Vapor barrier for a mansard roof which one to choose. How to choose a vapor barrier for a mansard roof

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 given to the attic vapor barrier, since this layer does not allow moisture to penetrate into the insulation and to the wooden elements of the truss frame, thereby extending their service life without loss of performance.

The main functions of the attic vapor barrier

To answer the question of which vapor barrier to choose for the attic, you need to know its purpose. When connecting streams of warm and cold air, steam and condensate are always formed, the accumulation of which will certainly lead to a decrease in the performance of any, even the most reliable building material.

Rotting wood reduces the strength of the entire structure, which causes the repair or complete replacement of the main parts of the structure. In addition, high humidity promotes the formation of mold and fungi, which release toxic substances. As a result, a person may experience malaise and headache, and even allergies.

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

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

Various materials can be used as a vapor barrier layer, including roofing material, 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

Such material is laid during the installation of the roof, a prerequisite for use is the creation of gaps for ventilation. This will prevent condensation from forming, since polyethylene is not able to pass air. Laying with the rough side facing out helps the vapor particles to evaporate.

Polyethylene film can be used for vapor barrier and waterproofing due to its versatility. Reinforcement with a special metal mesh helps to 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 condensate. 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 absorb fumes, will help solve the problem.

Vapor barrier reflective membranes

For this insulation, ventilation gaps are not needed, since the structure of the material is able to pass air and retain moisture. In addition, the membrane is characterized by high quality and reliability. Installation of the attic vapor barrier should be carried out on top of the insulation.

In addition, the vapor barrier is equipped with isospan or penoplex. These are high quality materials, characterized by low thermal conductivity, excellent waterproofing and vapor blocking properties. One of the advantages of using them is high temperature operation.

Vapor barrier installation rules

The reflective vapor barrier for the attic, installed in accordance with all the rules, can protect the insulation from moisture penetration and maintain its performance.

Firstly, it is necessary to 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 with double-sided adhesive tape. On wooden surfaces, the vapor barrier is fixed with nails or a construction stapler.

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

Fourth, for maximum efficiency, you should use a vapor barrier without damage. And during the installation process, the material should be stretched to avoid sagging.

When building a mansard insulated roof, a vapor barrier is required. The absence of this layer in the roofing cake leads to wetting of the insulation and premature destruction of the truss system.

Vapor barrier for a mansard roof protects the insulation and load-bearing wooden structures of the roof from saturation with wet vapors that appear as a result of human activity.

This reduces the risk of fungus and mold in the under-roof space.

Do not confuse vapor barrier with superdiffusion membranes. The latter are laid on top of the insulation and play the role of waterproofing, but at the same time retain the ability to "breathe" and remove moisture from the surface of the insulation.

Roof vapor barrier materials are represented by several types of films:

Single layer films made of polyethylene or polypropylene. They are characterized by low strength, with careless handling the film is easy to tear.

What vapor barrier to choose for the attic?

• Multilayer films- have higher strength and service life, can be additionally reinforced with a reinforcing layer.

  Reflective films with a reflex foil layer - allows you to keep warm in the room and will be an excellent solution when installing a roof over a sauna, swimming pool or bathroom.

See also: how to properly insulate the roof of the house.

1. If financial possibilities allow, choose Delta Reflex or AirGuard Reflective films.
   Delta DAWI GP is a little simpler and cheaper.
2. AirGuard Sd5 - suitable for houses with non-permanent residence.

   It has limited vapor permeability to remove residual moisture from the room.

3. Yutafol is a Czech film from Juta.

   A lot of good reviews from builders, an excellent choice in terms of price-quality ratio.

4. Ondutis and Izospan are an economy option.

Rules for installing a vapor barrier film

The vapor barrier film is laid on top of the insulation from the side of the attic and fixed with a construction stapler.

The joints of the canvases are glued with mounting tape to ensure tightness.

When working with the material, the following tips should be considered:

Cloths can be laid in any direction in the presence of a rough filing of insulation. When mounting directly on the rafters, it is better to place the sheets horizontally.

The minimum overlap of one sheet to another should be 10 cm.

Joints and junctions must be carefully glued.

