Insulation of floors with mineral wool and vapor barrier technology. Why do you need a ventilation gap in a frame house, a ventilation gap on facades? Is a ventilation gap necessary when insulating the floor?
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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 definitely need to 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 do not lose their properties as much. thermal insulation ability. 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, the 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 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 it be necessary? ventilation gap between the wall and the decorative covering:
- The material of the decorative layer promotes the formation of condensation.
- 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 sheathe 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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When insulating walls using the “ventilated facade” system, the insulation is constantly washed by a stream of air. That's why the most important characteristic The insulation used is its breathability. You need to know how freely air can move inside the insulation itself. This means reducing the thermal insulation characteristics of the layer, or even causing “its disappearance.” Depending on breathability mineral wool It may be necessary to use windproof membranes.
In a ventilated façade
When insulating using the “ventilated facade” system, the insulation is pressed against the wall using anchors, planks hung on the wall, etc. Between the insulation and external finishing a ventilation gap is left.
If the system is assembled correctly, then under the influence of heat passing through the heat insulator, as well as due to wind pressure, a natural, stable draft of air from bottom to top occurs in the ventilation gap.
In system curtain façade with a ventilation gap, the insulation is constantly exposed to air moving along the ventilation gap. But the air moves from bottom to top and through the insulation layer, i.e. directly on the insulation. And the greater the breathability of this material, the large quantity air will pass through it.
Heat escapes with the air
This movement of air through the insulation is essentially a direct leakage of heat 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 building envelope using the “ventilated facade” system by 20% or more.
If, during installation, tight contact of the insulation with the wall was not ensured, then convection heat loss increases significantly, and the effect of the insulation is reduced by 40 - 60%. This is very serious problem when insulating buildings using the specified technology.
Air flow speed and wind zones
Also, losses will increase with increasing 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 (wind zones 6 - 7) or for high-rise buildings(70 m from ground level) in any wind zone.
In what insulation based basalt wool Are there significant convection heat losses?
Density of mineral wool
For slabs made of basalt fiber with a density of 80 kg/m3 and more, this problem practically ceases to exist. Its manifestations can only occur if the insulation is not completely pressed against the wall, then it is possible to increase heat loss by 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 using mineral wool slabs with a density of 80 kg/m3 or more for insulation, convection heat loss will not be more than 2.5%.
Thus, the specified density basalt slabs is the limit for trouble-free operation in a ventilated façade system. And such slabs can be used without additional wind protection - without a superdiffusion membrane.
Should I use a membrane?
Sufficient resistance to air permeation can be achieved either by using a high-density heat insulator, or by increasing the resistance of the layer for air movement by installing additional windproof membrane.
Which way to solve the problem is better?
Use denser, and therefore more expensive, insulation in a thicker layer, or hang additional element systems, which, by the way, can become unusable and, at a minimum, create fire problems?
There is an opinion that it is better to use denser mineral wool, without an additional membrane, and, if required, in areas with significant wind loads, install basalt fiber insulation with a density of 180 kg/m3.
The problem of reducing heat loss from air convection must be solved by using insulation materials with appropriate characteristics.
What is more expensive and more effective – a membrane or...
The insulation itself will of course be more expensive, but taking into account the absence of a membrane, the increase in price will not exceed 2% of the cost of the entire ventilated facade system. At the same time, the reliability of the system increases significantly.
It should be noted that two-layer insulation 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 standard and the absence of gaps between the slabs during installation, which is difficult to ensure in practice.
At the same time, the use of single-layer insulation is more technologically advanced, and an increase in the cost of the entire system at the level of 2% should not affect the feasibility of this particular “ventilated facade” insulation technology.
Today, there are no standards and construction rules that would determine when it is possible to do without a windproof membrane in a ventilated façade system, and when it is not.
16.12.2009, 10:16
Eliseev ASVentilation 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 CatYes, somehow it’s completely wrong...
16.12.2009, 14:25
Eliseev AS17.12.2009, 00:05
jacksonThe 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_omskUse 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 walls17.12.2009, 10:00
Eliseev ASDear 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_omskAgain, 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_omsk50 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 ASCottage 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 ASI 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_omskThe 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 outer 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 ASSilicate 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 ASThe 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 teacher18.12.2009, 08:41
Eliseev ASAndrey, 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?
The use of mineral wool during the construction of a house 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 every 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?
Melts are used as raw materials for production rocks(basalts, dolomites). 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 its dependence thermal insulation properties from 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.
Under the inner decorative cladding a small ventilation gap of 1-2 cm is made. 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 effects of precipitation and strong direct wind. 
This scheme is valid when frame walls, floors, attic roof, ceiling residential floor if there is 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. wooden log houses from 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 is not required additional protection- well brickwork. During the construction of the wall, internal cavities are formed, which are subsequently densely filled with heat-insulating 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 there is possible contact between warm, humid air in a living room and insulation fibers.
Floor insulation with mineral wool in wooden house- it’s a responsible and quite complex matter. 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 construction
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 from 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 ordinary 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 first floor 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.
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 that is 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.