness of the rafter and the bending resistance of the wood.
Let's calculate all the elements of this formula. First of all, let's determine the load per linear meter of rafters. This is done according to the formula: Q r = A ∙ Q, where:
- Q r - calculated value;
- A - the distance between the rafters in meters;
The logic of the calculation is quite simple: the sparser the rafters are located and the fewer there are, the greater the load per linear meter will be.
We have already calculated the total load per 1 square meter of rafters. For our example, it is equal to 175.8 kg/m 2. Let's assume that A = 0.6 m. Then Q r = 0.6 ∙ 175.8 = 105.5 kg/m. This value will be required for further calculations.
Now let’s determine the cross-sectional width of the lumber according to GOST 24454–80 “Softwood lumber”. Let's look at what sections the wood is cut into - these are standard values.
Table: determination of standard values for the width of the board depending on its thickness
| Board thickness - section width, mm | Board width - section height, mm | ||||||||
| 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 | ||||||||
Let's decide on the thickness of the board (B). Let it correspond to the most commonly used edged lumber- 50 mm or 0.05 m.
Next, we need to know the largest rafter span (L max). To do this, you need to turn to the project and find a drawing roof truss, where all its dimensions will be indicated. In our case, let us take Lmax equal to 2.7 m.
The largest span of the rafter (Lmax) is an important component for calculating its cross-section and is determined from the drawing of the truss
The amount of bending resistance of the material (R bend) depends on the type of wood. For the first grade it is 140 kg/cm2, the second - 130 kg/cm2, the third - 85 kg/cm2. Let's take the value for the second grade: it is not very different from the first, but the second grade of wood is cheaper.
We substitute all the obtained values into the above formula and get H = 9.5 ∙ 2.7 ∙ √ (105.5)/(0.05x130) = 103.4 mm. With a rafter thickness of 50 mm no standard value width is 103.4 mm, so we take the one closest to it higher value from the table above. It will be 125 mm. Thus, the sufficient cross-section of lumber with a rafter pitch of 0.6 m, a maximum span of 2.7 m and a roofing load of 175.8 kg/m2 is equal to 50x125 mm.
- Mauerlat - 100x100, 100x150, 150x150;
- rafter legs and valleys - 100x200;
- crossbars - 100x150, 100x200;
- racks - 100x100, 150x150.
These are sections with a margin. If you want to save material, you can use the above method.
Video: calculation of loads on rafters and their cross-section
Rafter length
When making rafters, in addition to the cross-section, their length is also important. It depends, in particular, on the slope with which the roof will be built. The roof slope angle usually varies between 20 and 45 degrees, but varies depending on the roofing material used, since not every roofing material can be used with a roof of any slope.
The influence of the type of roofing material on the roof pitch angle
Permissible roof slope angles for roofing materials:
- roll coverings - flat and low-slope roofs (up to 22 o);
- bitumen roofing and seamed metal sheets- any slope;
- fiber cement sheets, corrugated sheets - from 4.5 o;
- metal tiles, bitumen, ceramic tiles, slate - from 22 o;
- high-profile piece tiles, slate - from 25 o.
Permissible roof slope angles are determined by the roofing material used
Despite the fact that the permissible roof slope angles can be very small, we still recommend making them large to reduce the snow load. For corrugated sheeting they can be from 20 o, metal tiles - 25 o, slate - 35 o, seam roofing - 18 - 35 o.
Rafter length different types roofs are considered differently. We'll show you how this is done for a pitched and gable roof.
Calculation of the length of the rafters of a pitched roof
The length of the rafter leg is calculated by the formula L c = L bc / sin A, where L bc is the amount by which the wall needs to be raised, and A is the roof slope angle. To understand the meaning of the formula for calculating L c, recall that the sine of an angle of a right triangle is equal to the ratio of the opposite leg to the hypotenuse. Thus, sin A = L bc /L c. The value of L bc can be calculated using the formula: L bc = L cd ∙ tg A, where L cd is the length of the wall of the house.
All formulas for calculating the rafter system pitched roof taken from a right triangle, which is a projection of the under-roof space onto the pediment
The easiest way to find the values of tg A and sin A is from the table.