When working with window openings, it is necessary to provide for a deformation margin (fold). Next to windows, it is important to pay special attention to sealing the junctions and protecting the material from sunlight.

After fixing the vapor barrier, a wooden crate is made with 25 mm slats.

It is needed for fastening the rough skin and the device for the ventilation gap. When finishing the ceiling and walls of the attic with drywall, a special metal profile is used instead of bars.

Competent and high-quality work on the attic vapor barrier will extend the life of the roof and save the owner of the house from costly repairs.

mvnvdanwamnbaa

Benefits of this option
What a cold roof
Installation steps
Roof construction for metals including waterproofing
Cold loft tools and accessories

Currently, specialists use all types of roof structures in the construction of a private house, but most often they build a cold roof.

This is ideal when the attic is not intended to be used as a residential building. Below we will talk about how to properly install a cold metal roof.

Which steam bari to choose for the attic?

Benefits of this option

The construction of such a roof is quite simple - you need to build a building, apply a layer of waterproofing, a box and a control panel, a roof. The main thing when installing a cold roof is to provide an air gap to allow the removal of condensed moisture. This is necessary to ensure that the supporting structure and roofing material are not exposed to moisture.

In itself, the installation of such a roof should not be accompanied by complications in the process of work, it is only necessary to correctly fix the roofing so as not to leave precipitation through the connection in the underground space. Before creating a mug on the roof of a cool attic, you need to perform a full list of calculations, determine the slope of the skateboard, rotate the basket and choose the appropriate method of fastening the sheet metal.

What a cold roof

The cold roof technology of metal roofs takes over the initial installation of the roofing system, after which a membrane and polyethylene film will be placed on it, which will provide waterproofing.

They fill the control box, assemble and lay the roof in the form of metal.

Characteristic of such a roof is that there is no need to install insulation - all that is needed is to equip vents under the ridge and on the slopes to remove moisture. Make sure all pre-calculations are accurately defined.

The roof installation has the following characteristics:

1. If you are planning to build a hot roof over time, then protecting the moisture barrier membrane must be thorough.

   If you plan to build an attic, a PVC membrane must be present.

2. If the roof does not need to be insulated in the future, it will be necessary to install micro-perforated waterproofing, which is used for cold roofs. It is impossible to install insulation with such a film, and in case of further insulation, you will need to buy a new membrane.

   Otherwise, the roof will be deprived of moisture protection in the future, the heaters will not have enough time to dry, and the roofing material will be brown in time.

Installation steps

When installing the moisture protection membrane, it should be noted that it must remain a small bead of at least 20 mm. In this way, condensation moisture can be achieved, thereby protecting the rafters and other roof elements from decay.

To ensure that the water does not evaporate in time, without stagnation and thereby creating an unfavorable environment, care should be taken to include in the project a fan steam, which is installed between the repellents to protect the film and the roof of the ridge.

Such a clearance will allow a simple circulation of the air flow in the room under the roof and the removal of all condensate. The built-in membrane must not be damaged or otherwise damaged. The best way to fix this is to use a structural stapler.

The membrane layers are laid with a slight overlap, and the edges with adhesive tape.

The design of the cold attic roof is such that it can be used in regions with any climatic characteristics. Many believe that this type of roof does not apply to the northern regions, although in fact this is not the case. Often in such regions, cold attic rooms are often installed.

The attic is insulated, and the cold roof does not affect the internal microclimate of the upper floors. The attic cannot be used because the installation of an insulating layer between the upper floor and the space under the roof eliminates all the nuances that affect heat loss.

When installing a cold metal roof, measures must be taken to isolate vents, chimneys, and exits in the attic.

In this case, you do not have to worry about the accumulation of condensate, icing, heat loss or rain and water melting.

A cold roof can be covered with almost all roof tiles, and due to the ease of installation, a metal roof is used much more often.

Some other types of roofing materials, especially soft tops, also work well in this situation, but they require a lot of time and money to install.

Roof construction for metals including waterproofing

To block a cold attic with a metal roof, the most convenient and easy way to install a roof.

