When planning your home design, you always want it to be warm and cozy.
To do this, you should follow the instructions when carrying out construction work.
It is also necessary to pay enough attention, in particular, to the competent provision of all types of insulation.
How to choose a vapor barrier for a roof and not make a mistake? First, let's get acquainted with the types of steam insulating materials.
In residential premises there is always water vapor that circulates inside it. And according to the laws of physics, it rises with the warm air. Over time, it will penetrate into the under-roof space, where it will begin to absorb insulation.
With the onset of cold weather, all the moisture that has undergone condensation forms an ice crust. And when spring comes, all the ice melts, and the resulting moisture washes away internal filling roofing structure. This will lead to its destruction and loss of basic properties: When the insulation is slightly moistened, heat loss increases significantly.
To avoid these consequences, it is necessary which should be present in any roofing pie. Some people believe that finishing the attic with cladding, which prevents moisture from entering, eliminates Negative consequences. But it is recommended to always use a special coating that is placed between the ceiling and the insulation.
Which vapor barrier to choose for the roof?
There are the following types of vapor barriers for roofs:
- painting;
- pasting.
Painting room
Used more often for high-rise buildings, soft roofs from roofing felt, iron roofing sheets, where insulation is not used. This vapor barrier is well suited for flat roof. The main difficulty in using mixtures of this kind is preparing the surface before application. For this type of insulation, the following compositions are used: 
How:
- hot bitumen;
- bitumen-kukersol mastic;
- varnish based on chlorinated rubber or polyvinyl chloride.
Pasting (membrane)
This type more popular, especially in individual construction . Materials for this type of insulation are produced in rolls and this provides some advantages:
- simplification of installation;
- ensuring a tight connection when overlapping;
- reduction in the number of seams.
NOTE!
The adhesive insulation is laid in one layer, if the room humidity is below 75%, otherwise add one more extra.
Types of adhesive vapor barrier materials
- Waterproofing. Prevents steam from penetrating into the insulation. Have special perforation, which allows steam to penetrate outside. It is mounted with some clearance from the roof covering, which promotes air circulation between the outer and under-roof space. Has unidirectional vapor permeability, keeps the insulation dry. You can talk about waterproofing materials.
- Anti-condensation. Equipped with special fleecy layer, which is located on their inner surface. It retains moisture and prevents contact with thermal insulation. Moisture quickly disappears due to air circulation in the gap. This type of insulation must be laid with an adsorbent layer to the inside of the room. Attached using a counter-lattice.
- Vapor tight. They provide impenetrable protection to the inside of the roof insulation. Sometimes they have a layer aluminum foil, which is capable of reflecting part of the radiant energy back inside. It is laid with a ventilation gap to the insulation. Provides good protection from moisture, while maintaining heat.
- Membranes. They are modern vapor barrier materials that can prevent moisture from escaping, while allowing air to pass through. When using membranes, providing an air gap is often not necessary. This material for roof vapor barrier has gained great popularity these days.
Do you need a vapor barrier for a cold roof?
The special design of such roofs does not require laying two layers: thermal insulation and vapor barrier. This saves money and construction resources. Water vapor that passes through the film ends up between the waterproofing and the corrugated sheet, from where it is removed by an air flow.
Therefore, the main task when installing cold roof is ensuring good ventilation, which is ensured by creating a gap using a counter-lattice.
Cold roof installation
Do you need a vapor barrier under the corrugated roof of a cold roof? No, it’s not necessary, the main thing is to take care of good ventilation.
Vapor barrier for attic roof
The most commonly used materials are glassine, roofing felt and foil insulation. Modern membranes are also quite effective, which have proven themselves in this sector and are excellent for vapor barriers of soft roofs.
First of all, it is necessary to carry out sealing and insulation various elements designs. The vapor barrier is laid on and secured using a method that matches the surface material. About insulation mansard roof can be read.
Fastening to concrete, brick and metal surfaces performed using double-sided adhesive tape, laid with a 10 cm overlap. And it is attached to the tree with nails or staples.
CAREFULLY!
The vapor barrier film must be installed without sagging, with slight interference.
