Is a ventilation gap necessary when insulating the floor? Is a vapor barrier necessary when insulating with mineral wool from the outside and inside? We answer the question why a ventilation gap is needed

Application mineral wool during the construction of a house, it is most often associated with the implementation of a number of measures designed to protect the insulation from getting wet.

Sometimes this is completely 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 insulated structures, it is necessary to clearly determine whether a vapor barrier is needed when insulating with mineral wool?

Rock melts (basalts, dolomites) are used as raw materials for production. Sometimes industrial slags are added. The molten mass is formed into fibers, which are then pressed into slabs or rolls.

The strength of the final products is determined by the degree of compression during pressing and the binders, which use phenol-formaldehyde or urea resins.

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

Density, depending on the release form, can fluctuate within a very significant range:

• Rolls – 20-50 kg/m3;
• Mats –50-80 kg/m3;
• Lightweight slabs – 80-120 kg/m3;
• Medium hardness slabs – 120-200 kg/m3;
• Rigid slabs – over 200 kg/m3.

Properties and application features of the material

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

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

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

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

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

An increase in the amount of water inside, between the fibers leads to a sharp drop thermal insulation characteristics. The situation is further aggravated by the fact that water that gets inside is extremely difficult to remove outside.

The insulation can absorb up to 70% of its mass in water. Naturally, under these conditions, the efficiency of its work will tend to zero.

Despite the criticality of getting wet, the scope of application 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 well masonry technology);
• External surface of wooden or brick walls;
• Internal partitions;
• Floors;
• Interfloor ceilings;
• Roof.

When is a vapor barrier necessary?

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

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

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

There is a small ventilation gap of 1-2 cm under the internal decorative lining. The insulation is installed inside the structure between the supports.

These can be vertical frame posts, floor joists or rafters. A wind-waterproofing barrier is installed on the outside (external) side, protecting from the influence of atmospheric precipitation and strong direct wind.

This scheme is valid when constructing frame walls, floors, attic roofs, and the ceiling of a residential floor in the presence of a cold attic above.

Internal partitions and ceilings between living spaces require a slightly different approach. In this case, humid air can penetrate the mineral wool from any side. To maintain the thermal characteristics 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 houses made of timber or logs. A vapor barrier is installed between the wall and the insulation slabs.

Excess moisture is removed through a 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. A characteristic feature for such situations there will be the presence of airtight layers:

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

Another situation when mineral wool does not require additional protection is well brickwork. During the construction of the wall, internal cavities are formed, which are subsequently densely filled with thermal insulation material.

Video instruction:

Based brief overview we can conclude that protecting mineral wool from the effects of water vapor is not always a mandatory operation.

It is necessary only in cases where contact of warm air is possible humid air living space and insulation fibers.

We always ask our readers to “decipher” questions and provide additional data that would help us understand what the problem is. For example, what exactly are you asking? It's understandable that you want the fiber insulation to stay dry. But what is the design of insulating a house? Do you insulate the frame by putting mineral wool between the posts? 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 just as many answers to your question. Alas, universal solution No.

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

Preventing moisture from penetrating into mineral wool is a feasible, but difficult task. To do this, the fiber insulation in as dry a condition as possible must be packaged in a completely airtight shell. For example, in durable plastic bags. However, this is not so easy to do, and carefully installing the mineral wool without damaging the shell is even more difficult. Bags with holes are of no use. Therefore, complete protection against moisture penetration is rarely used. An example of such a solution is the insulation of heating mains, where the shell is rolled bitumen waterproofing. As a rule, in above-ground building structures, fiber insulation is not so much isolated from the effects of moisture contained in the air, but rather they are tried to ensure the release of water vapor from the material. Let us consider in general terms the most common insulation designs country house:

• Frame house. Both insulation and wooden frame need protection from waterlogging. For most of the year, the air inside the house is more high humidity than outside. Therefore, first of all, a sealed seal is attached to the frame structure from the inside over the entire area. vapor barrier film. As the name suggests, it is impermeable to water vapor. But the insulation, without a sealed shell, will absorb moisture contained in the outside air. To prevent it from accumulating, it is necessary to ensure sufficiently effective ventilation of the mineral wool. At the same time, the wooden frame is also ventilated. To do this, between the sheathing and the insulation, securing the block, leave an unfilled 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.

Classic wall design frame house. A vapor barrier is placed on the inside, preventing the penetration of moist air from the house into the insulation. On the outside there is a ventilated gap that allows moisture to escape from the mineral wool covered with a windbreak

• Wooden house, external insulation: frame filled with mineral wool and sheathing on top of it. The walls of a log house made of wood need protection from moisture no less than fiber insulation. It is irrational to “pack” them from the inside with a vapor barrier; the advantages are lost natural wood. It is also not worth placing a vapor barrier layer between the log wall and the insulation; this can lead to waterlogging of the wood and its infection by fungus. You have to put up with the fact that water vapor will constantly penetrate the wooden walls from inside the house and escape outside through the insulation. To effectively remove this moisture, we make a ventilation gap, as in the case of a frame house. Cover the mineral wool with wind protection. Let us repeat, when insulating a log house, a vapor barrier is not needed.

