How to install a vapor barrier on a roof. Roof vapor barrier: main types of materials and efficiency of use. Do you need a roof vapor barrier?

Heat conservation is not only a component of saving. First of all, it is health and comfort. Excess moisture combined with cold air leads to the formation of dampness and mold. Being in a room where fungus has appeared is not only uncomfortable, but also unsafe. In addition, this leads to the inevitable destruction of building structures that are constantly exposed to moisture. A modern, reliable vapor barrier for the roof will help avoid the above problems.

The level of dryness, comfort, and heat retention in the room largely depends on the condition of the roof. It acts as a barrier between the cold external environment and the internal heat of the building. The use of insulation in the absence of waterproofing for the roof is ineffective. Waterproofing prevents the penetration of steam from the living space into the insulating layers.

For a long time, ordinary polyethylene film was used as a vapor barrier when constructing roofs. But this material is mechanically vulnerable. In addition, it is characterized by a fairly high level of moisture permeability. Modern vapor barrier film for roofing has a vapor permeability of 0.4 g/m², and ordinary polyethylene - 13-20 g/m². It is used for all types of roofs: flat, pitched, and when constructing an attic floor. Reliable vapor barrier of the ceiling is especially important in a cold attic.

The vapor barrier is one of the components of “ roofing pie", which also includes waterproofing and insulation. If the “pie” is laid correctly and from high-quality materials, then the main functions of the vapor barrier can be considered:

maintaining the microclimate, ensuring air exchange, maintaining optimal temperature conditions and humidity levels in the premises of the building;
protection of the roof structure from penetration of moisture from the outside and steam from the inside, preventing the formation of condensation, damage, fungus, mold;
reduction of heat loss during the cold season, which helps to save costs on coolants;
increasing the fire resistance of roof structures;

reducing the cost of repairing the roof and building.

The absence of implementation of at least one of the above functions indicates poor quality of the film or errors made during its installation.

Helpful advice! Before purchasing a vapor barrier material, it is necessary (if you lack knowledge) to consult with an experienced roofer. Incorrect selection may result in steam damage to the insulating material.

Types of vapor barrier and their features

Modern vapor barrier films, actively displacing simple polyethylene, roofing felt, glassine, are distinguished by a wide range and purpose. The most common types, available in price and installation method:

standard vapor barrier film. It prevents condensation from forming on the roof and insulation;
foil vapor barrier. Unlike the standard layer, it has a reflective function and provides an increased vapor barrier, and also reflects and returns some of the heat to the room;

membrane film. It has an insulation effect and limited vapor permeability, which allows you to control the removal of excess moisture from the room.

The vapor barrier film can be made of polyethylene or polypropylene. Polyethylene is a fragile material, therefore a polyethylene product is reinforced with a special fabric or reinforcing mesh. Polypropylene films are a woven material laminated on both sides with the finest polypropylene. This type of product is durable and resistant to ultraviolet radiation.

There are options when an antioxidant layer is applied to the polypropylene film, which absorbs and retains moisture, and after the steam stops flowing, the layer dries through ventilation. A vapor barrier device of this type allows it to be installed in only one way: the rough antioxidant layer is placed at the bottom, the smooth surface at the top.

Films laminated on one side with a foil layer are distinguished by the highest vapor barrier qualities and are the most suitable type of vapor barrier for the ceiling of rooms with high humidity (baths, saunas, swimming pools, etc.).

Types of membrane films

A special type of vapor barrier is under-roof membranes. This is a durable, temperature-resistant material. It does not have low vapor permeability, but is effective in the construction of certain types of roofs. Characterized by more complex structure than regular film. The pores of the membrane resemble microscopic funnels. Thanks to this property, it does not allow steam to pass through from the outside, but perfectly removes moisture from the inside. Currently, several types of roofing membranes are produced:

Perforated membrane. This is a reinforced film or a combined fabric with punctured holes. Used for arranging a cold sloping roof. It cannot be used for vapor protection of insulation. In frosty weather, steam may settle on the inner surface of the membrane.
Porous membrane. It has many interfiber pores for the passage of water vapor between them. The vapor permeability of a material can be different; it depends on the size of the pores and the degree of hydrophilicity of their walls. It is not recommended to use this type of vapor protection in highly dusty conditions. In dry and windy weather, dust can settle through the gaps onto the membrane and close the pores.
Three-layer superdiffusion membranes. Made from several layers. They have no openings into which dust or moisture can penetrate, which is a significant advantage. The membranes do not lose high vapor permeability in dusty environments. It is also worth noting their excellent windproof ability.
Double-layer film membranes. A cheaper version of a multilayer product. The absence of one of the protective layers significantly impairs reliability.

Vapor barrier materials must be elastic, durable and easy to use. When fastening with dowels, self-tapping screws, staples, nails, it is necessary that they do not tear, but at the same time fit tightly to the fastening.

Helpful advice! When choosing a vapor barrier material, special attention must be paid to quality, since this is the bottom layer of the roof structure and its repair is almost impossible.

Basics of making the right choice

When arranging a roof, it is important not only to know how to properly install a vapor barrier, but also how to decide on the right material. When choosing, it is necessary to take into account, first of all, the type of roofing material.

If the roof decking is planned to be made from materials with low thermal conductivity: slate, tiles, ondulin, onduvilla, diffusion vapor barrier membranes should be used.

Roofs made of metal tiles, corrugated sheets and seam roofing (joining sheets using a seam) are recommended to be protected using a vapor-proof film with an anti-condensation layer.

When choosing vapor barrier materials, the following parameters must be taken into account:

vapor permeability;
durability of operation;
installation features;
price.

The level of vapor permeability is measured in g/m² per day. The lower the permeability, the more reliably the insulation, finishing, and structural elements of the roof are protected from getting wet. To a certain extent, the film must provide air exchange, otherwise a greenhouse effect will be created for the room. Anti-condensation polypropylene films and breathable diffusion membranes provide optimal vapor protection.

The durability of vapor barrier materials is due to a number of qualities:

tensile and tear strength;
resistance to high temperatures;

immunity to ultraviolet radiation.

Budget polyethylene film can tear during installation and be destroyed by temperature changes. Vapor barrier membranes made of non-woven artificial fibers with a protective layer are distinguished by their durability. They are resistant to mechanical damage and temperature.

Installation features must be known before purchasing film, since the quantity can be calculated correctly only if you know the amount of overlap. Also, the purchase of related materials directly depends on the installation method. If the adhesion of the vapor barrier material to the mounting tape is low, this will inevitably subsequently lead to a violation of the tightness of the vapor barrier layer. Therefore, it is necessary to purchase a different type of adhesive tape.

The price of a vapor barrier for a roof directly depends on its quality. Budget options don't last long. It is necessary to be able to correctly calculate the cost of the material. A low price per roll may not mean optimal cost, but be a consequence of the small footage. Only price comparison per 1 m² various types vapor barrier will help you make the right choice.

Helpful advice! The quality of the film must match the quality of the roofing material. If the material is designed for long-term use, and the validity period of the vapor barrier is shorter, when replacing it you will have to dismantle the entire “roofing pie”.

