Simple geometry: calculating roof parameters


The gable roof has long become an architectural classic. The list of its advantages includes ease of installation, low maintenance costs and practicality in terms of the natural removal of rainwater and snow. To fully experience these advantages, it is necessary to correctly think over the roof project and calculate the dimensions. This is the only way to make the structure durable and maintain an attractive appearance for many years.

The main parameters of the gable roof

Selecting the optimal roof size is a complex process of finding a compromise between the desired appearance of the building and its safety requirements. In a properly designed roof, all proportions are close to ideal. The main parameters of a gable roof include the angle of inclination, the height of the ridge, the width of the roof and its overhangs.

Roof slope

Roof slope is a value that determines the position of the slope relative to the horizon line. The choice of this indicator is carried out at the design stage of the structure. Traditionally, both slopes of a gable roof are made with the same slope angles, but asymmetric varieties are also found.

Most often there are roofs with a slope of 20 ° to 45 °

The unit of measure for slope is degrees. Range 1 is accepted for roofs0-450... The larger the number, the sharper the structure, and vice versa, as the degree decreases, the roof becomes sloping. Depending on the slope, there are several types of roofs:

  • flat (less than 5 °), the advantages of which are low material consumption and ease of maintenance, and the disadvantages are the mandatory presence of a good waterproofing system and measures to prevent the accumulation of snow;
  • flat (up to 30 °), allowing the use of all existing materials as a roof covering, but more expensive in cost than flat;
  • steep (more than 30 °), capable of self-cleaning, but not resistant to wind load.

The tool for measuring the angle of the slope is an inclinometer. Modern models are equipped with an electronic scoreboard and a bubble level. When the device is oriented horizontally, the scale displays "0".

Manufacturers offer to purchase inclinometers with laser sensors that allow taking measurements at a distance from the object.

Photo gallery: roofs with different slope values

In a number of normative documents, for example, SNiP II-26-76 "Roofs", the slope is indicated as a percentage. There are no strict recommendations for a single parameter designation. But the value in percentage is very different from the option in degrees. So, 10 equals 1.7%, and 300 equated to 57.7%. For error-free and quick conversion of some units of measurement to others, special tables have been created.

Table: Relationship Between Slope Units

Slope, 0Slope,%Slope, 0Slope,%Slope, 0Slope,%
11,71628,73160,0
23,51730,53262,4
35,21832,53364,9
47,01934,43467,4
58,72036,43570,0
610,52138,43672,6
712,32240,43775,4
814,12342,43878,9
915,82444,53980,9
1017,62546,64083,9
1119,32648,74186,0
1221,12750,94290,0
1323,02853,14393,0
1424,92955,44496,5
1526,83057,745100

Ridge height

Another important roof parameter is the ridge height. The ridge is the upper point of the rafter system, located at the intersection of the slope planes. It serves as a support for the rafters, giving the roof the necessary rigidity, and allows you to evenly distribute the load on the entire structure. Structurally, it is a horizontal rib made of a wooden beam. If you imagine a gable roof in the form of a triangle, then the height of the ridge is the distance from the base to the top of the figure.

According to the rules of geometry, the height of the ridge is equal to the length of the leg of a right-angled triangle

Total roof width and overhangs

The total width of the roof is determined by the width of its box (the size of the rafter system) and the width of the eaves.

The overhang is the part of the roof protruding from the walls. The overhang width is the distance from the intersection of the load-bearing wall with the roof to the bottom of the roofing sheet. Despite its modest dimensions and a small percentage in the total area, the overhang plays a key role in the operation of the house. The cornice protects the outer walls from atmospheric precipitation, keeping their coating intact. It creates a shade in the local area in the summer heat and shelters people during a snowfall. In addition, the overhang facilitates the drainage of rainwater from the roof.

The required size of the eaves overhang B is obtained by lengthening or building the rafter legs

There are 2 types of overhangs, differing in location and width:

  • pediment - a small in width section of the roof slope, located on the side of the pediment;
  • cornice - a wider overhang that is located along the roof.

To protect the lower surface, the overhang is sheathed with edged board, siding or soffits

Photo gallery: roofs with different overhang widths

Factors affecting roof parameters

The first stage in the construction of a roof is the development and preparation of a technical plan. In it, it is necessary to take into account all the nuances that will affect the life of the roof. The design parameters are determined when considering a group of factors: the climatic characteristics of the region, the presence of an attic and the type of roofing material.

Depending on the area in which the building is located, it can be influenced by various natural forces and loads. Among them are wind, snow pressure and water impact. You can determine their value by contacting a special construction organization that performs such surveys. For those who are not looking for simple ways, there is an option to independently determine the parameters.

Wind load

The wind creates significant pressure on the walls and roof of the building. The air stream, which meets an obstacle in its path, is divided, rushing in opposite directions: to the foundation and the overhang of the roof. Excessive overhang pressure can cause the roof to break. To protect the building from destruction, the aerodynamic coefficient is estimated, which depends on the angle of inclination of the slope.The steeper the slope and the higher the ridge, the stronger the wind load per 1m2 surface. In this case, the wind tends to overturn the roof. The hurricane wind affects gently sloping roofs differently - the lifting force raises and carries away the crown of the house. Therefore, for areas with low to moderate wind strength, roofs with any ridge height and slope can be designed. And for places with strong gusts of wind, low-slope views from 15 to 25 ° are recommended.

