Modern roofing materials are an almost absolute guarantee that moisture will not penetrate into the roof, regardless of external conditions. However, from inside the premises, the roofing pie is not protected from this in any way. First of all, the thermal insulation material, which loses its performance characteristics when wet, is at risk. As a result, the house becomes cold and damp. A properly installed vapor barrier will help prevent this process.
The need for vapor barrier
The warm air in the room is saturated with vapor and rises, trying to escape through any openings. But since the air temperature and humidity in the under-roof space are much lower, condensation forms, which can be localized on the insulation, which can lead to its destruction.
Vapor barrier material protects insulation from the destructive effects of moisture
A more severe situation is observed in the cold season. The steam escaping into the under-roof space stops, but first turns into frost, after which it forms an ice crust that will freeze absolutely any insulation in a short period of time.
To preserve the insulation, a vapor barrier is needed
With the onset of spring, the ice in all pores begins to melt and erode the interior finish. This becomes the reason that the insulation ceases to perform its functions, and mineral wool will become unusable after just a year of such use, while polystyrene foam will last a little longer.
Without a vapor barrier, the insulation will last much less
That is why a vapor barrier layer is required. Its main task is to prevent condensation from reaching the insulation. This will warn:
- the appearance of mold;
- heat leakage from the premises of a private house;
- rotting of all wooden structures.
Materials used
There is a wide variety of modern building materials that have vapor barrier properties. Conventionally, they are divided into three groups:
- Polyethylene film. This type of material is universal because it can perform several functions at once. The film is covered with a special reinforced fabric. There are two types of this vapor barrier material: with and without perforation. But the holes are so small that they cannot be seen with the naked eye. For installation, it is necessary to use seals and connecting tapes, since the film is produced in rolls. The strips must be attached as tightly as possible, otherwise the functionality of the layer will be impaired. There are also polyethylene films with a foil layer that retains heat indoors.
Vapor barrier polyethylene film reinforced with fabric
- Polypropylene film. Used as a hydro- and vapor barrier material. On one side, the film is covered with an anti-condensation layer consisting of viscose-cellulose fiber. The principle of operation of this material is quite simple: condensate protruding from the side of the film that faces the insulation is absorbed into it and therefore does not get on the insulation. Since the installation of the roof implies the presence of a ventilation gap, the moisture absorbed into the vapor barrier dries out.
Polypropylene film has a smooth and rough side
- "Breathable" film. The most modern vapor barrier material. Combines vapor and water resistance properties. The main advantage is that there is no need to create a ventilation gap, and this allows you to significantly save under-roof space. This membrane allows moisture to pass through itself, which subsequently settles on the rough layer of material, after which it is absorbed into it and dries. This allows the insulation to remain dry. There are different types of vapor barrier membranes available, which can be single- or double-sided.
Single-sided membranes conduct steam in only one direction; double-sided membranes can be laid on either side
For vapor barrier, it is better to use non-perforated film, since perforated film is more suitable for waterproofing.
A very important stage in arranging a roof vapor barrier can be considered not only the process of its installation, but also the choice. The quality of the roofing as a whole, as well as its service life, depends on this. When choosing, remember that the more weight the material has, the stronger it is. Typically it ranges from 60 to 270 g/m2. As for the vapor permeability parameter, you need to choose a material with a minimum value. The recommended parameter is less than 1 g/m2 per day.
How to properly install roof vapor barrier
Before installation, it is recommended to once again make sure that you have purchased exactly the vapor barrier material. You should also make sure that the vapor barrier you purchase is compatible with your roofing material. In this case, “Izospan B” is universal, which can be used regardless of the type of roofing pie.
Which side to put the vapor barrier on the roof
There are certain rules for laying vapor barrier material. Regardless of the type, the film has two surfaces: one smooth, the other rough. You need to lay it with the smooth side on top of the insulation. At the same time, carefully ensure that the material fits as tightly as possible; gaps are not allowed.
