The work done to warm the building with mineral wool plates or other porous and fibrous materials can come to naught in a very short time. The reason for this is the ability of the insulation to absorb moisture, followed by a decrease in the heat-insulating properties of the material. In this case, in most cases, the wetting of the insulation does not occur due to direct ingress of moisture, but as a result of condensation of water vapor in the air inside the insulation layer.
Purpose and principle of operation of vapor barrier
In general, it is possible to ensure the protection of building structures from the penetration of air water vapor with any waterproof material: glass, plastic, metal, plastic film. However, such insulation will not only stop moisture, but also disrupt natural air exchange. As a result - stagnation of air, unpleasant and unhealthy mustiness will appear in the rooms.
Therefore, in order to exclude the possibility of moisture condensation inside the thermal insulation, it is protected with a special membrane-type film that allows water vapor to pass only in one direction, without delaying air molecules. It is because of this ability that vapor barrier is referred to as membrane type coatings, and not to waterproof waterproofing films.
Classification of vapor barrier films
Membranes for steam insulation are classified according to the principle of action, design and the material from which they are made. According to the principle of operation, 4 types of vapor barrier are distinguished:
- A - passes steam in one direction, while retaining moisture from the other. Used to remove moisture from the insulating layer. Only vertical and inclined planes greater than 35 ° can be used to ensure that droplets can freely slide along the smooth surface of the membrane inside the ventilation gap.
- B - such a membrane is able to pass air and stop water vapor in both directions. It has a two-layer structure, in which the first layer does not allow water vapor, and the second serves to drain condensed droplets.
- C - the same vapor barrier as type B, but more durable and durable. It is made of polymer films of increased thickness or additionally reinforced. It is used in non-insulated pitched roofs to protect wooden structures from moisture.
- D is a very strong, but also expensive, polymer membrane, one side of which is laminated and has water-repellent properties. It is recommended for use in rooms with high humidity. It can be used as an additional layer of waterproofing.
Vapor barrier membranes are made of polyethylene and polypropylene. By design, vapor barrier coatings are single-layer and two-layer, where the second layer has a rough outer surface. This allows you to stop the rolling of condensate droplets and contributes to their rapid evaporation.
In addition, insulating materials with a glued layer of aluminum foil can be purchased on the market. Such an additional coating improves the technical characteristics of thermal insulation systems due to the active reflection of thermal radiation.
Which side to install vapor barrier
When laying a vapor barrier film, it is necessary to correctly position its sides. Failure to comply with this rule may interfere with the free rolling of condensation droplets and the process of their evaporation. In order not to make a mistake, which side to put the vapor barrier on, you should pay attention to the pictograms and logos that the material manufacturers usually apply on the outer surface. Carefully read the instructions that came with the roll. There, this question is necessarily indicated.
How to distinguish the inside from the outside
How to distinguish the sides of waterproofing membranes? Here we give the following tips:
- Pay attention to the color of both sides. If it is different, then the lighter will be internal and fit into thermal insulation;
- put the roll on the floor and roll it out a little - the outer surface will be on top;
- the inside is always smooth, on the outside there are protrusions or pile;
- foil material is laid with metal in the direction of the insulation.
If there is no instruction in the package, and there are no logos on the surface of the material, then this is not a vapor barrier membrane, but a polymer film for hydraulic isolation. In this case, the question of which side to install the vapor barrier can not be considered at all.
What will happen if laid on the wrong side
If we treat insulation as anti-condensation protection, then the position of the sides does not play a significant role, since the dew point shift directly depends on the design of the insulation layer. An exception is the case of laying type A material. Since such a membrane passes water vapor in one direction, instead of taking moisture away, it will direct it to the insulation.
However, the arrangement of the sides of the vapor barrier membrane has a different meaning. The rough surface contributes to the efficient collection of condensate droplets and accelerates their evaporation. The smooth inner side allows water droplets to roll down inside the ventilation gap between thermal and steam insulation.
Vapor barrier technology
The installation method depends on the type of material and the structure of the insulated building structure. The differences in how to properly install vapor barrier are not so great, but they are.
General recommendations
There are several simple general rules for laying, regardless of the type of insulation and type of building structures:
- adjacent membrane strips should be overlapped with each other with an overlap of 150 mm;
- connecting joints, punctures and cuts should be glued with the material recommended in the instructions;
- between the thermal and steam insulation there should be a ventilation gap of 30-50 mm;
- when partially laying the material on an adjacent building structure, a small margin of 50-100 mm should be left for the final alignment and tension of the membrane.
Do not try to save on buying glue. Poor adhesion will lead to moisture penetration and damage to expensive insulation.
The inner surface of the outer walls
For the device of vapor protection of walls insulated from the inside, the type B membrane is fixed along the crate, inside which the insulation is already laid. Laying a vapor barrier between the heat-insulating layer and the wall does not make sense, since the access of water vapor from the room will remain free. To make 2 layers, external and internal, costs twice as much. More material on the topic here and here.
When insulating the facade
The technology of vapor barrier of facades depends on the material of the wall structure. For wooden and brick buildings with good breathability of enclosing structures, laying of two layers of vapor protection will be required. One, type C, is fixed along the outer wall of the building, and the second, type A, is used as wind protection along the crate from the side of the street. In this case, the ventilation gap is left between the second layer and the insulation. After that, the whole structure is closed with decorative panels.
In frame-type buildings, two layers of vapor barrier are also required. One on the inner surface of the wall from the side of the room, the second from the side of the street along the facade. For concrete buildings, one type A insulation layer on the street side lathing is sufficient.
On the floor
The method of creating a heat-insulating system for floor insulation and the method of laying vapor barrier depends on the chosen leveling technology. It can be lagged or provide a cement screed.
When installing floors on logs, one type C vapor barrier layer simply rolls along the floor slab with a film plant on the surface of the adjacent walls. The field for installing the log and laying the insulation, the second type A membrane is stretched along the supporting wooden blocks. It is recommended that the lags themselves be wrapped with steam insulation in one layer.
In the case of a cement or concrete screed device, the vapor barrier is installed only in the case of laying solid and durable insulation such as polystyrene foam, bitumen-cork mixture or polyethylene foam.
Attic and pitched roof
When attic rooms are insulated, one vapor-proof film of type A is laid along the crate, the second, type B, is attached to the rafters from the inside of the attic. Ventilation clearance is best left on both sides. The vapor barrier must cover all roof structures including the ridge and the Mauerlat. Foil materials are placed with a metal layer to the insulation.
In total, the presence of steam protection in thermal insulation systems increases the service life of the insulation and maintains its effectiveness. However, it should be remembered that positive materials directly depend on adherence to technology and ensuring a continuous coating without tears, holes and loose joints.