ᐅ New windows – what U-value for a 1978 older building?

Good evening,

we have recently purchased a new property and are currently focusing on the windows. We are unsure about the allowable U-value for installation.

Facts:
- Insulation approximately 5cm (2 inches) in the exterior wall
- Energy performance of the building envelope according to the energy certificate is 0.76 W/(m²·K)
- Existing windows are double-glazed, and two doors are single-glazed.

Are triple-glazed windows possible?

Thank you very much and kind regards

Triple glazing is certainly possible. The house will then be very well sealed (which is also the case with double glazing). So please ensure proper heating and ventilation. If necessary, install 2cm (1 inch) of insulation in the inner window reveal during installation.

My main concern is actually the risk of thermal bridges in the wrong places, which can lead to mold growth.

You write that the walls will perform better than normally good triple-glazed windows (the weak point is the frame, not the glass). And they are also better than double-glazed windows. Or do you have a more precise U-value for the exterior walls that differs from the value mentioned?

And to ease your concerns, I have already told you what needs to be done.

By the way, what do you mean by these "wrong spots" you mention? They can only be the reveals.