How and what to insulate the walls from the inside

Recommendation points

• What are the disadvantages of insulation from the inside
• A mystery covered in cotton wool. What happens in a wall insulated from the inside
• How to minimize the negative effects of wall insulation from the inside
• Which heat insulator to use
• Mineral wool
• Expanded polystyrene and EPS
• Polyurethane foam
• Other materials
• How thick should the insulation be
• Summing up

The outer walls are the most important element of the building, which, in addition to performing the load-bearing function, also protects the interior of the house from adverse weather conditions. Modern multilayer structures allow efficient energy consumption, significant savings on heating and building maintenance, which cannot be said about the “traditional” brick or panel buildings of the Soviet period. But the time has come to count the money – all that remains is to insulate what we have. In the article, we will consider topical issues of wall insulation from the inside.

Is it possible to insulate a room from the inside at all? In professional circles, there are serious disputes on this score. Manufacturers of thermal insulation materials and practicing builders have not come to a consensus about whether it is possible to insulate from the inside, this is a painfully risky enterprise. At the same time, everyone agrees that the best option in all respects is facade insulation..

What should a simple man in the street do, who is faced with the problem of a serious loss of heat through the outer walls, because the information is extremely contradictory, and there was no choice and there was no choice – it does not come out to be insulated outside. There can be many reasons for this situation: the apartment borders on unheated premises (elevator shaft, corridors, staircases), behind the outer wall there is an expansion joint between two adjacent houses, the facade has an expensive finish, the building is an architectural monument or is located in the historical part of the city, the authorities regulate urban planning activities in their own way – they simply prohibit the insulation of facades.

Certainly, GOSTs and SNiPs, which are in force in the countries of the post-Soviet space, bring some clarity to this issue, which strongly recommend placing “cold” layers inside the room, characterized by high thermal conductivity and minimal vapor permeability – concrete, brick, stone. The place for the insulation is clearly defined – this is the outer side of the enclosing structures. Moreover, even regulatory documents have exceptions. For example, in P3-2000 to SNiP 3.03.01-87 “Design and installation of thermal insulation of the enclosing structures of residential buildings” in section No. 7, dedicated to structural solutions, it is said that it is allowed to insulate the walls of individual apartments in multi-storey buildings if the installation of the heat insulator from the side facade is impossible for certain reasons.

What are the disadvantages of insulation from the inside

Let’s see why the internal insulation has so many opponents, what pitfalls await us. There are several negative points, some of them are not critical, you can put up with them, while others can have very serious consequences and force you to approach the issue of insulation from the inside with extreme caution:

1. The heat insulator placed on the inner surface of the wall “eats up” the useful area of ​​the dwelling. For example, if in a room measuring 4×5 meters, 50 mm of insulation is applied on two outer walls, we lose 0.5 m² from the total twenty squares.
2. Wall insulation works from the inside can only be carried out in a completely vacated, temporarily decommissioned room.
3. Installation of insulation on the walls will not end. In addition, it is necessary to take a number of serious measures to protect the enclosing structures from condensation and organize additional ventilation.
4. If everything is done correctly, then this method of insulation cannot be cheap, as it might seem at first glance..
5. This is not to say that the technology is simple and affordable. We repeat if everything is done correctly.
6. But the most important thing is the special thermophysical processes that take place in the walls, insulated from the inside. All the well-known “horror stories” related to the internal insulation of living quarters are indeed quite common. The appearance of water drips, the spread of fungus and mold, the destruction of finishes and load-bearing elements – all these are the consequences of an illiterate change in the thermal envelope of the room, which entailed a violation of the moisture state of the walls.

A mystery covered in cotton wool. What happens in a wall insulated from the inside

All processes of interest to us take place not only in subzero temperatures, but also in the autumn-spring period with a slight plus outside the window. There is nothing surprising in the fact that the main problems with the walls insulated from the inside appear in winter, when serious differences between the temperature outside and inside the premises are possible. It is the outer walls, or, as they are also called, “enclosing structures”, are the buffer that takes the blows of the elements.

It is necessary to consider the effect of temperature on multilayer structures only in conjunction with changes in their humidity. In fact, water is our main enemy. It is she who, freezing, expands and destroys building blocks, as well as their joints; it is she, penetrating into the layer of insulation, nullifies its thermal insulation characteristics; it is she is a prerequisite for the existence of harmful fungi and microorganisms.