The foil film is installed with a reflective layer inside the room so that thermal energy remained inside the building. A gap is provided between the thermal insulation and vapor barrier parts for ventilation, as well as to create a warm air barrier.
Detailed diagram of the device roofing pie mansard roof
The joints of the film are glued with tape made of a material with a similar coefficient thermal expansion. It is better to press the junctions of the foil to the wall with strips with sealant applied under them.
Vapor barrier under corrugated sheets or metal tiles
Metal tiles are a thermally conductive coating, so with the onset of cold weather, condensation causes irreparable damage to them. To solve this problem, it is necessary to provide the roof with proper vapor barrier and. Before choosing, you should decide what is more important: price or efficiency? Let's look at which vapor barrier is better for metal roofing:
Cheap option - glassine and polyethylene
Glassine can last a long time, while it has sufficient flexibility and low cost. However, a large mass bad smell when heated and difficulties during installation make it not the most the best option.
Polyethylene retains steam well and protects the thermal insulation layer from moisture. It is cheap, but polyethylene is very easy to damage. It is difficult to install it yourself. Due to its significant mass, it is difficult to install the film to the corrugated sheet using the standard method. Therefore, installation occurs to the inside of the cladding using a stapler. The film is mounted in two layers.
Reinforced film, foil, membranes
In terms of price, it is also an acceptable option. Reinforced film consists of several layers with a reinforcing fabric mesh that adds strength. Light weight and rigidity allow you to install such insulation yourself. Attached with self-adhesive tapes. A significant drawback is the lack of an anti-condensation layer, which can negatively affect the insulation.
Diagram of a metal tile roof
Which vapor barrier to choose for a roof under metal tiles? One of the best options is foil. It has low thermal permeability, which allows you to retain heat in the room, is lightweight and has sufficient strength. The big disadvantage of this material is its tendency to corrosion.
Useful video
We invite you to watch a video about the properties of vapor barriers:
Conclusion
The penetrating ability of steam is sometimes underestimated, which leads to rapid failure of thermal insulation. Therefore, it is necessary to take a responsible approach to the issue of vapor barrier and take into account all the nuances when choosing materials and carrying out work. This will ensure a long service life for the future building.
In contact with
Roof construction is an important stage of construction work that needs to be given Special attention. As soon as it comes to it, the following questions immediately arise: what kind of roof to make, what is its design, what to use as a flooring, insulate it or make it cold? You decide these questions yourself. We would like to draw your attention to the fact that there are plenty of materials for roof cladding. They all have their pros and cons. One of these popular materials is corrugated sheeting. It has many advantages, which is why it is so valued by builders. What can we say about vapor barrier? Is it necessary if you use corrugated sheeting? What materials are best suited for this purpose?
Let's look at the answers to these and other questions in detail.
A little about the cold roof
It is known that when installing a roof, work is carried out to insulate it. This is done to ensure that heat does not leave the building and cold does not get inside. It is especially important to do insulation when the roof is an attic. But there is another concept, the so-called “cold roof”. In this case, no insulation work is carried out; it is enough to make a sheathing and lay down the material. Using this type may be advisable if the roof does not need to be insulated. The advantage of a cold roof is its high efficiency, ease of operation and high speed of construction.
In what cases is it advisable to install a cold roof? For example, in a country house or in your own private house there is an attic that you will not use as an attic. Or, you need to block off a building that is not intended for permanent residence. In this case, it is rational to make the roof cold. At the same time, it is important to insulate the ceiling inside the building itself, and cover everything using corrugated sheeting. But the question arises: what can we say about vapor barrier, is it needed under the corrugated sheeting of a cold roof? Let's first figure out why a vapor barrier is needed in general.
She performs vital role- protects the thermal insulation material from moisture penetration. After all, warm and humid air will accumulate in the upper part and on the roof. If the vapor barrier is not performed correctly, this will lead to early roof repairs and a decrease in the life of the building. Yes and wooden structures will rot when exposed to moisture. But there is one nuance here. All this is rational when the attic or attic is insulated; as for a cold roof, everything is not so simple. Is a vapor barrier necessary in this case? After all, we learned that its main purpose is to protect the insulation layer. It is necessary, and there are reasons for that.
