Since the flat roof used to cover office buildings, industrial facilities and residential buildings does not have slopes, increased demands are placed on the quality of waterproofing. To avoid leaks, three to five layers of material are used, but a flat roof surface is not able to drain water as effectively as a pitched one. Because of this, areas are formed where moisture accumulates; they dry out only during the hottest periods of the year. The rest of the time, non-evaporating puddles negatively impact the waterproofing layer, destroying it.
In addition, in places where moisture accumulates, particles of soil and dust settle, forming a kind of substrate. The wind carries seeds into this favorable environment and they germinate. Destroying the roofing pie. In order to organize the removal of excess moisture and its movement to the drainage system, a flat roof slope is laid. So the name “flat” is just a figure of speech; in fact, its surface is located at a slight angle, invisible to the eye, without the use of a special geodetic instrument. What the slope should be and how it can be created, we will tell you in this article.
Building codes
The minimum slope of a flat roof is regulated by clause 4.3 of SP 17.1333, adopted and approved in 2011. It allows a roof surface inclination angle in the range of 1.5-10% or 1-6 degrees. That is, the smallest slope allowed by regulations, 1.5% or 1 degree, creates conditions for the movement of water to drainpipes and gutters and prevents stagnation. Steeper angles are rarely used, since on a large roof area, rolled waterproofing materials slide down to the base.
The process of creating a slope is called flat roof slope. This task is performed in various ways using:
- Thermal insulating material;
- Backfill materials;
- Lightweight mixtures of concrete with backfill materials;
- Lightweight mixtures of concrete and polymers.
- Plastic panels
Important! The slope of the flat roof in use should not exceed 3 degrees, as increasing it reduces the safety of use.
Deflection with thermal insulating materials
The structure of any flat roof implies the presence of a layer of thermal insulating material. To set the angle of the roof surface, adjust the thickness of the insulation. To prevent slipping and maintain a given angle, it is fixed to the base of the roof with self-tapping screws. If the base of the roof is well cleaned, the insulation can be glued to it or special plastic supports can be used to hold the layers of thermal insulation together.
This method of deflection has advantages; it is good because:
- It is relatively cheap. Since insulation is already necessary to form the roofing pie, costs increase only through the purchase of glue or fasteners.
- Quite accurate. Using this method, you can accurately set an angle of 1-4 degrees, which is quite sufficient for effective drainage.
- Light weight. Unlike most other methods, sloping a flat roof using insulation does not require reinforcement of the base, since the thermal insulating agent, most often mineral wool or expanded polystyrene, has a low mass.
Deflection with backfill material
Creating a slope angle for a flat roof using backfill material begins with the installation of waterproofing material. This role is most often played by glass insulation; it is a modern one based on fiberglass, due to which it has increased tensile strength and a service life of more than 20 years. Expanded clay or perlite is poured onto the glass insulation so as to maintain the required slope angle. After this, the backfill material is covered with a polyethylene film arranged in overlapping strips and the remaining layers of the roofing cake are laid according to the design.
However, this method of creating a flat roof slope has disadvantages:
- Large granules (more than 20 mm) do not allow you to accurately maintain the specified angle and make it smooth.
- The backfill material cannot be rigidly fixed, which is why it moves over time. Moreover, this can happen even at the stage of forming the roofing pie, if the expanded clay is not poured with cement laitance. However, in this case, the time spent on drying increases.
- Backfilling is done almost by eye, so it is impossible to maintain the exact angle of inclination.
- Due to the large weight of the backfill material, reinforcement of the concrete roof base is required.
Sloping with concrete mixtures
To set the slope, you can use concrete-based mixtures. This method is not suitable for reconstruction or partial repair; it can only be used for newly created roofs. In order to pitch the roof using concrete mixtures, special equipment and highly qualified workers are required. Two types of concrete mixtures are used:
- With the addition of expanded clay and perlite, slag.
- With the addition of polymer materials.
This method has only two disadvantages: the high cost, which consists of the wages of highly qualified workers and the high cost of polymers, and the second is the large weight of concrete, which increases the load on the base of the roof.
