Is a ventilation gap always necessary? Ventilation gap in three-layer walls Is a ventilation gap necessary?

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The ventilation gap in a frame house is a point 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 simply 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. outer layer. No organization here free space between the surface of the walls and the insulation 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 following types sheathing: 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 chips, 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 Wall material under decorative layer 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. 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.

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 example of installation 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. Ever since school we have known that warm air always goes up and cold always goes down. 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!

Insulating the floor with mineral wool in a wooden house is a responsible and quite complicated task. The finished floor appears to guests as simply beautifully laid boards, giving the room a special chic and nobility. And only the owner of the house knows what complex design lies under even rows of wooden floor boards and how much work needs to be put in to insulate the floor with your own hands and lay out the screed.

Floor arrangement

A properly laid floor in a wooden house is a multi-layer structure that provides reliable waterproofing, protection from cold and overheating, insects and fungi, as well as providing strength and durability to the entire house. also in correct design a ventilation gap is needed to ensure air circulation. Depending on the floor wooden house, the floor arrangement may be different.

The floor on which the room is located, the degree of humidity, as well as the purpose of the entire structure also dictates its requirements for floors: the requirements for floors in a country house, for example, are not as strict as for the flooring in a private country wooden house. The floor of the attic is also different from the floor of the first floor. The floor of the second floor is constructed differently than the floor of the first floor or attic. Most often, floors are arranged in the form of a so-called pie, by analogy with the famous puff pastry confectionery product. One of the layers of the floor cake is a layer of thermal insulation, along with wooden coverings, screed and other types of insulation layers.

Materials

The floor insulation material is selected depending on the characteristics of the room (floor, purpose, humidity, floor material), as well as climatic conditions the area in which the house is located.

The following materials are most often used as insulation:

Expanded clay is a porous and lightweight material made from baked clay;
Sawdust is a waste product from wood processing. Some of the cheapest materials. The cost of one laid m2 is almost nothing;
Foam plastic - porous polymer material, lightweight and moisture-resistant material. In addition to thermal insulation properties, it also has excellent waterproofing;
Penoplex - extruded polystyrene foam - is similar to polystyrene foam, but is much more durable and is considered to have better properties, but has more high price per m2;
Mineral wool- mats made of mineral fibers;
Glass wool is a mat made of fiberglass; it is generally accepted that its thermal insulation is not much worse than that of mineral wool, but its waterproofing performance is better.

All these materials have their advantages and disadvantages. For example, polystyrene foam, for all its thermal and waterproofing properties, has a fairly high fire hazard. Expanded clay is an excellent insulation material, but it is quite inconvenient to work with and has poor moisture-proof properties, and also has high cost per m 2. And all these materials are still better than simple sawdust, although their use increases the cost of each m2 of flooring.

In mid-latitudes, the most acceptable option is mineral wool. This material has long been familiar to everyone; it has high heat-protective and sound-proofing properties. In addition, what is important is that the price of one m2 of mineral wool and, especially the prices for laying m2, are among the lowest among all building materials. The material is so easy to use that even a non-specialist can install it with his own hands.

Mineral wool is supplied in rolls or mats of specific sizes and thicknesses. Mineral wool laminated with aluminum is also produced. The price of such cotton wool per m2 is higher than that of regular wool. However, the cost of laying one m2 does not differ between them. The thickness of this material varies from 50 mm to 200 mm or more, depending on the application. Unlike foam plastic or Penoplek, mineral wool does not require preliminary cutting to shape and size. The roll simply unwinds and the mineral wool is placed in the right place.

Sequencing

Floor insulation with mineral wool is part of a multi-stage floor installation process, which is carried out according to the following algorithm:

Alignment. The surface on which the floor will be laid must be perfectly flat;
Vapor barrier - laying a layer of vapor barrier material;
Installation of guides- wooden logs;
Laying insulation- filling each m2 of floor with insulating material;
Laying the flooring is the last one, finishing layer pirogue.

Actually, this entire process is carried out with the aim of ensuring reliable insulation and waterproofing of the room. Therefore, there is no point in considering the laying of mineral wool separately from the other stages.

Alignment

Leveling is especially important when laying the floor of the first floor on the ground. There are also unevenness and cracks in floor slabs. To eliminate unevenness in the first case, it is necessary to level the soil surface with a layer of crushed stone 10 cm thick, onto which a layer of sand of the same thickness must be poured.

You should know. When laying the floor on reinforced concrete slabs floors, a leveling screed is usually used. The screed is usually concrete or cement-sand. The absence of a screed can lead to the destruction of the entire floor due to unevenness and the associated uneven load on different areas floor surface. This circumstance forces us to install a screed even in the attic.

