Ventilation gap for mineral wool. Do I need a membrane over mineral wool

The use of mineral wool in the process of building a house is most often associated with the implementation of a number of measures designed to protect the insulation from getting wet.

Sometimes it is quite justified and necessary, and sometimes it will be an unnecessary transfer of funds.

In each specific case, depending on the expected operating conditions and the type of structures to be insulated, it is necessary to clearly determine whether a vapor barrier is needed when insulating with mineral wool?

Melts are used as raw materials for production rocks(basalts, dolomites). Sometimes industrial slags are added. Fibers are formed from the molten mass, which are then pressed into plates or rolls.

The strength of the final products is determined by the degree of compression during pressing and binders, which are used as phenol-formaldehyde or carbamide resins.

The greater the force applied at the molding stage and the higher the concentration of binders, the more dense and rigid the material obtained.

Density, depending on the form of release, can vary in a very significant range:

Rolls - 20-50 kg/m3;
Mats -50-80 kg/m3;
Lightweight slabs - 80-120 kg / m3;
Plates of medium hardness - 120-200 kg / m3;
Rigid boards – over 200 kg/m3.

Properties and features of the use of the material

The main property that determines the effectiveness of a particular insulation is the coefficient of thermal conductivity.

It characterizes the heat loss occurring through a layer of material 1 m thick in an area of 1 m2 for 1 hour at a temperature difference of 10 ° C on opposite surfaces.

For various forms production of mineral wool, this figure is 0.03 - 0.045 W / (m * K).

A distinctive feature of fibrous insulation is the dependence of their thermal insulation properties on moisture content.

When wet, water droplets envelop the fibers and gradually penetrate into the bulk structure, gradually displacing air from there.

An increase in the amount of water inside, between the fibers, leads to a sharp drop in thermal insulation characteristics. The situation is aggravated by the fact that the water that has got inside is extremely difficult to get out.

Insulation can collect up to 70% of water from its mass. Naturally, under these conditions, the efficiency of its work will tend to zero.

Despite the criticality to getting wet, the scope of mineral wool is extremely wide. When building a house, its use is possible almost everywhere where direct contact with water is excluded:

Hollow walls (frame and brick, made using the technology of well masonry);
External surface of wooden or brick walls;
Internal partitions;
floors;
Interfloor ceilings;
Roof.

When is vapor barrier needed?

It is definitely enough to simply formulate the condition whether a vapor barrier is needed. When insulating with mineral wool, protection against water vapor will be needed when there is a possibility of contact with air coming from the side of the room.

To provide effective work, each layer of the heat-insulating “pie” must pass air to one degree or another. In the direction from the room to the street, this ability should increase.

Thus, warm air from the room very slowly seeps between the fibers, displacing the cold from there.

Under the inside decorative trim a small ventilation gap of 1-2 cm is performed. The insulation is installed inside the structure between the supports.

It can be vertical racks frame, floor joists or rafters. On the outer (external) side, a wind-waterproof barrier is arranged that protects against exposure precipitation and strong direct wind.

Such a scheme is valid when making frame walls, floors, attic roofing, ceiling of a residential floor in the presence of a cold attic on top.

Internal partitions and ceilings between living spaces require a slightly different approach. Humid air in this case can penetrate into mineral wool from any direction. To maintain the thermal performance of the structure, a vapor barrier is installed on both sides.

Another case when protection from internal moisture is necessary is external insulation of wooden log cabins made of timber or logs. A vapor barrier is installed between the wall and the thermal insulation boards.

Excess moisture is removed through the ventilation gap left under the outer decorative facade.

Insulation scheme without the use of vapor barrier

Sometimes doubts about whether a vapor barrier is needed when insulating with mineral wool are quite justified. characteristic feature for such situations there will be airtight layers:

Interior or exterior non-porous finish;
A continuous sealed layer of waterproofing;
Brick wall;
Facade plaster;
Decorative facing brick.

Another situation where mineral wool does not require additional protection is well brickwork. During the construction of the wall, internal cavities are formed, subsequently densely filled with heat-insulating material.

Video instruction:

Based overview it can be concluded that the protection of mineral wool from the effects of water vapor is not always a mandatory operation.

It is necessary only in cases where contact is possible between the warm moist air of the living room and the fibers of the insulation.

The ventilation gap in a frame house is a moment that often raises a lot of questions from people who are engaged in warming their own homes. These questions appear for a reason, since the need for a ventilation gap is a factor that has a huge number of nuances, which we will talk about in today's article.