The smooth surface of the vapor barrier must be in contact with the insulation
When laying a vapor barrier membrane, it is necessary to provide a ventilation gap between the vapor barrier and the decorative roof sheathing. It should be at least 5 cm, and the type of roofing material in this case does not matter. A counter-lattice, which is mounted directly on the membrane, can provide this ventilation gap.
How to attach a vapor barrier to rafters
The material must be attached to the rafters from the inside of the insulation. For fastening, you can use different parts, for example, a construction stapler or galvanized nails. Try to minimize the number of punctures in the material, as this may cause condensation to penetrate through these holes during the operation of the roof.
You can use a stapler or nails to attach the vapor barrier.
The option of attaching a vapor barrier material to the rough lining of the attic is also allowed.
The material can be laid in horizontal or vertical strips, rolling out the entire coating without breaks. Additionally, it is necessary to process the joints, both vertical and horizontal. To do this, you need to lay the vapor barrier overlapping, the size of the overlap should be at least 15 cm. Next, seal the joints with a special tape, but you can only choose one that is designed to work with vapor barrier film.
All joints must be sealed with wide tape
It is also necessary to seal the joints of the material with a wooden or concrete base, even if a stapler or nails were used for fastening.
The vapor barrier film must be laid without sagging, it must be well stretched.
Video: rules for installing vapor barrier
Installation errors
Despite the fact that the process of installing a vapor barrier film is quite simple, sometimes mistakes cannot be avoided, but they are typical and can be prevented:
- loose connection of the film to the purlins, valley and ridge beams, especially for complex roof structures;
- the use of a narrow connecting tape, because of this, the sealing of the seam may be broken during the operation of the roof;
- lack of deformation reserve when installing a roof with windows;
- lack of internal protection of a vapor barrier film around the roof windows, due to which ultraviolet rays gain open access to this material and destroy it;
- the film bends around the rafter legs, which creates a gap through which moisture can pass and be absorbed into the insulation.
Video: consequences of improper vapor barrier
Steam is a substance that is quite difficult to block, so vapor barrier of the roof of a private house is a responsible mission. The safety of the roofing pie and wooden structures and the long service life of the roof can only be guaranteed by properly installing vapor-proof material.
Thermal insulation will only be effective if this layer remains dry. This can provide a hydro- and vapor barrier layer. As a result, the microclimate in the house will always be favorable.
Vapor barrier is most widespread in, since walls made of this material are most susceptible to the destructive effects of moisture.
Currently, you can find various vapor barrier materials. The choice is huge, and in order to decide and purchase the right material, it is worth familiarizing yourself with their main types.
Which side should I lay it on?
To prevent the formation of condensation, a vapor barrier is used, which is laid under the casing. Laying is carried out from the inside, on the side that faces the living space.
The vapor barrier film is fixed to the wall using lathing. Thus, an air gap is created between the inner cladding panel and the thermal insulation layer.
At the same time, the joints between the individual film sheets must be absolutely airtight. This is ensured by using adhesive tape, which is glued to the joints.
In order to avoid condensation collecting on the film, one of its sides is made rough. It is this rough side that should be turned toward the inside of the room when installing.
Many novice craftsmen do not understand which side the vapor barrier film is laid on. It has two sides, front and back. Most often they are the same, but if an anti-condensation film is used, its fabric side should be towards the room.
If used, then its foil side should be facing the heated room. If you purchase a membrane film, you can determine the outer side by color; it is brighter and more saturated.
Scope of application and operating principle
Thermal insulation, due to the fact that this layer is exposed to moisture, becomes useless and loses its properties.
Mineral wool insulation is exposed to negative factors both inside and outside the house. To protect your home from the cold, you need to create a high-quality vapor barrier layer.
Vapor barrier is designed to protect the structure from the negative effects of weathering, precipitation, internal vapors and wind, and dampness.
There are certain standards according to which insulation should be protected.
