ᐅ Is Exterior Wall Insulation Responsible for Mold Growth?

We are planning to make our dream of owning a house come true next year and currently still live in a rental. The rental building has an external thermal insulation composite system (ETICS), and for several years we have had serious problems with mold in the apartment. My wife has already developed an allergy to mold spores, so we now place a lot of importance on a healthy living environment.
Honestly, we suspect that the ETICS might be causing the mold, which is why we are unsure whether we should use this type of insulation for our own house.
My question to the experts in this forum is: Can an ETICS affect the breathability of a building and thus cause mold? Would it be better to opt for a thicker brick wall and avoid ETICS altogether?

ETICS (External Thermal Insulation Composite Systems) do not cause mold, and a house does not “breathe” in the literal sense. Mold always develops when moist air condenses (“dews”) on walls that are relatively cool. Insulated exterior walls tend to stay warm due to reduced heat loss. However, thermal bridges can exist, leading to relatively cold wall surfaces. The building would need to be examined in detail to provide more precise information.

Ventilation in a well-insulated house with airtight, insulated windows is also very important to replace stale air, which is always contaminated with germs/spores.

If you are planning to build your own house, exterior walls can be constructed using highly insulating masonry units without additional external insulation.
However, the physical conditions for mold formation remain the same: a certain low wall temperature and condensation. Both need to be avoided.

It is just as Mot says: one should check whether there is a thermal bridge in the wall. It is possible that the insulation thickness was underestimated, and the dew point is located within the wall. In this case, mold can naturally develop there.

With your own house, make sure to have a calculation done to determine the required insulation thickness, taking into account windows and doors as well, since these also need to be insulated.

Exactly, insulated walls cannot develop mold. Mold requires moisture to form and grow. Insulated walls typically have a surface temperature between 17 and 19 degrees Celsius (63 and 66 degrees Fahrenheit). Condensation can only occur at temperatures below 12 degrees Celsius (54 degrees Fahrenheit).

That is a useful tip regarding the calculation of insulation thickness. Precise calculations are especially important when dealing with mold growth. Mistakes in this area can lead to costly problems.

I agree with Nina, and I often experience that these calculations are not accurate. Precise work is essential at this point. In our case, the windows were insufficiently insulated, and condensation formed there.