Rating of vapor barrier films for the attic. Insulating the attic from the inside: possible problems and ways to solve them. Which vapor barrier to choose for the roof

Residential attic space called an attic. It must be warm and suitable for year-round use, so the roof is insulated. As warm insulating materials In residential premises, fiber insulation materials that are safe for humans are used. They have a number of advantages, but when wet they reduce their performance. This can happen due to roof leaks or condensation. In addition, over time, moisture leads to the destruction of materials, including the interior decoration of the attic, and to the appearance of mold. The article will discuss which waterproofing to choose for the attic.

The task of attic waterproofing is to protect the under-roof space and the room from moisture leakage due to rain or melting snow. Often moisture penetrates due to damage to the roof or due to a loose fit of the ridge and snow being blown under it.

Water getting on the insulation negatively affects its qualities, and with prolonged exposure leads to destruction. Traditionally, fiberglass treated with bitumen was used for this. But today modern materials have appeared that have best qualities. In addition, they are much more convenient to work with. First of all we're talking about about membrane films, which not only perform the function of waterproofing, but also prevent the formation of condensation, have the function of wind protection and vapor protection.

Vapor barrier and wind protection of attic roof

Due to air movement and steam pressure, condensation occurs. This is especially true in winter, when there is much more vapor in a warm room than outside. As a result, diffusion occurs, in which steam penetrates into the under-roof space.
When there is ventilation in the house, this leads to active air movement and increased pressure. Air and steam tend to escape through cracks or joints of materials.
Finishing materials, which are most often used to clad walls and ceilings, are vapor permeable and do not prevent moisture from penetrating the roof structures. Therefore, it is advisable to protect the thermal insulation from the inside with polyethylene films, membranes or foil films.

The film for waterproofing the attic from the inside is produced in wide rolls, which allows you to keep the number of joints to a minimum. A vapor barrier will only work if the fabric is absolutely intact, so all joints are made with an overlap, and the connections to the pipes are additionally glued.
The recommended overlaps are 10 cm and should be on the frame element in order to secure them most firmly with a construction stapler or lath. Minimum thickness films 0.15 mm.
If communications are planned to be carried out through the film, they must be tightly glued with reinforced tape.
When is thermal insulation performed? pitched roof attic, it is important to protect the insulation from cooling from blown cold air or wind. Special slab insulation, which has the highest compressive strength, copes well with this function. In terms of their vapor-permeable properties, they do not differ from other slabs, but they resist the wind in the best way. This insulation retains heat better and is an excellent soundproofing material. This is especially important if the roof is made of metal.

Tip: wind protection, vapor barrier and waterproofing of the attic are necessary when insulating it. Any roofing material on a pitched roof is not a continuous covering, so there is always a risk of moisture penetration from precipitation.

Materials for attic waterproofing

For waterproofing, films are used that are attached directly under the roofing material. These include:

polypropylene films;
non-woven membrane materials;
polyethylene films that do an excellent job of hydro- and vapor barrier in the attic.

Often these materials are interchangeable. Thus, vapor barrier films are used as under-roof waterproofing, and waterproofing films are used as a vapor barrier from the inside of the room.

Advice: there is so-called simple waterproofing, but for the attic it is better to use a waterproofing material with an anti-condensation effect. It has an absorbent fleecy layer that functions to retain drops of water, thereby preventing it from reaching the insulation.

Polyethylene film for attic waterproofing

Modern polyethylene films designed for waterproofing mansard roof, are reinforced with fabric or a special mesh. This material acquires high strength and does an excellent job of retaining moisture from the outside and steam from inside the room.

There are two types:
1. perforated. Its surface is covered with microholes. Which are able to retain moisture, but not steam. Therefore, its function is waterproofing;
2. non-perforated. It has a monolithic fabric that copes well with vapor barrier.
Regardless of the type used, a ventilation gap of 5 cm must be provided in the roof pie.
In addition to traditional films, roll polyethylene with an aluminum layer is on sale. It can be made of foil or sprayed aluminum. This reflective layer allows you to additionally retain heat in the room.
Foil polyethylene films from European manufacturers such as POLYCRAFT, JUTAFOL N AL, DELTA-REFLEX are of the best quality.
Their moisture-proof properties are very high, so they are suitable for use in roofs of any design.