What is the relationship between temperature and wall humidity, you ask? Now we come close to considering the phenomenon when, under certain conditions, water vapor from the air reaches critical saturation, and water appears on cold surfaces in the form of condensation. The temperature at which condensation forms on structures is called the building dew point. It directly depends on the relative humidity of the indoor air. The higher the humidity, the higher the dew point, the more it approaches the actual temperature (at 100% they are equal). A rather complex formula is used to calculate the exact dew point. The set of rules SP 23-101-2004 “Designing thermal protection of buildings” contains a table of dew point temperatures for various values ​​of humidity and indoor temperature.

If we take into account the sanitary rules for the operation of residential premises (GOST 30494 and SanPiN 2.1.2.1002), the normalized temperature in the home should be about 20-22 ° C, and the relative humidity should be no more than 55%. According to the table, the dew point will be +10.7 ° С. This means that where there is such a temperature in a multi-layer wall, moisture from the air can turn into water and fall out in the form of condensation..

Obviously, with significant changes in the outside temperature, the dew point moves inside the wall, closer or further from the inner space of the room, since on one side we heat the wall, including heating in winter, and from the street it is cooled. It’s a kind of tug of war.

The specific place in the enclosing structure, where condensation can fall out, largely depends on the thermal characteristics of the wall, the thickness and materials of each layer, their relative position.

1 – wall without insulation; 2 – wall with insulation from the inside

If the structure is not insulated, the dew point is inside the wall, thermal chambers show that it emits heat, it is cold in the room even when the heating is operating at full capacity – we lose heat.

With the external location of the heat insulator, the mass of the load-bearing wall completely warms up, accumulates heat, and the dew point shifts to the zone of the insulation, which must be freed from the moisture formed in it – hence the technology of ventilated facades.

Displacement of the dew point into the insulation with external wall insulation

The wall, insulated from the inside, completely freezes, as it is “fenced off” by a heat insulator from internal heat. This significantly reduces the service life of the load-bearing walls. The dew point in most cases is located on the inner surface of the enclosing structure, but when the ambient temperature rises, it can shift into the wall mass. As a result, moisture forms between the wall and the insulation, which impairs its thermal insulation characteristics. Freezing, it can destroy the adhesive bond of the heat insulator layer with the base. There is a threat of wetting the wall, the appearance of fungus and mold.

How to minimize the negative effects of wall insulation from the inside

SP 23-101-2004 “Designing thermal protection of buildings” says: “It is not recommended to use thermal insulation from the inside because of the possible accumulation of moisture in the thermal insulation layer, however, if such an application is necessary, the surface from the side of the room must have a continuous and durable vapor barrier layer. “.

So, our task is to make the wall warm and dry, for this you need to maximally protect the place where the dew point is located from the penetration of water vapor. For this, a whole range of measures is being taken:

1. The insulation layer is closed with high-quality vapor barrier films with sealing of joints and abutments.
2. A heat insulator with the lowest vapor permeability is used. Ideally, if it is less than that of the building envelope. Then the steam can be gradually discharged outside..
3. A layer of insulation is glued with a minimum gap from the wall, preferably not in a “beacon” way, but on a comb.
4. Insulated walls are faced with moisture-resistant plasterboard.
5. Additional air exchange is organized to reduce the humidity in the room. Mechanical ventilation systems are used, windows are supplied with control valves.

It is important to completely eliminate possible cold bridges. The fact is that by installing a heat insulator from the inside, we are not able to insulate the joints of floors and internal walls with enclosing structures. That is why the insulation must be done with a call to the adjoining walls and ceilings, then they should also be carefully isolated from vapors and, possibly, constructively decorated with boxes, false columns.

Which heat insulator to use

Mineral wool

Practice shows that in the overwhelming majority of cases, people insulate walls from the inside with the help of mineral wool. It is placed, without any vapor barrier, between the frame racks of plasterboard systems. In addition, rolled wool is often used, which is not intended for vertical structures, with a clearly insufficient coefficient of thermal resistance. Such insulation is done easily and very quickly, it is incredibly cheap, but not at all effective, and even harmful..