Bend using panels
The most innovative way to set the angle of the roof is to use special plastic panels. They, like pieces of a children's puzzle, are assembled and placed on a pre-prepared base, and then filled with liquid rubber. The different thicknesses of the panels ensure the most accurate observance of the angle of inclination of the surface. But this method also has its own characteristics:
Monitoring the effectiveness of the deviation
To check whether the slope is done properly and whether water is effectively drained from the roof surface, use one of two methods:
The slope, made in accordance with building codes, protects the upper floors from leaks and extends its service life.
Video instructions
When creating a roof, all details are taken into account. It is especially important to determine the slope of the surface, since not only the appearance, but also the durability of the structure depends on it. This indicator depends on many factors, including the climatic conditions of the area. In this case, it is taken into account that the roof provides protection from environmental influences, but it itself is exposed to all these negative factors. That is why it is important to calculate the slope of a flat roof before construction begins.
The nuances of choosing a slope angle
To begin with, the effect of wind on the coating is considered. In regions with strong winds, roofs with a slight slope are preferable. In this case, if there is a high roof, the likelihood that gusts of wind will tear off some of the material increases. To prevent this, it is necessary to make the rafter system more massive, which increases the cost of installing the structure, and also negatively affects the weight of the entire structure. In areas where precipitation falls especially frequently in winter, it is enough to make the roof slope within 45°. This will ensure free flow of snow and eliminate increased load on the roof surface.
If there is little snowfall in winter, you can limit yourself to a low-slope roof, that is, the slope in this case will be minimal. According to SNiP, when creating such a structure, it is recommended to use membrane materials to prevent leaks. When creating a flat surface, importance is also given to drainage; it is this that is entrusted with the function of draining water and preventing its accumulation on the surface. To reduce exposure to sunlight, you can use bitumen covers, green, turf or pebbles.
In regions where harsh climates often prevail in winter, it is recommended to combine external and internal drainage. The latter will no longer be exposed to negative natural factors.
The choice of materials depending on the angle of the slope
Each material has its own requirements for use. A rough roof surface will prevent water gadflies from draining away, while a smooth surface will facilitate this. The design of the rafter system is also important. When creating a flat roof, it can be lighter, but designed to withstand heavy loads from water and snow. From a roof that has a slope, water rolls off faster and snow does not linger, but the roof itself must be more durable due to the complexity of the design. The type of rafters and the pitch of the sheathing are also influenced by the choice of roofing material.
The choice of roofing material should depend on the level of slope. To create high roofs, the range of roofing coverings is wider, and externally such buildings are particularly attractive. In order to carry out roofing installation work correctly, you should adhere to the following rules::
Slope angle measurement
To correctly select materials and design of the rafter system, it is important to calculate the angle of the slope. This action is performed using a protractor or through mathematical calculations and is expressed in degrees, percentages and ratios.
The simplest is mathematical calculation. To do this, you need to know the width of the blood and its height. Using trigonometric formulas, the angle is calculated in the form of cosine, sine or tangent. The result obtained is converted into percentages using the table.
You can also calculate using another method. To do this, divide the height of the future roof by half the width of the room, and multiply the result by one hundred. The result is compared using a table to determine the slope and is also expressed as a percentage.
If you have a protractor, all actions consist of determining the angle and selecting materials to create the roof. Only after this can you make the right choice, be sure to compare it with the requirements of SNiP.
Features of creating a low-slope roof
Most often, the slope of a flat roof is carried out using the following methods:
- backfill insulation, that is, perlin, expanded clay and others;
- concrete mixtures based on insulation materials;
- polymeric materials and concrete mixtures based on them with the obligatory addition of fillers;
- use only insulating materials.
Each of the listed methods has its own advantages and disadvantages. Expanded clay and perlin can change position over time and disrupt the slope of the roof. As a result of this, the minimal slope after some time can become a flat roof. The size of the material also matters, since large components do not allow the slope to be made sufficiently uniform.
Concrete mixtures are especially often used for flat roofs. The main disadvantage of these materials is their weight. That is, it is necessary to calculate the additional load when developing the design of the rafter system. Considering this drawback, we can conclude that concrete mixtures can be used to create a flat roof during the construction phase or during major repairs. They are not suitable for partial repairs of flat roofs, as they cause additional stress.
