Vapor barrier and waterproofing: difference and purpose. External differences between vapor barrier and waterproofing Waterproofing and vapor barrier for roof application

Any home, no matter how beautiful it may be, should, among other things, be warm, safe and comfortable. To achieve this, it is not enough just to choose the most acceptable project, build everything and make it on a turnkey basis. It is important not to forget about an important detail: the means of ensuring the best microclimate in the room and maintaining the desired temperature. So, what is the difference between vapor barrier and waterproofing?

What is vapor barrier?

This term refers to a complex of specialized tools, materials and technologies aimed at protecting any building structures and structures, as well as insulating materials from getting inside the steam generated inside the room and absorbing the resulting condensate.

What is used for vapor barrier?

For the installation of such a system, special rolled or sheet geosynthetics, PVC membranes, roofing felt, glassine, roofing material, polymer varnishes are used. If you want to make a vapor barrier behind the batteries or, for example, in saunas or baths, that is, any rooms with high humidity and temperature, foil or thermofoil is used. Films for vapor barrier are a special sheet, equipped with a reinforcing film, made of polymers. There are several types of such films.

• Standard: a completely vapor-permeable material that is used for roofs in inhabited houses.
• With reflective layer: on the one hand, such a film is also reinforced, covered with foil or a layer of aluminum. It reduces heat loss, is completely impervious to moisture, and is used in bathrooms, swimming pools, kitchens, the same saunas or baths.
• Films with limited vapor permeability: made of non-woven fibers, allows you to evenly and easily remove excess moisture from the room without creating condensation under the roof. Best of all, this material is suitable for summer cottages, garden houses, that is, for houses where they live only from time to time.
• Material with variable vapor permeability: does not pass steam in dry form, but when humidity increases, it does not retain moisture, but brings it out. It is suitable for large-scale roof repairs, as it prevents water from penetrating inside the building and spoiling the finish.

What is waterproofing?

Understanding what is the difference between vapor barrier and waterproofing, it is worth finding out what waterproofing is. This is the name of a set of measures aimed at protecting any structures, houses, structures and building structures from external moisture entering from the outside, or from any contact with washer fluids with a neutral or aggressive composition.

What is the difference?

Water vapor is generated in nature all the time. He rises in the bathroom during water procedures, any washing, cooking almost any food. Even breath is essentially steam. And if there is no special protection from it in the room, then the existing insulation will absorb moisture, which will then condensate and cause the walls to become covered with mold, darken from dampness, and the insulation itself will simply fall off. What is the difference between vapor barrier and waterproofing? Everything is elementary. The first protects the house precisely from internal moisture. And the latter does not allow water from the external environment to get inside, protects the insulating materials from any condensates, precipitation formed under the roof. These may be the consequences of heavy rain, melted snow, any pipe leaks. It is waterproofing that is designed to extend the durability of the building and enhance its reliability, to ensure convenient and high-quality use of equipment and buildings.

Waterproofing materials

These are also mesh-reinforced film coatings made from the same polymers. They are of the following types:

1. universal(not leaking water ever and in any form);
2. anti-condensate(equipped with a layer of viscose and cellulose fabric, perfectly absorb water and retain it, while drying quickly);
3. equipped with microperforations(have a small permeability, require special installation);
4. with membranes(protect from moisture from the atmosphere, but do not release steam from the room).

The protection of the insulation layer in the roofing pie is performed by two types of insulating materials that are different in structure and purpose. Their illiterate use, incorrect selection according to technical indicators, incorrect installation leads to wetting of thermal insulation and to the loss of the qualities laid down by the manufacturer. As a result, instead of reducing heat loss, wet insulation will increase leakage, in rooms equipped in this way it will be excessively damp and cold.

To avoid the described negative, let's find out how vapor barrier differs from waterproofing, as using these protective films a roof insulation system is being built.

The pie of the insulated roofing system is a multilayer structure, each component of which must flawlessly perform the work entrusted to it. Its main component is represented by a heater, to protect it from getting wet, insulating films are installed on top and bottom, arranged ventilation ducts.