The gap itself is the space that is located between the skin and the wall of the house. A similar solution is implemented by means of bars that are mounted on top of the wind protection membrane and on the exterior trim elements. For example, the same siding is always attached to the bars that make the facade ventilated. A special film is often used as insulation, with the help of which the house, in fact, turns around completely.

Many will rightly ask about whether it is really impossible to just take and strengthen the sheathing directly on the wall? Do they just line up and form the perfect area for the skin to be installed? In fact, there are a number of rules that determine the need or uselessness of organizing a ventilation facade. Let's see if a ventilation gap is needed in a frame house?

When you need a ventilation gap (vent gap) in a frame house

So, if you are thinking about whether you need a ventilation gap in the facade of your carousel house, pay attention to the following list:

When wet If the insulation material loses its properties when wet, then a gap is necessary, otherwise all work, for example, on home insulation will be completely in vain
Steam Passage The material your home's walls are made of allows steam to pass through to the outer layer. Here, without the organization of free space between the surface of the walls and the insulation, it is simply necessary.
Prevent excess moisture One of the most common questions is the following: do I need a ventilation gap between the vapor barrier? In the case when the finish is a vapor barrier or moisture-condensing material, then it must be constantly ventilated so that excess water does not remain in its structure.

As for the last point, the list of such models includes the following types of sheathing: vinyl and metal siding, profiled sheet. If they are tightly sewn on flat wall, then the remnants of the accumulated water will have nowhere to go. As a result, materials quickly lose their properties, and also begin to deteriorate externally.

Do I need a ventilation gap between siding and OSB (OSB)

When answering the question of whether a ventilation gap is needed between siding and OSB (from English - OSB), it is also necessary to mention its need. As already mentioned, siding is a product that isolates steam, and OSB plate at all consists of wood shavings, which easily accumulates moisture residues, and can quickly deteriorate under its influence.

Additional reasons to use a vent

Let's analyze a few more mandatory points when the gap is a necessary aspect:

Prevention of rot and cracks Wall material under decorative layer prone to deformation and deterioration under the influence of moisture. To prevent rot and cracks from forming, it is enough to ventilate the surface, and everything will be in order.
Condensation Prevention The material of the decorative layer may contribute to the formation of condensation. This excess water must be removed immediately.

For example, if the walls of your house are made of wood, then an increased level of moisture will adversely affect the condition of the material. The wood swells, begins to rot, and microorganisms and bacteria can easily settle inside it. Of course, a small amount of moisture will collect inside, but not on the wall, but on a special metal layer, from which the liquid begins to evaporate and be carried away with the wind.

Do you need a ventilation gap in the floor - no

Here it is necessary to take into account several factors that determine whether it is necessary to make a gap in the floor:

If both floors of your house are heated, then the gap is not necessary. If only 1 floor is heated, then it is enough to lay a vapor barrier on its side so that condensate does not form in the ceilings.
The ventilation gap must be fixed only to the finished floor!

Answering the question of whether a ventilation gap is needed in the ceiling, it should be noted that in other cases this idea is exclusively optional, and also depends on the material chosen for floor insulation. If it absorbs moisture, then ventilation is a must.

When a vent is not needed

Below are a few cases where this construction aspect does not need to be implemented:

If the walls of the house are made of concrete If the walls of your house are made, for example, of concrete, then the ventilation gap can be omitted, because given material does not let steam from the room to the outside. Therefore, there will be nothing to ventilate.
If indoor vapor barrier If with inside If a vapor barrier was installed in the premises, then the gap also does not need to be organized. Excess moisture simply will not go through the wall, so you do not need to dry it.
If the walls are plastered If your walls are treated, for example, with facade plaster, then a gap is not needed. In case when outer material processing well passes steam, additional measures for ventilation of the skin are not required to be taken.

Installation example without ventilation gap

As a small example, let's look at an installation example without the need for a ventilation gap:

In the beginning comes the wall
insulation
Special reinforcing mesh
Fungus dowel used for fasteners
Facade plaster

In this way, any vapor that penetrates the structure of the insulation will be immediately removed through the plaster layer, as well as through the vapor-permeable paint. As you can see, there are no gaps between the insulation and the decoration layer.

