Physicist and astronomer Stefan Feeney of University College London, one of the...
A flat roof has advantages over a pitched roof in terms of its ability to withstand the challenges of bad weather.
The windage of a flat roof is much smaller, so it can withstand large wind loads.
But on a flat roof, a roof is laid, which is conditionally called flat, because it necessarily has a slope.
Why is a slope made on a flat roof?
The roof takes on all the effects of the environment and is designed to protect the building from them.
In addition to the wind, precipitation brings serious tests.
The function of the roof is to ensure that moisture does not linger, but flows down to the drainpipes.
Properly organized water flow significantly contributes to extending the life of the roof.
A flat roof, no matter what materials it is made of, will not withstand moisture if water lingers on it, especially during the cold months of the year.
The processes of turning water into ice and thawing will destroy the layers of the roof.
In stagnant puddles, dust settles over time, the wind brings plant seeds, which contributes to their germination.
This is how grass, bushes and even trees appear on the roof, which completely destroy the covering material with their root system.
To prevent these negative phenomena, a slope is made on a flat surface, and this process is called a slope.
Minimum roof pitch
The slope is a value that indicates at what angle the roof line is in relation to the base, it can be measured with a geodetic inclinometer tool.
These values are collected in a graph that makes it easy to determine which roofings correspond to which roof slope values.
In the same graph, you can convert the percentage value to degrees and vice versa.
There are tables of such translation.
If you divide the height of the roof by the width divided by two (the projection of the slope) and multiply the result by one hundred, you get the value of the slope as a percentage.
The slope is determined by the climatic conditions of the region, the purpose of the building, the type of coverage.
The angle at which the roof should be tilted is calculated at the design stage.
SNiP II-26-2010 “Roofs” defines its minimum value for roofing from rolled materials and from mastics from 1.5% (1 o) to 10% (6 o).
For operated roofs, its minimum value is within 1.5% ÷ 3% or 1 o ÷ 2 o.
A graph of the mutual conversion of percentages and degrees, expressing the slope and the compliance of the roofing material with it, is given below.
flat roof structure
The basis for a flat roof can be a reinforced concrete floor slab or metal profile sheets.
A flat roof consists of layers:
- cement-sand screed, if the base is concrete;
- vapor barrier using roll materials or bituminous mastics;
- insulation: mineral wool mats, polystyrene foam slabs, expanded clay bedding, concrete mixtures;
- waterproofing: several layers of rolled material.
If welded materials are used for a flat roof, then there will be slightly different components of the roofing pie.
In a building where the project provides for an internal drain, funnels for the catchment will be present in the roof device.
Materials used for spreading
Bulk insulation
Expanded clay, perlite, slag and other bulk heaters are used for slope planning on a flat roof.
The features of these materials, namely the fact that they are free-flowing, create some difficulties.
The minimum slope may be violated over time and the insulation will take a horizontal level.
In addition, if large granules are present, it will be difficult to create a slight slope.
Sometimes, when using loose insulation, a screed is made on top of it, which makes the roof heavier.
Glass isol is used as waterproofing.
Concrete mixtures
As a heater, concrete mixes with fillers from slag, expanded clay, perlite can be used.
Due to the fact that this material is heavier than other heaters, it is used during construction or if major repairs are being made.
Concrete mixtures are not suitable for partial repairs.
To carry out the work, skilled workers and special equipment will be required, which will increase the cost of construction.
Polymeric materials as a filler
Resin-filled concrete mixes are a good option for sloped flat roofs.
The disadvantage is that the weight of concrete, although lightweight, is much greater than that of other heaters.
And, as in the previous case, the involvement of specialists increases the cost of work.
Plastic panels
The modern method is the use of plastic panels with an individually set angle of inclination. The panels are assembled on the roof like puzzles, filled with liquid rubber.
The disadvantage of this method is the high cost of the material.
Warming materials
One of the most popular ways to ensure the slope of a flat roof is the use of heaters: mineral wool and foam boards.
Such materials are economical, easily attached to the base with mastics or adhesives.
Creating a Minimum Slope
The slope of the roof is created at the time of laying the insulation.
The method of forming the slope depends on the type of insulation chosen.
If bulk material, pour it, setting the required angle.
For fixing, pour cement milk.
From foam concrete, the slope will be performed by specialists; this method cannot be dispensed with without them.
When using heat-insulating materials to create a given slope, either heat-insulating plates made with a slope are used, or plastic supports are used that can be adjusted.
The main task of the slope is to ensure the unhindered movement of water to the catchment funnels anywhere on the roof.
