What is the minimum slope of a flat roof. Flat roof slope - building codes and recommendations Flat roof slopes diagram
At flat roof, which was built in accordance with the requirements of building codes and regulations, there is always a slight slope. If it is minimal, an inexperienced observer will not notice. But if there is no slope at all, it will be visible immediately. The fact is that in the absence of at least some slope of the structure, rain or melt water will necessarily collect on it.
Even if the surface of a flat roof is created perfectly flat, and, it would seem, there can be no talk of any puddles, the reality is different. Under the influence of wind, solar radiation, rains of various acidity, temperature changes, the roof deforms over time, zones are formed on it, in which water or dirt brought by the wind can linger. If there is minimum slope, the chances that water or snow will linger on the roof for a long time are much less.
What's the point in dodging
It would seem that sooner or later the snow lingering on the roof will melt, and the water will either dry up or the drainage system will cope with it. The experience that eventually resulted in the recommendation of the Building Code suggests otherwise. Water tends to destroy the structure of the roof in a variety of ways.
Firstly, the water on the roof is not completely distilled, its chemical analysis will show the presence of dissolved oxygen and a whole range of substances that will actively destroy the roof material. Secondly, in the cold season, water can change its state of aggregation several times a day. Among other things, it is also a change in volume, which carries a powerful destructive force.
The slope of a flat roof is also needed so that dust does not accumulate on it. Many saw vegetation on the roofs of residential and industrial buildings. It would seem, where does the grass and trees come from? But wind, water and sun do their work steadily. And the roots of plants, as you know, are able to destroy even very strong materials.
What is measured and how the slope is determined
The parameters of a flat roof, which include the minimum slope, are regulated by the set of rules SP 17.13330.2011 SNiP II-26-76. A document so complex in designation is easier to distinguish by name. It is called the "Code of Roofing Rules", or Theroofs in English.
The scope of the document is the design of roofs using rolled, bituminous and other roofing materials, several types of tiles, slates and tiles, galvanized steel and copper sheets, profiled sheets, aluminum, zinc-titanium and other structures.
Before considering the table available in the set of rules, it should be clarified that the slope of a flat roof can be measured either in degrees or as a percentage. There are also relative units like 10/12, but they are rarely used.
Slope Table
In paragraph 4.3. of the set of rules mentioned above, there is a table in which the norms are prescribed that determine the slope of a flat roof, that is, its minimum size. The values depend on the type of materials used for the arrangement of the roof, as well as on some other factors.
So, if the roof is equipped with roll materials or bitumen-based mastics, it should be sloped between 1° and 6° (1.5-10%) if gravel or other coarse-grained materials are placed on top. If upper layer- foil, the slope of a flat roof varies from 1 ° to 16 ° (1.5-25%).
When using polymer roll materials, the slope should not exceed 1° (1.5%) without a protective layer and 2° (3%) with a protective layer.
Quite different values are provided for piece materials, metal sheets and concrete structures. For shingles and slates, the minimum slope of a flat roof is between 12° (20%) and 22° (40%). Metal sheets can be placed at a minimum of 7° (12%), reinforced concrete trays - 3°-6° (5-10%).
The norms allow the use of significant slopes, but some additional requirements are required.
How slopes are created
The process of creating roof slopes is commonly referred to as sloping. This process uses:
- bulk materials, in particular perlite and expanded clay;
- lightweight concrete compositions based on the same perlite and expanded clay;
- lightweight concrete compositions based on polymeric materials;
- insulating materials.
Which material will be used depends on the design of the building, on the required slope and on some other factors. For example, lightweight concrete in some cases may be too heavy, creating a significant load. On the other hand, when using bulk materials, it is impossible to create a large angle. In general, different materials has its advantages, disadvantages and scope.
When building roofs for commercial and industrial buildings, at least the minimum must be done. An absolutely flat and even roof is ineffective as a water outlet. Atmospheric precipitation lingers on the roof, and over time, areas of stagnation appear, drying out only in extreme heat. From the side, such a roof looks flat, as in the photo, but at the same time, the efficiency of removal increases, and, accordingly, the service life increases. roofing.
Why is it necessary to make a slope
The formation of stagnation zones is harmful to roofing material. In the cold season, the water constantly freezes and melts, because of this, the roofing material is destroyed, and all conditions are created for the occurrence of corrosion.
The slope of a flat roof as a percentage should be 1.7-7%.