In this case, the roofing cake consists of a waterproofing material that is attached to the raft frame, battens and roofing (metal tiles). In fact, the application of such a coating is very fast. The insulating film is fixed with staples or nails, and then additionally pressed with a thread, self-tapping screws are screwed on. Laying rail guides is carried out taking into account the dimensions of the metal plate.

The cabinet plate is made from gauges from 25 to 100 mm, and sometimes plywood or chipboard is used if hard floors are needed.

Laying a film or membrane for attic waterproofing is loose, with some stretch.

However, it makes sense to ensure that the integrity of the coating is not interrupted, i.e. any holes or cracks are excluded. As a rule, the film can be stretched by 15-25 mm. In this way, ventilation of the inside of the waterproofing membrane is achieved, condensed moisture is removed at the handle and further into the drain. Ignoring such a simple rule will eventually lead to premature deformation of the roof frame and the entire roof.

A feature of metal tile roof is that cold roof film cannot reduce the noise that occurs when metal falls in heavy rains.

Therefore, living spaces with such a coating provide a layer of thermal insulation that absorbs a lot of noise. Without this layer, as a rule, only rooms for autonomous attics are equipped.

Thus, a cold roof will include the following layers:

• A vapor barrier for the cold roof is installed inside, which only emits moisture and prevents penetration into the living room.
• Then install the roof raft frame.
• The next layer is a waterproofing material.

  The film is laid with a recess for condensate drainage.

• A control grid is then attached, which compresses the waterproofing, fixes it and provides ventilation holes.
• The rack is then filled to repair the roof.

  It is made of 50 x 50 mm blades and laid along the ramps, divided into 35-45 cm. Depending on the type and degree of the roof beam, the pitch and thickness of the panel can be changed.

• The back floors are made of metal.

Cold loft tools and accessories

It is worth noting that you do not need too complicated professional construction tools for laying metal tiles.

You can use the basic set that every housewife has in the house.

In addition to the carcass frame, frames, slats and counterflow flasks require membrane or foil insulation for steam and waterproofing, as well as a sufficient number of metal tile sheets purchased from the same series.

Fastening of all elements is carried out using clamps, self-tapping screws, galvanized nails and even anchor bolts.

However, it should be remembered that they must be of high quality so that the roof does not deteriorate ahead of time.

As for the roofing roof, the evaluation lists are pasted, the necessary roof valley (internal and external), wreaths, wind and snow stations and watercourses.

The main difference between a cold roof and a warm one is the presence of thermal insulation material in the back layer, located between the water layer and the vapor barrier.

The main functions of the attic vapor barrier
Types of vapor barrier materials - which one is better to choose
Polyethylene films
Polypropylene films
Vapor barrier reflective membranes
Vapor barrier installation rules

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 given to the attic vapor barrier, since this layer does not allow moisture to penetrate into the insulation and to the wooden elements of the truss frame, thereby extending their service life without loss of performance.

The main functions of the attic vapor barrier

To answer the question of which vapor barrier to choose for the attic, you need to know its purpose.

When connecting streams of warm and cold air, steam and condensate are always formed, the accumulation of which will certainly lead to a decrease in the performance of any, even the most reliable building material.

Rotting wood reduces the strength of the entire structure, which causes the repair or complete replacement of the main parts of the structure. In addition, high humidity promotes the formation of mold and fungi, which release toxic substances.

As a result, a person may experience malaise and headache, and even allergies.

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

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

Various materials can be used as a vapor barrier layer, including roofing material, 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

Such material is laid during the installation of the roof, a prerequisite for use is the creation of gaps for ventilation.

This will prevent condensation from forming, since polyethylene is not able to pass air. Laying with the rough side facing out helps the vapor particles to evaporate.

Polyethylene film can be used for vapor barrier and waterproofing due to its versatility. Reinforcement with a special metal mesh helps to 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.

How to choose a vapor barrier for a mansard roof

The upper side of the reinforced film is covered with drops of condensate. 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 absorb fumes, will help solve the problem.

Vapor barrier reflective membranes

For this insulation, ventilation gaps are not needed, since the structure of the material is able to pass air and retain moisture.