Vapor barrier

A layer of vapor barrier on top of the screed must be laid in the floors of the first floor premises on every m2 of surface. This is necessary precisely when using mineral wool as insulation. Mineral wool easily becomes damp, which leads to a decrease in its thermal insulation properties. Also when laying finishing coating It is important to maintain a ventilation gap between the mineral wool and the floor surface.

You can use roofing felt as a vapor barrier - this material is best used in a country house, where the requirements for flooring are mainly limited by the price of materials and all work is done by hand. Film waterproofing is used as modern and reliable materials for vapor barrier:

polyethylene film, including those coated with aluminum;
polypropylene film;
vapor barrier membranes.

The most commonly used materials are polyethylene, polypropylene or aluminum-coated film. This is due primarily to the price of the material. However, the efficiency of such material is low due to the possibility of condensation accumulation on its surface. This can lead to moistening of the mineral wool and, consequently, a decrease in its thermal insulation properties.

The most modern and reliable material is multi-layer vapor barrier membranes of great thickness, made using more complex technology using many waterproofing materials. They are best used in country houses and cottages.

The vapor barrier layer is laid as evenly and tightly as possible to the surface of the ceilings and walls. In this case, there should be no ventilation gap left. Holes in the lower layer of vapor barrier will not lead to ventilation, but to the appearance of moisture on the insulation layer. This principle is maintained on all floors, including the attic.

Insulation

Mineral wool is laid on the first layer of vapor barrier. The mineral wool roll is unwound and laid in such a way as to leave no ventilation gaps between the wool and the joists, and also no ventilation gap between the wool and the first layer of vapor barrier to avoid the accumulation of moisture on the mineral fiber.

This prevents the fiber from getting wet and the mineral wool from losing its thermal insulation properties. The technology provides for the installation of special ventilation gaps between the insulation and the second layer of vapor barrier.

The thickness of the mineral wool sheet is selected depending on the purpose of the building and climatic conditions. So, in a country house used mainly only in the warm season, it is enough to use mineral wool 50 mm thick. The same applies to technical buildings and houses in southern regions, where it is still impossible to do without insulation completely, despite the milder climate. The thickness of mineral wool sheets used on the second and third floors, in the attic or in the attic can also not exceed 5 cm. This is due to lower requirements for floor insulation on the floors, as well as the need to maintain the volume of the room.

For your information. In private country houses it is better to use cotton wool with a thickness of 200 mm. Cotton wool of this thickness will provide reliable thermal insulation.

Having laid a layer of mineral wool, it is necessary to lay another layer of vapor barrier on top of it. This is especially important when installing a floor in the attic of a house or cottage. However, here the laying technology will be slightly different than in the first layer. To ensure ventilation and avoid the accumulation of moisture on the insulation layer, the technology provides for the construction of ventilation gaps - special holes between the sheets of vapor barrier film through which air will pass and moisture trapped under the vapor barrier will evaporate. Ventilation gaps are needed between all sheets of film or membrane.

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 general idea about 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 a rolled bitumen waterproofing. As a rule, in above ground structures In buildings, fiber insulation is not so much isolated from the effects of moisture contained in the air as they are tried to ensure the release of water vapor from the material. Let's consider in general outline 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, frame structure from the inside, a sealed seal is attached 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 provide enough effective ventilation 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. Recommended thickness ventilation gap- 40 mm, holes are made in the upper and lower parts of the walls, covering them with a mesh or grating. 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 outside.

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, as this can lead to waterlogging of the wood and damage to it by fungus. We have to put up with the fact that water vapor will constantly penetrate into wooden walls from inside the house and out through the insulation. To effectively remove this moisture, we do as in the case of frame house, ventilation gap. Cover the mineral wool with wind protection. Let us repeat, when insulating a log house, a vapor barrier is not needed.

Correct thermal insulation of a 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. Vapor barrier is not needed, and protection from precipitation and wind is provided by a thin layer facade plaster, reinforced polymer mesh. Only special mixtures intended for external thermal insulation systems can be used.

Now about the roof, let’s just consider 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 under-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.

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. To insulate the structure mansard roof always remained 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 (uninsulated) 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.

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 + 150mm mineral wool + (without a ventilation gap) half a brick, connecting each other with a masonry mesh 50*50*3 through 5 rows.. Along 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 - it’s a bit damp, the corners are damp in cold weather... 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 internal, facing brick is it 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 Nizhny Novgorod region. the thickness is about 130 mm in layered masonry, I took 150 mm, 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?