According to SNiP, polymer materials are ideal for such work. Given their wide range, they should be chosen not only depending on the angle of the slope, but also take into account the features of the rafter system.
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Choosing a roof slope only based on your aesthetic preferences would be somewhat reckless. Since the reliability and strength of the future structure largely depend on the correctly calculated value of the angle of inclination, taking into account the climatic features of the area. That is, the roof slope should be optimal from both a practical and aesthetic point of view.
The fact that ideally “flat” roofs simply cannot be beyond doubt. After all, rainwater must somehow be drained from it. Therefore, a slope is made on them in order to obtain at least the minimum slope of a flat roof.
It ensures the most efficient collection of rainwater from the surface of the roof covering and directs it either to the parapet or to the internal drains.
minimum roof angle
The minimum roof slope depends on many parameters, including the material of the waterproofing coating, the type of roof itself (standard or inverted), the number of waterproofing layers, and more.
Basic requirements that determine the slope of a flat roof: SNIP
What will be the minimum roof slope, depending on various factors, is dictated by special building rules and regulations.
The dependence of the roof slope angle on waterproofing is regulated by clause 4.3 of SP 17.13330 for 2011, according to which the slope of a flat roof varies in the range of 1.5–10%. Large angles (up to 24%) are performed extremely rarely, since the choice of material for waterproofing that would not slide to the base of the sloping roof when the temperature rises is very difficult.
Note
The smallest slope for a flat roof is 1.5% or 1°.
As a rule, a roof with a low slope has a fairly large surface area and achieving its ideal value is very problematic. There will likely be areas where water will stagnate, which can cause wear on the roofing material or leaks. You can perform the slope geometry relatively accurately using a screed. It is also possible to use polystyrene concrete or foam concrete filling. To increase strength, a thin layer of durable concrete screed is placed on top of the laid layer.
In turn, there is a specific connection between the steepness of the roof structure and the number of layers of waterproofing. The larger it is, the water naturally leaves faster, which means that fewer waterproofing layers will be required (clause 5.5).
The inclination can be easily checked using a bucket of water. Water is poured onto the selected area; if the water flows almost completely to the funnel, then the slope of the flat roof is sufficient. A similar check can be carried out on the entire roof surface.
At the design stage, it is determined by calculation how many water intake funnels are required for a given roof, and already during construction, with the help of slopes, it is necessary to ensure unhindered outflow of water into the funnel from any point on the roof.
How to calculate the roof slope: which method is better
As you know, in addition to flat (sloping) structures, there are also pitched and high ones, and there are even more materials for roofing. In order to correctly navigate this diversity, according to SNiP, special tables and diagrams have been developed that reflect the relationship between the steepness of the slope and the type of roof.
The roof slope is determined by the following parameters:
- the type and amount of material intended for roofing;
- necessary protection from wind and moisture;
- ridge height for repairing an existing roof.
How to calculate the angle of inclination in degrees and percentages
Calculator for calculating roof slope
Using this calculator is extremely simple. In fact, any roof can be divided into ordinary gable roofs, the calculation of which is based on a triangle. It is on this position that the work of the calculator is based. The following parameters are used:
- H – the height of the ridge, that is, the leg of a right triangle;
- W – second leg, equal to half the width of the base;
- L is the length of the rafters, also known as the hypotenuse.
By substituting two known parameters, you can almost immediately determine the slope angle of a roof with similar characteristics. By the way, the third parameter is calculated automatically. The calculator software uses the properties of an isosceles triangle and simple trigonometric formulas.
Using a protractor
This device, also called an inclinometer, has a simple design: several slats with marked divisions and a pendulum. When making calculations, the main rail is placed perpendicular to the ridge. The pendulum pointer indicates the required angle on the division scale. As you can see, nothing complicated.
Formula for calculating roof slope
And finally, the required steepness of the slope can be calculated mathematically without using slope measuring instruments. To do this you will need to know the value
- vertical height (H), measured from the highest point of the slope, usually the ridge, to the lowest point - the cornice;
- laying - the horizontal distance from the bottom to the projection of the top point of the slope.