Table: determining the values of trigonometric functions based on the roof slope angle
| Roof pitch angle, degrees | tg A | sin A | cos A |
| 5 | 0,09 | 0,09 | 1,00 |
| 10 | 0,18 | 0,17 | 0,98 |
| 15 | 0,27 | 0,26 | 0,97 |
| 20 | 0,36 | 0,34 | 0,94 |
| 25 | 0,47 | 0,42 | 0,91 |
| 30 | 0,58 | 0,50 | 0,87 |
| 35 | 0,70 | 0,57 | 0,82 |
| 40 | 0,84 | 0,64 | 0,77 |
| 45 | 1,00 | 0,71 | 0,71 |
| 50 | 1,19 | 0,77 | 0,64 |
| 55 | 1,43 | 0,82 | 0,57 |
| 60 | 1,73 | 0,87 | 0,50 |
Let's look at an example.
- Let's take the length of the house wall to be 6 m and the roof slope to be 30 degrees.
- Then the height of the wall is L bc = 6 ∙ tg 30 o = 6 ∙ 0.58 = 3.48 m.
- Length of the rafter leg L c = 3.48 / sin 30 o = 3.48 / 0.5 = 6.96 m.
Calculation of the length of the rafters of a gable roof
A gable roof can be imagined as an isosceles triangle formed by two slopes and a transverse ceiling beam.
A graphical representation of a gable roof in the form of an isosceles triangle allows you to determine the length of the rafter leg in two different ways
The length of the rafter leg (a) can be determined in two different ways.
- If the width of the house b and the angle of inclination of the roof A are known. Then a = b/ (2 ∙ cos A). Let's assume that the width of the house is 8 m, and angle A is 35 o. Then a = 8 /(2 ∙ сos 35 o) = 8/(2 ∙ 0.82) = 4.88. We add 0.5 m to the overhangs and get the length of the rafter leg equal to 5.38 m.
- If the width of the roof b and its height at the ridge h are known. In this case, a = √b 2 + h 2 . Let's assume that the height of the ridge is 2.79 m. Then a = √4 2 +2.79 2 = √16 + 7.78 = √23.78 = 4.88. We add 0.5 m to the overhang and as a result we have the same 5.38 m.
It must be kept in mind that standard length wood lumber is 6 meters. If they are longer, they will need to be either spliced or special ordered, which, naturally, will be more expensive.
Video: calculation of rafters
Calculation of rafter pitch
The pitch is the distance between adjacent rafters. It determines how many rafters we need for the roof. The step size is usually set to be from 60 cm to 1 m. To calculate a specific step size you need to:
- Select an approximate step.
- Determine the length of the slope. Typically this value is specified by the project.
- Divide the length of the ramp by the approximately selected step size. If the result is a fractional number, then the result is rounded up and 1 is added (this adjustment is necessary because there must be rafters along both boundaries of the slope).
- Divide the length of the slope by the number obtained in the previous paragraph.
For clarity, we will show the progress of the calculation using a specific example.
Let's assume that the approximate step is 1 m and the length of the slope is 12 m.
- We divide the length of the slope by the approximately selected step size: 12 / 1 = 12.
- We add 1 to the resulting number, we get 13.
- We divide the length of the slope by the resulting number: 12 / 13 = 0.92 m.
It is necessary to understand that the obtained value is the distance between the centers of the rafter joists.
The pitch between the rafters can also be determined from the table based on the given cross-section and the length of the rafter leg.
Table: calculation of rafter pitch depending on the length of the rafter leg and the section of the beam
| Rafter pitch, m | Rafter leg length in meters | ||||||
| 3,0 | 3,5 | 4,0 | 4,5 | 5,0 | 5,5 | 6,0 | |
| 0,6 | 40x150 | 40x175 | 50x150 | 50x150 | 50x175 | 50x200 | 50x200 |
| 0,9 | 50x150 | 50x175 | 50x200 | 75x175 | 75x175 | 75x200 | 75x200 |
| 1,1 | 75x125 | 75x150 | 75x175 | 75x175 | 75x200 | 75x200 | 75x200 |
| 1,4 | 75x150 | 75x175 | 75x200 | 75x200 | 75x200 | 100x200 | 100x200 |
| 1,75 | 75x150 | 75x200 | 75x200 | 100x200 | 100x200 | 100x250 | 100x250 |
| 2,15 | 100x150 | 100x175 | 100x200 | 100x200 | 100x250 | 100x250 | - |
Using the same table, you can determine the permissible cross-section of the rafters, knowing the size of the step and its length. So, with a step of 0.9 m and a length of 5 m, we get a section of 75x175 mm.
