How to make a roof vapor barrier. How to properly make a roof vapor barrier: technological principles of vapor barrier design. Vapor barrier for the roof: how to install it correctly using special technology
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;
- Financial capabilities of the owner.
By noticing the possible types of 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 is glued to the inner strip of film and covered 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 the 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.
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.
The standard composition of the roofing cake includes:
- Internal finishing layer;
- Lathing design;
- Counter-breach;
- (does not apply to a cold attic);
- (about);
- Ventilation shafts or gaps;
- Roofing covering.
Why do you need a roof vapor barrier? Vapor barrier layer protects the roof from the penetration of water vapor into the thermal insulation. The fact is that insulating materials for the most part have porous structure, since the air contained in them performs the function heat insulator. On contact with a colder environment, steam turns into condensate, which lingers 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 connections between cellular elements.
The main characteristic of vapor barrier material is vapor permeability, depending on the density of the material. The values of this indicator can be found in the passport of the packaged building material.
Form of release of vapor barrier films - 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 has little greater thickness, 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 may reduce the degree of vapor barrier.
Anti-condensation film
Made from 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 a vapor barrier provides an additional function heat loss protection.
Membranes (film for roof vapor barrier)
Membrane vapor barrier materials are divided into five main classes:
- Type A. 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 roof structures with a slope 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 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. Double layer material. Consists of a layer of vapor barrier film and spunbond. It is used to protect insulation from internal building vapors. Applicable 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 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:
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, installation of roof vapor barrier is carried out starting from ridge part roofs. Each subsequent stripe is superimposed on the previous layer with an overlap, the size of which should not be more than 10 cm.
CAREFULLY!
When joining elements, mandatory seam sealing, providing optimal protection against moisture ingress into the gap between them. Most often, sizing is done with single- or double-sided adhesive tape or tape. On roofs with a slope of up to 3 degrees additional fixation using wooden planks.
- The vapor barrier is attached to the wooden rafter elements using galvanized nails or a construction stapler.
- When installing films and membranes near roof hatches, you need to use a special vapor barrier apron, which is included as standard.
- At the junctions with ventilation pipes, film and membrane structures are folded down, wrapped around the pipe and tightly fixed with construction tape.
- After laying the vapor barrier layer, it is necessary to nail down 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 was damaged, then small cuts or holes can be seal with special tape for vapor barrier membranes.
Roofing pie diagram
Sealing joints with tape
Final vapor barrier option
NOTE!
A tightly stretched film is the key to a good vapor barrier.
Hydro and vapor barrier of the roof - what is the difference?
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 neglecting its structure can negate all material and physical efforts to create a high-quality roof. Therefore, you should not neglect this important element; it will significantly increase the service life of the entire building.
In contact with
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 equipped 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; 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.
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 facing 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 or moisture to pass through, while they can easily allow steam to pass through. Vapor barrier prevents this.
Types of vapor barriers
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. The material is laid from the inside 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 allows you 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. 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.
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 the 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 area, 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 for both pitched and flat roofs, 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 been used as vapor barriers. They have a wide temperature range of use 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 be held 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 truss 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 internal walls, chimneys, shafts and other elements, the nature of the surface to which the film will be attached should be taken into account. 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.