To do this, a vapor barrier material is placed between the thermal insulation layer from the inside of the house and the interior decoration. The work is carried out according to the instructions, since each vapor barrier material has its own characteristics.
There are two main types of materials - films and membranes:
- Reinforced films. Used to decorate the attic, gaps must be created for ventilation, since they do not allow steam to pass through.
- Films with microscopic holes, are used to create a vapor barrier in unheated attics. They retain moisture well.
- Anti-condensation film has an additional fleecy layer that allows you to retain water.
- Membrane insulation with one or several layers - the material is durable and resistant to various influences.
- Foil vapor barrier– has a metallized side, which should face the room.
The most commonly used material is polyethylene, which has become widespread. But you need to work with it extremely carefully to prevent excessive tension and damage.
Membrane films have an unusual ability to allow air to pass through, while at the same time providing excellent protection from moisture. This is a new material that has a specific structure. It ensures the dryness of the heat insulator for a long time. However, many membrane materials do not require the creation of an air gap.
What is the difference between vapor barrier and waterproofing?
It is worth understanding the difference between these two types of insulation. The main difference is that the vapor permeability is significantly different.
Waterproofing materials are responsible for keeping the interior warm while preventing moisture from entering. They protect surfaces from direct contact with water.
For example, when creating waterproofing, it allows water to be drained outside the construction site. In this regard, waterproofing is installed using a special technology.
Vapor barriers face a completely different task - protecting the thermal insulation layer from moisture and vapors entering it, which can destroy it. Steam is generated in most cases from the inside, which explains the laying of the material from the inside. For example, from the attic side or under the decorative decoration of the sauna room.
Waterproofing materials do not allow water and moisture to pass through, while they can easily allow steam to pass through. Vapor barrier prevents this.
Types of vapor barrier
Insulation of floors
The floor and ceiling are essentially frame structures. Therefore, their vapor barrier is mandatory. The vapor barrier film is laid under the main floor covering and above the ceiling sheathing, thereby creating an air gap.
Pauls
Performed in rooms located on the ground floor of the house, if there are basements below or, in baths and saunas. Laying the material from the inside is done after creating the waterproofing and heat-insulating layers. The material is secured with double-sided tape or using construction staples, the canvases are laid overlapping.
Roofs
Here it is better to use a double-sided diffuse membrane, installation of which is carried out on the inside and outside of the roof. They are fixed to the thermal insulation layer without leaving gaps. If roll hydrovapor barrier is used, the edges when creating an overlap are also sealed with tape.
A vapor barrier must be created in any case if tiles or metal profiles are used as roofing material.
Stan
There are internal and external. The material is secured around the perimeter using a stapler, the joining is made with an overlap of approximately 10-15 centimeters, and the joint itself is glued with tape. On top it is necessary to hammer wooden slats, which represent a lathing for thermal insulation.
The frame for thermal insulation can be made of metal profiles or wooden slats; a vapor barrier is created, which is attached to the wall using self-tapping screws.
Which side of the heat insulator should I mount it on?
- The vapor barrier is usually installed on the inside of the thermal insulation. But most often, a double-sided composition is created, which makes it possible to provide a reliable barrier between the outside of the building and the room.
- When insulating a façade, the film is placed on the outside of the heat insulator. When, the film is fixed on top of the mineral wool, as in. When creating a cold roof, a vapor barrier is placed under the rafters.
- When insulating the top covering, when an attic space is created, the barrier is laid underneath the thermal insulation material. When insulating walls internally, the film is fixed on top of the heat insulator, inside the heated room.
- Surfaces must be properly prepared before vapor barrier.
- If work is carried out in the cold season, the mastic is diluted with antifreeze.
- The ventilation gap width is at least 6 centimeters, which provides protection against condensation. The wall cladding should not come into contact with the film.
- When insulating the roof, the creation of a gap is ensured by sheathing, which is mounted from racks or horizontal profiles.
- The joints of the vapor barrier sheets must be glued. This is done using self-adhesive tapes. Scotch tape, especially narrow tape, is not recommended for this work.
