Grading on flat roofs

Flat roofing technology involves the creation of a slight slope so that rain and melt water can drain freely into storm systems.

The ways of forming the slope are as follows:

  • Laying with a slope of the supporting structures themselves (corrugated board or concrete slabs). It is mainly used for slopes from 5 to 10 degrees with pitched and gable roofs.
  • Screed from lightweight concrete with the creation of the required profile. A layer of lightweight concrete of variable thickness creates the necessary slope. Draft surfaces can have complex shapes.
  • Creation of a slope when forming a thermal insulation layer. This method is used when it is necessary to minimize the load on the roof as much as possible. For this, either foam glass or extruded polystyrene foam is used. A standard thermal insulation plate is given a variable thickness so that when laid out on a horizontal surface, the required slope is obtained.
  • Since the first method is carried out mainly during the general construction installation of a building, it is not advisable to consider it as a component of roofing work.
    The most common way of forming a slope on flat roofs is a claydite-concrete screed. In fact, this is not even expanded clay concrete, but mainly expanded clay with a small amount of cement and water, which are necessary as a minimum binder when forming this layer. The main advantage of this method is its high manufacturability and low cost. Modern technologies offer new and effective solutions. One of such solutions is the use of polystyrene concrete. Although it was developed in our country about 25 years ago, it has now received a rebirth. Polystyrene concrete refers to lightweight concrete as the main filler, which is polystyrene granules. The surface of the granules is processed to ensure their uniform distribution in the thickness of the material. The combination of insulating material (polystyrene) and concrete creates an optimal combination of load-bearing properties, thermal insulation, sound insulation and fire protection.

    Possessing almost the same cost as expanded clay concrete, polystyrene concrete surpasses it in such indicators as density, thermal conductivity, and manufacturability.

    The main comparative characteristics are shown below:

  • Expanded clay concrete
    Density (kg / m3): 850
    Coeffits. Thermal conductivity, W / (m * C): 0.38
    Water absorption,%: 10
  • Polystyrene concrete
    Density (kg / m3): 150-550
    Coeffits. Thermal conductivity, W / (m * C): 0.6-0.18
    Water absorption,%: 6
  • Higher manufacturability of polystyrene concrete is expressed in the following:

  • It is less laborious when preparing the mortar directly on the construction site.
  • Significantly less wears out equipment for the preparation and supply of concrete, in contrast to expanded clay, which acts as an abrasive.
  • The surface obtained after pouring is quite even and does not require the creation of a leveling screed. Mashing with a solution is enough.
  • In the event that the roof area has large dimensions, the reduction in such costs can be significant. The latter method of creating a slope is the most time consuming and costly. It is used in exceptional cases when the use of a concrete screed, for one reason or another, is not possible.

    The most suitable material for this is foam glass. With this installation, the thermal insulation layer:

  • Forms a monolith in strength that is not inferior to concrete, while remaining lightweight. Average density of foam glass 170 kg / m3.
  • Serves as a vapor barrier, preventing moisture from condensing on the underside of the waterproofing layer.
  • Serves as a root barrier on “green” roofs.
  • Among other things, it has stable characteristics over time. Virtually no material aging.
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