The upper and lower protective layer of roofing thermal insulation perform different types of work:

• The barrier laid on top protects the thermal insulation from atmospheric water falling in the form of liquid precipitation and formed during the melting of snow deposits. This layer is called waterproofing, it prevents the penetration of moisture from the outside of the insulation system, but does not interfere with adhering to inside moisture is free to leave the insulation.
• The insulation arranged from below protects the insulation from household fumes generated during the operation of the premises, when cooking, taking hygiene procedures, etc. This is a vapor barrier designed to prevent steam from entering the thermal insulation thickness.

The vapor barrier does not pass at all or passes a minimum of steam. Waterproofing by functional purpose must conduct the vaporous water coming from below. Hence the difference in structure, and differences in the work performed by materials.

Vapor permeability as the main indicator

Vapor permeability is one of the main characteristics of insulating roofing films, influencing the choice and determination of the location for their installation. It is indicated by the manufacturers of materials in the technical documentation, indicated in grams or fractions of a gram, which 1 m 2 of roll insulation can carry out per day (mg / m² per day).

Based on the ability of protective materials to pass steam, they are divided into two main classes:

• Vapor permeable. Includes all types of waterproofing membranes. The ability to conduct steam is in the hundreds and even thousands of milligrams.
• Vapor proof. Includes polypropylene and polyethylene films, anti-condensation membranes. Their ability to pass steam is equal to fractions of a milligram, several units or tens of milligrams.

According to building regulations, the components of the roofing cake are selected so that their ability to pass evaporation increases from the inside to the outside. Those. the lower film should have the lowest vapor permeability.

Insulation should be endowed with more steam permeability than vapor barrier, but they should be less than waterproofing. The described structure of the roofing cake is necessary so that all the moisture that may be in the thickness of the thermal insulation does not linger there and is freely removed outside the roofing system.

In a well-arranged pie, everything that managed to break through the vapor barrier rushed through the insulation to the waterproofing, which freely passes steam outside the structure, but excludes the penetration of raindrops and melt water into the thermal insulation.

A similar principle is observed in the arrangement of partitions and ceilings installed between rooms with different operating conditions. Simply put, a thermal insulation system should be installed between the heated rooms and the cold attic, deployed with a vapor barrier to the housing.

If, within the same floor, a room with standard operating conditions is adjacent, for example, to a steam room of a Russian bath, then a partition is insulated between them, installing a vapor barrier film first from the steam room.

However, for the perfect organization of the roofing system, it is not enough to divide the materials into classes according to their ability not to let through or easily part with steam. It is imperative to find out what materials are used as underlay films, what is the difference between the methods of vapor barrier and waterproofing, how the technology of their installation is implemented.

Types of vapor-tight options and their characteristics

Previously, the only vapor barrier option was glassine, which passed an average of about a hundred mg / m² per day. To install a vapor barrier from it, the roofer needed to show miracles of dexterity, because. the material was easily damaged during installation. There was a problem when connecting strips of glassine into a single sheet and when wrapping structures of a complex shape.

Polyethylene replaced glassine, later polypropylene, more precisely, a film made from it, was introduced into the vapor barrier sphere. It was they who became the basis for the development of an extensive line of polymer membranes used in vapor and waterproofing. The new generation of insulating materials is ahead of its predecessors in terms of strength, resistance to UV and unstable temperatures.

The list of polymeric vapor barrier types includes:

• foil membranes. Materials with a metal sheath arranged on the working side. They are used in the arrangement of hygienic premises that require the preservation of the temperature obtained during heating: saunas, steam rooms. The foil surface can serve as a reflector of thermal waves if a gap without ventilation is left between it and the skin.
• Anti-condensation films. Roll materials, one side of which has a rough texture, the other is smooth. A rough surface prevents the formation of dew on the vapor barrier, a smooth surface prevents the reverse flow of moisture that has penetrated or formed in the insulation.
• Polypropylene and polyethylene films. Most often, these are reinforced analogues of outdated polyethylene and polypropylene options. They are used in budget construction, although at a price per 1 m 2 they do not differ too much from new polymeric vapor barrier materials.