- Installation can be done using a stapler or nails with a wide head. But experienced builders recommend using counterbattens for these purposes.
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 the “roofing cake”, 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 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.
Useful 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. It is characterized by a more complex structure than conventional 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.
Useful 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 may be a consequence of small footage. Only comparing the price per 1 m² of different types of vapor barrier will help you make the right choice.
Useful 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 cake” 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 roll materials of 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.
Useful 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.
Useful 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 polyethylene product around the roof windows is not closed from the inside, as a result of which after some time it is destroyed by 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.
Useful 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 moved 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 required.
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.
Useful 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 into 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.
Useful 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 a high level of 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. By carefully studying how to properly install a vapor barrier, fulfilling all technical requirements, you can create a healthy microclimate in the premises and ensure the building as a whole will last for many years 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.
Each of us is trying to arrange our own home so that our family lives in complete comfort and does not need anything. To do this, you will need not only to correctly design the structure of the building, but also to take care of all sorts of nuances that affect the warmth and comfort in the house. These indicators primarily depend on the installation technology of the roofing system - it must be installed according to all the rules. To achieve the desired result, you will need instructions for installing a vapor barrier in the roof.
As you know, sealing walls and roofs is designed to provide protection against moisture penetration into the room. But it is necessary to take into account the formation of steam inside the building, which destroys the structure of the building materials used in the construction of the house. Especially to prevent the destructive effects of steam, maintain normal temperature and conserve heat energy inside the room, it is necessary to take care of the vapor barrier of the roof.
The need to use vapor insulation
Ever since the school curriculum, everyone knows that steam inside a room mixes with heated air and collects in its upper part. This happens because vapor deposits evaporate into the upper layers of the atmosphere, but since this is prevented by the roof of the building, they are absorbed into the thermal insulation material and begin their destructive effect.
The vapor barrier of the roof protects against moisture penetration into the room.
During the cold season, such a sharp drop in temperature outside will hold back steam in the layers of insulation. As a result, frost will begin to form from it, which will subsequently turn into ice. The thermal insulation layer will completely freeze and remain there until the onset of spring. As soon as the ice thaws, the insulation will lose its protective characteristics and become unusable. Thermal insulation based on mineral wool will deteriorate in 1 such cycle, while foam insulation can last a longer period.
In order to prevent such an outcome, it is necessary to install a vapor barrier material under the roof. It will be able to protect the thermal insulation layer from the penetration of moisture formed from steam. Thus, vapor insulation will protect the insulation layer from the appearance of fungal growth, the transmission of heat energy and the destruction of wood building materials.
The vapor barrier layer is used in any roofing structure (attic, straight, single-pitched and gable).
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Materials used as vapor barriers
In the past, the most common moisture barrier material was glassine. In order to reduce the cost of roofing, it is used even today. But this type of material does not meet modern vapor insulation standards because it has a relatively small safety margin.
Today, the most popular type of vapor barrier is polyethylene film with several layers and a special structure. The film is highly resistant to sudden temperature changes and moisture does not penetrate through it. Ordinary polyethylene allows only 15-25 g/m2 of steam to pass through during the day. The vapor barrier film holds back steam tens of times better. Its vapor permeability indicator is 0.4 g/m2.
Vapor barrier film is sold in roll form, so it is easy to work with when insulating the roof.
Polyethylene film has an elastic structure, so it is resistant to tearing. It is quite easy to work with and installation does not cause any inconvenience. If you fasten the film with self-tapping screws, it will not only not tear, but will also be installed hermetically. High-strength polyethylene is not damaged when in contact with other building materials due to its elasticity. It will be able to withstand even a massive heat-insulating layer laid on it.
Film vapor insulation is divided into 2 types:
- polyethylene;
- polypropylene.
The 1st type has a slightly smaller margin of safety, so polyethylene is equipped with a special reinforcing material, which can be either perforated or non-perforated. For the roofing system, non-perforated protection must be used, since perforated protection is usually used for waterproofing materials.