In addition to the horizontal impact, the wind exerts pressure in the vertical plane, pressing the roofing material against the sheathing

Calculating the wind load on a gable roof

The calculated wind load is the product of two components: the standard value of the parameter (W) and the coefficient (k), which takes into account the change in pressure depending on the height (z). The guideline value is determined using a wind load map.

The territory of the country is divided into 8 zones with different nominal wind load values

The height factor is calculated from the table below based on the respective terrain:

  1. A - coastal areas of water bodies (seas, lakes), deserts, steppes and tundra.
  2. B - urban area with obstacles and buildings with a height of 10–25 m.
  3. С - urban area with structures from 25 m in height.

Table: coefficient for calculating wind load

Height z, mCoefficient k for different types of terrain
BUTINFROM
up to 50,750,500,40
101,000,650,40
201,250,850,55
401,501,100,80
601,701,301,00
801,801,451,15
1002,001,601,25
1502,251,901,55
2002,452,101,80
2502,652,302,00
3002,752,502,20
3502,752,752,35
4802,752,752,75

Let's look at an example. It is necessary to determine the calculated wind load and make a conclusion about the acceptable roof slope. Initial data: region - Moscow city with terrain view B, house height 20 m.We find Moscow on the map - zone 1 with a load of 32 kg / m2... By combining the rows and columns of the table, we find that for a height of 20 m and a type of terrain B, the desired coefficient is 0.85. Multiplying two numbers, we determine that the wind load will be 27.2 kg / m2... Since the obtained value is not large, it is possible to use a slope of 35–45 °, otherwise the slope angle must be taken at 15–25 °.

Snow load

Masses of snow accumulating on the roof exert a certain pressure on the roof. The larger the drifts, the greater the load. But not only the pressure of the snow is dangerous, but also its melting when the temperature rises. Average weight of freshly fallen snow per 1 m3 reaches 100 kg, and in raw form this figure increases threefold. All this can cause deformation of the roof, a violation of its tightness, and in some cases lead to the collapse of the structure.

The greater the slope of the slope, the easier it is for snow deposits to be removed from the roof. In areas with heavy snowfall, a maximum slope steepness of 60º should be assumed. However, the construction of a roof with a slope of 45º contributes to the natural removal of snow.

Heat from below melts snow, increasing the risk of leaks

Calculation of snow load on a gable roof

The value of the snow load is obtained by multiplying the average load (S), characteristic for a certain type of terrain, and the correction factor (m). The average S value is found from the snow load map of Russia.

The territory of Russia includes 8 snow regions

The correction factor m varies depending on the slope of the roof:

  • with a roof angle of up to 250 m is 1;
  • average value of m for a range of 250–600 equals 0.7;
  • for steep roofs with an angle of more than 600 coefficient m is not involved in the calculations.

Let's look at an example. It is necessary to determine the snow load for a house with a slope angle of 350located in Moscow. From the map we find that the required city is located in zone 3 with a snow load of 180 kg / m2... The coefficient m is taken equal to 0.7. Therefore, the required value is 127 kg / m2 will be obtained by multiplying these two parameters.

The total load, consisting of the weight of the entire roof, snow and wind loads, should not be more than 300 kg / m2. Otherwise, you should choose a lighter roofing material or change the slope angle of the slope.

Roof type: attic or non-attic

There are 2 types of gable roofs: attic and non-attic. Their names speak for themselves. So, the attic (split) roof is equipped with a non-residential attic, and the attic (combined) roof is equipped with an exploited attic. If you intend to use the space under the roof for storing items that are not used in everyday life, then there is no point in increasing the height of the roof ridge. Conversely, when planning in an under-roof living room, the height of the ridge should be increased.

The height of any type of roof must be sufficient for internal repairs.

For non-residential roofs, the height of the ridge is determined by fire safety rules. Building regulations state that the attic must contain a through passage 1.6 m high and 1.2 m long. For residential roofs, the height is set based on the convenience of living and the problem-free placement of furniture.

Type of roofing material

Until recently, the construction market offered only a few types of roofing materials. It was traditional slate and galvanized steel sheet. Now the assortment has been significantly replenished with new products. When choosing a material for a roof, there are several rules to consider:

  1. With a decrease in the size of piece roofing materials, the angle of inclination is increased. This is due to the large number of joints that are potential leak points. Therefore, they try to make the descent of precipitation as fast as possible.
  2. For roofs with a low ridge height, it is preferable to use rolled roofing materials or large sheet canvases.
  3. The more the roofing material weighs, the steeper the roof slope should be.

The range of possible slopes is described in the manufacturer's instructions for installing the roof.

Table: Recommended roof pitch for different materials

Material typeMinimum slope, 0Note
Metal tile22Theoretically, it is possible to mount on a roof with an angle of 110–120, but for better sealing, choose a higher slope
Corrugated board5When the angle of inclination is changed to a larger side, the overlap of one sheet on another is increased
Asbestos-cement slate25If the slope is less than recommended, snow will accumulate on the roof, under the weight of which the roofing material will collapse
Soft roll roofing (roofing felt, ondulin)2The minimum draft angle depends on the number of layers: for one layer 20, and for three - 150
Seam roof7For roofs with a slight slope, it is recommended to purchase a double standing seam

Cost of a gable roof

It is logical that with an increase in the slope of the slope, the roof area increases. This leads to an increased consumption of sawing and roofing materials and components (nails, screws) for securing them. The cost of a roof with an angle of 60 ° is 2 times more than creating a flat roof, and a slope of 45 ° will cost 1.5 times more.