Vapor barrier materials with a vapor permeability of several tens of mg per 1 m 2 per day are still used in thermal insulation systems for cold attics, insulated with backfill material, for example, expanded clay. If there are real restrictions in the construction budget, then this type can be used in the arrangement of heated attics.

However, the difference between the cost of polyethylene with propylene and membrane barriers is such that there is little point in such savings. In addition, new types of vapor barrier protection are much stronger, they are difficult to damage during careless movements during installation. Anti-condensation membranes serve almost as long as roofing, i.e. during the entire operation of the roof, it will not be necessary to carry out major repairs.

Properties and types of vapor-permeable membranes

The main difference between polymeric membranes for waterproofing and materials for vapor barrier is that they freely pass out steam and condensate formed in the thickness of the insulation due to the difference in temperature indicators under and above the insulation system. Until invented material, which can prevent the appearance of moisture in the thermal insulation. However, there are technologies that allow you to get rid of water in the roofing cake, and materials for the implementation of such schemes.

As already mentioned, waterproofing is placed on top of the insulation. It is located under the roof. Between it and the heat-insulating layer, a ventilation gap is arranged or not, depending on the material used in the organization of the system.

The types of vapor-permeable, otherwise referred to as vapor-transparent materials that are in demand in construction include:

• Perforated films. Roll materials with specially shaped holes that allow steam to escape, but do not allow water to pass through from the outside. They serve mainly as insulation for slopes over cold attics, because. cannot fully perform waterproofing and windproof functions.
• Porous membranes. Materials with a fibrous structure, similar in structure to a filter. The vapor permeability of this type depends on the diameter of the pores and the ability of the fibrous tissue to pass vapor. This type of waterproofing is not used where there is a possibility of clogging of pores from excessive dust content.
• Superdiffusion membranes. The thinnest multilayer membrane systems, each layer of which performs a specific job. There are no holes in their structure that can become clogged with dust, therefore the materials of this group have the highest resistance to all kinds of pollution.

Superdiffuse membrane insulation comes in two or three layers. Two-layer varieties are inferior to three-layer counterparts in terms of strength criteria, tk. in their structure, one of the reinforcing substrates has been removed. In terms of cost aspects, both options do not differ too much, therefore, if possible, it is better to choose a three-layer material.

Porous and superdiffusion materials, together with waterproof duties, play the role of wind protection. They prevent the heat from being “washed out” by winds from light fibrous wadding insulation. Perforated films do not do this work, therefore, when used for insulation of mineral wool slopes, they require the installation of an additional windproof carpet, which sometimes nullifies the initial savings.

The installation of roofing waterproofing is necessarily accompanied by a ventilation system, which can be:

• single level. Predetermining the organization of ventilation ducts, air ducts, between the waterproofing barrier and the roofing. It is arranged when using superdiffusion and porous membranes, which are not forbidden to come into close contact with any type of insulation.
• duplex. Assuming the organization of two levels of ventilation. channels located between the thermal insulation and the hydro-barrier, then between it and the coating. the scheme is typical when using perforated films

Air ducts - ventilation ducts located parallel to the pitched roof are arranged by installing wooden lath with a wall height of at least 4 cm. For a two-level system, the river is fixed in two tiers: above the insulation and above the waterproofing. The crate formed with its help at the same time fixes the roll insulation, and also serves as the basis for laying the roof or solid flooring for soft types of coatings.

The nuances of laying roofing films

We found out that waterproofing materials that cover the cake from atmospheric negativity can be installed with one or two ventilation gaps. They are needed so that moisture does not accumulate in the multilayer roofing system, but is freely removed by the air flow through the vents formed by the slats.

An equivalent function is performed by ventilation gaps accompanying the installation of vapor barrier films. Regardless of the structure and composition of the material, they are installed with two tiers of ventilation located on both sides of the vapor barrier. Due to the low vapor permeability, this layer requires enhanced ventilation.

Most roofing films do not have the ability to stretch under tension. Therefore, they are laid on the rafter frame so that the roll insulation sags somewhat in the space between the rafters. The sag is necessary so that the material does not crack under tension during the standard movements inherent in wood systems.