Sequence of laying vapor barrier: basic rules

There are two types of vapor barrier: roll and sheet.

Installation of roll laying is carried out as follows:

the material is rolled out;
measure the required length of the canvases and place them with an overlay (100–200 mm) on adjacent fragments;
fixed with staples or wooden slats;
joints and overlaps are secured with vapor barrier tape (or other adhesive tape).

Sheet installation requires the preliminary creation of a wooden sheathing or profile frame into which the waterproofing will be laid. You can secure it with self-tapping screws or a stapler (according to the material).

When laying a “roofing pie” the question is: “Which side should I lay the vapor barrier on?” – appears among the first. A film that is identical on both sides does not cause any difficulties during installation: whichever side you place the vapor barrier on, the effect will be the same. The film, which has a two-layer structure, where one side is smooth and the other is rough (to retain condensation), is placed with the smooth side outward (adjacent to the insulation), and the rough side inside the room.

Related article:

Carrying out waterproofing work on the foundation using rolled materials various types: detailed instructions.

It is also easy to determine which side to lay the foil vapor barrier against the insulation. Since this type of vapor barrier is intended not only to block moisture vapor, but also to retain heat, the reflective side (foil) should be directed inward, towards the room.

Membrane vapor barrier can be double-sided, and then for its effectiveness it does not matter which side of the vapor barrier of this type is located to the insulation. If the membrane vapor barrier is one-sided, the manufacturer must indicate the wrong side.

Basic rules for installing vapor barrier:

cleaning and drying the coating;
the vapor barrier film should be installed without sagging, with slight tension;
a ventilation system is required for proper functioning;
Sealing of joints is required.

Helpful advice! When purchasing waterproofing, you should study the instructions (annotation). Sometimes not one, but two ventilation blows are required.

How to properly install a vapor barrier for a roof

Installing a roof vapor barrier is a process whose complexity depends on the type of roof.

The more intricate the rafter structure and, accordingly, the shape of the roof, the more expensive and difficult the task of high-quality insulation becomes. Installation of water vapor barrier for the roof should be carried out from the inside.

Laying of canvases can be done vertically and horizontally. If the horizontal method is chosen, then you need to start mounting from the top. Each subsequent canvas is laid on the previous one with an overlap of at least 10 cm. The seams are sealed with tape. You can use single-sided tape, it is applied on top. Double-sided tape is placed inside.

If the installation of vapor barrier for the roof is carried out along the rafter legs, i.e. vertically, then the overlap of the sheets should be done on wooden rafters. The vapor barrier material is attached to the wooden structural elements with staples or galvanized nails. It is advisable to reinforce the places where the joints are glued with pressure strips, which are especially important to use on roofs with a slope of up to 30 degrees and with low insulation density.

Helpful advice! Used wooden planks and bars must be treated with an antiseptic. This will significantly extend their full service life.

If the structure has skylights, hatches or other passages through the roof, then along their perimeter you need to stick a butyl rubber self-adhesive tape, which will prevent the passage of moisture and steam and firmly seal the cutouts in the vapor barrier film, even if they are adjacent to a not entirely flat surface. This type of tape has high water-repellent properties and good resistance to temperature influences. In addition, it easily levels out unevenness.

If ventilation pipes pass through the roof, the film must be wrapped and tightly wrapped around them, securely secured with one-sided adhesive tape.

Mistakes made during the installation of vapor barrier

In the absence of experience and professional advice, a number of mistakes are made when laying vapor barriers, which will subsequently significantly affect the efficiency of the vapor barrier. The most common of them:

loose connection of the film to purlins, crossbars, valley, spine and ridge beams;

not knowing which side to lay the vapor barrier against the insulation;
use for sealing narrow adhesive tapes (up to 50 mm);
when sealing openings, no deformation reserve of the film is left (20–30 mm);
the plastic product around the roof windows does not close with inside, as a result of which after some time it is destroyed under the influence of ultraviolet radiation and low temperatures;
the film goes around the rafter legs. Moisture will penetrate into the gap between the rafters and the vapor barrier;
In places where the film adjoins significantly uneven surfaces, no special glue is used. Construction tape, butyl and other types of adhesive tapes do not provide complete tightness in such cases.

Helpful advice! When laying a vapor barrier, you should not neglect even a seemingly insignificant rule or violate the installation sequence. A good result will be achieved only if all requirements are met.

Vapor barrier for ceilings in wooden floors

Wood is an organic material and therefore allows vapor to pass through. But excessive moisture with steam is also undesirable for it, since under its influence the tree expands and can rot. In order for the ceiling, which is located under a cold attic, to remain in normal condition, it is necessary to install the correct vapor barrier. It is important to follow the installation sequence here. The component that has minimal vapor barrier is placed first. It should be zero or close to zero. The following layers have a permeability higher than the previous one.

From the room, the vapor barrier should look like this:

vapor barrier. Polyethylene or polypropylene film, diffusion membrane. Placed on top of the ceiling;
thermal insulation. Roll, backfill or tile material. Fills the void between floor beams;
waterproofing. A layer of diffusion membrane or perforated polyethylene. Installed only when using an attic.

If you do not plan to use the attic space, then the waterproofing layer is transferred under the slopes, where it protects the entire roof.

Laying vapor barrier material on wooden floors is done around each beam. The strips are mounted perpendicular to the beams. In this case, the material is not stretched; slight sagging is mandatory.

With a panel wooden floor, each compartment is wrapped. The material is cut out according to the size of the shield and the height of the walls.

Helpful advice! You should not rewind the rolled vapor barrier material, so as not to confuse the side that should be in contact with the ceiling (it is indicated by the manufacturer).

Vapor barrier for a bath

A bathhouse is a room that requires high temperature and is characterized by a high level of humidity. The vapor barrier of this building is used to preserve the insulation, as well as to protect wooden structures from moisture. When choosing vapor barrier materials, it is necessary to take into account that it is advisable to use different insulation for different premises:

for a steam room, the best option is a foil vapor barrier that reflects heat and creates an additional thermos effect;
the shower room can be vapor-insulated with polyethylene or polypropylene film;

in the dressing room and rest room, a membrane vapor barrier will be appropriate, which will ensure the necessary air exchange.

One of the recognized modern vapor barrier materials is Izospan V. It has a fairly wide purpose. The instructions for use of the Izospan V vapor barrier indicate that it can be used for:

roofing structures;
gender;
walls, both outside and inside;
laminated floors and parquet.

The double-sided structure of this material allows it to be actively used for vapor barrier in bathhouses. How to lay a vapor barrier and which side to attach the Izospan B vapor barrier is suggested by the presence of a different structure of the sides: the rough surface is designed to absorb steam, therefore, it should be directed inside the room.

Is a vapor barrier necessary when insulating with mineral wool?

Mineral wool insulation is an effective type of thermal insulation that is actively used in modern construction. But it has one rather significant drawback: when it gets wet, mineral wool is destroyed and loses its heat-insulating properties. That is why the use of vapor barrier film, along with this insulation, is extremely necessary. It will create a barrier that will protect the thermal insulation layer from the effects of steam and make it possible to keep the rooms warm.