The greater the total load on the roof, the larger the cross-section of the timber is used for the rafter system. With a slight slope of the roof, the pitch of the lathing is reduced to 35–40 cm or the frame is made solid.

Calculation of roof dimensions without errors will save the family budget

Video: rafter system and roof parameters

Calculation of roof parameters

An online calculator can be used to quickly calculate roof dimensions. Initial data (dimensions of the base of the building, type of roofing material, lifting height) are entered into the fields of the program, and the result is the required value of the slope of the rafters, roof area, weight and amount of roofing material. A small minus - the stages of the calculation are hidden from the user.

For a better understanding and clarity of the process, you can carry out independent calculations of the parameters of the roof. There is a mathematical and graphical method for calculating the roof. The first is based on trigonometric identities. A gable roof is represented as an isosceles triangle, the dimensions of which are the parameters of the roof.

Trigonometry formulas can be used to calculate roof parameters

Calculation of the slope angle of roof slopes

The initial data for determining the slope angle is the selected roof height and half of its width. As an example, consider a classic gable roof with symmetrical ramps. We have: ridge height 3 m, wall length 12 m.

Dimensions c and d are usually called the laying of the roof.

Slope calculation sequence:

  1. We divide the conditional roof into 2 right-angled triangles, for which we draw a perpendicular from the top to the base of the figure.
  2. Consider one of the right-angled triangles (left or right).
  3. Since the construction is symmetrical, the projections of the slopes c and d will be the same. They are equal to half the length of the wall, i.e. 12/2 = 6 m.
  4. To calculate the slope angle of the slope A, we calculate its tangent. From the school course, we remember that the tangent is the ratio of the opposite leg to the adjacent one. The opposite side is the height of the roof and the adjacent side is half the length of the roof. We get that the tangent is 3/6 = 0.5.
  5. To determine what angle the resulting tangent has, we use the Bradis table. Having found the value 0.5 in it, we find that the slope angle is 260.

To convert tangents or sines of an angle to degrees, you can use simplified tables.

Table: determination of the slope of the slope through the tangent of the angle for the range of 5-600

Roof inclination angle, 0Tangensugla ASinusangle A
50,090,09
100,180,17
150,270,26
200,360,34
250,470,42
300,580,5
350,70,57
400,840,64
451,00,71
501,190,77
551,430,82
601,730,87

Calculation of the rise of the gable roof and the height of the ridge

The height of the roof is closely related to the steepness of the slope. It is determined in the opposite way to the method of obtaining the slope. The calculation is based on the angle of inclination of the roof, which is suitable for a given area, depending on the snow and wind load, the type of roof.

The more the slope, the more free space under the roof

The procedure for calculating the roof lift:

  1. For convenience, we divide our "roof" into two equal parts, the axis of symmetry will be the height of the ridge.
  2. We determine the tangent of the selected angle of inclination of the roof, for which we use Bradis tables or an engineering calculator.
  3. Knowing the width of the house, we calculate the size of its half.
  4. We find the height of the slope by the formula H = (B / 2) * tg (A), where H is the height of the roof, B is the width, and A is the slope angle of the slope.

Let's use the given algorithm. For example, you need to set the height of the gable roof of a house with a width of 8 m and an angle of inclination of 350... Using the calculator, we find that the tangent is 350 is 0.7. Half the width of the house is 4 m. Substituting the parameters into the trigonometric formula, we find that H = 4 * 0.7 = 2.8 m.

Competently calculated roof height gives the house a harmonious look

The above procedure refers to the definition of the roof lift, i.e. the distance from the bottom of the attic floor to the support point of the rafter legs. If the rafters protrude above the ridge beam, then the total height of the ridge is determined as the sum of the roof lift and 2/3 of the thickness of the rafter beam. So, the total length of the ridge for a roof with a rise of 2.8 m and a beam thickness of 0.15 m is 2.9 m.

In places where ledges are cut for assembly with a ridge run, the rafters are reduced by 1/3

Calculation of the length of the rafters and the width of the roof

To calculate the length of the rafters (hypotenuse in a right triangle), you can go in two ways:

  1. Calculate the size using the Pythagorean theorem, which says: the sum of the squares of the legs is equal to the square of the hypotenuse.
  2. Use trigonometric identity: the length of the hypotenuse in a right-angled triangle is the ratio of the opposite leg (roof height) to the sine of the angle (roof slope).

Let's consider both cases. Let's say we have a roof height of 2 m and a span width of 3 m.We substitute the values ​​in the Pythagorean theorem and we find that the required value is equal to the square root of 13, which is 3.6 m.

Knowing the two legs of the triangle, you can easily calculate the hypotenuse or the length of the slope.

The second way to solve the problem is to find the answer through trigonometric identities. We have a roof with a slope angle of 450 and a lift height of 2 m.Then the length of the rafters is calculated as the ratio of the lift number 2 m to the sine of the slope 450, which equals 2.83 m.

The width of the roof (in the figure Lbd) is the sum of the length of the rafters (Lc) and the length of the eaves (Lкc). And the length of the roof (Lcd) is the sum of the length of the wall of the house (Ldd) and two gable overhangs (Lfs). For a house with a box width of 6 m and overhangs of 0.5 m, the roof width will be 6.5 m.