Note that cotton wool, to put it mildly, is not very suitable for insulation from the inside. Fans of this material enthusiastically call it “breathing”, but in our case this is just its main drawback. Not only is there easy access to the dew point through the fibers, but the ability of mineral wool to absorb moisture also causes many problems. Of course, you can count on the fact that the cotton wool will never get wet, use special mineral plates, which are identical in terms of thermal characteristics to foamed polystyrene foam. You can carefully glue them and try to organize an absolutely sealed vapor barrier from the inside of the room. But the risk of dampening the insulation and the inner surface of the walls remains, then all efforts will be reduced to zero, moisture will find its way into the room, streaks or fungus. This is because the vapor permeability of any enclosing structure is several times worse than that of cotton wool.

Some craftsmen are making attempts to completely seal the mineral wool slabs – they also use an inner layer of vapor barrier, make “pillows” by sealing the cotton wool in a polyethylene sleeve. But other problems arise: the insulation is not fixed to the wall – gaps appear at the locations of the dew point, the plates are difficult to fit to each other without damaging the shells, the technological chain becomes more complicated.

Expanded polystyrene and EPS

At the moment, expanded polystyrene is one of the best materials for insulating walls from the inside, so from year to year it is increasingly used both in Russia and in many European countries. The popularity of expanded polystyrene is due to its excellent operational and heat engineering characteristics. Its undeniable advantages are:

1. Low thermal conductivity.
2. Minimal water absorption and vapor permeability.
3. Ability to withstand high loads, both compressive and tensile.
4. Ease of cutting and installation;
5. Light slab weight.

So, using foamed or extruded polystyrene foam, we can increase the thermal insulation of the structure to the norm with the minimum possible thickness of the insulation layer. Not only do foam and EPS do not absorb moisture and do not lose their insulating properties, but they also do not let water vapor into the dew point zone, additional film vapor barrier will be simply superfluous. Of course, for this, it is necessary to reliably isolate the joints of the plates and their abutment to the enclosing structures. This is quite easy to do using polyurethane foam. Moreover, some manufacturers produce slabs with stepped edges, due to which the insulation joins without gaps at all. Expanded polystyrene can be successfully mounted on the wall along the facade system, using both adhesives and fixing with disc dowels.

As we have already noted, the adhesive layer also performs an insulating function; polyurethane foam adhesive has proven itself especially well. The high strength of the material allows options for finishing insulated walls with a wet method directly on the heat insulator, without using frame technologies, while it is simply impossible to overload the wall due to the low specific gravity of the material. So, a square meter of a thermal insulation layer made of expanded polystyrene is 2–2.5 times lighter than a similar thickness made of mineral wool.

There is also one small drawback – polystyrene foam has poor sound insulation properties. The problems of the possible destruction of the heat insulator at temperatures above 80 degrees and the insufficient resistance of expanded polystyrene to the effects of many organic solvents, in our case, are perhaps not critical.

Polyurethane foam

This durable and lightweight material is also good for insulating walls from the inside. It has excellent insulating properties due to its cellular structure. The thermal conductivity coefficient of polyurethane foam is from 0.025 W / (m · K), which is one of the best indicators. The pores of the polyurethane foam are filled with air or inert gas, each such cell is hermetically sealed. That is why moisture is not absorbed into the material and does not pass through it – this is an excellent waterproofing of the building envelope.

Low thermal conductivity, minimum moisture absorption, maximum vapor barrier – that’s what we need. But this is not all, the polyurethane foam coating receives special properties due to its unusual method of application. The fact is that it is applied by spraying a liquid two-component substance, which foams on the treated surface and hardens within a few seconds..

• Polyurethane foam perfectly “sticks” to any substrates, including ceilings, there is no need to use fasteners that are cold bridges.
• The coating forms a single whole with the wall, preventing moisture from the room from the slightest chance to penetrate into the area where the dew point is located.
• The heat-insulating layer is monolithic, without seams and cracks. By spraying the substance, you can easily insulate curved, semicircular walls.
• Polyurethane foam is very quick to apply. The foaming of the insulation is carried out at the place of work, therefore, due to the small volume of the liquid initial substance, the costs of delivery and storage of materials are minimized.
• A layer of polyurethane foam can be plastered using facade technology using nylon mesh.