Waterproofing panels are spread out depending on the steepness of the structure. On steep roofs, the material is laid along the rafter legs; on sloping roofs, it is placed parallel to the ridge run. The vapor barrier strips are installed exclusively parallel to the ridge.

Laying of strips is carried out with an overlap, the value of which is indicated by the manufacturer of the insulation products. On the rolls, the side must be indicated, according to which the installation of the strips should be carried out. It is strictly forbidden to change sides, because. as a result, the vapor and water insulating properties will change.

When installing a hydroprotection laid parallel to the ridge rib, they start from the eaves line. For proper arrangement, the edge of the starting waterproofing strip should protrude beyond the edge of the eaves by 10 cm to a minimum. It is then taken out under a dropper or a cornice bar. The strips are laid so that the overlap of the upper panel overlaps the edge of the lower one.

The vapor barrier begins to be built, starting from the ridge rib. Each next panel must overlap the edge of the previous one. If you follow the described technique in the device of both types of insulation, a minimum of water enters the insulation.

Video about the differences between steam and hydro barriers

How to distinguish materials for vapor and waterproofing devices:

Rules for the use of roofing films of the Izospan brand:

The principle of operation of protection against evaporation and atmospheric water:

Information about the differences in the purpose, structure and rules for laying insulating roofing materials will help you correctly arrange the roof and protect its components from all types of water.

Every person dreams that the house in which he lives is warm and cozy. To do this, you need not only to choose the right insulation for walls and roofs, but also to protect it from moisture.

To create an excellent microclimate and maintain heat in the house, it is necessary that all construction work be carried out in compliance with the technologies, and you need to know how vapor barrier differs from waterproofing.

Purpose of isolation

Every house and every structure is exposed to atmospheric precipitation. Rain or snow, acting on building envelopes, can disrupt the performance of most building materials.

To protect them from dangerous and unwanted water penetration, vapor barrier and waterproofing are needed.

It's perfect different materials, they differ in their properties, and they cannot be confused.

The main part of precipitation falls on the roof, while the walls of the house are much better protected from moisture. When constructing a roof, it is necessary to take into account frequent temperature changes, heavy rains, hail, snow, hurricane winds and other weather disasters. The roof is a boundary that completely separates the air outside from the air inside the building. Warmer air, according to the laws of physics, moves up, and colder air sinks down. Under any roof covering, a layer of insulation is laid, which is needed to retain heat. On how well it was laid, and on the conformity of its thickness climatic conditions, depends on whether the roof will be warm.

Roofing materials prevent the penetration of moisture into the under-roofing space, but it is very difficult to ensure complete tightness only with their help. In addition, water vapor collects on the inside of the roof in condensate.

Only waterproofing will prevent the insulation from getting wet, because its task is to prevent moisture from entering the insulation from the external environment. If for any reason the waterproofing has not been laid, mineral wool, which is used for roof insulation most often, will be saturated with moisture and lose all its heat-insulating properties.

Vapor barrier does not allow water vapor from inside the house to enter the insulation. Water vapor is an inevitable consequence of human activity. It is formed during the use of a shower or bath, washing and drying wet linen in rooms, cooking, and even breathing. If the vapor barrier does not reliably protect the insulation, water vapor will penetrate into it, condense there, which will lead to dampness and mold in the premises. And if the roof structure is made incorrectly and there is no vapor barrier and waterproofing, then moisture will get not only into the thermal insulation, but also into all structures, moistening the rafters and destroying even the interior decoration.

Back to index

The main differences between insulating layers

The main difference between vapor barrier and waterproofing is that the former prevents the entry of moist air from different rooms of the building into the heat-insulating layer, and the second one does not allow atmospheric precipitation to seep through the roofing into the insulation, simultaneously releasing the warm and moist air that could seep out if the vapor barrier is not tightly laid in places.

Thus, waterproofing can only let air through, and vapor barrier does not let anything through. On closer examination, it can be seen that there are micro-holes on the waterproofing film for air passage.

