If previously a flat roof was mainly found on typical multi-storey buildings, industrial and production buildings, now horizontal roofing is widely used in urban and individual construction.
At the same time, installation of a flat roof requires a serious approach, any errors in design or non-compliance with technological standards can lead to serious consequences. In order to avoid problems during construction, and the project is accepted by regulatory authorities, it is necessary to carefully study the issue and properly prepare for work.
What is a flat roof?
A flat roof is a roof that visually appears horizontal. But in reality, there is a slope of 1-5 degrees (1.7-8.7%). This is enough for water and snow to flow toward the drains and not linger on the surface. If the installation is done correctly, there will be no streaks on the covering, which lead to mold and destruction of materials.
The main difference between flat roofs without a rafter system is that the floor is attached directly to the walls of the building. At the same time, the foundation for the support must be strong enough to withstand high loads for a long time. These can be reinforced concrete slabs, corrugated sheets, a base made of boards and plywood on wooden beams.
The roof itself has a multi-layer structure. The number and composition of layers depends on the type of construction, we will discuss this in more detail below.
Advantages of flat roofing
Private houses, offices, shops with flat roofs look quite fresh against the background of already typical buildings with pitched roofs. Despite the simplicity of the solution, such high-tech buildings look modern, fit well into both the urban landscape and the countryside.
Advantages of choosing a flat roof:
- High wind resistance. Initially, houses with flat roofs were built in Asia, on the coast of seas, oceans, near plains, where buildings are exposed to high wind loads. Even strong gusts of wind cannot damage the integrity of the roof.
- Savings. This is true, but only partly. A flat roof does require less building materials than a pitched roof, since the finishing area is smaller and there is no need to build a rafter system. But at the same time, you cannot save on vapor and waterproofing, otherwise the foundation will leak after 2-3 freeze/thaw cycles.
- Easy and safe maintenance. Removing snow from a flat roof is much safer and easier – no need to use insurance. You can freely move along the horizontal surface to check chimneys, antennas or ventilation systems.
Types of flat roofing and its components
The purpose of a flat roof depends on its structure and the materials used for insulation.
Unexploited roof
Its main purpose is to protect the building from negative environmental impacts. 1-2 people are allowed to be on the roof to carry out repair work, but it is not allowed to install equipment or furniture.
Let’s take a closer look at the structure of a standard non-exploitable roof:
- Foundation. Depending on the type of flooring, corrugated sheet or reinforced concrete can be used.
- Vapor barrier layer. It is laid from waterproofing film, bitumen-containing material or PVC membrane.
- Mineral wool insulation with a minimum thickness of 150 mm.
- Finish coating.
For strengthening, a cement-sand screed can be additionally laid.
The company Dorhan uses non-exploitable flat roofing for its modular houses. Features of the structure from outside to inside:
- Seam sheet 0.5 mm thick with polymer coating, color according to RAL catalog.
- Vapor barrier.
- The insulation material is a 150 mm thick mineral wool slab.
- Vapor barrier.
- Gypsum board sheet 10 mm thick.
Exploited roof
The exploited roof can be used all year round. The space is combined with the living space by one entrance. The roof has a multi-layer structure, which includes many components. The main differences in the design:
- The foundation must be rigid and have high compressive strength. Most often, it consists of reinforced concrete slabs with a slope-forming layer.
- It is mandatory to have a concrete screed between the hydro- and heat-insulating layer. A slight slope towards the drain is also provided.
- Paving slabs are suitable as the final covering. For additional protection from external factors, a layer of geotextile is placed under the slabs.
Such a roofing “pie” is capable of withstanding high loads, including those from various structures on the roof.
Inversion roof
The inversion roof can withstand multiple freeze/thaw cycles and strong ultraviolet radiation. That is, such an architectural solution is suitable for both the southern and northern regions of Russia.
The main difference is the enhanced protection of the thermal insulation layer. Here, an additional layer of insulation is laid over the waterproofing. This reduces the adverse effects of temperature and solar radiation.
The lower part of the roofing “pie” also consists of a reinforced concrete base. Extruded polystyrene foam or PIR boards are used as insulation. Both of these materials are characterized by high compressive strength. Particular strength is created by a double layer of insulation – ceramic gravel is laid on the base, and then covered with a cement-sand screed with reinforcement.
