Calculation of the size of the roof of a house. Roof calculator: calculation of roofing, rafter system, lumber. Rafter roof with attic

One of the most important components of any building is its roof.

It not only protects the wall of the house and its interior space, but also performs an important decorative function.

No matter how beautiful the walls of the house are, without a beautiful elegant roof the finished appearance will not work.

It is the shape of the roof that determines how integral and aesthetically pleasing your building will look as a whole.

Therefore, before proceeding with the installation of the roof, it is very important to make the correct calculations, model the parameters of the roof and its appearance.

And it should be taken into account very large number parameters.

The height of the roof is influenced by several main factors:

roof shape;
number of stingrays;
slope angles;
materials that are planned to be used to create the roof;
wind strength in a particular region;
amount of precipitation;
height of the constructed building;
wishes of the developer.

Types of roofs and calculation features

Roofs of houses exist:

single-pitched;
gable;
hipped;
attic.

And each type has its own calculation procedure.

After all, roof structures, despite all their apparent similarity, differ significantly from one another.

Naturally, the simplest is the calculation of a single slope.

Although the calculation of a gable roof cannot be called difficult.

With the correct calculation of the roof height, the costs of roofing and building materials will be optimal, and the structure will be reliable.

Calculation of the height of a gable roof

The height of the roof is directly related to the angle of the rafters.

The greater the slope, the higher the roof will be on your home.

Used for calculation simple formulas from a school geometry course.

You should also measure the length and width of the building and understand what the angle of inclination will be.

The angle can range from 11 to 30 degrees.

And it depends, first of all, on what material will be used to install the roof on the house and the climatic conditions.

The more snow falls in the area where the house is built during the season, the greater the angle of inclination.

There are special tables for this.

Wind loads are taken into account in the same way.

Now we perform a simple geometric calculation

The height of the ridge is the leg of the triangle.

The second leg is the width of your house, divided in half.

By the way, with this calculation you can also calculate the length of the hypotenuse.

This will be the length rafter legs your roof.

To determine the height of the ridge, you need to multiply the length of the leg by the tangent of our angle of inclination.

There is a ready-made table for determining tangents and sines:

For example, let's calculate a gable roof.

The width of the house is 6 meters.

The house has two slopes.

The slope angle of the slopes is the same and equals 40 degrees.

We look at the table and find out that the tangent of 40 degrees is equal to 0.84.

According to the formula:

6 / 2 x 0.84 = 2.5 meters.

The height of our roof is 2.5 meters.

Nothing complicated!

The main thing is to measure everything as accurately as possible!

Until the last centimeter.

Calculating the height of the hipped structure

Calculating a hip roof is a little more complicated.

After all, there are different roofs with four slopes.

For example:

hip;
tent;
half-hip;
forceps.

The easiest way to calculate roofs is if they have slopes in the shape of a regular trapezoid or triangle, and there are no kinks on the slopes.

However, now the majority are hip with a large number slopes shaped like a rhombus, rectangle and others geometric shapes.

Well, it’s clear when calculating the height of a hipped roof - it is no different from calculating the height of a gable roof.

But with other calculations it is more difficult.

Calculations should begin with drawing up a roof plan.

Take a tape measure and measure all available sizes.

If the roof is at different levels, then the drawing shows what height is where.

After detailed drawing composed, the roof should be decomposed into separate geometric elements.

When calculating the roof, certain rules should be followed:

the drawing is divided into several geometric shapes. Each figure is drawn into a separate drawing. All sizes are also transferable;
The length of one slope is determined. To do this, measure the distance from the ridge to the cornice;
calculate each slope. To do this, obtain the area of the figure and then multiply its value by the cosine of the angle of inclination;
if the slope is an irregular rectangle, then it, in turn, must be divided into several regular figures, and the area of each of them must be calculated separately, and then the resulting data must be added up.

Let's calculate a hipped roof as an example.

Let's assume that our roof consists of two regular trapezoids and two isosceles triangles.

The angle of inclination of the slopes will be 30 degrees.

We look at the plate and find out that the cosine of such an angle is equal to 0.87.

Trapezoidal slopes have side dimensions of 10 and 7 meters, and a height of 3 meters.

Triangular slopes have dimensions of two sides each of 3.34 meters, and the length of the third side is 4.8 meters.