In addition, the membrane is characterized by high quality and reliability. Installation of the attic vapor barrier should be carried out on top of the insulation.

In addition, the vapor barrier is equipped with isospan or penoplex.

These are high quality materials, characterized by low thermal conductivity, excellent waterproofing and vapor blocking properties. One of the advantages of using them is high temperature operation.

Vapor barrier installation rules

The reflective vapor barrier for the attic, installed in accordance with all the rules, can protect the insulation from moisture penetration and maintain its performance.

Firstly, it is necessary to 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 with double-sided adhesive tape. On wooden surfaces, the vapor barrier is fixed with nails or a construction stapler.

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

Fourth, for maximum efficiency, you should use a vapor barrier without damage. And during the installation process, the material should be stretched to avoid sagging.

Internal insulation of the attic is one of the most difficult construction tasks. And all because the result is important here: how the roofing pie will behave in winter, whether there will be smudges, whether there will be a smell of dampness and whether it will be necessary to disassemble it all later. Why such difficulties? The fact is that no matter how carefully the budget for building a house is planned, it, as a rule, is still not enough for everything. Up to the fact that even the owners of the future family nest decide to buy a laminate cheaper - just to finish the repairs and just start living. And the most popular item of expenditure, which is immediately reduced as soon as the lack of funds becomes clear, is the insulation of the attic. “Later, in the future,” the owners promise themselves, especially since warming the attic from the inside is not a problem at all, and you can start it at any time, even in winter.

In fact, there are a lot of subtleties and nuances, and therefore, if you have already taken up this matter, carefully study this article. And everything will work out!

Why are there problems?

There are statistics: up to 30% of attics have to be redone after the first winter. Roofing, interior trim and films are removed, and the insulation is dried. A lot of materials have to be thrown away, and this is another unplanned cost. Even if you hired a professional team of builders, this is still not a guarantee of the well-being of the future attic, especially if the roofing pie is thought out without taking into account the local climate.

Why it happens? So, in Russia, dampness, cold and round-the-clock negative temperatures are not uncommon. And the lower the ambient temperature, the greater the volume of steam that penetrates through the vapor barrier - all due to an increase in the partial pressure drop. And at the same time, the migration of moisture through the cold membrane slows down significantly, although it does not stop. Bottom line: the situation is even worse than under standard proven conditions. And therefore it is impossible to test the vapor permeability of a roofing pie in European conditions, and at the same time expect the same good result in the Siberian regions.

Here is a simple illustration to help you understand what we are talking about here:

Note that the maximum pressure of water vapor on the roofing pie is in the residential attic. And the point is not even that there is a person in such a room much more often than in an ordinary cold attic - it’s just that the pressure of warm air is additionally added to the vapor pressure. Moreover, these processes are so clear that they can be observed in the form of real leaks!

The fact is that wet insulation loses its properties very quickly. And the more humid the air that gets to it, the faster the thermal insulation decreases. For example, a basalt insulation with a moisture content of only 5% already loses its heat by 20% than a dry one.

For example, just one cubic meter of air space, if its relative humidity is 100%, at a temperature of 20C contains 17.3 grams of water - just in the form of steam. And the lower the temperature, the more difficult it is for air to hold water in a bound state. And when the temperature drops to 16C, there will already be only 13.6 grams of water vapor in the same air, and the rest will settle in the form of water in the heater. We conclude: moisture in the insulation appears due to the condensation of excess water vapor from the air in the process of lowering the temperature. And she needs to actively fight. And this is not the only problem - now we will deal with all.

Let's start warming - work technology

Let's start with the first problem - the insufficient thickness of the log if you insulate the attic after the construction of the whole house and the installation of the roofing. Why is that? Let's look at this issue in detail.

So, attic insulation can be divided into basic and additional. Basic - this is insulation, which is carried out even during the construction of the roof of the house and involves the use of light insulation directly into the truss structure. But additional insulation already turns a non-residential attic into a full-fledged attic.

With basic insulation, the main task is to minimize the heat loss of the house through the roof, and such basic insulation may well replace additional internal insulation, if only you correctly approach the choice of insulation, do not spare its thickness and think over the truss system well. This is often done by those builders of their own home who understand that even 20 rooms may not be enough in the future, and an additional room for a billiard room, a library or a sauna cannot interfere. And therefore, it is initially better to build it completely residential, and not to finish something later.