If in the attic rooms, some time after the housewarming party, the ceiling “wept” or wet spots were found in some places, then the first thing to check is whether the integrity of the roofing has been violated. And what to do if during the external examination no defects of the roof were revealed? This means that moisture "hangs" on the ceiling not because it got in from the outside, but because it did not find a way out of the premises. The couple who in large numbers present in every home, will tend upward under the roof. And if the roofing pie is mounted incorrectly, then moisture will not find a way to escape, but will settle on the ceiling and condensate when it gets colder. And all because during installation the films were mixed up, with the help of which vapor barrier and waterproofing are created.

Today, there are so many film coatings on the market that an inexperienced owner may well confuse their purpose. It happens that even roofers will not pay attention to this, and then the roof will start to get wet during operation. To avoid this, it is necessary to understand the purpose of vapor barrier and waterproofing and make right choice film material before the start of roofing work. If the roof has already leaked, then the only way out is to wait for warm days and dismantle the entire inner part roofing cake, throw away the wet insulation (it is no longer useful) and line the vapor barrier and waterproofing layers with the right materials, laying new insulation between them. To choose the right film insulation material, you need to understand the difference between vapor barrier and waterproofing.

Universal hydro-vapor barrier film

Waterproofing. The task of the waterproofing layer is to prevent water and moisture from the street from entering the under-roof space. Roofing material (slate, metal tiles, etc.) provides protection against direct precipitation, i.e. creates a barrier to rain and snow. But fog, haze or steam after a summer rain easily seep through these coatings inside. And inside the roof there is a heat-insulating layer, which should retain warm air as much as possible, without letting it out. If moisture penetrates the insulation and nourishes it, then the thermal insulation characteristics will drop sharply, because in winter all air pores will be “clogged” with ice crystals of frozen steam. This means that the insulation must somehow be protected from moisture coming from outside. And this should be done with a waterproofing film material.

Vapor barrier. The vapor barrier is created from the inside of the roofing pie. Its function is to protect the insulation from vapors from the interior. Even if excellent ventilation has been created in the house, steam will still be present, because people breathe, food is cooked, irons, humidifiers are turned on, baths are taken, plants are watered, etc. Naturally, warm steam will accumulate near the ceiling, and through it - make its way into insulation. Therefore, a vapor barrier must be placed in front of the heat-insulating layer.

Foil material is more expensive than other films, but, in addition to protection against steam, it also ensures the safety of heat in the house

How not to mix up insulating materials

Such films have an absolutely waterproof surface on both sides, i.e. They don't let any moisture in and they don't let any out. Most cheap option such a film is ordinary polyethylene, used in vegetable gardens. True, it can be used for roofing only as a last resort, because it is always hot under the roof, and the thin film is destroyed and stretched by temperature. The most optimal option is a multilayer film with a reinforcing frame made of polymers. The frame prevents it from stretching and sagging, and many layers ensure a long service life.

A more expensive, but very useful type of vapor barrier film is foil, i.e. on one side having a layer of foil. Such a film is spread with the foil side inside the roof to reflect infrared radiation, due to which the bulk of the heat leaves the premises. By using such a steam insulation film, you will automatically increase the level of heat retention, which means you will pay less for heating.

On the roll with the film it should be indicated that it is vapor barrier

Waterproofing films

For waterproofing, the films described above are not suitable, because they are absolutely waterproof. They, of course, will not let moisture in from the outside, but this is not enough for the normal functioning of the roofing pie. The fact is that the waterproofing layer performs another task: it removes accidentally trapped vapors from the insulation. The question may arise: where do they come from if there is a film barrier inside and outside too. It turns out that there is no such film in the world that would be 100% waterproof. Some of the steam will still seep out of the rooms or the ventilation layer, so you need to make sure that the moisture finds a way out. For this, special waterproofing films were invented, which are called membranes. They are made of polymers and are characterized by increased strength, resistance to temperature extremes, to ultraviolet radiation. But their most important property lies in the structure: it is porous. This is done so that steam can seep through the pores under the roof.

There are diffusion and superdiffusion membrane films. In both, the pores resemble microscopic funnels. The principle of operation is based on the fact that a water molecule has a larger volume than a vapor molecule. So steam escapes through the wide part of the funnel, and moisture from the outside cannot seep through the narrow “neck”. When using membranes, it is important to put them on the correct side: the wide part of the pores is towards the insulation, the narrow part is towards the roofing.