Building codes do not regulate a clear value for the length of the slope, it can be selected in a wide range of sizes

Calculation of the roof area

Knowing the length of the slope and the width of the roof, you can easily find its area by multiplying the indicated dimensions. For a gable roof, the total roof area is equal to the sum of the areas of both slope surfaces... Let's dwell on a specific example. Let the roof of the house be 3 m wide and 4 m long.Then the area of ​​one slope is 12 m2, and the total area of ​​the entire roof is 24m2.

Incorrect calculation of the roof area can lead to additional costs when buying roofing material

Calculation of materials for the roof

To determine the amount of roofing materials, you need to arm yourself with the roof area. All materials are overlapped, so when buying, you should make a small margin of 5-10% of the nominal calculations. The correct calculation of the amount of materials will significantly save the budget of construction work.

General rules for calculating sawn timber:

  1. Dimensions and section of the Mauerlat. The minimum possible cross-section of the bar is 100 × 100 mm. The length corresponds to the perimeter of the box, the margin for connections is set at around 5%. The volume of the bar is obtained by multiplying the dimensions of the section and the length. And if you multiply the resulting value by the density of the wood, then there is the mass of the lumber.
  2. The size and number of rafters. The calculation is based on the total load on the roof (pressure of the roofing cake, snow and wind). Suppose the total load is 2400 kg / m2... The average load per 1 m of rafters is 100 kg. Given this, the footage of the rafters will be equal to 2400/100 = 24 m. For a rafter length of 3 m, we get only 8 rafter legs or 4 pairs. The cross-section of the rafters is taken from 25x100 mm and above.
  3. The amount of material for the lathing. Depends on the type of roofing: for bituminous tiles, a continuous crate is built, and for corrugated board or asbestos-cement slate, thinned.

Let us consider the calculation of roofing materials using the example of metal tiles. It is a sheet material that is mounted on the roof in one or more rows.

On slopes longer than 4.5 m, it is recommended to lay the metal tile in 2 rows for ease of work

Calculation sequence:

  1. Determination of the number of sheets. The sheet of metal tile has a full 1180 mm and a working width of 1100 mm. The latter is smaller than the real one and is not taken into account in the calculation, since it is used to overlap the joints. The number of sheets is defined as the ratio of the total width of the roof (including overhangs) to the effective width of the sheet. Moreover, the result of division is rounded up to an integer value. So, for a roof with a slope width of 8 m and a sheet of Monterrey metal tiles with a width of 1.1 m, the number of sheets is calculated according to the formula: 8 / 1.1 = 7.3 pcs, and taking into account rounding 8 pcs. If the canvas is laid in several vertical rows, then the length of the slope is divided by the length of the roofing sheet, taking into account the overlap between the sheets of up to 15 cm.Considering that the roof is gable, the value is doubled, i.e. 16 sheets are required in total.
  2. Determination of the total area. To determine the total area of ​​the roofing material, the number of canvases is multiplied by the total area (product of the full width and length) of one sheet. In our case, 8 * (1.18 m * 5 m) = 47.2 m2... For gable structures, the result is multiplied by two. We get that the entire roof area is 94.4 m2.
  3. Determination of the amount of waterproofing. A standard roll of waterproofing material has an area of ​​65m2 without overlap. The number of rolls is obtained by dividing the total roof area by the area of ​​the film, i.e. 94.4 m2/ 65 m2 = 1.45 or 2 full rolls.
  4. Determination of the number of fasteners. 1 m2 the roof has 6-7 screws. Then, for our situation: 94.4 m2 * 7 = 661 self-tapping screws.
  5. Determination of the number of extensions (skates, wind bars). The total footage of the planks is 2 m, and the working area is 1.9 m due to partial overlap. Dividing the length of the slope by the working length of the slats, we get the required number of extensions.

Video: calculating materials for a gable roof using an online calculator

The graphical method for determining the parameters of the roof is to draw it on a reduced scale. For him you will need a piece of paper (plain or millimeter), a protractor, a ruler and a pencil. Procedure:

  1. The scale is being matched. Its optimal value is 1: 100, because for every 1 cm of paper sheet there is 1 m of the structure.
  2. A horizontal line is drawn, the length of which corresponds to the base of the roof.
  3. The midpoint of the segment is located, from the point of which a perpendicular is drawn upward (a vertical line at an angle of 900).
  4. With the help of a protractor, the required roof angle is laid from the border of the roof base and an inclined line is drawn.
  5. The intersection of the inclined line with the perpendicular gives the height of the roof rise.

Video: manual calculation of materials for a gable roof

The first thing that pays attention to is the visual appearance of the roof. Architects make sure that the roof is in harmony with the facade of the building. But beauty alone is not enough. It is important to correctly calculate the parameters so that the structure is durable and functional. Neglecting snow and wind loads, installing rafters at the wrong angle can cause the roof to collapse. And an incorrect determination of the roof area will lead to additional costs for the purchase of missing materials. Therefore, you should take a responsible approach to calculations, paying attention to all the nuances.


How to determine the slope of the roof in degrees

In order for the roof of the building to fully perform all the functions assigned to it, it is necessary to take into account a number of parameters when creating it. One of the most important parameters of the roof is its slope, which ensures the removal of precipitation from its surface and affects the ability to withstand external loads. How to calculate the slope of the roof, and will be discussed in this article.