But, if during the construction of your house you decided to get by with elementary thermal insulation and now you have enthusiastically taken up the arrangement of a residential and cozy attic, then the only option for you is additional internal insulation with all its nuances, the main of which is the insufficient thickness of the rafters, which were not originally designed for dense internal insulation. But the problem is completely solvable, as proof of which we have prepared a detailed master class for you:

And now we move on to more insidious moments that are no less important: proper vapor barrier and waterproofing, which you may need to redo.

No - dampness and smudges!

It is extremely important for any insulation to create the right conditions, otherwise the material will quickly become damp and instead of a heat source it will become a source of dampness, mold and cold. What are these conditions? Let's find out more!

What is dew point?

The first and most important quality of any insulation is low thermal conductivity. Thanks to it, the insulating layer rigidly separates the warm air inside from the cold outside. It would seem that they inserted a heater into the rafters, fixed it - and everything else is needed? It wasn't there!

Firstly, from the outside, this whole thing must be carefully waterproofed from rain and damp air, because. such a roofing cake in this regard is a real sponge. Secondly, any insulation also has a second quality - vapor permeability, i.e. "breathes". And now let's remember the physics: warm, moist air inside a room under a roof (always humid!) Without finding an obstacle, it easily passes inside the insulation and collides with its colder part, the one closer to the roofing pie. And there this air condenses, settling in the form of droplets, which is called the dew point. And then what's the point of external waterproofing? Mineral wool heaters are especially susceptible to this phenomenon, we note.

Therefore, our first task is to ensure that as little steam as possible passes through the insulation, because even super-diffuse membranes in the cold do not cope well with the removal of water vapor, due to a significant slowdown in moisture transfer processes. And this is already a question of the correct vapor barrier of the attic insulation.

Here is a clear example of the unpleasant consequences of ignoring the concept of dew point:

Vapor barrier: warm European winters and Russian frosts

In fact, in Western Europe, where winter has always been mild, there is no need for a vapor barrier with special properties - simple packaging films are quite similar. So they just sometimes end up in Russia, although their vapor barrier properties are not high. These are roll films of LDPE, which stands for "low density polyethylene". In such films, non-uniformity in thickness and microdefects are noticeable. Their main purpose is product packaging.

Slightly better are reinforced materials, which are made by hot pressing a film to a mesh of twisted thread. In production, such films are injured by mesh nodes, and as a result, low vapor barrier properties are further reduced. Although the film itself is much stronger than usual, of course.

More reliable can be called bag fabrics made of polypropylene yarns and spunbonds. The former are additionally laminated with molten HDPE, but a uniform and continuous film is still not obtained, however, the strength pleases. And the latter are made from non-woven polypropylene fiber, but its vapor permeability is still in the range of 15-25 g / m2 per day, and this is a very low figure.

And aluminum foil boasts the best vapor barrier properties, which is suitable even for arranging steam rooms, in which the pressure and volume of water vapor are the highest. The only point: such a vapor barrier additionally creates the effect of a thermos in the attic, simultaneously reflecting invisible heat rays back into the room. And therefore it is better not to insulate a small attic room like that, but for a spacious one - that's it.

Therefore, if you want to save heat as much as possible, or in the attic you plan to make a good sauna, then you need such a vapor barrier:

Or immediately purchase a heater with an aluminum side:

Close access to water vapor

But remember that a good vapor barrier film is still important to properly lay and waterproof, otherwise water vapor will still find its way.

The joints of the vapor barrier sheets are usually sealed with a special butyl rubber adhesive tape, but even in this case it is impossible to guarantee complete tightness. The thing is that over time, the adhesion of the sticky layer decreases, and with an additional load, the canvases become unstuck. That is why, when installing an exterior finish, when you can attach the same drywall directly to the vapor barrier, many put an additional crate. Its task is not so much to ensure that the finish is fixed more evenly (which is also important), but to press the tape or sealant with slats.

