What do we have to know about the internal thermal insulation

Compared to the external thermal insulation, the interior one has always represented the worse decision from the point of view of building physics.

  • There we cannot in practice avoid the formation of condensation on the inner side of the wall, between it and the thermal insulation. During the heating period the water vapors which are contained in the warm air transit (diffuse) through the wall outside and condense on it. Exactly this happens with the internal thermal insulation – after they overcome the thermal insulation layer the water vapors meet the cold wall and condensate on it (this way of thermal insulation, the wall temperature us constantly low as it is cooling from the outside, and the thermal insulation from the inside prevents its heating).


For this reason – the requirements for the thermal insulation material are going up – it has to be able to absorb the formed condensate without itself to get damaged. Simultaneously with this it has to be able to lead the condensed moisture to the surface of the wall – so that the construction will remains as dry as possible and a maximum amount of moisture to be evaporated through the inner surface during the summer period.

  • Another big disadvantage of the internal thermal insulation is that all connections of the insulated wall and ceiling with the neighboring walls represent a thermal bridge, as they interrupt the thermal insulation layer 
  • The building structure in this situation remains unprotected and exposed to weather conditions. Since a big part of the temperature difference between “in” and “out” is happening in the thermal insulation layer, the wall remains a bit warmer than the outside air. Therefore, it dries more slowly than if it is not insolated and the humidity in the wall remains higher

Large water pressures for the external walls represent the strong side rains, where under the influence of the strong wind in the wall is rammed a huge amount of rain water. Normally this does not cause damage, as the heat that passes through the wall (under the form of heat loss) pushes the water back from the wall and it dries it.


If, however, a well-functioning up to this moment wall construction is insolated from the inside – the penetrated in it water cannot be derived from the thermal energy and remains in the wall. In combination with the constantly low temperature of the wall in winter at ambient temperatures below 0°С this water in the wall freezes and causes destruction of the structure.

The frequent moisturizing of the building structures leads not only to damage to them, cause from moisture (efflorescence, freezing, mold and mildew), but to an accelerated weathering and destruction of the building material due to the impact of weather conditions. Especially at risk are the wooden surfaces and masonry works which have not been plastered. In these cases the moisture penetrates easily into the joints and dries very difficult. The situation is further complicated by the fact that the internally insulated walls are subjected to a greater thermal expansion and have a greater tendency to form cracks through which even a higher amount of water during side rains can penetrate.

  • In the cases when we apply an internal thermal insulation, a priority must be given to the problem of keeping the building construction and removing the moisture from it, rather than minimizing the heat loss and consciously using smaller thicknesses of insulating materials (and not to pursued at any cost to achieve the recommended norms in coefficients of thermal conductivity).

Theoretically speaking, the laying of a steam barrier on the inside (for example: bonding of aluminum foil) to the wall can solve the problem of condensation and reduce the accumulation of moisture to zero. The practice, however, shows that precisely this in any case should not be done because the barrier never stays solid over time (problems of the material, the occurrence of cracks due to operating construction elements and their movement). The problem is not only in the difficult sealing of all joints and holes in the wall (holes for switches and cables, doors, etc.), but mostly in the so-called flank diffusion (sideways through non-insulated neighboring walls), from where, even at perfectly laid and sealed vapor barrier in the construction, always penetrates moisture. Through these openings and breaches in the vapor barrier in the construction can enter large amounts of moisture during the warmest period precisely because of this vapor barrier the remaining water in the wall cannot be evaporated and stays accumulated in the wall.

Assuming that the accumulation of moisture in the construction of the interior thermal insulation is inevitable – it should be payed greater attention not so much on the prevention of its formation, rather than on how this moisture can be absorbed smoothly by the structure and how in the summer it can be as soon as possible evaporated. This can be done moisture-sensitive and capillary active building products and materials. The capillarity causes distribution of moisture and its transference to the surface of the construction element – where it can evaporate freely. In the name of this, accelerating the process of evaporation maximum, it has to be avoided placing an vapor barrier or to place a moisture-adaptive one (intelligent vapor barriers, which in winter are close for diffusion and open in summer).

In the ideal case, the formed condensation should be taken directly from the material from which the thermal insulated wall is made and from there, during the summer, evaporated outside. However, for this purpose, it should be build from capillary conductive material (the best option are soft baked bricks). Before the thermal insulation is placed, from its inner side all vapor barriers should be removed (cement plaster, waterproof paints, etc.)

In case the wall cannot or due to different reasons it should not absorb the formed condensate, this must be done by the thermal insulating layer. This can best be done by the thermal insulation boards of wood fiber or calcium-silicate insulation boards, which can be mounted so as to have the largest possible contact with the wall.



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  • 2
    Shelter4GreenDeal | 2021-10-01 08:22:36

    This is really a great post, and I greatly appreciate the information provided.

  • 1
    Shelter4GreenDeal | 2021-10-01 08:22:06

    This is really a great post, and I greatly appreciate the information provided.

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