Find the area of the trapezoid.

To do this, you need to add the lengths of the two horizontal sides, divide by 2 and multiply by the height.

It looks like this in our specific case:

S = ((10 + 7) /2) x 3 = 25.5 sq. meters.

Now multiply the resulting number by the cosine of 30 degrees:

25.5 x 0.87 = 22.185 km. meters.

And the resulting number is rounded up.

We get 22.5 sq. meters.

Now we calculate the area of the triangular slopes:

S = ((7 x 4.8) / 2) x cos 30 degrees =

16.8 x 0.87 = 14.7 sq. meters.

Now all the areas need to be summed up:

S total = 22.5 x 2 + 14.7 x 2 = 74.4 sq. meters.

And round up.

Total 75 sq. meters.

We calculate roofing material

Once we know the roof area, we can calculate the required amount of roofing material.

The opinion that the roof area in the drawing and the area of the roofing material are equal is erroneous.

After all, it’s all about the so-called “overlap”.

After all roofing material The joint is not laid joint-to-joint.

An overlap is made to prevent the roof from leaking.

In addition, the amount of overlap for each material is different.

Therefore, material consumption increases.

For a simple roof, it is easy to independently calculate the amount of material required.

For example, let’s calculate the amount of slate for our roof.

First, let's create a proportion:

In this proportion:

S is the area of our roof,

X is our margin of 15 percent.

After calculating the value of X, we add it to our resulting area.

As a result, we will get the area of our roofing material.

X = 15 x 75 / 100 = 11.25. Rounded to 11.5.

Area of our roofing material

11.5 + 75 = 86.25 sq. meters.

You should know that when directly performing roofing works material waste may increase.

In some cases by another 20%.

That is, a proportion is again drawn up in which the value of X is the flow rate.

We add the resulting result to the area.

Knowing the area of one sheet, it is easy to obtain the required number of sheets.

We calculate steam and waterproofing

Actually, the area of these materials is equal to the area of the slopes, to which 15% must be added for the overlap of the material sheets.

That is, if the area of the slope is 40 square meters. meters, then the waterproofing area is 40 + 15% = 60 sq. meters.

With vapor barrier everything is exactly the same.

Online calculations and calculation programs

It is very easy to calculate roof parameters and the amount of roofing material if the roof is of a simple shape.

What to do if the shape of the roof is complex?

Or very difficult?

In fact, everything is a little easier than it seems.

Because in the age of computerization, special online calculators and programs for calculations have been invented.

An online calculator differs from a program in that it does not need to be downloaded to your computer.

You just need to go to the website and there, in a special shell, everything will be counted for you.

Such calculators do not do complex calculations.

More complex detailed calculations make specialized programs.

Such programs must be downloaded and installed on your computer.

They have one drawback - most of these programs are paid.

So refresh your memory school course geometry and start taking measurements and calculations.

Well, if all else fails, use programs.

The developers guarantee the accuracy of the calculations.

Video about a construction calculator for roof calculations.

The roof of a building is designed to hold external loads and redistribute them to load-bearing walls or support structures. These loads include weight roofing pie, the mass of the structure itself, the weight of the snow cover, and so on.

The roof is located on the rafter system. That's what it's called frame construction, on which the roof is fixed. She takes it all external loads, distributing them among supporting structures.

The rafter system of a gable roof includes the following elements:

Mauerlat;
Struts and braces;
Side and ridge purlins;
Rafter legs.

A rafter truss is a structure that includes all of the listed elements with the exception of the Mauerlat.

Calculation of gable roof loads

Constant loads

The first type refers to those loads that always act on the roof (in any season, time of day, and so on). These include the weight of the roofing pie and various equipment installed on the roof. For example, the weight of a satellite dish or aerator. It is necessary to calculate the weight of all truss structure along with fasteners and various elements. To perform this task, professionals use computer programs, as well as special calculators.

Calculation gable roof is based on calculating the loads on the rafter legs. First of all, you need to determine the weight of the roofing cake. The task is quite simple, you just need to know the materials used, as well as the dimensions of the roof.

As an example, let’s calculate the weight of a roofing cake with ondulin material. All values are taken approximately; high accuracy is not required here. Usually builders perform calculations of the weight per square meter of roofing. And then this figure is multiplied by the total roof area.