The structure of both films differs in the number of pores. So, diffusion membranes require that their pores do not come into contact with the insulation, otherwise the funnels will be clogged with mineral wool and will not function. In such roofing pies, the waterproofing layer must be surrounded on both sides by ventilation gaps: one - between the insulation and the membrane, the second - between the membrane and the roofing material. The superdiffusion membrane has a much higher steam output, so the ventilation gap between the insulation and the membrane is not needed.

A ventilation gap must be created between the membrane and the roofing so that the released steam can escape with the air flow to the outside

Membrane films are not suitable for all types of roofing, but only for those that are not afraid of condensation on the back side. So, for example, metal tiles require a special waterproofing film, which is called anti-condensate. She does not release steam from the insulation, but accumulates it on her back surface with the help of many tiny villi. And already from there the moisture evaporates with the help of air currents of the ventilation gap.

Only the competent use of vapor barrier and waterproofing films will provide a dry ceiling and warm air in the premises.

Everyone wants the living conditions in the house to be equally comfortable as in summer heat, as well as in the winter cold. But what is needed to create a favorable atmosphere in the house? Of course, in the conditions of harsh Russian winters, the main thing will be, perhaps, high-quality insulation, which will help save a considerable amount on heating.

Mineral wool, which is a good heat insulator, is usually used as a floor, wall and ceiling insulation. However, mineral wool has at least one significant drawback - the ability to absorb moisture like a sponge, because of which it loses its ability to retain heat at times. To protect mineral wool from getting wet, materials such as hydro- and vapor barriers are used.

When arranging the roof, it is necessary to take into account the maximum possible temperature differences outside and inside the room, as well as precipitation in any form and winds up to hurricanes. After all, the roof of the house is in fact the boundary separating the air inside the room and outside. As we know from the laws of physics: the air that has a higher temperature will always rise up - under the ceiling. Therefore, insulation is laid under any roofing to keep the heat in the house. But in order for the insulation to last longer and not lose its thermal insulation properties, it must be protected from moisture.

Of course, themselves roofing materials they protect the insulation well from direct ingress of moisture inside, but they are unlikely to save from the formation of condensate in the under-roof space - they are not so tight as not to let water vapor through. In this case, high-quality waterproofing will come to the rescue, which will not let water vapor from environment into the heater.

It is worth noting the fact that many unfortunate builders neglect the waterproofing of the roofing insulation, buy cheap materials, or even completely replace waterproofing films with ordinary polyethylene from the garden or even vapor barrier, not finding any significant difference between them. Like, the film is also a film in Africa. Anyway.

As a result of such “minor” shortcomings, it turns out, for example, that after a year ago the installation of a new roof was completed, water suddenly starts to flow from the roof of the attic, wet stains appear on the ceiling. The owners are confused. They begin to look for damage and leaks in the roofing, but without revealing any defects in it, they come to the age-old questions - who is to blame and what to do? And then the laws of physics begin to come to mind and clever thoughts come that the moisture in the air, it turns out, can theoretically condense inside the room itself, forming streaks on the ceiling ...

But why were there no signs of condensation on the ceiling before the repair? It can be assumed that waterproofing was laid under the insulation instead of vapor barrier, as a result, the properties of the porous insulation clogged with water vapor with all the ensuing consequences have already been lost. If no insulating films were used at all, then moisture will “walk” throughout the structure, damaging not only the thermal insulation, but also contributing to the destruction truss system and even interior decoration.

So what is the difference between waterproofing and vapor barrier?

There are so many different film insulating materials on sale now that, out of ignorance, you can easily confuse them. Of particular difficulty is the initial misunderstanding of the differences between waterproofing and vapor barrier materials. The use of the concepts of "waterproofing" and "vapor barrier" as synonyms by "specialists" of pseudo-construction organizations and even sellers of some stores (this happens especially often in the provinces, where you can't find real craftsmen in the afternoon with fire) introduces even more confusion.

To avoid unpleasant surprises, such as the case with a “leaking” attic described above, you need to clearly understand the difference between vapor and hydroprotective films before starting the installation of a new roof and approach their choice consciously. Even if you are not going to insulate the roof with your own hands, then at least it is in your power and interests to control the progress of work and the correct selection of materials.

