The main task of the roof covering is protection from precipitation, but the coating is at risk of mechanical damage, and snow and water can be blown into the gaps between the elements of some coatings. This article discusses the main protection that the roof is exposed to - insulation, which has three main varieties.
Waterproofing
The main question that arises when a roof is being built is roofing and insulation: how to prevent moisture from penetrating under the coating, since the insulation loses its properties when wet, and wood structures begin to rot.
Waterproofing a metal roof or a roof made of any other material is designed to prevent these troubles. The difference between the temperature of the space under the roof and the temperature of the outside air leads to condensation from the air on the cold areas of the roof pie.
Waterproofing (Footnote 1) - protection of building structures, buildings and structures from the penetration of water (anti-filtration waterproofing) or the material of structures from the harmful effects of washing or filtering water or other aggressive liquids (anti-corrosion waterproofing).
In addition, quite often the “dew point” appears inside the heat-insulating material itself or on roofing elements made of wood, which makes it necessary to install such components of the roofing pie as ventilation circuits that remove water vapor from the under-roof space with the help of supply air, preventing them condensation.
In this case, the waterproofing of a pitched roof is also an element of its ventilation system, the type of which affects the number of circuits:
- One circuit between the roof and waterproofing;
- Two circuits between blood and waterproofing, as well as between insulation and waterproofing.
Waterproofing is considered to be installed correctly if the following conditions are met:
- Roof waterproofing materials are laid under the entire roof covering, including under the overhangs of gables and cornices;
- The lower sheet of waterproofing is brought out beyond the boundaries of the eaves into the drain or onto the frontal board;
- The film is adjacent to all pipes and walls on the roof.
vapor barrier
In any living space, water vapor is necessarily present, which rise from the bottom up, falling as a result into the under-roof space, where it is located roof insulationwhich must not be exposed to these vapors.
Therefore, a vapor barrier is a mandatory element that a roof and roof insulation must have. Finishing the walls of an attic or attic room with a material that does not allow vapors to pass through can sometimes prevent their penetration into the insulation, but most often it is necessary to use special vapor barrier films that are laid between the insulation and the ceiling, usually adjoining directly to the insulation material.
The most important quality of such a film is its vapor barrier, which is determined by the density of its material and expressed in g/m2(the higher the density, the more effective the vapor barrier).
In addition, the film must be sufficiently tear-resistant for two reasons:
- When the elasticity of the insulation is lost, the rafters cease to hold it, as a result of which the weight of the material falls on the vapor barrier, which must withstand such a load;
- High tensile strength allows the film to keep the vapor barrier intact even when mechanical stresses occur in the roof structure.
In modern construction, the following hydro- and vapor barrier materials are used:
- Polyethylene films used as hydro- and vapor barrier;
- Polypropylene films, used more often for waterproofing;
- "Breathable" non-woven membranes, commonly used as waterproofing.
The main purpose of materials for vapor and waterproofing is to protect the roof from moisture penetration, as well as to maintain the necessary mode of operation of the insulation under the roof.
Their main functions are:
- Preventing the penetration of moisture into the thermal insulation material, which sharply reduces its properties and often leads to its destruction;
- Participation in the operation of the ventilation system roofs, preventing the accumulation of moisture in the thermal insulation material and facilitating the removal of its vapors to the outside.
Waterproofing films should be used in the construction of pitched roofs, the coating of which does not form a continuous carpet, such coatings include:
- Tiles of all kinds;
- metal roofing;
- Slate.
These films also protect against moisture penetrating from the outside during strong winds or oblique downpours.
Vapor barrier films must be used in the construction of both pitched and flat roofs, regardless of the type of coating. They protect the layer roof insulation from water vapor penetrating from the interior, formed in the course of human activity and rising into the under-roof space as a result of convection and diffusion.
Below is a table by the manufacturer of roofing materials (Footnote 2) Physical and mechanical characteristics of vapor barrier membranes
| The name of indicators | Value | |||
| Alubar | Alubar 50 | Alubar 40 | Polybar | |
| Compound | high density polyethylene, aluminum foil, transparent polyester film | high density polyethylene, aluminum foil, transparent polyester film | high density polyethylene, metallized polyester | two layers of light-stabilized film and a reinforcing mesh made of polyethylene |
| Roll dimensions length m/width m/area m2 | 100/1,5/150 | 100/1,5/150 | 100/1,5/150 | 25/2,0/50 |
| Thickness µm | 101 | 73 | 112 | 300 |
| Specific gravity g/m2 | 120 | 95 | 109 | 110 |
| Tensile strength n/5cm in longitudinal direction / in transverse direction | 220/220 | 183/190 | 150/150 | 230/190 |
| Vapor permeability g/m2 per day | 0,03 | 0,03 | 1 | |
thermal insulation
The most popular type of roof for residential buildings is pitched, which provides sufficient air volume, and the room under the roof can be equipped for specific needs..
The main requirement for the construction of residential premises is high-quality thermal insulation of the roof, in which heat losses are minimized, sufficient living comfort is ensured and accumulation of condensate on surfaces is prevented.
The calculated or planned effectiveness of roof insulation can only be achieved by preventing the formation of cold bridges. Thermal insulation should be laid over roof rafters or special wood flooring. In extreme cases, the insulation is laid in a continuous layer below or on top of the rafters, preventing it from being interrupted by structural elements, which makes it possible to minimize the cold bridge near the rafters.
Important: the thermal insulation system is subjected to stresses such as wind, snow, roof self-weight, etc., so the material laid over the rafters must have sufficient strength.
When laying the insulation, it should not have depressions or cavities through which air can pass.
Consider the most common mistakes when laying thermal insulation (see. Fig.):
- The thermal insulation layer is too thin (a);
- Wrong insulation width selected (b);
- Wrong thickness of insulation (c);
- Thermal insulation material too wide (d).
Materials for thermal insulation must have the following qualities:
- Frost resistance of at least 20-25 cycles;
- Water resistance;
- Biostability;
- Lack of release of unpleasantly smelling and toxic substances.
When choosing a heater, you should pay attention to its coefficient of thermal conductivity. Another important characteristic of materials for thermal insulation is the ability to absorb and retain moisture.
Materials with high moisture absorption are unsuitable for operation, since this reduces their thermal insulation characteristics. The maximum density of the material used for insulation should be 250 kg/m3, which allows to provide an acceptable load on the floor structures.
All three types of roof insulation listed in this article are the most important elements of roof construction, because neglecting any of them will shorten its life and make living in this house quite uncomfortable.
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