Features of the device of gable roofs

Gable roofs are two rectangular inclined planes (slopes), which are supported by the rafter system. The side parts are made deaf or windows and cladding are installed on them. The main parameters of such a roof are: the angle of inclination and the location of the ridge relative to the center line passing through the walls perpendicular to the slopes. That is, the gable structure does not have to have the same slope of the slopes or have a symmetrical appearance.

Asymmetrical gable roof

Many original projects use an asymmetrical design of slopes to take into account some climate features, or in order to improve the design of the facade. It is worth noting that such solutions are very original, but in practice they are quite difficult to implement. This is due to the following reasons:

  • The load on the walls and foundation increases in the place where the roof ridge is displaced. As a result, calculations can be significantly complicated, especially when using heavy roofing materials such as slate or ceramic tiles.
  • It is required to produce separate structural elements for each slope, which can significantly increase the construction time.
  • The roof at large slope angles can be significantly influenced by the pressure of wind currents. Therefore, it will be necessary to take into account the preferred direction of the winds when calculating.

The main elements of the pitched roof system

Before making rafters on a gable roof, you need to create a project, and also study all the structural elements. You will need to design the following main nodes:

  • Mauerlat... Provides the transfer of the load of the roof structure to the load-bearing walls of the object, creating its uniform distribution The timber is made from hardwood such as larch, oak, ash. The minimum allowable section is 100x100 mm. It is allowed to use not only solid timber, but also glued timber, but with a section of 100x150 mm.
  • Rafters... The main element of the structure, which is designed to form a supporting frame, take the load of the roofing material through the sheathing and transfer the load to the Mauerlat. The distance between the rafters of a gable roof is between 0.6 and 1.2 m, depending on the weight of the roofing material and the amount of precipitation in a particular area.
  • Tightening... A special design used to fix two inclined beams of slopes at a given angle of inclination, which is fixed at a level slightly above the beams or slightly below the ridge. It is used in layered types of roofs.
  • Rack... It is a vertically installed and firmly fixed element that performs the load-bearing functions of the roof. It is usually installed on the walls of the building for partial transfer of the roof load. Provides additional rigidity to the structure.
  • Run... There are two types: side and ridge. The lateral one is a bar resting on the racks and parallel to the ridge beam. Allows to prevent the slope from bending under significant loads. The ridge run is installed along the line of abutment of one slope to another and serves as a support for the ridge.
  • Brace... Represents auxiliary supports for racks, which are located at an angle of 45 0 to the load-bearing ramps in order to increase the contact area with the racks and reduce the risk of deformation of the ramp.
  • Sill... Serves as a fulcrum for the brace and rack.
  • Lathing... It is used to fix the rafter system in the transverse direction, transfer the load of the roofing material and its fastening, as well as provide resistance to loads in the purlins between the load-bearing beams.

Structural elements of a gable roof

Types of gable frame systems

Do-it-yourself rafters for a gable roof can be hanging or layered. The hanging structure rests only on the side walls. Therefore, it is used only for installation on buildings with a distance between the walls of no more than 12 m. To prevent collapse of the structure, auxiliary horizontal or vertical elements are used to increase the strength and reliability of the structure. The most successful elements are: brace, crossbar or tightening. They can be attached not only to the ridge beam, but also directly to the pitched beams themselves at certain angles.

For buildings with load-bearing internal walls, it is allowed to install layered pitched beams due to the possibility of installing additional supports. As a result, the limitation of the hanging system can be avoided and load-bearing beams can be installed even when the distance between the walls is more than 10 m. The spacing between the supports is selected for each structure individually, taking into account the purpose of the building and the use of the attic space.

Rafter system of layered type

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Types of classic gable roofs

If everything is clear with the basic device, then it is still necessary to understand the specific solutions. Buildings are diverse and each requires specific solutions. There are a lot of different schemes, but they can all be divided into two types according to one criterion: ridge fastening. Let's consider them in more detail.

Layered rafter system

It should be noted right away that this design is loved by roofers for its reliability and easy installation.

The basis for attaching the rafter pairs in this system are maurlat and ridge girder, which is installed on vertical beams, which, in turn, are attached to the bed.

Thus, the following picture is obtained - each pair of roof rafters is rigidly attached in three places: two knots on maurlats and one on a ridge run. The result is a very sturdy construction with an excellent margin of safety.

Depending on the length of the rafters and the angle of inclination of the slopes, the structure can be supplemented with reinforcing elements: puffs, crossbars, struts, rafters, etc. Also, in the absence of a capital internal partition in the building, it is permissible to use a ceiling beam as a bed.

Hanging rafter system

The fundamental difference from the layered system is that only maurlats are used as a support for the rafters, i.e. wooden beams, rigidly fixed at the ends of the outer walls of the house. Above, on the ridge, the rafters have no support, they only hammer together, and, as it were, “hang” in space - this is the defining criterion of this technology.

This system is used when erecting buildings of small width, as a rule, it is no more than 7-8 meters. With an increase in these values, with this technology, it will be necessary to install additional elements - crossbars and tightenings, which to some extent will transform the forces of pressure on the outer walls and distribute the load more evenly.

The wider the building, the more reinforcing elements the roof will be equipped with.... The diagram above clearly shows the ratio of the width of the covered span to the number of additional parts.