The roofing pie consists of ondulin, a layer of waterproofing (in this case - insulation on a polymer-bitumen basis), a layer of thermal insulation (the weight of basalt wool will be calculated) and sheathing (the thickness of the boards is 25 mm). Let's calculate the weight of each element separately, and then add up all the values.

Roof calculation gable roof:

A square meter of roofing material weighs 3.5 kg.
A square meter of waterproofing layer weighs 5 kg.
A square meter of insulation weighs 10 kg.
A square meter of sheathing weighs 14 kg.

Now let's calculate the total weight:

3.5 + 5 + 10 + 14 = 32.5

The resulting value must be multiplied by the correction factor (in this case it is equal to 1.1).

32.5 * 1.1 = 35.75 kg

It turns out that square meter roofing cake weighs 35.75 kg. It remains to multiply this parameter by the roof area, then you can calculate a gable roof.

Variable roof loads

Variable loads are those that act on the roof not constantly, but seasonally. A striking example is the snow in winter time. Snow masses settle on the roof, creating additional impact. But in the spring they melt, and accordingly, the pressure decreases.

Variable loads also include wind. This is also a weather phenomenon that does not always work. And there are many such examples. Therefore, it is important to take into account variable loads when calculating the length of the rafters gable roof. When calculating, you need to take into account many different factors affecting the roof of a building.

Now let's take a closer look at snow loads. When calculating this parameter you need to use a special card. The mass of snow cover is marked there different regions countries.

To calculate this type of load, the following formula is used:

Where Sg is the terrain indicator taken from the map, and µ is the correction factor. It depends on the roof slope: the stronger the slope, the lower the correction factor. And here there is important nuance- for roofs with a slope of 60 o or more it is not taken into account at all. After all, the snow will simply roll off of them, and not accumulate.

The whole country is divided into regions not only by the mass of snow, but also by the strength of the winds. There is a special map on which you can find out this indicator in a certain area.

When calculating roof rafters, wind loads are determined using the following formula:

Where x is the correction factor. It depends on the location of the building and its height. And W o is the parameter selected from the map.

Calculation of the dimensions of the rafter system

When the calculation of all types of loads is finished, you can proceed to the calculation of dimensions rafter system. The work performed will differ depending on what kind of roof structure is planned.

In this case, a gable one is considered.

Section of the rafter leg

The calculation of the rafter leg is based on 3 criteria:

Loads from the previous section;
Remoteness of the railings;
Rafter length.

There is a special table of sections of rafter legs, in which you can find out this indicator based on the criteria described above.

Length of rafters in a gable roof

For manual calculations you will need basic knowledge geometry, in particular the Pythagorean theorem. Rafter - hypotenuse right triangle. Its length can be found by dividing the length of the leg by the cosine of the opposite angle.

Let's look at a specific example:

It is required to calculate the length of the rafters of a gable roof for a house with a width of 6 m, in which the slope of the slopes is 45 o. Let L be the length of the rafters. Let's substitute all the data into the formula.

L = 6 / 2 / cos 45 ≈ 6 / 2 / 0.707 ≈ 4.24 meters.

You need to add the length of the visor to the resulting value. It is approximately equal to 0.5 m.

4.24 + 0.5 = 4.74 meters.

This completes the calculation of the length of the rafters for a gable roof. It was manual method completing the task. There are special computer programs designed to automate this process. The easiest way is to use Arkon. This is completely free program, which even a person with little computer knowledge can easily understand.

It is enough to simply specify the input parameters based on the size of the house. The program will independently perform calculations and show the required cross-section, as well as the length of the gable roof rafters.

Most of the construction is already behind you, and your future home will delight you with a strong foundation and smooth walls? It's time to start building a roof that will protect your home comfort from dampness and bad weather. But the first thing to do is to design and calculate the entire structure down to the very last detail.

Remember that at height all work is more difficult, and therefore it is better not to redo anything. Moreover, the calculation of the rafter system of a gable roof itself is not complicated - now you will see this for yourself! By the way, a gable roof is also called a gable roof.

Mauerlat is the foundation of the roof, usually represented by a horizontal beam, on which the rafters rest.
Ridge beam.
Inclined beams and rafters.
Vertical racks.
Lathing and additional parts that give the necessary rigidity to the frame.