If the thickness of the rafter beams is greater than usual, the distance between the rafters can also be made larger.
Table: calculation of the pitch of rafters made of thick beams and logs
| Distance between the rafters, m | Maximum length of rafter leg, m | ||||||
| 3,2 | 3,7 | 4,4 | 5,2 | 5,9 | 6,6 | ||
| 1,2 | timber | 9x11 | 9x14 | 9x17 | 9x19 | 9x20 | 9x20 |
| log | 11 | 14 | 17 | 19 | 20 | 20 | |
| 1,6 | timber | 9x11 | 9x17 | 9x19 | 9x20 | 11x21 | 13x24 |
| log | 11 | 17 | 19 | 20 | 21 | 24 | |
| 1,8 | timber | 10x15 | 10x18 | 10x19 | 12x22 | - | - |
| log | 15 | 18 | 19 | 22 | - | - | |
| 2,2 | timber | 10x17 | 10x19 | 12x22 | - | - | - |
| log | 17 | 19 | 22 | - | - | - | |
Calculation of the number of rafters
- Depending on the load on the rafter system, we select the section of the rafter leg.
- Calculate the length of the rafters.
- Using the table, select the pitch of the rafters.
- We divide the width of the roof by the pitch of the rafters and get their number.
For example, let’s calculate the number of rafters for a gable roof 10 m wide with a rafter leg length of 4 m and its cross-section 50x150 mm.
- We set the step to 0.6 m.
- Divide 10 m by 0.6 m, we get 16.6.
- Add one rafter to the edge of the roof and round it up. We get 18 rafters per slope.
Calculation of the amount of wood required for the manufacture of rafters
Coniferous wood is most often used to construct rafters. Knowing how many rafters are required for the roof and how much wood is contained in one beam, we calculate required volume wood Let's assume that we have made a full calculation of the rafter system and found that 18 units of timber measuring 150x150 mm are needed. Next, look at the table.
Table: amount of timber per cubic meter of lumber
| Size timber, mm | Number of beams 6 m long 1 m 3 lumber, pcs. | Volume of one beam 6 m long, m 3 |
| 100x100 | 16,6 | 0,06 |
| 100x150 | 11,1 | 0,09 |
| 100x200 | 8,3 | 0,12 |
| 150x150 | 7,4 | 0,135 |
| 150x200 | 5,5 | 0,18 |
| 150x300 | 3,7 | 0,27 |
| 200x200 | 4,1 | 0,24 |
The volume of one beam 150 x 150 mm is 0.135 m 3. This means that the volume of lumber for 18 rafters will be 0.135 m 3 ∙ 18 = 2.43 m 3.
Video: calculation of material for gable roof rafters
Correct calculation of the main parameters allows you to make the rafter system safe, reliable and durable. Knowledge required volume wood allows you to save money on arranging rafters. Online calculators make it much easier to calculate everything technical characteristics roofing frame, save time on calculations and increase their accuracy.
A gable roof or gable roof is a roof with two slopes, i.e. having 2 inclined surfaces (slopes) of a rectangular shape.
Gable roof frame in effect design features ideally combines simplicity of design and maintenance with reliability and durability. These and many other parameters make the construction of a gable roof practical and rational decision for private and commercial housing construction.
In this article, we will look at how to make a rafter system for a gable roof with your own hands. For effective perception of the material, it is presented in the form of step-by-step instructions from A to Z, from selection and calculations, to installation of the Mauerlat and sheathing under the roof. Each stage is accompanied by tables, diagrams, drawings, drawings and photos.