Gable roof

It is necessary to find out everything related to the construction of the roof at the design stage. The most popular type of roof for most developers remains the classic gable roof, that is, a roof with two slopes.

Why this particular option? Because a gable roof has a number of undeniable advantages:

  • resistance to wind and snow loads
  • rapid runoff of precipitation
  • attractive appearance, the ability to use a variety of design techniques
  • a fairly simple design
  • the possibility of self-erection
  • the ability to equip a living room in the under-roof space - an attic
  • small consumption of materials.

Nevertheless, building a gable roof with your own hands implies the possession of certain skills and knowledge, it will be difficult to build such a roof without which it will be difficult. In addition, even before the start of construction, it is necessary to carry out accurate calculations of the roof. We will dwell on this separately after we describe the main stages of construction.

Materials required for installation:

  • Edged board with dimensions 150x50 mm
  • Wooden beam with a section of 150x150 mm
  • Fastening material: nails, screws, bolts, screws
  • Materials for the device of the roofing cake (waterproofing, vapor barrier, insulation)
  • Roofing materials (slate, corrugated board, metal, etc.).

The gable roof structure consists of two surfaces (two slopes) located at a certain angle to each other with one line of contact. The lower edges of the slopes rest on the walls of the house. The side mounts are called gables, and the line of contact of the slopes is the ridge.

The length and width of the slopes, the angle at which they are located, the length of the roof overhang can be very different and depend only on the project. Gable roofs can be:

  • with hanging rafters
  • with inclined rafters
  • with different slope angles
  • with various sizes of eaves.

The simplest design option implies that there will be a cold attic under the roof, intended for household needs. But this space can be used in a more practical way and equip a living space in it. In this case, a gable sloping roof can be built, windows are mounted in the slopes, or an extension can be added. However, it should be borne in mind that such projects are much more expensive, because they require high-quality insulation, careful insulation and, accordingly, higher costs of materials.

The structure of the gable roof consists of load-bearing beams covered with a crate, on which the roofing material is attached. Rafters and lathing are made of wooden beams and boards fastened together with ordinary nails, bolts, and sometimes special metal connecting elements. Metal profiles can also serve as rafters, allowing you to cover large spans without the use of additional stacks and struts. Such structures are prepared according to the drawings in the factory and have high accuracy, which allows installation by workers who do not have high qualifications. However, they are quite heavy, and this puts a lot of pressure on the walls of the building and makes it difficult to lift the structures.

The device of a gable roof is quite simple, it allows you to adapt it to the characteristics of a particular house to perform additional functions. For example, the ridge can be lengthened, as a result of which longer slopes extending far beyond the side walls serve as the roof of additional buildings, a veranda or a garage.

Only coniferous wood is selected for construction. Slats, boards and beams are used. The material should not be wet (moisture content is 20%). Otherwise, a high moisture content can lead to deformation of the main units and damage to the roof. Also, wood materials must be antiseptic.

The work takes place in three stages:

  • installation of supporting structures - beams
  • installation of the lathing
  • decking of roofing materials.

The installation of the roof begins with the installation of transfers (floor beams). First, the timber is laid - strictly on the drains of the walls, the strength of the entire structure depends on the accuracy of the laying. The beams are laid in such a way that the roof mounted on them protrudes at least 40 cm from the edge of the wall - this will provide reliable protection from precipitation and wind.

Then, over the entire area of ​​the house, an edged board is attached to the floor beams. If you do not plan to use the attic as a living space, boards of 50x150 mm are used, otherwise a large thickness of the boards is chosen. In the future, they can be used both as the floor of the attic room, and as a support for the attic racks. The board is fixed with nails or screws.

After fixing the racks, it is the turn of the rafter system. First of all, gables are installed. This is a continuation of the end walls of the house, flowing smoothly into the roof triangle. The top of these triangles are the points on which the ridge will rest. On the upper trim of the gables, boards 150x50 mm are placed on the edge.

It should be remembered that if you plan to equip an attic room, the rafter structure must be reinforced with strapping and fixing the edged board, laid with the edge up. These measures are necessary to strengthen the structure for the safety of the home owners.

You should also choose the right material for the rafters. The beams must be straight and free from knots. For the rafter "legs" use high-strength coniferous wood.

Naturally, the material for the rafters should also be selected correctly: smooth beams without cracks and knots. As a rule, high-strength pine wood is used for the rafter "legs". But it is not recommended to use twisted wood - in order to avoid the formation of irregularities in the construction of the roof.

The roof rafters should be attached as tightly as possible to the gables and fit snugly against them. For this, the lower parts of the boards are sawn off. This is done in the following way: the board is placed with an edge on the pediment part, in the places of contact with the translation, a line is drawn along which the cut is made. The result is a "thrust bearing" beveled at the required angle, which will lie tightly on the translation plane along its entire length. The upper part of the rafters is cut in a similar way. As a result, and at the top point, they fit snugly against each other.

The rafters are attached to the base with self-tapping screws or nails, and their upper part, in addition, is fixed with a metal bar or corner. Finally, the upper elements of the truss structure are fixed with a crossbar. The crossbar at the same time also acts as the ceiling of the attic. To give the rafters even greater rigidity, they can be fixed on top with metal plates.

