ᐅ Partial external wall insulation with new windows

Hello everyone,

We will soon be renovating part of our single-family house. As part of this, new windows need to be installed in this section because the rooms are being reconfigured and old windows are being bricked up.

Now we are wondering whether to choose double-glazed or triple-glazed windows. We understand that triple glazing is generally more efficient. Our main concern is whether "too airtight" windows could potentially cause thermal bridges and mold growth, for example, if the windows are more airtight than the surrounding masonry. Additionally, I have heard from acquaintances that triple-glazed windows tend to fog up and accumulate moisture more quickly compared to the more permeable double-glazed windows.

Our house was built in 1995, and the existing windows are double-glazed uPVC windows. According to the building specifications, there is 0.06 m (2.4 inches) of mineral wool insulation inside a 0.24 m (9.5 inches) calcium silicate brick wall. The U-value is therefore around 0.48 W/m²K (thermal transmittance coefficient).

What I should add is that due to the renovation work, the facade in the affected areas will be replaced and an external thermal insulation composite system (ETICS) with a plaster finish will be installed in front of the existing brickwork. This provides significantly better insulation in these sections. Only in this part (kitchen and living/dining area on the ground floor) will the windows be replaced. Do you see any issues here because there will now be improved insulation only in certain areas?

Thanks for your help and best regards!

FCBenne04 schrieb:

Now we are wondering whether to choose double-glazed or triple-glazed windows. We know that triple glazing is usually more efficient. Our main concern is whether "too airtight windows" could possibly cause thermal bridging and mold growth, for example if the windows are tighter than the masonry. Also, I have heard from acquaintances that triple-glazed windows fog up and create moisture much faster compared to the more permeable double-glazed windows.

There is no question here—you already answered it yourself in the first two sentences.

Airtight windows? Well, actually all windows are equally airtight. They are just installed more or less tightly. Today, a proper and standard installation means ALL windows are installed airtight, regardless of whether they have single, double, triple, or quadruple glazing, and whether they are single- or double-sash, etc.

What exactly did your acquaintances say? That triple-glazed windows fog up quickly on the inside? Then you should see a lawyer, because that means faulty windows were installed. Fogging on the outside? That is normal and a good sign. I just saw it myself this morning. The windows let through so little heat that the outermost pane cools down enough for moisture to condense.

Finally: If mold and moisture form anywhere in the home, in 95–98% of cases it is due to the residents’ habits, not the windows. Ventilation and heating are the key factors.

P.S. Windows tighter than masonry? What nonsense. As if masonry were not airtight. No air passes through there either; breathable walls are a myth.