Vapor barrier film is sold in roll form, so it is quite easy to handle during the roofing process.
In addition to the simplest reinforced polyethylene films, the modern market offers material covered with aluminum foil on one side. This type of vapor insulation is capable of retaining a large amount of vapor deposits, so it has found its application in the arrangement of premises where high temperatures are considered the norm (baths, boiler rooms, indoor swimming pools).
The 2nd type consists of woven fabric, which is covered with thin-layer polypropylene. This vapor barrier is considered highly durable and resistant to ultraviolet rays. Some varieties of polypropylene contain in their structure a special antioxidant material that prevents condensation. It operates on the principle of a sponge, which absorbs all available liquid and then dries very quickly under the influence of air exchange. The antioxidant material is contained on only one side of the polypropylene. During the installation process, this layer is laid facing the roof.
Roof vapor barrier requires the use of high-quality material, since it is located at the very base of the roof structure. In other words, it is extremely difficult to replace or restore it after installation.
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Materials and tools used for installing vapor barriers
To lay the vapor barrier layer you will need the following materials, tools and accessories:
- polyethylene or polypropylene film;
- construction tape or adhesive tape;
- mushroom dowels or metal staples;
- wooden blocks treated with an antiseptic;
- a set of tools (hammer, scissors, pliers).
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Do-it-yourself vapor barrier installation
The vapor barrier material is secured using construction tape.
When familiarizing yourself in detail with the methods of laying a vapor barrier layer, you must remember that installation work is carried out from the inside of the room. In this case, the vapor barrier layer needs to be installed only after the thermal insulation has been placed. The material can be mounted both horizontally and vertically, regardless of its type.
In the first case, placement must begin from the highest point of the roof. All strips must be overlapped with an overlap of at least 8 cm. The joints are carefully secured to each other using construction tape, which can be one-sided (glued from the outside) or double-sided (glued from the inside).
If the panels are placed parallel to the support beams, the overlap should be carried out directly on the wooden beams. This is relevant in cases where there is no rough filing of thermal insulation.
The vapor barrier must be attached to the structural wooden parts of the roof using metal brackets or special mushroom dowels.
Make sure all seams are securely joined and secured. It is recommended to fix the glued parts using clamping strips. The use of this method is especially relevant for roofs that have a slope of 30°, as well as with a thin layer of thermal insulation.
The areas where roof openings, frames and other passages are located must be insulated with a vapor-retaining apron, which is included in the standard kit of most materials. If the apron is not included in the vapor barrier kit, the circumference of the openings is covered with double-sided butyl tape.
In those parts where pipes for ventilation pass through the roofing system, the polyethylene material must be lowered downwards, the air exchange pipe must be wrapped and securely secured with construction tape.
Upon completion of the placement of the vapor barrier material, you need to secure the wooden blocks, which are pre-treated with an antiseptic, at intervals of 50 cm. This will help prevent contact between the ceiling cladding and the plastic film. In addition to the fact that the bars form an air space between the outer side of the ceiling and the film, they also help to reliably strengthen the layer of thermal insulation.
Free space can be used to accommodate electrical wiring and structural elements of lighting devices. If the ceiling cladding has a plasterboard base, it is more advisable to use galvanized fasteners. It must be taken into account that the polyethylene material is attached very tightly, that is, the canvas must fit snugly to the surface.
An innovative way to protect your home from moisture is a vapor barrier for the roof. Special materials laid under the roofing improve the quality of heat retention in the house and prevent the influence of internal moisture on the structure.
Lack of vapor barrier - consequences
Laying a vapor barrier on the roof prevents the destruction of the thermal insulation layer and the roof structure. The steam that arises from cooking, cleaning, bathing and other household chores rises under the roof. When exposed to low temperatures, condensation forms, which, without a vapor barrier layer, penetrates the fibers of the warm material and violates its integrity.