Nothing complicated - the gable roof is just what makes us happy:

Standard and sloping gable roof

The project of a standard gable rafter system consists of two inclined planes rectangular shape and smooth vertical ends on the sides, called pediments. Such a roof is one of the simplest structures, the construction of which can be successfully completed by even inexperienced specialists.

But the sloping gable roof has a different architecture. Here, the upper flatter roof is usually built with a slope of 30°, and the lower steep roof with a slope of 60°.

A sloping gable roof is good because snow and ice almost does not linger on it, but attic room They turn out to be much more convenient and cozy. Moreover, in the lower plane of such a roof it is rational to do skylights, which on flatter surfaces usually become a problem of leaks and dampness - rainwater lingers on them longer.

Note that one of the most best options for buildings 6-8 m wide. Moreover, it will be easier for you to assemble a broken profile - for this you just need to mount the necessary components directly on the ground, and simply cut all the posts and rafters according to the template:

How to calculate a gable rafter system?

So, the first thing when designing and calculating is to decide usable area attic, and based on this data, decide how high the vertical racks will be. And the attic is usually built in such a roof - it’s convenient.

For convenience, we suggest understanding the concepts:

We calculate the angle of inclination of the slopes

Now we calculate the slope of the slopes. So, if your home has standard width 6-8 m, then a slope angle of 45° will leave too little space for the attic living space. Do 60° - this is the best option, although it will cost you more. In addition, already with a 45° slope you can use any roofing materials.

It is rare, but it happens when a gable roof is initially planned to be asymmetrical - if only so that there is room in the attic space for arranging a residential attic. But in any case, calculate the angle of inclination of a standard gable roof based on the wind and snow loads of your region.

But keep in mind that with an increase in the angle of inclination of the slopes, the consumption of materials will also increase, although performance characteristics such a roof will also be higher:

Gable roofs with unequal slope angles are also built to express original design. It has many shortcomings, and therefore we advise you to plan a symmetrical roof, at the base of which there are isosceles triangles.

Deciding on the type of rafters

A gable roof has only two of them.

Hanging rafters

A distinctive feature of this type of rafter system is that the support here is only on the side walls of the structure, i.e. the rafters are simply hanging. This process in construction is considered negative, because Such design leads to a bursting load on the roof and over time the walls may even become deformed. And over the decades, it even becomes skewed. That is why, for a more harmonious and safe distribution of the load, consider additional and auxiliary elements - tightening, headstock, and bevels.

But the hanging rafter system also has its advantages:

The installation work of such a roof is quite simple.
There are no complex components or other elements for system reliability.
The entire truss structure has high degree rigidity.

Layered rafters

The layered rafter system is characterized by the presence of an internal supporting partition, which is located at the same distance from the opposite walls. The entire roof rests on it, and therefore you cannot do without a layered system if the roof has a serious weight or size.

Distributing the load of the rafters

Now it is important to redistribute the load of all rafters onto the floor beams as much as possible. If the rafters need to be strengthened, then add additional linings to the project or a larger section of the beam than planned.

Weight of the rafter system and roofing covering

We calculate everything using the following tables:

The project may also have inclined racks, which strengthen the rafter system. Next, the gabled roof truss will need to be reinforced with a headstock - a central post that will connect the ceiling and ridge beams.

In addition, it is important that the roof can easily survive climatic dissonances. It is easiest to calculate and design roofs in small countries where the climate is the same throughout the entire territory. That is why the Irish tend to build some structures, in hot countries - others, and the Swedes - others. It’s just that in such areas, building traditions have been developing for centuries, which have actually been tested in practice by more than one generation.

But in Russia, such traditions are ambiguous: somewhere they build flat, low roofs and houses almost in the ground, and somewhere, on the contrary, high sharp slopes near the same high towers. The fact is that the climate in our country is varied (naturally, due to its vast territory), and in some areas they are trying to cope with tons of snow, while in others they are trying to prevent a stray wind from tearing off all the roofs in the village. Therefore, still focus on the experience of your region and do not make too radical decisions in calculating the rafter system.

So, the force of the wind exerts lateral pressure on the roof. When faced with an obstacle, the wind is divided into two flows: down to the foundation and up, under the eaves. If you calculate everything correctly, your roof will serve you faithfully until your great-grandchildren, and if you make a mistake with the calculations, the consequences will be sad. Moreover, if the wind tears off the roof in the literal sense of the word, some kind of minor repairs– you will have to rebuild the entire rafter system.