The popularity of the house roof is due to a number of advantages:
- design variability;
- simplicity in calculations;
- naturalness of water flow;
- integrity of the structure reduces the likelihood of leaks;
- efficiency;
- preservation usable area attic or the possibility of arranging an attic;
- high maintainability;
- strength and wear resistance.
Types of gable roof
The installation of a gable roof truss system depends, first of all, on its design.
There are several options for gable roofs (types, types):
The most common roof installation option due to its simplicity and reliability. Thanks to symmetry, a uniform distribution of loads on the load-bearing walls and mauerlat is achieved. The type and thickness of the insulation does not affect the choice of material.
The cross-section of the timber makes it possible to provide a reserve bearing capacity. There is no possibility of rafters bending. Supports and struts can be placed almost anywhere.
An obvious drawback is the impossibility of arranging a full attic floor. Due to sharp corners, “dead” zones appear that are unsuitable for use.
The arrangement of one angle of more than 45° leads to a reduction in the amount of unused area. There is an opportunity to do living rooms under the roof. At the same time, the requirements for calculations increase, because the load on the walls and foundation will be distributed unevenly.
This roof design allows you to equip a full second floor under the roof.
Naturally, a simple gable rafter roof differs from a broken line, not only visually. The main difficulty lies in the complexity of the calculations.
Design of a gable roof truss system
Building a roof of any complexity with your own hands requires knowledge of the purpose of the basic structural elements.
The locations of the elements are shown in the photo.
- Mauerlat. Designed to distribute the load from the rafter system onto the load-bearing walls of the building. To arrange the Mauerlat, a timber made of durable wood is selected. Preferably larch, pine, oak. The cross-section of the timber depends on its type - solid or glued, as well as on the expected age of the structure. The most popular sizes are 100x100, 150x150 mm.
Advice. For a metal rafter system, the Mauerlat must also be metal. For example, a channel or an I-profile.
- Rafter leg. The main element of the system. To make rafter legs, a strong beam or log is used. The legs connected at the top form a truss.
The silhouette of the roof truss defines appearance buildings. Examples of farms in the photo.
The parameters of the rafters are important. They will be discussed below.
- Puff- connects the rafter legs and gives them rigidity.
- Run:
- Ridge run, is mounted at the junction of one rafter to another. In the future, the roof ridge will be installed on it.
- Side purlins, they provide the truss with additional rigidity. Their number and size depend on the load on the system.
- Rafter stand- vertically located beam. It also takes on part of the load from the weight of the roof. In simple gable roof usually located in the center. With a significant span width - in the center and on the sides. In an asymmetrical gable roof, the installation location depends on the length of the rafters. With a broken roof and arrangement of one room per attic attic- the racks are located on the sides, leaving free space for moving. If there are supposed to be two rooms, the racks are located in the center and on the sides.
The location of the rack depending on the length of the roof is shown in the figure.
- Strut. Serves as a support for the stand.
Advice. Installing the brace at an angle of 45° significantly reduces the risk of deformation from wind and snow loads.
In regions with significant wind and snow loads, not only longitudinal struts are installed (located in the same plane as the rafter pair), but also diagonal ones.
- Sill. Its purpose is to serve as a support for the rack and a place for attaching the strut.
- Lathing. Designed for movement during construction work and fixation of roofing material. Installed perpendicular to the rafter legs.
Advice. An important purpose of the sheathing is to redistribute the load from the roofing material to the rafter system.
Having a drawing and diagram indicating the location of all the listed structural elements will help in the work.
Advice. Be sure to add information about the passage structure to the gable roof rafter system diagram ventilation shaft and chimney.
The technology of their installation is determined by the type of roof.
Selection of material for rafters
When calculating the material for a gable roof, you need to choose high-quality wood without damage or wormholes. The presence of knots for beams, mauerlat and rafters is not allowed.
For sheathing boards, there should be a minimum of knots, and they should not fall out. The wood must be durable and treated with the necessary preparations that will increase its properties.
Advice. The length of the knot should not exceed 1/3 of the thickness of the timber.
Calculation of the rafter system of a gable roof
Calculation of material parameters important stage, so we present the calculation algorithm step by step.