Although the room will be well ventilated, it will still suffer from precipitation. Corrugated sheeting cannot 100% prevent moisture from penetrating under the roof. Snowfall, heavy rain along with wind can take their toll and liquid will get inside. This is fraught with the fact that metal elements the inside will become rusty and fail. The same goes for wooden products(built, sheathing, etc.), which will rot and deform.
So, we learned that a vapor barrier under corrugated sheeting is still needed, even when installing a cold roof. But how to do this? Let's look at the main vapor barrier materials that can be used under corrugated sheeting.
Glassine as a vapor barrier
All vapor barrier materials are manufactured in the form of films. The material consists of several layers that perform their role or task. One such material is glassine. This, one might say, is a classic for both warm and cold roofs. This material has been used for decades. It is quite reliable and does its main task well. In addition, this vapor barrier will cost you the least. However, use the material for residential buildings It's better not worth it.
If there is a living space immediately under the roof, then it will suffer from the properties of glassine. The point is that when the material heats up, it doesn't quite emit pleasant aroma. It is not dangerous for life, just like vapors of roofing felt, but not really for permanent residence perfect option. Moreover, as roofing material corrugated sheeting is used, which, like all metals, will become very hot when exposed to the sun, especially in summer.
Another disadvantage of glassine is its heavy weight and narrow rolls, so installation will be quite problematic and inconvenient. To summarize, we can note all the pros and cons of the material.
Pros:
- strength;
- reliability;
- flexibility;
- durability;
- low cost.
Minuses:
- when heated, an unpleasant aroma appears;
- has a lot of weight;
- complexity of installation.
We can conclude: the material is not the best option for a living space, but it may be suitable for a dacha with uninhabited attic or baths.
Polyethylene film
Ordinary household polyethylene is also suitable for vapor barrier of a corrugated roof. It is quite famous and has been used for many years. Polyethylene is able to perfectly retain moisture and water vapor, protecting and insulating the structural elements of the roof from the inside. One of its main advantages is that it is cheap, so you will need less money to install a roof. Polyethylene is able to provide good vapor barrier, no worse than specialized films and various membranes.
But these are all advantages of this material. Cheapness is fraught with complexity and impracticality. As you know, polyethylene is not the strongest material, so it can easily be damaged during installation. To avoid this, experts recommend using a thicker whip. This makes it difficult to fix it without outside help. And yet, such weight becomes an obstacle in that it will be difficult to attach it to the corrugated sheet using standard methods.
When you are limited in funds, then polyethylene is quite suitable for a vapor barrier layer. It is attached with construction stapler to the sheathing inside. The film fastening step depends on its thickness. Usually it is about 1-1.5 m. To prevent condensation from getting inside, it is important to seal all places with punctures and joints with construction tape.
Note! In order for the vapor barrier layer to be reliable and fully perform its functions, it is better to attach it in two layers.
Now let’s summarize and understand the advantages and disadvantages of polyethylene.
Pros:
- low cost;
- very low permeability.
Minuses:
- insufficient strength;
- short service life;
- heavy weight;
- complexity of installation;
- A lot of condensation forms, it drains and does not linger on the surface.
Polyethylene is not the best option, but if you lack funds, you can resort to it.
Vapor barrier reinforced polyethylene film
Roof vapor barrier films, as already mentioned, consist of several layers. The base is polyethylene, which is reinforced auxiliary materials. The most budget-friendly of them is reinforced film. It consists of several layers of polyethylene film, and is also necessarily supplemented with an additional reinforcing mesh made of polypropylene or fabric. Thanks to this structure, the material is strong and it will be difficult to tear it with your own hands. In addition, an accidentally dropped tool will not damage it either, which is quite practical.
In addition to everything, this film has greater rigidity than conventional polyethylene. But despite a large number of layers, its weight is not that great. Therefore, it will be easy for you to install the material on a corrugated roof. And the film can be secured and joined with special self-adhesive tapes.
Pros:
- high strength;
- light weight;
- multiple layers ensure reliability and durability;
- relatively low price;
- ease of installation;
- has low vapor permeability.
Minuses:
- as in the case of ordinary polyethylene, a lot of condensation forms, it flows off and does not linger on the surface.