Therefore in construction world it is customary to pay special attention the so-called roof aerodynamic coefficient. It depends on its angle of inclination: the steeper it is, the greater the load will be and it will be easier for the wind to overturn the roof. The lower you go, the more difficult it is, but here the wind will act as a lifting force, trying to catch it on the cornice and tear it off like a mushroom cap. Therefore, the ideal roof for windy regions is one with a slight angle of inclination and a minimal eaves. And certainly not with hanging rafters.

Another dangerous point: in such areas, the wind often breaks branches from trees and carries other objects. And the higher the roof, the more likely it is that all this debris will collide with it. A couple of scratches and corrosion is guaranteed. Therefore from metal coating I'll have to give it up too. In addition, if there are strong winds in your area, lay the mauerlat close to the edge outer wall It is not recommended that gusts of wind could disrupt it.

Snow load

Snow cover in winter periods actually puts quite a bit of pressure on the roof. And what north of the area, the more such precipitation there is, and the greater the threat of a roof failure, especially at a low angle of inclination. Therefore, this final element of the building must be designed and calculated carefully, taking into account all the subtleties and nuances.

It's especially difficult to think through reliable roof in areas where periodic temperature changes are the norm. The fact is that the constant melting of snow and its freezing the next day has a bad effect on any roofing. As a result, the entire rafter system is deformed, waterproofing and insulation are destroyed, and constant roof leaks lead to unpleasant dampness and regular repairs. Yours are similar weather conditions? Place your bet on maximum roof protection!

The formula for calculating the roof slope angle in this case is simple: the higher the slope, the less snow is retained. In snowy regions also forget about complex forms roof and numerous elements. Just count simple design with a high angle of inclination, on which it will be necessary to install snow holders (so that precipitation does not destroy the drainage system).

Modern programs for calculating a gable roof

Naturally, draw the entire rafter system with your own hands, as in the official project documentation, quite difficult, unless you are trained as an architect. But it is quite enough to have the theoretical knowledge that this article gives you and at least make a sketch so that you can already purchase building material. And you can go another way - use modern 3D programs. It will be difficult to understand things like AutoCAD and 3D Max, but in Arkon everything necessary calculations and sketches are easy to make.

Also, if you still have questions, you will always find on our website who will quickly perform all the necessary calculations.

Before starting calculations, you need to understand that roof and roofing are not identical concepts. By “roof” we mean the entire system that stands on the mauerlat: rafters, sheathing and counter-lattice, all kinds of insulation and, finally, the roofing material, that is, the “roof” itself. An online roof calculator with drawings allows you to obtain data on both the roof and the roof - in a format convenient for you.

Ready calculation of the rafter system and metal roof tiles (as well as other types roofing coverings) can be saved as simple numbers by the quantity of building materials, and in the form of drawings and 3D models. You can save the result on the PC or mobile device from which you entered the data, and also send it by e-mail to yourself or the specialist who designed your facility. By the way, before purchasing, it is recommended to consult with him or a professional estimator: online calculator for roof calculations with roof drawings is designed for standard initial data - your object may have features that the service will not take into account.

Using the service you can make calculations:

single-slope, double-slope, four-slope, including hip roof;
any of the listed types of roofs, including the attic;
any of the listed types of roofs, taking into account different angles of inclination;
roof area.

All data is entered in centimeters - for example, the length of the roof along the ridge, which will be 12 meters, must be indicated as 12,000 centimeters; The service also displays results in centimeters.

If necessary, you can put checkboxes under the basic data for accounting additional materials: Mauerlat, counter-lattice, waterproofing and insulation. The service takes into account the most used types and brands of materials.

The rafter system is the main part of the blood, which absorbs all the loads acting on the roof and resists them. To ensure high-quality functioning of the rafters, it is required correct calculation parameters.

How to calculate the rafter system

To make calculations of the materials used in the rafter system on your own, simplified calculation formulas are presented in order to increase the strength of the system elements. This simplification increases the amount of materials used, but if the roof has small dimensions, then such an increase will be unnoticeable. Formulas allow you to calculate the following types of roofs:

single-pitched;
gable;
attic.