The angle of inclination of the roof is calculated in degrees or percentages and indicated in the drawing by the letter “i”.
Mathematically, the percentage of roof slope is calculated as follows.
i = H: L, i.e. the roof slope angle is found from the ratio of the roof height to the pitch.
Then, to obtain the desired value as a percentage, the value of the resulting ratio is multiplied by 100. A special table of ratios helps express the slope value in degrees.
It has a number of advantages, such as: its installation will require less materials, ease and simplicity of installation and additional usable territory.
Many people do not associate the phrase flat roof with a slope. Although this is far from true. Even the smoothest roof has its own slope, even if it is minimal.
At a minimum, this is necessary so that melt water and water after rain can easily flow into the installed funnels, which are part of the internal drainage system, or into the gutter of the external system.
In addition, it is easy and simple to install additional necessary equipment on such a roof. To date, There are several types of flat roofs:
- Operable roof;
- Unused roof;
- Traditional roofs;
- Inversion roofs.
The slope that should be on this type of roof is is approximately 1-5 degrees, if you neglect this, then water, both rain and melt, will accumulate, which in turn will damage the roof.
In summer, you may not encounter such a problem, since rainwater dries out under the rays of the sun. In winter and autumn, such water can freeze at night and melt during the day.
Puddles form, which ultimately leads to moisture gradually penetrates into the insulation. The essence of the mechanism is that moisture penetrates into the layer, which means that inevitable leaks occur.
But this is not the only problem. In addition, puddles on the roof can contain dust, which eventually settles to the bottom. Seeds of various herbs and plants can fall into this puddle and germinate there.
Often on the streets you can find houses with grass or thin trees on their roofs. It is logical that this spoils the roof and also spoils the aesthetic appearance of the entire building.
To avoid such a nuisance, and thereby extend the life of your roof, it is necessary to carry out the roof tilting procedure. Such complex manipulation is carried out at the time of construction itself.
The process itself is quite complex and includes many different structured activities. The purpose of this procedure is to ensure that the roof itself acquires the required slope.
But before you start pitching the roof, you need to find out what a flat roof consists of.
Flat roof
In essence, it is a cake made of several layers:
- Direct basis, which is reinforced concrete slabs that have a certain wave height;
- , which can be made from different materials, such as bitumen, or roll materials;
- Next layer -, which can be made of mineral wool or other durable material.
The components of such a pie can be changed if the builder wants to make the entire roof using new building materials. It is worth understanding that such a procedure as slope, carried out immediately at the time of laying the insulation.
It is important that in addition to these main layers of the roof, there must also be water intake funnels or gutters.
The angle of the roof slope is very important, and it depends on many parameters. The first thing you should pay attention to is the wind exposure. If you live in an area where there are frequent strong winds, then it is worth making a small angle of inclination.
CAREFULLY!
If you make a strong slope of a flat roof, then the wind can tear out roofing sheets. It is important to note that the angle of the roof dictates the necessary conditions for the rafter system, as well as for all components of the roof, namely: rafters, sheathing pitch.
Obviously, the steeper the slope of the roof itself, the faster the outflow of water.
Slope in percent
Minimum angle and calculation of roof slope
The minimum slope angle can be determined based on the materials of the roof itself:
- If the roof is made of , then its minimum inclination must be at least 12 degrees(according to SNiP). If the roof is made of, the angle increases to 15 degrees. It is important to understand that the cracks in the material and other joints must be treated with a special sealant - frost-resistant/water-resistant. If the angle of inclination is 15 degrees, then the sheets of material should be overlapped by about 200mm, if the angle is smaller, then the overlap should increase;
- The minimum slope angle may be in cases where if the roof of your house is made of artificial materials. These, in turn, include membrane coatings and bitumen-based materials. It is logical that by the magnitude of the slope angle, The number of layers of the roof also affects. If, for example, the roofing is carried out in two layers. then a tilt angle of 15 degrees is quite sufficient;
- Having covered the roof, it is worth understanding that 11 degrees of inclination angle is quite enough, but in this case you need to make a continuous type of sheathing.