If you need to make a good vapor barrier, but you do not have huge funds, then reinforced film is optimal solution. This is an ideal price-quality ratio option for your residential building.
Polypropylene film
It is made exactly according to the same pattern as the multilayer reinforced polyethylene. Polypropylene is used to increase the strength of the film. Its installation is also simple. A feature of polypropylene films is the presence of an additional relief layer. What is it for? A lot of condensation forms on the foam, which negatively affects the structural elements.
So that moisture does not harm the insulation (if any) or structural elements, an additional anti-condensation layer is applied to the polypropylene film, which consists of a mixture of cellulose and viscose. The layer absorbs condensation without problems, preventing the formation of condensation drops. This layer is rough, and during installation it should be placed towards the room, with the smooth side facing out.
Advice! Before starting work, read the instructions from the manufacturer.
Pros:
- light weight;
- high strength;
- reliability and practicality;
- ease of installation;
- low vapor permeability.
Minuses:
- material without anti-condensation coating spoils the insulation and structural elements.
Vapor barrier film with foil
This is one of the types of previous films. But, the material not only has an additional reinforcing layer, but is also equipped with an aluminum layer that reflects heat. What does this give? This layer reflects infrared rays, preventing them from leaving the house. Thanks to this, a certain “thermos effect” is created. Foil film is intended for baths and greenhouses, but it has begun to be used as a vapor barrier for roofs made of corrugated sheets and other materials. It is highly efficient, reducing heat loss through the roof by 10-15%. This allows you to significantly save energy that goes into heating. For example, using Izospan under corrugated sheeting increases the room temperature by only 2˚, while the costs are still the same.
Note! The reflective effect is possible only in air, so when mounting the film with foil it is important to leave a gap of 4-5 cm.
Pros:
- light weight;
- high strength and reliability;
- durability;
- low vapor permeability;
- not harmful to humans;
- reflects infrared radiation, retaining heat.
Minuses:
- high price.
Foil film is one of the best, but, as they say, you have to pay for quality. If you have enough funds, then it is better to use it to make a vapor barrier under the corrugated sheeting on the roof. Still, what choice to make is up to you.
When installing a roofing structure, the waterproofing, thermal insulation and vapor barrier properties of the roof are provided. Purposes of waterproofing and thermal insulation materials obvious, they are necessary to maintain heat in the room and protect against moisture penetration under the roof. But for many, the question of the need to form a vapor barrier layer remains open. What is a vapor barrier and why is it so important to use it when installing a roof?
Condensation, regardless of the type of roof, clearly negatively affects the practicality and durability of roofing materials. At the same time, it reduces thermal insulation properties insulation materials used in roofing and reduce their service life.
For example, when relative humidity air in 1%, the thermal conductivity of materials used for insulation increases by approximately 30%, and when air humidity increases to 5%, the level of thermal conductivity doubles.
Vapor barrier under corrugated sheeting is definitely necessary. She will give additional protection for metal roofing from the effects of condensation and will maintain the functionality of thermal insulation materials.
The use of expensive thermal insulation materials will not lead to the desired result without good protection of the roof from steam penetration and condensation formation. The protection of the roof structure from the penetration of cold into the room must be and, in total, have waterproofing, thermal insulation and vapor barrier properties.
How to deal with snow blowing under a ridge?
For information on how to deal with snow blowing under the ridge, see the article “How to choose the right sealant for corrugated sheeting and roof ridge.”
What kind of vapor barrier is there for corrugated sheets?
The choice of vapor barrier materials depends on the result that is necessary for high-quality improvement of the structure and the budget allocated for protecting the roof from moisture.
Glassine and plastic film - a budget option
Glassine
Glassine is one of the classic materials, which is used as a vapor barrier for roofing structures.
Advantages:
- Strength
- Durability
- High performance indicators
- Low cost
Flaws:
- Difficult installation;
- Heavy weight;
- At an air temperature of 30 degrees Celsius and clear summer weather, the profiled flooring heats up to a temperature of about 80 - 90 degrees, and glassine, under the influence high temperature, begins to emit unpleasant odors. These are not toxic emissions, but still, such odors in a residential building are not very pleasant.
