New windows: double or triple glazing for buildings constructed in 1995

Hello everyone,

we will soon be renovating part of our single-family house. In this process, windows also need to be installed in this part, as the rooms are being rearranged and old windows are being bricked up.

Now we are wondering whether we should choose double-glazed windows or triple-glazed windows. We are aware that triple glazing is generally more efficient. Our main concern with this question is whether "too tight windows" could possibly lead to thermal bridges and mold formation, for example if the windows are more airtight than the masonry. Furthermore, I have heard from acquaintances that the windows fog up very quickly and moisture forms compared to the more permeable double-glazed windows.

Our house was built in 1995 and the existing windows are double-glazed plastic windows. According to the building description, insulation consists of 0.06 m mineral wool in a 0.24 m calcium silicate wall. The U-value is therefore 0.48 W/m²K (thermal transmittance coefficient).

What I need to mention is: Due to the renovation work, the facade in the affected areas will be redone and a thermal insulation composite system with a plaster facade will be installed, which will be placed in front of the existing brickwork. Thus, there is significantly better insulation in these areas. Only in this part (kitchen and living/dining area on the ground floor) will the windows be replaced. Do you see any problems here because there is now partially better insulation?

Thank you for your help and best regards!

Have it calculated by the energy consultant or calculate it yourself with the Ubakus.

Have it calculated by the energy consultant or calculate it yourself with the Ubakus.

It's not about calculating U-values or efficiency, but about possible mold formation, etc. The window should somehow fit the building.

And this is exactly about U-values. That windows and walls fit together.

Otherwise, you cannot really assess this from a distance. Then we can only offer platitudes like "Good ventilation prevents mold!"

Our main concern with the question is whether "too tight windows" could possibly lead to thermal bridges and mold formation, e.g. if the windows are tighter than the masonry

You have thermal bridges when there is inadequate insulation somewhere. Besides the classic outer corner (due to geometry), these are any penetrating parts, e.g. balcony supports. Good windows do not cause thermal bridges.

Furthermore, I have heard from acquaintances that the windows fog up very quickly and create moisture compared to the more permeable double-glazed windows.

And that is nonsense as well. A window – like a wall – fogs up when the temperature on the inside falls below the dew point. The dew point, in turn, depends on air temperature and humidity. Better windows raise the dew point. In practice, most people ventilate far too little, and sometimes heat too little as well. This leads to high humidity and a high dew point. Old, leaky windows provide forced ventilation; as soon as you replace them with tight windows, the humidity rises and mold forms on the walls, especially in corners. The solution here is not a bad window, but proper ventilation. I would also consider retrofitting a decentralized ventilator.

So even with the 1995 standard with 0.48 w/mk, there is actually no danger that the windows are better than the wall. Therefore, condensation should still occur in the area of the windows.

Roughly speaking, triple-glazed windows can be installed from the 1st Thermal Insulation Ordinance of 1977.

An appropriate "ventilation concept" must of course be planned to get the moisture out of the house. However, this has less to do with double or triple glazing and more with the fact that the new windows are tighter than the old ones (more or better seals). So the easiest way is to buy a few hygrometers and ventilate if the value is too high.

Partial insulation of individual walls does not initially pose a problem. However, if less heating is used due to the new insulation, the old walls will become colder than before and condensation could occur. But with a construction year of 95, I see fewer problems there as well.

An energy consultant for possible funding of the measure is of course always a good idea.