It is important to know: the entire rafter system consists of many triangles, as the most rigid element. In turn, if the stingrays have different shape, i.e. are an irregular rectangle, then you need to divide it into separate components and calculate the load and amount of materials for each. After calculations, summarize the data.
1. Calculation of the load on the rafter system
The load on the rafters can be of three types:
- Constant loads. Their action will always be felt by the rafter system. Such loads include the weight of the roof, sheathing, insulation, films, additional roofing elements, finishing materials For . The weight of the roof is the sum of the weight of all its constituent elements; such a load is easier to take into account. On average, the constant load on the rafters is 40-45 kg/sq.m.
Advice. To make a safety margin for the rafter system, it is better to add 10% to the calculation.
For reference: The weight of some roofing materials per 1 sq.m. presented in the table
Advice. It is desirable that the weight of roofing material per 1 sq.m. roof area did not exceed 50 kg.
- Variable loads. They act at different times and with different strengths. Such loads include: wind load and its strength, snow load, precipitation intensity.
In essence, the roof slope is like a sail and, if you take into account the wind load, the entire roof structure can be destroyed.
The calculation is carried out according to the formula: wind load is equal to the regional indicator multiplied by correction factor. These indicators are contained in SNiP “Loads and Impacts” and are determined not only by the region, but also by the location of the house. For example, on a private house surrounded by multi-story buildings, there is less load. Standing separately Vacation home or the cottage experiences increased wind loads.
2. Calculation of snow load on the roof
The roof calculation for snow load is carried out according to the formula:
The total snow load is equal to the weight of the snow multiplied by the correction factor. The coefficient takes into account wind pressure and aerodynamic influence.
The weight of snow that falls on 1 square meter. roof area (according to SNiP 2.01.07-85) is in the range of 80-320 kg/sq.m.
Coefficients showing the dependence on the slope angle are shown in the photo.
Nuance. When the slope angle is over 60 ° the snow load does not affect the calculation. Because the snow will quickly slide down and will not affect the strength of the beam.
- Special loads. Accounting for such loads is carried out in places with high seismic activity, tornadoes, and storm winds. For our latitudes, it is enough to make a safety margin.
Nuance. The simultaneous action of many factors causes a synergy effect. This is worth considering (see photo).
Assessment of the condition and load-bearing capacity of walls and foundations
It should be borne in mind that the roof has significant weight, which can cause damage to the rest of the building.
Determining the roof configuration:
- simple symmetrical;
- simple asymmetrical;
- broken line
How more complex form roof, the greater the number of trusses and sub-rafter elements needed to create the necessary safety margin.
The angle of inclination of a gable roof is determined primarily by the roofing material. After all, each of them puts forward their own demands.
- soft roof - 5-20°;
- metal tiles, slate, corrugated sheets, ondulin - 20-45°.
It should be noted that increasing the angle increases the area of space under the roof, but also the amount of material. What affects the total cost of work.
Nuance. The minimum angle of inclination of a gable roof must be at least 5°.
5. Calculation of rafter pitch
The pitch of the gable roof rafters for residential buildings can range from 60 to 100 cm. The choice depends on the roofing material and the weight of the roof structure. Then the number of rafter legs is calculated by dividing the length of the slope by the distance between the rafter pairs plus 1. The resulting number determines the number of legs per slope. For the second, the number must be multiplied by 2.
The length of the rafters for the attic roof is calculated using the Pythagorean theorem.
Parameter "a"(roof height) is set independently. Its value determines the possibility of arranging a living space under the roof, the convenience of being in the attic, and the consumption of material for the construction of the roof.
Parameter "b" equal to half the width of the building.
Parameter "c" represents the hypotenuse of the triangle.
Advice. To the obtained value you need to add 60-70 cm for cutting and moving the rafter leg beyond the wall.
It is worth noting that maximum length timber - 6 m.p. Therefore, if necessary, the timber for the rafters can be spliced (extension, joining, joining).
The method of splicing rafters along the length is shown in the photo.
The width of the roof rafters depends on the distance between opposite load-bearing walls.
7. Calculation of the rafter cross-section
The cross-section of the rafters of a gable roof depends on several factors:
- loads, we have already written about it;
- type of material used. For example, a log can withstand one load, timber - another, laminated timber - a third;
- rafter leg lengths;
- the type of wood used in construction;
- distances between rafters (rafter pitch).