Correct thermal insulation wooden house: 1 – insulation; 2- windproof film; 3 – casing. The frame is filled with bars (counter battens), a ventilation gap is provided between the sheathing and the wind protection, thanks to which the wood and mineral wool remain dry

Ventilated facade option - multi-layer stone wall, made of aerated concrete with brick lining. There is a ventilation gap and windproofing. In the lower and upper areas of the cladding it is necessary to leave ventilation holes sufficient area

• Stone house, ventilated facade. Similar to the thermal insulation system of a wooden house. The presence of a ventilation gap and windproofing on the outside according to the scheme already known to us is mandatory. Vapor barrier is a little more complicated: if the walls are made of non-hygroscopic (not absorbing moisture) 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 “breathable” materials, cellular concrete, brick - vapor barrier is not needed, it will only do harm.

General design of a ventilated façade

• Plaster facade - rigid mineral wool is attached directly to the wall, and the slabs are plastered on top. A vapor barrier is not needed, and protection from precipitation and wind is provided by thin-layer facade plaster reinforced with a polymer mesh. Only special mixtures intended for external thermal insulation systems can be used.

Now about the roof, let’s consider only pitched structures:

• Combined (insulated) attic roof. It is a frame structure, in many ways similar to the walls of a frame house. A vapor barrier from the inside, a ventilated gap and wind protection from the outside are required. When choosing a windproofing film, it should be taken into account that most roofing coverings are condensation-forming: under certain conditions, dew or frost forms on the side facing the inside of the roof. This is the biggest sin steel roofs, sometimes the amount of condensate is quite large. To prevent water flowing from the roofing from soaking the insulation, special roofing films, so-called diffusion membranes, are used as wind insulation. They have the property, by freely allowing water vapor to pass out, to prevent liquid water from penetrating inside. The drops simply roll down and flow off the roof.

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

An example of a combined pitched roof. In order for the insulation in the attic roof structure to always remain dry, it is necessary to ensure its ventilation. Ventilation (shown in the diagram by arrows) is carried out in the spaces between the counter-battens packed into the rafters. The insulation should be protected from below by a vapor barrier (Izospan in the diagram), and from above by a diffusion membrane (Izospan AM).

• Cold (not insulated) attic roof. Ventilation attic spaces organized through vents in the gables, cracks in the sheathing, aerators in the covering. Since the roof is not insulated, only protection against condensation is needed without the function of removing water vapor. The most rational thing is between roofing covering And rafter system place a vapor barrier film. A diffusion membrane is also suitable, but it costs more.

If you have any questions, we are ready to answer them. An urgent request: please be more specific in your messages. It’s difficult for us to answer questions in a question-and-answer format. general. And you probably do not receive the information you are looking for in full.

Ventilation gap in frame house- this is a moment that often raises many questions among people who are involved in insulating their own home. These questions arise 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 sheathing and the wall of the house. A similar solution is implemented using bars that are attached on top of the wind barrier membrane and on the external finishing elements. For example, the same siding is always attached to bars that make the facade ventilated. A special film is often used as insulation, with the help of which the house, in fact, is completely wrapped.

Many will rightly ask, is it really not possible to just take and attach the sheathing directly to the wall? Do they just line up and form an ideal area for installing sheathing? In fact, there are a number of rules that determine the necessity or unnecessaryness of organizing a ventilation facade. Let's figure out whether a ventilation gap is needed in a frame house?

When is a ventilation gap (vent gap) needed in a frame house?

So, if you are thinking about whether a ventilation gap is needed in the facade of your carcass 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 insulating a home, will be completely in vain
• Steam Permeation The material from which the walls of your home are made allows steam to pass through into the outer layer. Here, without organizing free space between the surface of the walls and insulation, it is simply necessary.
• Preventing excess moisture One of the most common questions is the following: is there a need for a ventilation gap between vapor barriers? If the finish is a vapor barrier or moisture-condensing material, it must be constantly ventilated so that excess water is not retained in its structure.

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

Is there a need for a ventilation gap between siding and OSB?

When answering the question of whether a ventilation gap is needed between the siding and OSB (from English - OSB), it is also necessary to mention its need. As already stated, siding is a product that insulates vapor and OSB board completely consists of wood shavings, which easily accumulate residual moisture and can quickly deteriorate under its influence.

