Internal or External insulation? Which one is better ?

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House insulation from the inside is used very rarely. No wonder, because this method of isolation is advised against by all specialists. It is definitely less beneficial than warming from the outside. In addition, even if it is made perfectly, there is no guarantee that fungi and mold will not appear in a moment. It can only be used when there is no other option. What problems may arise after using this method?


Insulation from the inside is a must, only in certain situations

Insulation from the inside can be used, for example, when the house is under conservation supervision or has a facade that we do not want or cannot destroy – clinker, stone or historic. There are also situations when a house is part of a semi-detached or row house, and the owners of the remaining parts do not want to insulate the whole thing together. Sometimes it also happens that the owners have the right to only part of the house, e.g. the first floor or the ground floor, and the co-owners do not wish to insulate the entire building.

It is a risky way of insulation – When using internal insulation, moisture often condenses on the part of the insulation that is installed inside the building. This is the most important reason why this type of solution is not recommended or even considered inappropriate by specialists.

Moisture condensation occurs when the temperature inside is much higher than outside – Example: What happens when we blow on a cold window? – Water vapor appears on it. The same happens with insulation from the inside, but the steam penetrates into the insulation layer, e.g. mineral wool, which has a cold wall on one side and a warm one on the other.


There is no good way to warm from the inside

There are more and more new solutions, such as a special paint or a putty with a thickness of a few millimeters, recommended by retailers in supermarkets. However, the methods can never replace polystyrene fifteen centimeters thick. There are no good solutions for thermal insulation from the inside. However, if we have no other option, we must first of all pay attention to the very precise execution of such insulation.

It is important to minimize the risk of water vapor entering the insulation layer. The most common is the so-called dry building. A grate is placed and the plaster board is screwed to it. The space between the plate and the grate is filled with mineral wool. We must also remember about the vapor barrier, which we make by installing an appropriate vapor barrier material to the grate. A system constructed in this way should be carefully sealed. Another solution may be to stick foamed polystyrene on the wall, make a reinforced layer and finish such an arrangement with putty or other internal mass.

It is also worth noting that when we decide to insulate from the inside, we lose a few cm of our room inside the house. In addition, the cold that penetrates into the larger layer of the wall, if we only have insulation from the inside.


Wall insulation – why is it better from the outside, not from the inside?

Proper insulation of a building requires taking into account two physical phenomena – energy transport, i.e. heat, and water vapor diffusion in sandwich partitions. Insulating the walls from the inside causes the wall freezing zone, and thus also the water vapor condensation zone, to shift towards the inside, which may cause the partition to become damp and reduce its durability. With traditional insulation from the outside, these phenomena do not occur. The wall is always located in the warm zone (outside the frost zone) and, importantly, it heats up with the room. It has the same temperature as the air inside. It stabilizes the operation of the heating system due to its high thermal inertia and has a positive effect on the interior microclimate and thermal comfort due to the humidity capacity. There is no condensation of water vapor in the wall and there are no large differences in temperature between summer and winter, which ensures the stability of the structure. Therefore, whenever possible, it is recommended to lay insulation on the outer side of the wall.


Project EWI Specialist LTD-After


Project EWI Specialist LTD-Before



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