Wall insulation from the inside: is it possible, how to do it right

If you have even the slightest opportunity to insulate the walls from the outside – do it. This is the best option, because insulating walls from the inside is a headache. There are only two correct and more or less acceptable options, and then, one takes up a lot of space, and the second requires significant costs during the winter. There is another way suitable for warming balconies and loggias. And for now, that’s all. All other options with mounting foam, liquid ceramic thermal insulation, penofol and other materials bring only dampness and mold. 

Wall insulation from the inside: what’s the problem

Everyone who insulated the outer walls of a house or apartment from the inside – from the room – is faced with the problem of the appearance of fungi, mold and high humidity. These consequences are natural, and appear regardless of the type of insulation used. You can get rid of moisture and fungi only by removing the internal insulation, making a major overhaul of the walls, treating them with antifungal compounds and plastering.

Let’s look at the reasons. The so-called dew point is to blame. This is the line where warm and cold air meet, and where, as a result, condensation forms.

The figure on the left shows the situation with the dew point if the wall is not insulated. It is located somewhere in the thickness of the wall, depending on temperature and humidity, it shifts either one way or the other, but it is always far enough from the inner surface. In this case, moisture accumulates in the wall, freezes. In the spring, as it thaws, it evaporates, and evaporates into the atmosphere. In the room, if dampness is observed, then for a short time and at the level of sensations.

In the center, the photo shows a situation where the wall is insulated from the inside. In this case, condensate falls in the insulation, or, if this is not possible (expanded polystyrene is used, for example), at the border of the insulation and the wall. Even if the wall freezes and the condensate turns into ice, it will melt in the spring, the insulation, wall material and finish will get wet. Since there is a large distance to the outer surface facing the street, moisture dries in this case very badly, which “climbs out” in the form of dampness, mold and all the accompanying delights.

And the third option is to insulate the wall from the outside. In this case, the dew point is in the insulation. How to get it out of there is another story (making a ventilated facade or choosing the right vapor permeability of materials), but for our topic it is important to understand that in this case the wall inside the room will definitely be dry and warm.

Summing up, we can say, if possible, make insulation from the outside. Wall insulation from the inside of the premises has to be done only in a few cases:

• if they are not allowed to be insulated from the outside (the building is a historical monument or a ban by local authorities);
• if the wall goes into a joint between two buildings;
• the wall opens into an elevator shaft.

But before you start this work, inspect the floor, ceiling, windows well. Sometimes most of the heat leaves not through the walls, but through these surfaces, and it is easier to insulate them (in the sense, there is less trouble with the dew point).

Proper internal wall insulation in a house or apartment

There are only two ways to insulate the walls in the rooms from the inside and not get a problem in the form of dampness:

• recreating a multi-layer wall (place a half-brick wall with insulation at some distance);
• make the wall heated, and then insulate it.

These options work, but as you can see, they “eat up” a significant amount of space and cost decent money. In each case, it is necessary to consider what kind of insulation and how much is needed, but the wall cake remains the same.

Second wall

At some distance from the main wall, a second wall is installed with a thickness of 10-12 cm. Between the two walls, a layer of insulation is attached to the inner one, which is required for these conditions. At the same time, a ventilation gap of at least 3 cm should remain before the outer wall. In total, this entire structure will be 20-25 cm from the main wall. It will “eat” a very considerable area.

As you can see, in this case, the dew point can be located inside the insulation or on the inner surface of the wall facing the street. To be able to remove the formed moisture, you can make forced ventilation by installing one or two exhaust fans.

Since in this case the insulation will get wet, it is necessary to choose one that is not afraid of moisture. These are polyurethane foam, expanded polystyrene, foamed glass. You can use some types of stone wool, but only those that are not afraid of moisture (there are some).

It is necessary to fix the heat-insulating material simultaneously with the construction of the walls. They laid it out to a certain height, fixed the thermal insulation. It is inconvenient to work, but there is no other way out.

Heating with electricity

The idea of ​​this method is to transfer the dew point inside the wall during internal insulation of a concrete or brick wall. To do this, it must be heated. The easiest way is to attach an electric floor heating mat. At some distance from it, a heater is installed, on top of which there is a finishing layer.

In this case, there are no problems with the removal of moisture, and much less space is required for the installation of the system: from 8 cm (with a ventilation gap of 3 cm and a heater thickness of 5 cm).

With this method, the heat-insulating material can be any. To install it, first a crate is made, then a counter-crate, and a suitable insulation is already attached to it.

Option for warming the balcony from the inside

In the case of a loggia and a balcony, the situation is often quite different. If the authorities do not allow the installation of a wall, they demand that the existing reinforced concrete screen be left, it is cut off from the warm air with careful thermal insulation made of extruded polystyrene foam (EPS).

In this case, it is better to make the insulation redundant than at least slightly insufficient. The total thickness is divided into two layers. They are laid without a gap (preferably with locks), and so that the seams of the first layer overlap the sheet of the second. There should be no through access of warm air to the screen.

Very carefully it is necessary to approach the issue of warming the floor and ceiling of the loggia / balcony, to ensure tightness at their junction with the walls. Also pay attention to how the glazing will be installed: there may also be problem areas: the joint with the screen, walls, the insulation of the part above the frames. All of them must be well finished, excluding the possibility of contact between warm / cold air. In this case, there will be no problems. Even if the balcony is combined with the room.