You can determine the cross-section of the beam for the rafters, knowing the distance between the rafters and the length of the rafters using the data below.
Rafter cross-section - table
Advice. How more step installation of rafters, the greater the load on one rafter pair. This means that the cross-section of the rafters needs to be increased.
Dimensions of lumber (timbers and boards) for a gable rafter system:
- thickness (section) of the Mauerlat - 10x10 or 15x15 cm;
- the thickness of the rafter leg and tie is 10x15 or 10x20 cm. Sometimes a beam of 5x15 or 5x20 cm is used;
- run and strut - 5x15 or 5x20. Depending on the width of the foot;
- stand - 10x10 or 10x15;
- bench - 5x10 or 5x15 (depending on the width of the rack);
- thickness (section) of the roof sheathing - 2x10, 2.5x15 (depending on the roofing material).
Types of gable roof rafter system
For the roof structure under consideration, there are 2 options: layered and hanging rafters.
Let's consider each type in detail in order to make an informed choice.
Hanging rafters
They are used for roof widths of no more than 6 lm. Installation of hanging rafters is carried out by attaching the legs to the load-bearing wall and ridge run. The design of hanging rafters is special in that the rafter legs are under the influence of a bursting force. Hanging rafters with a tie installed between the legs reduce its impact. The tie in the rafter system can be wooden or metal. Often the puffs are placed at the bottom, then they play a role load-bearing beams. It is important to ensure reliable fastening tightening on the rafter leg. Because a bursting force is also transmitted to it.
Advice.
The higher the tightening is located, the greater strength it should have.
If the tightening is not installed, the load-bearing walls may simply “move apart” from the pressure created by the rafter system.
Layered rafters
They are used for arranging roofs of any size. The design of layered rafters provides for the presence of a beam and a stand. The bench lying parallel to the Mauerlat takes on part of the load. Thus, the rafter legs are, as it were, inclined towards each other and supported by a stand. The rafter legs of the layered system work only in bending. And the ease of installation also tips the scales in their favor. The only drawback is the presence of a stand.
Combined
Due to the fact that modern roofs are distinguished by a wide variety of shapes and complexity of configurations, used combined view rafter system.
After choosing the type of rafter system, you can accurately calculate the amount of materials. Write down the calculation results. At the same time, professionals recommend drawing up drawings for each roof element.
Installation of a gable roof rafter system
After the gable roof rafters have been calculated, installation can begin. We will divide the process into stages and give a description of each of them. It will turn out to be unique step-by-step instruction, containing additional information for each stage.
1. Attaching the Mauerlat to the wall
The beam is installed along the length of the wall on which the rafters will rest.
In log houses, the role of the mauerlat is played by the upper crown. In buildings built from porous material (aerated concrete, foam concrete) or brick, the Mauerlat is installed along the entire length load-bearing wall. In other cases, it can be installed between the rafter legs.
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Since the length of the Mauerlat exceeds standard sizes lumber, it has to be spliced.
The connection of the Mauerlat to each other is done as shown in the figure.
How to connect the Mauerlat?
The beams are cut only at an angle of 90°. Connections are made using bolts. Nails, wire, wooden dowels are not used.
How to attach the Mauerlat?
The Mauerlat is installed at the top of the wall. The installation technology provides several ways to attach the Mauerlat:
- strictly in the center of the load-bearing wall;
- with a shift to one side.
Advice.
The Mauerlat cannot be placed closer than 5 cm to the outer edge of the wall.
To protect the timber for the mauerlat from damage, it is laid on a layer waterproofing material, which most often is ordinary roofing felt.
Reliability of Mauerlat fastening important aspect construction. This is due to the fact that the roof slope is like a sail. That is, it experiences strong wind load. Therefore, the Mauerlat must be firmly fixed to the wall.
Methods for attaching the Mauerlat to the wall and rafters
Anchor bolts. Ideal for monolithic structures.
Wooden dowels. Used for log houses and beams. But, they are always used with additional fasteners.
Staples.
Stud or fittings. It is used if the cottage is built from porous materials (aerated concrete, foam concrete).