Polypropylene film for attic waterproofing

Reinforced polypropylene films compare favorably with their polyethylene counterparts due to their much higher strength. They are not afraid of ultraviolet rays and will reliably protect the attic space from precipitation.

One side of this film has an anti-condensation coating. In this way, it protects the thermal insulation material from the formation of condensation. This coating is made from viscose fibers with cellulose. It is characterized by high moisture absorption and ability to retain it. According to experiments, the anti-condensation layer absorbs a large number of water and, holding it, does not form drops, which is guaranteed to protect the insulation and roof structures from getting wet.
When the conditions that caused the condensation to form disappear, the air flow of the ventilation gap will quickly dry the material.
When using such films, it is important not to mix up the sides; the glossy layer is placed on the outside, and the absorbent, rough layer is placed towards the insulation.

Anti-condensation films for attic waterproofing

This is a type of waterproofing material, one side of which is rough. It absorbs moisture formed by condensation and retains it. When water accumulates, it does not form into droplets. And it is securely held by the material until air circulation in the ventilation gap between the film and the insulation brings it out.

In addition, anti-condensation films have excellent moisture-resistant characteristics and will protect the ceiling from water leaks that could get through cracks in the roof.

Vapor barrier films for attic waterproofing

It protects against small particles of water and steam. It only works if the fabric is solid, and if there is the slightest tear or gap at the joint, moisture will penetrate into the insulation.
Not only the joints of the fabric are sealed, but all places where the vapor barrier film adjoins the walls and communications are sealed.
When using a vapor barrier in the attic, there should be a ventilation gap of 2-3 cm between it and the finishing material to prevent condensation from forming on the attic. inside material.
It also has 2 sides, the manufacturer indicates on the packaging how to position it correctly.

Diffusion membrane for attic waterproofing

This is a modern breathable material that is completely vapor permeable, but at the same time protects the roof from precipitation, condensation and wind. Hence the second name - vapor-permeable wind-moisture-proof membrane.
It is made in a non-woven way from synthetic fibers. Its main advantage is the saving of under-roof space, because the height of the ceilings of the attic floor is usually small. This is possible due to its characteristics and the ability to attach directly to the insulation, without installing a ventilation gap. You can use the resulting space differently - add an additional layer of thermal insulation.

They are most often used not only in the construction of new houses with attic floor, but also when arranging a cold attic into a living space. In this case, there will be no need for reconstruction rafter system.
The initial cost of diffusion membranes differs slightly from the price of other vapor barrier materials. But during operation it will show maximum energy efficiency and allow you to save on heating.

How to choose waterproofing for the attic

The material used to waterproof the roof in the attic depends on several indicators.

First of all, this is the angle of the roof. If the angle is sharp, then it is enough to install an under-roof windproof or vapor barrier membrane. A roof pie whose slopes are more gentle will already require a waterproofing anti-condensation film.
When there are 2 ventilation gaps in the attic roof structure, simple waterproofing materials are used. And with a single ventilation circuit, preference is given to diffusion membranes.

Since we are talking about waterproofing a residential heated attic, it is better to provide two layers of moisture-proof films. For example, with a conventional vapor barrier film and a windproof membrane. Or with only one vapor barrier anti-condensation membrane, but with two ventilation circuits.

Advice: the best solution will be the design of insulation and waterproofing mansard roof with 3 films. If we start from the living space, the pie looks like this: drywall, vapor barrier film, insulation, windproof film, ventilation gap, plastic film, ventilation gap and roofing material.

The film should be stored in a dark, closed room. If it has already been mounted on the roof or walls, then it must be closed immediately facing material. The membrane is destroyed quite quickly under the influence of ultraviolet radiation and wind. Indoors, non-woven vapor barrier should not be located near lamps or heaters. This also leads to the destruction of its structure.

How to waterproof an attic with your own hands

Since it is impossible to insulate an attic without waterproofing, this process must be considered in its entirety.

The roofing material does not have heat-preserving qualities. Therefore, if we are talking specifically about a residential attic, then it should be used only environmentally safe materials. Most often this is mineral wool or glass wool. Both of these materials have high heat and sound insulation properties. This is especially important if the roof is made of metal. But all these qualities are reduced to zero when the insulation gets wet. Therefore, it is necessary to properly think through all the components of the design.
If the house is new, then it is easier to carry out work from the bottom up, starting from the lower layers and ending with the roof. If the house has already been built, and the roof is insulated during operation, then there is no choice and the work proceeds in the opposite direction. Consider the option of working in a house under construction.