In addition, this crate (usually with slats up to 3 cm thick) additionally allows you to lay electrical wires directly under the sheathing, and not through the insulation, as many do and which can hardly be called a technically competent solution.

But the places where the vapor barrier adjoins passing pipes and brick walls must be insulated with special sealants or tapes.

Another important point: never stretch the vapor barrier - fasten with a small margin. The fact is that all wooden structures, which is what the truss system is, naturally dry out and become a little smaller. The frame itself becomes mobile, and under the roof outside and under the sheathing inside, there is a risk of ruptures. And then - a surprise!

Does external waterproofing "breathe"?

So, on the warm inner side of the insulation we put a vapor barrier, which does not allow moist air to flow from the room. And on the outer, colder side, we are already fixing waterproofing, which will protect the insulation under the roofing pie from external accidental leaks of melt water or rain.

And the further development of events already depends on how “breathable” the upper waterproofing film will be. So, if you purchased the most common roll of inexpensive waterproofing, things are bad, moisture from the roofing pie will evaporate for a long time and hard, as a result - dampness and gradual destruction of the insulation. But modern vapor-permeable membranes are called “smart” for a reason: they do not let moisture in, but take water vapor out. It's all about their unusual, well-thought-out structure. Why does it turn out that when using cheap barrier films, even expensive insulation does not last long, and repairs are not far off.

Please note that the diffuse membrane should fit as tightly as possible to the insulation, without any gap, like with a conventional film. Otherwise, the membrane material will cool more strongly, and the temperature will become lower than the steam migrating through the insulation. You will see the result in the form of ice right on the membrane, which will make it lose its vapor-permeable properties even more.

When should the roof be removed?

Quite often, during the construction process, roofing material or reinforced films are installed as roof waterproofing. And after a couple of years, when the attic turned out to be very necessary and all the households enthusiastically began to repair it, it turns out that nothing will work without a complete analysis of the roof.

What's the matter? The fact is that such waterproofing does not “breathe” at all, and any insulation under it will completely bend. That is why, if the roof of your house is still under construction, but you are thinking about how to postpone attic insulation for the future, immediately use a good super-diffuse membrane as waterproofing.

But how can something get into the insulation if we have already installed a vapor barrier? The fact is that not a single film in the world is capable of 100% retaining water vapor - they are very small. And no matter how hard manufacturers try, there is no absolute barrier. And even more: modern vapor barrier films, in fact, do not even half do their job, and only the highest quality ones are able to retain steam by 75-80%. Everything else, unfortunately, gets inside the roofing pie.

let's sum it up ogi. You should end up with a roofing pie with two films that have absolutely opposite properties: the inner one does not let steam into the insulation, and the second saves it from a small amount that accidentally got there.

Thermal insulation of complex structural elements

If you have decided on a heater and insulating materials - congratulations! Prepare everything carefully, calculate everything you need and boldly proceed. Most importantly, do installation work only in a well-ventilated area. And, finally, when working with modern heaters, many manufacturers advise using a vacuum cleaner before insulating the attic roof from the inside, and at the end.

It is not difficult to insulate pitched and straight attic walls, and the first difficulty you will encounter is windows and other complex structural elements. It is also important to properly insulate them, leaving no chance for moisture or water vapor to seep through. Do you know what are usually the most problematic places in attic rooms that “please” with mold and smudges? Therefore, take this question seriously:

Here is another tricky moment when the attic floor is not made of logs, but with a solid slab. You need to warm it up like this:

And, finally, after insulating the attic, make sure that snow does not accumulate later in the drains and on the ridge - the entrance and exit of the movement of under-roof air. For this, it is more rational to install ventilation pipes along the entire roof ridge, and make the ridge itself non-ventilated. That's all the difficulty!

One of the most important tasks in the construction of the attic is to protect it from the formation of condensate, which can lead to damage to the roof system and thermal insulation material, as well as to increased costs for heating the house. Proper attic vapor barrier should be laid 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 for the rehabilitation of the attic, will only be commensurate with the new stage of construction.