After strengthening, the verticality of the pediments must be checked. And their tops, which must correspond to the same level. The final fastening with nails, staples and soft wire is carried out only after checking the verticality of the gables and leveling the level of the tops of the rafters.
When the process of installing the rafters ends, the structure is reinforced with struts to prevent them from sagging and increase rigidity. The braces are attached at one end to the rack, and the other to the middle of the rafter leg. Before nailing the brace to the rafter leg, a groove is cut out at this end of the brace.

After that, a lathing of ordinary slats with a section of 25x25 mm is laid on the rafters. To prevent damage to the roofing material after shrinkage of sawn timber, the lathing is laid apart. The type of lathing, its pitch depends on the selected roofing material. The installation of the lathing is carried out with projections above the gables by 300-400 mm.

On this, the work on the construction of the roof frame can be considered complete, further actions concern already roofing materials.

Before laying the roof directly, it is necessary to prepare preliminary layers: steam and waterproofing, insulation. This stage is also associated with calculations, the weight of the roofing cake must be calculated so that the roof can withstand its own weight, and the weight of the materials laid on it, and additional loads in the form of snow, wind and rain.

Additional layers are mounted inside the structural frame, which is why they are called frame pie. Properly installed, this "pie" increases the lifespan of the roof, keeps the house warm, reduces heating costs, and protects the room from moisture penetration. All layers are connected to each other, but fulfill their own purpose. Mistakes made during the installation of layers lead to a reduction in the life of the roof and the entire house and to a decrease in performance.

Correctly assembled roofing cake will prevent many problems from arising:

  • reduce heat loss
  • will not allow condensation to appear
  • eliminates the possibility of ice and icicles.

Insulation - used to reduce heat loss. Effective roof insulation is one of the basic requirements for quality residential buildings. It is especially important to have insulation for roofs provided for living space. In this case, the insulation not only prevents the appearance of condensation and minimizes heat losses through the roof, but also reduces them on the floor located below. As a result, heating costs are reduced by 20-50%, in the hot season, the roof space heats up less, and the room receives additional sound insulation.

Insulation is installed between the rafters. The required thickness in most regions of Russia according to SNIP II-3-79 * is 250 mm. The choice of material remains with the developer. Currently, the market offers a variety of both well-known and new materials, differing in quality, weight, ease of installation and price: from glass wool and foam to expanded polyester.

Vapor barrier and waterproofing

Vapor barrier prevents steam from entering the insulation from indoor spaces. For its device, a film is attached to the supporting wooden elements from the inside. Fastening is done with a mechanical stapler with staples or galvanized nails with flat heads. The film must be laid with an overlap of 10-15 cm, both vertically and horizontally. Separate strips of the roll must be tightly fastened to each other with a connecting tape. The ceiling of living quarters should not touch the vapor barrier, therefore, after installation, the film is fixed with slats.

Waterproofing, on the other hand, acts as a barrier for condensation that forms on the inner surfaces of roofing materials. The film is fixed horizontally over the rafters. The width between the rafters should not exceed 1.2 meters. The sagging of the waterproofing film up to 2 centimeters is permissible, but it should not come into contact with the insulation. Therefore, before the roofing material is installed, after fixing the film on the rafters, counter-battens are nailed.

Another essential way to deal with dampness is to ventilate the space. Moist air is removed from the roof space either by natural draft or by special ventilation valves. The air must pass through the space formed by the structural elements - the battens and counter battens. Arrangement of the ventilation system requires additional costs, but they are justified, since they significantly extend the life of the roof.

The attic space is often used to house various ventilation ducts and ducts.
Roofs of this type can be installed not only with wooden rafters and trusses, but also with elements made of reinforced concrete or steel. However, the installation of such structures is associated with many difficulties and it will not be possible to build a gable roof from them on your own.

Gable roofs do not restrict builders in the choice of roofing material. A gable roof can be made of flexible tiles, metal tiles, galvanized and copper sheets, slate, corrugated board, corrugated bitumen sheet, natural tiles, etc. The choice of material depends on the wishes of the owners of the house, and the installation in each case must meet its own individual requirements.

Let's return to the question of calculating the roof. Construction requires utmost precision and correct calculations. Some of them can be performed using electronic calculators offered by construction sites. But a really accurate calculation can only be done "manually", taking into account the characteristics of a particular object.

The concept of calculating the roof includes the height, slope, area, the amount of required materials. Figures are needed not only to match the design documentation and theoretical calculations. They help you understand how much of what material is needed. In addition, taking into account the characteristics of the slopes will help with the selection of material for the roof.

Calculating a gable roof is much easier than calculating most other structures.

Without proper slope, precipitation will collect on the roof. The slope calculation gives an idea of ​​the height of the ridge rise and allows you to calculate the amount of material required.

The tilt angle can be between 11 ° and 70 °, however, tilting above 45 ° is impractical. A steep slope is not needed in warm and dry climates. And areas with snowy and cold winters require a large slope. An angle of 45 ° relieves the roof from the snow load, but increases the wind pressure. In this case, the lathing and rafters need to be strengthened. A larger slope requires more roofing material.

To a large extent, this indicator also depends on the choice of material for roofing work. For example, metal roofing or roll materials require a slope of 15-27 °.

In the following table, the slope is shown in degrees and percent, and in the last column, the roof lift coefficient is given, which is equal to the rise of the ridge to a height of 1 meter.