A vapor barrier film is nailed onto the roof rafters from below with a tight tension using a construction stapler. To prevent the staples from tearing the material, it is pressed on top of the fastenings to each rafter with a lath, which is mounted on self-tapping screws (in the case of a wooden structure).
In the resulting cells, the walls of which are rafters, and the bottom is a vapor barrier, thermal insulation material is laid in a checkerboard pattern with overlaps. With a thickness of 5 cm, 3 layers are made.
The top is covered with windproof waterproofing. The top is also fixed with slats. Their thickness will provide the necessary ventilation gap. The width of the ventilated gap directly depends on the roof material. So, if you choose corrugated sheeting, metal tiles or ondulin with a profile, then it is enough to leave 2.5 cm for air flow. For flat material, the ventilation circuit between the waterproofing material and the sheathing under the roof is provided at least 5 cm. Ventilation will be carried out from the eaves of the roof to its ridge.
Practice shows that the best effect in protecting the insulation under the roof can be achieved by using modern materials from trusted manufacturers, such as Izospan or Tyvek. Using regular polyethylene film gives worse results due to the formation of condensation, and the old way waterproofing with roofing felt, according to professionals, is unacceptable.

Advice: all seams and joints of films are taped with tape; this is the only way to guarantee that moisture will not penetrate inside.

DIY waterproofing

Do you need waterproofing in an unheated attic?

If the house is being built taking into account that in the future it is possible to convert the attic into an attic, then waterproofing will significantly speed up this process. But, if there is no such desire, is it necessary to install protection from moisture and wind under the roof without thermal insulation material?

Even if there is absolute confidence in the quality roofing material, in his correct installation, which guarantees protection of roof structures from penetration of moisture from slanting rain or blowing snow, it is still necessary to stretch a waterproofing film over the rafters. Since moisture penetrates not only from the outside, but also from the inside in the form of condensation. Water droplets form on the roof covering and lead to its corrosion.
For an unheated attic, you can use any type of waterproofing material: polyethylene film, diffusion membrane or anti-condensation film. Preference is given to anti-condensation materials, since they are cheaper than diffusion materials. And unlike polyethylene films, they can for a long time hold the condensation until it evaporates naturally.
Condensation forms especially often in cold attics when communications such as fireplace pipes, chimneys, etc. pass through them. Even if they are securely closed with thermal insulation material, some of the heat will still pass out, which will lead to a temperature difference and the formation of condensation.

If you still plan to convert the attic into warm attic, then waterproofing must initially be carried out using diffusion materials.

P When deciding to operate an attic, a private homeowner should first of all think about insulation and vapor barrier of this room. The comfort of living in the attic, as well as heating costs, depend on the competent execution of these works. We will talk about how to do a vapor barrier in an attic with your own hands in this article.

Condensation or water vapor, worst enemy rafters and roof insulation. The scope of work for attic repairs can be compared with new construction, which indicates the importance of monitoring work on vapor barrier equipment. The attic vapor barrier is installed from the inside of the room.

When designing and constructing attics, it is necessary to take into account two main mechanisms for the movement of water vapor and, as a consequence, humidification of the structure - diffusion and convective transfer of vaporous moisture.

What is diffusion

Diffusion is the movement of vapor from an area with high partial pressure to an area with lower pressure.
In the cold season, this transfer occurs from the warm interior of the attic towards the cold street with low partial pressure. In summer, the direction of diffusion transfer changes, and water vapor, which is in large quantities in the outside air, tends to enter the relatively cool and dry attic room.

The greater the difference in temperature and humidity between the street and the room, the stronger the diffusion flow. In the path of this flow is the entire attic structure - diffusion roofing film, insulation, vapor barrier material and interior decoration. Therefore, the diffusion permeability of these materials determines the amount of vapor passing through diffusion. Since the roofing film and mineral insulation have very low vapor permeability resistance, these layers can be ignored and the vapor permeability of the structure can be assessed only by its properties vapor barrier material, which is expressed by Sd [m] – equivalent thickness of water vapor diffusion resistance.

What is convection

Convection is the uncontrolled movement of air and the water vapor it contains through uncompacted layers of insulating materials. The intensity of this transfer is influenced by the wind speed outside the building and the size of the cracks. IN modern designs attics with one ventilation gap and a diffusion under-roof membrane and vapor barrier perform the function of air insulation. Both protective layers are reduced to a safe level or completely eliminate the convective transfer of moisture contained in the warm air of the attic (exfiltration) during the cold season and the infiltration of external humid and hot air into the attic in the summer.