If you check - pour a bucket of water, it should leave without delay.
High-quality roofing work will significantly extend its service life.
Video about the device of a flat roof.
Sergey Novozhilov is an expert in roofing materials with 9 years of practical experience in the field of engineering solutions in construction.
Choosing the type of roof, determining the angle of inclination and other parameters of the roof is an important and responsible task that requires knowledge of the standards and taking into account the climatic features in the region. The article describes a flat roof, its advantages and features. It explains in detail why it is needed and how the slope of a flat roof is made. The information will be useful to all owners of plots planning the construction of a residential building, auxiliary or outbuildings.
flat roof structure
A flat roof is a single sheet, not divided into separate sections, having a certain slope to organize the flow of water. There are buildings of complex architecture, consisting of several departments with different levels of height. Each part usually has its own roof, but the general rules for each individual section remain.
Flat roofs are traditional for the architecture of southern countries, but in the northern regions they are used mainly for non-residential buildings - utility or auxiliary. The reason for this attitude is the abundance of precipitation, which does not occur in such quantities in regions close to the equator.
The traditional device of flat roofs consists of a support system (rafters) that forms an inclined plane with selected parameters. On top of the rafter system, a flooring is created from boards, on which the roofing sheet is attached. This design is simple, built quickly enough and allows you to ensure the removal of moisture from the under-roof space.
The disadvantage is the use of wood, which has a tendency to warp, rot and present a fire hazard. In addition, wooden rafters have a limited load-bearing capacity, requiring careful calculation to meet snow loads. A considerable danger is the impact of wind, strong gusts of which can tear off the roof, causing significant damage.
In order to increase the strength and increase the bearing capacity of flat roofs, a construction technique has been developed in which the construction of the truss system is abandoned, replacing it with a dense bulk layer - a slope. it is laid at a certain angle to the horizon, forming an inclined plane on which the roofing is laid. As a result, the ceiling of the upper floor becomes the support system, and the slope of the flat roof strengthens it and forms the required angle of inclination, which is optimal for given conditions and materials.
Advantages of flat roofs
The main advantage of a flat roof is the simplicity and cost-effectiveness of construction. Such a surface is comfortable and safe, allowing maintenance or repair work to be carried out under optimal conditions. The surface area of such a roof is much smaller than that of pitched structures, which allows significant savings on roofing material.
An additional advantage of flat roofs is the convenience and ease of installation on them of various technical devices and equipment - satellite dishes, solar panels, etc. simplifies the repair and maintenance of equipment, which can be carried out at any time of the year.
There are flat roofs, the surface of which is equipped for lawns, pools, recreation areas and other areas. In these cases, the use of the surface is most efficient, although it requires significant costs for the design and maintenance of the sites.
Slope for a flat roof: a whim or a technical necessity
Slope is a necessity that an abundance of precipitation causes. Rain or melt water must be able to be removed from the surface, otherwise the roofing will quickly collapse and fail. In the summer, stagnant rainwater will provoke an aggressive effect of chemical elements and oxygen dissolved in the mass of precipitation. In winter, the presence of moisture is even more dangerous - when the temperature drops, it will freeze and begin to expand. The smallest cracks in the surface, where moisture penetrates, will increase.
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To organize the operational flow of water, at least a minimum slope of a flat roof is required, which allows water to be removed by gravity from the roof. The best option for solving the problem for roofs of a large area is to flatten the flat roof with bulk materials, forming a plane with the desired angle and simultaneously performing the functions of insulation and sound insulation.
Minimum and maximum slope of flat roofs according to SNiP
The angle of inclination of the roof is a value regulated by technical standards. In SNiP there is SP 17.13330.2011, or, more simply, in the Code of Roofing Rules. It defines the normative values of the angle of inclination of the roofing, depending on the structure of the roof, as well as the materials used. The values that the flat roof slope has are determined by SNiP in accordance with the surface properties of various roofing coverings. The degree of roughness of the metal sheet is much less than that of soft or wavy surfaces.
The slope is measured in various units:
In percentages.
Height to length ratio.
In degrees.
Such an abundance of units of measurement is caused by the specifics of construction work - it is much more difficult to control the angle using a protractor on the site than to measure linear dimensions.
The situation is somewhat more complicated when building a roof with a large area. Making a bias in such conditions is not always rational. The solution to the problem is the slope of a flat roof with an internal drain, when the entire canvas is divided into relatively small sections with drain funnels. Water, getting into them, is discharged through the pipeline system into the storm sewer. This roof design is more complicated and requires the creation of a system of drainage communications, but on large buildings this option is optimal.