As a result of constant wetting, wooden floors begin to rot, and major repairs may soon be needed. To extend the life of your roof, do not neglect preventive maintenance. 
Is there a difference between vapor barrier and waterproofing?
When creating roof waterproofing protection, it is important to take into account its difference from waterproofing. The main point is the vapor permeability of the materials used:
- Waterproofing is installed in places where moisture drips, and condensation along the envelope edges drains from the roof.
- Elimination of steam formation is necessary to block steam from entering the inner layers of insulation.
- Waterproofing is placed under the main coating material, and vapor barrier is placed on the attic side.
Waterproofing layers protect against the spread of water, but do not prevent the effects of steam, so it is important to choose the right material to eliminate evaporation. 
Selection of vapor barrier material
The simplest option is roofing felt, but its flooring requires a significant amount of time. Progressive owners of private houses give preference to high-quality building materials. Which vapor barrier to choose from the modern materials existing on the market? Each of them has a number of advantages and disadvantages, so it is advisable to pay attention to the technical characteristics.
Polyethylene vapor barrier
Polyethylene film serves as a membrane that prevents moisture from penetrating into the insulation. Due to its ability to block moisture, it is used as waterproofing.
To prevent the appearance of fumes, the perforated film is laid in 2 layers - on top (moisture does not enter from the outside) and below (steam generated in the house does not penetrate) of the insulation. When planning which side to lay the vapor barrier on, take into account the texture of the material. The smooth side is attached to the insulation, and the rough side is visible from the outside.
An incorrectly fixed layer will accumulate condensation without releasing steam to the top. To avoid leaking or rotting of the new roof, follow the installation techniques:
- laying the film starts from the top, always with an overlap of 10 cm;
- the joints are fixed with stationery tape;
- The film is attached to the rafters using construction staples.
When purchasing a polyethylene vapor barrier material, pay attention to its quality - a cheap one will quickly become unusable and will not provide adequate protection. 
Polypropylene vapor barriers
Vapor barriers made of polypropylene are an economical product with smooth and rough sides. You need to lay the vapor barrier according to the previous technique - with the smooth side facing the thermal insulation surface. A self-installed polypropylene layer requires compliance with the work algorithm:
- installation occurs with an overlap of 10 cm.
- the barrier must be carefully secured to the rafters. Use an adhesive based on synthetic rubber, a mixture of polyurethane and acrylic. Scotch tape is not able to support the weight of the material.
- The gluing areas are reinforced with pressure beams.
After laying propylene, be sure to apply an antioxidant compound to the surface - this will prevent the formation of condensation. 
Penofol vapor barrier
The material consists of two layers - polyethylene foam and a thin aluminum part glued to the base. The foil layer is fixed with a reflective surface indoors. The laid penofol also copes with the task of thermal insulation, because... capable of reflecting infrared rays.
When carrying out construction tasks, use the following techniques:
- The insulation is attached to the rafters using a stapler or wide-headed nails.
- To ensure the tightness of the joints, adhesive tape is used.
- in places where the material adjoins the wall, a layer of sealant is applied and the film is ironed.
The optimal thickness of penofol for high-quality insulation from steam is 10 mm. 
Diffuse membranes
Perforated non-woven material with small holes is available in the form of film. Small cells allow steam to pass through and water to be retained. Laying of diffuse membranes is carried out, excluding the ventilation gap, close to the insulating layer.
Features of product installation include the following points:
- The membrane is fastened with brackets to the rafters.
- During installation, the material is slightly stretched; sagging of 1-2 cm is allowed.
- The joints are taped with special adhesive tape.
The total cost of the work will depend on the density of the film, but you cannot skimp on the quality of the vapor barrier.
Antioxidant films
The main advantage of antioxidant films is their texture. The inner surface consists of a fleecy non-woven material that absorbs moisture. The fleecy side prevents moisture from entering the insulation, and the moisture in it dries due to air movements in the gap. Installation occurs similarly to other diffuse membranes or penofol.