The service life of a roof largely depends on correct calculation

Video: calculation of the rafter system

Calculation of the load on the rafters of a gable roof

To build a sloping roof you need a load-bearing durable frame, to which all other elements will be attached. When developing a project, the required length and area are calculated cross section rafter beams and other parts of the rafter system that will be subject to variable and constant loads.

To calculate the system, it is necessary to take into account the characteristics of the local climate

Loads that act continuously:

the mass of all elements of the roof structure, such as roofing material, sheathing, waterproofing, thermal insulation, internal lining of the attic or attic;
a lot of equipment and various items that are attached to the rafters inside the attic or attic.

Variable loads:

load created by wind and precipitation;
the mass of the worker who performs the repair or cleaning.

Variable loads also include seismic loads and other types of special loads that place additional demands on the roof structure.

The angle of inclination of the slope depends on the wind load

In most areas Russian Federation The problem of snow load is acute - the rafter system must absorb the fallen mass of snow without deforming the structure (the requirement is most relevant for pitched roofs). As the roof slope decreases, the snow load increases. Arrangement pitched roof with a slope close to zero requires the installation of rafters with large area cross section, with small steps. It will also need to be cleaned regularly. This also applies to roofs with an angle of up to 25 degrees.

Snow load is calculated using the formula: S = Sg × µ, where:

Sg is the mass of snow cover on a flat horizontal surface measuring 1 m 2. The value is determined according to the tables in SNiP “Rafter Systems” based on the required area in which construction is being carried out;
µ is a coefficient that takes into account the angle of inclination of the roof slope.

At an angle of inclination up to 25 0 the value of the coefficient is 1.0, from 25 o to 60 o - 0.7, over 60 o - the value of snow loads is not included in the calculations.

The amount of precipitation affects the calculation of the roof

Wind load is calculated using the formula: W = Wo × k, where:

Wo is the magnitude of the wind load, determined according to the table values, taking into account the nature of the area where construction is taking place;
k is a coefficient that takes into account the height of the building and the nature of the terrain.

With a building height of 5 m, the value of the coefficients is kA=0.75 and kB=0.85, 10 m - kA=1 and kB=0.65, 20 m - kA=1.25 and kB=0.85 .

Section of the rafters on the roof

Calculating the size of the rafter beam is not difficult if you take into account the following point - the roof is a system of triangles (applies to all types of roofing). Having overall dimensions building, the value of the angle of inclination of the roof or the height of the ridge and using the Pythagorean theorem, the size of the length of the rafters is determined from ridge beam to the outer edge of the wall. The length of the cornice is added to this size (in the case where the rafters protrude beyond the wall). Sometimes the cornice is made by installing fillies. When calculating the roof area, the values of the lengths of the fillies and rafters are summed up, which allows you to calculate required quantity roofing material.

The cross-section of timber for rafters depends on many parameters

To determine the cross-section of the timber used when constructing any type of roof, in accordance with the required length of the rafters, the pitch of its installation and other parameters, it is best to use reference books.

The range of rafter beam sizes ranges from 40x150 to 100x250 mm. The length of the rafter is determined by the angle of inclination and the distance between the walls.

An increase in the slope of the roof entails an increase in the length of the rafter beam, and, accordingly, an increase in the cross-sectional area of the beam. This is necessary in order to ensure the necessary structural strength. At the same time, the level of snow load is reduced, which means that rafters can be installed in larger increments. But by increasing the step, you increase the total load that will affect the rafter beam.

When making calculations, be sure to take into account all the nuances, such as humidity, density and quality of lumber if the roof is made of wood, and the thickness of the rolled steel used if the roof is made of metal.

The basic principle of calculations is as follows - the magnitude of the load acting on the roof determines the cross-sectional size of the beam. The larger the cross-section, the stronger the structure, but the greater its total mass, and, accordingly, the greater the load on the walls and foundation of the building.

How to calculate the length of the rafters of a gable roof

The structural rigidity of the rafter system is a mandatory requirement, and its provision eliminates deflection when exposed to loads. Rafters bend if errors are made in the calculations of the structure and the size of the step with which the rafter beam is installed. If this defect is identified after completion of the work, it is necessary to strengthen the structure with the help of struts, thereby increasing its rigidity. When the length of the rafter beam is more than 4.5 m, the use of struts is mandatory, since deflection will be formed in any case under the influence of the beam’s own weight. This factor must be taken into account when performing calculations.