Roof slope options
Flat roof slope can be done in the following ways:
- using materials for insulation;
- with the use of expanded clay, perlite and other backfill materials;
- with the use of light concrete mixtures based on bulk insulation;
- using lightweight concrete mixtures based on polymer fillers.
Most often, backfill materials are used, but the slope with their help has several disadvantages. This is, first of all, the displacement of the backfill material over time, due to which the angle of inclination changes. Over time, such a decompression may become ineffective. In addition, the large size of the expanded clay unit (approximately 20 mm) does not allow you to create a smooth slope.
Razklonka with the use of lightweight concrete is devoid of these shortcomings, but it can not always be done. The design has a significant mass, which creates a load on a flat roof. Therefore, demolition with concrete can only be done during the construction of the building or overhaul roofs.
If you need to tweak the roof a little, then the slope of a flat roof can be made using special polymeric materials, for example, extruded polystyrene.
Usually a flat roof consists of:
- supporting structure;
- leveling cement-sand screed;
- a layer of vapor barrier materials;
- layer thermal insulation materials;
- waterproofing from roofing roll material.
In addition to these layers, a flat roof must have water inlets if an internal drain is created. If the drainage system is external, water intake gutters are installed, which are attached either to outer wall buildings, or under the roof. Naturally, it is necessary to calculate correctly.
If a profiled sheet of metal was used as the base, a profiled sheet structure can also be used for waterproofing. A flat roof may have a different structure, but as a rule, general scheme remains the same.
Razklonka bulk materials
Razklonka inexpensive filling materials are done in the following way:
- A layer is laid on a reinforced concrete base waterproofing material- glass isol. This material has a long service life - up to 30 years.
- Expanded clay is poured onto the glass isol in accordance with the project. Large expanded clay granules do not make it possible to accurately measure the angle, so they have to be poured “by eye”.
- Expanded clay is covered with a plastic film overlapped. After that, the roof is made based on the project, while creating each new layer, you need to control the angle.
Making a slope of a flat roof in this way is inconvenient for the reason that the angle of inclination cannot be accurately calculated, moreover, the displacement of expanded clay begins even when the screed is poured. This can be avoided if expanded clay is poured with cement milk, but the drying time is significantly increased. Plus, there is a load on the floor, as the weight of a flat roof increases significantly.
Razklonka foam concrete
Instead of expanded clay and cement mortar, foam concrete can be used. First, a layer of foam concrete is poured onto the base in accordance with the angle of inclination, then a foam fiber concrete screed is made. A waterproofing material is laid on top of this.
Such a roof has good thermal insulation and mechanical characteristics. But it also has disadvantages - the main among them is high price. It is also worth considering that it is unlikely that you can do the laying out of foam concrete on your own, so you will have to hire specialists.
Razklonka with heat-insulating materials
Rauzklonka using heat-insulating materials is inexpensive and easy to perform. You can do the slope both during the construction of the roof and during repairs. The most profitable, based on financial costs and thermal insulation qualities, is a ramp using polystyrene and mineral wool. The undoubted advantage is the low weight of these materials. When using them, there is no need to strengthen the roof.
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 less, 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 over all influences 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 reinforced concrete slab ceilings or sheets of metal profiles.
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 boards, 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
Polymer-filled concrete mixes are 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
Modern way - application plastic panels with 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 - roofing materials expert with 9 years of experience practical work in area 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 general rules for each individual section are saved.
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. over truss system a flooring is created from the 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. she fits under certain angle to the horizon, forming an inclined plane on which the roofing is laid. As a result support system the overlap of the upper floor becomes, 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, allows maintenance or repair work V 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 summer time stagnant rainwater will provoke an aggressive impact chemical elements and oxygen dissolved in the mass of sediments. IN winter time 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.
On our website you can find the most . In the filters, you can set the desired direction, the presence of gas, water, electricity and other communications.
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 The solution to the problem for roofs of a large area is the slope of a flat roof with bulk-type materials, which forms a plane with the desired angle and simultaneously performs 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 construction works- 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 issue is the slope of a flat roof with an internal drain, when the entire canvas is divided into relatively small areas with water funnels. Water, getting into them, is discharged through a system of pipelines to 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 countries. 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, the capabilities and preferences of the owner. All these factors are equally important, but it is recommended to give priority in decision-making to representatives construction company with experience and specialized 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. Fashion for similar 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.