In practice, the angles of inclination are much smaller and largely depend on local climatic conditions. Main factors that influence the choice are:
Amount of snow in winter.
The strength of the winds prevailing in this region.
The weight of the snow is a significant load. It can be determined from the tables in the annexes of SNiP, which indicate the average annual values for different regions of the country. The lower the angle, the less the possibility of independent descent of snow masses. At the same time, a large angle of inclination increases wind loads, which are dangerous because the roofing can be torn off the supporting surface. The destruction that occurs in this case can lead to human casualties and threaten not only this building, but also all objects located nearby.
The choice of angle is based on the magnitude of the expected loads and is taken in accordance with them. If the roof structure consists of strong materials that can withstand the static load of the weight of snow, then usually try to minimize wind effects that are dynamic and unpredictable in direction.
How to calculate the slope of a flat roof
A specialized calculation of the angle of inclination is an extremely difficult engineering task. The requirements of SNiP in this matter are advisory and determine only the permissible limits for each type of roofing. For an unprepared person, performing such a calculation is inaccessible and even dangerous. It is necessary that the design is carried out by competent and experienced specialists.
Alternatively, you can use the online calculator, which is available in abundance on the Internet. The resulting value is recommended to be duplicated on another resource in order to compare the data and balance the results. It should be borne in mind that online calculations are only advisory and should not be used in the construction of critical structures.
Roofing materials for a flat roof, depending on the angle of its slope
The choice of roofing material in the first place should be determined by the angle of the roof. There is a mass options:
roofs from piece materials and corrugated sheets
metal roof.
Soft roof.
An angle of inclination can be formed by creating a supporting structure of the desired configuration or by filling the surface with an inclined layer of insulation. There are also specialized types of materials, for example, a wedge-shaped insulation from TechnoNIKOL, the roof slope with which is created by laying plates of a specific shape.
The choice of the most suitable material is made by comparing local climatic conditions, building parameters, capabilities and preferences of the owner. All these factors are equally important, but it is recommended to give priority in decision-making to representatives of a construction company with experience and special knowledge.
Video description
In the video you can see the device of flat roofs:
Conclusion
In conclusion, it should be noted the increase in the number of buildings with a flat roof. The fashion for such architectural solutions, which came from Europe, requires the use of appropriate technologies and materials. It is irrational and impractical to approach construction with the usual standards common in Russia. For buildings with flat roofs, a special project is required, taking into account the climate, material properties, and hydrogeological conditions.
It has a number of its advantages, such as: its installation will take less materials, ease and simplicity of installation and additional useful territory.
For many, the phrase flat roof is in no way associated with a slope. Although this is far from true. Even the most even roof has its slope, even if it is minimal.
At a minimum, this is necessary so that melt water, and water after rain, can safely drain into the installed funnels, which are part of the internal catchment area, 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:
- Operated roof;
- unused roof;
- Traditional roofs;
- Inversion roofs.
The slope that should be on this type of roof, is about 1-5 degrees If this is neglected, 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 up 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 the fact that moisture gradually penetrates the insulation. The essence of the mechanism is that moisture penetrates the layer, which means that inevitable leaks occur.
But this is not the only problem. In addition, puddles on the roof can be covered with dust, which at one time settles on the bottom. Seeds of various herbs and plants can fall into this puddle and germinate there.
Often on the streets you can find houses on the roofs of which there is grass or thin trees. 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, Roof sloping needs to be done.. Such complex manipulation is carried out at the time of construction itself.
The process itself is quite complex, and includes many activities of different structure. The purpose of this procedure is for the roof itself to acquire the necessary slope..
But before you start the slope of the roof, you need to find out what a flat roof consists of.
Flat roof
In fact, it is a pie with several layers:
- Immediate foundation, which is reinforced concrete slabs that have a certain wave height;
- , which can be made from different materials, such as bitumen, or roll materials;
- The next layer is, which can be made of mineral wool or other durable material.
The ingredients of this pie can be changed if the builder wants to do the whole roof with the new building materials. It should be understood that such a procedure as a bias, carried out directly at the time of laying the insulation.
It is important that in addition to such 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 to pay attention to is wind effect. 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 the sheets of the roof. It is important to note that the angle of the roof dictates the necessary conditions for the truss system, as well as for all components of the roof, namely: rafters, sheathing step.
Obviously, the steeper the slope of the roof itself, the faster the outflow of water.