For vapor barrier of roofing metal profile In residential premises, glassine would not be the most suitable option.
Polyethylene film
Polyethylene film is divided into two types - perforated and non-perforated. For waterproofing roof structures, experts recommend using non-perforated polyethylene film.
Advantages:
- Low cost;
- Low vapor permeability.
Flaws:
- Short service life;
- Complex installation in several layers;
- Easily damaged.
Polyethylene vapor barrier film with reinforcement
Reinforced polyethylene film- this is not a bad option for multi-layer vapor barrier materials for buildings with a good supply and exhaust system. Polypropylene fabric or mesh is used to reinforce the material. The main function of reinforcement is to ensure the strength of the vapor barrier structure. Most often, the installation of such vapor barrier occurs using self-adhesive films.
Advantages:
- High strength
- Good functionality
- Light weight
Flaws:
- The polyethylene coating has a structure that is not capable of holding a large amount of condensate on itself, and the resulting drops begin to flow onto the surface of the insulation.
Polypropylene film for corrugated sheets
Polypropylene differs from polyethylene vapor barrier in structure. That negative property, described in the above-mentioned vapor barrier material, is eliminated due to the additional relief layer. The anti-condensation fabric layer does not allow liquid to accumulate in the form of droplets on the material.
Advantages:
- High strength
- Great functionality
- Light weight
- High vapor rejection rate
Flaws:
- The use of film with an anti-condensation layer requires a special approach to installation, in which it is necessary to leave ventilation gaps for moisture evaporation.
Important! Polypropylene film is installed with the porous structure facing down. It is the porous structure that has anti-condensation functions, retaining moisture in uneven areas.
Experienced craftsmen recommend, when forming a vapor barrier layer, to take into account small ventilation gaps, which must be evenly distributed over the entire area. The holes are made carefully and small in size so as not to cause the vapor barrier material to delaminate and deteriorate.
Foil vapor barrier film
Foil vapor barrier film is one of the types of vapor barrier using polypropylene or polyethylene as the main material. This multilayer film is characterized by reinforcement and a reflective aluminum layer, which creates a thermal effect that prevents infrared radiation leave the premises.
Foil vapor barrier material was originally intended for use in bathhouses and greenhouses, but is now often used for ordinary residential premises. Its efficiency is quite high - on average, heat loss is reduced by 10-15%, which allows you to significantly save on heating your home.
Important! The foil vapor barrier film is installed with the reflective element down and the joints of its connection are glued with a special foil film.
Advantages:
- High strength
- Great functionality
- Light weight
- High vapor rejection rate
- Additional heat retention due to the heat-reflecting element
Flaws:
- High price
An excellent option for those who are willing to spend a little more money on roof vapor barrier than when purchasing budget materials. Such an overpayment will definitely pay off in the future operation of the house due to heat conservation.
How to choose a vapor barrier for corrugated sheeting?
Choice vapor barrier material is determined by several criteria:
- Firstly, it is necessary to understand the purpose of the structure itself. If this is a non-residential building, then glassine will be excellent option, because its disadvantage lies only in the emission of unpleasant odors when heated. This disadvantage compensated by low cost.
- The second sign that you should focus on is the desired result. If you are willing to overpay a little for a vapor barrier when installing a roofing structure in order to save money in the future due to heat conservation, then the best option would be a foil vapor barrier film.
- It is worth taking into account the climatic features of the region. If thermal insulation properties are not so important, then polypropylene film would be an excellent option for vapor barrier.
- Ventilation of the room is also one of the criteria when choosing a material for roof vapor barrier. If we are talking about a room that is not subject to accumulation of humidity in the air due to excellent supply and exhaust system, then polypropylene film can be used as a vapor barrier for the roof.
Features and characteristics of vapor barrier films
The characteristics of films can be divided according to the following criteria:
- Strength. This is an important factor that manifests itself already during film installation.
- Vapor permeability. The main function of a vapor barrier film.
- Water column pressure. An indicator of the volume of water that the film can hold on itself at one time.
- Fastening. Possibility of film fastening during installation.
Of course, in addition to all the above criteria, many are also based on the cost of materials. Each case is a personal decision, but you shouldn’t save much on thermal insulation.