Which side should the vapor barrier be placed if mineral wool insulation is used?

If a double-sided film with a moisture-absorbing layer is used, it should be directed towards the room from which steam flows rise. The smooth side is adjacent to the insulation. When using a material with a foil-coated surface, the aluminum coating will become a barrier to the penetration of moisture into the heat-insulating material. Therefore, it is this surface that should be directed towards the room.

Helpful advice! If mineral wool is used to insulate rooms with high levels of humidity, then it is more reliable to use a vapor barrier with a foil-coated layer, since it has the lowest level of vapor permeability.

Prices and manufacturers

TechnoNIKOL company is a leading manufacturer of vapor barrier materials in Russia and the CIS. The products are manufactured on a polymer basis. There are the following types of TechnoNIKOL vapor barriers:

for pitched roofs (has the ability to partially allow steam to pass through);
For flat roofs(has high strength and elasticity);
reinforced (reinforced three-layer film of high strength);
universal (used for all types of roofs).

The average price of TechnoNIKOL vapor barrier per m² is 20 rubles. This is a low price level with good quality.

Vapor barrier Yutafol – products from a European manufacturer, which are distinguished by their variety, satisfying various purposes when installing vapor barriers. For the convenience of the buyer, in order to easily distinguish between the materials and not to confuse waterproofing, windproofing and vapor barrier, they have the names Yutakon, Yutavek and Yutafol (respectively). In addition to standard types of products, this Czech company produces Yutafol N110 Special film with a self-extinguishing reagent that reduces the level of flammability to a minimum. The price of this film per 1 m² is from 17 rubles. Reducing the cost of products due to simple packaging is a successful decision by the company.

Vapor barrier Axton – products of the French company Leroy Merlin. It has three types: B, C and D. Axton B - polyethylene film, a budget option. It will last a considerable time if you avoid mechanical damage and fix it correctly, using not a stapler, but special nails with wide heads. This material is used for indoor installation only.

Axton C is a polypropylene product, more durable and versatile. Has different permeability indicators. This is a two-layer material, it is recommended for insulated and non-insulated types of roofs with a variety of designs. Axton D looks like an awning. Used for water and vapor barrier. Characterized by high strength and ease of installation. The products of this company are distinguished by high level environmental friendliness

Vapor barrier materials Tyvek are produced at the plant in Luxembourg. The base is high quality polyethylene, non-woven structure. The main difference between the products is environmental friendliness and “breathable” membranes with controlled vapor permeability created using innovative technologies. The price of Tyvek vapor barrier is 7–10 percent higher than the cost of domestic analogues.

The price of a vapor barrier for a ceiling most depends on the quality of the material, its density and manufacturer. That is why branded products from foreign companies are more expensive.

Roof vapor barrier:modern solution for moisture protection

The roof is a structural element that can withstand constant double load. From the outside, it is exposed to atmospheric phenomena: precipitation, sunlight, low temperatures, wind. On the inside, it experiences internal effects of temperature and humidity. In such conditions, it is simply impossible to overestimate the need for proper vapor barrier installation, the absence of which can lead to the destruction of the roof and subsequently the building itself.

Modern technologies have made it possible to create films from polymers that can provide vapor barrier of the required level. A wide selection of material allows it to be used in accordance with the conditions and intended purpose. Having carefully studied how to properly install a vapor barrier, doing everything technical requirements, you can create a healthy microclimate in the premises and provide the building as a whole with many years of existence without major repair work, while maintaining an aesthetic appearance.

There is no reason to consider the price of vapor barrier for roofing per m² to be high, which makes the material affordable for any developer.

Making an informed and rational choice of materials and correctly installing a vapor barrier is the desire of every homeowner. The content of the article is intended to help you install the vapor barrier yourself. But even if such a solution is unacceptable, you need to be aware in order to correctly assess your costs and the quality of work of the hired specialists.

Almost every owner of a private house or country house knows that the main “enemy” of the roof is the steam emitted by a person when breathing, formed during cooking, which is converted into condensation and settles in the roofing carpet. This can lead to deterioration in the functioning of the thermal insulation layer and, ultimately, to the destruction of the roofing.

To avoid such situations, it is necessary to use a vapor barrier when laying the roofing. For this purpose, special building materials with a vapor permeability coefficient are used, which will reduce the risk of damage to the insulation.

Laying a vapor barrier has its own characteristics and subtleties, which you need to know about if you are going to carry out the installation yourself.

It is important to note: If there are stove or fireplace pipes on the roof, then a double layer of vapor barrier is required next to them, since one can be damaged by the heat emanating from them.

Leave a gap between the vapor barrier material and the insulation for additional heat retention. The choice of film is best made taking into account the climatic conditions of your region, the area where the house is built and the type of roofing used.

Note to owners of houses made of timber: When building a house made of timber, you can refuse vapor barrier, since this natural material has the ability to absorb moisture, thereby preventing the formation of condensation.

Instructions for laying roof vapor barrier

wooden house

It is important to note: In order to maintain the integrity of the vapor barrier of the entire house, it is necessary to ensure that the film is covered with a continuous carpet without tears, scratches or holes.

In general, the arrangement of the roofing carpet should look like this:

insulating film

Using a vapor barrier also helps prevent the formation of mold and mildew. By using this layer, you, first of all, take care of the health of your loved ones.

The roof structure is a complex system. It consists of several layers of dissimilar materials, each of which performs its own unique function.

To ensure comprehensive protection of the building from environmental influences, it is necessary to carry out all installation work with high quality, as well as the correct choice of basic and insulating materials. This whole process is briefly called roof insulation.

The standard composition of the roofing cake includes:

Why do you need a roof vapor barrier?

The vapor barrier layer protects the roof from the penetration of water vapor into the thermal insulation. The fact is that most insulating materials have a porous structure, since the air they contain acts as a heat insulator. When it comes into contact with a colder environment, the steam turns into condensate, which is retained in the voids.

This can lead to disruption of the functionality of the heat-insulating material, as well as the occurrence of decomposition and rotting processes in the summer. In winter, freezing water expands, thereby destroying the bonds between the cellular elements.

The release form of vapor barrier films is a roll.

Vapor barrier can be made from various materials. Some of them have additional positive properties that increase the efficiency of operation of the building’s interior. Installing a vapor barrier on a roof is not as difficult as it seems at first glance, but it requires a careful approach and accuracy.

Types of vapor barrier

Single layer polyethylene films

Made from low-density polyethylene, which provides an increased degree of steam penetration. This material often has defects due to the ingress of foreign particles during manufacturing. The cheapest type of insulating material.

Polyethylene films with reinforcement

Compared to single-layer polyethylene, reinforced vapor barrier is slightly thicker, since it includes a reinforcing frame. It consists of polymer twisted threads located in mutually perpendicular directions. The mesh is attached to the polyethylene base by warm pressing.

This technique does not affect the waterproofing and mechanical properties of the material, but can reduce the degree of vapor barrier.

Anti-condensation film

It is made of two layers: smooth and fleecy. The smooth layer is attached to the insulated surface.