As a rule, in real conditions construction, both mechanisms of humidification are present, but if diffusion transfer depends on the choice of vapor barrier and partial pressure difference, then convective transfer is 100% dependent on the quality insulation works and from the complete set with system accessories - adhesives and tapes. When comparing diffusion and convection in terms of moisture in the structure, convection is a disproportionately more dangerous process due to the amount of water vapor entering the roof structure.

Study of air movement in the attic

The Institute of Building Physics (Germany, Stuttgart) in 1989 conducted research and comparative calculations of moisture transfer by both processes, which were subsequently confirmed by laboratory tests. The results were published in the German Construction Journal (Deutsche Bauzeitschrift, No. 12/89, p. 1639). Studies have shown that, depending on the pressure difference between the street and the interior of the attic, convective moisture transfer is hundreds of times greater than humidification due to diffusion. The main negative consequence of dampening thermal insulation is a significant reduction in the heat transfer resistance of the entire structure, which leads to increased operating costs.

In addition, conditions are created for moisture and mold damage to load-bearing roof structures (wooden and metal). Increased breathability significantly reduces air quality during interior spaces at home by transferring both construction dust, and external. The microclimate and comfort of living in the attic are deteriorating. It is not uncommon for homeowners to complain about “cold from the floor” when the heating of a private home is fully turned on. And the source of cold can be breathable walls, especially if they are framed, ceilings, wall and floor junctions, windows, electrical appliances, heating equipment pipes and wiring. It’s no wonder that one of the common sayings among roofing inspectors is “Outlet Tornado” when a draft speed of more than 4-6 m/s is recorded.

Numerous tests carried out in different countries determine the highest speed air flow at 0.2 m/s, which is not perceived by humans as uncomfortable. The maximum permissible speed according to European standards is 2 m/s. In private houses equipped with climate control systems, it is especially important to provide high-quality protection from convective air movement, since a breathable roof and walls significantly reduce the efficiency of their operation and also lead to increased costs for maintenance and air conditioning of the house. Practical experience roofing works in Europe and Russia fully confirms that the greatest danger to an insulated roof is posed by loose overlaps of the vapor barrier and its connection to walls and other structural elements of the roof. The job of a professional roofer is to eliminate or minimize the uncontrolled movement of air and the water vapor it contains through the roof structure.

Selection of vapor barrier material

Currently, designers and roofers have a wide selection of vapor barrier materials at their disposal; moreover, the best developers and manufacturers offer a system of vapor barrier materials that combines films, tapes and adhesives, as well as technical solutions. As a rule, the type and characteristics of vapor barrier depend on the design features of the attic and the temperature and humidity operating conditions of the room.

Vapor barrier materials

Single layer films

Single-layer films made of polyethylene (advantages: transparent material allows you to easily control the quality of insulation, high Sd (more than 100 m) with a thickness of more than 200 microns, sufficient elongation at break; disadvantages: low strength in places where the stapler is attached with staples).

Reinforced multilayer films

Reinforced multilayer films made of polyethylene (advantages: transparent material and increased strength; disadvantage: low Sd due to the strong thinning of the layers in the places where the reinforcing mesh is interlaced). In Europe, reinforced films weighing at least 200 g/m2 are used to a limited extent.

Polymer woven films

Polymer woven films with a single layer lamination (advantage: high strength; disadvantages: not transparent material, low Sd due to a thin continuous layer of polymer and very low elongation at break).

Multilayer films made of polyethylene

Multilayer films made of polyethylene with a reflective layer (advantages: high strength and diffusion resistance Sd > 100...150 m, heat conservation due to its re-reflection into the attic, self-adhesive tapes along the edge of the roll; disadvantage: opaque material).

Self-adhesive roll polymer-bitumen materials

Self-adhesive roll polymer-bitumen materials are very simple to use - they are glued to a solid base (for example, OSB or concrete) over a layer of primer, can be used on steep surfaces and do not require additional gluing of overlaps with tapes.
OSB - used as a vapor barrier only in rooms with normal humidity and in houses without wet finishing work. The main segment of such vapor barrier is frame and prefabricated houses or houses insulated with blown-in cellulose wool. It is necessary to use tapes for gluing overlaps and junctions. On roofs with complex geometry, the use of OSB vapor barrier is associated with very high installation complexity and cost additional accessories. Therefore, OSB is recommended for use on houses with simple geometry, and in wet rooms of such houses, additional film vapor barrier should be installed. It is not allowed to use OSB on logs and timber houses due to the large settlement of the walls.