Important! When building a house, it is better to reduce the cost of materials that will not be difficult to replace during the operation of the premises.
If we are talking about vapor barrier of a roof in a residential building, then it can be divided into several different sections. If the garage of a residential building is not basement room, but an extension to a residential building, it is not necessary to use expensive materials for vapor barrier of the roof above it. The situation is similar with the bathhouse, the gym and other premises not intended for full-time living.
Roofing profiled metal sheets are one of the most common roofing materials. The popularity of corrugated sheeting is due to its affordable price, ease of installation, and low weight. However, along with obvious advantages, this material has no less noticeable disadvantages. One of them is increased condensation. At certain conditions Heavy dew falls on steel sheets, both outside and inside. Because of this, at times there is literally a light drizzle under the roof. Wooden structures and insulation have to be protected from condensation. The authors of some articles posted on the Internet claim that under steel sheets a waterproofing layer should be placed and even allow themselves to give advice on the choice of material. However, in fact, waterproofing under corrugated sheeting is not necessary, and sometimes is contraindicated.
It should be understood: not all materials designed to protect against moisture are waterproofing.
Waterproofing
Absolutely waterproof, withstands quite high water pressure (continuous flow of water), very durable and resistant to atmospheric influences, ultraviolet radiation, which allows it to be used in open form. Waterproofing is carried out during the construction of hydraulic and underground structures, building foundations, and flat roofs. Waterproofing materials include bitumen and bitumen-polymer roll insulation, mastics, polymer membranes, special cement-polymer penetrating compositions, bentonite clay slabs.
When installing flat roof the waterproofing layer can simultaneously serve as a roof covering
Vapor barrier
As the name suggests, it does not allow water vapor to pass through. Both rolled waterproofing materials and polymer membranes cope with this task, but they are inconvenient for use in lightweight wall and roofing structures. It is much easier to attach thin and light reinforced polyethylene vapor barrier films to the frame. And they are much cheaper. The vapor barrier is also waterproof and can protect against rain. But it does not have sufficient mechanical strength and resistance to ultraviolet radiation, which does not allow the vapor barrier to be used in the open, but only under the protection of the roofing and wall cladding.
Reinforced polyethylene and polypropylene vapor barrier films are mainly used for roofing. Mounted truss structures in the warm season, it is allowed to leave it uncoated for a couple of months, under the protection of only a vapor barrier. It will protect the wood from precipitation. But not longer, the film’s resistance to ultraviolet radiation is limited, snow load she may also not be able to stand it
Wind and moisture insulation
Wind and moisture insulation for roofing can protect fiber insulation from wind blowing, retains liquid water to a certain extent, but at the same time freely allows water vapor to pass through. Due to such selective properties of moisture transmission, wind and moisture insulating films are also called diffusion membranes. They can be made of polymer fibers (non-woven canvas) or perforated film, there are also combined options.
Due to the presence of pores, the diffusion, wind and moisture-proof membrane allows water vapor to pass through. But the size of these pores is so small that drops of water falling on the surface do not penetrate the film. The force of surface tension prevents this from happening. However, if the membrane is wetted long time and abundantly, sooner or later it will get wet and “leak.” Wind and moisture protection is not suitable as protection against heavy rain, immediately after its installation the roof should be covered roofing covering
What is a roofing film (membrane)
It’s clear: if the film is under-roofing, it means that it is placed directly under the roofing covering. One of its main functions is to protect the rafter system and insulation (if any) from condensation, which can fall abundantly on profiled metal sheets. Any of the insulation materials listed above can handle it: hydro(vapor) insulation, diffusion membrane (wind insulation). However, these are not all the problems that under-roofing film is designed to solve. What exactly is required of it and how to choose the right under-roofing film (membrane) directly depends on the type of roof. Let's consider two types of roofs: cold attic and warm attic.
IN Lately There has been a tendency to call vapor barrier a roofing film, and wind and moisture insulation - a roofing membrane. This is not an entirely correct use of the terms, but that’s the way it is. The main thing is the difference in the physical properties of these materials
It is important to know: unfortunately, the Internet is full of confusion on this topic; ignorant sellers of building materials and illiterate builders also contribute. Wind and moisture insulation and vapor barrier are often called waterproofing. This is wrong, you need to understand that these are not the same thing, the materials have different physical properties, intended for different types roofs
Roof over a cold attic
There is no need to insulate the attic roof, but you can ventilate it by making holes in the gable walls or sheathing.