We answer the question why you need a ventilation gap

The gap is necessary for air convection, which is able to dry excess moisture, and positively affect the safety building materials. The very idea of this procedure is based on the laws of physics. We have known since school that warm air always rises and cold air sinks. Therefore, it is always in a circulating state, which prevents liquid from settling on surfaces. In the upper part, for example, the siding sheathing is always perforated, through which the steam comes out and does not stagnate. Everything is very simple!

When the walls are insulated according to the “ventilated facade” system, the insulation is constantly washed by a jet of air. That's why the most important characteristic the applied insulation is its air permeability. You need to know how freely the air can move inside the insulation itself. This means reducing the thermal insulation characteristics of the layer, or even creating “its disappearance”. Depending on the breathability of the mineral wool, it may be necessary to use windproof membranes.

in a ventilated façade

When insulating according to the “ventilated facade” system, the insulation is pressed against the wall with the help of anchors, planks hung on the wall, etc. Between the insulation and exterior trim leaving a ventilation gap.

If the system is assembled correctly, then under the influence of heat passing through the heat insulator, as well as due to wind pressure, in the ventilation gap there is a natural steady draft of air from the bottom up.

In system hinged facade with a ventilation gap, the insulation is constantly exposed to air moving along the ventilation gap. But the air moves from the bottom up and through the insulation layer, i.e. right on the heater. And the greater the breathability of this material, the large quantity air will pass through it.

Heat escapes with air

This movement of air through the insulation is, in fact, a direct heat leakage from the building, reducing the effect of insulation. This is the so-called convection heat transfer by air, a phenomenon that reduces the heat transfer resistance of the enclosing structure according to the “ventilated facade” system by 20% or more.

If, during installation, close contact of the insulation with the wall was not ensured, then convection heat losses increase significantly, and the effect of the insulation is reduced by 40 - 60%. This is a very serious problem when insulating buildings using this technology.

Air velocity and wind zones

Also, losses will increase with an increase in the speed of air movement through the ventilation gap. There is a significant increase in convection heat loss in the insulation layer in areas where there are frequent winds (6 - 7 wind zones) or for high-rise buildings (70 m from ground level) in any wind zone.

In which heaters based on basalt wool significant convection heat loss?

Density of mineral wool

For basalt fiber slabs with a density of 80 kg/m3 or more, this problem practically ceases to exist. Its manifestations can only be if the insulation is not completely pressed against the wall, then it is possible to increase heat loss up to 5%, but due to the movement of air in the cracks between the insulation and the wall.

Now it can be argued that when used for insulation mineral wool boards with a density of 80 kg / m3 and more, convection heat loss will not be more than 2.5%.

Thus, the indicated density basalt slabs is the boundary for problem-free operation in a ventilated facade system. And such plates can be used without additional wind protection - without a superdiffusion membrane.

Whether to use a membrane

Sufficient resistance to air penetration can be provided either by using a heat insulator high density, or by increasing the layer's resistance to air movement by installing an additional windproof membrane.

What is the best way to solve the problem?

Apply a denser, and therefore more expensive insulation with a thicker layer, or hang additional element system, which, by the way, can become unusable and at least create fire problems?

There is an opinion that it is still better to use denser mineral wool, without an additional membrane, while, if required, in areas with a significant wind load, install basalt fiber insulation with a density of 180 kg / m3.

The problem of reducing heat loss from air convection should be solved by using heaters with appropriate characteristics.

Which is more expensive, more efficient - a membrane or ....

In this case, the insulation itself will certainly be more expensive, but taking into account the absence of a membrane, the rise in price will not exceed 2% of the cost of the entire ventilated facade system. At the same time, the reliability of the system is significantly increased.

It should be noted that two-layer heaters can also be used, in which the cheaper and warmer layer is covered with a wind-resistant dense layer. But this option requires a higher construction culture, the absence of gaps between the plates during installation, which is difficult to ensure in practice.

At the same time, the use of single-layer insulation is more technologically advanced, and the increase in the cost of the entire system at the level of 2% should not affect the feasibility of just such a “ventilated facade” insulation technology.

To date, there are no building codes and regulations that would determine when it is possible to do without a windproof membrane in a ventilated facade system, and when it is impossible.

We always ask our readers to “decipher” questions, provide additional data that would help to understand what the problem is. For example, what exactly are you asking about? It's understandable that you want the fiber insulation to stay dry. But what is the design of the thermal insulation of the house? Do you insulate the frame by putting mineral wool between the racks? Or is it a brick house with external insulation? Or maybe wooden frame? Or internal insulation? Are you interested in the roof? Then which one: combined attic or cold attic? There are many options for thermal insulation of buildings and as many answers to your question. Alas, there is no universal solution.