Percent slope
Minimum angle and roof slope calculation
The minimum slope angle can be determined based on the materials of the roof itself:
- If the roof is made of then its minimum slope must be at least 12 degrees(according to SNiP). If the roof is made of angle increases up to 15 degrees. It is important to understand that the gaps of the material, and other joints, must be treated with a special sealant - frost-resistant / waterproof. If the angle of inclination is 15 degrees, then the sheets of material should overlap 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, materials based on bitumen. It is logical that by the value of the slope angle, affects the number of layers of the roof. If, for example, the roof is carried out in two layers. then an angle of inclination of 15 degrees is quite enough;
- Having covered the roof, it is worth understanding that quite enough and 11 degrees of inclination angle, but at the same time you need to make a crate of a solid type.
Such a process as a flat roof slope, made from these 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. Before starting work, it is necessary to correctly calculate the angle of inclination itself. In fact, it is quite easy to carry out this calculation, for this you need to use a goniometer, or with fairly simple mathematical formulas.
Despite the fact that a flat roof is called a flat roof, it still needs a slope. The minimum slope for a flat roof is 1 degree or 1.7%.
The instructions for using bituminous and polymer coatings for sloping indicate that the optimum angle of inclination should be 1.5 degrees. An inclination of 1-2 degrees is acceptable.
Everything is very simple here. You need to know the height of the roof and its width. Further, simple trigonometric formulas will help calculate the direct angle (sine, cosine, tangent). And according to 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 height of the roof must be divided by half the width, and the result already obtained is multiplied by one hundred, after that, in the table, you can find out the percentage value of the future angle of inclination. This option is faster, but they are both correct in terms of accuracy.
Minimum slope
Sloping a flat roof with bulk materials
If you decide that the slope procedure will be carried out using bulk materials, then the first thing worth noting is the scheme by 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 a high waterproofing performance;
- Farther, 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 it is necessary to cover the layer of expanded clay with a special polyethylene film. It is important to note that it must be overlapped;
- Further, it is necessary to apply the prepared sand-cement screed doing it smoothly, slowly. Its essence is to level the layer of poured expanded clay;
- After these events, you can start carry out the formation of 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 a sand-cement screed on top of it, you can fill it with cement milk. But it is worthwhile to understand that because of him, the design 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 is quite enough.
bulk material
Thermal insulation materials
Another good material for roof slopes are thermal insulation materials. Experts claim 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, the best material. The scheme of the process is quite simple.
It is necessary to attach the material to the base itself, using self-tapping screws or dowels. Some prefer sheets of such cotton wool to be glued to a previously cleaned base with special glue. Such a process can be performed both during and during the installation of the roof.
Thermal insulation material
foam concrete
A good material that can be used to flatten a flat roof is foam concrete. It should immediately be noted that this procedure must be carried out using special equipment.
On the base itself, a layer of foam concrete is poured, but at the same time the angle of inclination itself is noted, and after make a special screed of foam fiber concrete. Next, it is important to apply waterproofing material.
A huge plus of this kind of razuklonka - high rate of thermal insulation, as well as other mechanical characteristics. For example strength and durability.
Speaking of cons, they are here too, or rather one. This is the price. She is high enough. And again, to carry out such a procedure on your own will not work. Therefore, in this case, it is worth contacting 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 done exclusively to the side (funnel, gutter);
- If your roof is bituminous, it is worth making 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 values of the slope angle, it is necessary to carry out ventilation of the under-roof space itself, with all the slopes. 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 December 27, 2017
- In the warm season of the year, rainwater with well-equipped roof waterproofing quickly or slowly evaporates from it. However, during the cold period, water puddles constantly freeze and thaw. As a result, the roof coating begins to collapse, and the liquid begins to penetrate into the thermal insulation material.
- With a small slope of a flat roof, moisture stagnates on it and penetrates under the waterproofing layer. This provokes its leakage into the premises of the building.
- Dust and soil particles brought with the wind accumulate in permanent water puddles. He also delivers seeds of various plants there. They successfully take root in this favorable environment. Therefore, often there are roofs on which grass and moss grow. Their roots gradually destroy the roof lining.
- climatic features of the area;
- the purpose of the building;
- type of roofing material.
- for flat roofs lined with roll and membrane coatings, polymer and bituminous mastics, the slope angle should be from 1.5% (1˚) to 10% (6˚).
- for operated and inverted structures, the slope can be from 1.5% (1˚) to 3% (2˚).
- bulk substances (blast-furnace slag, expanded clay granules, perlite sand);
- lightweight concrete with the above fillers;
- polymer concrete mixtures;
- thermal insulation boards and mats.
- Over time, this layer shifts. In this case, the structure of the slope is violated. This creates barriers to water drainage.