Before talking about the differences between hydro and vapor barriers as materials, you need to clearly understand the functions that they must perform.

What is waterproofing for?

The main function of the waterproofing film is to prevent the ingress of moisture from the street. “And why do we need it, especially on the roof, where the roof will not let any water inside? Extra costs and that's it, you say. And, perhaps, you will be right if you just need to replace the roof over the heated part of the room, for example, in an ordinary attic.

Roof waterproofing is necessary when it is planned to lay a layer of mineral wool insulation, which is mandatory in the case of an attic, since the roof can only retain falling precipitation in the form of snow and rain, but will not provide protection against the penetration of water vapor after summer rain or fog. This steam, in the absence of an insulating layer, will go directly into the roofing insulation, which is mainly mineral wool, as a result of which all its air pores will be “clogged”, which will negatively affect the thermal insulation properties. And this will be especially noticeable in winter period when moisture vapor crystallizes in the pores of the insulation material. Therefore, the heat-insulating layer must be protected from moisture from the outside. And the film waterproofing material will help us in this.

Why is vapor barrier needed?

Vapor barrier films, unlike waterproofing, are designed to be laid from below under a layer of roofing insulation to protect it from warm vapors seeping from the ceiling that are present in any room even with amazing ventilation, and all because we breathe, use steam irons or cooking, showering, watering flowers, etc. Thus, vapor protection in front of a layer of thermal insulation is a very necessary thing.

The main difference between waterproofing and vapor barrier is that modern waterproofing membranes are able to pass steam in one direction(at correct installation- out of the heater), while preventing the penetration of water from the outside.

Protecting the roof insulation from getting wet using a waterproofing membrane and vapor barrier

It should be noted that the vapor barrier layer, when viewed from inside the room, is always performed last layer(before finishing, of course). For example, if this is a floor above an unheated underground (basement), then the vapor barrier is not mounted along the ceiling (below), but from above, right under the finishing “clothes” of the floor. It's the same with walls.

Remember: water vapor always diffuses in the direction of colder air. And the first barrier on the way of steam to the insulation should be the vapor barrier! And that part of the steam that nevertheless seeps through it into the insulation layer must freely exit it through the vapor-permeable membrane and, being picked up by air flows, escape into the atmosphere.

External differences between vapor barrier and waterproofing

What is the difference between waterproofing and vapor barrier? This question can be answered by analyzing the structure of both materials.

Structure of vapor barrier films

Vapor barrier differs from waterproofing mainly in that both sides of it are completely waterproof. The vapor barrier should not allow steam or water to pass both outside (into the house) and inside the insulation. Conventional polyethylene can be attributed to a cheap version of such a film. However, it is not recommended to use it as a vapor barrier for a roofing “pie” due to the fact that under the roof, especially in summer, the film will get very hot, which will lead to its stretching and, possibly, damage. And since we cover the roof for more than one year, it is optimal to use a film of several layers with a polymer reinforcing frame, which prevents the film from stretching.

Installation of vapor barrier is carried out from the inside of the ravine

sheathing inner surface a mansard roof with a film covered with foil on one side will cost a little more than use different kinds vapor barrier materials, however, in addition to creating a reliable vapor barrier, it will also be possible to retain heat in the house. The installation of this film is carried out with a foil surface inside the room, which contributes to the reflection of infrared radiation from it, with which the main part of the heat from the dwelling disappears. Thus, the use of such a vapor barrier allows you to kill two birds with one stone, reducing heat loss through the roof of the house to a minimum, which in turn will allow you to save quite a lot on heating.

Before buying any film, be sure to make sure that it is a vapor barrier, as indicated by the inscription on the package.

Structure and types of waterproofing films

It may well seem to an amateur that if the vapor barrier is completely waterproof, then it may well serve as a replacement for the waterproofing layer. It can be assumed even out of ignorance that the vapor barrier better waterproofing which is fundamentally wrong.

Both vapor barrier and waterproof film materials serve a specific purpose, and if you substitute one for the other, this can lead to unpredictable consequences and additional monetary costs.