Owners of private houses prefer one-sided and two-sided materials. The former can conduct steam in one direction, while the latter can be placed on the insulation on either side. Give preference to multilayer membranes that accumulate evaporation and remove it gradually. 
Ways to protect the roof from fumes
Before starting construction work, identify the areas of greatest risk - the boundaries of contact between cold and heat on the roof. Depending on the complexity of the event, you need to choose an acceptable vapor barrier method.
Laying rolled vapor barrier
Penofol, diffuse membranes or polyethylene can provide high-quality blocking of evaporation. The rolls need to be rolled out and the required length measured. Then the canvas is secured horizontally with wooden slats or aluminum profiles. A ventilation gap of 4 cm should be arranged between the interior finishing and the vapor barrier layer. The strength of the fastening is controlled by the tension of the material.
Formation of a leaf system
To attach the sheet vapor barrier, a profile frame is installed. The material is inserted into the structure, fixed with self-tapping screws, and the joints are sealed with PVC or isospan. When fastening, it is important to take into account the laying features of the material. 
How to choose the right side for placing a vapor barrier?
The vapor barrier film consists of two layers. The side with a rough surface retains condensing drops and gradually evaporates them. A smooth layer is needed for a high-quality connection with the insulation and return of heat to the home, so the material should be fixed to it.
General algorithm for installing vapor barrier materials
All vapor barrier materials differ only in structure, but are installed in the same way. By following the instructions below, even a novice builder will figure out how to properly install a vapor barrier on the roof.
- Installation takes place on the inside of the roof in a horizontal or vertical manner.
- With the horizontal technique, you should roll out the canvas from above, section by section.
- The rolls are laid with an overlap of 10 cm and taped with stationery tape 10 cm wide.
- Double-sided tape is glued to the inside of the overlap on the bottom layer, then the protection is removed and the top layer is glued to the tape.
- Using a vapor barrier for wooden buildings, lay the material along the rafters, securing it with a stapler or galvanized nails.
- When working on a roof with a loose heat-insulating coating, press the vapor barrier with special strips.
- At the point where the rolls adjoin the hatch, attic windows or entrance areas, an apron is made or the window openings are taped with butyl tape.
- If there are communications, the pipes are wrapped in vapor barrier material and sealed with electrical tape.
- The vapor barrier is laid in layers - behind the roofing and behind the insulation. A gap must be maintained, which creates a ventilation effect and promotes high-quality drying of fumes.
Installation of vapor barrier should be carried out simultaneously with roofing work, since prolonged exposure of the film to the sun reduces its insulating properties. 
Common installation mistakes
How to install a vapor barrier without mistakes? Pay attention to the shortcomings that can be made in a hurry or with insufficient knowledge about the installation process:
- defects in the connection to roof elements occur without sealing the material with glue and adhesive tape. The more complex the roof structure, the more expensive the vapor barrier process.
- Narrow adhesive tape (up to 50 mm) should not be used. Work with stationery tape that is at least 10 cm wide.
- do not forget to leave a deformation reserve of material for window openings.
- If the vapor barrier material around the windows is not protected with interior decoration, it will quickly lose its properties.
- The vapor barrier film should not bend around the rafters. Moisture will enter the resulting space and cause the wood to decompose.
- The film at the junction points must be sealed tightly. Consider the characteristics of the material, because adhesive tape is not compatible with everyone. Use glue based on acrylic or polyurethane mixtures or synthetic rubber.
- loosely sealed joints between sheets lead to loss of vapor barrier properties. Carefully glue the places where the material overlaps each other.
- the use of polyurethane adhesive tapes based on butyl rubber contributes to the depressurization of vapor barriers due to their insufficient adhesive properties.
Carrying out vapor barrier work will help achieve the optimal ratio of humidity and temperature conditions in the house and increase the service life of the roofing deck. By following simple rules, you can perform a vapor barrier yourself.