Permeable waterproofing membrane: types, applications and reviews

After you have insulated the walls of the house, in the process of which inexpensive mineral wool was chosen, there may be a problem that some areas of the walls are dampened. In order to eliminate such negative effects, a vapor-permeable membrane should be used.

vapor permeable membrane

Feature of application

The process of wall insulation and arrangement of roofing structures involves the use of such films, which are placed under a layer of mineral wool. If you are faced with the task of warming from the inside, then you need to provide a barrier to water vapor. It is not recommended to use material that has perforation or pores. The vapor permeability coefficient of this layer should be minimal. It is preferable to use a film of polyethylene, which can be reinforced.

Not superfluous and aluminum foil coating. We should not forget that when using vapor barrier it is necessary to think about the presence of a ventilation system. There are also special films on sale that are coated with an anti-condensate coating. Such a vapor-permeable membrane cannot form condensate on its surface. The material is usually enclosed under layers that are susceptible to corrosion. These include galvanized sheet, corrugated sheet metal and metal (the latter does not have a protective inner coating).

The film will not allow wet vapor to reach the metal. To do this, there is a rough fabric layer on the reverse side, which is necessary for collecting moisture. It is necessary to lay the film with anti-condensate coating with the fabric side down, departing about 2-6 cm from the layer of mineral wool. Those building membranes that can transmit evaporation are used for wall insulation outside, they protect materials from wind gusts and can be laid in the construction of pitched roofs. Their use is also advisable in leaky facades, when it is necessary to lay a protective layer from moisture. For vapor permeability, the films have perforations and microscopic pores. Moisture that accumulates in the insulation must pass through them into the ventilation system.

vapor-permeable waterproofing membrane

The main types of vapor-permeable waterproofing membranes

The vapor-permeable membrane is of several types. It:

  • material of diffusion type;
  • diffusion membrane;
  • super diffusion membrane.

The first variety is able to skip about 300 g of vapor per day. This indicator is relevant for each square meter. If we are talking about a diffusion membrane, the coefficient of vapor permeability can vary from 300 to 1000 g / m2. In superdiffusion membranes, this indicator exceeds 1000 g / m2. Because the diffusion membranes protect against moisture, they can be used under the roof as an outer layer. It is necessary to provide an air gap between the insulation and the film.

When facade insulation such materials can not be used, because they do not let the steam. After all, when it is rather dry outside, dust can get into the pores from ventilation. This will cause the film to stop “breathing” and condensate will settle on the insulation layer.

wind vapor permeable membrane

Reviews permeable membrane

The vapor-permeable membrane must be laid using a special technology. If we are talking about a diffusion or superdiffusion membrane, then the pores are quite large, so they will soon become clogged. This necessitates the presence of an air gap for ventilation from the bottom. According to users, it does not have to bother with the installation of sheathing and counter racks. Not only diffusion films can be found on sale, but also their bulk version. As buyers emphasize, the interlayer for ventilation is located inside. Due to this, condensate is not able to penetrate inside the metal roof. The principle of operation of such material is the same as that of the anti-condensate film. However, there are differences. As the home craftsmen emphasize, the volume membrane is capable of removing moisture from the insulation. After all, if the metal roof has a slight slope ranging from 3 to 15 °, then the condensate from the lower side will not be able to flow down. It will erode the galvanized coating and gradually completely destroy it.

vapor barrier waterproof membrane

How to install the membrane - from the inside or outside of the insulation?

Vapor-permeable waterproofing membrane must necessarily be laid according to a certain method. If it is necessary to insulate the facade, then the film for steam removal should be placed on the outside. Whereas if it is necessary to insulate the roof, then a film with an anti-condensate coating of bulk or diffusion type is laid on top of the mineral wool. In this case, it is necessary to follow the technology that is used in the construction of ventilated facades. If the roof does not have a heater, then the film layer should be below, under the rafters. When insulating the upper ceiling of rooms under the attic, the vapor-permeable membrane must be laid at the bottom of the insulation. Vapor-permeable waterproofing membrane should also be used for internal wall insulation. In this case, it should not have perforations, but should be laid on top of mineral wool, inside the room.

windproof vapor barrier membrane

How to lay the membrane - inside out or face?

As practice shows, for many people it remains a mystery which side to lay the vapor-permeable membrane. If the film has the same seamy and front side, the question is immediately removed. However, it is not always possible to find in the sale of double-sided films. If we are talking about anti-condensate varieties, then there will be a fabric side from the inside, and during installation it should be turned inside the room. Here you should turn the metal coating on the foil membrane.

If a vapor-permeable diffusion membrane was acquired, then you should familiarize yourself with the instructions. In it, the manufacturer usually indicates the technology of laying material. However, the same company can produce unilateral and bilateral films. Identify the outer and inner sides by color. If the membrane has two sides, then one of them is painted in a brighter shade, usually the outside of the material.

windproof vapor permeable membrane

How to choose a membrane

If you need a wind-moisture vapor-permeable membrane, then you can pay attention to the most frequently purchased by customers option "Izospan A", which is designed for laying in the roofing space. It is used to protect the elements of the walls and roof against condensation and wind when building a building. The membrane should be located under the roof covering or wall cladding on the outside of the insulation. The outer side is a water-repellent smooth surface, while the inner side has a rough anti-condensate structure. It is intended to delay moisture and then evaporate in the air stream. This windproof, vapor-permeable membrane is easy to use, it is characterized by high mechanical strength and environmental safety. In the evaporation there are no harmful substances, and the properties of the material can survive for a long time. The material is resistant to bacteria and chemicals.

hydro windproof vapor permeable membrane

Features of laying material "Izospan A"

The wind-vapor-permeable membrane "Izospan A" is used as a wind-proof membrane in the construction of insulated roofs, the angle of which should not be less than 35 °. Profiled sheets or shingles may be used as the outer covering.

Megaflex membrane features

Do you need a vapor-permeable membrane? Which is better, you need to decide before visiting the store. One of the types of such materials is Megaflex, which is a three-layer structure. The two outer layers are micro-perforated, and the inner layer is a reinforced film. Reinforcing mesh gives the material strength, while double-sided lamination provides waterproofing properties.

The material has a micro-perforation, which ensures the ventilation of water vapor coming from the interior. This waterproof vapor-permeable membrane is able to protect the under-roof space from moisture, dust and soot, to protect materials from external moisture and internal condensate. If wind protection is necessary, the “Megaflex D 110 Standard” variety should be used, which is rolled out in horizontal sheets with overlap in 15 cm.


Hydro-windproof vapor-permeable membrane that protects materials from moisture, wind and fumes must be present in insulated roofs and ventilated facades. In the first case, the gap is equipped with a method of constructing a counter-grille, whereas when we insulate the facade, the gap can be obtained when mounting horizontal profiles or racks.

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