Without going into the specifics of specific designs, we will try to give general idea how to keep the insulation dry. In this case, we will assume that precipitation or water from the soil in building construction your house is not penetrated, the roof does not leak, there are no holes in the lining of the walls, the walls are waterproofed from the foundation, etc. We will not consider the insulation of the building from the inside as irrational.

To prevent the penetration of moisture into the mineral wool is a task, although feasible, but difficult. To do this, the fibrous insulation in the most dry state must be packed in a completely sealed shell. For example, in strong plastic bags. However, this is not so easy to do, and carefully mounting the mineral wool without damaging the shell is even more difficult. From leaky bags there is no sense. That's why full protection from moisture penetration is rarely used. An example of such a solution is the insulation of heating mains, where the shell is roll bituminous waterproofing. As a rule, in the aboveground structures of buildings, fibrous insulation is not so much isolated from the effects of moisture contained in the air, as they try to ensure the release of water vapor from the material. Consider in in general terms the most common insulation designs country house:

Frame house. Both a heater and wooden frame need protection from waterlogging. Most of the year, the air inside the house has a higher humidity than outside. Therefore, first of all frame structure from the inside, an airtight seal is fixed over the entire area vapor barrier film. As the name implies, it is impervious to water vapor. But the insulation, not having a sealed shell, will absorb the moisture contained in the outside air. So that it does not accumulate, it is necessary to ensure sufficiently effective ventilation of mineral wool. At the same time, the wooden frame is also ventilated. To do this, between the skin and the insulation, having fixed the bar, leave an empty gap. The recommended thickness of the ventilation gap is 40 mm; holes are made in the upper and lower parts of the walls, covering them with a mesh or grate. To prevent gusts of wind from blowing through the insulation, a windproof film is attached on top of it, which does not prevent water vapor from escaping to the outside.

Classic wall design frame house. A vapor barrier is placed inside, which excludes the penetration of moist air from the house into the insulation. Outside - a ventilated gap that ensures the removal of moisture from the mineral wool, closed by a windshield

Wooden house, external insulation: a frame filled with mineral wool and sheathing on top of it. The walls of the log house, made of wood, need protection from moisture no less than fibrous insulation. “Packing” them from the inside with a vapor barrier is irrational, the benefits are lost natural wood. It is also not worth placing a vapor barrier layer between the log wall and the insulation, as this can lead to waterlogging of the wood and damage to it by a fungus. We have to put up with the fact that water vapor will constantly penetrate the wooden walls from the inside of the house and go outside through the insulation. To effectively remove this moisture, we do, as is the case with frame house, ventilation gap. We close the mineral wool with a windshield. Again, when insulating a log house, vapor barrier is not needed.

Proper thermal insulation wooden house: 1 - insulation; 2- windproof film; 3 - sheathing. Bars (counter-rail) are stuffed on the frame, a ventilation gap is provided between the sheathing and wind protection, thanks to which the wood and mineral wool remain dry

Variant of ventilated facade - multilayer stone wall made of aerated concrete with brick cladding. There is a ventilation gap and wind insulation. Ventilation openings of sufficient area must be left in the lower and upper areas of the cladding

Stone house, ventilated facade. Similar to the thermal insulation system of a wooden house. The presence of an outside ventilation gap and wind insulation according to the scheme already known to us is mandatory. With vapor barrier it is a little more difficult: if the walls are made of non-hygroscopic (non-moisture-absorbing) material, a vapor barrier is needed between the wall and the insulation. We are talking about reinforced concrete (including prefabricated panels) and expanded clay concrete blocks. If the walls are made of "breathing" materials, cellular concrete, brick - vapor barrier is not needed, it will only harm.

General arrangement of a ventilated facade

Stucco facade - rigid mineral wool is attached directly to the wall, plastered on top of the slabs. Vapor barrier is not needed, and thin-layer facade plaster reinforced with a polymer mesh serves as protection against precipitation and wind. Only special mixtures intended for external thermal insulation systems can be used.

