Flat roofing on reinforced concrete flooring slabs is a classic solution for multi-storey residential buildings, industrial hangars and modern shopping centers. Unlike pitched structures, such a system experiences enormous loads from the weight of snow and water, and is also subject to temperature expansions of concrete itself. That is why the issue of tightness and the correct choice of materials is especially acute here.
Many property owners face leaks precisely because of the violation of the technology of laying layers or the use of incompatible materials. Roofing pie in this case, it is a complex multilayer structure, where each element performs its function: from the load-bearing capacity to vapor isolation. Understanding the physics of the processes occurring within these layers avoids costly repairs in the future.
In this article, we will discuss in detail all the stages of creating a reliable roof, starting from the preparation of the base and ending with the finishing surface. You will know why you are saving money. gradientation It could lead to a disaster, and what are the current polymeric They can last for more than 50 years without losing their properties.
Base preparation and plate defects
The first and perhaps the most critical stage is the careful preparation of the surface of reinforced concrete slabs. The concrete base shall not show visible cracks, chips or protruding fittings. Any defects must be repaired, as sharp edges can damage the waterproofing carpet, and cracks will become bridges for heat leakage.
It is important to ensure the perfect levelness of the surface, but small differences in height are permissible if they are compensated by a layer of screed or insulation. Before the start of work, the surface is cleaned of construction debris, dust and oil stains. The humidity of concrete is a key parameter: it should not exceed 4-5%, otherwise the moisture trapped inside, when heated, will turn into steam and break the waterproofing.
⚠️ Warning: Never start installing the wet-based materials. Water, evaporated under the influence of the sun, will create excess pressure, which will soar roofing carpet in the first months of operation.
For sealing seams between plates and cracks, special repair compounds on a cement basis with high adhesion are used. If the elevation differences are significant, a cement-sand-lined screed, often reinforced mesh, is required to prevent cracking when shrinking.
☑️ Verification of the basis
Formation of water drainage slopes
A flat roof does not mean a completely horizontal surface. For effective removal of precipitation, it is necessary to create slopes towards water intake funnels or parapets. The minimum angle of inclination is usually 1.5-2%, which ensures the flow of water even with heavy rains.
There are two main ways to create a bias. The first is the use of loose materials (ceramzit) or light concrete, which are laid with a layer of variable thickness. The second, more modern and accurate method is the use of wedge-shaped plates from extruded polystyrene foam (PHOTOS).XPS) or mineral wool. This method avoids "wet" processes and significantly speeds up installation.
The use of wedge-shaped plates gives the advantage of accuracy in geometry. The plates are laid out according to a certain scheme, creating the necessary "crushes" to the funnels. This is especially important for large areas, where a mistake of a few centimeters can lead to the formation of stagnant zones (puddles), which in winter will turn into ice lenses that destroy the coating.
Why are puddles dangerous for flat roofing?
Stagnant water is not just an aesthetic defect. Constant exposure to moisture accelerates the aging of bitumen materials, and the freezing and thawing cycles create mechanical stress in the structure of the waterproofing carpet, leading to microcracks and eventual leaks.
Selection and installation of thermal insulation
The energy efficiency of the building depends on the quality of the insulation. For roofing on floor plates, hard wool slabs or extruded polystyrene foam are most often used. Mineral wool It has excellent fire resistance and vapor permeability, which makes it preferable for residential buildings.
The insulation is placed in one or two layers. With two-layer laying, the junctions of the plates of the lower and upper layers should not coincide, which excludes the formation of through seams - cold bridges. Fastening is carried out mechanically using telescopic fasteners with a wide hat that run through the entire pie to the base.
If used polystyreneIt is necessary to take into account its combustibility. In such cases, a combined method is often used: the lower layer of non-combustible mineral wool, and the upper layer of foam. This allows (combining) fire safety and high thermal insulation characteristics.