Additional reasons to use a ventilation gap

Let's look at a few more mandatory points when clearance is a necessary aspect:

• Preventing rot and cracks The wall material under the decorative layer is prone to deformation and deterioration when exposed to moisture. To prevent rot and cracks from forming, just ventilate the surface, and everything will be fine.
• Preventing condensation 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 increased level moisture will negatively affect the condition of the material. Wood swells, begins to rot, and microorganisms and bacteria can easily settle inside it. Certainly, 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.

Is there a need for a ventilation gap in the floor? No

Here you need to take into account several factors that determine whether you need to make a gap in the floor:

• If both floors of your house are heated, then a gap is not necessary If only the 1st floor is heated, then it is enough to lay a vapor barrier on its side to prevent condensation from forming in the ceilings.
• The ventilation gap must be attached only to the finished floor!

When answering the question of whether a ventilation gap is needed in the ceiling, it should be noted that in other cases this idea is purely optional and also depends on the material chosen for insulating the floor. If it absorbs moisture, then ventilation is simply necessary.

When a ventilation gap 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 you don’t need to make a ventilation gap, because this material does not allow steam to pass from the room to the outside. Consequently, there will be nothing to ventilate.
• If there is a vapor barrier inside the room If with inside If the room has a vapor barrier installed, then the gap also does not need to be organized. Excess moisture simply will not come out through the wall, so there is no need to dry it.
• If the walls are treated with plaster If your walls are treated, for example, with facade plaster, then a gap is not needed. In case outer material processing allows steam to pass through well, additional measures It is not required to ventilate the casing.

Installation example without ventilation gap

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

• At the beginning there is a wall
• Insulation
• Special reinforcing mesh
• Mushroom dowel used for fastening
• Facade plaster

Thus, any amounts of steam that penetrate the structure of the insulation will be immediately removed through the layer of plaster, as well as through vapor-permeable paint. As you may have noticed, there are no gaps between the insulation and the decoration layer.

We answer the question why a ventilation gap is needed

The gap is necessary for air convection, which can dry out excess moisture and have a positive effect on the safety building materials. The very idea of ​​this procedure is based on the laws of physics. Since school, we have known that warm air always rises and cold air sinks. Consequently, it is always in a circulating state, which prevents liquid from settling on surfaces. In the upper part, for example, of the siding, perforations are always made, through which steam escapes out and does not stagnate. Everything is very simple!

• 16.12.2009, 10:16

  Eliseev AS

  Ventilation gap in three-layer walls

  Hello, can anyone help... I'm going to build a one-story brick house, 10*9m, (the gables are also brick), with mineral wool insulation (150mm). The cake is like this - from the inside to the outside - half a brick (125mm) + mineral wool insulation (150mm) + half a facing brick (125mm). The question is: is there a need for a ventilation gap between the mineral wool and the facing brick, if not, will the walls become damp and humid in the house? I really don’t want to make this ventilation gap. And will it be enough? bearing capacity half a brick interior wall?? Please answer in more detail if possible, thanks in advance.

• 16.12.2009, 13:07

  Green Cat

  Yes, somehow it’s completely wrong...

• 16.12.2009, 14:25

  Eliseev AS

• 17.12.2009, 00:05

  jackson

  The internal wall must be made brick thick.
  The ventilation gap, in my opinion, is not needed. All the same, over time, there will be nothing left of it - mineral wool will fill the void.

• 17.12.2009, 09:19

  tomcat_omsk

  Use granulated foam glass instead of cotton wool and you don’t need any gaps. This insulation has similar properties as brick, which means nothing will accumulate anywhere.
  Regarding whether half a brick is enough or not, look at Tise 3. Everyone admires its excessive stability, but in essence it is the same as two half-brick walls, the main thing is not to forget to connect the walls

• 17.12.2009, 10:00

  Eliseev AS

  Dear tomcat_omsk. Mineral wool has already been purchased - Isorok with a density of 50KG/M3, i.e. granulated foam glass disappears.. If I do this --- from the inside - half a brick + 150 mm mineral wool + (without a ventilation gap) half a brick, connecting each other with a masonry mesh 50 * 50 * 3 through 5 rows.. On the top in front of the ceilings, additionally reinforce the masonry with 8-10 reinforcement .. The foundation is a shallow strip foundation. The question of strength probably disappears? The question is again about humidity?? Will it be humid in the house and will the corners get damp? I just know from the experience of operating a brick house made of well masonry filled with slag that it’s a bit damp and cold raw corners...Or will everything be OK with mineral wool without a ventilation gap??? Please answer...

• 17.12.2009, 11:14

  tomcat_omsk

  Again, IMHO, mineral wool has greater vapor permeability than inner part The walls are made of brick and moisture should not accumulate. Some comrades, to be sure, do not seal the vertical seams between some bricks (in the outer wall), but this is not an acquired taste. If you plaster the internal walls everything should be ok (vapor permeability will further decrease).

  Regarding strength, how many floors will your building be? Where do you live? How is your seismic situation?