Adaptive attic vapor barrier

Adaptive attic vapor barrier with variable vapor permeability made of polyamide is used only for renovation of rooms with normal humidity. Its use in new construction or reconstruction of buildings with high humidity is not allowed.

During new construction or renovation pitched roofs use only system solution can guarantee high reliability and durability of the roof. Therefore, the use of films alone, even the best ones, will not answer modern requirements the customer – to protect his roof from bad weather and provide comfortable living conditions. Ultimately, the home owner evaluates the quality of roof insulation based on the comfort of living and the cost of operation.

Taking into account the constant increase in energy, protecting insulation from steam and convective air exchange is becoming one of the most important from the point of view of the homeowner’s costs for heating and air conditioning his home. Most often, problems appear in the most difficult places of the roof - junctions with walls, pipes and roof windows, in valleys and ridges, when installing roof penetrations and in places where rolls overlap. Therefore, the use of adhesives, connecting and sealing tapes is a necessary factor for solving problems in such critical areas of the roof. A wide variety of accessories allows a professional roofer to choose the most suitable method for installing the unit, depending on the quality of the surface and the conditions of use.

Quality control of vapor barrier and air permeability

The installation of a vapor barrier is a hidden work, so it is necessary to check and accept the work before installing the finishing material. It is recommended to take photographs or videos of completed work. Particular attention should be paid to overlaps and junctions of vapor barriers, as well as sealing engineering communications.
Unfortunately, the laying of pipes and wiring most often causes damage to the vapor barrier layer and subsequent problems with the formation of condensation and moisture in the entire structure.

However, carrying out only a visual inspection cannot guarantee a reliable result, since it is impossible to identify all defects. In Europe, instrumental testing has long been practiced, which provides almost 100% reliability of inspection and detection of defects. In practice, the simplest and most obvious methods are most often used using powder, smoke (smoke generator) or water mist (ultrasonic steam generator).

These tools are only indicators that identify problem areas. For quantification air permeability, thermal anemometers are used, which are capable of measuring the local air flow speed in specific place vapor barriers. Overall rating the tightness of the vapor barrier of the entire house is achieved by the BLOWER DOOR method (see the article “BLOWER DOOR Technologies”, ROOFING, 01-2008).

Conclusions:

Abundance on the Russian market vapor barrier films different brands, it would seem, makes it possible to ensure that the attic vapor barrier works without problems. However, truly professional quality can only be achieved by using an insulation system:
A film correctly selected for a specific roof structure and the temperature and humidity conditions of the building;

Thermal insulation of the attic is a very important process, since a large amount of heat escapes through the roof and walls. To reduce the loss of thermal resources, it is necessary to carefully consider the structure of the roofing pie and ensure the effective functioning of each layer.

An important role in this process is played by the attic vapor barrier, since this layer does not allow moisture to penetrate into the insulation and to wooden elements rafter frame, thereby extending their service life without loss performance characteristics.

The main functions of the attic vapor barrier layer

To answer the question of which vapor barrier to choose for the attic, you need to know its purpose. When warm and cold air flows combine, steam and condensate always form, the accumulation of which certainly leads to a decrease in the performance characteristics of any, even the most reliable building material.

Wood rotting reduces the strength of the entire structure, which becomes the reason for repairs or complete replacement main parts of the structure. Besides high humidity promotes the formation of mold and fungi that release toxic substances. As a result, the person may feel unwell and headache, and even allergies.

The joint work of insulation and vapor barrier not only prevents the penetration of steam, but also retains maximum heat in the attic room.

Types of vapor barrier materials - which one is better to choose

Can be used as a vapor barrier layer various materials, including roofing felt, glassine and various films.

The most popular today are polyethylene and polypropylene films, as well as vapor barrier membranes. To understand which vapor barrier is best for the attic, you should get acquainted with the basic materials.

Polyethylene films

This material is laid during the installation of the roof, prerequisite use is to create gaps for ventilation. This will prevent the formation of condensation, since polyethylene is not capable of allowing air to pass through. Laying with the rough side facing out promotes the evaporation of steam particles.

