Control of interstice condensation

The condensation of vapor contained in the air can occur either on the inner surface of the wall, or actually inside the wall itself. In the first case signs of damage appear on the wall surface with the formation of dusty deposits from electrophoresis;  in the second case, the materials used for insulation deteriorate.

The formation of condensation happens when the pressure of water vapor is higher than or equal to the pressure of saturation.

The formation of water vapor inside the wall must, if possible, be avoided. In the case where it is not, the quantity of water vapor condensed during the winter months needs to be checked and contained within limits in order to avoid compromising the minimum thermal resistance levels set for the wall, and to ensure that the quantity of water can completely evaporate during the summer months.
The testing of water levels can be carried-out using Glaser's mathematical model which is based on the comparison of trends of the saturation pressure (internal/external temperatures and the transmittance of materials) inside the wall, and of the partial pressure of vapor (internal/external humidity and the permeability to vapor of the various layers).
From the illustration the advantages of using an external isolation system to reduce/eliminate condensation are clearly apparent.


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