• 17.12.2009, 11:16

  tomcat_omsk

  50 kg/m3 is not enough for walls; you will have to increase the density by tamping down the insulation (without fanaticism), otherwise it will sag noticeably

• 17.12.2009, 11:40

  Eliseev AS

  Cottage 10*9m along the external walls, brick gables (half a brick) in the future I plan residential attic, the ceiling is wooden, the location of the house is Nizhny Novgorod region, no earthquakes are expected....

• 17.12.2009, 11:43

  Eliseev AS

  I took the density of mineral wool according to the manufacturer’s recommendations; Rockwell generally recommends caviti with a density of 45 units, for layered masonry.
  During prolonged rains, will the masonry and insulation not get wet? If so, is this not fatal for mineral wool? And how will all this evaporate from there and affect the insulation?

• 17.12.2009, 12:28

  tomcat_omsk

  The mineral wool will be moistened not from rain, but from moisture from the house. It will come from a brick and leave through it in the direction from the house to the outside.
  Vapor permeability outside wall no less than the interior, is the facing brick ceramic? You need to work through this issue.

  More than sufficient stability. If you were building two-storey house with reinforced concrete floors, then probably half a brick interior wall it would not be enough, and then a reinforced concrete armored belt would solve this problem.

• 17.12.2009, 13:35

  Eliseev AS

  Silicate brick, both internal and outer wall, it’s just that there is no ceramics manufacturing plant near us, it’s time to choose silicate

• 17.12.2009, 13:59

  Eliseev AS

  The question about the foundation is here, if possible.
  I’m designing a foundation based on Sazhin’s book, Bury the Foundations Deep. The soil is fine sand up to 1.4-1.5m, then loam, clay, water at a depth of 0.8 to 1m. Below is quicksand. The foundation for this house is obtained from the surface of the earth downwards - reinforced concrete 0.3 m high, 0.6 m wide, a cushion of coarse sand 0.5 m high and 1 m wide. I reinforce 3 reinforcement bars at the top and bottom of the tape, diameter 12mm. I reinforce it transversely with wire with a diameter of 4 mm to create cells of 200 * 200 mm. Does this option have a foundation for life??? Freezing depth --- Nizhny Novgorod region On top, as I wrote, there is an armored belt along the entire perimeter of the walls, its height is 300mm.
  Is my foundation strong enough???

• 17.12.2009, 21:52

  Andrey teacher

• 18.12.2009, 08:41

  Eliseev AS

  Andrey, teacher, I took into account the thickness of the insulation. for the Nizhny Novgorod region. thickness is about 130 mm in layered masonry, I took 150mm, I hope it will be enough? Will the cotton wool not dry at all or will it dry slowly?
  And the question is --- if God forbid it rains during the laying and I don’t have time to cover it, will the cotton wool dry out normally?
  Based on the foundation, why is it low? one floor, the height of the masonry to the top is 3.60 m, is the foundation not strong enough?

A question about house cladding is asked by Arkady Karpov, Moscow: Hello, I want to ask you a question. Now a team is doing the sheathing of my house, insulating it and covering it with siding. After laying the film, siding is immediately sewn on top of it. I say – where is the gap? They say no need, we always do this. Are they doing the right thing and doing it the right way?

Answered by Andrey Volokolamtsev, foreman of Avgust LLC, Podolsk.

Hello, Arkady. Perhaps what your builders are doing is not entirely correct, or perhaps it is not at all correct. So that you have a normal and systematic understanding of this issue, let’s first look at your case, and then see if a ventilation gap needs to be done and when.

So let's figure it out. If the walls are made of vapor-permeable material, then if you use a decorative layer of siding, you must make a ventilated gap. Because the moisture from interior spaces your home in the form of steam will penetrate through the walls into the insulation and moisten it.

This type of insulation does not like moisture very much. When they get wet by at least 15 percent, they already lose 50 percent in their thermal resistance.

There are, however, insulation materials that are not so susceptible to moisture and that do not lose their heat-insulating ability as much. This primarily applies to polyurethane foam, which can be sprayed onto the walls of a house.

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 cases:

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

The last point can be fully attributed to vinyl siding, metal siding and profiled sheets. 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 allow steam to pass from the interior to the outside, for example, concrete.
• The insulation on the interior side is well insulated with a vapor barrier.
• External material allows steam to pass through well, for example, facade plaster.

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

Any vapor that gets into the insulation is released 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 covering:

1. The material of the decorative layer promotes the formation of condensation.
2. The wall material under the decorative layer can deteriorate from moisture (rot, cracks, etc.).

Let me give you a simple example. If you are planning to cover a wooden house with a metal profiled sheet, then you cannot do without a ventilation gap.

Otherwise, all the moisture that will condense on inner surface corrugated sheet will be absorbed, which will be destroyed as a result.

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 air current that 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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