The length of the rafters depends on their location in the system

Determining the distance between rafters

The standard step with which rafters are installed in a residential building is about 600–1000 millimeters. Its value is influenced by:

beam section;

roof characteristics;

roof angle;

width of insulation material.

It is not recommended to artificially reduce or increase the pitch of the rafters

Determining the required number of rafters takes into account the step with which they will be installed. To do this:

The optimal installation step is selected.
The length of the wall is divided by the selected step and one is added to the resulting value.
The resulting number is rounded to the nearest whole number.
The length of the wall is again divided by the resulting number, thereby determining the required installation step of the rafters.

Area of the rafter system

When calculating the area of a gable roof, the following factors must be taken into account:

The total area, which consists of the area of two slopes. Based on this, the area of one slope is determined and the resulting value is multiplied by the number 2.
In the case where the sizes of the slopes differ from each other, the area of each slope is determined individually. The total area is calculated by adding the obtained values for each slope.
In the case when one of the angles of the slope is more or less than 90°, in order to determine the area of the slope, it is “divided” into simple figures and their area is calculated separately, and then the results are added up.
When calculating the area, the area of chimney pipes, windows and ventilation ducts is not taken into account.
The area of gable and eaves overhangs, parapets and firewalls is taken into account.

The calculation of the rafter system depends on the type of roof

For example, a house is 9 m long and 7 m wide, the rafter beam is 4 m long, the eaves overhang is 0.4 m, and the gable overhang is 0.6 m.

The value of the slope area is found by the formula S = (L dd +2×L fs) × (L c +L ks), where:

Ldd – wall length;
L fs – length of the pediment overhang;
L c – length of the rafter beam;
L ks is the length of the eaves overhang.

It turns out that the area of the slope is S = (9+2×0.6) × (4+0.4) = 10.2 × 4.4 = 44.9 m2.

The total roof area is S = 2 × 44.9 = 89.8 m2.

If tiles or soft covering in rolls, the length of the slopes will become 0.6–0.8 m less.

The size of a gable roof is calculated to determine the required amount of roofing material. As the angle of inclination of the roof increases, the consumption of material also increases. The margin should be about 10–15%. It is caused by overlapping laying. To determine exact quantity material, taking into account the slope of the slopes, it is best to use reference books.

Video: gable roof rafter system

How to calculate the length of the hip roof rafters

Despite the variety of roof types, their design consists of the same elements of the rafter system. For hip roofs:

Video: hip roof rafter system

What affects the angle of the rafters

For example, slope pitched roof is equal to about 9–20 o, and depends on:

type of roofing material;
climate in the region;
functional properties of the structure.

In the case when the roof has two, three or four slopes, then in addition to the geography of construction, the purpose will also have an impact attic space. When the purpose of the attic will be to store various property, then a large height is not required, but if used as a living space, a high roof with a large angle of inclination will be required. This is what follows:

appearance of the front part of the house;
roofing material used;
influence of weather conditions.

Naturally, for areas with strong wind optimal choice there will be a roof with a small angle of inclination - to reduce the wind load on the structure. This also applies to regions with hot climates, where precipitation is often minimal. In areas with high precipitation (snow, hail, rain), a maximum roof slope is required, which can be up to 60 degrees. This tilt angle minimizes snow load.

The slope angle of any roof largely depends on the climate

As a result, to correctly calculate the angle of inclination of the roof, it is necessary to take into account all the above factors, so the calculation will be carried out in the range of values from 9 o to 60 o. Very often the result of calculations shows that perfect angle the inclination ranges from 20° to 40°. With these values, the use of almost all types of roofing materials is allowed - corrugated sheets, metal tiles, slate and others. But it should be noted that each roofing material also has its own requirements for roof construction.

Without having the dimensions of the rafters at your disposal, you cannot begin to build a roof. Take this issue seriously. Do not limit yourself only to the calculations of the rafter system, the choice of its design and the determination of the operating loads. Building a house is an integral project in which everything is interconnected. In no case should elements such as the foundation, load-bearing structure walls, rafters, roofing. A high-quality project must take into account all factors comprehensively. And if you plan to build housing for your own needs, then the best solution will turn to specialists who will solve pressing issues and carry out design and construction without errors.