Sliding mount (hinge). Tying in this way allows for the displacement of the rafter legs when the house shrinks.
Annealed wire (knitting, steel). Used as additional fastening In most cases.
2. Manufacturing of trusses or pairs
Installation is carried out in two ways:
- installation of beams directly on the roof. It is not used often, since it is problematic to carry out all the work, measurements, and trimming at height. But it allows you to completely do the installation yourself;
- assembly on the ground. That is, individual elements (triangles or pairs) for the rafter system can be assembled below and then raised to the roof. The advantage of such a system is faster execution high-altitude work. The disadvantage is that the weight of the assembled truss structure can be significant. To lift it you will need special equipment.
Advice. Before assembling the rafter legs, you need to apply markings. It is very convenient to use templates for these purposes. The rafter pairs assembled according to the template will be absolutely identical. To make a template, you need to take two boards, the length of each of which is equal to the length of one rafter, and connect them together.
3. Installation of rafter legs
The assembled pairs rise to the top and are installed on the Mauerlat. To do this, you need to make a gash at the bottom of the rafter legs.
Advice. Since the slots on the Mauerlat will weaken it, you can only make cuts on the rafter leg. To ensure that the cut is uniform and fits tightly to the base, you need to use a template. It is cut out of plywood.
Methods of fastening the rafter leg are shown in the figure.
Start installation rafter pairs needed from opposite ends of the roof.
Advice. To correctly install the rafter legs, it is better to use temporary struts and spacers.
A string is stretched between the fixed pairs. It will simplify the installation of subsequent rafter pairs. It will also indicate the level of the ridge.
If the rafter system is mounted directly on the roof of the house, then after installing the two outer rafter legs, the ridge support is installed. Next, the halves of the rafter pair are attached to it.
It is worth noting that the opinions of professionals differ on this issue. Some advise using a staggered fastening pattern, which will allow the increasing load to be distributed more evenly on the walls and foundation. This order involves installing one rafter in a checkerboard pattern. After part of the rafter legs is installed, the missing parts of the pair are mounted. Others insist that it is necessary to mount each pair in a sequential manner. Depending on the size of the structure and the configuration of the truss, the rafter legs are reinforced with supports and racks.
Nuance. Connect additional elements structures using cutting. It is preferable to fix them with construction staples.
If necessary, you can lengthen the rafter leg.
Methods for splicing rafter legs are shown in the photo.
Advice. The method by which the mauerlat is lengthened (cut at 90°) cannot be used in this case. This will weaken the rafter.
4. Installing the ridge of a gable roof
The roof ridge unit is made by connecting the rafter legs at the top.
Roof ridge structure:
- Method without using a support beam (see figure).
- Method using rafter beams. Timber is needed for large roofs. In the future, it can become a support for the rack.
- Method of laying on timber.
- More modern variety The method shown in the photo can be considered for making a ridge assembly.
- Cutting method.
After the rafter system is installed, we perform major fastening of all structural elements.
5. Installation of roof sheathing
The sheathing is installed in any case, and is designed for more convenient movement along the roof during work, as well as for fastening roofing material.
The sheathing pitch depends on the type of roofing material, for example:
- for metal tiles - 350 mm (the distance between the two lower boards of the sheathing should be 300 mm).
- for corrugated sheets and slate - 440 mm.
- under soft roof We lay a continuous sheathing.
Rafter system of a gable roof with an attic - video:
Conclusion
As you can see, despite its apparent simplicity, the installation of a gable roof rafter system contains many pitfalls. But, based on the recommendations given, you can build without any problems reliable design with your own hands.
All parameters must be specified in millimeters
B- Roof length.
Y- Height.
C— Overhang distance.
X— Roof width.
Y2- Extra height.
X2— Additional width.
This program will help you perform an accurate calculation of building materials for roofing: the number of rafters and sheathing boards, roofing material (roofing felt, glassine), quantity sheet material(metal tiles, slate, nulin or ondulin).
Our online calculator will calculate other useful roof dimensions.
The presented program performs calculations in two versions: type 1 - simple gable roofs, type 2 - gable roofs with 2 side gables.