Now about the roof, consider only pitched structures:

Combined (insulated) mansard roof. It is a frame structure, in many respects similar to the walls of a frame house. Be sure to need a vapor barrier from the inside, a ventilated gap and wind protection from the outside. When choosing a wind insulation film, it should be taken into account that most roof coverings are condensate-forming: on the side facing the inside of the roof, under certain conditions, dew or frost falls. Most of all, steel roofs sin with this, sometimes the amount of condensate is very large. So that the water flowing from the roofing does not soak the insulation, special roofing films, the so-called diffusion membranes, are used as wind insulation. They have the ability to freely pass water vapor to the outside, to prevent the penetration of liquid water inside. Drops simply roll down and flow out of the roof.

The diffusion membrane has many pores. They are too small to prevent liquid water from passing through, but large enough to allow water vapor to escape.

An example of a combined pitched roof. To insulate in the design mansard roof always remained dry, it is necessary to ensure its ventilation. Ventilation (shown in the diagram by arrows) is carried out in the intervals between the counter-rails, stuffed along the rafters. From below, the insulation should be protected by a vapor barrier (Izospan On the diagram), from above - a diffusion membrane (Izospan AM).

Cold (uninsulated) attic roof. Airing attic space organize through vents in the gables, slots in the filing, aerators in the coating. Since the roof is not insulated, only protection against condensate is needed without the function of removing water vapor. The most rational between roofing And truss system place a vapor barrier. Diffusion membrane is also suitable, but it is more expensive.

If you have any questions, we are ready to answer them. Urgent request: specify, please, your messages. In a question-and-answer format, it is difficult for us to give answers to general questions. Yes, and you probably do not get the information of interest in full.

Arkady Karpov, Moscow, asks a question about the cladding of the house: Hello, I want to ask you a question. Now the team is doing the sheathing of the house for me, they are insulating and sheathing with siding. After the film has been laid, the siding is immediately sewn on top of this. I say - where is the gap? They say no, we always do it. Are they doing the right thing and how to do it right?

Andrey Volokolamtsev, foreman of Avgust LLC, Podolsk, answers.

Hello Arkady. Perhaps what your builders are doing is not quite right, and perhaps not at all right. In order for you to have a normal and systematic understanding of this issue, let's first analyze your case, and then we'll see if it is necessary to make a ventilation gap and when.

So let's figure it out. If the walls are made of a vapor-permeable material, then in the case of using a decorative layer of siding, you definitely need to make a ventilated gap. Because the moisture interior spaces your house in the form of steam will penetrate through the walls into the insulation and moisten it.

Type heaters do not like moisture very much. When they get wet by at least 15 percent, they already lose 50 percent of their thermal resistance.

There are, however, such heaters that are not so susceptible to moisture, which do not lose their heat-insulating ability so much. This primarily applies to polyurethane foam, which can be applied to the walls of the house by spraying.

When exactly is a ventilation gap needed?

So, in your case, a ventilated gap between the insulation and the outer decorative layer will definitely be needed in the following options:

The use of any insulation that loses its properties when wet.
The material of the walls of the house passes steam from the interior to the outer layer.
Decorative finish is a layer of vapor barrier or moisture-condensing material.

The last point can be fully attributed to vinyl siding, metal siding and profiled sheet. These materials will not allow moisture to escape from the insulation if they are tightly sewn onto the insulation layer.

When is a ventilation gap not needed?

In what cases can a ventilation gap be omitted:

The material of the walls of the house does not let steam from the interior to the outside, for example, concrete.
The insulation from the interior is well insulated with a vapor barrier.
The outer material is well steam-permeable, for example, facade plaster.

On this ability facade plaster built when the walls can be insulated with foam or basalt wool.

Any steam that enters the insulation is removed directly through the plaster layer and vapor-permeable paint. In this case, there is no ventilation gap between the insulation and the decorative layer.

When else is a ventilation gap necessary?

In what other cases will you need a ventilation gap between the wall and the decorative coating:

The material of the decorative layer contributes to the formation of condensate.
The material of the walls under the decorative layer can deteriorate from moisture (rot, cracks, etc.).

I will give a simple example. If you are planning to sheathe a wooden house with a metal profiled sheet, then you cannot do without a ventilation gap.

Otherwise, any moisture that will condense on inner surface profiled sheet, will be absorbed, which will be destroyed from this.

In the case of a ventilation gap, moisture, of course, condenses on the inner surface of the profiled sheet - this is metal. But direct contact with the surface wooden walls does not have. And the current of air, which is present in the ventilation gap, carries away this moisture in the form of steam and removes it from the space between the decorative layer and the wall.

Consider which of the above cases is yours, and choose whether you need a ventilation gap or not. See what kind of wall material you have.

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