In our case, the fundamental difference between a cold attic and an attic (combined) roof is how they are ventilated, how excess moisture is removed from the wood and insulation
In this way, moisture from inside the attic is removed thanks to good internal ventilation, you just need to protect the structures from condensation formed on bottom side roofing covering. It is possible to install waterproofing under corrugated sheets. They once did this, they rolled out roofing material under wavy asbestos-cement sheets (slate). Theoretically, you can use old linoleum, sheets of plastic, tin, etc. unnecessary trash, impermeable to water. However, a special vapor barrier film will last longer, is easier to install, and is very inexpensive. Can also be used diffusion membrane, but there is not much point in this: it will cost more, and its properties of transmitting water vapor will not be in demand.
The roof structure of a cold attic must include a vapor barrier film
Important to know: for cold attic roof the best under-roofing film is a vapor barrier, but any type of moisture-wicking material will do
Roof over a warm attic
The attic roof must be insulated, and insulation and wooden structures have the ability to absorb moisture from the air. It will not be possible to ventilate them from below, from the side of the premises; the air there is more humid than outside. On the contrary, the roof needs to be protected from moisture from the inside by covering the rafters vapor barrier film. The only way to prevent wood and mineral wool from becoming damp is to ensure their ventilation from the outside, be sure to leave a ventilated air gap of at least 4 cm high between the roofing covering and the under-roofing film. Hydro (vapor) insulation will not ensure the release of water vapor, therefore for attic roofs only vapor-permeable wind and moisture insulation is used (diffusion membrane).
Correct design mansard roof and walls frame house. The structure must be protected from the inside by a vapor barrier, and from the outside by wind and moisture protection. But not the other way around!
Important to know: the only suitable option roofing film (membrane) for standard design attic roof - diffusion membrane.
There is an option for a combined (attic) roof, in which a vapor-tight hydro or vapor barrier is used as an under-roofing film. But in this case, it is necessary to ensure effective ventilation of the space both above and below the film; the total height of the ventilation gaps will reach 10 cm. This solution is effective, but complicates the design and is not used often. Please note that the under-roofing film (4) closer to the overhang is placed on top of the steel apron (15), which is placed in the gutter of the drainage system. This should always be done to ensure that condensate drains beyond the roof structure.
In conclusion, we will say that not only the comfort of living in the house, but also the durability of the structure depends on how correctly the roof structure is selected and the materials for its installation are selected. If you do not have sufficient knowledge in the field of construction, do not have the time or desire to delve into the intricacies modern technologies, the best solution will entrust the execution of responsible work to experienced professionals.
Video: what is waterproofing for?
No roofing material is perfect. Even in its main quality - protection from moisture. And in cases where the roof is covered impeccably, and there are no leaks during rain or melting snow, condensation still remains on inside roofs.
To protect the rafter system and the attic of a cold roof from condensation, waterproofing is installed as part of the roofing pie. And the fact that it also protects against “small” leaks is a bonus in the form of a time reserve to eliminate roof leaks.
In what cases is waterproofing needed for a cold roof?
There are not that many roofing materials available. If we consider only, the list will be reduced to several species. And depending on the characteristics of the material itself, the installation technology and the purpose of the building, waterproofing is not always necessary.
Metal roofing
Metal roofing can be sheet or piece. Sheet materials- This , . Piece covering - roofing checker and roofing scales.
Regardless of the size of the element and the laying technology, the “layering” is the same for everyone:
- rafters;
- waterproofing;
- counter-lattice to ensure the required ventilation gap;
- sheathing;
- roof.
The presence of waterproofing and a ventilation gap in the under-roof space is also mandatory for heated houses year-round residence, and for unheated dachas or outbuildings.
Anyone roofing metal high thermal conductivity and low heat capacity. As the temperature drops daily, the roof cools much faster than the air inside the attic. And it will appear almost every day, even in summer.