When laying two layers of insulation, always place plates with shifting seams. This rule of "brickwork" is critical to keeping warm and preventing deformities of the roofing carpet.
Steamproofing and priming
The vapor insulation layer is necessary to protect the insulation from moisture rising from the inside of the room. In winter, warm air inside the building tends to come out, and without a barrier, condensate can accumulate in the insulation, drastically reducing its efficiency.
As vapor insulation, bitumen-polymer materials or special films are used. The floatable materials are laid with a overlap of 8-10 cm, and the joints are carefully warmed up by a burner. It is important to ensure the tightness of adjoining vertical elements: ventilation shafts, parapets and pipes.
Before laying the main waterproofing carpet, the surface is treated primer. It is a bitumen primer that binds the dust residues, improves adhesion and fills the base micropores. The primer must completely dry (stop sticking) before the start of the main work.
| Type of material | Basis | Melting point | Term of service |
|---|---|---|---|
| Technoelast | polyester | up to +100°C | till 30 |
| bicrosth | Glass canvas | up to +80°C | 15 years |
| Uniflex | Polyester/Glassglass | up to +95°C | before 25 |
| linocrosm | Glasswork | up to +85°C | 15 years |
Waterproofing carpet: installation technologies
The main stage of work is the installation of waterproofing. For bitumen-polymer materials (T., PVC, floatable roll) is used by the method of fusing with gas burners. The master rolls out the roll, warms up the lower layer and the surface of the base, providing monolithic bonding.
Modern. PVC membranes They are installed by mechanical or ballast method. They are welded with hot air with the help of a special apparatus, forming a seam that is not inferior in strength to the material itself. This allows you to block huge areas without using open fire, which increases the fire safety of works.
Particular attention is paid to the places of adjoining. Here an additional strip of material is used, which is wound on a vertical surface. The adjoining angle is formed from a galtel (triangular bar or insulation) to avoid breaking the material under 90 degrees, which will inevitably lead to a crack.
⚠️ Attention: When melting bitumen materials, overheating should not be allowed. The appearance of an open flame from under the roll indicates the burnout of the modifier, which makes the material fragile and brittle at the site of overheating.
Protective layer and operation
The finish layer of the roof often performs the function of protection from ultraviolet light and mechanical damage. For the materials to be floated, the top layer has a sprinkle of coarse-grained granulate (shale, basalt), which reflects the sun’s rays and protects bitumen from destruction.
If the roof is operated (for example, there is a terrace or parking), a separation layer (geotextile) is arranged on top of the waterproofing and paving tiles are laid on the supports or a screed is poured. This allows you to use the roof as a useful area, maintaining the tightness of the underlying layers.
Regular maintenance prolongs the life of the roof. Twice a year (spring and autumn) it is necessary to clean the funnels from foliage and debris, check the integrity of the seams and abutments. Timely detection of bloating or a small crack allows you to eliminate the problem with local repairs, without resorting to capital restoration of the entire coating.
Frequently Asked Questions (FAQ)
Can I put a new roof on top of the old one?
Technically, this is possible, but only after a thorough defect of the old coating. If there is moisture in the old cake, the new roof will bake that moisture and it will continue to destroy the structure. It is recommended to completely dismantle the old layers to the ground.
What is the best grade for a flat roof?
The optimal is considered a slope in the range of 2-5%. A smaller angle (may lead to) stagnation of water, and a larger one to slide materials and increase wind load, although this is less relevant for overlapping plates than for lightweight structures.
How often should I change the roof on a bitumen basis?
The service life depends on the quality of materials and installation. Budget options (e.g., glass canvas-based) last 10-15 years, while premium polyester-based materials with protective powder can last 25-30 years or more.
What is an aerator and why is it needed?
An aerator (flugar) is a device for ventilation of a roofing carpet. It allows you to remove moisture from the insulation and the space under waterproofing, preventing the material from swelling in summer and the formation of ice in winter.