The fleecy layer is created from cellulose fibers. When steam hits such a surface, it clings to the fibrous structure, thereby preventing moisture from flowing onto the underlying structures of pitched roofs. Excess water is removed along with the air through the ventilated space.

Polymers with foil layer

They are made of penofol or foamed polypropylene, coated with a thin layer of metal. Due to the reflective properties of metal surfaces, such vapor barrier provides an additional function of protection against heat loss.

Membranes (film for roof vapor barrier)

Membrane vapor barrier materials are divided into five main classes:

Has increased resistance to moisture and wind. It is laid between the roofing covering and the heat-insulating layer. Manufacturing technology: spunbond.

This vapor barrier does not allow moisture to flow through the cracks of the roofing material, as well as from the condensation that forms. The absence of a laminating layer allows the use of such membranes in roofing structures with a slope of more than 35 degrees. To remove excess moisture, it is necessary to install ventilation holes from a double sheathing located between the membrane and the insulation. Type AM.

Unlike Type A, it has a multilayer structure. It is placed between the insulation and the roof to provide adequate protection from negative atmospheric influences. The most common is a three-layer construction, consisting of two layers of spunbond with a diffuse film located between them.

It acts as a waterproofing agent, as it allows steam to pass through but retains water. Laying is done directly on the heat-insulating layer, which reduces labor costs for creating a ventilation gap. Type B. Two-layer material.

Consists of a layer of vapor barrier film and spunbond. It is used to protect insulation from internal building vapors. Used only in insulated roof structures. Type C.

It is manufactured similarly to type B membranes. It has a stronger and thicker layer of spunbond, which provides better protection of the insulation from moisture. Used in insulated and non-insulated, pitched and flat roofs. Type D.

Consists of polypropylene fabric, protected on one side with a laminating polymer coating. The structure of the material allows it to withstand significant mechanical stress. This dictates its installation between the insulation and the attic floor screed, as well as in non-insulated roof structures.

Which side is the vapor barrier for the roof laid on?

The principle of installation of vapor barrier materials depends on which side the layer responsible for repelling water vapor is located:

ordinary and reinforced polyethylene films, as well as membranes of type A and AM can be laid on the insulation on either side. Anti-condensation vapor barriers are laid with the smooth side towards the insulation, and the fleecy side towards the vapor formation. Foil elements are laid with a metal layer inside the room, since this is where the light coming out of the building should be reflected heat. Type B membranes are laid with the film side to the thermal insulation layer. Type C and D membranes must be adjacent to the insulation with their rough side.

We have figured out which side to lay the vapor barrier on the roof, now we will look in detail at how to properly lay the vapor barrier on the roof.

Vapor barrier for the roof: how to install it correctly using special technology

Laying a vapor barrier on the roof is carried out as follows:

Laying can be done vertically and horizontally. In the second option, the installation of roof vapor barrier is carried out starting from the ridge part of the roof. Each subsequent strip is superimposed on the previous layer with an overlap, the value of which should not be more than 10 cm.

To wooden ones rafter elements the vapor barrier is attached using galvanized nails or a construction stapler. When installing films and membranes near attic hatches, you need to use a special vapor barrier apron, which is included in the standard package. At the junction with ventilation pipes, film and membrane structures are folded down, wrapped around the pipe and tightly fixed construction tape. After laying the vapor barrier layer, it is necessary to nail wooden blocks.

The rules for laying vapor barrier on the roof dictate the following rule - the pitch between the sheathing bars should be 500 mm. In this case, a ventilation gap is formed, and additional fastening of the vapor barrier layer is carried out. Now you know how to lay a vapor barrier on a roof, you can move on to the issue of waterproofing. If the vapor barrier for the roof has been damaged, then small cuts or holes can be sealed with special tape for vapor barrier membranes.

Roofing pie diagram

Sealing joints with tape

Final vapor barrier option

Hydro and vapor barrier of the roof - what is the difference?

Waterproofing materials also serve the function of protecting structural elements from moisture. However, unlike vapor barriers, they are not resistant to moisture-saturated air masses.

That is, steam coming out of the premises will freely penetrate through the insulating layer. Therefore, when purchasing vapor barrier films and membranes, make sure that they are intended for the correct purpose. Read more about roof waterproofing here.

Useful video

And now we invite you to familiarize yourself with the video instructions on roof vapor barrier:

Conclusion

Vapor barrier is the lightest and thinnest layer of the roof. But neglect of its structure can nullify all material and physical efforts to create quality roof. Therefore, you should not neglect this important element; it will significantly increase the service life of the entire building.

In contact with

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Country expert

Modern film vapor barrier is designed to increase the effective service life of heat-insulating materials, wooden and metal structures. Indeed, during the operation of a residential building, residents use many sources of intense evaporation - hot baths or showers, aquariums.

If the roof is equipped with a hydrobarrier, water vapor will condense on it from the inside, constantly moistening the insulation and building construction. Wooden elements are exposed to mold fungi, and metal elements are subject to intense corrosion processes.

Application area

Today, modern SNiP standards regulate the use of vapor barriers in the following cases:

When installing a heat-insulating layer of roofing coverings in warm attics and attics.

In the case of insulation of walls of buildings from the inside. This is especially true for metal structures - garages, cabins, insulated containers and others. This measure will significantly increase the service life of mineral wool or expanded polystyrene used as insulation.

For vapor barrier of wooden floors of the first floor.

Often, in our conditions, the floors of the first floor are also equipped with an insulating layer to prevent heat from escaping from the room in winter. And if there is a significant difference in internal and external temperatures, drops of condensed moisture will naturally appear on cold floor surfaces. The result is, again, saturation of the insulation with water, which leads to a significant deterioration of its thermal insulation qualities and premature destruction of wooden floor structures.

Technology for proper installation of vapor barrier with your own hands

When laying a vapor barrier with your own hands, you should follow simple rules:

The film must be mounted with the smooth side to the vapor barrier surface - insulation of the roof, walls or floor. If a foil modification of the film is used, it should be laid with the polyethylene side facing the surface to be insulated, and with the reflective screen facing the inside of the room. It will be especially effective when equipping internal hot rooms - baths and saunas.

They are laid exclusively overlapping with an overlap of at least one hundred millimeters. Preliminary fastening to wooden structures is carried out using a construction stapler with staples, a hammer with galvanized nails or a screwdriver with anodized screws.

A prerequisite is the tightness of its execution. In practice, this means the need for careful gluing of all canvases in areas of overlap and around the perimeter. For these purposes, it is recommended to use high-quality double-sided tape, and its width should not be less than 100 millimeters.

Features of laying vapor barrier film on various structural elements of buildings

Direct installation of the vapor barrier is carried out as follows:

In the case of a vapor barrier for the floor covering, the film is spread and fixed on the surface of the subfloor. After gluing all the overlaps and the perimeter, you can lay the finished floor and floor covering.

For walls and pitched roofs, it is possible to lay a vapor barrier film with the panels arranged vertically or horizontally.

When arranging a vapor barrier for a flat insulated roof, after laying it, it is necessary to fill a frame of wooden slats 10-20 millimeters thick on top of the film. These slats serve as additional fasteners for the film material and provide ventilation between the vapor barrier and the finishing of the flat roof.