In winter, if the building is heated, the air in the attic will be even warmer - any thermal insulation of the ceiling is not absolute. Just like any vapor barrier does not provide complete protection against vapor penetration warm air into the attic from the room. And there are also chimneys and ventilation ducts, which also serve as a source of heat.
Waterproofing protects the attic and rafter system. And to prevent the counter-lattice and sheathing from getting wet, there must be a ventilation gap in the under-roof space.
Slate and ondulin
Although these materials are different in composition, the likelihood of condensation appearing on their surface is low.
Slate is best in this regard. Its surface texture can be compared to an anti-condensation waterproofing film. A rough surface can retain condensation until conditions for its evaporation and weathering occur. Therefore, waterproofing is not needed for a cold slate roof.
An example is apartment buildings Soviet-built - most “Khrushchev” buildings have slate laid over lathing without waterproofing. And the only reason the attic gets wet is roof leaks.
Ondulin has almost the same properties. On the manufacturer’s website, as one of the “economy” options for installing a cold roof, a laying diagram without waterproofing is given. And this option is suitable for country houses and summer cottages for seasonal residence, summer kitchens and outbuildings.
For permanent residences, roofing made of slate and ondulin without waterproofing is considered not reliable enough. And here it is recommended to lay waterproofing roll materials. standard - the film is attached to the rafters with a slight sag, counter-lattice beams are stuffed on top and.
Roof tiles
There are several types of roofing material where this term is present:
Bituminous shingles. Waterproofing is provided at the level of installation technology from the manufacturer. This is one that also serves as an additional fixing element. The bitumen contained in shingles and carpet bakes together when the roof heats up from the sun.
Composite tiles. This is a kind of metal tile with a small sheet size. The differences lie in the composition of the protective and decorative layer. As for any metal roofing It is necessary to lay waterproofing underneath it.
Ceramic and cement-sand tiles. They differ from each other in composition, shape, manufacturing technology. But despite this, installation proceeds according to general principles. And the manufacturers of these types of roofing also stipulate the presence of waterproofing when describing them.
What waterproofing materials can be used
There are three types of modern materials:
Superdiffusion membranes. They have good waterproofing properties and high vapor permeability. Rarely used in cold roofs due to high cost and excessive “breathing” properties. The main purpose is to protect the insulated roof. It is installed on non-insulated roofs if there are plans for further insulation and the attic is in use.
Diffusion membranes. Good waterproofing properties and average vapor permeability. Optimal choice for slate, ondulin, ceramic and cement-sand tiles.
Water vapor barrier films with anti-condensation surface. This universal material, which is characterized by high waterproofing properties and limited vapor permeability. Such materials can also be used as a vapor barrier.
Recommended as . They block most of the water vapor in the warm air, which is then ventilated through the eaves and ridge vents of the attic ventilation and through the dormer window.
How to lay film correctly
The waterproofing film is mounted from bottom to top with an overlap of panels of at least 15 cm. The fastening is carried out to the rafters. The film should sag between the rafters, but no more than 2 cm. Additionally, a sealing tape is glued on top, and then a counter-lattice block is nailed.
If it is necessary to increase the length of the canvas, then the joint should be at rafter leg. Extensions are also done with an overlap of 15 cm.
The superdiffusion film is laid on the ridge without tearing. When installing other types waterproofing materials in the ridge area, a “gap” of about 5 cm should be left on each side.
Is it possible to use roofing felt?
Sometimes as waterproofing pitched roof roofing felt and its analogues are used. But these materials are intended for waterproofing flat roofs over a continuous floor.
IN technological map TechnoNikol company for installation of bitumen roll materials It is indicated that the roofing material is attached to the base using mastics or fusing.
Mechanical fasteners at large roof pitch angles are used as additional “point” fixation to prevent slipping bitumen waterproofing V hot weather. And this limits the scope of use of roofing felt on pitched roofs.
On those roofs where the slope angles are large and the technology for laying the roof is continuous, sheathing is not needed, it is not economically profitable to install it, even though roofing felt is cheaper waterproofing films. But only mechanical fastening along a row sheathing does not provide sufficient reliability of fixation due to the low tensile strength of roofing material.