Such a process as the slope of a flat roof, made from such materials:
- Extruded polystyrene (technoNIKOL);
- Wool, both mineral and glass/basalt based;
- Polyurethane foam;
- Foam concrete;
- Foam glass;
- Various types of backfill materials.
Each of the materials has its pros and cons. And before you start work, it is worth correctly calculating the angle of inclination. In fact, this calculation is quite easy to carry out; for this you need to use a protractor, or use fairly simple mathematical formulas.
Despite the fact that a flat roof is called flat, it still needs a slope. The minimum slope for a flat roof is 1 degree or 1.7%.
The instructions for using bitumen and polymer coatings for slope indicate that the optimal slope angle should be 1.5 degrees. A tilt of 1-2 degrees is acceptable.
Everything is very simple here. You need to know the height of the roof and its width. Next, simple trigonometric formulas will help you calculate the immediate angle (sine, cosine, tangent). And from the existing table, which was calculated earlier, you can find out the value as a percentage.
There is another way to calculate - the value of the roof height must be divided by half the width, and the result already obtained must be multiplied by one hundred, after which, in the table, you can find out the percentage value of the future angle of inclination. This option is faster, but in terms of accuracy they are both correct.
Minimum slope
Sloping a flat roof using bulk materials
If you decide that the tilting procedure will be carried out using bulk materials, then the first thing worth noting is the diagram according to which such a procedure must be carried out:
- First of all, on the concrete base itself, it is necessary to lay a layer of glass insulation. This material not only has a long service life (30-35 years), but also has high waterproofing performance;
- Further, it is necessary to pour the main material on it - expanded clay. But at the same time, everyone needs to create the right bias;
- Necessarily you need to cover a layer of expanded clay with a special plastic film. It is important to note that it must be overlapped;
- Next, it is necessary to apply the prepared sand-cement screed, doing it smoothly, slowly. Its essence is to level the layer of expanded expanded clay;
- After these events you can begin shape the roofing “pie”, according to the developed .
Remember that when laying each layer, you need to ensure that the previously prepared angle of inclination is maintained.
ATTENTION!
If you are worried that the expanded clay will move when you start laying sand-cement screed on top of it, you can fill it with cement laitance. But it is worth understanding that because of it, the structure becomes heavier.
If you want to create a minimum angle of inclination, and the roof area is not particularly large, then a sand-cement mortar will be enough.
Bulk material
Thermal insulation materials
Another good material for pitching the roof is thermal insulation materials. Experts say that this is the most affordable option.
Its advantage is that it is quite light and quite cheap, which plays a very important role in construction. Mineral wool is the best material. The process diagram is quite simple.
It is necessary to attach the material to the base itself, using self-tapping screws or dowels. Some people prefer to glue sheets of such cotton wool onto a previously cleaned base using special glue. This process can be performed both during and during roof installation.
Thermal insulation material
Foam concrete
A good material that can be used to slope a flat roof is foam concrete. It is immediately worth noting that this procedure must be carried out using special equipment.
A layer of foam concrete is poured onto the base itself, but at the same time the angle of inclination is noted, and only after make a special screed from foam fiber concrete. Next, it is important to apply waterproofing material.
A huge advantage of this tilt option is high thermal insulation, as well as other mechanical characteristics. For example, strength and durability.
Speaking of minuses, there are some here too, or rather one. This is the price. She's tall enough. And again, it will not be possible to carry out such a procedure on your own. Therefore, in this case it is worth turning to professionals.
- If the roof has a minimum slope, then it is important to note that in this case, proper drainage systems must be installed. The slope itself is made exclusively to the side (funnel, gutter);
- If your roof is bitumen, you should make the slope angle less than 6 degrees, while The bottom layer of waterproofing must be made of membrane materials;
- It is important to know that with small slope angles, it is necessary to ventilate the under-roof space itself, what does all the stingrays have to do with it. The thickness of the gap also depends on the value of the angle (the larger the angle, the smaller the thickness and vice versa). VKontakte