Using double-sided tape

Double Sided Adhesive Tyvek Tape for Sealing Vapor Barrier

When organizing a vapor barrier layer, the following types of double-sided tape are used:

paper based; polypropylene based.

The second option is of better quality in terms of durability and ability to withstand external destructive factors - moisture and high temperatures.

The use of double-sided polypropylene tape is especially justified when installing vapor barriers in extremely hot and humid rooms, for example, in Russian baths.

Double-sided tape is used as follows:

First, the material is unwound and glued to the edge of the lower joining sheet with the release paper facing up.

Then the next sheet of vapor barrier tape is laid out and secured with the required amount of overlap.

After this, the layer of anti-adhesive paper is removed from the top side of the tape and, with light pressing and smoothing, both layers of the vapor barrier film are securely fastened together.

If you follow all the technological nuances of installing vapor barrier materials, using only high-quality products, you can significantly extend the effective life of the building’s structural elements - floors, walls, ceilings, roofing and the building as a whole.

Remember that your costs for installing a high-quality vapor barrier layer in a residential building will be disproportionately less than the costs of repair work due to the premature loss of insulation, load-bearing wooden structures and interior finishing materials. Therefore, insignificant savings on vapor barrier during construction of a building can result in significant losses in the future.

For more information about the technology of laying and fastening vapor barriers for a warm roof with your own hands, watch the video.

Currently, vapor barrier is one of the components of any construction. First of all, we are talking about roof vapor barrier.

The fact is that there is moisture in any room. The water itself isn't that scary. The most destructive effect on roofing materials is caused by condensation that forms on the inner surface of the roof in hot weather.

Scheme of vapor barrier of walls from the inside.

Laying a vapor barrier on the roof means protecting all building and finishing materials from the harmful effects of moisture. This is especially true for private houses and cottages, where in most cases mineral wool is used as insulation.

Condensation can penetrate its structure, destroying it and significantly reducing its service life. Below you will find instructions on how to install a roof vapor barrier. This is where it is worth fighting condensation.

Materials used for roof vapor barrier

Currently, a huge variety of materials are used that are used for vapor barrier. When it comes to roofing, the choice is simply huge. Until recently, roofing felt was the main material used for roofing.

IN Lately People began to refuse it because it has a limited service life. Under the most favorable conditions, roofing material will last no more than five years. In addition, there are now many materials with similar composition and properties.

Glassine is a material that is very often confused with roofing felt. They are similar in appearance, but the production technology is somewhat different.

In the production of glassine, cardboard is also the main substance. This material lasts much longer than roofing felt. It is perfect for roof vapor barrier.

Properties and scope of application of vapor barrier materials.

Films have also found quite wide application in roof vapor barrier. They are mainly installed in private houses, where a residential attic, that is, an attic, is equipped. There are several types of polyethylene films used for vapor barriers.

For example, reinforced materials have found wide application in this area. Don't forget about polypropylene films. They are currently becoming increasingly popular as they have a fairly long service life.

Today, breathable films are the most widely used. They are also called membranes. They differ from each other in the installation method.

Modern membranes can be single-sided or double-sided. Many experts unanimously claim that membranes can reduce the cost of air conditioning and heating a room several times. This is a fairly profitable option for roof vapor barrier.

It is membranes that are currently used most often for these purposes. Moreover, you don’t have to be a construction specialist to lay such material on your roof. It is worth noting the fact that membranes are installed in our country using a variety of technologies.

This is due to the fact that in Russia there is no strict rule according to which this should be done. Each specialist and company does the work in their own way. Basically there is nothing wrong with this.

Now it’s worth touching on the topic of vapor barrier instructions. It is worth considering the main aspects associated with the arrangement of this layer on your roof.

Every person dreams of his home being cozy and warm. To achieve this goal, it is not enough to choose a suitable project; you must also ensure that all construction work, including roof installation, is carried out in strict accordance with technology. Everyone knows that roofing materials must protect the house from penetration of external moisture. However, we should not forget about the destructive properties of steam, which is formed indoors during cooking, cleaning, washing, etc. In order for the house to have a normal microclimate and retain heat, a roof vapor barrier is required.

According to the laws of physics, warm air saturated with vapor rises and accumulates near the ceiling. It tends to go beyond the living space, into the under-roof part, where the humidity and temperature are lower. If there is unprotected thermal insulation in the way, the steam will penetrate into the insulation and begin to destroy it.

With the onset of winter, the following will happen: the low temperature on the outside of the insulation will stop the steam, it will first turn into frost, and a little later into an ice crust that will freeze the insulation, filling all its cracks. With the onset of spring, the ice will melt and flow, eroding the interior finish. The thermal insulation material will lose its properties and become unusable. Mineral wool will deteriorate in one winter, polystyrene foam will last a little longer.

To avoid such consequences, it is necessary to install a vapor-tight barrier, the main task of which is to prevent condensate from entering the thermal insulation layer. This will protect the insulation from moisture, thereby preventing the formation of mold, heat loss from the room and rotting of wooden structures.

Vapor barrier is used both for pitched roofs, and for flat ones, regardless of the type of coating

What materials are used to protect against internal moisture?

For a long time, the main material for vapor barriers was glassine. Particularly economical builders even now use it. However, if we take into account modern requirements for strength, service life, environmental friendliness and insulation characteristics, this is yesterday.

Recently, film materials with a complex multilayer structure have begun to be used as vapor barriers. They have a wide temperature conditions applications and high vapor permeability. Thus, the vapor permeability of simple polyethylene is 13-20 g/m2 per day, and that of a more modern vapor barrier material is about 0.4 g/m2.

Film materials are elastic, tear-resistant and easy to use. This is very important because:

when fastening with dowels and self-tapping screws, the material does not tear, but tightly grips the fastening itself;
a durable film will maintain its integrity even if mechanical damage occurs in the roof structure;
the film must withstand the load that will fall on it if the insulation loses its elasticity and cannot stay on the rafters.

Vapor barrier films are of two types:

polyethylene;
polypropylene.

Film-type vapor barrier materials are produced in rolls, which greatly facilitates their installation.

Polyethylene films are not very strong, so they are reinforced with special fabric or reinforcing mesh. They can be perforated or non-perforated.

Important! For roof vapor barrier, non-perforated polyethylene films should be used; perforated ones are more suitable for waterproofing.

In addition to conventional reinforced polyethylene films, films laminated on one side with reflective aluminum foil are also available. The vapor barrier properties of such films are very high, so they are used primarily for vapor barrier in hot and humid rooms - saunas, baths, swimming pools, etc.

Polypropylene films are a woven material laminated on both sides with the finest polypropylene. They are characterized by higher strength and resistance to ultraviolet radiation. In addition, polypropylene films can have a special antioxidant layer that prevents the formation of condensation. It easily absorbs and retains all resulting moisture, and after condensation conditions disappear, it dries quickly due to ventilation. Obviously, the antioxidant film has a one-sided application - the antioxidant rough layer is down, and the smooth surface is up.

It is very important that the vapor barrier material is of high quality, because it is located at the very base of the roof structure and is difficult to access for repairs.