Before deciding which vapor barrier to choose for a mansard roof, it is necessary to understand the mechanism of formation and movement of water vapor. There are two principles of transfer and formation of condensate:

1. Diffusion is the movement of vapor from an area of ​​high pressure to a place of low pressure. In winter, such a transfer is carried out from a warm, heated room to a cold outside, where a low partial pressure is observed. In summer, the direction of the flow changes, and the steam from the warmer and more humid outdoor air is directed to the drier and cooler attic space. Mansard roof structures (waterproofing, insulation, vapor barrier, finishing) are on the way of the diffusion flow. 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. That is why it is so important to choose a high-quality vapor barrier for the attic.

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

1. Convective is the movement of air and steam flows through loose layers of coatings and heat-insulating 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.

In actual roof operation conditions, both mechanisms of moisture penetration are present. At the same time, the intensity of the diffusion process is directly related to the choice of a good vapor barrier and pressure drop. In turn, the convective process depends entirely on the quality of the insulation work and the use of sealing tapes and mastics.

Attention! When comparing the degree of wetting of roof structures during a diffuse and convective process, it can be said that the latter of them is much more dangerous, since more water vapor penetrates into the structures.

Consequences of wetting structures

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

• The entire structure reduces the resistance to heat transfer. This leads to higher operating costs.
• Mold and moisture can damage roof structures (both metal and wood).
• Due to the increased air permeability of structures and the ingress of dust, the air quality in the house is reduced. The favorable microclimate and the comfort of living in attic rooms 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 properly install the material. Of particular danger from the point of view of poor-quality vapor barrier are loose overlaps of vapor barrier material, poor-quality junctions with walls and other structural components of the roof.

Important! The main task in the arrangement of the roof is to exclude or minimize the uncontrolled movement of air containing water vapor through the roof structures.

Varieties 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 roofing. The choice of characteristics and type of vapor barrier material is directly related to the design features of the 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:

1. 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 minuses, it is worth mentioning the low strength of the material in the places of fixation with staples.
2. Polyethylene multilayer films with reinforcement. Pros: high strength and transparency. Cons: low resistance to vapor diffusion due to the thinness at the point of interweaving of the fibers of the reinforcing mesh. It should be noted that films weighing at least 200 g / m² are more often used.
3. Polymer films 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 a small elongation at break.
4. Multilayer foil polyethylene film. The advantages include the high density of the material and a relatively good vapor diffusion resistance coefficient, as well as additional heat preservation in the room due to the reflex layer. Self-adhesive tapes go along the edge of the material for a more hermetic laying. The only downside is the lack of transparency.
5. Polymer-bitumen rolled self-adhesive vapor barriers. They are quickly mounted, as they are simply glued to a solid base of concrete or OSB on a primer layer. Such products can be used on a sheer surface without additional gluing of overlaps.
6. 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 is not used. Their sphere of use is prefabricated and frame structures. The junctions and overlaps must be additionally glued with tapes. OSBs are only suitable for roofs with simple geometries. Above wet rooms, it is required to lay a layer of film vapor barrier. This material is not suitable for use in timber and log houses due to high shrinkage.
7. The adaptive polyamide vapor barrier has a variable vapor permeability and is only suitable for repairing areas 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 condensate. 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 layer tightness, as well as the use of the right technical solutions.

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

Answer:

Your question, Ivan Mikhailovich, is very relevant, since the attic needs protection from heat loss. Help in this as best as possible the vapor barrier layer, which does not allow moisture to destroy structural elements and lead to their decay.

As materials for the vapor barrier layer, polyethylene film, membranes or polypropylene film can be used.

• • polyethylene film is stretched directly during installation and due to its impermeability, condensation forms inside it. Due to the fact that the film is laid with the rough side outward, the 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- Differs in the highest durability and firmness. This material has one drawback that you should be aware of. The fact is that condensation often forms on the front side of the reinforced material, to protect against which it will be necessary 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 ingress and steam escape.

For laying the membrane, an additional heat-insulating layer is required.

Modern vapor barrier film is an excellent choice

In addition, many new materials have recently appeared, such as isopsan, NPP LF foam, 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, among which are both advantages and disadvantages, as well as cost, since many of the listed materials are not cheap.