Features of flat roofing
When installing a flat roof, you need to pay close attention to the design of the drainage and ventilation system.
Drainage device
The horizontal base has a more complex drainage system than the pitched ones. The main thing is to think through a small slope angle (1-2%) so that water, even in small quantities, does not linger on the roof. For further drainage of rain and melt water, the following systems are used:
- External. Water is collected using gutters or gutters complete with funnels. The system is installed along the eaves overhangs on the outside of the load-bearing walls. The solution is suitable for residential and non-residential buildings. External drainage has proven itself best in low-rise construction, but it can also be used in buildings up to 5 stories high.
- Internal. Special funnels are installed in the roof to collect water. Water flows into them under gravity, is collected and discharged through internal risers.
If there are several water intake funnels installed on the roof, a watershed must be installed, that is, a system of slopes that will direct the flow of water into each individual funnel.
An external drainage system on a flat roof is recommended in southern regions, where the water in the pipes does not freeze in winter or this happens extremely rarely. But in regions with a moderate climate, it is better to give preference to internal systems.
Parapet device
Parapets are protective fencing that perform important tasks:
- Holds snow masses on the roof and prevents them from accidentally falling on passers-by.
- Prevents accidental falls of people during inspection or repair and restoration work. The installation of parapets is mandatory for an exploited roof where an observation deck or recreation area is organized.
- Protects the roof from strong gusts of wind, improves the waterproofing qualities of the roofing “pie”.
- Prevents sparks or open flames from reaching the roof and acts as a fire barrier.
Parapets also have an important decorative function, masking communications, ventilation pipes, and air conditioners.
The parapet requires double thermal insulation, since with one-sided insulation the wall under the ceiling is likely to freeze.
On unexploited roofs, fencing is optional, on used roofs – mandatory. The height is regulated by SNiP standards.
If the roof has structures over 10 cm high, a protective curb of up to 45-50 cm will be needed. When arranging the exploited space, parapets up to 1.2 m should be installed. However, such a height may be inappropriate when organizing an observation deck, cafe or other public place on the roof. Here, builders resort to trickery – they install a monolithic curb (30-40 cm), and a metal fence, glass or plastic fences are mounted on top.
Rules for the operation of a flat roof
The efficiency and service life of a flat roof depends on compliance with maintenance rules. Without maintenance, any roof will sooner or later leak, deteriorate from excess ice, and snow load.
Preventive examination is recommended to be carried out 4 times a year, at the end of each season. During the examination, it is necessary to pay attention to the following factors:
- The integrity of the roof covering, the presence of cracks, dents and swelling.
- The condition of the materials in the area of adjoining parapets, connecting seams. Here it is necessary to ensure that the material does not move away from the base or slide.
- Accumulation of debris, dust, moss, and other vegetation.
- Reliability of fastenings.
Proper use of roofing with bitumen and bitumen-polymer coating includes following simple rules:
- In winter, the first thing to do is to get rid of excess snow. It is especially important to remove precipitation from parapet areas. There are no strict rules for cleaning, but during periods of heavy snowfall, the snow is not completely cleared, leaving up to 10 cm of the layer. This is necessary for additional thermal insulation and to avoid collapse due to a strong difference in weight.
- In summer and autumn, the condition of the drain funnels is checked for contamination and the drains are cleared of leaves and debris.
- In spring, it is necessary to prevent the formation of ice plugs in external and internal drainage.
If damage to the roof covering is found, a patch can be installed.
Maintenance of a flat roof with a PVC membrane surface occurs according to the same principle, with the exception of a few points:
- The roof can only be cleaned with a plastic or wooden shovel; an iron one can damage the surface.
- It is not allowed to leave any metal objects on the roof. If nails or screws accidentally get here, they must be removed.
- The coating can also be damaged by fats, oils and petroleum products.
If you follow all these simple rules, a flat roof can last up to 30 years or more.
The main rule when constructing a flat roof is not to save on materials and especially on specialists. So you won’t be able to save much when choosing such a solution. But if you approach the matter correctly, you will get a beautiful, stylish and durable roof with great potential.