Three-layer polypropylene hydrophobic membrane

How to install vapor barrier

How a roof vapor barrier is performed + video and photos of installation can be found on the Internet. Let's take a closer look at how this process should work:

Installation of vapor barrier should be carried out from inside the room after installing thermal insulation.
Vertical and horizontal laying of canvases is allowed.
Horizontal laying should start from the top. Each subsequent sheet is laid on top of the previous one with an overlap of at least 10 cm, with the seams necessarily sealed using single-sided or double-sided adhesive tape. Single-sided tape is glued on the outside of the overlap, and double-sided tape on the inside.
If the installation is carried out along the rafter legs, and there is no rough filing of the insulation, then it is recommended to overlap the panels on wooden rafters.
The vapor barrier material is attached to the wooden structural elements with staples or galvanized nails.
All joints must be tightly connected. It is advisable to reinforce the gluing areas with pressure strips. It is especially important to use such strips on roofs with a slope of up to 30 degrees and with low insulation density.
In areas adjacent to skylights, hatches and other passages through the roof, it is necessary to use a vapor barrier apron included with them. If there is none, then double-sided butyl tape must be glued around the perimeter of the frame.
In places where ventilation pipes pass through the roof, the film must be folded down, wrapped around the pipe and sealed tightly with one-sided adhesive tape.
After laying the vapor barrier film, it is necessary to attach antiseptic-treated bars in increments of 500 mm so that the inner ceiling lining does not come into contact with the film. The bars perform several functions at once: they fix the thermal insulation layer and form an air gap between the inner lining and the vapor barrier. Various communications can be installed in the resulting space. When finishing a room with plasterboard, galvanized profiles should be used instead of bars.

Important! The vapor barrier film should be installed without sagging, with slight interference.

The vapor barrier film is laid along the lower plane of the rafters and fixed with staples or nails

Common installation errors

If the installation of vapor barrier on the roof is carried out without the help of professionals, then mistakes may be made:

The most common vapor barrier defects are considered to be unsealed connections of the film to purlins, crossbars, ridge, valley and ridge beams. The more complex the rafter structure and, accordingly, the shape of the roof, the more expensive and difficult the task of high-quality insulation becomes.
To seal seams, you cannot use narrow (up to 50 mm) tapes. The width of the adhesive tape must be at least 100 mm.
When vapor barriering window openings, they often forget to leave a deformation reserve of the film (a fold of 20-30 mm for the draft).
If the plastic film around the roof windows is not protected with interior decoration, then after a few months it will completely collapse under the influence of sunlight.
The film should not be allowed to go around the rafters. In this case, moisture will enter the gap between the vapor barrier and the rafters, and when the “dew point” is reached, condensation will form on cold surfaces.
In places where the vapor barrier adjoins the internal walls, chimneys, shafts and other elements should take into account the nature of the surface to which the film will be attached. If the surface is rough (brick wall, unplaned wood), then the film can only be glued using special adhesives made from polyurethane or acrylic mixtures and synthetic rubber. Widely used butyl rubber and polyurethane adhesive tapes, as well as adhesive tapes, cannot be used, as there may be a loss of tightness due to poor adhesion.

To seal the joints of foiled polyethylene films, it is recommended to use aluminum-coated adhesive tapes

Water vapor has a very high penetrating ability, so installing a vapor barrier is a responsible process. Specialists who know all the subtleties and nuances will help you complete all the work efficiently. The main thing is to choose the right materials and do everything in the right sequence. Only a properly laid roofing pie will provide the residents of the house with a carefree and pleasant existence for a long time.

The humidity inside a building is always higher than outside. In the space limited by building structures, the air is regularly saturated with vapors released during breathing, cooking, washing, cleaning and other everyday household activities.

The water suspension rushing upward has a negative impact on the wooden elements of the rafter system, the thickness of the insulation and the roof itself. In order to eliminate it, you need to know how to properly make a roof vapor barrier, how to protect it from fumes harmful to building materials.

Vapors suspended in the air constantly rush to occupy “free positions”, i.e. move to where their percentage is lower. Since the relative humidity inside the house is always higher than outside it, it is easy to guess in which direction the water suspended in the air regularly moves.

A ventilation system is installed to remove water-saturated air, but it is unable to collect and remove all the evaporation generated inside the premises. It is especially difficult to remove from rooms with characteristic high humidity: bathrooms, showers, steam rooms, kitchens, swimming pools, etc.

Steam that is not removed by ventilation “attacks” building structures, tends to penetrate through the fences to the outside, and when cooled, settles inside them or on the surface. Moreover, the predominant part of the steam flow, amounting to 30 to 40%, is directed towards the roof. After all, it is picked up by warm air, which, according to physical instructions, moves upward.

A certain proportion of vapors must penetrate through the roofing system to the outside, as well as through the walls and basement. However, if not properly installed, it settles on building structures or lingers in the roofing pie.

The phenomenon of steam penetration into building structures and subsequent release into the atmosphere is called diffusion. If the roof is constructed correctly, it is not dangerous. But if there are disturbances, the steam turns into condensate, which promotes the settlement of fungal colonies that actively begin to destroy the wood. In addition, moisture retained in the thickness of the insulation significantly reduces the thermal insulation properties.

In order to prevent the impact of steam on the system materials, reliable protection is needed - a vapor barrier. It is made in the form of an insulating shell, which either does not allow steam to pass through at all, or conducts it through minimum quantities. Moisture that penetrates through this protection does not accumulate in the pie, but is removed through the elements of under-roof ventilation: vents, pitched and ridge aerators.

Schematic diagram of a vapor barrier

We have already said that steam spontaneously moves to where the air is less saturated with moisture and, as a rule, has a lower temperature. In accordance with our climatic realities, the flow of evaporation passes through building structures and is directed into environment. This is exactly what happens for most of the year. Only in hot weather summer days, which, unfortunately, are few in number, vapors from outside can rush indoors.

The vapor barrier is arranged in full accordance with the prevailing direction of the diffusing steam flow. It is installed very first on the inside of pies of all types of enclosing structures, including roofs. Those. First, on the side of the premises there is a film that protects the insulation and the roofing pie as a whole from steam, then other components come.

All materials used in roof construction have some degree of vapor permeability. It can vary from zero or thousandths of one to 3000 mg/m². This characteristic tells about the ability of the material to pass a specific volume of moisture per day. To form a barrier against moisture suspended in the air, options with the lowest vapor permeability are chosen.

The main principle of constructing a roofing pie is that on the side of the room there is material with the lowest vapor permeability:

With zero vapor permeability values, the film will not allow household fumes to penetrate into the thickness of the roofing pie at all. Condensation formed there due to the difference in temperature on the outer and inner sides of the roof is evaporated in such cases through vents or accumulates on the waterproofing, after which it flows into the gutter.
With permeability values other than zero, a certain amount of vapor penetrates into the roofing pie. In this case, there is a need for effective moisture removal. To remove steam, an under-roof ventilation system is installed, and dormer windows are constructed to ventilate non-residential attics and attics.