Polyethylene film can be used for vapor barrier and waterproofing due to its universal characteristics. Reinforcement with a special metal mesh helps increase the strength of the material.

Polypropylene films

High durability and strength are the main characteristics of this material, but at the same time it has one significant drawback.

The upper side of the reinforced film is covered with drops of condensation. If the choice of vapor barrier for the attic is made in favor of this material, then laying an additional layer of viscose or cellulose, which absorbs fumes, will help solve the problem.

Vapor barrier reflective membranes

For this insulation is not needed ventilation gaps, since the structure of the material is capable of allowing air to pass through and retain moisture. In addition, the membrane is characterized by high quality and reliability. The attic vapor barrier should be installed on top of the insulation.

In addition, a vapor barrier is installed using isospan or penoplex. These are high quality materials, characterized by a low thermal conductivity coefficient, excellent waterproofing and vapor blocking properties. One of the advantages of their use is operation at high temperatures.

Rules for installing vapor barriers

Protect the insulation from moisture penetration and preserve it performance maybe a reflective vapor barrier for the attic, installed according to all the rules.

Firstly, you must first seal and insulate the main structural elements and all protruding parts of the structure.

Secondly, the method of attaching the vapor barrier material depends on the type of surface. The material is attached to concrete, bricks or blocks using double-sided adhesive tape. On wooden surfaces The vapor barrier is fixed using nails or a construction stapler.

Thirdly, when using foil vapor barrier for the attic, the reflective layer must be turned inward.

Fourthly, for maximum efficiency vapor barrier should be used without damage. And during the installation process, the material should be tensioned to avoid sagging.

There is an attic, which my wife and I recently decided to insulate. I read many articles on your site, and still did not understand what is the best vapor barrier to choose for underlaying insulation. We went shopping, the choice was quite extensive, many types. Please tell me and recommend a reliable vapor barrier that will not let you down and will last a long time. Ivan Mikhailovich.

Answer:

Your question, Ivan Mikhailovich, is very relevant, since the attic needs protection from heat loss. He can help you with this in the best possible way. namely the vapor barrier layer which does not allow moisture to destroy structural elements and lead to their rotting.

Polyethylene film, membranes or polypropylene film can be used as materials for the vapor barrier layer.

- polyethylene film it is tensioned directly during installation and, due to its impenetrability, condensation forms inside it. Due to the fact that the film is laid with the rough side facing outwards, steam particles have the opportunity to evaporate. This material is perfect for both waterproofing and vapor barrier. To increase the strength of the film, it is reinforced with a special metal mesh;

- polypropylene film– characterized by the highest strength and durability. This material has one drawback that you should be aware of. The fact is that on the front side reinforced material Condensation often forms to protect against which you will have to additionally put a layer of cellulose or viscose on the surface;

breathable membranes have numerous advantages, among which it is worth noting quality, reliability, protection against water getting inside and steam escaping outside.

To lay the membrane, an additional thermal insulation layer will be required.

Modern vapor barrier film is an excellent choice

In addition, many new materials have recently appeared, such as isopsan, penotherm NPP LF, armitex And . All of them have excellent thermal insulation, low thermal conductivity, as well as excellent waterproofing and vapor barrier properties.

When choosing a material, many factors are taken into account, including advantages and disadvantages, as well as cost, since many of the listed materials are not cheap.

One of the most important tasks when constructing an attic is to protect it from the formation of condensation, which can lead to damage to the rafter system and thermal insulation material, as well as increased costs for heating the house. Correct vapor barrier attics should be laid out at the design stage. But if mistakes were made during the construction of the structure, then the volume of subsequent repair work, as well as measures to renovate the attic will be comparable only with a new stage of construction.

Before deciding which vapor barrier to choose for an attic roof, you need to understand the mechanism of formation and movement of water vapor. There are two principles of transfer and formation of condensate:

Diffusion is the movement of steam from an area with high pressure to a place with low pressure. In winter, such a transfer is carried out from a warm heated room towards the cold outside, where low partial pressure is observed. In the summer, the direction of flow changes, and steam from the warmer and more humid outdoor air is directed into the drier and cooler space of the attic. In the path of the diffusion flow there are attic roof structures (waterproofing, insulation, vapor barrier, finishing). It is the diffusion permeability of these materials that determines the amount of vapor that can penetrate due to diffusion. Since the layers of waterproofing and insulation practically do not resist the passage of steam, they can be ignored. In such a design, only the qualities of the vapor barrier material are important. This is why it is so important to choose a high-quality vapor barrier for your attic.