- An excessively large diameter (about 1.5–2 cm) of expanded clay particles does not make it possible to form a smooth slope.
- EPS (extruded polystyrene foam);
- dense basalt wool in slabs;
- sprayed polyurethane;
- lightweight gas and foam concrete.
- To set the design angle of the slope, the plates of the insulating material are fixed to the roof overlap with self-tapping screws or dowels.
- Sometimes the heat insulator is glued to the base with bituminous mastic or special glue. It should be borne in mind that the reliability of the adhesion of surfaces must exceed the tensile strength of the insulation.
- First, they apply a layer of foam-reinforced concrete solution to the roof with a pump and form slopes from it.
- When the screed dries, it is covered with rolled roofing.
Specialization: philological education. Experience as a builder - 20 years. Of these, for the last 15 years he led a brigade as a foreman. I know everything about construction - from design and the zero cycle to interior design. Hobbies: Vocal, psychology, quail breeding.
Greetings, my dear readers.
Although the roof is called flat, this does not mean that it must be made absolutely flat horizontally. All roofs must have a slope. It is necessary so that storm and melt water can freely flow into the funnels with internal drainage or gutters with an external drainage system.
Let's figure out what the slope of a flat roof should be and how to equip it.
Why do you need a slope on a flat roof?
To stop all these problems and increase the life of the roofing pie, a roof slope is necessary. It is formed at the stage of construction of the roof.
Slope for a flat roof
The slope indicates the angle at which the roof plane is located relative to the base. It is calculated using a geodetic instrument - an inclinometer. All types of roofing have a minimum and maximum roof slope in degrees defined by the standards.
These values are collected in the published graph. From it it is very easy to find out which material is optimal for the design slope of the roof. Looking at this graph, it is possible to convert the percentage parameter to degrees and vice versa.
This can also be done manually. To do this, you need to divide the height of the roof by the width divided by 2 (this is the projection of the slope). If you multiply the result by 100, you will find out the slope of the roof as a percentage.
The slope of a flat roof is determined:
The angle at which a flat roof needs to be tilted is determined during its design. In SNiP No. II-26/76 "Roofs" its minimum and maximum values \u200b\u200bare indicated:
Methods for creating minimum slopes on a flat roof
Flat roof slope can be done with the help of such materials:
It is worth warning that bulk materials have several disadvantages.:
There are no such disadvantages for a light concrete screed. But it can not always be used. Such a design has significant weight.
This creates an excessive pressure on the base of the roof. It is possible to use concrete mortar to create slopes on the roof at the stage of its construction or during major repairs.
For the arrangement of the slope, you can use the following types of heat-insulating materials:
Creating slopes with bulk materials
The algorithm for arranging the expansion of expanded clay is as follows:
| Photo | Stage of work |
 |
Step 1
Rolled waterproofing is laid on the reinforced concrete floor or the bearing corrugated board of a flat roof. It can be hydroisol, glass isol. These materials reliably insulate the roof from moisture and have a long service life (about 30 years). |
 |
Step 2
The thickness of the bedding should be at least 10 cm. Slopes on the roof are formed from this layer. |
 |
Step 3
Then a second layer of waterproofing is placed on the embankment. It can be a polyethylene film. Its panels are overlapped by 10 cm, and the joints are sealed with adhesive tape. |
 |
Step 4
After that, the film is poured with a leveling screed. It can consist of concrete or sand-cement mortar. |
 |
Step 5
Lastly, the roofing is laid. This is done in such a way that the resulting slope is preserved. |
So that the expanded clay bedding does not move when laying concrete, it is advisable to fix it with cement milk. But it should be remembered that then the roofing cake will become heavier and the load on the base will increase.
When it is necessary to equip the minimum slopes on a flat roof with a small surface area, they can be made with a sand-cement mortar.
The use of insulating materials
Now the use of insulation is the least expensive and time-consuming method of forming slopes on a flat roof. Heat insulators are inexpensive and weigh little.
The best option- use expanded polystyrene or stone wool for spreading:
Formation of slopes using foam concrete
Foamed concrete mixes are made on special equipment. Experienced specialists should lay the slope of them:
With this method of forming a slope, the roof is durable, reliably heat and waterproof.
Conclusion
To give a minimum slope to a flat roof, you can use different methods. The main thing at the same time is to correctly choose its angle. In this case, the water will go into the drainage system without obstacles.
If you have any questions, you can ask x in the comments. I say goodbye and good luck in your endeavours.
December 27, 2017If you want to express gratitude, add a clarification or objection, ask the author something - add a comment or say thanks!