Any of the steam protection options installed on the side of the premises must make it difficult for water suspended in the air to seep into the roofing pie. However, if it does penetrate, the structure should be arranged in such a way that complete moisture removal is guaranteed. This means that the layers following the vapor barrier should allow it to pass through freely.

Therefore, when constructing roofs, the order of the layers, determined by the vapor permeability indicators, must be observed. The first of them should allow the least amount of water to pass through, followed by those with the highest ability. The specified arrangement of protective layers at the same time prevents the passage of cold air flows from the outside into the building.

How to choose a vapor barrier material

Before laying a vapor barrier on the roof, it is worth understanding the types of materials used and the difference in technology of use. They are now produced in a huge assortment, which is easy to get confused. The “pioneer” in the vapor barrier business was glassine, which is still used as budget option. Later, polyethylene film joined the fight for protection against evaporation, and then polypropylene roll types appeared.

Common vapor barrier options

The development and implementation of new types is based on already well-known and tested vapor barrier barriers. It is associated with the desire to increase strength indicators, increase resistance to temperature fluctuations and resistance to ultraviolet radiation.

A wide range of vapor barrier membranes are produced based on polymer compounds. These include types with and without foil casing. If the foil material is installed so that its metal shell is turned inside the room, then in addition to protecting against the penetration of vapors, it functions as a reflection of heat waves. This is a priority quality when arranging saunas and steam rooms.

Among polymer membranes There are anti-condensation materials, one of the sides of which has a rough surface. This type of insulating film unfolds towards vapors with its rough side, which prevents dew from falling on the material. The second, smooth side prevents water from leaking from the outside, therefore anti-condensation membranes are used both to form protection against steam and for waterproofing.

The use of vapor barrier material depends on the presence of insulation in the roofing pie:

Glassine and vapor barrier membranes with a vapor permeability not exceeding 100 mg/m² per day are laid on the inside of cold roofs. Both types can be used as the bottom layer of insulated flooring in unheated attics.
Polyethylene and polymer single-layer membranes are used as inexpensive vapor barriers attic structures with a small construction budget.
Polymer two- and three-layer superdiffusion membranes have been used most often recently. Most of these materials are universal, used both as a vapor barrier and a water barrier.

Among two- and three-layer polymer membranes, there are products that do not differ too much from polyethylene in terms of price. Almost all two-layer films are budget types. In terms of strength properties and wear resistance, they are inferior to their three-layer counterparts, the service life of which is almost equal to the similar characteristics of the roof itself.

Insulating materials with a steam transmission capacity of more than 100 mg/m² per day are not used in the steam protection device. They are intended for laying waterproofing that protects the insulation from the outside from atmospheric water and from the wind carrying away heat from its thickness.

Criteria for selecting a vapor barrier film

In addition to the price, the size of which corresponds to the construction budget, and vapor permeability, which determines the scope of application of the material, the choice is influenced by a lot of significant criteria, these are:

Strength. High quality insulating materials cannot be damaged by dropping a tool or stepping, and cannot be torn when applying force and attaching them to the elements of the rafter frame.
Low temperature resistance. Superdiffusive species can be left for the winter as a “cover” of an unfinished building without a laid roof. It will easily withstand both frost and snow deposits. Plastic film cannot be used like this; after a week of exposure to low temperatures, it will crack and crumble.
Resistance to water pressure. During the construction of the roofing pie, it may rain before the roof is laid. When using a membrane, there is no fear that atmospheric water will penetrate into the room and delay further stages of work. If the device is planned for the spring or autumn, it is better to prefer polymer roll material.
UV resistance. Polymer varieties can be safely used as temporary roofing. Unlike polyethylene and glassine, these materials will not lose their original properties under direct sunlight. This characteristic is important if the roof installation will be carried out in the summer.
Fastening. Before making a purchase, be sure to familiarize yourself in detail with the specifics of fixing the material. There is a vapor barrier, the fastening of which is carried out only with the help of nails with a wide head or only with the help of wooden slats. There are options that are simply attached with a stapler.

All details about installation, the formation of overlaps, the need to connect the panels with double- or single-sided tape must be carefully clarified before purchasing. This information is needed for correct calculations of material footage, as well as the consumption of fastening and connecting means. When using vapor barrier membranes in cold structures, for example, gluing them into a single sheet is not required, because The overlap is quite enough.

Some insulating materials do not necessarily require the individual strips to be joined together by gluing. If you need to glue it, then before you buy and lay a vapor barrier on the roof, you should find out whether adhesive tape from the same company as the protective film is available for sale. The use of consumables similar in purpose, but made differently, may not provide the required gluing effect, because it may differ in chemical composition.

Rules for installing a vapor barrier layer

Depending on the quality of the film, it can be laid before installing the roofing pie or after performing the specified work. Naturally, the choice of the optimal time for installation depends not only on the preferences of the roofers, but also on the ability of the material to resist weather influences, as well as on its strength properties.

The main rule that should be remembered and strictly followed by those who are going to lay a vapor barrier on the roof with their own hands is: the roll must be rolled out the way it was wound by the manufacturer. It is necessary to strictly follow all installation instructions and follow the directions indicated on the material.

There is no need to rewind the roll, trying to turn over the side whose function the manufacturer has included direct contact with steam. If the film is laid on the opposite side, it will not retain evaporation and will allow more water into the insulation than is allowed according to the technical parameters of the thermal insulation.

The second mandatory postulate of installing a vapor barrier is that the film cannot be attached “with tension.” The material should be fixed so that it sag slightly between adjacent rafters. The recommended sag amount is approximately 2 cm. A system made of wood will always “play” slightly: swell and expand during the rainy season, shrink and contract in hot weather. To prevent the vapor barrier from breaking through when the wood moves, this reserve is created.

Most manufacturers of vapor barrier materials allow both horizontal and vertical spreading patterns. But you should not unconditionally rely on the opinion of the majority; you must carefully study the instructions attached to the material, which must indicate possible options layouts and nuances of their application.

Usually on the vapor barrier film along the edge there is also a distance for overlap. The instructions for use indicate the width of the overlap depending on the steepness of the roof being installed.

In addition to the width of the overlap, the slope of the slopes also affects the direction of the stripes. On flat structures, roll insulation is most often rolled out perpendicular to the rafters. To attach steep structures to frame systems, membranes are often spread along the rafters. A longitudinal arrangement is preferable, especially if it is possible to cover the slope with one sheet without forming transverse seams - the most common cause of leaks.

According to roofers with extensive experience in arranging roofs, vapor flows move upward and sideways. This direction must be taken into account when arranging the film panels. When the strips are located across the rafters, laying the vapor barrier begins from the ridge and moves towards the edge of the slopes.

To prevent condensation, when it is likely to form, from flowing into the roofing pie of the attic roof and from soaking the insulation, the vapor barrier strips are glued together with tape. The material is laid so that each lower strip overlaps the already secured upper strip by the amount of overlap specified by the manufacturer. This is the main difference between the installation technology and the waterproofing device, the upper strips of which overlap the underlying ones.

When using slats to fix a vapor barrier layer, they must first be antiseptic, because the wood will have to come into contact with the material of other heating equipment, which is fraught with the formation of condensation. Note that attaching the film using a block has a significant advantage - it can simultaneously serve as the basis for installing the inner lining, as well as for forming ventilation ducts.