Important! The greater the difference in temperature and humidity between indoors and outdoors, the greater the diffusion flow.

Convective is the movement of air and steam flows through loose layers of coatings and thermal insulation materials. The intensity of this transfer is directly related to the strength of the wind and the dimensions of the cracks. In modern roof systems, the function of air protection is performed by layers of hydro- and vapor barrier. They can completely eliminate the possibility of convective moisture transfer.

Under actual roof operating conditions, both mechanisms of moisture penetration are present. In this case, the intensity of the diffusion process is directly related to the choice of good vapor barrier and pressure drop. In turn, the convective process completely depends on the quality of insulation work and the use of sealing tapes and mastics.

Attention! When comparing the degree of humidification of roof structures during the diffuse and convective processes, we can say that the latter is much more dangerous, since a larger amount of water vapor penetrates into the structure.

Consequences of dampening structures

Vapor barrier of an attic roof is an important component of the roofing pie design. If we choose a low-quality vapor barrier material or install it in violation of the technology, then home owners may face the following negative consequences of waterlogging of the thermal insulation material:

The entire structure reduces heat transfer resistance. This leads to higher operating costs.
Mold and moisture can damage bearing structures roofs (both metal and wood).
Due to increased air permeability of structures and dust ingress, the air quality in the house decreases. The favorable microclimate and comfort of living in attic spaces suffer significantly.

That is why, when arranging the roof structure and the roof itself, it is important not only to know which vapor barrier film is better, but also to install the material correctly. A particular danger from the point of view of poor-quality vapor barrier is represented by loose overlaps of vapor barrier material, poorly executed connections to walls, and others. structural units roofs.

Important! The main task when arranging a roof is to eliminate or minimize the uncontrolled movement of air containing water vapor through roof structures.

Types of materials

Today we can choose not only high-quality vapor barrier materials, but also entire vapor barrier systems, which include special films, adhesive tapes and mastics, as well as ready-made technical solutions for roof installation. The choice of characteristics and type of vapor barrier material is directly related to design features attic room and its temperature and humidity conditions.

Below we provide a list of the most common vapor barrier systems with their pros and cons:

Single-layer polyethylene films. The advantages include high vapor diffusion resistance (more than 100 m) with a small material thickness (200 microns), the ability to control the quality of insulation due to the transparency of the material, as well as good elongation at break. Among the disadvantages is the low strength of the material in places of fixation with staples.
Polyethylene multilayer films with reinforcement. Pros: high strength and transparency. Disadvantages: low resistance to vapor diffusion due to the thinness of the interweaving of the reinforcing mesh fibers. It is worth noting that films weighing at least 200 g/m² are most often used.
Films made of polymers on a woven basis with lamination in one layer. The advantages include high strength. The disadvantage is the lack of transparency, low diffusion resistance due to the presence of a continuous thin polymer layer, as well as low elongation at break.
Multilayer foil polyethylene film. The advantages include the high density of the material and a relatively good coefficient of resistance to vapor diffusion, as well as additional saving heat in the room due to the reflex layer. For a more airtight installation, self-adhesive tapes are used along the edges of the material. The only disadvantage is the lack of transparency.
Polymer-bitumen roll self-adhesive vapor barriers. They are quickly installed, since they are simply glued to a solid base of concrete or OSB on a layer of primer. Such products can be used on a vertical surface without additional gluing of overlaps.
OSB can be used as a vapor barrier, but this material is only suitable for places with normal humidity in buildings where wet Finishing work. Their scope of use is prefabricated and frame structures. Places of junctions and overlaps must be additionally taped. OSB is only suitable for roofs with simple geometry. A layer of film vapor barrier must be laid over wet rooms. This material is not suitable for use in houses made of timber and logs due to high shrinkage.
Adaptive polyamide vapor barrier has variable vapor permeability and is only suitable for renovation of places with normal humidity. It is not used in new construction.

As you can see, the abundance of vapor barrier systems allows you to reliably protect roof structures from condensation. However, the effectiveness of any material is directly related to the correct choice of it, taking into account the temperature and humidity conditions of the room and the roof structure, the use of accessories for better tightness of the layer, as well as the use of the right technical solutions.