Other materials

There are other, often “innovative” wall insulation materials on the market, whose manufacturers claim their outstanding properties. However, they are all a little cunning, hiding obvious shortcomings or hushing up about serious problems in the implementation of the corresponding technological chains. For example, warm plaster is several times inferior to foam materials in terms of its thermal characteristics, and it is also hygroscopic and vapor permeable. Foamed polyethylene foam has a very low thermal conductivity, but only on one condition – it must be mounted in such a way that an air gap remains between the insulation and the wall, as well as the sheet cladding. To make two sealed gaps, to fix the material well, while it is almost impossible to qualitatively isolate joints and abutments. Therefore, in most cases, polyethylene strips are simply nailed with dowels to the outer wall with the inevitable loss of the declared characteristics. Liquid thermal insulation based on ceramics with a layer thickness of 1 mm replaces 50 mm of mineral wool – as its manufacturers say. A thermal conductivity coefficient of 0.0016 looks fantastic, to say the least, especially when you consider that the ultra-thin coating consists of air-filled ceramic bubbles. But ceramics has a thermal conductivity of 0.8-0.15, and air – 0.025. “Termokraska” – the material is new and has not been properly studied yet, but there are already examples of non-working insulation of apartment buildings. Perhaps, under certain conditions, such an insulator has the right to exist..

How thick should the insulation be

The correct choice of thermal insulation materials is one of the key aspects of competent wall insulation from the inside, now it is necessary to determine its thickness:

1. First, using the formula R = D / L (where D is the thickness of the structure, and L is the value of the thermal conductivity of the material), we calculate the real resistance to heat transfer of the wall without a heat insulator. For example, if we have a cladding structure made of bricks 500 mm thick, then the thermal conductivity resistance will be: R = 0.5 / 0.47 = 1.06 m²° С / W.
2. Now we can compare this figure with the standardized one. For example, the resistance to heat transfer for building envelopes in Moscow and the region must be at least 3.15 – the difference is 2.09. It needs to be filled with insulation, since the thermal conductivity of the structure consists of the sum of the coefficients of its layers.
3. We calculate the required thickness of the insulation according to the formula D = L · R. For example, if we want to use expanded polystyrene (L = 0.042), then we need D = 0.042 · 2.09 = 0.087 – a foam layer of 87 mm. Naturally, it is better to overestimate the minimum indicators and apply 100 mm of expanded polystyrene, then there is a chance to transfer the dew point inside the layer of completely moisture-proof insulation.

Summing up

Insulating walls from the inside is an extreme measure in a situation where there is no way to fix the heat insulator from the side of the facade. It is technologically difficult to competently perform such work. Internal insulation is not as cheap as it seems at first glance, therefore, it is most likely that it will not be possible to save significantly.

You can formulate the basic requirements for high-quality wall insulation from the inside:

1. It is necessary to organize a hermetic vapor barrier of the wall.
2. The thickness of the insulation should be no less than the calculated one to ensure the normalized thermal conductivity of the enclosing structure for a certain climatic zone.
3. It is imperative to take measures to improve the ventilation of the room..
4. The heat insulator should be glued using a comb or solid strips.
5. It is also necessary to insulate sections of floors and partitions adjacent to the outer walls.
6. It is better to sheathe the outer walls with moisture-resistant plasterboard on a metal frame.
7. To ensure the tightness of the cladding, do not place sockets, switches, lamps, sconces on it.
8. The adjoining of sheet materials to the enclosing structures must be sealed with acrylic or silicone.
9. U-shaped brackets are mounted to the base only through insulating gaskets.
10. All work on wall insulation should be carried out after they have been treated with antifungal compounds. The substrate must be completely dry. In advance, it is necessary to exclude the wetting of the structure from the outside – all roofing, facade and window works must be completed, all systems must function properly.

It should be noted that not always the reason that the room is cold is poor thermal insulation of the outer walls. It is worth paying close attention to the heat-technical characteristics of the floor, ceiling, window blocks. Maybe this is where the cause of all the troubles lies, and perhaps the problem is in the incorrect operation of the heating or errors in its design. If this is so, then even ideally executed wall insulation will not bring the desired effect, and the temperature in the room will rise by only 1-2 degrees.