Video about the specifics of roof vapor barrier installation

A step-by-step description of laying a vapor barrier film will help you understand the essence of the process:

Common mistakes made by self-builders:

Video explaining the principle of operation of a vapor barrier membrane:

Compliance with the technological rules for installing a vapor barrier layer guarantees a long service life of the roof, ensures the thermal properties specified by the design, and eliminates the likelihood of leaks and the need for unplanned repairs.

An important element in the roofing pie is the vapor barrier of the roof. In short, a layer of vapor barrier material protects the insulation from oversaturation with moisture and, as a result, loss of its thermal insulation properties. To avoid this situation, it is necessary to perform both hydro and vapor barrier of the roof.

Well, if it’s completely to the point, then the answer is already clear from the subtitle. Installing a vapor barrier on the roof protects or insulates the insulation from vapor.

It's that simple. But where does the steam come from? There is such a thing as moisture transfer. The room inside becomes damp for several reasons:

Cooking food;
Human breath;
Taking a shower;

It's no secret that warm air tends to rise. In addition, its ability to transfer moisture (steam) is much higher than that of cold water. This means that it also carries moisture with it. What obstacles does this couple encounter on its way? It can be:

Concrete and wooden floors;
Internal ceiling and roof lining.

However, some of the steam still reaches the very top of the roof - the place where the roofing pie is located. And if there were no vapor barrier for the roof, all this steam would directly get into the insulation.

Considering that foam plastic (penoplex) is not insulated inside, insulation means mineral wool, which is used most often.

For example, here is a statement that can be found on the official website of the TechnoNikol company, a large manufacturer of stone wool:

“Rock wool should not be directly soaked, as it loses its properties once wet.”

Total: why do you need a vapor barrier? We found out that the inside of the insulation needs to be covered with vapor film to prevent steam from getting into it. The roof must first be insulated, and only then covered with film from the inside.

Protective membrane on the outside

A waterproofing coating is used under the main roof covering (for example, for a metal tile roof). Since from the outside the insulation will be affected not only by steam, but also by water in two other states, for example in the form of rain, waterproofing is needed there. Using a vapor barrier membrane like Izospan B for outdoor use would be a big mistake.

By the way, the video below tells you very interestingly and scientifically about whether a vapor barrier is needed.

What to use

As with many things, there are different materials used to accomplish the same task. Roof insulation is no exception.

Polyethylene films

To install a vapor barrier on a roof, high strength of the material is sometimes necessary, for example, if we are talking about insulating the attic floor. To increase the strength of polyethylene, they began to reinforce it. There are two types of such films:

Perforated;
Non-perforated.

Separately, it is worth mentioning the films on one side, covered with aluminum foil. Their ability to resist steam is much higher than that required for ordinary premises. Most often, such films are used for saunas and baths, so there is no point in choosing them for the roof.

However, there are films that have two significant advantages over polyethylene films.

Polypropylene films

The notorious advantages of such films are:

Higher strength;
Resistant to ultraviolet rays.

For example, such films can protect exposed rafters from rain and snow throughout the year.

There is a particularly attractive type of film made from this material. Films with antioxidant coating. On one side, such films are covered with a layer of viscose fiber with cellulose. This coating is capable of absorbing moisture (condensed steam) and storing it for a certain time. After the cause of condensation disappears, the layer dries quickly, preventing moisture from penetrating into the thermal insulation. It is important to install this film correctly. The antioxidant layer should face down from the insulation.

The most commonly purchased films are the following brands:

TechnoNIKOL,
Izospan;
Klober;
Tyvek;
Juta;
Nikofol;
Everlasting.

Did you know?

Glassine was previously used to insulate the roof. Now this material is practically not used. There are much more advanced and relatively inexpensive materials. Also previously used were roofing felt, roofing felt, or ordinary polyethylene film.

Which vapor barrier to choose for the roof? As we have seen, this mainly depends on two factors:

Places where insulating material is used;
Owner's financial capabilities.

Having noticed possible types vapor barrier, you can more clearly understand which vapor barrier is better for the roof. We settled on polypropylene films with an antioxidant coating.

Principles of vapor barrier installation

Installing a roof vapor barrier is not a complicated process in itself, however, there are some nuances here too. So, we can highlight the following:

You need to lay a vapor barrier on top of the thermal insulation. Both horizontal and vertical film laying is possible. You need to lay the film horizontally (transversely to the rafters) starting from the top row and moving down. It is definitely important to make an overlap of 10, and preferably 15 centimeters. The films are nailed to the sheathing with a construction stapler. To fix joints, two types of tapes are used: double-sided and single-sided. Double sided tape stick to the inner strip of film and cover with the next one. Single-sided tape is used to secure the seams from the outside and is glued directly at the joint.
If you need to lay the insulation vertically, make sure that the joint is on the sheathing, otherwise the film may tear, even if it is glued with tape. (Besides, it is very uncomfortable when weighed).
In places where the film adjoins the windows (if the roof is attic), use a special apron. If such an element is not included with the film, apply special tape to the joint.
An additional beam is attached on top of the laid insulation as a sheathing. This is necessary so that the vapor barrier for the roof and the internal cladding have a ventilation gap between them and air circulation is possible. The minimum thickness of the timber is 25 mm, preferably 50 mm.
Avoid sagging foam. Mount it tensioned.

What is neglected

As already mentioned, installing a vapor barrier on a roof is not a difficult task, but here there are several common flaws. For example, good, expensive European films are purchased, and, say, connecting tapes are ordered from China. Doing this is extremely wrong. Or the material is not used at all for its intended purpose. For example, Izospan V is used as waterproofing.

Also, puncture sites with self-tapping screws should always be fixed with aluminum-coated tape. Unfortunately, you can often find torn insulation on the roof. Holes greatly reduce protection and steam quickly penetrates the mineral wool, forming frost and damaging the heat-saving layer.

Cost calculation

How much will it cost to create a vapor barrier for a roof? The price depends on the density (measured in grams per square meter) and the brand of the manufacturer. Rolls come in widths from 1 to 3 meters (rolls wider are rare).

For example, a Tyvek Airguard SD5 vapor barrier membrane, a roll 1.5 m wide and 50 m long, costs 9.5 thousand rubles. ($164). This means that 1 square meter of such insulation will cost 126 rubles or $2.17.

A roll of Izovek V Eco costs only 540 rubles or 9.3 dollars. (Size 1.6 by 44 m). Thus, 1 square meter of vapor barrier will cost 7.67 rubles or $0.13. In our example, the last option will be 17 times cheaper.

Izospan RS of approximately the same size will cost about 1,800 rubles ($30).

Don't forget to include joining strips, tape, and stacked staples in your calculations. When ordering a complex roof, laying a vapor barrier (the work itself) will cost 40-80 rubles per square meter.

Roof vapor barrier is the most expensive, but important element of the roofing pie. Vapor and waterproofing reliably protects rafter system from rotting, and the insulation performs its functions.

Real mistakes on real objects 3 videos

See how an incorrectly installed layer of insulation can damage the sheathing.