How much insulation is too much?!

It may be that the pros here find my question silly but we are complete laymen in this field and you hear quite a bit... Anyway, the question is whether it is true that you are not allowed to properly insulate an old building (terraced house from 1976) afterwards... Is that true? It would supposedly be bad because the building would then no longer be able to "breathe"?! What we definitely want to do is: optimize roof insulation if necessary and install new windows and doors with triple glazing, in that case should we better not have additional thermal insulation plaster applied or should we? And what we have also heard: for a terraced house the subsequent facade insulation would not be worthwhile anyway because the improvement would be minimal... So what is true now and what would you do (have done)?! Thanks in advance for your answers.

Hello,

What is correct now and what would you do (have done)?

Hire a professional! ;) => Economic efficiency calculation. Just a thermal insulation plaster makes no sense at all, you don't have to calculate for that. By the way: walls do not "breathe". Best regards.

Sure - with a mid-terrace house, two sides are already "insulated". However, the costs for insulating the two uninsulated sides are also lower. On the subject of insulation thickness: you can basically say: the thicker, the better. Only at some point, a thicker insulation no longer brings any (or almost no) benefit and only costs more. Since walls do not "breathe" and air exchange takes place almost exclusively through the windows, a professionally installed insulation combined with proper ventilation behavior should not cause building damage. Installing new windows without insulating the exterior walls is not ideal, as then the exterior walls, rather than the windows, become the coldest surfaces (risk of mold). Regards