The main functions of waterproofing are as follows:

• protection against ingress of external moisture into the insulation layer;
• removal of accidentally trapped water vapor from the heater.

But how can steam suddenly appear in a heater? The thing is that not a single film in the world, it would seem, hermetically closing the insulation on both sides, does not have absolute vapor tightness. The proportion of water vapor, albeit insignificant, somehow penetrates through the film insulation from the ventilation gap and from the inside of the room into the insulation, which means that it is necessary to ensure that this moisture can escape to the outside. This purpose is served by waterproofing films, otherwise referred to as membranes.

Waterproofing polymer films have a number of useful properties:

• resistance to ultraviolet radiation;
• resistance to temperature fluctuations;
• high strength properties.

However, this is all secondary. Most important property waterproofing film is porous structure of this material . The meaning of the idea is to enable that part of the water vapor, which somehow got into the insulation, to freely exit it into the under-roof space. This is precisely what contributes to the pores, which are very similar in shape to funnels, through the wide part of which steam exits the insulation. The narrow part of the pores, with proper installation, should be turned outward, which prevents the penetration of moisture into the pores in the form of a liquid from the atmosphere, since the volume of a water molecule is larger than that of vapor molecules. When using waterproofing membranes, it is important not to confuse and put the film with the correct side to the insulation.

According to the type of porous structure, membrane films can be:

• diffusion;
• superdiffusion.

These structures differ from each other in the number of pores. In diffusion membranes, there are fewer pores, and, accordingly, the level of vapor removal is significantly lower. Such a vapor barrier cannot be placed directly on the insulation itself, therefore it is necessary to leave a ventilated gap not only between the roofing and waterproofing, but also between the film and the insulation. Otherwise, the contact of the pores of the diffusion membrane with the insulation material will lead to blockage of the “funnel” of the waterproofing with mineral wool and the loss of its functional properties.

Superdiffusion membranes are significantly superior to diffusion films in terms of vapor removal, and it is not required to create a ventilation gap between the waterproofing and the insulation.

The organization of a ventilation gap between the roofing and the membrane is mandatory in any case, in order to allow water vapor to escape with the air flow into the atmosphere.

However, it is not recommended to use membrane waterproofing films with any type of roofing, but only with those that are resistant to the damaging effects of condensate accumulating from the back of the roof. So, for example, in the case of roofing with metal tiles, it is necessary to use special anti-condensation films. Such waterproofing does not allow steam to escape from the insulation, but accumulates it through a huge number of tiny villi located on its back surface, from where moisture leaves with air flows through the ventilation gap.

Waterproofing is laid on top of the roof insulation

The choice of vapor barrier and waterproofing

When choosing the type of vapor and waterproofing, it is necessary first of all to take into account their characteristics. Consider, for example, what are the modifications of Izospan vapor barrier.

IZOSPAN "A" is a vapor-permeable film designed to protect walls, roofs and ventilated facades insulated from the outside from the effects of wind and moisture.

IMPORTANT! Such waterproofing materials should always be laid with a smooth water-repellent surface on the outside, and a rough surface through which steam escapes from the insulation, inside. To facilitate the task of determining the sides, let's reveal one secret - the inscription on any film during installation should be at the top.

IZOSPAN "V" - has both hydro and vapor barrier properties. It is used for vapor waterproofing of roofs, installation is carried out from the inside. It can also be used for insulation of ceilings and walls, installation is carried out from the side of the thermal insulation facing the inside of the room.

IZOSPAN "C" is the most dense material used for waterproofing.

IZOSPAN "D" is a universal, durable vapor-permeable waterproofing that can be mounted both on the outside and on the inside of the insulation.

IZOSPAN "FB" is a material intended exclusively for hydro- and vapor barriers for swimming pools, saunas and baths.

The whole process of insulation, vapor barrier and waterproofing of the roof is clearly shown in the video.

Video "How to insulate the attic roof"

Video "Heater. Waterproofing. Vapor barrier and insulation of the attic roof

Only the competent use of waterproofing and vapor barrier films can ensure the preservation of heat in the house and prevent the appearance of dampness and mold in the premises.