If the designed roof has only one side gable, then in this case we perform calculations according to type 1, and then according to type 2. Based on the calculation results, you will be able to determine the required volume of materials: roofing, sheet, rafters and sheathing boards.
Otherwise, you will make a mistake in the calculation, since the program takes into account the cutouts for the side fronts when calculating the parameters of the main roof.
Based on the calculation results, you receive the volume and size of the material for one roof slope, and the entire volume and size will be indicated in parentheses.
When calculating the volume and useful dimensions of an additional roof, you receive two parameters in brackets: the volume and size of one or two additional roofs.
Important! It is worth considering that the program performs calculations over the entire roof area when determining the number of sheets of roofing material.
For example, it takes 7.7 sheets per row, and only 2.8 rows. Based on the calculation results, you will receive 3 real building rows.
If you want to get the exact number of sheets for the future roof, you need to reduce their height until you get a whole number of rows.
Don't forget to set the exact length of the overlap.
Important! In type 2 mode, when calculating the volume of material for the rafters of the main roof, the program does not take into account the cutouts for the side gables. This calculation of the gable roof truss system is related to the design of the program itself.
You can also use the remaining building material for the rafters to build or repair a house, otherwise you can make corrections to the calculations.
Exact calculation approximate cost roof depends on correct basic measurements.
Important! Don’t forget to purchase building materials with a 5-10% reserve for waste.
DIY gable roof
First of all, we need a diagram (drawing or design) of a gable roof, according to which we will make all the calculations (indicated above).
The procedure for constructing a roof is quite simple, but the sequence of certain steps must be followed.
Before installing beams or transfers for the future floor, you need to determine whether the attic will be built or just attic space. As a rule, for a simple attic it is enough to choose a 150x150 mm board. If you are planning to build an attic, then it is best to choose a beam with the same size. To increase the strength of the frame, beams or boards should be mounted exclusively on the walls.
The process of fixing the beams is carried out taking into account the release from the outer edge of approximately 400 mm to prevent precipitation or wind from getting under the roof.
We will use a board cut to 50X150 mm when arranging the attic frame, and fixation is carried out with roofing nails. To give the gable roof stability, it is necessary to carry out all measurements correctly, trying to eliminate errors.
Now we move on to assembling the truss structure, starting with the installation from the gables, using the method already described above. At the same time, we saw off the lower parts of the boards, which will give our rafter structure additional stability.
When the structure is fully erected for gable roof, we begin to cover with roofing materials.
Advantages of a gable roof:
- This design is quite simple to construct, which allows you to do all the work yourself without the expensive help of specialists;
- The building materials used are affordable;
- The large angle of inclination of the roof perfectly drains water during precipitation;
- Absence complex structures and kinks, greatly facilitate the construction and cladding of the roof.
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The strength of the roof directly depends on how accurately the calculation of the rafter system is made, in which the angle of inclination of the slopes and the length, as well as the cross-section of the beams, are important.
Choosing a rafter structure
The strength of the roof is determined not only by the material from which the rafters are made, but also by the pattern of their assembly. For example, someone may decide that metal trusses would be the most reliable solution for roofing, but remember that this will create additional stress on the walls and foundation, which will have to be reinforced. Therefore, lumber is often used for rafters, among which are timber, boards, and also strips of different sections for sheathing. Round timber is used less frequently.
Wood is quite durable, but it is very important to balance the roof area with the length and cross-section supporting elements. That is why the Mauerlat (supporting horizontal beams along the upper edge of the walls along the entire perimeter of the house) is selected with a large margin of safety. In addition, all parts are calculated so that they can withstand their own total weight along with the roof and additional temporary load (long-term or short-term). All this must be taken into account directly in the house design.
Regardless of the design, only certain elements are used in it, namely: rafter legs, racks, struts installed at an angle, and a ridge beam. Also necessary are crossbars and support beams, which provide rigidity to the roof frame. But since the fundamental factor is the roof area and its slope, calculations are made only regarding the rafters: their length, cross-section and angle to the horizon, as well as the distance between them. It is known that a triangle best resists loads, so this particular figure is formed using crossbars installed as cross members between the rafters of a gable roof.