Calculation example:
House 8 m wide with a roof slope of 40 °. Half the width (4 m) is multiplied by the ridge factor taken from the table. For 40 °, it will be 0.839.
We get 0.839 * 4 = 3.356.
The rise of the ridge of such a roof will be 3.356 meters.

The importance required to find out the amount of roofing material. Likewise, the selection of the drainage system, the diameters of the drainpipes and gutters depends on the angle of inclination and on the area of ​​the roof. A slope with an area of ​​50 m2 will cost a chute with a diameter of 125 mm. And an area of ​​100 m2 will require gutters with a diameter of 150 mm. Downpipes are calculated as follows: for every 10 m of gutter - one downpipe.

If the roof consists of two equal parallelograms, the calculation of its area is not difficult. The height of the parallelogram (a) is multiplied by the width (b), then the resulting figure is multiplied by 2 to get the total area:
ab + ab = 2ab = S total

It should be noted that the material must be purchased with a margin, since its sheets are always overlapped. The amount of overlap depends on the selected material. It is important to remember that the calculations are carried out not along the walls, but along the overhangs of the cornice.

It is impossible to neglect such calculations, this leads not only to unnecessary expenditure of funds, but also to the fact that the roof can be damaged or destroyed already during the operation of the house. It is quite possible to make a calculation of a gable roof on your own, while more complex roof shapes require a professional approach.


Design of roof systems and rafters

Designing a rafter system is a rather complex task that requires special skills and knowledge. To do this, it is necessary to correctly calculate the snow and wind, the optimal weight of the system.

Therefore, the greatest efficiency and durability of a built house can be achieved if the calculation and drawing of the rafter system is performed by a competent qualified specialist with experience in performing such work.

The most important points to consider when designing a roof are:

  • Roof type
  • Slope angles
  • The material used to cover the roof
  • selection of rafter section
  • Structural analysis of the rafter system.

Type of roof being erected Angles of inclination of the slopes Material used for covering the roof selection of the rafter section Calculation of the structure of the rafter system.

At the same time, the slope of the slopes also affects the calculation of the strength of the supporting structure and the choice of material with which the roof will be covered.

Most of these materials directly affect the design of the rafter system, therefore, the material for the coating must be selected at the design stage.

The rafter structure should be carefully calculated when designing the roof, since the shortcomings made in assessing the loads can cause both deformation of the rafter structure and violation of the roof covering during operation, and the collapse of the entire roof.

The supporting structures of the roof, consisting in the case of a pitched roof, of sheathing and rafters, ensure its stability and strength.

The structural layout of the rafters depends on the following parameters:

  • Roof shape
  • The presence of internal supports and their location
  • The length of the space to overlap.

When making a drawing of rafters, it should be borne in mind that rafters or trusses of rafters are hanging and layered (the most widespread type).

Most often, the structure of the rafters is made in the shape of a triangle, which provides maximum rigidity and economy.

Complex rafter trusses include a number of different additional elements, such as:

  • Rafter beams, also called rafter legs
  • Puffs
  • Rigeli
  • Racks
  • Braces, etc.

Let's take a closer look at the two main types of rafters:

  1. Reinforced rafters are installed in houses where the load-bearing wall is the middle one. They include two rafter legs, the lower ends of which rest on the Mauerlat - load-bearing bars, and the upper ends on the ridge run, which is supported by the racks. The uprights are installed on a bench located on the load-bearing inner wall. The Mauerlat and the bed are used to distribute the load on the walls. In the absence of longitudinal internal walls, the rafters should be supported on transverse internal walls or on pillars, the distance between which does not exceed 6.5 meters. With one additional support, the width of the room to be covered can be increased up to 12 meters, and with two supports - up to 15 or 16 meters. The increase in the span complicates the design, since it becomes necessary to introduce additional, such as struts and struts, which make it possible to increase the stability and lateral rigidity of the rafter system, turning the rafter structure into a truss.
  2. they are used in the absence of internal supports and are based only on external walls. The structure of the hanging rafters includes inclined rafter legs and a stretch, which is a horizontal bar that receives a thrust from the rafter legs. The lower ends of the rafter legs rest on the Mauerlats by tightening, and for the upper ends, the rafters are fastened in the ridge. The simplest version of hanging rafters is a triangular symmetrical truss, and the volume of the overlapped space can be from 7 to 12 meters. You can strengthen the structure with a special tie - crossbar.

Important: it should be noted that the manufacture of hanging rafters is a rather laborious process, and their cost significantly exceeds the cost of layered ones. Therefore, quite often, in order to reduce the cost of construction, they equip combined rafter systems, which include both hanging and inclined rafters.


Features of the

Additional elements are needed as facade cladding, without them it is unrealistic to carry out roofing work. They play a protective role - they do not allow precipitation to seep into the roof, and prevent the release of heat

It is very important to know exactly the purpose of the elements, the methods of their fastening, as well as the sequence of work. All these little details play a very important role.

In addition to a protective one, they also play a decorative role, since any roof covering, without these parts, will have an unworthy appearance. To select the desired shade, the RAL catalog is used, which includes a wide variety of color options, as well as standard colors.

Additional elements are divided into three types: roofing, facade, for parapets and fences. Divide them depending on the application. But this division is conditional, since some parts are used for other types of structures. Nevertheless, any product is created for certain functions, because of this, additional elements cannot be called interchangeable. For a person who has no experience, it will be rather problematic to choose the elements on their own.



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